Systems and methods of automated doppler ultrasound quantification for vascular applications

Abstract

Systems and methods are provided for reducing the reliance on operator skill during vascular ultrasound procedures. The placement of an ultrasound probe to assess perfusion associated with a wound may be facilitated by receiving input suitable for identifying an anatomical region associated with the wound and providing an indication of a suitable initial probe position, and optionally, probe orientation, for acoustically interrogating a target arterial vessel known to provide perfusion to the anatomical region associated with the wound. Regions exhibiting arterial flow may be detected as the probe is moved, enabling arterial vessel detection and localization. A subregion within the detected arterial vessel and a beam steering angle may be autonomously determined for spectral Doppler data collection, enabling the measurement of hemodynamic measures associated with the arterial vessel. Example apparatus for securing the probe to the patient and facilitating probe positioning to search for a target vessel are disclosed.

Description

SYSTEMS AND METHODS OF AUTOMATED DOPPLER ULTRASOUND QUANTIFICATION FOR VASCULAR APPLICATIONSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 652,517, titled “SYSTEMS AND METHODS OF AUTOMATED DOPPLER ULTRASOUND QUANTIFICATION FOR VASCULAR APPLICATIONS” and filed on May 28, 2024, the entire contents of which is incorporated herein by reference, and also claims priority to U.S. Provisional Patent Application No. 63 / 667,996, titled “SYSTEMS AND METHODS OF AUTOMATED DOPPLER ULTRASOUND QUANTIFICATION FOR VASCULAR APPLICATIONS” and filed on July 5, 2024, the entire contents of which is incorporated herein by reference, and also claims priority to U.S. Provisional Patent Application No. 63 / 707,400, titled “SYSTEMS AND METHODS OF AUTOMATED DOPPLER ULTRASOUND QUANTIFICATION FOR VASCULAR APPLICATIONS” and filed on October 15, 2024, the entire contents of which is incorporated herein by reference.BACKGROUND

[0002] The present disclosure relates to diagnostic ultrasound. More particularly, the present disclosure relates the Doppler ultrasound for the detection of vascular pathology.

[0003] The imaging and measurement of vascular blood flow is critical to properly diagnose and treat diseases such as chronic limb threatening ischemia. Ultrasound has been proven to be a useful tool to evaluate perfusion with measures such as pedal acceleration time (PAT) and volumetric flow.

[0004] Ultrasound imaging, particularly Doppler ultrasound, demands a high level of skill, expertise, and experience due to its intricate nature and critical role in medical diagnostics. Doppler ultrasound involves assessing blood flow by detecting changes in frequency caused by moving red blood cells. To obtain a high-quality Doppler assessment, sonographers perform a number of maneuvers to the probe while interpreting the image on the screen and adjust a variety of parameters manually to obtain the best possible flow profile for the anatomy of interest. These include settings for transmission and reception of the acoustic beam such as gain, pulse repetition frequency (PRF), and wall filter cutoff. The optimal values for theseparameters can be beneficial to ensure a high quality Doppler signal during color flow and spectral Doppler imaging.

[0005] Standard ultrasound probes are typically held and manipulated in the user’s hand during imaging. When the user wants to document an image and / or quantitative measure, they typically implement a screen capture for later viewing. This typically works well in the diagnostic clinic setting because the imaging is not needed for an extended amount of time. However, during surgical / interventional procedures such as peripheral revascularization, the physician requires ultrasound readings at various time points throughout the procedure (e.g. before and after each of numerous attempts to open various lesions throughout the vasculature). These procedures typically last 1 .5-3 hours and typically require 3-10 measurements. In the case of peripheral revascularization, these measurements typically only focus on 1 or 2 arteries in the foot and typically do not need to change location along the artery.

[0006] In theory, a vascular sonographer can be present during the whole procedure and place the probe in the appropriate location each time an ultrasound reading is required. A physician could also perform the readings. In practice, however, it is not an efficient use of resources for an ultrasound sonographer to be present for the whole procedure when their actual sonographic work would only amount to a few minutes total. Furthermore, physicians are typically involved in the therapeutic aspect of the procedure, and it is a distraction for them to stop and perform ultrasound throughout the procedure.

[0007] In addition, to have adequate sensitivity and accuracy in obtaining quantitative measurements from the Doppler waveform, it is also important to set the Doppler beam steering and angle correction correctly to ensure that the Doppler angle is favorable. A Doppler angle less than 60 degrees is ideal for vascular quantification. Many ultrasound systems today have predefined combinations of these parameters (referred to as presets) to produce the best flow signal. However, not all settings, e.g. beam steering angle and angle correction, can be easily predefined since they depend on the orientation of the vessel with respect to the ultrasound probe which can vary from one individual to another, and depends on how the probe was placed, its angulation, and where the imaging plane intersects the vessel.

[0008] Sonographers navigate through a series of ultrasound imaging modes from the moment the probe is placed on the skin until they obtain the required Doppler flow profile. Typically, this involves starting with B-mode imaging, where a grayscale image is used to identify the anatomy. When the desired anatomy is visible, color flow Doppler mode and / or power Doppler mode is turned on to confirm the presence of flow and the type of vessel, e.g. artery or vein. A sample volume is then placed at the desired location to switch the ultrasound system to spectral Doppler mode to obtain the flow spectrum.

[0009] Navigating these different ultrasound modes to accurately localize and measure the flow profile, determining and applying the optimal ultrasound parameter settings, and interpreting the ultrasound image for diagnosis requires specialized knowledge and skill. Lack of access to such skilled personnel severely limits access to ultrasound in non-traditional settings and inhibits its ability to foster new clinical applications.SUMMARY

[0010] Systems and methods are provided for reducing the reliance on operator skill during vascular ultrasound procedures. The placement of an ultrasound probe to assess perfusion associated with a wound may be facilitated by receiving input suitable for identifying an anatomical region associated with the wound and providing an indication of a suitable initial probe position, and optionally, probe orientation, for acoustically interrogating a target arterial vessel known to provide perfusion to the anatomical region associated with the wound. Regions exhibiting arterial flow may be detected as the probe is moved, enabling arterial vessel detection and localization. A subregion within the detected arterial vessel and a beam steering angle may be autonomously determined for spectral Doppler data collection, enabling the measurement of hemodynamic measures associated with the arterial vessel. Example apparatus for securing the probe to the patient and facilitating probe positioning to search for a target vessel are disclosed.

[0011] Accordingly, in a first aspect, there is provided an autonomous method of guiding placement of an ultrasound probe for assessment of vascular pathology associated with a wound of a subject, the method comprising: receiving, from a user, wound location input suitable for identifying, from a pre-determined set of anatomical regions, a selected anatomical region associated with the wound;processing the selected anatomical region to autonomously determine an initial probe position, such that when the ultrasound probe is placed on the subject according to the initial probe position, a spatial region interrogated by the ultrasound probe will be proximal to a target vessel associated with perfusion of the selected anatomical region; displaying a guidance image showing: a visual anatomical representation; and an indication of the initial probe position relative to the visual anatomical representation, thereby providing guidance to the user for placing the ultrasound probe relative to the subject for assessment vascular disorder associated with the wound.

[0012] In another aspect, there is provided a system for guiding placement of an ultrasound probe for assessment of vascular pathology associated with a wound of a subject, the system comprising: processing circuitry comprising a processor and associated memory, the memory comprising instructions executable by the processor for performing operations comprising: receiving, from a user, wound location input suitable for identifying, from a pre-determined set of anatomical regions, a selected anatomical region associated with the wound; processing the selected anatomical region to autonomously determine an initial probe position, such that when the ultrasound probe is placed on the subject according to the initial probe position, a spatial region interrogated by the ultrasound probe will be proximal to a target vessel associated with perfusion of the selected anatomical region; displaying a guidance image showing: a visual anatomical representation; and an indication of the initial probe position relative to the visual anatomical representation, thereby providing guidance to the user for placing the ultrasound probe relative to the subject for assessment vascular disorder associated with the wound.

[0013] In another aspect, there is provided an ultrasound system comprising: an ultrasound probe comprising: an elongate housing;an ultrasound transducer array supported within the elongate housing, wherein array elements of the ultrasound transducer array extend longitudinally along an ultrasound transducer array axis within the elongate housing; a support frame comprising an aperture; an attachment means for securing the support frame to a skin surface of a subject; the support frame being configured to removably and pivotably secure the ultrasound probe such that, when the support frame is secured to the skin surface by the attachment means and the ultrasound probe is secured by the support frame: a distal energy emitting surface of the ultrasound probe is contacted with the skin surface of the subject through the aperture; and an orientation of the ultrasound probe is variable, by varying a pivot angle of the ultrasound probe about a pivot axis relative to the support frame, for scanning an ultrasound energy beam emitted by the ultrasound probe, while maintaining contact of the distal energy emitting surface with the skin surface; the ultrasound system further comprising a locking mechanism for locking the pivot angle of the ultrasound probe.

[0014] A further understanding of the functional and advantageous aspects of the disclosure can be realized by reference to the following detailed description and drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Embodiments are described with reference to the accompanying drawings. In the drawings, like reference numbers can indicate identical or functionally similar elements.

[0016] FIG. 1 is a flow chart showing an example method of guiding the placement of an ultrasound probe for the interrogation of arterial vessels associated with perfusion of an anatomical region having a wound.

[0017] FIGS. 2A, 2B and 2C show an example user interface for guiding the selection of a region associated with a wound.

[0018] FIG. 3 is a table associating a respective dominant perfusing arterial vessel with various pedal regions.

[0019] FIG. 4 shows an example user interface for guiding the motion of an ultrasound probe to search for an arterial vessel associated with perfusion of an anatomical region having a wound.

[0020] FIG. 5 is a flow chart showing an example method of performing autonomous arterial vessel detection.

[0021] FIGS. 6A and 6B show an example user interface for providing guidance to a user to facilitate the detection of an arterial vessel associated with perfusion of an anatomical region having a wound.

[0022] FIG. 7A shows an example pulsatility map of a detected arterial vessel.

[0023] FIG. 7B shows an example colour Doppler image including an arterial vessel and other features associated with venous blood flow.

[0024] FIG. 8 shows an example colour Doppler image of an arterial vessel.

[0025] FIG. 9 shows an example user interface indicating that an arterial vessel has been identified.

[0026] FIG. 10 is a flow chart showing an example method of determining a suitable subregion for performing spectral Doppler data acquisition within a detected arterial vessel.

[0027] FIG. 11A shows an example user interface indicating the subregion identified within a detected arterial vessel for subsequent spectral Doppler processing.

[0028] FIG. 11B illustrates an example case in which multiple arterial vessels have been detected.

[0029] FIG. 12A shows an example user interface image showing a spectral Doppler waveform collected from the selected subregion.

[0030] FIG. 12B shows a waveform detailed view indicating the selection of the time points ts and td for the computation of acceleration time is shown.

[0031] FIGS. 13A, 13B, 13C, 13D, 13E, 13F and 13G illustrate an example workflow involving the detection of an arterial vessel and the determination of a suitable subregion for performing spectral Doppler data acquisition.

[0032] FIG. 14 shows an example system for performing autonomous processing of Doppler ultrasound data for the detection of an arterial vessel and the computation of associated hemodynamic measures.

[0033] FIGS. 15 and 16 show exploded views of the example ultrasound probe positioning apparatus.

[0034] FIGS. 17A and 17B show the use of a strap to secure the ultrasound probe in the example ultrasound probe positioning apparatus.

[0035] FIG. 18A shows a top view of the example ultrasound probe positioning apparatus.

[0036] FIG. 18B shows a cross-sectional view of the example ultrasound probe positioning apparatus as defined by line AA in FIG. 18A.

[0037] FIG. 19 shows the example ultrasound probe positioning apparatus with the housing and probe shown in a rotated position.

[0038] FIG. 20A, 20B and 20C show views of an example ultrasound probe and the ultrasound beam emitted therefrom, with FIG. 20C showing angled steering of the ultrasound beam.

[0039] FIGS. 21A shows an image of a foot and an example vessel, where the vessel is generally parallel to the long axis of the foot.

[0040] FIGS. 21 B shows the example ultrasound probe positioning apparatus and ultrasound probe placed on top of the foot oriented so the ultrasound probe and emitted ultrasound beam are substantially parallel to the vessel in the foot.

[0041] FIG. 22A shows a front view of the example ultrasound probe positioning apparatus and ultrasound probe as placed on the foot in FIG. 21 B along with the cross section of vessel and the emitted ultrasound beam. In this position, the ultrasound beam is parallel to the long axis of the vessel, but is off-axis.

[0042] FIG. 22B shows how the probe receptacle has been pivoted relative to the support structure to facilitate alignment of the ultrasound beam with the target vessel.

[0043] FIG. 23 shows the example ultrasound probe positioning apparatus and ultrasound probe placed on top of the foot oriented so the ultrasound probe and ultrasound beam are substantially perpendicular to the vessel in the foot.

[0044] FIG. 24A shows a front view of the ultrasound probe positioning apparatus and ultrasound probe as placed on the foot in FIG. 23 along with the cross section of vessel and the ultrasound beam.

[0045] FIG. 24B shows a side view of the ultrasound probe positioning apparatus and probe as placed on the foot in FIG. 23. The angle of the emitted ultrasound beam improves the Doppler angle relative to the vessel.

[0046] FIG. 25A shows a top view of an alternative example embodiment of an ultrasound probe.

[0047] FIG. 25B shows an isometric view of the alternative example embodiment of the ultrasound probe.

[0048] FIG. 25C shows a front view of the alternative example embodiment of the ultrasound probe.

[0049] FIG. 25D shows a side view of the alternative example embodiment of the ultrasound probe.

[0050] FIG. 26A shows a top view of an alternative example embodiment of an ultrasound probe positioning assembly.

[0051] FIG. 26C shows a bottom view of the alternative example embodiment of the ultrasound probe positioning assembly.

[0052] FIG. 26D shows an isometric view of the alternative example embodiment of the ultrasound probe positioning assembly.

[0053] FIG. 26E shows a side view of the alternative example embodiment of the ultrasound probe positioning assembly.

[0054] FIG. 27A shows a photograph of the upper surface of the alternative example embodiment of the ultrasound probe positioning assembly.

[0055] FIG. 27B shows a photograph of the bottom surface of the alternative example embodiment of the ultrasound probe positioning assembly.

[0056] FIG. 28A shows an isometric exploded view of the alternative example embodiment of the ultrasound probe and the positioner assembly.

[0057] FIG. 28B shows an isometric view of an alternative example embodiment of an ultrasound probe positioning system.

[0058] FIG. 28C shows an isometric image of the alternative example embodiment of the ultrasound probe positioning system.

[0059] FIG. 29A shows a photograph of the probe and positioner assembly affixed to the top of the foot.

[0060] FIG. 29B shows a photograph of the positioner straps wrapped around the bottom of the foot with the hook and loop straps affixed to each other.

[0061] FIG. 30 shows an image of the adhesive-backed hook and loop pad affixed to the bottom of the foot and the straps affixed to each other and the pad.

[0062] FIG. 31 A shows a top view of the adhesive-backed hook and loop pad.

[0063] FIG. 31 B shows a front view of the adhesive-backed hook and loop pad.

[0064] FIG. 31 C shows an isometric view of the adhesive-backed hook and loop pad.DETAILED DESCRIPTION

[0065] Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well- known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure.

[0066] As used herein, the terms “comprises” and “comprising” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms “comprises” and “comprising” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.

[0067] As used herein, the term “exemplary” means “serving as an example, instance, or illustration,” and should not be construed as preferred or advantageous over other configurations disclosed herein.

[0068] As used herein, the terms “about” and “approximately” are meant to cover variations that may exist in the upper and lower limits of the ranges of values, such as variations in properties, parameters, and dimensions. Unless otherwise specified, the terms “about” and “approximately” mean plus or minus 25 percent or less.

[0069] It is to be understood that unless otherwise specified, any specified range or group is as a shorthand way of referring to each and every member of a range or group individually, as well as each and every possible sub-range or sub-group encompassed therein and similarly with respect to any sub-ranges or sub-groups therein. Unless otherwise specified, the present disclosure relates to and explicitly incorporates each and every specific member and combination of sub-ranges or subgroups.

[0070] As used herein, the term "on the order of", when used in conjunction with a quantity or parameter, refers to a range spanning approximately one tenth to ten times the stated quantity or parameter.

[0071] As described above, the conventional workflow for performing clinical assessment of vascular perfusion via Doppler ultrasound involves a complex, manual workflow requiring significant operator skill, judgement, and knowledge of thevarious Doppler modes and when to use them during the diagnostic procedure. This workflow, while appropriate for skilled sonographers, can be overly complex to implement in a clinical setting involving less skilled technicians. This present disclosure addresses this problem and need by providing systems and methods that employ automated guidance to facilitate the determination of quantitative clinical Doppler flow measures (e.g. indices) without requiring expert sonographer proficiency. According to various example embodiments of the present disclosure, probe placement guidance and autonomous Doppler processing enables an unskilled user to perform diagnostic procedures involving the detection and localization of arterial vessels and the generation of Doppler hemodynamic measures from spectral Doppler data associated with the arterial vessels.

[0072] Referring now to FIG. 1 , an example flow chart is provided that illustrates a method of providing guidance to a user to aid in the placement of a Doppler ultrasound probe for the detection of Doppler ultrasound data from arterial vessels based on the location of a wound of a subject (e.g. patient). In step 100, input is received from a user that facilitates the identification of an anatomical region in which the wound is located, where the anatomical region may be one of a set of predetermined anatomical regions. The user input may be provided in any form that enables a determination of the anatomical region in which the wound is located, such as, but not limited to, textual input, voice input, and selection on a user interface. In some example implementations, the user input may directly identify the anatomical region in which the wound is located, while in other example implementations, the user input may provide a specific anatomical location of the wound, and the specific anatomical location may be processed to determine which of the pre-determined anatomical regions encompasses (includes) the specific anatomical location of the wound.

[0073] FIGS. 2A and 2B illustrate an example implementation involving selection of a wound location on a user interface. In FIG. 2A, the user provides input identifying the left foot as having the wound. In FIG. 2B, the user provides input indicating that the wound is located on the top surface of the big toe of the left foot.

[0074] Referring again to FIG. 1 , in step 110, the anatomical location associated with the wound is employed to autonomously determine an initial position, and optionally, an initial orientation, of an ultrasound probe, such that the initial position (and optionally, orientation) is suitable for acoustically interrogating a spatial region,within the subject, that is proximal to (and thus may include) one or more vessels known to be associated with perfusion of the selected anatomical region including the wound.

[0075] This step may be performed based on a pre-determined relationship or association establishing, for each anatomical region of the pre-determined set of anatomical regions, a respective probe position (and optionally, a respective ultrasound probe orientation). For example, for each anatomical region, a reference anatomical model may be employed to determine a target arterial vessel responsible for perfusion of the anatomical region, and the position and orientation of the target arterial vessel, relative to the anatomy, may be employed to determine a suitable position (and optional orientation) of the ultrasound transducer for the collection of Doppler ultrasound signals.

[0076] An example of an association between anatomical regions and target arterial vessels is shown in FIG. 3, which provides a table associating a respective dominant perfusing arterial vessel with pedal regions of a set of pedal regions. In cases in which two or more arterial vessels are identified as perfusing a given anatomical region, the ultrasound probe position (and optionally, the ultrasound probe orientation) may be determined as an average position (and optionally, an average orientation) based on positions and orientations associated with each vessel, or may be determined based on one vessel that is known to be a dominant vessel, or for example, a vessel that is known to be indicative of vascular pathology.

[0077] It will be understood that the recommended ultrasound probe position (and optional orientation) may not result in immediate detection of the target artery, with the ultrasound probe position (and optionally, the ultrasound probe orientation) resulting in the ultrasound energy beam emitted from the ultrasound transducer not immediately overlapping the target vessel. Accordingly, the position and orientation of the ultrasound probe is considered an initial position and orientation, and the user may need to reposition and / or reorient the ultrasound probe to achieve suitable spatial overlap of the ultrasound beam with the target vessel.

[0078] As shown in step 120 of FIG. 1 , a guidance image is displayed to the user, the guidance image indicating the initial position (and optionally, an initial orientation) of the ultrasound probe relative to a visual representation of the anatomy. For example, as shown in FIG. 2C, an elliptical region is illustrated illustrating a recommended probe position for interrogating an arterial vessel associated withperfusion of the big toe. While not shown in FIG. 2C, the guidance image may also show a recommended initial orientation for orienting the ultrasound probe relative to the anatomy. In some example embodiments, the initial probe position may correspond to an anatomical landmark.

[0079] In some example implementations, the visual representation of the anatomy is generated according to a digital anatomical model, and may include an anatomical surface and / or volumetric anatomical landmarks that can assist in placement of the ultrasound probe. In implementations in which a recommended initial ultrasound probe orientation is provided, the digital anatomical model may be processed to dynamically display the initial probe position and the initial probe orientation according to a plurality of orientations of the anatomical surface, thereby enabling the user to observe the initial probe position and the initial probe orientation from multiple perspectives. In some example implementations, the plurality of orientations of the anatomical surface may be shown in an animation. In other example implementations, the plurality of orientations of the anatomical surface are shown according to orientation selection input provided by the user.

[0080] In some example implementations, the visual anatomical representation may be generated based on surface data characterizing an anatomical surface of the subject. For example, surface data associated with the anatomy of the subject may be obtained using a surface detection device such as a structured light imaging device, a depth camera, a laser radar device, or stereographic imaging system, while in other example implementations, surface data may be obtained by employing spatial segmentation to segment the anatomical surface from volumetric data, such as, for example, computed tomography data or magnetic resonance imaging data. The initial probe position relative to the visual anatomical representation generated based on surface data may be determined based on the initial probe position as determined relative to a reference anatomical model. For example, a morphing algorithm (such as linear interpolation or mesh-based morphing) may be employed to map initial probe position as determined relative to a reference anatomical model onto the visual anatomical representation generated based on surface data associated with the subject.

[0081] The ultrasound probe may employ any transducer configuration that is suitable for detection of Doppler ultrasound signals capable of characterizing blood flow in arterial vessels. In some example implementations, the ultrasoundtransducer may include a one-dimensional array, and the ultrasound probe may include, or may be interfaced with suitable driving / or beamforming circuitry to facilitate imaging via linear array based imaging or phased array imaging, such that two-dimensional image data is generated associated with a planar imaging volume. Alternatively, the ultrasound probe may include a single element transducer that is mechanically scanned to acquire Doppler ultrasound image data. The initial probe position (and optionally, the initial probe orientation) may be determined such that at least a portion of the target vessel lies proximal to the planar imaging volume. The initial probe orientation may be determined such that at least a portion of the target vessel lies within or substantially parallel to the planar imaging volume. Non-limiting examples of suitable ultrasound probe configurations and ultrasound transducer configurations are described, for example, in International Patent Application No. PCT / CA2023 / 050413, filed March 28, 2023 and titled “SYSTEMS, DEVICES AND METHODS FOR ULTRASOUND DETECTION OF VASCULAR HEMODYNAMIC MEASURES”, which is incorporated herein by reference in its entirety. Various example probe positioning mechanisms are described in further detail below.

[0082] In other example embodiments, the ultrasound probe may include a two- dimensional array of ultrasound elements configured to generate three-dimensional image data associated with a volumetric imaging volume. In some example implementations, the initial probe position (and optionally, the initial probe orientation) is determined such that at least a portion of the target vessel lies within or lies proximal to the volumetric imaging volume.

[0083] In one example implementation, a two-dimensional ultrasound array can additionally or alternatively be employed in a bi-plane mode, where instead of producing a volume, two bidirectional imaging planes are generated. In some example implementations, these imaging planes are orthogonal to each other, while in other example implementations, the imaging planes are oriented at a user-defined angle, for example, through electronic steering. While a bi-plane mode can be implemented using a two-dimensional transducer array as noted above, in other example implementations, a mechanical biplane transducer could be employed in the alternative, where two one-dimensional transducer arrays are placed in a mechanical fixture in a pre-determined orientation to produce imaging in the two planes.

[0084] Referring again to FIG. 1 , as described above, the recommended initial ultrasound probe position (and optional initial ultrasound probe orientation) may lack sufficient positional and orientational accuracy to ensure that when the ultrasound probe is placed on the subject, the target arterial vessel will be within the imaging field of view of the ultrasound probe. Accordingly, as shown at step 130 in FIG. 1 , the user may be instructed to move the ultrasound probe in order to facilitate arterial vessel detection during initial collection of Doppler ultrasound image data (e.g. data suitable for colour or power Doppler image generation). The guidance may include, for example, instruction to translate the ultrasound probe along a prescribed direction, relative to the initial probe position, for aligning the ultrasound probe with the target vessel, and / or instruction to tilt the ultrasound probe about to a prescribed axis for aligning the ultrasound probe with at the target vessel. The prescribed axis may be associated with a known orientation of the arterial vessel within the anatomy. For example, the example user interface guidance image shown in FIG. 4 shows a specific initial position and orientation of the ultrasound probe, and a prescribed axis of recommended rotation of the ultrasound probe to facilitate search for a target arterial vessel.

[0085] The present disclosure also provides example systems and methods that provide guidance, while moving an ultrasound probe relative to a subject and collecting Doppler ultrasound image data, to facilitate the search and detection of an arterial vessel, as illustrated by the method shown in the flow chart presented in FIG. 5. Such methods may, for example, be employed to facilitate arterial vessel detection, after having performed the initial steps shown in FIG. 1 , as shown by the optional step 140, indicated by the dashed arrow at the top of the flow chart in FIG. 5. It will be understood, however, that the method shown in FIG. 5 is not limited to being executed only after having previously performed the steps of FIG. 1 , and that in some example implementations, an alternative probe position initialization method is performed prior to performing the method illustrated in FIG. 5. For example, in some implementations, the steps performed in FIG. 5 relate to diagnostic investigations that are not associated with the presence of a wound.

[0086] As shown at step 200 in FIG. 5, as an ultrasound probe is moved relative to a subject to search for an arterial vessel, the ultrasound probe is autonomously controlled to collect a Doppler ultrasound image dataset that may be processed to detect a presence or an absence of arterial blood flow, such that a plurality ofDoppler ultrasound image datasets are collected, with at least two Doppler ultrasound image datasets corresponding to different positions and / or orientations of the ultrasound probe. Each Doppler ultrasound image dataset may contain data suitable for generating a colour Doppler image, although in some example implementations, a colour Doppler image is not displayed while searching for an arterial vessel.

[0087] The ultrasound probe may be configured according to one or more presets suitable for the anatomical region of interest. For example, the gain, pulse repetition frequency, wall filter, line density may be selected and / or optimized for the anatomy of interest. In some example implementations, the ultrasound system includes a library of presets for different anatomical regions, such as presets for diagnostic ultrasound performed on the pedal region. As part of the preset, the Doppler acquisition image window (colour box) may be selected, for example, to cover the entire region of the B-mode image region, or, for example, a subset of the B-mode image region. In some example implementations, the ultrasound beam is steered so that the acoustic beam is oriented at an angle, relative to the external anatomical surface, and such that the colour box has a trapezoid shape.

[0088] In some example implementations, the Doppler ultrasound image datasets contains sufficient time-dependent data to facilitate a measure of pulsatility. Various example methods of processing a given Doppler ultrasound image dataset for the detection of arterial blood flow are described below.

[0089] As shown in optional example step 210 (shown having a dashed border indicative of its optional status), a guidance image is displayed to the user while the ultrasound probe is moved relative to the subject, the guidance image showing, in real time (defined as having a refresh rate of less than 100 ms), or near real-time (defined herein as having a refresh rate of less than 500 ms, less than 1 s, less than 1 .5 s, or less than 2s), image regions associated with arterial blood flow, thus providing for immediate or nearly immediate feedback. In some example implementations, the pixel intensity of the guidance image is associated with an intensity of local arterial blood flow. In some example implementations, the guidance image includes structural B-mode image data, thereby enabling the user to observe structural vessel features neighbouring regions of arterial blood flow.

[0090] In one example implementation involving the use of a two-dimensional ultrasound array operated in bi-plane mode, or involving the use of a mechanicalbiplane transducer, during the arterial vessel localization phase, each of the planes could be independently imaged, and the Doppler (and optionally B-mode) image dataset from each image can be employed for the generation of guidance images and / or for the autonomous localization of the arterial vessel, as described below. Depending on the orientation of the vessel, Doppler (and optionally B-mode) image data could be collected and processed for both the longitudinal orientation and transverse orientation of the vessel, optionally being employed to generate navigation images to facilitate the search for an arterial vessel and alignment of the ultrasound probe with the arterial vessel. In some example implementations, the ultrasound dataset collected based on the longitudinal orientation (i.e. determined numerically by having larger area and a rectangular shape compared to circular) can be used to estimate the Doppler angle and proceed for analysis with Spectral Doppler, as per the workflow described below.

[0091] It will be understood that the ultrasound image data (Doppler and / or structural) can be processed according to a wide variety of approaches to detect arterial blood flow. In one example implementation, the Doppler ultrasound image dataset is processed to detect arterial blood flow by detecting one or more image regions satisfying pulsatility criterion associated with arterial pulsation.

[0092] For example, pulsatility may be calculated as follows. For each pixel in a Doppler ultrasound image data set, a time-series plot can be generated which would contain N points. The Fourier spectrum of these N points can be computed, and the frequency with the highest energy may be determined. A numeric filter can be applied to determine whether or not the frequency falls within the physiological cardiac heart rate frequency range. Pixels having frequencies that fall within the physiological cardiac heart rate frequency range are labeled as arterial flow. In this manner, a pulsatility map can be generated. The number of frames N can be determined from experimental data, for example, based on a tradeoff between latency in updating the pulsatility map and obtaining a robust measurement. Such a pulsatility may be generated in real time or near real time. In some example implementations, the pulsatility map is overlaid on top of the existing ultrasound image (e.g. B-mode and pulsatility; B-mode, colour Doppler mode and pulsatility; colour Doppler mode and pulsatility). In some example implementations, a separate pulsatility image is presented in addition to one or more standard ultrasound images.

[0093] In some example implementations, at least one image region satisfies criteria (one or more criterion) indicative of arterial blood flow. In some example implementations, at least one image region satisfies at least two criteria indicative of arterial blood flow. Non-limiting examples of suitable criteria for inferring local arterial blood flow include a pulsatility threshold and a threshold associated with a pulse repetition frequency.

[0094] In some example implementations, at least one criterion indicative of arterial blood flow is associated with a structural vessel feature associated with 13- mode structural image data. Non-limiting examples of criteria associated with structural vessel features indicative of arterial blood flow include vessel wall thickness, vessel compressibility, and vessel directionality.

[0095] FIG. 6A shows an example user interface in which a guidance image is provided, while repositioning an ultrasound probe, where the guidance image shows regions of arterial pulsatility. As shown in the figure, the system continues to instruct the user to reorient the ultrasound probe as the Doppler ultrasound image data is collected (e.g. until an arterial vessel satisfying sufficiency criteria is detected, as described in further detail below). FIG. 6B shows the same user interface, where the ultrasound probe has been moved to a location / angle showing an increased pulsatility signal.

[0096] In some example implementations, the guidance image showing arterial blood flow is generated in the absence of displaying colour Doppler image data. Indeed, the present inventors have found that by displaying guidance images that show regions of arterial blood flow, but do not show the full data that would be presented in a colour Doppler image, the user can focus on the relevant arterial flow portion of the image. Accordingly, the guidance image can be presented with less visual complexity and can thus be beneficial for avoiding confusion in users that lack expert training or are minimally skilled. For example, FIG. 7 A shows a guidance image that only shows regions arterial blood flow, while FIG. 7B shows a guidance image that includes full colour Doppler data. FIG. 7A provides a clearer and simpler image that directly shows regions of arterial flow without the complexity of non- arterial regions shown in FIG. 7B.

[0097] For example, in some example implementations, the guidance image provided for facilitating arterial vessel localization is generated as a power Doppler image, which can, in addition or in alternative to colour Doppler, be used to identifythe locations with flow and thus determine the orientation and location of the vessel. The regions of arterial flow identified via power Doppler can then used to determine the suitable volume for spectral Doppler data acquisition, as described below.

[0098] Power Doppler is a specialized ultrasound imaging technique that visualizes blood flow. Unlike conventional colour Doppler, which displays the speed and direction of blood flow, power Doppler focuses on the amplitude (strength) of the Doppler signal. It typically displays this information as a single color (often orange or shades of red / yellow) with varying brightness, where brighter areas indicate stronger signals and thus more blood flow. Power Doppler is particularly useful for localizing blood vessels due to its enhanced sensitivity to low-velocity and small-volume blood flow, which are often difficult to detect with standard colour Doppler.

[0099] In some example implementations, directional power Doppler may be employed to facilitate the visualization and localization of an arterial blood vessel. Directional Power is an advanced ultrasound imaging technique that aims to combine the high sensitivity of conventional power Doppler with a degree of directional information, typically presented as a subtle color hue. While traditional power Doppler displays only the strength of the Doppler signal (i.e., the amount of blood flow) without indicating direction, directional power Doppler provides directional information alongside the intensity information. It does this by analyzing the phase shift of the Doppler signal allowing it to differentiate between flow moving towards or away from the transducer. The visual output often appears as a single color (e.g., orange or red) where the brightness still represents the strength of the flow (like standard Power Doppler), but a very slight hue variation or a subtle dualcolor scheme (e.g., warmer shades for one direction, cooler for the other) can indicate the general direction. Accordingly, to provide guidance that facilitates vessel localization, the Directional Power image can be employed, in addition to or in alternative to colour Doppler, to identify the locations with flow and hence determine the orientation and location of the vessel. The determined location can then be used to position the sample volume for spectral Doppler acquisition.

[0100] In some example embodiments that involve the presentation, while searching for an arterial vessel, of a guidance image that shows regions of arterial blood flow, a color Doppler image, or another Doppler image variation (e.g. power Doppler), is overlaid with the arterial blood flow image (e.g. generating a composite image). In other example implementations, a color Doppler image, or anotherDoppler image variation, is displayed an additional image, in addition to the arterial blood flow image. An example colour Doppler image associated with an arterial vessel is shown in FIG. 8.

[0101] Referring again to the example workflow illustrated in FIG. 5, as shown at optional steps 220 and 230, as the ultrasound probe is moved to search for an arterial vessel, the Doppler ultrasound image datasets acquired as the probe is moved are processed until arterial blood flow is detected. If arterial blood flow is not detected, steps 200 may be 220 are repeated as the probe is moved to interrogate an adjacent region.

[0102] In some cases, while moving the ultrasound probe to search for an arterial vessel, arterial blood flow can be detected corresponding to a weak signal that would be insufficient to perform spectral Doppler analysis. For example, such a weak signal may arise from cases involving very small vessels, or when there is insufficient spatial overlap between the ultrasound energy beam and larger arterial vessel. Accordingly, as shown at step 240, a Doppler ultrasound image dataset containing regions of arterial blood flow is processed to determine whether or not one or more regions of the image satisfy arterial vessel detection criteria (one or more criterion) indicative of a sufficiency of arterial Doppler signal for performing spectral Doppler measurement.

[0103] As shown at example step 232, if arterial blood flow is detected in step 230, then the user is be instructed to maintain the current position and orientation of the ultrasound probe to facilitate the subsequent determination, in step 240, of whether or not a given region of arterial blood flow satisfies arterial vessel criteria indicative of a sufficiency of arterial Doppler signal for subsequent spectral Doppler analysis. Alternatively, the system can proceed, after having detected arterial blood flow in step 230, directly to step 240, for example, if the assessment of the arterial vessel criteria in step 240 can be made with sufficient speed, relative to changes in the position and / or orientation of the ultrasound probe, without needing to instruct the user to maintain the probe position and orientation.

[0104] While it can be advantageous and / or practical to first assess the Doppler ultrasound image data for the assessment of arterial blood flow prior to the determination of whether or not the Doppler ultrasound image data includes one or more image regions that satisfy arterial vessel criteria, in other example embodiments, the Doppler ultrasound image data collected as the probe is moved isdirectly processed, as per step 240, to determine whether or not one or more regions of the image satisfy arterial vessel detection criteria (one or more criterion) indicative of a sufficiency of arterial Doppler signal for performing spectral Doppler measurement. Accordingly, to indicate this optional nature of the arterial blood flow pre-assessment workflow, steps 220, 230 and 232 are shown in dashed outline. In some example implementations, these steps are optionally be included as a group of steps as indicated at 234.

[0105] Referring again to steps 240 and 250, when at least one image region is found to satisfy the arterial vessel detection criteria, the user is instructed to maintain the current position and current orientation of the ultrasound probe, so that spectral Doppler ultrasound data can be acquired, as shown at step 260 of FIG. 5. If the implementation of the method includes step 232, and the user had already been instructed to maintain the position and orientation of the ultrasound probe, the user may be instructed, in step 260, to further maintain the position and orientation of the probe, for example, via newly a communicated additional instruction, or via a persistence of the previous instruction.

[0106] It will be understood that the arterial vessel detection criteria can include one or more criterion associated with a sufficiency of Doppler signal originating from arterial blood flow. In one example embodiment, the arterial vessel detection criteria is based on a spatial measure (e.g. a spatial dimension or area) characterizing a connected set of arterial flow pixels in a pulsatility image that exceed a prescribed threshold value, such that when a connected set of pixels has exceeds a minimum size criteria or minimum area criteria, a determination is made that the connected region of arterial flow corresponds to an arterial vessel having a sufficiently strong signal to facilitate the measurement of spectral Doppler data and the subsequent processing of the spectral Doppler data to generate one or more hemodynamic measures.

[0107] FIG. 9 shows a user interface image highlighting a connected region 280 of arterial flow pixels satisfying arterial vessel detection criteria, with the user interface indicating to the user that the current position and orientation of the ultrasound probe has resulted in the detection of an arterial vessel with sufficient arterial flow for subsequent processing.

[0108] In an example implementation of such an embodiment, a Doppler window (e.g. 2 mm by 2 mm section) applied to the input color flow image, produces anestimate of pulsatility by estimating the Fourier spectrum of the color flow value as a function of time. In some example implementations, the Fourier analysis window size can be equivalent of 2-3 seconds to obtain enough periodicity. In the Fourier spectrum, the Fourier magnitude or energy value of the highest peak in the frequency range of 0.5 to 2.5 Hz is obtained (can adapted as a hyperparameter during model validation and testing). Thus, the window determines the value from the highest peak in the Fourier spectrum. This process is repeated for all windows across the entire image. Subsequently, all points in the resulting pulsatility image having a value greater than a pre-determined threshold are determined. This threshold can be estimated, for example, by computing the noise floor on the spectrum when there is no flow. According to one example implementation, a binary map is generated for all points in the pulsatility map exceeding the threshold, and any suitable methods for determining a set of connected pixels in a binary image is employed to identity one or more connected pixel regions of arterial pulsation exceeding the threshold. Non-limiting example of suitable algorithms for determining regions of connected vessels include the connected components detection and analysis algorithm known from the computer vision and image understanding / processing domain. The present example method produces a labeled binary map where the regions of connected pixels can be identified as an arterial vessel. In some example implementations, if the area and / or size (e.g. at least one spatial dimension) of the vessel exceeds a pre-determined threshold, it is determined that an arterial vessel sufficient for spectral Doppler analysis has been detected, and the user can be instructed to stop moving the ultrasound probe.

[0109] Referring again to FIG. 5, after having determined that an arterial vessel has been detected, spectral Doppler data (or another form of Doppler data) can be collected within a selected subregion of the arterial vessel. This subsequent processing, or other forms of subsequent processing of Doppler and / or structural ultrasound data associated with the detected arterial vessel, is illustrated by arrow 270, indicating further ultrasound data acquisition and / or processing steps.

[0110] An example subsequent spectral Doppler processing method is illustrated in FIG. 10. In some example implementations, this workflow continues from step 270 of FIG. 5, as shown by the dashed arrow labelled 270 at the top of FIG. 10, while in other example implementations, the workflow continues from another method of autonomous arterial vessel detection. As shown at step 300 of FIG. 10, a subregionis determined, within a detected region of arterial blood flow, for the acquisition of spectral Doppler data. An arterial vessel angle associated with the subregion is also determined, thereby facilitating the determination of a Doppler angle for autonomous Doppler correction. Also, as shown in step 300, a beam steering angle is determined for steering the ultrasound energy beam emitted by the ultrasound energy beam. This beam steering angle is selected to improve or optimize the Doppler signal, for example, to achieve a sufficiently small Doppler angle based on the steering angle range achievable by the ultrasound transducer array.

[0111] In some example implementations, the subregion and beam steering angle are determined as follows. The region of arterial flow satisfying the arterial vessel detection criteria is first processed to determine the local arterial vessel axis, enabling the determination of the Doppler angle based on a given beam steering angle. The local arterial axis can be determined, for example, by first, computing the principal components from spatial coordinates of the identified points where arterial flow has been identified, second, taking a few points at a time traversing the vessel along the largest principal component direction (which is the vessel orientation), computing the centroid of the collection of points to find the vessel center at that position, and third, repeating the above step until all points have been included in the centroid calculation. Once the center line of the vessel is identified, the geometric angle between the acoustic beam and the vector passing through all the center-line points is computed using first principles trigonometry. The location of the subregion and the beam steering angle are selected such that the subregion resides within the region of arterial flow associated with the detected arterial vessel, and the resulting beam steering angle provides the smallest Doppler angle. In some example implementations, the subregion location and beam steering angle may be constrained such that the resulting Doppler angle is less than 60 degrees.

[0112] Another criterion that can be employed to determine a suitable location for the spectral Doppler subregion is based on the connectedness of pixels in the pulsatility map. For example, locations where arterial flow is detected for the most pixels in a predefined neighborhood may be identified as being suitable for locating the subregion.

[0113] After the system has autonomously computed the location of the subregion, a determination of a preferred beam steering angle, and the local vessel axis, this information is employed by the transmit circuitry of the ultrasound system inpreparation for spectral Doppler data acquisition. FIG. 11 A shows an example user interface displaying the location of the subregion 350 suitable for performing spectral Doppler data acquisition. The figure also shows the local arterial vessel axis 360 and autonomously computed beam steering direction 370.

[0114] The angle between the local arterial vessel axis 360 and the beam steering direction 370 is the Doppler angle and may be autonomously employed to perform Doppler angle correction. The angle correction is applied to spectral Doppler data to ensure that an accurate velocity measure is obtained. The velocity calculation employs the cosine of the angle between the vessel and the ultrasound acoustic beam, as per the following equation:Af = 2*v*cos(0)*fo / c , Eqn. (1 ) where Af is the frequency shift measured by the ultrasound system, fo is the transmit frequency, c is the speed of sound and v is the blood velocity to be determined. For the chosen sample volume and beam steering angle, the angle 0 can be calculated and is referred to as the Doppler angle.

[0115] While the present example workflow illustrated in FIG. 10 shows step 300 as occurring after having instructed the user to maintain the current position and angle of the ultrasound probe relative to the subject (with this step shown in FIG. 5), it will be understood that in some example implementations, any one or more of the operations performed in step 300 can be performed prior to instructing the user to maintain the current position and angle of the ultrasound probe relative to the subject.

[0116] Furthermore, although the example workflow of FIG. 10 shows step 300 as occurring after having determined that the arterial vessel detection criteria has been satisfied by one or more regions of arterial flow, it will be understood that the step of determining the subregion suitable for performing spectral Doppler data acquisition can, in some example implementations, form at least one component or one aspect of the arterial vessel detection criteria. That is to say, the determination of the presence, within the Doppler ultrasound image dataset, at least one subregion suitable for performing spectral Doppler data acquisition may be performed directly, without having first confirmed that separate arterial vessel detection criteria has been satisfied, as the existence of such a subregion is direct confirmation of sufficiency of arterial flow and the presence of an arterial vessel sufficient for performing spectral Doppler data acquisition. Alternatively, the step of determining the presence, withinthe Doppler ultrasound image dataset, of at least one subregion suitable for performing spectral Doppler data acquisition, may be considered to constitute, at least in part, the determination of the subregion satisfying the arterial vessel detection criteria.

[0117] For example, in one example implementation, after one or more regions of connected pixels are identified from a binary pulsatility map, the decision logic to select a subregion for suitable for performing spectral Doppler data acquisition is directly applied, effectively as a component of the arterial vessel detection criteria. For example, a threshold can be applied on the ranked score for determining the best location for the subregion. If at least one location exceeds that score, it can be concluded that a suitable location for the subregion has been found and the user can be instructed to hold the probe steady. Such an example implementation ensures that when the user is told to maintain the probe position and orientation, a suitable subregion for performing spectral Doppler data acquisition has already been found.

[0118] In some example implementations, the arterial vessel detection criteria may result in the identification of more than one vessel. For example, FIG. 11 B illustrates an example case in which three arteries (400, 410 and 420) have been identified by evaluation of the arterial vessel detection criteria. Given the three detected arteries, an algorithm can be employed to select an arterial vessel (e.g. determine which artery would be preferred or most suitable) for the subsequent measurement of spectral Doppler data, thereby enabling a determination of suitable artery for placement of the subregion for spectral Doppler data acquisition. For example, the size of the region of flow may be employed when multiple independent flow regions are detected, with the largest detected region is considered to represent arterial flow.

[0119] In some example implementations, the selection of a preferred arterial vessel, among multiple detected arterial vessels, for placement of the subregion for subsequent spectral Doppler data acquisition, is made based on a spatial measure associated with the region of connected arterial flow pixels associated with each detected arterial vessel. In other example implementations, one or more other measures are employed, in addition or in alternative to a spatial measure associated with the region of connected arterial flow pixels, to select one detected arterial vessel for placement of the subregion for subsequent spectral Doppler processing.

[0120] For example, in one example implementation, an adjacency matrix (an example of a spatial measure) can be computed for multiple points on each vessel. The adjacency matrix will show how many adjacent points have strong pulsatility. The strength can be determined by computing the correlation coefficient between the pulsatility pattern for each of these points. This provides a measure of how robust the arterial flow is in each vessel candidate location.

[0121] In another example implementation, the orientation of the vessel and the Doppler angle (another example of a spatial measure) which represents the angle between the flow direction and the acoustic beam may be employed to select an arterial vessel. For example, a table of Doppler angle values can be generated for multiple points within each of the vessels, taking into account the possible beam steering angle values.

[0122] In another example implementation, a spatial measure associated with the distance between each detected vessel and the transducer aperture is employed for facilitating the selection of an arterial vessel for placement of the spectral Doppler subregion. For example, the spatial position of the points in each vessel candidate can be determined, and a table can be generated showing how far each point is from the edge of the transducer aperture.

[0123] In some example implementations, one or more of the preceding example criteria may be employed to perform arterial vessel selection and location of a subregion for performing spectral Doppler measurements. For example, an optimal location may be determined based on the following criteria: the smallest Doppler angle (closer to 0 the better), the maximum number of neighboring points with correlation greater than a predefined threshold (e.g. 0.9 normalized correlation coefficient), and the largest azimuth (horizontal) distance from the end elements of the transducer.

[0124] In one example implementation, a ranked list is created by first computing a total score for each location, and then sorting the list in descending order of this total score. To compute the total score, for example, each location can be assigned a score between 0 and 1 for each of the above categories (i, ii, iii) where 0 is the least favorable value and 1 is the most favorable value. Each of the above factors can be weighted equally or with pre-determined weighting. For the case of the example illustrated in FIG. 11 B, applying the criteria outlined above, the centervessel would be the best with the beam steered from the top right to the bottom left with a sample volume placed around the center of the vessel.

[0125] Referring again to FIG. 10, as shown in step 310, after having determined the subregion, spectral Doppler data is acquired from the subregion. In some example embodiments, this step is performed autonomously, after having identified the arterial vessel and determined the subregion location, without user intervention. For example, this step can be performed directly without requesting confirmation or authorization from a user.

[0126] The resulting spectral Doppler data is then processed in step 320, for example, to generate one or more hemodynamic measures associated with the detected arterial vessel. Non-limiting examples of hemodynamic measures that can be computed based on the acquired spectral Doppler data include peak systolic velocity, mean velocity, end-diastolic velocity, time-averaged maximum velocity, maximum velocity envelope, acceleration time, deceleration time, heart rate, resistance index (measure of peripheral vascular resistance), and local pulsatility index.

[0127] In some example embodiments, the anatomical region interrogated by the ultrasound probe may be a pedal region (a region of the foot) and the spectral Doppler data may be processed to determine a pedal acceleration time (PAT). Nonlimiting examples of methods of calculating the PAT are described, for example, in United States Patent No. 11 ,903,688, filed on February 7, 2020 and titled “VASCULAR FLOW DIAGNOSTIC SYSTEM”, which is incorporated herein by reference in its entirety.

[0128] One example method for calculating the PAT is described as follows. This example method involves the initial determination of a maximum velocity waveform. The maximum velocity waveform is based on the calculation of the integrated power spectrum from the spectral Doppler waveform, and the application of a threshold on the maximum value to assign a maximum frequency / velocity. The integrated power spectrum is computed by performing a cumulative sum of the spectral energy at every frequency bin (i.e. along Y-axis of the Doppler spectrum) for every time interval (i.e. one time value on the X-axis). This plot will plateau as the maximum velocity point is approached. A threshold (e.g. 2% below the maximum) is applied on this integrated power plot to determine the frequency bin (i.e. velocity value) corresponding to the maximum velocity. This is performed for each time interval andthe resulting points, when connected, result in the maximum velocity envelope. From the maximum velocity envelope, the PAT estimation algorithm can operate according to the following steps:

[0129] Step 1 : the frequency spectrum of the maximum velocity envelope is computed. From the frequency spectrum, the period T of the waveform is determined. Within every T seconds, the peak and the time of the peak is determined. This peak is the maximum velocity in each cardiac cycle.

[0130] Step 2: for each peak recorded in Step 1 above, the time instant when this peak occurs (ti) is determined.

[0131] Step 3: moving down the envelope to the left, the time instant when the velocity is the lowest is identified. This time is referred to as systolic up-rise point (td).

[0132] Step 4: from td, moving to the right, the local slope is computed, such as the slope through every pair of points. The first instant where the slope reduces by a predetermined amount, such as, for example, 10% compared to the previous point, is determined. When this occurs, the second point in the most recent slope calculation is identified as the peak of systole (referred to as ts). It is noted that while ti and ts may overlap, this is not necessary, especially when the waveform is muted (i.e. flat) at the end where the peak may occur later in time but is not the appropriate time point for PAT measurement.

[0133] Step 5: from tsand td, the acceleration time is calculated as ts-td for this cardiac cycle, and the result is recorded.

[0134] Step 6: steps 2 to 5 are repeated for each detected peak.

[0135] Step 7: the average of the PATs from Step 6 is computed and reported / recorded as the PAT value.

[0136] FIG. 12A presents an example user interface image showing a spectral Doppler waveform collected from the selected subregion. The spectral Doppler waveform is annotated to show the measurement points for computing the acceleration time for two representative cardiac cycles. A more detailed case of showing the selection of the time points tsand tdfor the computation of acceleration time is shown in FIG. 12B.

[0137] Referring now to FIGS. 13A to 13G, an example workflow is shown that illustrates a subset of the steps shown in FIG. 5 and FIG. 10. FIG. 13A shows the spatial map of detected arterial and venous flow (typical of what is commonly referred to as a Duplex Color flow image in the clinical ultrasound domain). FIG. 13Bshows the time-dependent pulsatile flow profile corresponding to the artery location (circle) in FIG. 13A. This profile is obtained by plotting the color pixel (specifically the R channel) value at the circle location across all the frames in the sequence. FIG. 13C again shows the spatial map of detected arterial and venous flow, while FIG. 13D shows the non-pulsatile flow profile corresponding to the venous location (circle) in FIG. 13C. The horizontal axis on FIG. 13B and FIG. 13D represents the frame number with a frame rate of 20 Hz. Hence, the total time duration is 3 seconds. In an automated system, the pulsatile behavior of FIG. 13B (representative of arterial flow) can be automatically identified and distinguished from FIG. 13D (representative of venous flow) using Fourier spectral analysis where FIG. 13B provides a dominant frequency component at 1 Hz compared to FIG. 13D which does not have such a periodic dominant frequency.

[0138] Referring now to FIGS. 13E and 13F, FIG. 13E again shows the map of detected arterial and venous flow, while FIG. 13F shows only the segmented arterial flow region. FIG. 13G shows the result of the application of criteria for the determination of a suitable location for the subregion for spectral Doppler acquisition, as well as the computed beam steering angle.

[0139] Many of the example embodiments described above have been presented as a two-step ultrasound acquisition workflow that involves (i) the initial acquisition of a Doppler dataset suitable for generating spatial representations of blood flow that facilitate arterial vessel identification and localization, and also enable the determination of the subregion for the collection of a spectral Doppler dataset (as well as an arterial vessel angle and a beam steering angle), and (ii) the subsequent acquisition of a spectral Doppler dataset from the identified subregion. However, in other example embodiments, alternative ultrasound beamforming methods may be employed to facilitate the acquisition of a raw RF ultrasound dataset that can be retrospectively processed to generate visualizations suitable for vessel identification and localization, such as colour Doppler, power Doppler, directional power Doppler, or variations thereof, and with the same raw RF ultrasound dataset being processed to generate, from an identified arterial flow location, spectral Doppler ultrasound data.

[0140] Indeed, unlike conventional duplex Doppler methods (Color flow / Power Doppler / Directional Power) that involve the acquisition of an initial Doppler dataset and the that facilitates vessel visualization and the determination of a sample volumefor spectral Doppler acquisition, followed by the subsequent acquisition the spectral Doppler dataset, “flash” insonification methods which insonify a broad region of interest and involve the collection of RF data (such as, for example, plane wave imaging with parallel beamforming) leverage the high spatiotemporal sampling capabilities afforded by transmitting unfocused plane waves and simultaneously receiving echoes across a wide aperture using parallel beamforming. This "flash" insonification of a broad region of interest enables the capture of raw ultrasound [radiofrequency (RF)] data from a wide range of relevant locations concurrently. Subsequently, retrospective beamforming is performed on this acquired dataset to computationally generate a map of Color Flow, Power Doppler and / or Directional Power. A vessel localization algorithm (e.g. such as those described above) may then employ one (or optionally more) of these datasets (spatial maps) to determine the location of the flow. At an identified location corresponding to flow (e.g. a peak Doppler power, or other measure such as those described above), a full Doppler spectrum is then retrospectively computed (as opposed to being newly acquired) from the same raw RF data, providing comprehensive quantitative information on blood flow velocity, pulsatility, and spectral broadening, without the need for additional transmit sequences or user intervention. Such methods can significantly enhance workflow efficiency and reduce inter-operator variability by automating both vessel detection and the precise acquisition of a diagnostic Doppler spectrum, improving the accuracy and consistency of vascular assessments.

[0141] Accordingly, in some example embodiments of the workflow outlined in FIGS. 5 and 10, the ultrasound Doppler dataset collected in step 200 may be based on a distributed, unfocused, broad insonification method, with the ultrasound dataset including RF data, such as plane wave ultrasound RF data, that can be retrospectively processed to generate both spatial flow image datasets (e.g. colour flow Doppler, power Doppler and directional power Doppler image datasets) in step 220 of FIG. 5 and also spectral Doppler datasets characterizing temporal signatures within a region of interest in step 320 in FIG. 10, with the secondary acquisition step 310 of FIG. 10 being omitted.

[0142] FIG. 14 shows an example system for performing ultrasound measurements using an ultrasound transducer array 740. The example system includes ultrasound device 730 that includes ultrasound transducer array 740, a transmit beamformer 700 with pulser-receiver circuitry 720 (e.g. including a Tx / Rxswitch), a receive beamformer 710 and control and processing hardware 600 (e.g. a controller, computer, or other computing system).

[0143] Control and processing hardware 600 is employed to control transmit beamformer 700 and receive beamformer 710, and for processing the beamformed receive signals. As shown in FIG. 14, in one embodiment, control and processing hardware 600 may include a processor 610, a memory 620, a system bus 605, one or more input / output devices 630, and a plurality of optional additional devices such as communications interface 660, display 640, external storage 650, and data acquisition interface 670.

[0144] The present example methods involving the control of the ultrasound transducer array 740 for performing hemodynamic measurements (e.g. the detection of PAT) can be implemented via processor 610 and / or memory 620. As shown in FIG. 14, the control of the ultrasound transducer array 740 may be implemented by control and processing hardware 600, via executable instructions represented as hemodynamic calculation module 690. The control and processing hardware 600 may include and execute scan conversion software (e.g. real-time scan conversion software).

[0145] In some example implementations, the transducer array 740 is controlled to obtain one or more Doppler (flow velocity) waveforms, as indicated by Doppler processing module 680. In some example embodiments, the transducer array may be controlled to scan the ultrasound beam and generate an ultrasound image, for example, as controlled via image processing module 685. Each Doppler waveform may correspond to a different location, such as a location within an image acquired by the ultrasound transducer array 740. The ultrasound image may be a Doppler ultrasound image.

[0146] In some example implementations, the control and processing hardware 600 may be employed to process a given Doppler waveform in order to calculate one or more hemodynamic measures, such as the PAT, as schematically shown by hemodynamic calculation module 690. For example, a Doppler waveform may be processed to calculate the PAT by calculating the time from the beginning of systole to the peak of systole. Velocity waveforms may also be captured.

[0147] It will be understood that the PAT is but one example of a hemodynamic measure that can be determined via the processing of one or more Doppler waveforms. Non-limiting examples of additional or alternative hemodynamicmeasures include flow volume, peak velocity, beats per minute, and velocity slope from start to end of systole.

[0148] In some example implementations, the ultrasound beam transmitted by the ultrasound transducer array 740 may be scanned in order to identify one or more regions associated with a sufficiently high Doppler signal, such as a location corresponding to an arterial vessel of interest for performing hemodynamic measurements. For example, the transmit beamformer 700 can be controlled to scan the ultrasound beam across a 1 D or 2D angular range (2D if the transducer array is a 2D transducer array) and the Doppler signals may be processed to determine an angle that corresponds to maximal signal, as schematically shown by scanning module 695. In some example implementations, a preferred angle may be determined by processing the collected Doppler signals according to a machine learning algorithm, such as a neural network, that was trained with Doppler signals having a desired shape and / or signal-to-noise ratio.

[0149] The functionalities described herein can be partially implemented via hardware logic in processor 610 and partially using the instructions stored in memory 620. Some embodiments may be implemented using processor 610 without additional instructions stored in memory 620. Some embodiments are implemented using the instructions stored in memory 620 for execution by one or more general purpose microprocessors. In some example embodiments, customized processors, such as application specific integrated circuits (ASIC) or field programmable gate array (FPGA), may be employed. Thus, the disclosure is not limited to a specific configuration of hardware and / or software.

[0150] It is to be understood that the example system shown in FIG. 14 is not intended to be limited to the components that may be employed in a given implementation. For example, the system may include one or more additional processors. Furthermore, one or more components of control and processing hardware 600 may be provided as an external component that is interfaced to a processing device. For example, as shown in the figure, any one or more of transmit beamformer 700 and receive beamformer 710 may be included as a component of control and processing hardware 600 (as shown within the dashed line), or may be provided as one or more external devices.

[0151] While some embodiments can be implemented in fully functioning computers and computer systems, various embodiments are capable of beingdistributed as a computing product in a variety of forms and are capable of being applied regardless of the particular type of machine or computer readable media used to actually effect the distribution.

[0152] At least some aspects disclosed herein can be embodied, at least in part, in software. That is, the techniques may be carried out in a computer system or other data processing system in response to its processor, such as a microprocessor, executing sequences of instructions contained in a memory, such as ROM, volatile RAM, non-volatile memory, cache or a remote storage device.

[0153] A computer readable storage medium can be used to store software and data which when executed by a data processing system causes the system to perform various methods. The executable software and data may be stored in various places including for example ROM, volatile RAM, nonvolatile memory and / or cache. Portions of this software and / or data may be stored in any one of these storage devices. As used herein, the phrases “computer readable material” and “computer readable storage medium” refers to all computer-readable media, except for a transitory propagating signal perse.

[0154] The preceding example embodiments, and variations thereof contemplated by the present disclosure, may be beneficial in addressing the aforementioned problems associated with need for skilled ultrasound sonographers during vascular ultrasound procedures. Indeed, by providing autonomous guidance in which the user need only be responsible for physically moving the ultrasound probe, the present systems and methods autonomously interpret the Doppler signals, provide feedback to the user whether additional movement is needed or not for arterial vessel detection, and autonomously compute relevant hemodynamic measures associated with detected arterial vessels, significantly reducing the required skill level and experience of the user.

[0155] While the preceding example embodiments have disclosed the autonomous determination of the subregion for subsequent spectral Doppler analysis, it will be understood that in some alternative implementations, input from the user can be employed to control selection of the subregion location and / or the beam steering angle.

[0156] Moreover, while some of the preceding example embodiments autonomously instruct the user as to when to maintain the position and orientation of the ultrasound probe for the acquisition of spectral Doppler data from a detectedarterial vessel, in other example embodiments, the preferred position and orientation of the ultrasound probe can be determined by the user. For example, the user may determine the preferred position and orientation based on feedback from the guidance images showing detected regions of arterial blood flow. One or more other feedback measures may be provided in addition or in the alternative.

[0157] For example, the system can provide both Doppler audio and a visual Doppler image to the operator, or, alternatively, solely Doppler audio. The operator can use this feedback to steer the beam so as to identify a suitable probe position and orientation. As the beam is steered closer to the vessel, the audio volume will increase, the Doppler sound will become more of a well-defined pulsatile flow sound, the velocity waveform will become more defined, and systolic peaks will increase. As the beam is steered further from the vessel, the audio volume will decrease, the Doppler sound will become less of a well-defined pulsatile flow sound, the velocity waveform will become less defined, and systolic peaks will decrease.

[0158] Many of the preceding example embodiments refer to the use of an ultrasound probe that can be secured to the subject and varied in orientation to search for a vessel via Doppler ultrasound. Accordingly, there is a need for a support structure that can support an ultrasound probe in place throughout a procedure, such as on the foot or another anatomical region suitable for interrogating the peripheral vasculature, for providing Doppler ultrasound guidance prior to and during peripheral revascularization procedures. Furthermore, it would be beneficial for the ultrasound probe to be adjustable when secured in place, to assist in vessel localization. Such adjustability can be beneficial in locating a vessel and re-locating the vessel in the event that the support structure and / or ultrasound probe is accidentally moved out of place via patient movement and / or inadvertent contact. Moreover, it would be beneficial for the ultrasound probe to be removable and replaceable in the same position and orientation, for example, to permit fluoroscopic imaging and / or vascular access in the vicinity of the vessel.

[0159] Referring now to FIGS. 15 and 16, an example of such an ultrasound probe positioning system is illustrated. The example ultrasound probe positioning system includes an ultrasound probe 810 and an ultrasound probe positioning apparatus 800. The ultrasound probe positioning apparatus 800 mechanically supports the ultrasound probe 810 while permitting rotation of the ultrasound probe 810 about a pivot axis. The ultrasound probe 810 includes an elongate housing 812 having anassociated longitudinal direction 813. As described in further detail below, an ultrasound beam is emitted through a distal energy-emitting surface 814 of the housing.

[0160] The ultrasound probe 810 is connectable to external processing and drive circuity via a cable 818 extending from an end surface 816 that resides perpendicular to the longitudinal direction of the housing 812. This configuration advantageously reduces or avoids the application of torque by the cable when the ultrasound probe resides in a given orientation during imaging, which can reduce noise associated during the measurement process. The low profile of the transducer and side exit cable thus helps to eliminate long lever arms which can produce large rotational forces and move the positioner out of position.

[0161] Although the housing 812 is shown in the present example implementation as having a shape that includes an upper chamfered rectangular prism and a lower rectangular prism with a narrower width, it will be understood that the housing 812 can take on a wide variety of shapes.

[0162] As shown in FIGS. 15 and 16, the example ultrasound probe positioning apparatus 800 includes a substrate 860 configured to be attachable to a skin surface, such as the surface of a foot of a subject, with a window region 862 that facilitates acoustic coupling of the distal energy-emitting surface 814 of the ultrasound probe 810. In one example implementation, the substrate 860 can be provided as an adhesive-backed foam, optionally with a removable liner on its underside that exposes the adhesive for attachment to the skin. The substrate 860 thus defines a flange that facilitates securing of the ultrasound probe positioning apparatus 800 to the subject. The substrate 860 may be flexible or rigid, and in some example implementations, the substrate 860 may be formed in a shape that is configured to facilitate placement on the subject, optionally via indexing to one or more anatomical features (e.g. bony structures). The substrate 860 may include one or more holes (apertures) suitable for marking a desired location of the ultrasound probe positioning apparatus.

[0163] The substrate 860 rigidly supports a support frame 850, for example, via an adhesive. The support frame 850 is configured to pivotally support a probe receptacle 820, which in turn is configured to securely receive and support the ultrasound probe 810. As shown in the non-limiting example implementation illustrated in FIG. 16, the probe receptacle (cradle) 820 includes holes 880 and 890that receive and engage pins 900 and 910 disposed on the support frame 850, such that the probe receptable 820 is pivotable about a pivot axis defined by the pins 900 and 910. It will be understood that a wide variety of mechanical configurations could be employed to pivotally support the probe receptacle 820 relative to the support frame 850, such that the probe receptacle 820 is capable of rotating, relative to the support frame 850, about a pivot axis. For example, in an alternative example implementation, one or more pins could extend from the probe receptacle 820, and one or more corresponding holes could be defined in the support frame 850.

[0164] As further illustrated in FIGS. 15 and 16, pivotal motion of the probe receptable 820 relative to the support frame 850, about the pivot axis defined by the pins, is further constrained to reside within a limited pivot angle range. In the example implementation shown in FIGS. 15 and 16, the pivot angle range is dictated by a slot 835 that is formed in the support frame 850, which limits motion of a shaft 830 extending from the probe receptable 820 and passing through the slot 835. It will be understood that such a pivot angle constraint could be enforced by a wide range of mechanical limiting features. For example, in another example implementation, the pivot angle could be limited by a pair of structural stops residing on the support frame 850 that limit the range of motion of a protuberance residing on the probe receptable 820 (or vice versa).

[0165] As shown in FIGS. 15 and 16, the ultrasound probe positioning apparatus 800 also includes a locking mechanism capable of locking a pivot angle (an orientation) of the probe receptable 820 relative to the support frame 850. While the example implementation shown in FIGS. 15 and 16 employs a nut 840 that threads onto the shaft 830 and can be tightened to lock a given pivot angle, or loosened to permit variation in the pivot angle, it will understood that other locking mechanisms may be employed in the alternative. Examples of locking mechanisms that may be employed, include, but are not limited to, locking screws / knobs, clamping collars and other clamping mechanisms, latches, and other suitable fixation mechanisms. The locking means may be actuated after determining, based on the detection or monitoring of Doppler ultrasound signals, that the ultrasound transducer is aligned on a vessel of interest.

[0166] In some example embodiments, a scale (e.g. an angle scale or a linear position scale with a set of markings) may be provided to facilitate the visual determination of a given angle or position of the ultrasound probe relative to thesupport frame. For example, the support frame and / or the probe receptacle may include an orientation scale that permits visual determination of the orientation of the ultrasound transducer relative to the support frame.

[0167] In some example implementations, an encoding mechanism may be employed to facilitate encoding of the angle of the probe receptable / ultrasound probe relative to the support frame. For example, an optical encoder or electrical encoder (e.g. conductive or potentiometer based) may be employed. The encoding mechanism may include an encoding interface, such as a reflective interface or conductive interface with a set of markings or conductive features, and an encoding sensor, such as an optical emitter / detector or a conductivity / resistance detection circuit, where the encoding sensor moves relative to the encoding interface, or vice versa. The signal from the encoder sensor may be employed and processed by control and processing circuitry to determine an angle of the probe receptable / ultrasound probe relative to the support frame.

[0168] As shown in FIGS. 17A and 17B, the probe receptacle 820 is configured to rigidly and removably secure and support the ultrasound probe 810, such that the ultrasound probe 810 rotates in unison with the probe receptacle 820. The ultrasound probe 810 may be rigidly and removably secured within the probe receptacle 820 according to a variety of means, including, for example, a friction fit, a clasp, and a strap. In some example implementations, a hinged plastic latch can hold the probe in place. Foam placed on the latch can compress between the latch and the top of the probe to create a spring force pressing the probe against the skin of the subject. Alternatively, an elastic bandage, or similar structure, can be wrapped around the entire foot to help hold the assembly in place. In some example implementations, a sterile pouch (not shown) may be placed around the ultrasound probe and cable prior to insertion of the ultrasound probe into the probe receptable.

[0169] FIGS. 17A and 17B illustrate the use of a strap to secure the ultrasound probe, where FIG. 17A shows the ultrasound probe received within the probe receptacle 820 and FIG 17B shows the ultrasound probe secured within the probe receptacle 820 by a strap (clasp) 870. The strap may be made, for example, from an elastomeric material such as silicone. The example strap 870 shown in FIGS. 17A and 17B has a hole that receives a domed post residing on an outer surface of the probe receptacle 820. In use, the user places the ultrasound probe 810 in the probe receptacle 820, and then secures the free end of the strap 870 to the housing bypushing the strap hole through the domed post protruding from the probe receptacle 820 as shown in FIG. 17B. Multiple holes may exist in the strap free end (not shown). The ultrasound probe can be easily removed by releasing the secured end of the strap.

[0170] Depending on the hole position used and the elasticity of the strap, the force applied to the skin surface by the energy emitting surface of the ultrasound probe can be adjusted. Additionally or alternatively, a depth adjustment mechanism may be integrated into the support structure and / or the probe receptacle that permits adjustment of the vertical offset between the energy emitting surface of the ultrasound transducer and the skin surface. For example, a slider mechanism with a locking screw, or a rack and pinion adjustment mechanism, may be integrated to facilitate depth adjustment.

[0171] Additional views of the example ultrasound probe positioning apparatus 800 are shown in FIGS. 18A and 18B. FIG. 18A shows an overhead view and FIG. 18B shows a cross-sectional view as defined by line AA in FIG. 18A, showing the engagement of the locking nut 840 with the threaded shaft 830. FIG. 19 shows the example ultrasound probe positioning apparatus with the housing and probe shown in a rotated position.

[0172] FIG. 20A, 20B and 20C show views of an example ultrasound probe and the ultrasound beam emitted therefrom, with FIG. 20C showing angled steering of the ultrasound beam. In the present example embodiment, the ultrasound probe 810 is generally elongate in shape, housing an ultrasound array, with the cable exiting the probe housing from a longitudinal side. In one example implementation, the ultrasound transducer is a 1 D linear array oriented along an ultrasound array axis that extends substantially parallel to the longitudinal direction (axis) of the elongate probe housing, while in other example implementations, other type of ultrasound transducers, such as 1 D phased array transducers and 2D transducers, may be employed.

[0173] In some example implementations, the ultrasound transducer is a linear ultrasound array that includes 50-100 ultrasound array elements, 64-128 ultrasound array elements, 100-200 ultrasound array elements, or 128-256 ultrasound array elements. It will be understood that a wide variety of ultrasound devices may be employed according to the embodiments disclosed herein. For example, ultrasound transducers can be formed from piezo-electric, capacitive micromachined ultrasoundtransducer (CMUT), and polymer CMUT (PolyCMUT) materials. PolyCMUT materials have the advantage of being mechanically flexible, low cost, radio- translucent, optically transparent, light-weight, small, and consume low energy.

[0174] The inventors have found that a linear array is beneficial in interrogating peripheral vessels for Doppler ultrasound because of the ability to insonify a vessel in a longitudinal manner, such that at least a longitudinal portion of the vessel lies within the planar sheet of ultrasound energy emitted by the 1 D linear array transducer. Moreover, by suitably phasing the excitation of the 1 D ultrasound array, the planar ultrasound beam can be steered, which can be beneficial in improving or optimizing the Doppler angle during longitudinal insonification. For example FIG. 20C shows the steering of the ultrasound energy beam emitted by a 1 D ultrasound array in a lateral direction, which enables insonification of a vessel along its length with a well-defined beam steering angle.

[0175] FIGS. 21 A and 21 B illustrate the positioning of the example ultrasound probe positioning apparatus 800 on a foot for interrogation of a target pedal vessel 1000 (e.g. during a peripheral vascular procedure). FIG. 21 A shows an image of a foot indicating the location and orientation of the target vessel 1000 (for example, with the vessel location and orientation shown on a user interface, as determined based on a selected location of a wound that is perfused by the target vessel, as per the aforementioned example embodiments). In the present non-limiting example implementation, the target vessel is generally parallel to the long axis of the foot. FIGS. 21 B shows the example ultrasound probe positioning apparatus 800 and ultrasound probe 810 placed on top of the foot and oriented so the ultrasound probe 810 and emitted ultrasound beam are substantially parallel to the vessel in the foot. In this configuration, the 1 D ultrasound array within the ultrasound probe 810 is orientated for the longitudinal insonification of the target vessel.

[0176] In practice, despite having aligned the ultrasound probe positioning apparatus 800 according to expected location and orientation of the vessel, there will often be a misalignment between the emitted ultrasound beam and the target vessel. This misalignment is illustrated in FIG. 22A, which shows a front cross-sectional view perpendicular to the axis of the target vessel 1000. As shown in FIG. 22B, the probe receptacle 820 has been pivoted relative to the support structure 850 to facilitate alignment of the ultrasound beam 950 with the target vessel 1000, for example, according to the image guidance methods described above.

[0177] As can be seen in FIGS. 22A and 22B, an advantage of the design of the present example ultrasound probe positioning apparatus is that after securing the ultrasound probe within the probe receptable, the process of finding a vessel involves a single degree of freedom (probe orientation angle), resulting in a vessel search process that is amenable to guidance by a user interface (as per the example embodiments described above) and successful implementation by an unskilled or minimally skilled operator / technician.

[0178] Also, as can be seen in FIG. 22B, the present design is advantageous in that the ultrasound probe may be removed from the ultrasound probe positioning apparatus 800 while maintaining, in a locked configuration, the orientation angle of the probe receptable 820. In effect, the present design decouples the locking of the orientation of the ultrasound probe from the ultrasound probe itself, enabling the removal and replacement of the ultrasound probe without losing alignment with a target vessel.

[0179] Another significant advantage of the present design is that the pivot axis (pivot point) is proximal to the energy emitting surface of the ultrasound transducer, which assists in maintain the distal energy emitting surface of the ultrasound probe in contact with the skin as the probe orientation angle is varied, and can also ensure that the distal energy emitting surface of the ultrasound probe continues to compress the skin surface as the probe orientation angle is varied, thus ensuring sufficient acoustic coupling while the probe orientation angle is varied. As can be seen from the figure, by maintaining the pivot axis at location 960 proximal to the energy emitting surface (and the substate), a much smaller change in lateral position of the emitted beam occurs at the skin surface, for a given change in probe orientation angle, than what would result if the pivot axis were located at a more vertically offset position, such as at position 970. Accordingly, in some example embodiments, the offset of the pivot axis relative to the energy emitting surface of the ultrasound transducer (or alternatively relative to the top surface of the substrate) is less than 1 mm, less than 2 mm, less than 3 mm, less than 4 mm, or less than 5 mm.

[0180] While longitudinal positioning of the ultrasound transducer relative to the target vessel may be preferred in many clinical implementations, it is also possible to employ an alternative positioning approach in which the ultrasound probe is aligned to insonify the target vessel in a transverse configuration. An example of such a transverse positioning and orientation of the ultrasound probe positioning apparatus800 is shown in FIG. 23. FIG. 24A shows a first cross-sectional view of this configuration, in an orientation perpendicular to the axis of the vessel 1000, showing the transverse orientation of the emitted ultrasound beam 950, while FIG. 24B shows a side view, in which the angle of the emitted ultrasound beam has been steered to improve the Doppler angle relative to the vessel axis.

[0181] In one example implementation, the example ultrasound probe positioning apparatus 800 may be employed to align the ultrasound probe 810 relative to a pedal vessel as follows. Ultrasound gel is first applied to the foot, and the ultrasound probe 810 is employed, without the ultrasound probe positioning apparatus 800, to localize the vessel of interest. For example, the ultrasound probe 810 is manually moved so that it is either parallel to or perpendicular to the vessel of interest so that the desired image and / or spectral doppler waveform is found (for example, according to the image-guided workflows described above). A surgical marker or other marking means may be employed to mark the outline of the probe (or to mark one or more reference locations indicative of the probe position). The ultrasound probe is then removed and the ultrasound gel is cleaned from the foot.

[0182] The ultrasound probe positioning apparatus is then secured to the skin surface. For example, an adhesive backing is removed from the substrate (e.g. a foam pad), and the ultrasound probe positioning apparatus is applied to the foot, centering the marked outline of the probe within the frame / foam window. Ultrasound gel is the reapplied to the foot through the window, and the ultrasound probe is inserted into the probe receptable, and secured in place (e.g. using a strap). With the ultrasound probe locking mechanism (e.g. locking nut) loosened, the probe receptacle / probe is pivoted to align the ultrasound beam with the target, with image guidance as described above. The probe receptacle / probe is then pivoted to improve or maximize the Doppler beam angle. When a desired Doppler signal is obtained (e.g. sufficient arterial flow is observed and / or autonomously detected), the locking mechanism is employed (e.g. the locking nut is tightened) to fix the pivot (rotation) angle and secure the orientation of the probe receptacle / probe relative to the support frame. The procedure (e.g. a revascularization procedure) is then performed, assisted by Doppler ultrasound monitoring of blood flow characteristics within the vessel.

[0183] If it is determined that minor adjustments to the probe orientation are needed, the locking nut can be loosened, the probe can be rotated, and nut can beretightened. Moreover, if probe needs to be removed during procedure, such as for intraoperative fluoroscopy and / or surgical access, the strap can be released and the ultrasound probe can be removed, and subsequently replaced when the ready. When the procedure is complete, the ultrasound probe is removed, and the ultrasound probe positioning apparatus may optionally be left in place, enabling optional post-procedure monitoring (e.g. to monitor perfusion) by re-inserting and securing the probe into the ultrasound probe positioning apparatus.

[0184] In some example implementations, the substrate 860 and the support frame 850, and probe receptacle 820 are radio-translucent, such that fluoroscopy images may be obtained while maintaining the ultrasound probe positioning apparatus secured to the patient in the absence of the ultrasound probe. After performing fluoroscopy, the operator can re-insert and secure the ultrasound probe in the probe receptacle, without modifying the orientation of the probe receptacle, thus facilitating the collection of ultrasound Doppler images and / or waveforms in the same orientation as previously employed (e.g. an orientation deemed to provide a sufficiently high signal, such as an orientation associated with the targeting of a particular vessel of interest).

[0185] Referring now to FIGS. 25A-25D, 26A-26E, 28A and 28B, an alternative example of an ultrasound probe positioning system is illustrated. The example ultrasound probe positioning system includes an ultrasound probe 1100, shown in FIGS. 25A-25D and an ultrasound probe positioning assembly 1200 shown in FIGS. 26A-26E.

[0186] As shown in FIGS. 25A-25D, the ultrasound probe 1100 includes an elongate housing 1112 having an associated longitudinal direction 1113 (shown in FIG. 25B). An ultrasound beam is emitted through a distal energy-emitting (e.g. bottom) surface 1114 of the housing, for example, illustrated in the previous example embodiment described above and shown in FIGS. 20A to 20C.

[0187] Although the housing 1112 is shown in the present example implementation as having a shape that includes an upper chamfered rectangular prism and a distal curved portion (e.g. in the shape of a truncated cylinder), it will be understood that the housing 1112 can take on a wide variety of shapes, such as, for example, the shape of the alternative embodiment illustrated in FIGS. 20A-20C and described above, and variations thereof.

[0188] In some example implementations, the distal portion of the housing 1112 may include an acoustic lens that contacts the tissue, and through which the ultrasound energy is transmitted and received (optionally through an acoustic impedance matching layer). In some example implementations, the center of curvature of the distal energy emitting surface of the housing 1112 may be concentric with a pivot axis of the ultrasound probe 1110 when the ultrasound probe is pivotably supported by the support frame (described below), while in other example implementations, the center of curvature of the distal energy emitting surface of the housing 1112 may be off-center with a pivot axis of the ultrasound probe. The probe housing 1112 may be made of a plastic such as ABS. The lens may be made of polyurethane, silicone, or other similar material.

[0189] As in the previous example embodiment, the ultrasound probe 1110 is connectable to external processing and drive circuity via a cable 1118 extending from the housing 1112. This configuration advantageously reduces or avoids the application of torque by the cable when the ultrasound probe resides in a given orientation during imaging, which can reduce noise associated during the measurement process. The low profile of the transducer and side exit cable thus helps to eliminate long lever arms which can produce large rotational forces and move the probe out of position.

[0190] In the present example embodiment, the ultrasound probe housing 1112 is generally elongate in shape, housing an ultrasound array, with the cable exiting the probe housing from a longitudinal side. In one example implementation, the ultrasound transducer is a 1 D linear array oriented along an ultrasound array axis that extends substantially parallel to the longitudinal direction (axis) of the elongate probe housing, while in other example implementations, other type of ultrasound transducers, such as 1 D phase array transducers and 2D transducers, may be employed.

[0191] In some example implementations, the ultrasound transducer is a linear ultrasound array that includes 50-100 ultrasound array elements, 64-128 ultrasound array elements, 100-200 ultrasound array elements, or 128-256 ultrasound array elements. It will be understood that a wide variety of ultrasound devices may be employed according to the embodiments disclosed herein. For example, ultrasound transducers can be formed from piezo-electric, capacitive micromachined ultrasound transducer (CMUT), and polymer CM UT (PolyCMUT) materials. PolyCMUTmaterials have the advantage of being mechanically flexible, low cost, radio- translucent, optically transparent, light-weight, small, and consume low energy.

[0192] As noted above, the inventors have found that a linear array is beneficial in interrogating peripheral vessels for Doppler ultrasound because of the ability to insonify a vessel in a longitudinal manner, such that at least a longitudinal portion of the vessel lies within the planar sheet of ultrasound energy emitted by the 1 D linear array transducer. Moreover, by suitably phasing the excitation of the 1 D ultrasound array, the planar ultrasound beam can be steered, which can be beneficial in improving or optimizing the Doppler angle during longitudinal insonification.

[0193] FIGS. 28A and 28B illustrate how the ultrasound probe positioning assembly 1200 mechanically supports the ultrasound probe 1100 while permitting rotation of the ultrasound probe 1112 housing (and the ultrasound transducer array residing within the housing) about a pivot axis.

[0194] As shown in FIGS. 26A-26E, 27A, 28A and 28B, the ultrasound probe positioning assembly 1200 includes a support frame 1210 that is capable of removably and pivotably securing the ultrasound probe 1100 such that a distal energy emitting surface of the ultrasound probe 1112 extends through an aperture 1230 in the support frame 1120. The ultrasound probe 1100 is supported by the support frame 1210, such that when the support frame 1210 is secured to a skin surface (e.g. by the strap mechanism described below, or another example attachment mechanism), the distal energy emitting surface of the ultrasound housing 1112 is contacted with the skin surface through the aperture 1230. An orientation of the ultrasound probe 1100 is variable, by varying a pivot angle of the ultrasound probe 1100 about a pivot axis relative to the support frame 1210, for scanning an ultrasound energy beam emitted by the ultrasound probe, while maintaining contact of the distal energy emitting surface of the probe housing 1112 with the skin surface. A photograph of a prototype system, with the ultrasound probe 1100 engaged with the support frame 1210 of the ultrasound probe positioning assembly 1200, is shown in FIG. 28C.

[0195] In some example implementations shown in the present figures, the support frame 1210 and the ultrasound probe 1100 each include mating features that engage to pivotally and removably secure the ultrasound probe 1100 to the support frame 1210. FIGS. 26A-26E illustrate a non-limiting example of a support frame 1120 that includes a pair of protrusions 1220 (e.g. semi-circular saddle features) that arepositioned to receive corresponding collar features 1125 and 1126 of the ultrasound probe 1100 that are visible in FIGS. 25A and 25D. The support frame 1210 may be made from a rigid plastic material, such as, for example, acrylonitrile butadiene styrene (ABS), or, for example, an elastomer such as polyurethane.

[0196] In some example implementations, the ultrasound probe 1100 is configured to engage with the support frame 1210 via frictional engagement that permits the ultrasound probe 1100 to pivot relative to the support frame 1210. For example, the ultrasound probe 1100 may be affixed to the support frame 1210 by snapping the collar features 1125 and 1126 and into the semi-circular protrusions of the support frame 1210. This holds the ultrasound probe 1100 and support frame 1210 together while allowing the probe to rotate about the center axes of the collars 1125 and 1126. As shown in the figure, the proximal collar 1125 may reside adjacent to, or be integrated with, a strain relief assembly extending from the probe housing 1112 and supporting the distal portion of the signal delivery cable 1118. The strain relief assembly may be made of PVC, another elastomer, or a rigid material such as ABS.

[0197] While the present example embodiment is illustrated based on the use of the protrusion / collar pivotal engagement mechanism shown in the figures, it will be understood that this example implementation is merely intended to be illustrative of a broader set of pivotal attachment mechanisms that may be employed to pivotally secure the ultrasound transducer probe 1100 to the support frame 1210. Moreover, in cases in which the pivotal attachment mechanism includes mating features, with a first type of feature residing on the ultrasound transducer probe 1100 and a second type of feature residing on the support frame 1210, an alternative example implementation may be provided with these features switched, such that the second type of feature resides on the ultrasound transducer probe 1100 and the first type of feature resides on the support frame 1210. Non-limiting examples of alternative pivotal and removable attachment mechanisms that can be implemented to pivotally secure the ultrasound probe 1100 to the support frame 1210 include, for example, a removable pin joint, a saddle or cradle support and associated pin / cylinder, a sliding lock pin, magnetic ball and socket joint, and a quick release axle.

[0198] The support frame 1210 may be secured to the skin surface of a subject, for example, via an attachment means such as the straps 1241 and 1242 shown in the present illustrative example implementation (alternatively, a single strap can be employed, where the one side of the strap is secured to one side of the supportframe 1210, and another side of the strap passes through a slot formed in the opposite side of the support frame 1210). It is noted that ultrasound probes typically require the liberal use of acoustic coupling gel during use. One of the challenges that may be encountered when trying to secure an ultrasound probe to the patient is that the gel can migrate and may severely reduce the efficacy of any adhesive straps that contact the gel. The strap configuration of the present example embodiment solves this issue by eliminating the need for a skin adhesive near the probe.

[0199] In other example implementations, another means of attaching the support frame to the skin surface may be employed in the alternative, such as, for example, an adhesive substrate as described in the previous example embodiment and as illustrated, for example, in FIG. 16.

[0200] In the example implementation illustrated in FIGS. 26A-26E, the straps 1241 and 1242 are secured to opposing sides of the support frame 1210, on either side of the central aperture 1230. For example, the straps 1241 and 1242 can be rigidly affixed to the support frame 1210, or, for example, the straps may slide in laterally, in a direction perpendicular to the longitudinal direction of the straps, as shown in FIG. 26A. In some example implementations, the support frame 1210 may include protrusions located adjacent to the lateral edges of the straps to limit their lateral movement. The straps may be made from a wide variety of materials, and in some non-limiting example implementations, the straps may be made from a textile such as woven nylon or urethane, an elastomer such as silicone, or a foam such as EVA.

[0201] As shown in FIGS. 26A-26E, 27A and 27B, the straps 1241 and 1242 may have a first portion 1250 of hook and loop mechanism residing on one surface of one or both straps, and a second portion 1260 of hook and loop mechanism residing on an opposing surface of one or both straps, thereby facilitating the attachment of the straps to secure the straps around a bodily portion (e.g. a limb, torso, neck, head or other bodily portion). While the figures show each strap 1241 and 1242 including, on opposing surfaces, both portions of the hook and loop mechanism, it will be understood that in other example implementations, each strap may only include one respective portion of a hook and loop mechanism. It will be understood that the hook and loop mechanism illustrated in the figures is but one example of a suitable strap attachment mechanism, and that other example mechanisms may be employed in the alternative, such as, for example, a clasp, a buckle, and an adhesive.

[0202] In some example implementations, pivotal motion of the probe housing1112 relative to the support frame 1210 may be constrained to reside within a limited pivot angle range by one or more structural features configured to limit the rotational freedom of the probe housing 1112, such as, for example, one or more structural stops residing on the support frame.

[0203] As in the previous example embodiment, the present example ultrasound probe positioning system may include a locking mechanism for locking a desired pivot angle of the probe housing 1112 (and the internal ultrasound transducer array). In the example implementation shown in the figures (for example, FIGS. 25A and 25D), at least a distal portion of the distal collar 1126 is threaded and configured to engage with a corresponding threaded portion of distal knob 1130. The knob 1130 therefore screws into and out of the distal collar 1126 along the longitudinal axis 1113. As can be seen in FIG. 28B, when the ultrasound probe 1100 is pivotally engaged with the ultrasound probe positioning assembly 1200, rotating the knob1113 forces the front face of the probe against the frame and friction prevents the probe from rotating relative to the support frame 1210, thus locking the pivot angle of the ultrasound probe 1100. Rotating the knob in the opposite direction allows the probe to be rotated. To remove the ultrasound probe 1100 from the support frame 1210, the collars 1125 and 1126 can be unsnapped via application of a sufficient force.

[0204] The threaded collar 1126 may be made of rigid plastic such as ABS or PC or may be a metal such as stainless steel, aluminum, or brass. The threaded portion of the distal collar 1126 may be made of rigid plastic such as ABS or PC or may be a metal such as stainless steel, aluminum, or brass. The knob 1130 may be made, for example, from a rigid plastic material such as ABS. It will be understood that other locking mechanisms may be employed in the alternative. Examples of locking mechanisms that may be employed, include, but are not limited to, locking screws / knobs, clamping collars and other clamping mechanisms, a bayonet mount, latches, and other suitable fixation mechanisms. The locking means may be actuated after determining, based on the detection or monitoring of Doppler ultrasound signals, that the ultrasound transducer is aligned on a vessel of interest.

[0205] In some example embodiments, a scale (e.g. an angle scale or a linear position scale with a set of markings) may be provided to facilitate the visual determination of a given angle or position of the ultrasound probe relative to thesupport frame. For example, the support frame 1210 and / or the probe housing 1112 may include an orientation scale (e.g. a pointer and dial) that permits visual determination of the orientation of the ultrasound transducer housing relative to the support frame.

[0206] In some example implementations, an encoding mechanism may be employed to facilitate encoding of the angle of the ultrasound probe relative to the support frame. For example, an optical encoder or electrical encoder (e.g. conductive or potentiometer based) may be employed. The encoding mechanism may include an encoding interface, such as a reflective interface or conductive interface with a set of markings or conductive features, and an encoding sensor, such as an optical emitter / detector or a conductivity / resistance detection circuit, where the encoding sensor moves relative to the encoding interface, or vice versa. The signal from the encoder sensor may be employed and processed by control and processing circuitry to determine an angle of the ultrasound probe relative to the support frame.

[0207] The methods illustrated in FIGS. 21 A and 21 B, which pertain to the previously described example ultrasound probe positioning system, illustrate the positioning that may also be achieved with the present ultrasound positioning apparatus on a foot for interrogation of a target pedal vessel (e.g. during a peripheral vascular procedure). As also illustrated in FIGS. 22A and 22B, an advantage of the both the present and previously described ultrasound probe positioning systems is that after pivotally securing the ultrasound probe, the process of finding a vessel involves a single degree of freedom (probe orientation angle), resulting in a vessel search process that is amenable to guidance by a user interface (as per the example embodiments described above) and successful implementation by an unskilled or minimally skilled operator / technician.

[0208] In one example implementation, the example ultrasound probe positioning apparatus may be employed to align the ultrasound probe 1100 relative to a pedal vessel as follows. The user can first pivotally secure (attach) the ultrasound probe 1100 to the support frame 1210 (e.g. as shown in FIGS. 28A and 28B). The user can then apply ultrasound gel to the probe window (e.g. through the aperture 1230). The user can then place the ultrasound probe 1100 and support frame 1210 in a desired location to target a vessel of interest, for example, as per the vessel guidance workflows described above. The user can slide the ultrasound probe andsupport frame laterally relative to the straps if required, for example, to localize the vessel of interest. For example, the ultrasound probe and support frame may be manually moved so that it is either parallel to or perpendicular to the vessel of interest so that the desired image and / or spectral Doppler waveform is found (for example, according to the image-guided workflows described above). A surgical marker or other marking means may be employed to mark the outline of the probe (or to mark one or more reference locations indicative of the probe position).

[0209] The user can then apply the straps (or an alternative attachment mechanism) as described above to secure the ultrasound probe positioning system to the subject. For example, the ultrasound probe positioning apparatus can be secured to the foot (or another suitable body portion of interest) using the straps, centering the marked outline of the probe within the frame / foam window. Ultrasound gel may then optionally be reapplied to the foot through the aperture, and the ultrasound probe pivotally secured to the support frame 1210. With the ultrasound probe locking mechanism (e.g. locking nut) loosened, the ultrasound probe is pivoted to align the ultrasound beam with the target, with image guidance as described above. The ultrasound probe may then be pivoted to improve or maximize the Doppler beam angle. When a desired Doppler signal is obtained (e.g. sufficient arterial flow is observed and / or autonomously detected), the locking mechanism is employed (e.g. the locking nut is tightened) to fix the pivot (rotation) angle and secure the orientation of the ultrasound probe relative to the support frame. The procedure (e.g. a revascularization procedure) is then performed, assisted by Doppler ultrasound monitoring of blood flow characteristics within the vessel.

[0210] If it is determined that minor adjustments to the probe orientation are needed, the locking nut can be loosened, the probe can be rotated, and nut can be retightened. Moreover, if probe needs to be removed during procedure, such as for intraoperative fluoroscopy and / or surgical access, the strap can be released and the ultrasound probe can be removed, and subsequently replaced when the ready. When the procedure is complete, the ultrasound probe is removed, and the ultrasound probe positioning apparatus may optionally be left in place, enabling optional post-procedure monitoring (e.g. to monitor perfusion) by re-inserting and securing the probe into the ultrasound probe positioning apparatus.

[0211] In some example implementations, the support frame 1210, and optionally at least a portion of the straps that resides proximal to the support frame 1210, maybe radio-translucent, such that fluoroscopy images may be obtained while maintaining the ultrasound probe positioning apparatus secured to the patient in the absence of the ultrasound probe. After performing fluoroscopy, the operator can reinsert and secure the ultrasound probe in the support frame 1210.

[0212] The photographs shown in FIG. 29A and 29B illustrate how the ultrasound probe positioning system can be affixed to the top of the foot by wrapping the straps around the foot with the hook and loop holding them together.

[0213] FIG. 30 shows a photograph illustrating the use of an adhesive-backed hook or loop pad (having either a hook or a loop material) to secure the ultrasound probe positioning system to the patient (in the present case, on the bottom surface of the foot). An example of such an adhesive-backed pad is illustrated in FIGS. 31 A- 31 C, which show an adhesive-backed substrate 1300 having a hook or loop material 1310 provided on the opposing surface as the adhesive. One (or both) of the straps is provided with a mating hook or loop region (configured to mate with the hook or loop material on the adhesive-backed pad). After placing the adhesive-backed substrate on the body portion, the strap is then placed around the body portion, such that the mating hook or loop region on the strap aligns with the corresponding hook or loop material on the adhesive-backed substrate, thereby enabling the strap to secured to the pad, and thus, to the patient. This configuration allows for a secure attachment to the skin (adhesive), preventing slippage or misalignment of the ultrasound probe positioning system after it is secured to the patient. Such an embodiment also permits the straps to be applied and removed multiple times without having to remove the adhesive each time, and enables the ultrasound probe positioning system to be removed and replaced in a similar location on the body with ease.

[0214] While the first example embodiment of the ultrasound probe positioning system shown in FIGS. 15-19 shows an example attachment means for securing the support frame to the skin surface in the form of an adhesive-backed substrate 860, and the second example embodiment of the ultrasound probe positioning system shown in FIGS. 25A-28C shows an example attachment means for securing the support frame to the skin surface in the form of a strap (1241 and 1242), it will be understood that either of these example embodiments could be implemented with a wide range of attachment mechanisms, including the adhesive backed substate, one or more straps, or other example mechanisms, such as a vacuum-based attachmentmechanism involving the application of suction to secure the support frame to the skin surface.

[0215] In some example embodiments, friction between the support frame and the ultrasound probe is sufficiently low to permit the ultrasound probe to be pivoted by a user, but sufficiently high to maintain the ultrasound probe in a desired orientation in the absence of an external applied force, as described in International Patent Application No. PCT / CA2023 / 050413. Such example embodiments may be implemented in the absence of a locking mechanism, or may include a locking mechanism to further secure the orientation of the ultrasound probe.

[0216] The example embodiments of an ultrasound probe positioning apparatus and associated system described above may provide several benefits when compared to conventional clinical practice. For example, using such a system, the user can first quickly find the vessel freehand using the ultrasound probe prior to securing the ultrasound probe positioning apparatus, and mark the desired probe location. Since very slight movements will cause the vessel to move in and out of plane, it is likely that when the positioner is placed and the probe inserted, it will not be in the ideal plane. The pivot angle adjustment allows the user to then make fine adjustments to realign the ultrasound beam with the vessel while maintaining position (i.e. without translation). The system also enables variable pressure to be applied between the probe and the patient’s skin via the elastic strap and / or a variable depth mechanism. As noted above, the ultrasound probe positioning apparatus also enables the quick removal and replacement of the probe for fluoroscopic purposes and / or vessel access.

[0217] It will also be understood that while the present example embodiments have referred to orienting the ultrasound probe by the user, it will be understood that in other embodiments, the probe orientation may be robotically controlled, for example by a robotic arm having one or more motorized joints controlled by processing and control hardware interfaced with the ultrasound probe. In such cases, the robotic system may be controlled by a user, or may be autonomously controlled, with probe orientation (and optionally position) being autonomously controlled to search for an arterial vessel and maintain the position and orientation of the ultrasound probe during spectral Doppler data acquisition. Accordingly, the adjustment of the orientation of the ultrasound probe may be performed in a manual, autonomous, or semi-autonomous manner. For example, a robotic arm or assemblymay be employed to control the angulation and / or positioning of the ultrasound transducer assembly relative to the support frame. This may be achieved, for example, using one or more motors operably coupled to the probe receptacle, e.g. directly coupled, or coupled through an intermediate actuation mechanism or member extending from the support frame.

[0218] While the systems and methods described and illustrated herein refer to applications involving pedal wounds and pedal ultrasound vascular diagnostic assessment, it will be understood that the embodiments described herein can be employed or adapted to be employed for other anatomical locations, such as, but not limited to, the carotid artery and the hand. For example, Doppler waveforms collected from vessels residing within the hand may be processed to determine a measure such as the “hand acceleration time (HAT)”, which may be clinically useful in the setting of upper extremity arterial disease or steal from arterio-venous fistula.

[0219] Various example embodiments of the present disclosure can be employed for remote monitoring and diagnostics. In some example implementations, the device is placed on the patient skin by the patient and data is remotely delivered, optionally in real time, to a remote operator (e.g. clinician) residing at a different physical location that is remote from the patient’s home. The remote operator can control one or more of the device parameters (optionally in real time) to facilitate, for example, remote control of beam steering, gain, and other parameters, for example, to obtain a suitably high or optimal signal, and to monitor and / or diagnose a health condition of the patient. Moreover, it will be understood that the systems and methods disclosed herein can be employed for diagnostic and / or therapeutic procedures.Enumerated Embodiments

[0220] Embodiment 1 . An autonomous method of guiding placement of an ultrasound probe for assessment of vascular pathology associated with a wound of a subject, the method comprising: receiving, from a user, wound location input suitable for identifying, from a pre-determined set of anatomical regions, a selected anatomical region associated with the wound;processing the selected anatomical region to autonomously determine an initial probe position, such that when the ultrasound probe is placed on the subject according to the initial probe position, a spatial region interrogated by the ultrasound probe will be proximal to a target vessel associated with perfusion of the selected anatomical region; displaying a guidance image showing: a visual anatomical representation; and an indication of the initial probe position relative to the visual anatomical representation, thereby providing guidance to the user for placing the ultrasound probe relative to the subject for assessment vascular disorder associated with the wound.

[0221] Embodiment 2. The method according to embodiment 1 , further comprising processing the selected anatomical region to autonomously determine an initial probe orientation, the initial probe orientation being determined according to an expected orientation of the target vessel within the selected anatomical region.

[0222] Embodiment 3. The method according to embodiment 1 or 2, wherein the pre-determined set of anatomical regions are displayed on an anatomical image, and wherein the wound location input identifies the selected anatomical region.

[0223] Embodiment 4. The method according to any one of embodiments 1 to 3, wherein the selected anatomical region is determined by: displaying an anatomical image to the user; receiving the wound location input, the wound location input identifying a selected location on the anatomical image; and processing the selected location to determine the selected anatomical region corresponding to the selected location.

[0224] Embodiment 5. The method according to any one of embodiments 1 to 4, wherein the initial probe position is determined based on a pre-determined relationship establishing, for each anatomical region of the pre-determined set of anatomical regions, a respective probe location.

[0225] Embodiment 6. The method according to embodiment 2, wherein the initial probe orientation is determined based on a pre-determined relationship establishing, for each anatomical region of the pre-determined set of anatomical regions, a respective probe orientation.

[0226] Embodiment 7. The method according to any one of embodiments 1 to 6, wherein the visual anatomical representation is generated according to a digital anatomical model.

[0227] Embodiment 8. The method according to embodiment 2, wherein the visual anatomical representation is generated according to a digital anatomical model, and wherein the digital anatomical model is processed to dynamically display the initial probe position and the initial probe orientation according to a plurality of orientations of the visual anatomical representation, thereby enabling the user to observe the initial probe position and the initial probe orientation from multiple perspectives.

[0228] Embodiment 9. The method according to embodiment 8, wherein the plurality of orientations of the visual anatomical representation are shown in an animation.

[0229] Embodiment 10. The method according to embodiment 8, wherein the plurality of orientations of the visual anatomical representation are shown according to orientation selection input provided by the user.

[0230] Embodiment 11 . The method according to any one of embodiments 1 to10, wherein the visual anatomical representation is generated based on surface data characterizing an anatomical surface of the subject, and wherein the initial probe position relative to the visual anatomical representation is determined based on the initial probe position as determined relative to a reference anatomical model.

[0231] Embodiment 12. The method according to any one of embodiments 1 to11 , wherein the initial probe position corresponds to an anatomical landmark.

[0232] Embodiment 13. The method according to embodiment 2, wherein the ultrasound probe comprises a linear array of ultrasound elements configured to generate two-dimensional image data associated with a planar imaging volume, and wherein the initial probe position and the initial probe orientation are determined such that at least a portion of the target vessel lies within or proximal to the planar imaging volume.

[0233] Embodiment 14. The method according to embodiment 2, wherein the ultrasound probe comprises a two-dimensional array of ultrasound elements configured to generate three-dimensional image data associated with a volumetric imaging volume, and wherein the initial probe position and the initial probeorientation are determined such that at least a portion the target vessel lies within or proximal to the volumetric imaging volume.

[0234] Embodiment 15. The method according to any one of embodiments 1 to 12, further comprising: instructing the user to move the ultrasound probe to facilitate the detection of an arterial vessel suitable for performing spectral Doppler analysis.

[0235] Embodiment 16. The method according to embodiment 15, wherein instructing the user to move the ultrasound probe comprises providing probe alignment instructions to the user to facilitate alignment of the ultrasound probe with the target vessel associated with perfusion of the selected anatomical region, the probe alignment instructions comprising at least one of: instruction to translate the ultrasound probe along a prescribed direction, relative to the initial probe position, for aligning the ultrasound probe with the target vessel; and instruction to tilt the ultrasound probe about a prescribed axis for aligning the ultrasound probe with the target vessel.

[0236] Embodiment 17. The method according to embodiment 15 or 16, further comprising: while the ultrasound probe is moved relative to the subject to search for the arterial vessel suitable for performing spectral Doppler analysis, autonomously controlling the ultrasound probe to collect a Doppler ultrasound image dataset.

[0237] Embodiment 18. The method according to embodiment 17, wherein the guidance image is a first guidance image, the method further comprising: while the ultrasound probe is moved relative to the subject, displaying a second guidance image showing image regions associated with arterial blood flow.

[0238] Embodiment 19. The method according to embodiment 18, wherein a pixel intensity of the second guidance image is associated with an intensity of local arterial blood flow.

[0239] Embodiment 20. The method according to embodiment 18, wherein the second guidance image is generated in the absence of displaying colour Doppler image data.

[0240] Embodiment 21 . The method according to any one of embodiments 18 to 20, wherein the second guidance image further comprises structural B-mode image data.

[0241] Embodiment 22. The method according to any one of embodiments 17 to 21 , further comprising: processing the Doppler ultrasound image dataset to determine whether or not arterial vessel detection criteria has been satisfied in one or more image regions.

[0242] Embodiment 23. The method according to embodiment 22, further comprising: determining that the arterial vessel detection criteria has not been satisfied, and continuing to acquire and process the Doppler ultrasound image dataset as the user continues to move the ultrasound probe relative to the subject, until the arterial vessel detection criteria is satisfied in one or more image regions.

[0243] Embodiment 24. The method according to embodiment 22, further comprising, prior to determining whether or not the arterial vessel detection criteria has been satisfied in one or more image regions: processing the Doppler ultrasound image dataset to detect a presence or an absence of arterial blood flow; and determining that the one or more image regions satisfy arterial blood flow criteria associated with a presence of arterial blood flow.

[0244] Embodiment 25. The method according to embodiment 24, further comprising, prior to determining that the one or more image regions satisfy arterial blood flow criteria associated with a presence of arterial blood flow: detecting an absence of arterial blood; and continuing to acquire and process the Doppler ultrasound image dataset as the user continues to move the ultrasound probe relative to the subject until a presence of arterial blood flow is detected.

[0245] Embodiment 26. The method according to embodiment 24 or 25, further comprising, after the one or more image regions are deemed to satisfy arterial blood flow criteria associated with a presence of arterial blood flow, instructing the user to maintain a current position and a current orientation of the ultrasound probe.

[0246] Embodiment 27. The method according to embodiment 24, wherein the arterial blood flow criteria comprises at least two arterial blood flow criterion.

[0247] Embodiment 28. The method according to embodiment 24, wherein the arterial blood flow criteria comprises a pulsatility threshold.

[0248] Embodiment 29. The method according to embodiment 24, wherein at least one arterial blood flow criterion of the arterial blood flow criteria is associated with a pulse repetition frequency.

[0249] Embodiment 30. The method according to embodiment 24, wherein at least one arterial blood flow criterion of the arterial blood flow criteria is associated with a structural vessel feature associated with B-mode structural image data.

[0250] Embodiment 31 . The method according to embodiment 30, wherein the at least one criterion associated with the structural vessel feature is associated with one or more of vessel wall thickness, vessel compressibility, and vessel directionality.

[0251] Embodiment 32. The method according to any one of embodiments 22 to 31 , further comprising: determining that the arterial vessel detection criteria has been satisfied by at least one image region; and instructing the user to maintain a current position and a current orientation of the ultrasound probe.

[0252] Embodiment 33. The method according to embodiment 32, further comprising: autonomously identifying a subregion suitable for collecting a spectral Doppler dataset; autonomously calculating an arterial vessel angle associated with the subregion; and autonomously determining a beam steering angle for steering an ultrasound energy beam emitted by the ultrasound energy beam such that Doppler angle criteria is satisfied.

[0253] Embodiment 34. The method according to embodiment 33, wherein a determination that the arterial vessel detection criteria has been satisfied comprises, at least in part, identification of the subregion suitable for collecting a spectral Doppler dataset.

[0254] Embodiment 35. The method according to embodiment 33, wherein at least one of the subregion, the arterial vessel angle and the beam steering angle are determined prior to instructing the user to maintain the current position and current orientation of the ultrasound probe.

[0255] Embodiment 36. The method according to any one of embodiments 33 to35, wherein the one or more image regions satisfying the arterial vessel detection criteria include a plurality of image regions, and wherein the subregion for collecting the spectral Doppler dataset is selected according to selection criteria comprising at least one of: a Doppler angle associated with each image region based on an optimal beam steering angle; a spatial measure associated with each image region; and a distance between each image region and a transducer array of the ultrasound probe.

[0256] Embodiment 37. The method according to any one of embodiments 33 to36, further comprising obtaining the spectral Doppler dataset associated with the subregion, the spectral Doppler dataset being autonomously angle corrected based on the arterial vessel angle and the beam steering angle.

[0257] Embodiment 38. The method according to embodiment 37, wherein the spectral Doppler dataset is obtained in the absence of user intervention.

[0258] Embodiment 39. The method according to any one of embodiments 33 to 38 further comprising processing the spectral Doppler dataset to determine one or more hemodynamic measures.

[0259] Embodiment 40. The method according to embodiment 39 wherein the one or more hemodynamic measures are processed in the absence of user intervention.

[0260] Embodiment 41 . The method according to any one of embodiments 1 to 39 wherein the wound is a pedal wound.

[0261] Embodiment 42. The method according to embodiment 39 wherein the wound is a pedal wound, wherein the one or more hemodynamic measures comprises a pedal acceleration time.

[0262] Embodiment 43. The method according to any one of embodiments 17 to 42, wherein each Doppler ultrasound image dataset corresponds to a two- dimensional image frame.

[0263] Embodiment 44. The method according to embodiment 43, wherein each Doppler ultrasound image dataset corresponds to a volumetric image frame.

[0264] Embodiment 45. The method according to embodiment 42 wherein the pedal acceleration time is generated according to an average over a plurality of cardiac cycles.

[0265] Embodiment 46. The method according to embodiment 42 wherein the pedal acceleration time is obtained by:

[0266] processing the spectral Doppler dataset to obtain a maximum velocity envelope;

[0267] processing the maximum velocity envelope to determine a systolic uprise time and a peak systole time; and

[0268] computing the pedal acceleration time as a difference between the peak systole time and the systolic uprise time.

[0269] Embodiment 47. A system for guiding placement of an ultrasound probe for assessment of vascular pathology associated with a wound of a subject, the system comprising: processing circuitry comprising a processor and associated memory, the memory comprising instructions executable by the processor for performing operations comprising: receiving, from a user, wound location input suitable for identifying, from a pre-determined set of anatomical regions, a selected anatomical region associated with the wound; processing the selected anatomical region to autonomously determine an initial probe position, such that when the ultrasound probe is placed on the subject according to the initial probe position, a spatial region interrogated by the ultrasound probe will be proximal to a target vessel associated with perfusion of the selected anatomical region; displaying a guidance image showing: a visual anatomical representation; and an indication of the initial probe position relative to the visual anatomical representation, thereby providing guidance to the user for placing the ultrasound probe relative to the subject for assessment vascular disorder associated with the wound.

[0270] Embodiment 48. An ultrasound system comprising: an ultrasound probe comprising: an elongate housing;an ultrasound transducer array supported within said elongate housing, wherein array elements of said ultrasound transducer array extend longitudinally along an ultrasound transducer array axis within said elongate housing; a support frame comprising an aperture; an attachment means for securing said support frame to a skin surface of a subject; said support frame being configured to removably and pivotably secure said ultrasound probe such that, when said support frame is secured to the skin surface by said attachment means and said ultrasound probe is secured by said support frame: a distal energy emitting surface of said ultrasound probe is contacted with the skin surface of the subject through said aperture; and an orientation of said ultrasound probe is variable, by varying a pivot angle of said ultrasound probe about a pivot axis relative to said support frame, for scanning an ultrasound energy beam emitted by said ultrasound probe, while maintaining contact of said distal energy emitting surface with the skin surface.

[0271] Embodiment 49. The ultrasound system according to embodiment 48 wherein said distal energy emitting surface is a curved surface.

[0272] Embodiment 50. The ultrasound system according to embodiment 49 wherein said curved surface is concentric with the pivot axis.

[0273] Embodiment 51 . The ultrasound system according to embodiment 48 wherein said support frame and said ultrasound probe comprise mating features that frictionally engage to pivotally and removably secure said ultrasound probe to said support frame.

[0274] Embodiment 52. The ultrasound system according to any one of embodiments 48 to 51 wherein said support frame comprises: a support base; and an ultrasound probe receptacle pivotally secured to said support base, said ultrasound probe receptacle being capable of removably securing said ultrasound probe.

[0275] Embodiment 53. The ultrasound system according to embodiment 52 wherein said ultrasound probe receptacle is pivotally secured to said support frame such that when said ultrasound probe is received and secured within said ultrasoundprobe receptacle, a pivot axis of said ultrasound probe receptacle is offset from said distal energy emitting surface of said ultrasound probe by less than 5 mm.

[0276] Embodiment 54. The ultrasound system according to any one of embodiments 48 to 53 wherein said attachment means comprises a strap extending from opposing sides of said support frame, said strap comprising a fastening mechanism for securing said strap around a body portion of the subject.

[0277] Embodiment 55. The ultrasound system according to embodiment 54 further comprising a substrate having a first surface and a second surface, said first surface having an adhesive coating provided thereon suitable for securing said substrate on the subject, said second surface comprising a first portion of a hook and loop fastening mechanism; and wherein a surface region of said strap located remote from said support frame comprises a second portion of said hook and loop fastening mechanism, such that when said substrate is secured on a body portion of the subject and said strap is secured around the body portion such that said first portion of said hook and loop fastening mechanism is contacted with and removably adhered to said second portion of said hook and loop fastening mechanism, slippage of said strap and translation of said support frame relative to the body portion is prevented.

[0278] Embodiment 56. The ultrasound system according to any one of embodiments 48 to 55 further comprising a signal delivery cable extending, in a longitudinal direction, from said elongate housing such that the pivot axis resides with a portion of said signal delivery cable that is proximal to said elongate housing.

[0279] Embodiment 57. The ultrasound system according to any one of embodiments 48 to 55 wherein said support frame comprises a pair of saddle features residing on opposing sides of said aperture, each saddle features being configured to receive and pivotally secure a corresponding cylindrical member extending from said elongate housing.

[0280] Embodiment 58. The ultrasound system according to embodiment 57 further comprising a signal delivery cable extending, in a longitudinal direction, from said elongate housing such that the pivot axis resides with a portion of said signal delivery cable that is proximal to said elongate housing, and wherein one or said cylindrical members is adjacent to, and mechanically supports, a strain-relief portion of said signal delivery cable.

[0281] Embodiment 59. The ultrasound system according to any one of embodiments 48 to 58 further comprising a locking mechanism for locking the pivot angle of said ultrasound probe.

[0282] The specific embodiments described above have been shown by way of example, and it should be understood that these embodiments may be susceptible to various modifications and alternative forms. It should be further understood that the claims are not intended to be limited to the particular forms disclosed, but rather to cover all modifications, equivalents, and alternatives falling within the spirit and scope of this disclosure.

Claims

CLAIMS1 . An autonomous method of guiding placement of an ultrasound probe for assessment of vascular pathology associated with a wound of a subject, the method comprising: receiving, from a user, wound location input suitable for identifying, from a pre-determined set of anatomical regions, a selected anatomical region associated with the wound; processing the selected anatomical region to autonomously determine an initial probe position, such that when the ultrasound probe is placed on the subject according to the initial probe position, a spatial region interrogated by the ultrasound probe will be proximal to a target vessel associated with perfusion of the selected anatomical region; displaying a guidance image showing: a visual anatomical representation; and an indication of the initial probe position relative to the visual anatomical representation, thereby providing guidance to the user for placing the ultrasound probe relative to the subject for assessment vascular disorder associated with the wound.

2. The method according to claim 1 , further comprising processing the selected anatomical region to autonomously determine an initial probe orientation, the initial probe orientation being determined according to an expected orientation of the target vessel within the selected anatomical region.

3. The method according to claim 1 or 2, wherein the pre-determined set of anatomical regions are displayed on an anatomical image, and wherein the wound location input identifies the selected anatomical region.

4. The method according to any one of claims 1 to 3, wherein the selected anatomical region is determined by: displaying an anatomical image to the user; receiving the wound location input, the wound location input identifying a selected location on the anatomical image; andprocessing the selected location to determine the selected anatomical region corresponding to the selected location.

5. The method according to any one of claims 1 to 4, wherein the initial probe position is determined based on a pre-determined relationship establishing, for each anatomical region of the pre-determined set of anatomical regions, a respective probe location.

6. The method according to claim 2, wherein the initial probe orientation is determined based on a pre-determined relationship establishing, for each anatomical region of the pre-determined set of anatomical regions, a respective probe orientation.

7. The method according to any one of claims 1 to 6, wherein the visual anatomical representation is generated according to a digital anatomical model.

8. The method according to claim 2, wherein the visual anatomical representation is generated according to a digital anatomical model, and wherein the digital anatomical model is processed to dynamically display the initial probe position and the initial probe orientation according to a plurality of orientations of the visual anatomical representation, thereby enabling the user to observe the initial probe position and the initial probe orientation from multiple perspectives.

9. The method according to claim 8, wherein the plurality of orientations of the visual anatomical representation are shown in an animation.

10. The method according to claim 8, wherein the plurality of orientations of the visual anatomical representation are shown according to orientation selection input provided by the user.11 . The method according to any one of claims 1 to 10, wherein the visual anatomical representation is generated based on surface data characterizing an anatomical surface of the subject, and wherein the initial probe position relative tothe visual anatomical representation is determined based on the initial probe position as determined relative to a reference anatomical model.

12. The method according to any one of claims 1 to 11 , wherein the initial probe position corresponds to an anatomical landmark.

13. The method according to claim 2, wherein the ultrasound probe comprises a linear array of ultrasound elements configured to generate two-dimensional image data associated with a planar imaging volume, and wherein the initial probe position and the initial probe orientation are determined such that at least a portion of the target vessel lies within or proximal to the planar imaging volume.

14. The method according to claim 2, wherein the ultrasound probe comprises a two-dimensional array of ultrasound elements configured to generate three- dimensional image data associated with a volumetric imaging volume, and wherein the initial probe position and the initial probe orientation are determined such that at least a portion the target vessel lies within or proximal to the volumetric imaging volume.

15. The method according to any one of claims 1 to 12, further comprising: instructing the user to move the ultrasound probe to facilitate the detection of an arterial vessel suitable for performing spectral Doppler analysis.

16. The method according to claim 15, wherein instructing the user to move the ultrasound probe comprises providing probe alignment instructions to the user to facilitate alignment of the ultrasound probe with the target vessel associated with perfusion of the selected anatomical region, the probe alignment instructions comprising at least one of: instruction to translate the ultrasound probe along a prescribed direction, relative to the initial probe position, for aligning the ultrasound probe with the target vessel; and instruction to tilt the ultrasound probe about a prescribed axis for aligning the ultrasound probe with the target vessel.

17. The method according to claim 15 or 16, further comprising: while the ultrasound probe is moved relative to the subject to search for the arterial vessel suitable for performing spectral Doppler analysis, autonomously controlling the ultrasound probe to collect a Doppler ultrasound image dataset.

18. The method according to claim 17, wherein the guidance image is a first guidance image, the method further comprising: while the ultrasound probe is moved relative to the subject, displaying a second guidance image showing image regions associated with arterial blood flow.

19. The method according to claim 18, wherein a pixel intensity of the second guidance image is associated with an intensity of local arterial blood flow.

20. The method according to claim 18, wherein the second guidance image is generated in the absence of displaying colour Doppler image data.21 . The method according to any one of claims 18 to 20, wherein the second guidance image further comprises structural B-mode image data.

22. The method according to any one of claims 17 to 21 , further comprising: processing the Doppler ultrasound image dataset to determine whether or not arterial vessel detection criteria has been satisfied in one or more image regions.

23. The method according to claim 22, further comprising: determining that the arterial vessel detection criteria has not been satisfied, and continuing to acquire and process the Doppler ultrasound image dataset as the user continues to move the ultrasound probe relative to the subject, until the arterial vessel detection criteria is satisfied in one or more image regions.

24. The method according to claim 22, further comprising, prior to determining whether or not the arterial vessel detection criteria has been satisfied in one or more image regions: processing the Doppler ultrasound image dataset to detect a presence or an absence of arterial blood flow; anddetermining that the one or more image regions satisfy arterial blood flow criteria associated with a presence of arterial blood flow.

25. The method according to claim 24, further comprising, prior to determining that the one or more image regions satisfy arterial blood flow criteria associated with a presence of arterial blood flow: detecting an absence of arterial blood; and continuing to acquire and process the Doppler ultrasound image dataset as the user continues to move the ultrasound probe relative to the subject until a presence of arterial blood flow is detected.

26. The method according to claim 24 or 25, further comprising, after the one or more image regions are deemed to satisfy arterial blood flow criteria associated with a presence of arterial blood flow, instructing the user to maintain a current position and a current orientation of the ultrasound probe.

27. The method according to claim 24, wherein the arterial blood flow criteria comprises at least two arterial blood flow criterion.

28. The method according to claim 24, wherein the arterial blood flow criteria comprises a pulsatility threshold.

29. The method according to claim 24, wherein at least one arterial blood flow criterion of the arterial blood flow criteria is associated with a pulse repetition frequency.

30. The method according to claim 24, wherein at least one arterial blood flow criterion of the arterial blood flow criteria is associated with a structural vessel feature associated with B-mode structural image data.31 . The method according to claim 30, wherein the at least one criterion associated with the structural vessel feature is associated with one or more of vessel wall thickness, vessel compressibility, and vessel directionality.

32. The method according to any one of claims 22 to 31 , further comprising: determining that the arterial vessel detection criteria has been satisfied by at least one image region; and instructing the user to maintain a current position and a current orientation of the ultrasound probe.

33. The method according to claim 32, further comprising: autonomously identifying a subregion suitable for collecting a spectral Doppler dataset; autonomously calculating an arterial vessel angle associated with the subregion; and autonomously determining a beam steering angle for steering an ultrasound energy beam emitted by the ultrasound energy beam such that Doppler angle criteria is satisfied.

34. The method according to claim 33, wherein a determination that the arterial vessel detection criteria has been satisfied comprises, at least in part, identification of the subregion suitable for collecting a spectral Doppler dataset.

35. The method according to claim 33, wherein at least one of the subregion, the arterial vessel angle and the beam steering angle are determined prior to instructing the user to maintain the current position and current orientation of the ultrasound probe.

36. The method according to any one of claims 33 to 35, wherein the one or more image regions satisfying the arterial vessel detection criteria include a plurality of image regions, and wherein the subregion for collecting the spectral Doppler dataset is selected according to selection criteria comprising at least one of: a Doppler angle associated with each image region based on an optimal beam steering angle; a spatial measure associated with each image region; and a distance between each image region and a transducer array of the ultrasound probe.

37. The method according to any one of claims 33 to 36, further comprising obtaining the spectral Doppler dataset associated with the subregion, the spectral Doppler dataset being autonomously angle corrected based on the arterial vessel angle and the beam steering angle.

38. The method according to claim 37, wherein the spectral Doppler dataset is obtained in the absence of user intervention.

39. The method according to any one of claims 33 to 38 further comprising processing the spectral Doppler dataset to determine one or more hemodynamic measures.

40. The method according to claim 39 wherein the one or more hemodynamic measures are processed in the absence of user intervention.41 . The method according to any one of claims 1 to 39 wherein the wound is a pedal wound.

42. The method according to claim 39 wherein the wound is a pedal wound, wherein the one or more hemodynamic measures comprises a pedal acceleration time.

43. The method according to any one of claims 17 to 42, wherein each Doppler ultrasound image dataset corresponds to a two-dimensional image frame.

44. The method according to claim 43, wherein each Doppler ultrasound image dataset corresponds to a volumetric image frame.

45. The method according to claim 42 wherein the pedal acceleration time is generated according to an average over a plurality of cardiac cycles.

46. The method according to claim 42 wherein the pedal acceleration time is obtained by: processing the spectral Doppler dataset to obtain a maximum velocity envelope;processing the maximum velocity envelope to determine a systolic uprise time and a peak systole time; and computing the pedal acceleration time as a difference between the peak systole time and the systolic uprise time.

47. A system for guiding placement of an ultrasound probe for assessment of vascular pathology associated with a wound of a subject, the system comprising: processing circuitry comprising a processor and associated memory, the memory comprising instructions executable by the processor for performing operations comprising: receiving, from a user, wound location input suitable for identifying, from a pre-determined set of anatomical regions, a selected anatomical region associated with the wound; processing the selected anatomical region to autonomously determine an initial probe position, such that when the ultrasound probe is placed on the subject according to the initial probe position, a spatial region interrogated by the ultrasound probe will be proximal to a target vessel associated with perfusion of the selected anatomical region; displaying a guidance image showing: a visual anatomical representation; and an indication of the initial probe position relative to the visual anatomical representation, thereby providing guidance to the user for placing the ultrasound probe relative to the subject for assessment vascular disorder associated with the wound.

48. An ultrasound system comprising: an ultrasound probe comprising: an elongate housing; an ultrasound transducer array supported within said elongate housing, wherein array elements of said ultrasound transducer array extend longitudinally along an ultrasound transducer array axis within said elongate housing; a support frame comprising an aperture; an attachment means for securing said support frame to a skin surface of a subject;said support frame being configured to removably and pivotably secure said ultrasound probe such that, when said support frame is secured to the skin surface by said attachment means and said ultrasound probe is secured by said support frame: a distal energy emitting surface of said ultrasound probe is contacted with the skin surface of the subject through said aperture; and an orientation of said ultrasound probe is variable, by varying a pivot angle of said ultrasound probe about a pivot axis relative to said support frame, for scanning an ultrasound energy beam emitted by said ultrasound probe, while maintaining contact of said distal energy emitting surface with the skin surface.

49. The ultrasound system according to claim 48 wherein said distal energy emitting surface is a curved surface.

50. The ultrasound system according to claim 49 wherein said curved surface is concentric with the pivot axis.51 . The ultrasound system according to claim 48 wherein said support frame and said ultrasound probe comprise mating features that frictionally engage to pivotally and removably secure said ultrasound probe to said support frame.

52. The ultrasound system according to any one of claims 48 to 51 wherein said support frame comprises: a support base; and an ultrasound probe receptacle pivotally secured to said support base, said ultrasound probe receptacle being capable of removably securing said ultrasound probe.

53. The ultrasound system according to claim 52 wherein said ultrasound probe receptacle is pivotally secured to said support frame such that when said ultrasound probe is received and secured within said ultrasound probe receptacle, a pivot axis of said ultrasound probe receptacle is offset from said distal energy emitting surface of said ultrasound probe by less than 5 mm.

54. The ultrasound system according to any one of claims 48 to 53 wherein said attachment means comprises a strap extending from opposing sides of said support frame, said strap comprising a fastening mechanism for securing said strap around a body portion of the subject.

55. The ultrasound system according to claim 54 further comprising a substrate having a first surface and a second surface, said first surface having an adhesive coating provided thereon suitable for securing said substrate on the subject, said second surface comprising a first portion of a hook and loop fastening mechanism; and wherein a surface region of said strap located remote from said support frame comprises a second portion of said hook and loop fastening mechanism, such that when said substrate is secured on a body portion of the subject and said strap is secured around the body portion such that said first portion of said hook and loop fastening mechanism is contacted with and removably adhered to said second portion of said hook and loop fastening mechanism, slippage of said strap and translation of said support frame relative to the body portion is prevented.

56. The ultrasound system according to any one of claims 48 to 55 further comprising a signal delivery cable extending, in a longitudinal direction, from said elongate housing such that the pivot axis resides with a portion of said signal delivery cable that is proximal to said elongate housing.

57. The ultrasound system according to any one of claims 48 to 55 wherein said support frame comprises a pair of saddle features residing on opposing sides of said aperture, each saddle features being configured to receive and pivotally secure a corresponding cylindrical member extending from said elongate housing.

58. The ultrasound system according to claim 57 further comprising a signal delivery cable extending, in a longitudinal direction, from said elongate housing such that the pivot axis resides with a portion of said signal delivery cable that is proximal to said elongate housing, and wherein one or said cylindrical members is adjacent to, and mechanically supports, a strain-relief portion of said signal delivery cable.

59. The ultrasound system according to any one of claims 48 to 58 further comprising a locking mechanism for locking the pivot angle of said ultrasound probe.

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