Generating ultrasound device interaction indicators

Abstract

An acoustically translucent standoff layer is disposed between the ultrasound device and the subject. Ultrasound echoes received by the ultrasound device, including from the standoff layer, are processed to determine a deformation of the standoff layer caused by an axial force or pressure applied by the ultrasound device. The deformation of the standoff layer along with a property of the standoff layer is used to generate an ultrasound device interaction indicator. In another aspect, one or more properties of the acoustically translucent standoff layer and the ultrasound signal are processed to determine a measure of strain hysteresis of the acoustically translucent standoff layer, and in response to a determination that the measure of strain hysteresis exceeds a predetermined hysteresis threshold, an indication is generated that the acoustically translucent standoff layer requires replacement.

Description

[Technical field]

[0001] The present invention relates to the field of ultrasound imaging, and in particular to point-of-care ultrasound imaging. In particular, one aspect of the present invention relates to generating an ultrasound device interaction indicator. Another aspect of the present invention relates to determining whether an acoustically translucent standoff layer requires replacement. [Background technology]

[0002] US Patent Application Publication No. 2011 / 0040187 discloses a method for simplifying operations related to detection of absolute pressure applied to a test piece by an ultrasonic probe.

[0003] Point-of-care ultrasound imaging is becoming increasingly prevalent as technological advances such as smaller form factors, lower cost systems, artificial intelligence, and the digital cloud improve the utility and reduce the cost of point-of-care ultrasound.

[0004] The rise of point-of-care ultrasound has led to many new ultrasound applications, such as patches for long-term monitoring, and hemodynamic monitoring (e.g., non-invasive blood pressure estimation).

[0005] One problem with point-of-care ultrasound is that it is typically performed by clinicians with little or no training in ultrasound imaging. Such clinicians are less skilled at reducing disturbances to the subject during imaging procedures and may not be able to judge when the right amount of force is being applied when coupling the ultrasound probe to the skin. Insufficient force can result in suboptimal images and / or image artifacts. Meanwhile, prolonged contact between the ultrasound probe or patch and the subject's body can cause bed sores. This is particularly problematic for patch-based applications, which are often designed to monitor subjects over time. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, there is a need for improved information regarding the force and / or pressure of an ultrasound transducer on a subject. [Means for solving the problem]

[0007] The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

[0008] According to an example according to one aspect of the present invention, a processing system is provided for generating an ultrasound device interaction indicator representative of at least an orientation of an ultrasound device relative to a subject.

[0009] The processing system is configured to perform the steps of acquiring, at the input interface, one or more properties of an acoustically translucent standoff layer between a surface of the ultrasound device and the skin of the subject; acquiring, at the input interface, ultrasound signals from the ultrasound device, the ultrasound signals representing a plurality of ultrasound echoes received by the ultrasound device from different depths for each of one or more scan lines; processing the ultrasound signals to determine measurements of deformation of the acoustically translucent standoff layer; and processing the measurements of deformation and the one or more properties of the acoustically translucent standoff layer to generate an ultrasound device interaction indicator.

[0010] The use of an acoustically translucent standoff layer allows for an indication of the force / pressure applied to a subject when an ultrasonic device is coupled to the subject at which the ultrasonic waves are generated, by determining a measure of the deformation of the acoustically translucent standoff layer caused by the force applied by the ultrasonic device.

[0011] The inventors have recognized that a measure of deformation or force or pressure across the ultrasound device can be used to provide information about the orientation of the ultrasound device by identifying differences in the deformation or force / pressure measures across an acoustically translucent standoff layer (i.e., in a direction perpendicular to the imaging direction). An inclined position of the ultrasound device (i.e., the imaging axis is not perpendicular to the subject's skin) results in a decrease in image quality because the effective aperture width is truncated and the beamformed signal summation is reduced. Therefore, it is desirable to provide information that allows the user to determine whether the orientation of the ultrasound device is correct.

[0012] This method for generating an ultrasound device interaction indicator uses ultrasound echoes received as part of the operation of the ultrasound device and avoids the need for a separate sensor to measure the force or pressure applied by the ultrasound device.

[0013] An acoustically translucent standoff layer is a layer disposed between an ultrasound imaging device and a subject's skin that has sufficient acoustic transparency so as not to significantly degrade the quality of the image produced by the ultrasound imaging device.

[0014] The ultrasound device may be, for example, a handheld ultrasound probe or an ultrasound patch.

[0015] In some examples, the generated ultrasound device interaction indicators are output at an output interface. The ultrasound device interaction indicators may be used, for example, to control or define user-perceivable output provided to the output user interface.

[0016] In some instances the interaction indicators are not on the display for the clinician but are consumed internally by the ultrasound system. Based on the applied force, the ultrasound system can change behavior such as adaptively changing the transmit beam angle, changing system power settings or TGC (time gain compensation) gain settings, activating an imaging mode, warning the user that the pressure is not suitable for an elastography scan, etc.

[0017] In some examples, the one or more properties of the acoustically translucent standoff layer include at least one of a thickness in a zero force state, a thickness at a predetermined non-zero compressive force or pressure, and / or a modulus of elasticity.

[0018] One or more properties of the acoustically translucent standoff layer may further include hysteretic behavior.

[0019] In some examples, the processing system is configured to determine the deformation measurement by identifying a plurality of ultrasonic echoes from each of one or more scan lines in the ultrasonic signal, for each of the scan lines, processing the plurality of echoes to determine a depth of a distal surface of the acoustically translucent standoff layer, and processing the depth of the distal surface for each of the one or more scan lines to determine the deformation measurement.

[0020] This method is based on the recognition that deformation of the acoustically translucent standoff layer affects the thickness of the acoustically translucent standoff layer (and therefore the depth at which the distal surface is detected).

[0021] The distal surface of the acoustically translucent standoff layer is the surface furthest from the ultrasound device (i.e., the surface of the acoustically translucent standoff layer that faces the skin) that is at the interface with an adjacent layer, which may be the subject's skin or a layer (e.g., adhesive, sterile film, air, water, sweat, etc.) disposed between the acoustically translucent standoff layer and the subject's skin, that is detectable by a difference in acoustic impedance between the acoustically translucent standoff layer and the adjacent layer.

[0022] The processing system may be configured to determine the depth of the distal surface for each scan line by processing multiple echoes from the scan line to identify the echo whose signal intensity value first exceeds an intensity threshold and selecting the depth of the identified echo as the depth of the distal surface.

[0023] The intensity threshold may be a predetermined threshold or a threshold determined by the processing system based on the ultrasound signal (eg, based on a signal intensity value of the ultrasound signal).

[0024] For example, the intensity threshold can have a predetermined value determined based on the characteristics of the ultrasound device and the acoustically translucent standoff layer (e.g., the acoustic transparency of the acoustically translucent standoff layer).

[0025] In some examples, a processing system is configured to determine the measure of deformation by processing the ultrasonic signal to generate an image including at least a portion of the acoustically translucent standoff layer and performing a cross-correlation of the generated image with a reference image to determine the measure of deformation.

[0026] The reference image may be an image of the acoustically translucent standoff layer when no force is applied. The cross-correlation may be a series of 1D A-line correlations or a 2D cross-correlation.

[0027] In some examples, the generated images may be processed, for example, by performing axial interpolation and / or azimuthal decimation, prior to performing cross-correlation. Image processing parameters may be defined based on the imaging frequency of the ultrasound device and one or more characteristics of the acoustically translucent standoff layer.

[0028] The processing system is configured to generate the ultrasound device interaction indicator by selecting one of a plurality of predetermined ultrasound device interaction indicators.

[0029] In other words, the ultrasound device interaction indicators can be binary or categorical indicators, which can be particularly beneficial in point-of-care ultrasound applications where users may lack the expertise to interpret numerical values ​​of force / pressure / orientation angle.

[0030] A given ultrasound device interaction indicator may have various levels of granularity. For example, an ultrasound device interaction indicator may represent three states: a first state where the force or pressure is below a first threshold, a second state where the force or pressure is above the first threshold but below a second, higher threshold, and a third state where the force or pressure is above the second threshold.

[0031] The indicator may be, for example, a text indicator (e.g., "too little pressure," "good pressure," and "too much pressure"). In another example, different colors may be used to represent different conditions.

[0032] The ultrasound device interaction indicator may be a numerical value of the force or pressure exerted by the ultrasound device on the subject.

[0033] When an ultrasound interaction device indicator is provided in the output user interface, the numerical value allows the clinician to make their own assessment of whether the force / pressure or orientation angle exerted by the ultrasound device is appropriate and to determine changes needed if either the force / pressure is insufficient or excessive, or the orientation angle is inappropriate.

[0034] In some examples, the clinician can select the level of granularity of the ultrasound device interaction indicators (e.g., the clinician can choose between categorical indicators and indicators that include numerical values ​​of force / pressure / orientation angle), while in other examples, the level of granularity can be automatically selected according to the type of ultrasound application.

[0035] In some examples, the ultrasound device interaction indicator may comprise both a predetermined ultrasound device interaction indicator and a numerical value.

[0036] The force, pressure or orientation angle values ​​may also be used internally by a processing system, for example to control an ultrasound system.

[0037] In some examples, the processing system is further configured to process one or more characteristics of the acoustically translucent standoff layer and the ultrasonic signal to determine a measure of strain hysteresis of the acoustically translucent standoff layer, and in response to determining that the measure of strain hysteresis exceeds a predetermined hysteresis threshold, generate an indication that the acoustically translucent standoff layer needs to be replaced and output the indication that the acoustically translucent standoff layer needs to be replaced at the output interface.

[0038] In another aspect of the present invention, a computer-implemented method is proposed for determining whether an acoustically translucent standoff layer between a surface of an ultrasound device and a subject's skin requires replacement. The method comprises: obtaining one or more characteristics of an acoustically semi-transparent standoff layer at the input interface; acquiring, at an input interface, ultrasound signals from an ultrasound device, the ultrasound signals representing a plurality of ultrasound echoes received by the ultrasound device from different depths for each of one or more scan lines; processing the ultrasonic signals to determine a measure of deformation of the acoustically translucent standoff layer; processing one or more properties of the acoustically translucent standoff layer and the ultrasonic signal to determine a measure of strain hysteresis of the acoustically translucent standoff layer; in response to determining that the measure of strain hysteresis exceeds a predetermined hysteresis threshold; generating an indication that the acoustically translucent standoff layer needs to be replaced; and outputting the indication that the acoustically translucent standoff layer needs to be replaced at an output interface. Includes.

[0039] The strain hysteresis of the hydrogel increases with continued application of force. Identifying when hysteresis effects are large enough to affect the outcome of the deformation determination allows users of the processing system to replace the acoustically translucent standoff layer when this occurs.

[0040] Also proposed is a system for providing an ultrasound device interaction indicator indicative of a force or pressure applied by an ultrasound device to a subject, the system comprising an ultrasound device configured to transmit and receive ultrasound waves and generate ultrasound signals indicative of a plurality of received ultrasound waves from different depths for each of one or more scan lines, an acoustically translucent standoff layer disposed between a surface of the ultrasound device and the skin of the subject, and a processing system as described above.

[0041] In some examples, the acoustically translucent standoff layer comprises a water-based gel pad.

[0042] Water-based gel pads are known in the art and are widely available, and therefore can be readily sourced according to user specifications.

[0043] In some examples, the acoustically translucent standoff layer includes a bond for securing the acoustically translucent standoff layer to an ultrasound device.

[0044] This allows for rapid placement of the acoustically translucent standoff layer on the ultrasound device and can assist the clinician in properly positioning the acoustically translucent standoff layer.

[0045] The acoustically translucent standoff layer may include, for example, mechanical fasteners such as clips, or an adhesive "skirt" that surrounds the periphery of the acoustically translucent standoff layer.

[0046] The thickness of the acoustically translucent standoff layer may be selected according to the target imaging anatomy.

[0047] The desired thickness of the acoustically translucent standoff layer depends on the imaging application.

[0048] According to another aspect of the invention, a computer-implemented method is provided for generating an ultrasound device interaction indicator representative of the force or pressure exerted by an ultrasound device on a subject and / or the orientation of the ultrasound device relative to the subject.

[0049] The computer-implemented method includes acquiring, at an input interface, one or more properties of an acoustically translucent standoff layer between a surface of the ultrasound device and the skin of the subject; acquiring, at the input interface, ultrasound signals from the ultrasound device, the ultrasound signals representing a plurality of ultrasound echoes received by the ultrasound device from different depths for each of one or more scan lines; processing the ultrasound signals to determine a measurement of deformation of the acoustically translucent standoff layer; and processing the measurement of deformation and the one or more properties of the acoustically translucent standoff layer to generate an ultrasound device interaction indicator.

[0050] A computer program product is also proposed comprising computer program code which, when executed on a computing device having a processing system, causes the processing system to perform all of the steps of the above-mentioned method.

[0051] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0052] For a better understanding of the invention and to show more clearly how it may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief description of the drawings]

[0053] [Figure 1] 1 illustrates an exemplary ultrasound system. [Diagram 2] 1 illustrates a system for providing an ultrasound device interaction indicator, according to an embodiment of the present invention. [Figure 3A] 1 illustrates a method for determining a measure of deformation of an acoustically translucent standoff layer in accordance with an embodiment of the present invention. [Figure 3B] 3B illustrates how the method of FIG. 3A can be used to determine a measure of deformation. [Figure 4]1 illustrates a method for determining a measure of deformation of an acoustically translucent standoff layer according to another embodiment of the present invention. [Diagram 5] 13 illustrates an exemplary output corresponding to an ultrasound device interaction indicator. [Figure 6] 1 illustrates an exemplary acoustically translucent standoff layer including bonding. [Figure 7] 1 illustrates a computer-implemented method for generating an ultrasound device interaction indicator, according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] Next, the present invention will be described with reference to the drawings.

[0055] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the figures to denote the same or similar parts.

[0056] In accordance with the concepts of the present invention, a system and method are proposed for generating an ultrasound device interaction indicator representative of the force or pressure applied by the ultrasound device and / or the orientation of the ultrasound device relative to a subject. An acoustically translucent standoff layer is disposed between the ultrasound device and the subject. Ultrasound echoes received by the ultrasound device, including ultrasound echoes from the standoff layer, are processed to determine a deformation of the standoff layer caused by the axial force or pressure applied by the ultrasound device. The deformation of the standoff layer, together with properties of the standoff layer, are used to generate an ultrasound device interaction indicator.

[0057] The embodiments are based at least in part on the realization that the force / pressure applied by the ultrasound device to the subject deforms a standoff layer between the ultrasound device and the subject, and that ultrasound imaging data acquired by the device can be used to determine the deformation of the standoff and thus the force / pressure applied by the ultrasound device. Measuring the deformation of a standoff layer with known properties provides a more reliable indication of force or pressure than measuring the deformation of tissue (e.g., skin), because tissue properties vary from subject to subject and further depend on environmental conditions, etc. The inventors have further realized that the deformation or force / pressure across the standoff layer provides information about the orientation of the ultrasound device.

[0058] Exemplary embodiments may be used, for example, in ultrasound imaging systems, such as point-of-care ultrasound systems.

[0059] With reference to FIG. 1, since the present invention is concerned with processing signals measured by a transducer array, the general operation of an exemplary ultrasound system will first be described with emphasis on the signal processing functions of the system.

[0060] The system includes an array transducer probe 4 having a transducer array 6 for transmitting ultrasound waves and receiving echo information. The transducer array 6 may include CMUT (Capacitive Micromachined Ultrasound Transducer) transducers, piezoelectric transducers formed from materials such as PZT (Lead Zirconate Titanate) or PVDF (Polyvinylidene Difluoride), or any other suitable transducer technology. In this example, the transducer array 6 is a two-dimensional array of transducers 8 capable of scanning either a 2D plane or a three-dimensional volume of an area of ​​interest. In another example, the transducer array may be a 1D array.

[0061] The transducer array 6 is coupled to a microbeamformer 12 which controls reception of signals by the transducer elements. The microbeamformer is capable of at least partial beamforming of signals received by subarrays of transducers (commonly referred to as "groups" or "patches") as described in U.S. Patents 5,997,479 (Savord et al.), 6,013,032 (Savord), and 6,623,432 (Powers et al.).

[0062] It should be noted that the microbeamformer is entirely optional. Additionally, the system includes a transmit / receive (T / R) switch 16 to which the microbeamformer 12 may be coupled to switch the array between transmit and receive modes and to protect the main beamformer 20 from high energy transmit signals when the microbeamformer is not used and the transducer array is operated directly by the main system beamformer. The transmission of ultrasound beams from the transducer array 6 is directed by a transducer controller 18 coupled to the microbeamformer by the T / R switch 16 and a main transmit beamformer (not shown) that may receive input from user operation of a user interface or control panel 38. The controller 18 may include transmit circuitry configured to drive the transducer elements of the array 6 (directly or via the microbeamformer) during transmit mode.

[0063] In a typical line-by-line imaging sequence, the beamforming system in the probe may operate as follows: During transmit, the beamformer (which may be a microbeamformer or a main system beamformer, depending on the implementation) activates a transducer array, or a subaperture of a transducer array. A subaperture may be a one-dimensional line of transducers, or a two-dimensional patch of transducers within a larger array. In transmit mode, the focus and steering of the ultrasound beam generated by the array or a subaperture of the array is controlled as described below.

[0064] Upon receiving the backscattered echo signals from the subject, the received signals undergo receive beamforming (as described below) to align the received signals, and if subapertures are used, the subapertures are shifted, for example, by one transducer element, and then the shifted subaperture is activated and the process is repeated until all of the transducer elements of the transducer array have been activated.

[0065] For each line (or sub-aperture), the total received signal used to form the associated line of the final ultrasound image is the sum of the voltage signals measured by the transducer elements of the given sub-aperture during the receive period. The resulting line signals, following the beamforming process, are usually referred to as radio frequency (RF) data. Each line signal (RF data set) generated by the various sub-apertures then undergoes additional processing to generate a line of the final ultrasound image. The change in amplitude of the line signal with time contributes to the change in brightness of the ultrasound image with depth, with high amplitude peaks corresponding to bright pixels (or groups of pixels) in the final image. Peaks appearing near the beginning of the line signal represent echoes from shallow structures, while peaks appearing gradually later in the line signal represent echoes from structures of greater depth within the subject.

[0066] One of the functions controlled by the transducer controller 18 is the direction in which the beam is steered and focused. The beam may be steered straight ahead (orthogonal) from the transducer array, or at a different angle to a wider field of view. The steering and focusing of the transmit beam may be controlled as a function of the activation time of the transducer elements.

[0067] Two methods can be distinguished in general ultrasound data acquisition: plane wave imaging and "beam steering" imaging. The two methods are distinguished by the presence of beamforming in the transmit ("beam steering" imaging) and / or receive modes (plane wave imaging and "beam steering" imaging).

[0068] Looking first at the focusing function, by activating all of the transducer elements simultaneously, the transducer array creates a plane wave that diverges as it travels through the subject. In this case, the beam of ultrasound remains unfocused. By introducing position-dependent time delays in the activation of the transducers, it is possible to focus the wavefront of the beam to a desired point, called a focal zone. A focal zone is defined as a point where the lateral beam width is less than half the transmit beam width. In this way, the lateral resolution of the final ultrasound image is improved.

[0069] For example, if a time delay activates the transducer elements successively, starting with the outermost elements of the transducer array and finishing with the central elements, a focal zone is formed along the central elements at a predetermined distance from the probe. The distance of the focal zone from the probe varies according to the time delay between each subsequent round of transducer element activation. After the beam passes through the focal zone, it begins to diverge, forming a far-field imaging region. It is noted that with focal zones located close to the transducer array, the ultrasound beam diverges rapidly in the far field, leading to beamwidth artifacts in the final image. Typically, the near field located between the transducer array and the focal zone shows little detail due to the large overlap of the ultrasound beams. Thus, changing the location of the focal zone can result in significant changes in the quality of the final image.

[0070] It should be noted that in transmit mode, only one focal point may be defined, unless the ultrasound image is divided into multiple focal zones (each of which may have a different transmit focal point).

[0071] Also, when echo signals are received from within the subject, the above process can be reversed to achieve receive focusing. In other words, the input signals can be received by the transducer elements and subjected to an electronic time delay before being passed to the system for signal processing. The simplest example of this is called delay-and-sum beamforming. It is possible to dynamically adjust the receive focus of the transducer array as a function of time.

[0072] Looking now at the function of beam steering, through the correct application of time delays to the transducer elements, it is possible to give the ultrasound beam a desired angle as it exits the transducer array. For example, by activating transducers on a first side of the transducer array and then activating the remaining transducers in a sequence ending on the opposite side of the array, the wavefront of the beam is angled toward the second side. The magnitude of the steering angle relative to the normal of the transducer array depends on the magnitude of the time delay between the activation of subsequent transducer elements.

[0073] Furthermore, it is possible for the total time delay applied to each transducer element to focus the steering beam with the sum of both the focusing time delay and the steering time delay, in which case the transducer array is called a phased array.

[0074] For CMUT transducers that require a DC bias voltage for activation, the transducer controller 18 can be coupled to control a DC bias control 45 for the transducer array. The DC bias control 45 sets the DC bias voltage applied to the CMUT transducer elements.

[0075] For each transducer element of the transducer array, an analog ultrasound signal, typically called channel data, enters the system via a receive channel, where a partially beamformed signal is generated from the channel data by the microbeamformer 12 and then passed to the main receive beamformer 20, where the partially beamformed signals from the individual patches of the transducer are combined into a fully beamformed signal, called radio frequency (RF) data. The beamforming performed at each stage may be performed as described above or may include additional functions. For example, the main beamformer 20 may have 128 channels, each of which receives partially beamformed signals from patches of tens or hundreds of transducer elements. In this way, the signals received by the thousands of transducers of the transducer array can be efficiently contributed to a single beamformed signal.

[0076] The beamformed received signals are coupled to a signal processor 22. The signal processor 22 may process the received echo signals in various ways, such as bandpass filtering, decimation, I and Q component separation, and harmonic signal separation, which acts to separate linear and nonlinear signals to allow identification of nonlinear (harmonic of fundamental frequency) echo signals returning from tissue and microbubbles. The signal processor may also perform additional signal enhancements, such as speckle reduction, signal synthesis, and noise removal. The bandpass filters in the signal processor may be tracking filters whose passbands slide from higher to lower frequency bands as echo signals are received from increasing depths, thereby eliminating noise at higher frequencies from greater depths that typically lack anatomical information.

[0077] The beamformers for transmit and receive can be implemented with different hardware and have different functionality. Of course, the receiver beamformer is designed to take into account the characteristics of the transmit beamformer. In Fig. 1, for simplicity, only the receiver beamformers 12, 20 are shown. In a complete system, there is also a transmit chain with a transmit microbeamformer and a main transmit beamformer.

[0078] The function of the microbeamformer 12 is to provide an initial combination of signals to reduce the number of analog signal paths, which is typically performed in the analog domain.

[0079] Final beamforming occurs in the main beamformer 20, typically after digitization.

[0080] The transmit and receive channels use the same transducer array 6 with a fixed frequency band. However, the bandwidth occupied by the transmit pulses can vary depending on the transmit beamforming used. The receive channels can capture the entire transducer bandwidth (classical approach) or, by using bandpass processing, extract only the bandwidth containing the desired information (e.g. harmonics of the main harmonic).

[0081] The RE signal may then be coupled to a B-mode (i.e., intensity mode, or 2D imaging mode) processor 26 and a Doppler processor 28. The B-mode processor 26 performs amplitude detection on the received ultrasound signals to image body structures such as organ tissues and blood vessels. In the case of line-by-line imaging, each line (beam) is used to generate an intensity value whose associated RE signal amplitude is assigned to a pixel in the B-mode image. The exact location of the pixel in the image is determined by the location of the amplitude measurement associated with the RE signal and the number of lines (beams) of the RF signal. B-mode images of such structures may be formed in harmonic or fundamental imaging modes, or a combination of both as described in US 6,283,919 (Roundhill et al.) and US 6,458,083 (Jago et al.). The Doppler processor 28 processes the time-distinct signals resulting from tissue motion and blood flow for detection of moving material such as flow of blood cells within the image field. The Doppler processor 28 typically includes a wall filter with parameters set to pass or reject echoes returned from selected types of material within the body.

[0082] The structural and motion signals generated by the B-mode and Doppler processors are coupled to the scan converter 32 and the multiplanar reformatter 44. The scan converter 32 arranges the echo signals in the spatial relationship from which they were received, in the desired image format. In other words, the scan converter acts to convert the RF data from a cylindrical coordinate system to a Cartesian coordinate system suitable for displaying ultrasound images on the image display 40. For a B-mode image, the brightness of a pixel at a given coordinate is proportional to the amplitude of the RF signal received from that location. For example, the scan converter may arrange the echo signals in a two-dimensional (2D) sector format, or a pyramidal three-dimensional (3D) image. The scan converter may overlay a B-mode structural image with a color corresponding to the motion at the point in the image field, where the Doppler estimated velocity produces a given color. The combined B-mode structural image and color Doppler image depict the tissue motion and blood flow within the structural image field. The multiplanar reformatter converts echoes received from points in a common plane within a volumetric region of the body into an ultrasound image of that plane, as described in U.S. Patent Application Publication No. 6,443,896 (Detmer). The volume renderer 42 converts the echo signals of the 3D data set into a projected 3D image viewed from a given reference point, as described in U.S. Patent Application Publication No. 6,530,885 (Entrekin et al.).

[0083] The 2D or 3D images are coupled from the scan converter 32, multiplanar reformatter 44, and volume renderer 42 to the image processor 30 for further enhancement, buffering, and temporary storage for display on the image display 40. The imaging processor may be adapted to remove certain imaging artifacts from the final ultrasound image, such as acoustic shadowing caused by strong attenuators or refraction, back enhancement caused by weak attenuators, and reverberation artifacts where highly reflective tissue interfaces are located in close proximity. In addition, the image processor may be adapted to process certain speckle reduction functions to improve the contrast of the final ultrasound image.

[0084] In addition to being used for the images, the blood flow values ​​produced by the Doppler processor 28 and the tissue structure information produced by the B-mode processor 26 are coupled to a quantification processor 34. The quantification processor produces measurements of different flow conditions, such as volumetric velocity of blood flow, in addition to structural measurements such as organ size and gestational age. The quantification processor can receive input from a user control panel 38, such as the points within the anatomical structures in the image where measurements are to be taken.

[0085] Output data from the quantification processor is coupled to a graphics processor 36 for reproducing measurement graphics and values ​​with images on a display 40 and audio output from the display device 40. The graphics processor 36 can also generate graphic overlays for display with the ultrasound images. These graphic overlays can include standard identification information such as the patient name, date and time of the image, imaging parameters, etc. For these purposes, the graphics processor receives inputs such as the patient name from a user interface 38. The user interface is also coupled to a transmit controller 18 for controlling the generation of ultrasound signals from the transducer array 6 and, therefore, the generation of images generated by the transducer array and the ultrasound system. The transmit control function of the controller 18 is only one of the functions performed. The controller 18 also takes into account the operating mode (given by the user) and the corresponding required transmitter settings and bandpass settings in the receiver analog-to-AD converter. The controller 18 can be a state machine with fixed states.

[0086] The user interface is also coupled to a multiplanar reformatter 44 for selection and control of multiple multiplanar reformat (MPR) image planes that can be used to perform quantified measurements in the image field of the MPR images.

[0087] 2 illustrates a system 200 for generating an ultrasound device interaction indicator, according to one embodiment of the present invention. The ultrasound device interaction indicator is an indicator representative of the force or pressure exerted by an ultrasound device on a subject 210 and the orientation of the ultrasound device relative to the subject. The system 200 includes a processing system 220, an ultrasound device 230, and an acoustically translucent standoff layer 240. The processing system is itself an embodiment of the present invention.

[0088] An acoustically translucent standoff layer 240 is disposed between the surface of the ultrasound device 230 and the subject's skin 215. The acoustically translucent standoff layer is a layer of material having acoustic transparency that allows for ultrasound imaging through the material (i.e., imaging of structures beyond the material). Suitable materials for an acoustically translucent standoff layer will be readily apparent to one of ordinary skill in the art. For example, the acoustically translucent standoff layer may include a water-based gel pad (e.g., a water-based hydrogel pad). Water-based gel pads are known in the art and are commonly used to provide acoustic coupling between the ultrasound device and the skin when imaging areas that are difficult to visualize. Acoustically translucent standoff layers are described in more detail below.

[0089] The processing system 220 obtains one or more properties 245 of the acoustically translucent standoff layer 240 at or from the input interface 221. The one or more properties of the acoustically translucent standoff layer are properties that may be used in combination with the deformation measurements to generate an ultrasound device interaction indicator representative of force, pressure, and orientation. For example, the one or more properties of the acoustically translucent standoff layer may include at least one of a thickness in a zero force state, a thickness at a predetermined non-zero compressive force or pressure, and / or a modulus of elasticity. The use of these properties to generate an ultrasound device interaction indicator is described in more detail below.

[0090] The one or more characteristics 245 of the acoustically translucent standoff layer 240 may be obtained from a memory unit 250, as shown in Figure 2. In some examples, some or all of the one or more characteristics may be obtained via user input from a user input device.

[0091] The ultrasound device 230 is a device capable of transmitting and receiving ultrasound. Any suitable ultrasound device may be used, including handheld ultrasound probes and ultrasound patches. The system 200 is particularly useful for point-of-care ultrasound applications, which are often performed by users who are less skilled in determining the appropriate amount of pressure to apply themselves.

[0092] The ultrasound device 230 generates ultrasound signals 235 representing multiple ultrasound echoes received by the ultrasound device from different depths for each of one or more scan lines, and the processing system 220 acquires the ultrasound signals from the ultrasound device at or from the input interface 221.

[0093] The different depths may include at least one depth corresponding to an acoustically translucent standoff layer and at least one depth corresponding to a layer beyond the acoustically translucent standoff layer (i.e., a layer on the opposite side of the acoustically translucent standoff layer from the ultrasound device, e.g., a skin layer). In other words, the received ultrasound may include echoes from the acoustically translucent standoff layer and echoes from another layer transmitted through the acoustically translucent standoff layer.

[0094] The processing system 220 then processes the ultrasonic signals 235 to determine a measure of deformation of the acoustically translucent standoff layer 240. The measure of deformation may include, for example, an axial strain and / or a deformed thickness of the acoustically translucent standoff layer.

[0095] In some examples, the processing system determines the measure of deformation based on a depth of a distal surface (i.e., the surface furthest from the ultrasound device 230) of the acoustically translucent standoff layer 240. In other words, the measure of deformation may be determined based on a depth of a boundary between the acoustically translucent standoff layer and a layer opposite the acoustically translucent standoff layer relative to the ultrasound device (e.g., the subject's skin 215). In other examples, the processing system determines the measure of deformation based on cross-correlation with a reference image.

[0096] 3A illustrates a method 300 for determining a measure of deformation of an acoustically translucent standoff layer according to one embodiment of the present invention. In method 300, processing system 220 determines the measure of deformation based on a depth of a distal surface (i.e., the surface facing the skin) of the acoustically translucent standoff layer. This method provides a simple method for determining the measure of deformation at the data detection stage that can be easily implemented, for example, in a field programmable gate array.

[0097] The method 300 begins at step 310 where a number of ultrasound echoes are identified in the ultrasound signal 235 for each of one or more scan lines. Methods for identifying ultrasound echoes in an ultrasound signal will be apparent to those skilled in the art.

[0098] In step 320, multiple echoes from each scan line are processed to determine the depth of the distal surface of the acoustically translucent standoff layer 240 for each scan line.

[0099] The depth of the distal surface for a particular scan line may be determined by processing multiple echoes from the scan line to identify the echo whose signal intensity value first exceeds an intensity threshold. Because layers adjacent to the distal surface (e.g., skin, adhesive, air, etc.) generally have a different acoustic impedance than the acoustically translucent standoff layer, the boundary between the acoustically translucent standoff layer and the adjacent layer is characterized by an upward transition in signal intensity.

[0100] The multiple echoes may be processed in order of increasing depth, and the first echo to be identified as having a signal intensity value above a predetermined intensity threshold is then selected as the echo corresponding to the distal surface of the scan line. The depth of the identified echo is selected as the depth of the distal surface of the scan line. This process is repeated for each scan line.

[0101] The intensity threshold may be a predetermined threshold or a threshold determined based on the ultrasonic signal 235. The predetermined intensity threshold may be determined, for example, based on characteristics of both the ultrasonic device 230 and the acoustically translucent standoff layer 240. In some examples, multiple predetermined intensity thresholds for each different combination of ultrasonic device and acoustically translucent standoff layer may be stored in the memory unit 250, and an appropriate predetermined intensity threshold may be selected based on user input from a user input device.

[0102] In some examples, the processing system 220 may determine the intensity threshold value by processing the ultrasound signal 235. This allows the distal surface depth to be identified without the need for additional information (such as acoustically translucent standoff layers and characteristics of the ultrasound device) and is not affected by user-applied global gain changes.

[0103] The processing system can determine the intensity threshold based on the signal strength values ​​of the ultrasound signals (e.g., based on an average minimum signal strength and an average maximum signal strength). For example, the intensity threshold may be set to a value between the average minimum signal strength and the average maximum signal strength (e.g., the midpoint of these signal strengths, or a value between the midpoint and the average maximum signal strength).

[0104] The ultrasound signal 235 may be pre-processed prior to step 320. For example, automatic time gain compensation (TGC) may be used to automatically normalize the intensity across multiple scan lines at a set of depths or throughout the depth of each scan line.

[0105] In step 330, the distal surface depth of each of the one or more scan lines is processed to determine a measure of deformation. The distal surface depth corresponds to a current thickness of the acoustically translucent standoff layer 240. In some examples, such as when the measure of deformation is or includes axial strain, the determination of the measure of deformation may be further based on one or more properties 245 of the acoustically translucent standoff layer (e.g., thickness at zero force state). In other words, the distal surface depth may be used in conjunction with known properties of the acoustically translucent standoff layer to determine the deformation of the acoustically translucent standoff layer.

[0106] In some examples where multiple scan lines are used, the determined distal surface depths may be pre-processed prior to determining the deformation measure, for example, outlier analysis may be applied to the determined distal surface depths to identify false positives, which may be excluded from the distal surface depths used to determine the deformation measure.

[0107] The distal surface depth may be averaged over multiple scan lines before determining the measure of deformation, and the number of scan lines over which the distal surface depth is averaged may depend on the desired level of granularity. In some examples, the number of scan lines over which the distal surface depth is averaged may be selected to produce one average depth per scan frame (e.g., the distal surface depth may be averaged over approximately 128 scan lines).

[0108] 3B shows a portion of an ultrasound image 350 illustrating the idea behind this approach: the layer closest to the ultrasound device is the acoustically translucent standoff layer, which is primarily anechoic, and the next layer is not, so a sharp difference in signal intensity is observed at the boundary between these layers.

[0109] Line 355 depicts the boundary detected using a grayscale threshold (with the threshold at 75% of the difference between the average minimum and maximum signal intensities). The displacement of this boundary from the ultrasound emitting face of the ultrasound device gives the current thickness of the acoustically translucent standoff layer, which can then be used to determine the force or pressure applied by the ultrasound device. In FIG. 3B, the displacement is greater on one side and decreases across the field of view. This shows an angled ultrasound device (i.e., an ultrasound device with an imaging axis that is not perpendicular to the surface of the subject's skin).

[0110] 4 illustrates another method 400 for determining a measure of deformation of an acoustically translucent standoff layer in accordance with an embodiment of the present invention. In method 400, processing system 220 determines the measure of deformation based on cross-correlation. This method may provide a more robust determination of the measure of deformation, and may be used in particular when a layer adjacent to the acoustically translucent standoff layer has a similar acoustic impedance as the acoustically translucent standoff layer (where it is difficult to detect the distal surface of the standoff layer).

[0111] The method 400 begins at step 410 where an ultrasound image is generated by processing the ultrasound signal 235. The ultrasound image is an image that includes at least a portion of the acoustically translucent standoff layer.

[0112] In step 420, a cross-correlation is performed between the generated image and a reference image, the reference image being an image that corresponds to an ultrasound image of the acoustically translucent standoff layer 240 in the absence of any force deforming the acoustically translucent standoff layer (e.g., an image taken in air or an image obtained such that the pressure on the standoff layer is zero).

[0113] Cross-correlation is a well-known technique in image processing that can be used to measure the displacement of structures between two images, see, for example, Bilgen and Insana (1996), "Deformation models and correlation analysis in elastography," J. Accoust. Soc.Am., 99(5):3212-3224, and Pinton et al. (2006), "Rapid tracking of small displacements using ultrasound," IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 53(6):1103-1117.

[0114] By cross-correlating an ultrasound image of the deformed acoustically translucent standoff layer 240 with an ultrasound image of the undeformed acoustically translucent standoff layer (i.e., when no force is applied), the displacement along the imaging axis (i.e., axial strain) can be determined. The cross-correlation can be a series of 1D azimuth line correlations or a 2D cross-correlation.

[0115] In some examples, a reference image may be acquired by a user of an ultrasound system imaging the acoustically translucent standoff layer 240. The user may be prompted to take this image, for example, by outputting a user command on a user interface.

[0116] In another example, a reference image may be generated from the ultrasound signal 235. The processing system may process the ultrasound signal to generate multiple frames, and the first frame with image content (i.e., the first frame that is not completely black) may be selected as the reference image, while a later frame may be selected as the ultrasound image to cross-correlate with the reference image. This approach may be used when the ultrasound device 230 begins acquiring ultrasound signals before the ultrasound device is pressed against the subject 210.

[0117] In yet another example, the reference image may be a simulated image generated from data representing an acoustically translucent standoff layer when no force is applied.

[0118] The generated image (and / or the reference image) may be pre-processed before cross-correlation is performed. Parameters used in pre-processing may be selected based on the imaging frequency used by the ultrasound device 230 when acquiring the ultrasound signal 235 and one or more characteristics of the acoustically translucent standoff layer. Suitable image processing techniques for pre-processing the generated image, such as axial interpolation and azimuth decimation, will be apparent to those skilled in the art.

[0119] A measure of deformation is determined based on the cross-correlation results, at step 430. The measure of deformation may be axial strain, determined from the displacement along the imaging axis based on the cross-correlation.

[0120] 2, upon determining the measure of deformation of the acoustically translucent standoff layer 240, the processing system 220 processes the measure of deformation and one or more properties 245 of the acoustically translucent standoff layer to generate an ultrasound device interaction indicator that is indicative of the force or pressure applied by the ultrasound device 230 to the subject 210 and the orientation of the ultrasound device relative to the subject.

[0121] The relationship between force / pressure and axial strain (or deformed thickness) is very well known, and therefore it will be readily apparent to one skilled in the art how to generate an ultrasound device interaction indicator representative of the force or pressure applied by the ultrasound device 230 based on measurements of the deformation and one or more properties of the acoustically translucent standoff layer 240. If the ultrasound device interaction indicator includes a pressure value, the ultrasound device interaction indicator may be generated further based on the surface area of ​​the ultrasound emitting face of the ultrasound device (i.e., the surface in contact with or closest to the acoustically translucent standoff layer). The surface area may be obtained, for example, via user input or may be stored in the memory unit 250.

[0122] An ultrasound device interaction indicator representing the orientation of the ultrasound device 230 relative to the subject 210 may be generated based on the difference in deformed thickness, force, and / or pressure across the acoustically translucent standoff layer 240. The gradient of the pressure, force, or thickness also indicates the direction of the probe orientation. If the pressure, force, or thickness is the same or substantially the same across the acoustically translucent standoff layer, this indicates that the imaging axis of the ultrasound device is perpendicular or substantially perpendicular to the subject's skin. If the deformed thickness is less or the force / pressure is greater, on one side of the acoustically translucent standoff layer, this indicates that the ultrasound device is tilted toward this side of the acoustically translucent standoff layer.

[0123] The ultrasound device interaction indicator may be a numerical indicator (e.g., a numerical value of the angle of orientation by the ultrasound device 230 or of the ultrasound device), a categorical indicator (e.g., "too much pressure", "correct pressure", "too little pressure", "too much force", "correct force", "too little force", "correct direction", "tilted left", "tilted right"), or a binary indicator (e.g., "coupled" or "not coupled").

[0124] A categorical or binary ultrasound device interaction indicator may be generated, for example, by selecting one of a plurality of predefined ultrasound device interaction indicators. One or more thresholds (i.e., pressure value, force value, or deformation measure thresholds) may be used to determine which of the plurality of predefined ultrasound device interaction indicators to select.

[0125] For example, if there are three predefined ultrasound device interaction indicators (e.g., "too low pressure," "too correct pressure," and "too high pressure"), the processing system 220 may select a first predefined ultrasound indicator (e.g., "too low pressure") in response to a determination that the measure of force, pressure, or deformation does not exceed a first predefined threshold, and a second predefined ultrasound indicator (e.g., "too correct pressure") and a second predefined ultrasound device interaction indicator (e.g., "too high pressure") in response to a determination that the measure of force, pressure, or deformation exceeds the first predefined threshold but does not exceed a second, higher predefined threshold.

[0126] In another example, if the ultrasound device interaction indicator is a binary indicator (e.g., “coupled” or “uncoupled”), the processing system 220 may select a first predetermined ultrasound device interaction indicator (e.g., “uncoupled”) in response to a determination that the deformation force, pressure, or measurement does not exceed this threshold, and may select a second predetermined ultrasound device interaction indicator (e.g., “coupled”) in response to a determination that the deformation force, pressure, or measurement exceeds this threshold.

[0127] In some examples, the processing system 220 may determine one or more thresholds based on one or more characteristics of the acoustically translucent standoff layer 240. For example, if the one or more characteristics include at least one thickness at a predetermined non-zero compressive force or pressure, the predetermined force or pressure may be selected as the threshold force or pressure. The thickness at the predetermined force or pressure may then be defined as the threshold thickness, and a measure of deformation, including the deformed thickness of the acoustically translucent standoff layer, may be compared to the threshold thickness. Thus, a categorical ultrasound device interaction indicator representative of the force or pressure (e.g., whether the force / pressure is too high, too low, or at a desired level) may be generated directly from the measurement of the (current) deformed thickness of the acoustically translucent standoff layer.

[0128] In some examples, ultrasound device interaction indicators may be used to control or define user perceptible outputs, such as audio and / or visual indicators. For example, ultrasound device interaction indicators may be used to control or define sounds, lights, images, and / or text displays.

[0129] The processing system 220 can output the ultrasound device interaction indicators at the output interface 222 to the output user interface 260. Although in FIG. 2 the ultrasound device interaction indicators are provided on a smartphone display, the output user interface can be any device suitable for providing a user perceptible output. For example, the output user interface can be or comprise a display device, a speaker, or a light. In some examples the output user interface can also be configured to receive user input (e.g., the output user interface can be a touch screen device).

[0130] Figure 5 shows an example output corresponding to an ultrasound device interaction indicator on a smartphone or tablet display as part of an ultrasound application such as Philips Lumify.

[0131] The example output 510 includes a text display reading “Not Attached.” This output may be provided in response to an ultrasound device interaction indicator indicating that the ultrasound device 230 is not applying force or pressure to the subject 210.

[0132] An exemplary output 520 includes a text display containing multiple possible force / pressure states ("OFF", "LOW", "MEDIUM", and "HIGH") and an arrow indicating which state corresponds to the ultrasound device interaction indicator.

[0133] Exemplary outputs 530 include a text display that provides a numerical value of the force exerted by the ultrasound device interaction indicator.

[0134] Further examples of suitable user-perceptible outputs controlled or defined by an ultrasound device interaction indicator will be apparent to those skilled in the art, for example, color highlighting may be used to indicate which of a number of states corresponds to the ultrasound device interaction indicator, or a diagram may indicate the orientation of the ultrasound device.

[0135] In some examples, in addition to or instead of being provided in an output user interface, ultrasound device interaction indicators may be used to control operation of the ultrasound device 230. For example, the processing system 220 may obtain measurements of the anatomical structure by controlling the ultrasound device to obtain ultrasound imaging data of the anatomical structure in response to a determination that the force or pressure exceeds a desired force or pressure. In another example, the determined force or pressure may be used as a threshold trigger in strain elastography.

[0136] As mentioned above, the present invention utilizes an acoustically translucent standoff layer to generate an ultrasound device interaction indicator. The (zero force state) thickness of the acoustically translucent standoff layer can be selected according to the type of ultrasound imaging application or target imaging anatomy. A thicker acoustically translucent standoff layer increases the field of view of the ultrasound device, but also increases the difficulty of imaging through bone and other highly attenuating materials. Thus, a thin acoustically translucent standoff layer, e.g., 3 mm, may be preferred for transcranial and apical cardiac applications, for example, while a thicker acoustically translucent standoff layer, e.g., 7 mm, may be used for vascular applications.

[0137] Other factors may also influence the selected thickness of the acoustically translucent standoff layer, for example, the ease of measuring deformation increases with increasing thickness (longer compression travel), but thicker acoustically translucent standoff layers have increased fragility and attenuation.

[0138] Acoustically translucent standoff layers can exhibit hysteresis behavior. Strain hysteresis is a well-known phenomenon that affects the determination of force / pressure from axial strain. The hysteresis effect becomes larger with the application of continuous force.

[0139] In some examples, one or more properties of the acoustically translucent standoff layer may include hysteresis behavior, allowing this behavior to be taken into account when generating the ultrasound device interaction indicator.

[0140] In some examples, the processing system 220 may be configured to monitor hysteresis in the acoustically translucent standoff layer. For example, the processing system may process one or more characteristics of the acoustically translucent standoff layer and the ultrasonic signal 235 to determine a measure of strain hysteresis of the acoustically translucent standoff layer. The processing system may then generate an indication that the acoustically translucent standoff layer requires replacement in response to determining that the measure of strain hysteresis exceeds a predetermined hysteresis threshold, and output the indication at the output interface 222 (e.g., to the user output interface 260). The predetermined hysteresis threshold may be defined according to a desired level of uncertainty of the ultrasound device interaction indicator.

[0141] In some examples, an acoustically translucent standoff layer can be selected to reduce the effects of hysteresis. For example, the stiffness of the acoustically translucent standoff layer affects the hysteresis behavior. The acoustically translucent standoff layer may be formed of a material having a stiffness higher than that used in conventional gel pads (e.g., Parker Aquaflex® gel pads) to reduce hysteresis effects and improve the reliability of the ultrasound device interaction indicator. However, increasing the stiffness of the acoustically translucent standoff layer also increases the difficulty of determining a measure of deformation, and thus there is a tradeoff between reduced hysteresis and the ability to determine a measure of deformation.

[0142] In another example, the hysteresis problem may be avoided by using the acoustically translucent standoff layer only once. In other words, the acoustically translucent standoff layer may be a disposable standoff layer that is stored in an airtight package. This has the added advantage that the acoustically translucent standoff layer may be provided as a sterile standoff layer.

[0143] An acoustically translucent standoff layer 240 is disposed between the ultrasound device and the subject's skin 215. In some examples, the acoustically translucent standoff layer may include bonds to secure the acoustically translucent standoff layer to the ultrasound device, which aids in the placement and positioning of the acoustically translucent standoff layer.

[0144] FIG. 6 illustrates an exemplary acoustically translucent standoff layer 640 including bonding. The exemplary acoustically translucent standoff layer 640 comprises a gel pad 641 and an adhesive "skirt" 642 that surrounds the periphery of the acoustically translucent standoff layer. The adhesive skirt is attached to the gel pad and has an adhesive surface that allows the acoustically translucent standoff layer to be attached to an ultrasound device. The adhesive skirt has a notch in its center such that the acoustically translucent standoff layer can be placed on the ultrasound device such that the notch area corresponds to the ultrasound emission area of ​​the ultrasound device, ensuring that the adhesive skirt does not affect the ultrasound signal acquired by the ultrasound device.

[0145] Other attachments are envisioned and suitable attachments such as clips, clamps, straps, etc. will be apparent to one of ordinary skill in the art. For example, the acoustically translucent standoff layer may be attached to a rigid case that is clipped onto the ultrasound probe.

[0146] 7 illustrates a computer-implemented method 700 for generating an ultrasound device interaction indicator according to one embodiment of the present invention. An ultrasound device interaction indicator is an indicator that represents the force or pressure exerted by an ultrasound device on a subject and / or the orientation of the ultrasound device relative to the subject.

[0147] The method begins at step 710 where one or more characteristics of an acoustically translucent standoff layer between a surface of an ultrasound device and the skin of a subject are obtained.

[0148] In step 720, ultrasound signals are acquired from the ultrasound device. The ultrasound signals represent a number of ultrasound echoes received by the ultrasound device from different depths for each of one or more scan lines.

[0149] In step 730, the ultrasonic signals are processed to determine a measure of deformation of the acoustically translucent standoff layer.

[0150] In step 740, the deformation measurements and one or more properties of the acoustically translucent standoff layer are processed to generate an ultrasound device interaction indicator.

[0151] It will be understood that the disclosed methods are computer-implemented methods, and therefore also the idea of ​​a computer program comprising code for implementing any of the described methods when said program is run on a processing system is proposed.

[0152] Those skilled in the art will be able to readily develop a processor to perform the methods described herein, and each step of the flowchart may therefore represent a different action performed by a processor and may be executed by a respective module of the processor.

[0153] As described above, the system utilizes a processor to perform data processing. The processor can be implemented in a number of ways using software and / or hardware to perform the various functions required. The processor typically uses one or more microprocessors that can be programmed using software (e.g., microcode) to perform the necessary functions. The processor can also be implemented as a combination of dedicated hardware to perform some functions and one or more programmed microprocessors and associated circuitry to perform other functions.

[0154] Examples of circuitry that may be used in various embodiments of the present disclosure include, but are not limited to, conventional microprocessors, application specific integrated circuits (ASICs), and field programmable gate arrays (FPGAs).

[0155] In various implementations, a processor may be associated with one or more storage media, such as volatile and non-volatile computer memory, such as RAM, PROM, EPROM, and EEPROM. The storage media may be encoded with one or more programs that, when executed on the one or more processors and / or controllers, perform the necessary functions. The various storage media may be fixed within the processor or the controller may be transportable such that one or more programs stored thereon may be loaded into the processor.

[0156] Variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0157] The functions implemented by a processor may be implemented by a single processor or by multiple separate processing units, which may be considered to constitute a "processor". Such processing units may possibly be remote from each other and in communication with each other in a wired or wireless manner.

[0158] Measures recited in mutually different dependent claims can be combined to advantage.

[0159] The computer program may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, provided together with or as part of other hardware, but may also be distributed in other forms, such as over the Internet or other wired or wireless telecommunications systems.

[0160] It should be noted that when the term "adapted for" is used in the claims or description, it is intended to be equivalent to the term "configured for." When the term "apparatus" is used in the claims or description, it is intended to be equivalent to the term "system," and vice versa.

[0161] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. 1. A computer-implemented method for generating an ultrasound device interaction indicator representative of an orientation of an ultrasound device relative to a subject, the computer-implemented method comprising: acquiring, at an input interface, one or more characteristics of an acoustically translucent standoff layer between a surface of the ultrasound device and the skin of the subject; acquiring, at the input interface, ultrasound signals from the ultrasound device, the ultrasound signals representing a plurality of ultrasound echoes received by the ultrasound device from different depths for each of one or more scan lines; processing the ultrasonic signals to determine a measure of deformation of the acoustically translucent standoff layer; processing the measure of deformation and one or more properties of the acoustically translucent standoff layer to generate an ultrasound device interaction indicator indicative of an orientation of the ultrasound device relative to a subject; The method comprising:

2. The method of claim 1 , wherein the ultrasound device interaction indicator further represents a force or pressure exerted by the ultrasound device on the subject.

3. 3. The method of claim 1 or 2, wherein the one or more properties of the acoustically translucent standoff layer include at least one of a thickness in a zero force state, a thickness at a predetermined non-zero compressive force or pressure, and / or a modulus of elasticity.

4. The method of claim 3 , wherein one or more properties of the acoustically translucent standoff layer further comprise hysteretic behavior.

5. identifying a plurality of ultrasound echoes from each of one or more scan lines within the ultrasound signal; processing a plurality of echoes from each scan line to determine, for each scan line, a depth of a distal surface of the acoustically translucent standoff layer, the distal surface of the acoustically translucent standoff layer being distal to the ultrasound device; processing the depth of the distal surface for each of the one or more scan lines to determine a measure of the deformation; 5. The method of claim 1 , further comprising:

6. processing a plurality of echoes from the scan line to identify an echo whose signal intensity value first exceeds an intensity threshold; selecting the depth of the identified echo as the depth of the distal surface; The method of claim 5, further comprising:

7. processing the ultrasound signals to generate an image having at least a portion of the acoustically translucent standoff layer; performing a cross-correlation between the generated image and a reference image to determine a measure of the deformation; 5. The method of claim 1 , further comprising:

8. generating said ultrasound device interaction indicator by selecting one of a plurality of predetermined ultrasound device interaction indicators; The method of any one of claims 1 to 7, further comprising:

9. 9. The method of claim 1, wherein the ultrasound device interaction indicator is a numerical value of the force or pressure exerted by the ultrasound device on the subject.

10. processing one or more properties of the acoustically translucent standoff layer and the ultrasonic signal to determine a measure of strain hysteresis of the acoustically translucent standoff layer; in response to determining that the measure of strain hysteresis exceeds a predetermined hysteresis threshold; generating an indication that the acoustically translucent standoff layer requires replacement; outputting, at an output interface, an indication that the acoustically translucent standoff layer requires replacement; 10. The method of claim 1, further comprising:

11. 1. A computer-implemented method for determining if an acoustically translucent standoff layer between a surface of an ultrasound device and a subject's skin requires replacement, the method comprising: obtaining one or more characteristics of the acoustically translucent standoff layer at an input interface; acquiring, at the input interface, ultrasound signals from the ultrasound device, the ultrasound signals representing a plurality of ultrasound echoes received by the ultrasound device from different depths for each of one or more scan lines; processing the ultrasonic signals to determine a measure of deformation of the acoustically translucent standoff layer; processing one or more properties of the acoustically translucent standoff layer and the ultrasonic signal to determine a measure of strain hysteresis of the acoustically translucent standoff layer; in response to determining that the measure of strain hysteresis exceeds a predetermined hysteresis threshold; generating an indication that the acoustically translucent standoff layer requires replacement; outputting, at an output interface, an indication that the acoustically translucent standoff layer requires replacement; 13. A computer-implemented method comprising:

12. A processing system configured to carry out the method of any one of claims 1 to 11.

13. 1. A system for providing an ultrasound device interaction indicator, comprising: an ultrasound device configured to transmit and receive ultrasound waves and generate ultrasound signals representative of a plurality of received ultrasound waves from different depths for each of one or more scan lines; an acoustically translucent standoff layer disposed between a surface of the ultrasound device and the skin of the subject; The processing system according to claim 12. The system has:

14. 14. The system of claim 13, wherein the acoustically translucent standoff layer comprises a water-based gel pad.

15. 15. The system of claim 13 or 14, wherein the acoustically translucent standoff layer comprises a bond for securing the acoustically translucent standoff layer to the ultrasound device.

16. 16. The system of claim 13, wherein a thickness of the acoustically translucent standoff layer is selected according to a target imaging anatomy.

17. A computer program product comprising computer program code which, when executed on a computing device having a processing system, causes said processing system to perform the steps of the method according to any one of claims 1 to 11.

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