A portable imaging device for medical use and method for its operation

Abstract

A handheld imaging device (100) for medical use comprising: a housing (106); and a sensor base (101) connected to the housing (106). The sensor base (101) comprises a first acoustic transducer array for imaging a sub-dermal structure in a first plane and a second transducer array for imaging the sub-dermal structure in a second plane. A processor (205), operable under control of electronic program instructions, activates transducer elements of the first transducer array (102) (e.g. operable in continuous wave Doppler ultrasound mode) and the second acoustic transducer array (103) (e.g. operable in A-mode ultrasound) to transmit signals and process receive signals reflected by the sub-dermal structure (104) to display an image of the sub-dermal structure (104), e.g. a vein. The processor (205) calculates characteristics of the sub-dermal structure (104) from the first and second imaged planes. The device (100) may be used in medical ultrasound to facilitate procedures such as cannulation and venepuncture.

Description

A PORTABLE IMAGING DEVICE FOR MEDICAL USE AND METHOD FOR ITS OPERATIONTECHNICAL FIELD

[0001] The present invention relates to a portable imaging device, preferably a handheld imaging device for blood vessel visualisation, and a method for its operation.BACKGROUND ART

[0002] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0003] Vessel localisation is an important step in various vascular access procedures, for example cannulation. Traditionally, vessels are located by a clinician or nurse by visually inspecting the patient’s anatomy and / or by palpating a patient’s skin. However, vascular access can prove difficult in certain patient populations, especially when using traditional techniques for vessel localisation. As such, ultrasound is often used to visualise and locate suitable vessels for vascular access in difficult patient populations.

[0004] Ultrasound may assist the clinician in not only locating a vessel but also evaluating its suitability for vascular access. Clinicians may select a suitable vessel based on vessel characteristics such as vessel depth, vessel diameter and the vessel pathway. Generally, vessels that are relatively large, straight and close to the skin surface are preferred for vascular access. Improper vessel selection may lead to complications such as extravasation, infiltration, occlusion and vascular access device dislodgement. Additionally, measurements of vessel characteristics can aid in appropriate vascular access device selection, particularly relating to catheter gauge and length, both associated with dwell time and vessel health preservation.

[0005] T raditional ultrasound systems rely on the clinician’s judgement to ascertain vessel depth and diameter using scale bars and / or user-controlled measurement tools. Hence, vessel depth and diameter measurements using traditional ultrasound systems can be imprecise and variable between clinicians. Moreover, measuring vessel depth and diameter using the prior mentioned techniques may slow down the vascular accessprocedure and delay the delivery of therapeutic care to the patient, especially for clinicians that are untrained or inexperienced with ultrasound-guided procedures.

[0006] Additionally, visualisation of the vessel pathway is often difficult or not possible using traditional ultrasound systems. Typically, vessels are visualised in either the transverse or longitudinal plane, limiting the clinician’s ability to see lateral positional changes of the vessel pathway. Hence, clinicians are unable to assess the vessel pathway and its tortuosity to determine suitability of the vessel for vascular access.

[0007] The present invention has been developed against the above background.SUMMARY OF INVENTION

[0008] In one aspect, the present invention provides a handheld imaging device for medical use comprising: a housing; a sensor base connected to the housing, the sensor base comprising a first transducer array for imaging a sub-dermal structure in a first plane and a second acoustic transducer array for imaging the sub-dermal structure in a second plane; and a processor, operable under control of electronic program instructions, for activating transducer elements of said first transducer array and said second acoustic transducer array to transmit signals and receive signals reflected by the sub-dermal structure for processing to display an image of the sub-dermal structure, wherein the processor calculates characteristics of the sub-dermal structure from the first and second imaged planes.

[0009] At least one transducer array, which may be the first transducer array or in some embodiments the second transducer array as well, advantageously comprises a plurality of parallel acoustic transducer arrays, each array comprising a plurality of acoustic transducer elements, the parallel transducer arrays being angled at an angle of insonation for continuously transmitting acoustic energy towards, and receiving acoustic energy reflected from, the sub-dermal structure in continuous wave Doppler ultrasound mode to enable imaging of the sub-dermal structure, conveniently in coronal plane.

[0010] The second transducer array may comprise a single acoustic element configured for continuously transmitting acoustic energy along a beam line towards the sub-dermal structure, wherein the single acoustic element is disposed oblique to the sub-dermal structure being disposed at an angle of insonation. The angle of insonation (9), desirably in the range 45 to 80°, allows capture of a Doppler shifted signal representative of flow in the sub-dermal structure, where vasculature. In either of these embodiments, the processor comprises a continuous wave doppler (CWD) module for extracting a desired characteristic, advantageously depth information, for the sub-dermal structure such as a vein or artery. Such depth information is helpful to a health care professional in conducting a cannulation or venepuncture procedure. The handheld imaging device is capable of acting as a clinical decision support tool which may provide suggestions for cannula or vascular access device selection as well as insertion angle.

[0011] The single acoustic element of the second transducer array may be operated in both A-mode and continuous wave (CW) mode. In such embodiments, the processor may include both A-mode and CW processing pathways, conveniently integrated in the same AFE, in particular for ultrasound.

[0012] The at least one transducer array as described above may be used for imaging in either the first or second imaged planes, conveniently coronal plane as first image plane and transverse or sagittal plane as second image plane respectively.

[0013] Characteristics of the sub-dermal structure, in particular depth, may be extracted from processing of acoustic receive signals by the CWD module of the processor. The CWD module may detect a maximum depth of the sub-dermal structure at a determined minimum signal to noise ratio at which the processor has capacity to discriminate the Doppler shifted signal from background noise. The CWD module may iteratively activate acoustic elements, desirably in a predefined scanning order, to provide acoustic energy to penetrate to differing tissue depths, for example through variation of transmission voltage or frequency. The echo or receive signal may then be processed by the processor to calculate depth of the sub-dermal structure. Where the sub-dermal structure is vasculature, depth determination may be dependent on detection of flow. For cannulation and venepuncture applications, the CWD module and processor may be configured to achieve a maximum penetration depth of 15mm, preferably 30mm and most preferably 50mm. A beam line to the maximum penetration depth may conveniently be divided intoa plurality of segments, for example of length 1 mm to 5mm, to allow calculation of depth at a suitable resolution to properly assist the cannulation or venepuncture procedure.

[0014] Preferably, transducer elements of the second acoustic transducer array are interleaved with acoustic transducer elements of the first transducer array. This allows acquisition of multiple transverse views and a plurality of extractions of the characteristic of the sub-dermal structure along a path of the sub-dermal structure. This assists visualisation of vasculature.

[0015] The second acoustic transducer array of the handheld imaging device may be operated in A-mode, comprising at least one acoustic element disposed perpendicular to tissue for transmitting acoustic energy towards the sub-dermal structure and receiving an echo signal representative of backscattered acoustic energy from the sub-dermal structure. Single or plural A-mode activated acoustic element(s) may be used in the second acoustic transducer arrays. Embodiments, including that described above with the obliquely disposed single acoustic element, providing A-mode configuration may convert the echo signals to A-mode signals or data from which a second plane imaging module of the processor can, by an A-mode processing pathway, detect the position of the sub-dermal structure and calculate at least one of the depth and dimension, including diameter, of the sub-dermal structure using A-mode data. The second acoustic transducer array may be a phased array for focussing acoustic energy to a selected focus depth, optionally < 5mm, more preferably > 15mm and most preferably 5-15mm. The A- mode data can then be used to reconstruct a coronal image of the sub-dermal structure. If required, the first transducer array may be operated in continuous wave Doppler (CWD) mode to enable imaging of the sub-dermal structure, conveniently in the coronal plane.

[0016] Imaging of the sub-dermal structure may be conducted by operating a handheld imaging device on the basis of A-mode data alone and as described above (paragraph

[0015] ), using a sensor base comprising a transducer array comprising a plurality of transducers operated solely in A-mode. CWD or other imaging modalities, useful in identifying vasculature as described elsewhere in the description, are not necessary in such embodiments.

[0017] The A-mode processing pathway may be configured to track movement of peaks in the A-mode data during compression to detect convergence of peaks indicative of the presence of a sub-dermal structure. The A-mode processing pathway may be configured to track cyclical movement of peaks between A-mode transmit signals. Such cyclicalmovement may be indicative of the presence of an artery, particularly where Doppler shift is captured by transducer elements, including the A-mode transducer element, operated in continuous wave mode.

[0018] Although the handheld imaging device is preferably an ultrasound device, the first transducer array may allow a different form of imaging, for example infrared (IR) imaging in which case the transducers are conveniently near IR (NIR) LEDs. In one embodiment, where the sub-dermal structure is a blood vessel, the second transducer array may comprise at least one near infrared (NIR) emitter and the first transducer array is operated in continuous wave Doppler mode. If (a) the blood vessel is detected by both said at least one NIR emitter and the first transducer array, depth of the blood vessel is determined according to said at least one NIR emitter wavelength. If (b) the blood vessel is detected only by the first transducer array, depth of the blood vessel is determined to be below the penetration depth of the at least one NIR emitter. If (c), no blood vessel is detected either by the at least one NIR emitter or the first transducer array, the processor detects no blood vessel below the at least one NIR emitter or the first transducer array.

[0019] Where the at least one transducer array is the second acoustic array, a subset of the acoustic elements of the second acoustic array may be disposed oblique to the sub- dermal structure in a transverse plane such that the beam path of each acoustic element of the subset of acoustic elements intersects the beam line of a perpendicular acoustic element. The location of intersection of beam path and beam line may then be used to calculate depth of the sub-dermal structure through an iterative approach.

[0020] The imaging device conveniently comprises an integral display screen configured to display an image of the sub-dermal structure and a characteristic of the sub-dermal structure. A colour gradient representative of the characteristic of the sub-dermal structure may be overlaid over the image of the sub-dermal structure to provide a convenient depiction to a health care professional. Variation in sub-dermal structure characteristics, such as a depth gradient, is conveniently reflected by a variation in colour. The display screen may provide coronal, transverse and sagittal views of the sub-dermal structure, preferably simultaneously. For example, a transverse view of the sub-dermal structure may be windowed over a coronal view of the sub-dermal structure.

[0021] In another aspect, the present invention provides a method for imaging a sub- dermal structure comprising:transmitting energy from a first transducer array towards the sub-dermal structure; transmitting energy from a second acoustic transducer array towards the sub- dermal structure; receiving energy reflected from the sub-dermal structure following transmitting energy from the second transducer array towards the sub-dermal structure; processing energy received from the sub-dermal structure for producing an image; imaging the sub-dermal structure in a first plane; imaging the sub-dermal structure in a second plane; and calculating characteristics of the sub-dermal structure from the first and second imaged planes.

[0022] Further embodiments comprise methods of use of the handheld imaging device as described above.

[0023] The handheld imaging device, and associated methods of use, through capability to provide high resolution depth data as well as of other vessel characteristics including pathway, facilitates clinical procedures in particular cannulation and venipuncture. The handheld imaging device primarily relies on continuous wave doppler ultrasound modality. However, other transducer elements or arrays may be included, where desired, to achieve a more beneficial visualisation with accurate vessel depth determination.BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further features of the portable ultrasound device of the present invention are more fully described in the following description of several non-limiting embodiments thereof. This description is included solely for the purposes of exemplifying the present invention. It should not be understood as a restriction on the broad summary, disclosure or description of the invention as set out above. The description will be made with reference to the accompanying drawings in which:

[0025] Figure 1A is a schematic perspective view of a handheld imaging device for visualising a vein according to a first embodiment of the present invention.

[0026] Figure 1 B is a schematic perspective view of a handheld imaging device for visualising a vein according to a second embodiment of the present invention.

[0027] Figure 2 is a schematic block diagram for the handheld imaging device shown in Figs. 1A and 1 B.

[0028] Figure 3A is a schematic front view of a sensor base for determining vein depth using A mode ultrasound imaging using the handheld imaging device shown in Figs. 1A- 2.

[0029] Figure 3B is a schematic side view of the sensor base of Fig. 3A.

[0030] Figure 4A is a schematic view of a sensor base for determining vein depth using continuous wave doppler (CWD) variable penetration depth imaging with a single transducer.

[0031] Figure 4B is a voltage vs depth graph relating to the CWD variable penetration depth imaging using the sensor base of Fig. 4A.

[0032] Figure 5A is a schematic front view of a sensor base for determining vein depth using continuous wave doppler imaging with an obliquely angled transducer array.

[0033] Figure 5B is a schematic side view of the sensor base of Fig. 5A.

[0034] Figure 6 is a workflow for visualisation of a vein using the handheld imaging device of embodiments of the disclosure.

[0035] Figure 7(a) is a schematic illustration showing two embodiments (1 ) and (2) for display of a vein on the screen of the handheld imaging device of embodiments of the disclosure.

[0036] Figures 7(b)-7(d) are schematic illustrations showing different embodiments of depth indications for display of a vein on the screen of the handheld imaging device of embodiments of the disclosure.

[0037] Figure 8 is a schematic block diagram of a handheld imaging device comprising A mode and continuous wave mode functionality using a shared transducer for visualising a vein according to a second embodiment of the present invention.

[0038] Figure 9 is a schematic block diagram of a handheld imaging device comprising A mode and continuous wave functionality using separate transducers for visualising a vein according to a third embodiment of the present invention.

[0039] Figures 10(a) and 10(b) provide schematic front views of a sensor base for determining vein depth using A mode ultrasound together with corresponding signal graphs illustrating the behaviour of blood vessels without applied compressive forces (Fig. 10(a)) and under compressive forces (Fig. 10(b)).

[0040] Figures 11 (a) and 11 (b) provide schematic front views of a sensor base for determining vein depth using bimodal energy as provided by ultrasound energy and near infrared (NIR) energy.DESCRIPTION OF PREFERRED EMBODIMENTS

[0041] In the following description, a “transducer array” may comprise one or more transducers or transducer elements. A transducer or transducer element may comprise a transmitter and / or receiver element. A receiver element, for example, in the case of an NIR transducer may also be referred to as a detector.

[0042] Referring to Figs. 1 A and 2, there is shown one embodiment of a handheld vessel imaging device in the form of an ultrasound device 100 capable of performing bi-plane imaging of sub-dermal structures, in particular vasculature or blood vessels, wherein a first imaging plane and / or a second imaging plane may be selected to calculate blood vessel characteristics from the plane. “Imaging”, as that term is used in this specification, includes visualisation of detected blood vessel(s) as well as providing a representation, graphical or otherwise, indicative of detected blood vessel(s). For example, a processed A-mode ultrasound signal would provide, as described below, a graphical representation - typically by corresponding peaks, of a detected blood vessel.

[0043] Ultrasound device 100 is provided with a screen to display sub-dermal or subcutaneous structures. In some embodiments, ultrasound device 100 can be used in the medical field for inspection of vascular vessels, such as arteries and veins. Such an inspection may be useful to healthcare professionals (HCP) inserting a cannula or other vascular access device (such as a needle for a venipuncture procedure) as known in the art of vascular access devices into a vascular vessel, in particular a vein as referred to in following description. In that regard, ultrasound device 100 aids the HCP in finding asuitable vein for venepuncture by providing information in two planes about the vein to assist in inserting a cannula.

[0044] Ultrasound device 100 comprises a housing having a sensor base 101 positioned at the base of the housing to allow contact with a patient, for example on the skin of the patient’s forearm. Sensor base 101 comprises an array of acoustic transducers 102 for the purpose of imaging a first plane. Sensor base 101 further comprises an array of acoustic transducers 103 for the purpose of imaging a second plane. In some embodiments, the two sets of acoustic transducers may differ in size, orientation, angle, frequency and other transducer characteristics as known in the art of transducer design to optimise imaging in the respective first or second plane. In preferred embodiments, the first plane of imaging relates to a coronal plane (‘bird’s eye view’) and the second plane of imaging relates to a transverse plane (cross-sectional view).

[0045] In the embodiment shown in Fig. 1A, the first image plane acoustic transducer array 102 comprises a plurality of parallel transducer arrays, each array comprising a plurality of transducer elements, conveniently in a linear array of 1 D transducer elements as known in the ultrasound art though other array geometries and transducer dimensions may be used in alternative embodiments. The plurality of parallel transducer arrays provides the ability to image vein 104 in multiple transverse planes to display the coronal view of the vein 104 on a display screen 106 (as shown in Fig. 7) of ultrasound device 100. For this purpose, each of the plurality of transducer elements may be selectively activated in a scanning pattern as described in the Applicant’s International Patent Application No. PCT / AU2025 / 051094, the contents of which are hereby incorporated herein by reference.

[0046] The parallel transducer arrays 102 are angled at an angle of insonation, 9, where 45<6<80° to ensure that a Doppler effect, where present due to blood flow, is captured enabling imaging of vein 104 on further processing of the received ultrasound signals. The parallel transducer arrays 102 are operated in a continuous wave doppler (CWD) modality and the methodology of transmitting receiving and reconstructing the ultrasound signals to a coronal view image is described in the Applicant’s co-pending International Patent Application No. PCT / AU2025 / 051094, filed 29 September 2025, the contents of which are hereby incorporated herein by reference.

[0047] The second image plane acoustic transducer array 103 is positioned in front of the coronal imaging acoustic transducer array 102 to provide a transverse view of thevascular structure or vessel as shown in Fig. 7. Transducer array may also, or alternatively, extract transverse characteristics such as the depth 105 of the vessel 104. In another embodiment, Fig 1 B, multiple second image plane acoustic transducer arrays103 are interleaved in parallel with the coronal imaging acoustic transducer arrays 102 to allow for multiple transverse views or characteristic extraction along the path of the vessel 104. Depth measurements, 105, from each transverse transducer along the path of the vein can then be compared to corroborate depth estimations, typically made empirically. Furthermore, the number of elements contained per acoustic transducer array 103 may vary between embodiments. Preferably, a minimum number of transducer elements would be 3 to facilitate receive and transmit side beam forming. In some embodiments, second image plane transducers may be centred along the midline of the first image plane transducers. Knowledge of depth 105 is beneficial to an HCP in determining if the vessel104 of interest is a suitable target for cannulation (or other vascular procedure such as venepuncture for blood collection) and the angle at which to insert the cannula or other vascular access device. In following description of preferred embodiments, vessel 104 is a vein. In a further embodiment, all transducer elements of the sensor base, which conveniently comprise a single transducer array, may be operated in A-mode to enable , with depth and dimension information, construction of an image of vessel 104, conveniently using techniques as described below. In this embodiment, each transducer element of Fig. 1 B would be oriented perpendicular to the sensor base 101 and the patient’s skin (tissue).

[0048] Fig. 2 shows a functional block diagram of portable ultrasound device 100. One or more components of portable ultrasound device 100 may be configured to extract characteristics, in particular depth, for vein 104 using the extraction methodology options described further below. Transducer array 201 of portable ultrasound device 100, as controlled by electronic module 203, allows imaging in the coronal plane and transducer array 202 of portable ultrasound device 100, as controlled by electronics module 204, allows imaging in the transverse plane. Each “module” may be embodied in software, hardware and / or firmware and may be located and / or operated within portable ultrasound device 100.

[0049] Operation of transducer array 201 and reconstruction of the first image plane of underlying vein 104 is described in detail in International Patent Application No. PCT / AU2025 / 051094 incorporated by reference.

[0050] In summary, the first image plane pathway includes a plurality of parallel transducer arrays 201 that are configured to operate in CWD mode. Electronic module 203 comprises acoustic transmitters, continuous wave (CW) mixer(s), analog-to-digital converters (ADC) and a processor 205 programmed with electronic instructions to process the CWD signals. First, the acoustic transmitters activate the first image plane transducer elements in a predefined scan order, as determined by processor 205, to continuously transmit and receive Doppler shifted acoustic signals. Second, the received Doppler shifted acoustic signals are processed by a CW mixer to isolate the Doppler shifted component of the received signals. This signal is then sampled by the processor 205, through the ADC, where it is further processed to a coronal view of the underlying vein 104 (or in other embodiments, another vessel). The coronal view is then displayed to the HCP through the display 106 in a readily interpretable image, preferably an easily interpretable image of the pathway of the underlying vein 104 within the field-of-view of the first image plane parallel transducer arrays 201. In this regard, the portable ultrasound device 100 is intended for use by HCPs without specialised training in ultrasonic imaging techniques.

[0051] In other embodiments, the portable ultrasound device 100 may include alternative transducer elements to ultrasound transducers for coronal plane imaging. For example, the first image plane transducer elements 201 may comprise infrared (IR) LEDs and first plane imaging electronic module 203 may comprise the electronics required to process the received IR data to a coronal view of vein 104 for display 106. In another embodiment, the first image plane transducers 201 may be acoustic transducers operating in modalities besides CWD such as B-mode or pulse wave Doppler. In yet another embodiment, the first plane image transducer elements 201 may be surface mounted electrode(s) configured to transmit a current and measure the returning impedance to reconstruct an image of vein 104 using electrical impedance tomography.

[0052] The second image plane pathway comprises an acoustic transducer array 202, the transducer elements of which are configured to transmit and receive acoustic energy towards vein 104 (or, in other embodiments, another target vessel) in one or more transverse planes. The corresponding second image plane electronic module 204 comprises the electronics and electronic instructions and other software required to reconstruct the acoustic signals to a transverse view of vein 104. It is to be understood that the second image plane acoustic transducer array 202 and its associated electronic module 204 (comprised in the second image plane pathway) may not be mutuallyexclusive with the first image plane pathway and that similar electronics may be used for either pathway.

[0053] Below are described a number of options for reconstructing the second image plane of vein 104 as follows: (i) A-mode based reconstruction alone; (ii) CWD based reconstruction alone; and (iii) a combination of A-mode and CWD doppler based reconstruction.(i) A-mode Reconstruction

[0054] Referring to Figs. 3A and 3B, there is described one embodiment of the second image plane pathway, with the purpose of detecting the position and depth of vein 104 within the underlying tissue. The transducer array for imaging the second image plane comprises, in one embodiment, a single acoustic element 202 configured to transmit transient acoustic energy 301 towards vein 104. Unlike the acoustic elements of the first plane transducers 201 that are configured to transmit continuous acoustic energy 306 at an angle of insonation 9, to capture Doppler effect or shift representative of blood flow, the acoustic element 202 is oriented perpendicular to the tissue. Backscattered energy reflected from the tissue and vein 104 is then received by the same acoustic element 202. In an alternative embodiment, the transducer array for imaging the second image plane may comprise a plurality of acoustic elements oriented perpendicular to the tissue, all operated in A-mode as described below.

[0055] In a still further embodiment, the second image plane transducer array may comprise a plurality of acoustic transducer elements, allowing utilisation of a phase-array to focus the acoustic energy wave. Advantageously, this can be configured to have a selected focus depth to allow maximum signal for different applications. For example, the acoustic energy beam may be controlled by processor 205 to have a focus depth preferably in the range of 5-15mm. Focus depth may be < 5mm for venipuncture or >15 mm for midline PIVC insertion.

[0056] The receive signal is then processed by the second plane imaging module 204 and converted to A-mode data. The second plane imaging module 204 contains a depth dependent gain function that is applied to the return signal to account for the attenuation of the transmit and receive signal as it propagates through the tissue. Such gain function may be implemented in the analog domain through the use of the time gain compensation pathways of ultrasound common analog front end (AFE). Advantageously, an availableultrasound AFE also contains a CW mixing pathway so that both first and second imaging plane pathways can use the same AFE reducing the size of portable ultrasound device 100. Referring now to Fig. 8, one such embodiment shares a common transducer 801 , transmitter 802 and AFE 809 enabling combined A-mode and CW operation. Transducer 801 is desirably oriented at an oblique angle to a base of ultrasound imaging device 100. In typical operation, transducer 801 would be operated in CW mode until a vein is detected before briefly manually or automatically switching to A-mode to drive a single transducer element (or set of transducer elements) located superior to the identified vein. Transmitter 802 would be responsible for enabling and disabling switches 806 and 807 to connect either the A-mode pulser 804 or CW-mode pulser 805 to the common transducer 801 . Once depth information has been ascertained, the ultrasound imaging device 100 would resume operation in CW-mode until prompted to the contrary. Depending on the efficacy of A-mode depth visualisation, A-mode and CW-mode may require equivalent voltages, significantly simplifying channel isolation methods and device powering requirements. More typically, A-mode operation of ultrasound imaging device 100 would require higher driving voltages and a high voltage transmitter 804 and T / R switch 803 to isolate signal processing channels during pulse transmission. A single AFE 809 could, in embodiments, contain processing pathways for both CW and A-mode output data, allowing each transducer element to share the same signal processing device. Transmitter 802 and AFE 809 channels would then be connected and co-ordinated by multiplexer 808.

[0057] The transmitter 802 may contain switches to individually output either higher voltage A-mode pulses or lower-voltage CW pulses, depending on the selected operating mode for ultrasound device 100. The output channel signal processing channel is protected from A-mode transmit voltages via a T / R switch 803. A multiplexer 808 connects the transmit and AFE components, selecting between A-mode and CW output channels. The AFE includes a low noise amplifier (LNA) 810 common to both output channels, before branching off into a voltage-controlled amplifier (VCA) 811 and ADC 812 for the A-mode and a CW mixer 813 for the CW mode. ADC 812 desirably offers a sufficiently high sampling rate to capture all high frequency behaviour of the A-mode echoes. This high sampling rate typically facilitates post-processing stage 814 which may involve processing techniques such as matched filtering, envelope detection, and peak detection, etc.

[0058] Referring now to Fig. 9, an alternative embodiment provides separate respective transducers 902, 903 for CW and A-mode operation. Functionally, the system would remain identical, beyond the transmit components, to the system shown in Fig. 8. To avoid simultaneous excitation of both transducers 902, 903, a separate transmit channel is necessary for each. Isolating the high voltage A-mode channel from the CW channel would have the added benefit of reducing switching complexity in the transmitter. The T / R switch 804 would desirably remain inside the A-mode transducer to block high voltage driving pulses from saturating the sensitive CW post-processing channel.

[0059] The expression of the gain is given by Eqn. 1 : gain = depth (1 )

[0060] In order to convert the receive signals to A-mode depth data, the processor 205 of portable ultrasound device 100 is further configured to calculate the time of propagation of the return signal. The equation to calculate depth is given by Eqn. 2:D = Ct / 2 (2) where:D = depth, c = speed of propagation in tissue, and t = time of propagationThe factor of 2 in the equation accounts for the transmit and receive path of the acoustic energy.

[0061] Frequency of the A-mode pulse waveform may also be varied to better suit transducer characteristics and desired depth profiles. Driving transducer 902 with its resonant frequency will maximise acoustic output for a given drive voltage. However, applying a non-resonant frequency pulse may reduce ring-down artefacts in the transducer 902. Ring-down is undesirable as it may conceal surface structures by obscuring echoes from those depths. Higher frequency pulses are more easily attenuated in tissue, reducing the maximum discernible depth. However, for a given pulse duration, higher frequency enables more cycles per pulse which increases energy per pulse and, consequently, signal strength too. Conversely, by using a shorter pulseduration, longitudinal resolution for vascular structure visualisation is improved. Pulse frequency and cycle quantity per pulse are therefore carefully controlled to optimise imaging of veins at estimated depths. Such depths may be estimated empirically given knowledge of typical depths and depth ranges of veins for cannulation or other vascular procedure.

[0062] In some embodiments, transmit beamforming is implemented by the A-mode transducer array. The transducer element positioned immediately superficial to the CW identified vein site may be denoted as the primary transducer element. A combination of transducer elements adjacent to the primary transducer element may be excited with an appropriate delay to maximise pulse signal convergence at a target vein depth. Delays are chosen to ensure phase alignment for constructive interference at the target vein depth. Return signals from the target vein depth then feature enhanced signal to noise ratios, facilitating vein detection.

[0063] Alternative embodiments may employ apodisation, a process of applying adjusted weightings to reduce the voltage amplitude sent to outer transducer elements, i.e. those transducer elements further away, in some embodiments in a linear array, from the primary transducer element. The weighting process may rely on mathematical functions, including window functions such as Hamming or Gaussian windows, to reduce sidelobe amplitude. Sidelobes are undesirable as they may produce weak echoes which can interact with off-axis reflectors, interfering with the interpretation of on-axis objects, in some embodiments a vein for potential cannulation.

[0064] Receive beamforming may also be implemented by the A-mode transducer array. Signals received at each of the transducer elements could be processed by introducing delays corresponding to the anticipated propagation time between the target vein and each receiver transducer element. Again, by designating the transducer element immediately superficial to the vein path as the primary transducer element, echo signals from adjacent transducer elements could be combined using appropriate techniques as known in the medical ultrasound art to enhance constructive interference at the target vein depth. In one such embodiment, a non-adaptive technique - such as a delay-and- sum (DAS) technique - may be implemented, wherein delayed signals are summed to generate a focussed beam output. Weightings may, if desired, be applied to the delayed signals before summing. In alternative embodiments, adaptive beamforming techniques - such as minimum variance beamforming - may be employed. In such embodiments,adaptively updated weightings may be applied to each transducer element to minimise total output power whilst preserving the desired signal, thereby suppressing off-axis noise and improving resolution of the target vein.

[0065] Referring back to Fig. 3A, a simplified A-mode plot is shown of an imaged vein 104 where peaks can be seen for the anterior 304 and posterior 303 walls of vein 104. Also present are regions of low amplitude plateaus which represent tissue above the vessel wall 305 and the lumen 302 of the vein 104. This is attributable to the lack of boundaries in tissue above vein 104 and the low backscattering of energy associated with the blood cells flowing in the lumen 302.

[0066] To extract the depth 105 of the underlying vein 104, the processor 205 is further configured to analyse the backscatter A-mode data to detect the depth of the anterior wall 304. According to one embodiment, an algorithm peak detection is used to detect peaks in the A-mode data, preferably up to 15mm deep, more preferably 30mm deep and most preferably 50mm deep. The detection of peaks within signals may be accomplished by any number of techniques well known in the signal analysis art and accordingly need not be further described here.

[0067] In the case of multiple peaks, selection of the anterior and posterior walls 303, 304 may be done with filtering of paired peaks to common vessel of interest diameters. For example, in the case of common cannulation veins, diameters between 2mm and 6mm would be of interest.

[0068] First, peaks are filtered using a threshold representing the minimum amplitude of a venous wall in A-mode data. Next, each peak pair is then further filtered to remove peak pair diameters that fall outside of the predefined range (2-6mm diameter). The strongest amplitude peak pair may then be assumed to be the underlying vein anterior and posterior walls 303, 304 and the depth of the vein 104 is taken as the depth of the anterior wall 304.

[0069] In reality, the surrounding tissue may be more heterogeneous containing muscle, fat and other common superficial tissue, resulting in more backscattering of the transmit signal. This may lead to a noisy A-mode region representing the surrounding tissue 305 causing false vessel wall detection in the previously described depth extraction process. To account for such additional noise, the diameter of vessel 302 may be used as an input to the depth extraction algorithm. The diameter (0) 302 of the vessel 104 can becalculated by processor 205 from the first image plane of the vessel and applied to the transverse view of vessel 104 assuming, on one convenient basis, that the underlying vessel is circular. The known diameter 302 can then be used to provide a more accurate and narrow peak pair diameter filtering.

[0070] Where A-mode echo waveforms are less easily discernible, typically due to noisy reflection (such as ring-down artefacts) in the heterogeneous medium, additional postprocessing techniques may be used as known in the medical ultrasound art to assist vein detection. Firstly, a simple bandpass filter may be applied to remove out-of-band (pulse frequency) noise. Secondly, returning echoes are typically expected to match the carrier frequency of the transmitted ultrasound pulse, only delayed and scaled. A matched filter may be applied to convolve the echo signal with a time-inverted, conjugated copy of the pulse waveform. Applying such a filter enables signal processing to differentiate between erroneous noisy peaks and genuine pulse reflections representative of the target vein.

[0071] A simple pulse of ultrasound energy constant in frequency and length may still somewhat resemble noise. Efficacy of the matched filter can therefore be enhanced by increasing the uniqueness of the A-mode transmit pulse, i.e. employing uniquely coded pulses. In one such embodiment, aiming at enhanced resolution, the transmitter may produce a CHIRP signal, a pulse featuring a sweep of frequencies, centred around the resonant frequency of the transducer element. Provided that effective matching can be performed in post-processing, the pulse length may be substantially extended to increase the energy content and subsequently the signal strength, and signal-to-noise ratio, of the return echoes. Loss of axial resolution is avoided through use of a matched filter which produces a narrow auto-correlation main lobe peak only where the echo waveform matches the filter. A CHIRP pulse would still typically present with small non-zero sidelobes, ‘ghost’ echoes which may trigger false positives, confusing peak detection software. A convolution method as known in the medical ultrasound art may be used to remove such sidelobes. In one embodiment, a Golay code pulse, comprising two complementary pulses whose auto-correlation sidelobes theoretically cancel, may be employed. As this requires two transmit and receive events per line, the potential acquisition time is halved, however, this is typically less of a concern with an A-mode system. An alternative convenient embodiment may employ a Barker pulse, a unique binary sequence (maximum 13-bits) with aperiodic autocorrelation minimised with respect to the primary main lobe.

[0072] Following application of the matched filter, relevant information for target vein visualisation is predominantly contained in the amplitude rather than phase of the resulting waveform. Accordingly, in some embodiments, a Hilbert transform of the receive ultrasound signal from the transducer elements may be applied during signal processing. An envelope detector may then be applied after the matched filter. This smooths the complex-valued oscillating waveform output of the matched filter to yield a positive, slowly varying and interpretable receive or echo signal. In alternative embodiments, simplified envelope extraction techniques such as low-pass filtering configured to suppress carrier frequency components may be applied. Preferred embodiments retain baseband amplitude modulation, thereby facilitating detection of echo peaks as a function of depth.

[0073] Time-gain compensation techniques may also be applied with the voltage- controlled amplifier 811 to preferentially boost weaker A-mode echoes from deeper structures which may or may not be vascular structures. This allows for a steady amplitude input to following signal processing steps.

[0074] In another embodiment, the second plane image module 204 exploits the highly compliant nature of veins in order to discriminate vessel wall peaks (typically two peaks) from a noisy ultrasound signal comprising a plurality of peaks. Fig. 10 illustrates an A- mode signal graph for compliant vessels under compression forces. As previously described, additional peaks 1002a and noise 1003a may be introduced into the return amplitude signal due to tissue layers 1002 and heterogeneous structures above the underlying vessel 1001. Interfaces with large acoustic impedance difference, such as a change in tissue 1002, may cause large reflection echoes 1002a that can be mistaken as the superior 1001 a and inferior 1001 b vessel wall.

[0075] Under a compressive force 1004, the low pressure, highly compliant veins are first to occlude compared to other structures. This is reflected in the receive echoes where the superior 1001 a and inferior 1001 b echoes are closer due to the decreased vertical diameter of the vein under compression. Conveniently, the second image module 204 of the processor is programmed with electronic instructions to track the movement of peaks to determine the corresponding vein paired peaks. First, the second image plane transducer 202 is aligned to vein 1001 and starts collecting A-mode signals. Whilst the ultrasound imaging device 100 continuously collects A-mode signals at a desired and efficient rate, an external force 1004 may be applied through the ultrasound imaging device 100 and second image plane transducer 202. This force may be applied by theuser of the device 100 after a prompt from the device 100. As shown, over consecutive A-mode signals, the peaks corresponding to vessel walls 1001 a, 1001 b approach each other in contrast to other provisionally paired peaks, the vein representative peaks eventually collapsing to a single echo signal. Once this is detected by the second image module 204 of the processor, the vein depth can be extracted using the peak representative of the superior wall 1001 a.

[0076] Such a compression method may also be used to identify if the underlying vessel is an artery. Due to their low compliance and high pressure, arteries resist complete occlusion under external compression. Instead, arteries maintain pulsatile flow with arterial walls exhibiting reciprocal motion where they alternately expand and contract in opposite directions with each pulse cycle. The second image plane module 204 is conveniently programmed with electronic instructions to enable tracking of movement of peaks when sufficient compression has been applied to detect peaks that demonstrate cyclical, negatively correlated movement across consecutive A-mode signals to differentiate between veins and arteries.(ii) CWD Based Reconstruction

[0077] Referring now to Fig. 4A, there is described depth extraction by use of the second image plane pathway as described above. Such depth extraction has the purpose of detecting the depth of vessel 104 within the underlying tissue. The acoustic array 202 for the second image plane conveniently comprises a single acoustic element, configured to transmit continuous acoustic ultrasonic energy 401 towards the vein 104. Similar to the acoustic arrays for the first image plane, these ultrasound transducers are oblique to the underlying vessel 104, creating an angle of insonation 9 for capturing the Doppler effect or shift representative of blood flow. It is to be understood that an array of acoustic transducer elements may also be utilised to allow depth extraction along an axis and take advantage of beamforming of the acoustic ultrasonic energy wave.

[0078] The acoustic array 202 transmits a continuous wave along a beam line at programmable penetration depths under control of second plane imaging (CWD) module 204. ‘Penetration depth’ is defined as the depth when a high signal-to-noise ratio can be maintained. In a CWD modality, it is the maximum depth for when a Doppler shifted signal from vein 104 can be discerned from background noise. The maximum penetration depth along the beam line (represented by dk 403) equates to the maximum depth that can be extracted with this embodiment, preferably up to 15mm depth, more preferably30mm deep and most preferably 50mm deep. To determine the depth of the underlying vein 104, the beam line is divided into a number (k) of segments shown as d-i-dk 02 which correspond to different penetration depths of the continuously transmitted acoustic energy 401. Segments are preferably between 1 mm and 5mm long, where a larger segment reduces the required components in the second imaging plane electronic module 204.

[0079] The processor 205 is configured to drive a preset scan pattern of the transducer elements of linear acoustic transducer array 202 and analyse the Doppler echo signal received from each segment d-i-dk to determine the presence of blood flow within the segment. Processor 205 may activate acoustic array 202 in a number of routines to scan across the depth segments d-i-dk. In one routine, processor 205 activates the acoustic array 202 to achieve a penetration of dk with receive signals being analysed for the presence of blood flow using similar methodology to the first image plane pathway as described above. Scan patterns may be conducted in a number of ways as described in the Applicant’s International Patent Application No. PCT / AU2025 / 051094, the contents of which are incorporated herein by reference.

[0080] If blood flow is detected in the beam path of dk, then acoustic energy transmission to penetration depth of dk-i is activated with receive signals being analysed for the presence of blood flow. This loop is repeated until no blood flow is detected for penetration depth dn, where the extracted depth is given as a range between dnand dn+i. In the case where di returns with a presence of flow, the extracted depth is given as a range between dskin and di.

[0081] It is to be understood that the processor may cause the algorithm to start from any depth segment as long as all segments are completed. Advantageously, use of larger segments requires less iterations of the loop, resulting in a faster extraction of vessel depth. This would result in a lower depth resolution; however, this may be practical for some applications. For example, a dual segment approach is suitable when inserting a cannula, where an HCP may only require binary knowledge, i.e. is the vein SHALLOW or DEEP, to inform them on insertion angle. This may be beneficial to the HCP as it supports a clinical decision as to suitable cannula length and insertion angle. For the cases of a shallow vein, the HCP may decide to utilise a smaller length cannula and insert at an angle between 10-30°, whereas in a deep vein, the HCP may decide to utilise a smaller length cannula and insert at an angle between 30-45°. Processor 205 may beprogrammed to provide a recommended cannula length and insertion angle for display screen 106.

[0082] The penetration depth into tissue of an acoustic wave is affected by several factors. To achieve a variable penetration depth, the second plane imaging module 204 allows control over at least one of these factors. Fig. 4B shows the effect of variation on penetration depth of the transmission or transmit voltage, by second plane imaging module 204, for the acoustic array 202. The maximum penetration depth of the nthscan 402 is mapped to a corresponding voltage 404. The direct proportionality between transmission voltage and acoustic wave penetration depth is evident. The processor 205 stores and utilises the relationship, as graphically depicted in Fig. 4B, to determine the transmission voltage required for scan n to achieve a required penetration depth n into tissue.

[0083] Similar relationships may be derived between penetration depth and other selected factors, for example transmission or transmit frequency may be varied to achieve the required penetration depth. An increase in transmission frequency causes more energy loss from tissue absorption, giving rise to an inverse relationship where an increase of frequency reduces the penetration depth. In one such embodiment, second plane imaging module 204 may include a variable frequency continuous wave transmitter that activates a broadband acoustic transducer. The processor 205 stores and utilises the relationship to determine the transmission frequency for scan n to achieve desired penetration depth n.

[0084] Referring to Figs. 5A and 5B, a continuous wave doppler modality may also be implemented for the second image plane pathway with the purpose of detecting the depth of a vessel (typically a vein) 104 within the underlying tissue of a patient. Here, the acoustic array 202 for the second imaging plane comprises an array of acoustic transducer elements, configured to continuously transmit acoustic energy 501 toward vessel 104. Similarly to the above-described acoustic array 102 for the first imaging plane, the acoustic elements of acoustic array 202 are oblique to the underlying vessel 104 in the sagittal plane, creating an angle of insonation 9 for capturing the Doppler effect or shift representative of blood flow. As with acoustic array 102, the angle of insonation (6) is desirably in the range 45<6<80°. Additionally, in this embodiment, a subset 502 of the acoustic elements are also oblique in the transverse plane such that the beam path of the acoustic elements 502 intersects the beam path of a perpendicular acousticelement 505. Such an acoustic array 202 for the second imaging plane may have transducer elements with differing thickness of acoustic lens on the face for controlling penetration depth.

[0085] The perpendicular acoustic element 505 continuously transmits acoustic energy along a beam line to a maximum penetration depth. In the same way as above described, the maximum penetration depth of the perpendicular acoustic element 505 equates to a selected maximum depth, preferably up to 15mm deep, more preferably 30mm deep and most preferably 50mm deep. In this embodiment, maximum depth is reflective of the configuration of the ultrasound components within ultrasound device 100 and its application to assisting cannulation or venipuncture procedures by an HCP with limited or no specialised training in ultrasound.

[0086] To determine the depth of the underlying vessel, vein 104, the perpendicular beam line is split into k depth segments, where the kthsegment 504 is the maximum depth extraction. Each segment represents an intersection with another acoustic element beam path. The segment length determines the depth resolution and is here determined by a combination of beam width, beam width divergence angle, transverse plane acoustic element angle and number of elements. The actual parameters and number of elements are here selected with reference to the cannulation or venipuncture application. A different combination of any of the same or additional parameters affecting depth resolution could be selected in other embodiments. Segment length is preferably chosen to be between 1 mm and 5mm, where a grouping of acoustic elements may be utilised to achieve larger segment length.

[0087] To ensure that an adequate Doppler echo signal is received from deeper segments, the second imaging plane module 204 may adopt techniques, for example as above described, to increase acoustic energy penetration depth. Additionally, larger gain may be applied to deeper intersecting beam paths to ensure echo levels are similar across the oblique acoustic elements 502. For example, an increase in transmission power (which may be achieved by variation of transmission voltage as described above) may be applied to the oblique elements 502 dependent on their distance to the perpendicular acoustic element 505.

[0088] The processor 205 is configured to drive a preset scan pattern of the acoustic array 202 and analyse the Doppler echo signal received from each segment to determine the presence of blood flow within the segment. In one embodiment of a preset scan pattern,the perpendicular acoustic element 505 is first activated and analysed for the presence of blood flow, i.e. presence of a vascular structure in particular a target vein, using similar methods to the first image plane pathway as described above to capture the corresponding Doppler shift.

[0089] The deepest intersecting acoustic element Txk of acoustic element subset 502 is activated next and analysed for the presence of blood flow. If segment dk does not contain blood flow, then the next acoustic element Txk-i of acoustic element subset 502 is activated and its receive signal analysed. This loop is repeated until blood flow, i.e. presence of a vascular structure in particular a target vein, is detected for intersection depth dn, where the extracted depth is given as the boundary of the segment of intersection depth dn. For example, if beam n intersects between 3-4mm, then the extracted depth is given as 3-4mm.

[0090] In the case where di returns no presence of flow, the processor 205 extracted depth is given as the segment length of the non-intersecting depth do 503. The processor 205 may be further configured to analyse if an intersecting depth contains arterial or venous flow. Advantageously, this allows for discerning the depths of multiple blood vessels that may exist within the perpendicular beam path.

[0091] In a further embodiment, the CWD modality may, using the second image plane pathway, detect the depth of a blood vessel within the underlying tissue. The second image plane acoustic array 202 is not required for this embodiment where the processor 205 is further configured to extract depth from the CWD signals from the first image plane acoustic array 102. The processed echo CWD energy is dependent on various blood vessel characteristics such as depth, diameter and blood velocity but not necessarily limited to these.

[0092] Depth and diameter are inversely proportional to reflected acoustic energy, where a deeper and larger blood vessel results in a lower energy spectrum.

[0093] Velocity is proportional to the reflected acoustic energy, where a higher velocity results in a higher energy spectrum.

[0094] Given the above relationships, a depth characteristic equation and the equivalent characteristic curve can be derived as Eqn. 3:D = f(E, 0, V) (3)where:D = depth,E = processed received echo CWD energy,0 = diameter; andV = velocity

[0095] Energy, diameter and velocity can be extracted from the first image plane pathway. These variables can then be inputted into characteristic Eqn. 3 to calculate a depth for the underlying blood vessel. It is to be understood that this methodology for extracting depth is not intended to be limiting. Other approaches or combination of the Eqn 3 approach with other techniques, to extract a more accurate depth measurement, could be adopted.Workflow

[0096] Referring to Fig. 6, one embodiment of a workflow is described for a handheld imaging device 100 with the object of locating and visualising a blood vessel in one, or more preferably two, planes. The workflow is described with reference to a second plane imaging module in one dimension, meaning that depth of the blood vessel is extracted at a point location in the x-axis. Advantageously, this configuration allows for a second plane imaging module that is smaller, requiring less electronic space, and requires less power to operate.

[0097] Initially, the health care professional (HCP) attempts to localise the underlying vessel using traditional techniques of visual inspection and palpation 601 . If the HCP fails to find a blood vessel using visual inspection and palpation 601 , the handheld imaging device 100 is then used to locate the blood vessel by using the first plane imaging module 602 to visualise the vessel pathway.

[0098] Once the blood vessel is located, either initially through traditional techniques 601 or with the first plane imaging module 602, the user may line up imaging device 100 with the second plane transducer 603. Preferably, to simplify the alignment, the one dimensional second plane imaging module is located at the anterior centre of the sensor base 101. This then requires the HCP to align the identified or target vein 104 to the centre of imaging device 100. Imaging device 100 can then, through processor 205,extract an accurate depth measurement 604 using any of the depth extraction techniques described above. The HCP can then, for example, cannulate the vein 104 using the visualised vessel pathway and extracted depth measurement as guidance. Imaging device 100 can thus act as a clinical decision support tool for the HCP.

[0099] Referring to Figs. 11 (a) and 11 (b), the illustrated ultrasound imaging device 100 includes one or more near-infrared (NIR) emitter and receiver (or detector) as the second image plane sensor 202. In some embodiments, the NIR emitters and detectors may be coupled to the base of the ultrasound imaging device 100 or on any other faces permitting transmission to the tissue. The NIR emitters are configured to emit electromagnetic waves 1103 in an optical window 650nm and 1000nm towards the target tissue. The NIR receivers are configured to detect the reflected electromagnetic waves from the target tissue, mainly underlying structures and vessels 1101. Infrared radiation is absorbed by haemoglobin in the blood vessels while the surrounding tissue other than blood vessels reflects it. The second image plane module 204 is configured to detect the difference in the NIR reflection levels between blood vessels and surrounding tissues.

[0100] The penetration depth of NIR energy 1103 is lower than acoustic energy 1102. Advantageously, the second image plane module 204 is further configured to process both the first image plane sensor (CW mode) and second image plane sensor (NIR) to detect the presence of an underlying vascular structure, e.g. a vein, in none, either or both of the first and second image plane sensors. When both sensors are aligned above a vein, reflected energy is sensed from both emitters. If the vessel is detected by both NIR and CW modes, then the depth of the vein is determined within the penetration depth of the NIR emitters (as in Fig. 11 (b)). If the vein is only detected by the CW mode (as in Fig. 11 (a)), then the depth of the vein is determined to be below the penetration depth of the NIR emitters. If no vein is detected by either NIR or CW modes, then it is determined that there is no vein below the first and second image plane sensors. Conveniently, the wavelength of the NIR emitter is set such that the penetration depth is 5mm. This embodiment provides a simple way in which to provide a bimodal depth of underlying veins (or other vasculature), i.e. depth <5mm or >5mm.

[0101] Referring to Fig. 7(a), depth extraction from any of the techniques described above is advantageously displayed on display screen 106 of imaging device 100. The depth 105 of the vessel of interest, vein 104, is extracted from the second image planeview and displayed to HCP(s) in an easy and comprehensible manner, whether the HCP is a general or specialised user.

[0102] In one embodiment, the blood vessel pathway 701 is overlaid with a gradient of colour 702 that is representative of blood vessel depth 105, where the brightness / darkness of colour is indicative of the magnitude of blood vessel depth 105. For example, shallower areas of the blood vessel path 701 may be brighter in colour, whereas deeper areas may be darker in colour.

[0103] To achieve multiple depth measurements along the blood vessel pathway 701 , multiple transverse (second plane) imaging transducers 103 may be interleaved with the coronal imaging (first plane) transducers 102 to allow for multiple characteristic (in particular depth) extractions along the blood vessel pathway 701. The depth 105 along the blood vessel pathway 701 can then be calculated as a linear interpolation between each depth point / extraction and mapped to a selected colour gradient. The selected colours for the colour gradient, other than being clear to the HCP, are not important.

[0104] Depth information is visually conveyed to the HCP via the colour gradient overlay and its corresponding demonstrative legend 702 that relates colour brightness to blood vessel depth with a depth gradient being reflected by a variation in colour. The colour legend 702 is windowed over the coronal view of the vessel pathway 701 so that it is visible to the HCP whilst presenting a minimal obstruction to viewing of the blood vessel pathway 701 . Fig. 7(a) is an example of a blood vessel that is deeper towards the top of display screen 106. The HCP may use this information to determine, for example, an appropriate cannula length and insertion angle for vascular access. In one example, the HCP may opt to use a smaller length cannula and an insertion angle between 10-30° for shallow vasculature. Conversely, the HCP may decide to use a longer length cannula and an insertion angle between 30-45° for deeper vasculature.

[0105] The processor 205 of imaging device 100 could be programmed with electronic instructions to provide suggestions as to cannula length, type and / or insertion angle. The processor 205 could also, or alternatively, be programmed with electronic instructions to prevent display - on display screen 106 - of certain vasculature dependent on the HCP using the imaging device 100. In this regard, imaging device 100 may be provided with an input means configured to identify a user whether using numeric or biometric information. In such embodiments, an inexperienced HCP may be prevented,by processor 205, from seeing deep blood vessels on display screen 106 because such blood vessels may be difficult for them to cannulate.

[0106] In another embodiment, blood vessel depth 105 may be displayed to the HCP using a simplified transverse view 703, akin to a traditional B-mode image. The simplified transverse view 703 is shown simultaneously with the coronal view of the blood vessel pathway 701 so that it is visible to the user whilst minimally obstructing the user’s view of the blood vessel pathway 701. Within the simplified transverse view 703, the blood vessel is represented, assuming a circular vessel, as a circle with a depth d below the skin surface. The blood vessel can be represented using both depth 105 and diameter 302 information of the blood vessel obtained using the above-described depth extraction methods.

[0107] A further embodiment to communicate depth information to the HCP is shown in Fig. 7(b). Vessel depth 705, corresponding to vessel portion 706 at the bottom of the screen may be displayed alongside depth indicator icon 707. The vessel depth measurement 705 may update upon movement of the ultrasound imaging device 100. The vessel depth measurement 705 is the indicated depth at one singular point (at the bottom of the screen). To allow further insight into depth behaviour throughout the pathway of the vessel, pathway depth indicators 704 may overlay the vessel pathway. The vessel pathway depth indicators 704 may, without excluding other indicator forms, take the form of flat horizontal lines or lines with troughs or peaks to indicate the vessel’s unchanged depth, becoming deeper or shallower respectively. This indication is in relation to the numerical depth measurement 705. In another embodiment, the vessel pathway depth indicators may be downwards or upwards arrows, which - in similar manner to the previously described embodiment - communicate to the HCP the change in depth behaviour along the vessel pathway by reference to numerical depth measurement 705.

[0108] Further embodiments for displaying vessel depth information are shown in Figs. 7(c) and 7(d). These displays convey information regarding the depth gradient along the vessel pathway and its gradient (severity) and nature. Fig. 7(c) displays a windowed panel across the top quarter of the screen. This panel depicts the depth profile view 708. This profile shows the depth profile line 710 corresponding to the vessel pathway 701 seen on the display screen 106. With the aid of the depth scale indications 709 on the side of the panel, the HCP can see the depth behaviour of the vessel, inparticular a target vein for cannulation. This would assist the HCP to locate a vessel section which does not change depth or, alternatively, provide the HCP with further information to aid in selecting angle of insertion and advancement of a cannula. Guidelines 711 may be seen in both the depth profile view 708 and standard blood vessel view. These are reference markers to provide consistent positional alignment so that the same relative location can be quickly identified across both views. This enables vein depth information as well as vein pathway information to be used in combination to support the HCP to perform cannulation safely and effectively.

[0109] Fig. 7(d) shows a display which communicates depth gradient information using contour lines. The display 106 shows the vessel pathway with a contour line overlay. In areas where the gradient is gentle (depth changing very gradually), the contour lines are far apart 712a. Alternatively, in areas of steep depth gradient (depth changing rapidly), the contour lines 712b are much more tightly packed as appreciated in the art of topology. This portrayal of depth information indicates the severity of the depth gradient (changing fast or slow) but does not indicate, in the case of changing depth, the behaviour of the change (vessel deeper or shallower).

[0110] In preferred embodiments, imaging device 100 includes features to make its use more comfortable for an HCP or other possible users. Imaging device 100 may be made ergonomic in shape in a manner avoiding the need for wrist flexing during use and resulting higher risk of strain injury. The Applicant’s International Patent Application No. PCT / AU2025 / 051046, filed 17 September 2025, and the contents of which are hereby incorporated herein by reference provide more detail on ergonomic design options for imaging device 100.

[0111] Those skilled in the art will appreciate that the imaging device of the present invention as described herein is susceptible to variations and modifications other than those specifically described. The invention includes all such variations and modifications. The invention also includes all of the steps, features, formulations and compounds referred to or indicated in the specification, individually or collectively and any and all combinations or any two or more of the steps or features.

[0112] The invention described herein may include one or more range of values (e.g. depth, voltage and spacing etc). A range of values will be understood to include all values within the range, including the values defining the range, and values adjacent tothe range which lead to the same or substantially the same outcome as the values immediately adjacent to that value which defines the boundary to the range.

[0113] Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness.

[0114] Throughout this specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

CLAIMS1 . A handheld imaging device for medical use comprising: a housing; a sensor base connected to said housing, said sensor base comprising a first acoustic transducer array for imaging a sub-dermal structure in a first plane and a second transducer array for imaging the sub-dermal structure in a second plane; and a processor, operable under control of electronic program instructions, for activating transducer elements of said first transducer array and said second acoustic transducer array to transmit signals and processing receive signals reflected by said sub-dermal structure for processing to display an image of the sub-dermal structure, wherein said processor calculates characteristics of said sub-dermal structure from said first and second imaged planes.

2. The handheld imaging device of claim 1 , wherein said first transducer array comprises a plurality of parallel acoustic transducer arrays, each array comprising a plurality of acoustic transducer elements, said parallel transducer arrays being angled at an angle of insonation for continuously transmitting acoustic energy towards, and receiving acoustic energy reflected from, said sub-dermal structure, wherein said transducer array captures a Doppler shifted signal representative of flow in said sub-dermal structure; and wherein said processor comprises a continuous wave doppler (CWD) module for extracting depth information for said sub-dermal structure.

3. The handheld imaging device of claim 1 , wherein said second transducer array is a single acoustic transducer element configured to continuously transmit acoustic energy along a beam line towards the sub-dermal structure, wherein said single acoustic transducer element is disposed oblique to the underlying vessel being disposed at an angle of insonation to capture the Doppler shifted signal representative of flow in said sub-dermal structure; and said processor comprises a Continuous Wave Doppler (CWD) module for extracting depth information for said sub-dermal structure.

4. The handheld imaging device of claim 3, wherein said single acoustic transducer element is operable in both A-mode and CW mode.

5. The handheld imaging device of any one of claims 2 to 4, wherein said angle of insonation is between 45 and 80°.

6. The handheld imaging device of any one of claims 2 to 5, wherein said CWD module detects a maximum depth of said sub-dermal structure at a determined minimum signal to noise ratio at which the processor has capacity to discriminate the Doppler shifted signal from background noise.

7. The handheld imaging device of any one of claims 2 to 6, wherein said acoustic transducer elements are activated by the processor in a predefined scanning order.

8. The handheld imaging device of any one of claims 2 to 7, wherein said beam line is divided into a plurality of segments of defined length, d-i-dk where k is an integer from 2 to n, corresponding to different penetration depths programmed in the processor and the processor is configured to:(a) activate an acoustic element to transmit acoustic energy along the beam line to segment dk;(b) analyse the acoustic signal received from segment dk to determine presence of flow within segment dk; and(c) where flow is detected in segment dk, activating the first acoustic element to transmit acoustic energy along the beam line dk-i and analysing the echo signal received from segment dk; and(d) repeating step (c) until no flow is detected for a penetration depth dnwhere extracted depth is given as a range between dnand dn+i9. The handheld imaging device of claim 8, wherein, in the case that analysing di detects presence of flow, the extracted depth is given as a range between dskin and di.

10. The handheld imaging device of claim 8 or 9, wherein said defined length of a segment is between 1 mm and 5mm.

11. The handheld imaging device of any one of the preceding claims, wherein transducer elements of the second acoustic transducer array are positioned in frontof transducer elements of the first acoustic transducer array to provide a transverse view of said sub-dermal structure.

12. The handheld imaging device of any one of the preceding claims, as dependent from claim 2, wherein transducer elements of the second acoustic transducer array are interleaved with transducer elements of the first array of acoustic transducers to provide multiple transverse views and a plurality of extractions of the characteristic of said sub-dermal structure along a path of said sub-dermal structure.

13. The handheld imaging device of any one of claims 1 to 10, wherein the second transducer array is operable in A-mode and comprises at least one acoustic transducer element disposed perpendicular to skin of a patient for transmitting acoustic energy towards said sub-dermal structure and receiving an echo signal representative of backscattered acoustic energy from said sub-dermal structure.

14. The handheld imaging device of claim 13, wherein said second transducer array comprises a plurality of transducer elements disposed perpendicular to skin of a patient.

15. The handheld imaging device of claim 13 or 14, wherein said first acoustic transducer array is a phased array for focussing acoustic energy to a selected focus depth.

16. The handheld imaging device of any one of claims 13 to 15, wherein said focus depth is 5mm-20mm.

17. The handheld imaging device of any one of claims 13 to 16, wherein said processor comprises a second plane imaging module for processing the echo signals to signals transmitted from the second acoustic transducer array; converting the echo signals to A-mode data; and analysing said A-mode data by an A-mode processing pathway to detect position of the sub-dermal structure and calculate at least one of the depth and dimension, including diameter, of said sub-dermal structure.

18. The handheld imaging device of claim 17, wherein said processor, using said A- mode data, enables construction of an image of the sub-dermal structure in a coronal plane.

19. The handheld imaging device of claim 17, wherein the second plane imaging module contains a depth dependent gain function that is applied to the echo signalsto account for the attenuation of the transmit and receive signals as said signals propagate through tissue.

20. The handheld imaging device of claim 19, wherein said depth dependent gain function is implemented in the analog domain through time gain compensation in an ultrasound analog front end (AFE).21 . The handheld imaging device of any one of claims 17 to 20, wherein the A-mode transducer array and processor pathway are configured for at least one of transmit beamforming and receive beamforming.

22. The handheld imaging device of claim 21 , wherein, in A-mode, a non-resonant frequency pulse is applied to the perpendicularly disposed acoustic transducer element.

23. The handheld imaging device of any one of claims 17 to 22, wherein the A-mode data contains peaks, said peaks being detectable at a determined depth being up to 15mm deep, preferably 30mm deep and most preferably 50mm deep.

24. The handheld imaging device of claim 23, wherein the A-mode processing pathway is configured to track movement of peaks during compression to detect convergence of peaks corresponding with a vein wall.

25. The handheld imaging device of claim 23 or 24, wherein the A-mode processing pathway is configured to track cyclical movement of peaks between A-mode transmit signals, said cyclical movement of peaks being indicative of an artery.

26. The handheld imaging device of any one of claims 22 to 25, wherein pairs of detected peaks are filtered to a selected diameter or selected diameter range for said sub-dermal structure.

27. The handheld imaging device of claim 26, wherein pairs of detected peaks are filtered using a threshold representing the minimum amplitude of a venous wall in A-mode data; and further filtered to remove peak pair diameters outside the selected diameter or diameter range.

28. The handheld imaging device of claim 27, wherein the strongest amplitude pair of detected peaks is determined to correspond with respective anterior and posterior walls of said sub-dermal structure, optionally with depth of said structure being defined as the depth of the anterior wall of said structure.

29. The handheld imaging device of any one of the preceding claims, as dependent from claim 2 or 3, wherein said CWD module calculates diameter of said sub- dermal structure, said sub-dermal structure diameter being used as a parameter in filtering the peak pair diameters30. The handheld imaging device of claim 4, wherein the CWD module and A-mode module use the same ultrasound AFE.31 . The handheld imaging device of claim 8, wherein a subset of the acoustic elements of the first transducer array are disposed oblique to the sub-dermal structure in a transverse plane such that the beam path of each acoustic element of the subset of acoustic elements intersects the beam line of a perpendicular acoustic element.

32. The handheld imaging device of claim 31 , wherein said acoustic elements are activated by the processor in a predefined scanning order.

33. The handheld imaging device of claim 31 or 32, wherein said beam line is divided into a plurality of segments of defined length, di-dk where k is an integer from 2 to n and is the maximum depth extraction, corresponding to different penetration depths programmed in the processor and the processor is configured to:(a) activate the perpendicular acoustic element to transmit acoustic energy along the beam line to segment dk;(b) analyse the acoustic signal received from segment dk to determine presence of flow within segment dk; and(c) where no flow is detected in segment dk, activating the deepest intersecting acoustic element Txk of the subset of acoustic elements and determining presence of flow;(d) activating a shallower intersecting acoustic element Txk-i of the subset of acoustic elements and determining presence of flow;(e) repeating step (d) until flow is detected for an intersection depth dnwhere extracted depth is given as a boundary of the segment of intersection depth dn.

34. The handheld imaging device of claim 33, wherein, in the case that analysing di detects no presence of flow, the extracted depth is given as the segment length of the non-intersecting depth do.

35. The handheld imaging device of claim 33 or 34, wherein said defined length of a segment is between 1 mm and 5mm.

36. The handheld imaging device of claim 2 or 3, wherein the processor extracts a characteristic of the sub-dermal structure as a function of processed received CWD signals and sub-dermal structure parameters.

37. The handheld imaging device of claim 36, wherein said sub-dermal structure parameters are selected from the group consisting of depth, diameter and flow velocity for said sub-dermal structure.

38. The handheld imaging device of claim 37, wherein said extracted characteristic is depth.

39. The handheld imaging device of any one of claims 36 to 38, wherein said sub- dermal structure is a vascular structure selected from the group consisting of a vein or artery.

40. The handheld imaging device of any one of the preceding claims, wherein said first image plane is a coronal plane of the sub-dermal structure and the second image plane is a transverse or sagittal plane of the sub-dermal structure.

41. The handheld imaging device of any one of claims 36 to 40, wherein said first transducer array comprises at least one transducer element selected from the group consisting of infrared LEDs, acoustic transducers operating other than by CWD and surface mounted electrodes.

42. The handheld imaging device of claim 41 , wherein said sub-dermal structure is a blood vessel, the second transducer array comprises at least one near infrared (NIR) emitter and the first transducer array is operated in continuous wave Doppler mode, wherein:(a) if a blood vessel is detected by both said at least one NIR emitter and the first transducer array, depth of the blood vessel is determined according to said at least one NIR emitter wavelength;(b) if a blood vessel is detected only by the first transducer array, depth of the blood vessel is determined to be below the penetration depth of said at least one NIR emitter; and(c) if no blood vessel is detected either by said at least one NIR emitter or the first transducer array, the processor detects no blood vessel below said at least one NIR emitter or said first transducer array.

43. The handheld imaging device of any one of the preceding claims, comprising a display screen configured to display an image of the sub-dermal structure and a characteristic of the sub-dermal structure.

44. The handheld imaging device of claim 43, wherein a colour gradient representative of the characteristic of the sub-dermal structure is overlaid over the image of the sub-dermal structure.

45. The handheld imaging device of any one of the preceding claims, wherein said characteristic is depth and the processor calculates depth along a pathway of the sub-dermal structure, a depth gradient being reflected by at least one of variation in colour and a visual indicator other than colour.

46. The handheld imaging device of claim 43, wherein said image is a transverse view of said sub-dermal structure.

47. The handheld imaging device of claim 46, wherein said transverse view of said sub-dermal structure is windowed over a coronal view of the sub-dermal structure.

48. The handheld imaging device of claim 2 or 3, wherein a second imaging plane module, optionally a CWD module, includes a variable frequency continuous wave transmitter that activates a broadband acoustic transducer.

49. A method for imaging a sub-dermal structure comprising: transmitting energy from a first transducer array towards the sub-dermal structure; transmitting energy from a second acoustic transducer array towards the sub-dermal structure; receiving energy reflected from the sub-dermal structure following transmitting energy from the second transducer array towards the sub- dermal structure; processing energy received from the sub-dermal structure for producing an image;imaging said sub-dermal structure in a first plane; imaging said sub-dermal structure in a second plane; and calculating characteristics of said sub-dermal structure from said first and second imaged planes.

50. A handheld imaging device for medical use comprising: a housing; a sensor base connected to the housing, the sensor base comprising a transducer array comprising a plurality of transducers operated in A- mode; and a processor, operable under control of electronic program instructions, for activating transducer elements of said transducer array to transmit signals and processing echo signals reflected by said sub-dermal structure, wherein said processor converts the echo signals to A-mode data and analyses said A-mode data by an A-mode processing pathway to detect position of the sub-dermal structure and calculate depth and dimension, including diameter of said sub-dermal structure so that said processor enables construction of an image of the sub-dermal structure in a coronal plane.

51. The handheld imaging device of claim 50, wherein said sub-dermal structure is a blood vessel.

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