AU2011100029A4 - Mechanically Driven Medical Scanning Device - Google Patents

Description

IP0171P AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT Invention Title: Mechanically Driven Medical Scanning Device Name of Applicant: Signostics Limited Address for Service: 40-46 West Thebarton Road Thebarton, S.A. 5031 The invention is described in the following statement: 2 TITLE MECHANICALLY DRIVEN MEDICAL SCANNING DEVICE TECHNICAL FIELD The present invention relates to the field of medical ultrasound scanning 5 apparatus, in particular hand-held medical ultrasound apparatus. BACKGROUND ART Ultrasound was first investigated as a medical diagnostic imaging tool in the 1940's. This was based on the use of A-mode (amplitude mode) ultrasound, which is a form of echo ranging. This simply gives a plot of returned echo 10 intensity against time, which, by knowing the speed of sound in the target media, gives the distance of the features returning the echo from the transducer. In order to obtain valid information from such a scanline it is necessary that the direction of the transmitted ultrasound beam be constant and known. 15 In order to provide an imaging system, it is necessary to insonify a larger area, at least a two dimensional slice of the target. It is also necessary to receive returned echoes from this area and to display this information in correct spatial relationship. Since the only information received by an ultrasound transducer is echo 20 intensity over time, spatial information can most easily be added by knowing the direction from which the echo was received. This means knowing the position and orientation of the transducer at all times and this was most easily achieved by controlling the movement of the transducer. This led to B-mode (brightness mode) scanning, where the ultrasound output is 25 pulsed and the transducer is mechanically scanned over the target. The transducer detects the echo from each pulse as intensity versus time, called a scanline. The scanlines are displayed with brightness being proportional to echo intensity, thus forming an image. In the early 1950's there existed a B-mode scanning system using a 30 mechanically mounted rotating transducer.

3 Ultrasound technology developed significantly in the 1960's with the development of articulated arm B-mode scanners. Articulated arm scanners, also known as static mode scanners, connect the ultrasonic transducer to a moveable arm, with movement of the arm mechanically measured using 5 potentiometers. The articulated arm also ensures that the degree of freedom of movement of the transducer is limited to a defined plane. This allowed the position of the transducer to be known with considerable accuracy, thus allowing the scanlines recorded by the transducer to be accurately located in space relative to each other for display. 10 Static mode ultrasound scanners were in wide use until the early 1980s. The static mode scanners were large cumbersome devices, and the techniques used are not readily suited to a handheld ultrasound system. In the mid 1970's real-time scanners were developed where an ultrasonic transducer was rotated using a motor. A motor rotates an ultrasonic transducer 15 in order to produce images in real-time. Motor driven transducers removed the need for precise knowledge of the position of the transducer housing, since the operator needed only to hold the transducer housing still and the motor would sweep the transducer rapidly to produce a scan arc. This resulted in an evenly distributed set of scanlines, in a 20 single plane, whose spatial relationship was known because the sweep characteristics were known. These devices brought their own problems. The motor driving circuitry added size, power consumption, complexity and cost to the device. Additionally, the motor itself and associated moving parts reduced the reliability of the device. 25 A solution to these problems has been sought in electronic beam steering transducers. These include a number of electronic crystals where the transmitting pulse can be delayed in sequence to each crystal and thus effect an electronic means to steer the ultrasound beam. The basic technique is still in wide use today, with nearly all modern medical ultrasound equipment using 30 an array of ultrasonic crystals in the transducer. The early designs used at least 64 crystals, with modern designs sometimes using up to a thousand crystals or more.

4 Electronic beam steering removes the need for a motor to produce real time images. The scanlines resulting from the use of an array transducer are contained within a defined plane, or in the case of 2-D arrays within a defined series of planes. The scanlines may therefore be readily mapped onto a flat 5 screen for display. However, the cost of producing transducers with arrays of crystals is high. There is also a high cost in providing the control and processing circuitry, with a separate channel being required for each crystal. The transducers are usually manually manufactured, with the channels requiring excellent channel to 10 channel matching and low cross-talk. The power consumption for electronic systems is also high, and is generally proportional to the number of channels being simultaneously operational. In parallel, solutions to the problem of tracking a transducer without using articulated arms were pursued. These involved tracking the transducer, or a 15 component with a fixed relationship to the transducer, in relation to an external reference frame. These generally involved electromagnetic tracking using one or more fixed transmitters separate from the transducer unit, and a receiver on the transducer unit. Visual tracking using cameras was also employed. These all suffered from the need to establish the frame of reference, in some 20 cases only being of use in specifically equipped rooms. They also suffered from the problem of interference with the tracking signals by people and equipment moving in the field of reference. These problems, in particular made these systems unsuitable for hand-held use. Much of the prior art in ultrasound technology is directed to improving the 25 performance of ultrasound systems enabling them to be used for an ever increasing range of diagnostic applications. The result has seen significant advances in ultrasound systems with transducers using ever increasing numbers of crystals, and host systems with ever increasing processing power. The result has seen systems with 3D and real-time 3D (or 4D) capability. 30 These high cost, high power consumption devices are unsuitable for broad point-of-care application outside of specialist sonography facilities. In particular, these systems are unsuitable for application to hand-held devices.

5 Hand-held devices which are battery powered have two general requirements, these being small size and low weight and low power consumption. Small size and low weight are necessary to allow for convenient and comfortable use when the unit is entirely or substantially held in the hands 5 during use. Large size is awkward, and weight makes the device tiring to use over long periods. Small size and low weight are also advantageous for allowing a user to carry the device about their person, ready for use. For a device to be truly hand-held, it must be free of a requirement to be permanently attached to a mains power supply. This means that the device 10 must depend upon battery power. Currently available practical batteries have relatively low energy storage density. Accordingly, a small, lightweight battery will have relatively low storage capacity. It is inconvenient to recharge or change batteries often. If a hand-held device is to have sufficient endurance to allow it to be conveniently used for extended periods, low power consumption 15 is preferred. Transducer arrays with digital beamformers have relatively high power consumption, making their use in hand-held devices problematic. Motorised movement of a scanning transducer will contribute significantly to power consumption. There will also be a significant weight and size associated 20 with the motor for driving the transducer. Manual scanning requires additional complexity since it is necessary to add components to sense the position and orientation of the transducer, and processing capability to interpret those sensor readings. All of the above mentioned solutions add significantly to the cost of the device. 25 It is an object of the present invention to provide an ultrasound scanning device that overcomes or at least substantially ameliorates the problems associated with the devices of the prior art or at least provides the public with a useful alternative. Other objects and advantages of the present invention will become apparent 30 from the following description, taken in connection with the accompanying 6 drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. DISCLOSURE OF THE INVENTION In one form of this invention although this may not necessarily be the only or 5 indeed the broadest form of this there is proposed a hand-held ultrasound scanning device including an ultrasound transducer adapted to be moved relative to a probe housing to scan an area of a target body wherein the transducer is moved by non-motorised mechanical means. In preference, the mechanical means includes a potential energy storage 10 means selected from a spring and a torsion member. Preferably, the transducer is pivoted such that the movement of the transducer describes an arc in a single plane. In preference, the transducer is a single crystal transducer which transmits and receives substantially in one direction only. The transducer transmits ultrasound energy and receives echoes from 15 that transmission while moving, to isonify an area which is a sector of a circle. The received echoes produce a series of scanlines, which may be displayed on a display device. In preference, there is a cocking mechanism adapted to allow a user to manually move the mechanical means in order to store potential energy in the 20 potential energy storage means. In preference the potential energy storage apparatus is a spring and the cocking mechanism includes a manually moveable member adapted to be moved by a user to rotate the transducer movement apparatus to compress the spring. 25 In use, a user holds the probe unit stationary against the patient or other body to be scanned. The mechanism of the transducer movement is the activated to sweep the transducer, transmitting and receiving ultrasound pulses, in an arc. Mechanical movement of the transducer provides an accurate sector scan, where the relative position of the scanlines is known because the 30 characteristics of the movement of the transducer are known. This means the scanlines can be displayed with a minimum of further processing.

7 Mechanical or optical means for tracking the position of the transducer may be employed to more accurately locate the scanlines with respect to each other. For a better understanding of this invention it will now be described with respect to a preferred embodiment which shall be described herein with the assistance 5 of drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a view of a hand-held ultrasound scanning device according to a preferred embodiment of the present invention; Figure 2 is a detail view of the actuation mechanism of the embodiment shown 10 in Figure 1. Figure 3 is a block diagram of the electronic components of the embodiment of Figure 1. Figure 4 is an illustration of the scanline pattern produced by the embodiment of Figure 1. 15 Figure 5 is a sectioned view of hand-held ultrasound scanning device according to a further embodiment of the invention. Figure 6 is a representation of the scanline pattern of the embodiment of figure 5. BEST MODE FOR CARRYING OUT THE INVENTION 20 Now referring to the illustrations, and in particular to Figure 1, there is an ultrasound scanning device including a probe unit 10 and a display and processing unit (DPU) 11, connected by an interface cord 16. The DPU includes a display 18 and a user input control in the form of a thumbwheel 19. 25 The probe unit 10 is adapted to be held by a user against a target body during ultrasound scanning. There is a transducer housing 12 made of substantially ultrasound transparent material which surrounds and protects ultrasonic transducer 13. The transducer housing is substantially liquid tight. In an embodiment, it is filled 30 with a liquid to assist with impedance matching between the transducer and the 8 target body. In an alternative embodiment, the transducer is shaped to match the housing profile and the transducer remains in contact with the inner wall of the housing throughout its travel, avoiding the need to impedance match. The transducer is supported by transducer support member 14, which is 5 pivoted such that the transducer is able to move in an arc in a single plane. There are further provided a moveable handgrip 15 and an actuation button 17. The mechanical action of the device is illustrated in Figure 2 which shows a detail of the actuation mechanism which is contained within the probe unit 10 of figure 1. 10 In operation, handgrip 15 is compressed by a user, driving the transducer support member into a cocked position and storing potential energy in a torsion member or spring When a user initiates a scan, this energy is released to drive the transducer in an arc to obtain a sector scan. Referring now to Figure 2, transducer support member 14 is held at the pivot 15 point by torsion member 25. This torsion member is adapted to store potential energy when force is applied to rotate the transducer support member. Cocking member 26 is adapted to bear against the cocking support portion 24 of the transducer support member 14. When the handgrip is compressed, this cocking member urges the transducer support member into a cocked position, 20 twisting the torsion member 25 and storing potential energy. The cocking support portion is forced past stop member 23, which allows the member past, but prevents it from returning when the handgrip is released. The transducer support member is now in a cocked condition, with the tension in the torsion member urging the transducer support member to move, but this 25 being prevented by the stop member. There is an actuation button 17. When a user wishes to make a scan, this button is depressed by the user. This pushes down actuation member 21, which, by the action of pivot member 22, raises stop member 23. transducer support member 14 is now free to move, and the tension in torsion member 25 30 drives the transducer support member and its attached transducer through an arc.

9 The particular geometry of the cocking mechanism and the release mechanism are illustrated for one embodiment only. Many other methods could be employed to allow an external manual control to turn the transducer into a cocked position, compressing a spring or twisting a torsion member, to hold 5 that transducer in that cocked position, and to release it by user action. A block diagram of the electronic components of the device is shown in Figure 3. There is a probe unit 10 and a DPU 11. The probe unit includes a controller 351 which controls all of the functions of the probe. 10 The DPU includes a main CPU 340. The probe unit 10 communicates with the DPU 11 via a low speed message channel 310 and a high speed data channel 320. The message channel is a low power, always on connection. The data channel is a higher speed and hence higher power consumption bus 15 which is on only when required to transmit data from the probe unit to the DPU. The probe unit includes a transducer 13 which acts to transmit and receive ultrasonic signals. A diplexer 311 is used to switch the transducer between transmit and receive circuitry. On the transmit side the diplexer is connected to high voltage generator 312, 20 which is controlled by controller 351 to provide a pulsed electrical input signal to the transducer 13. The transducer produces an interrogatory ultrasonic pulse in response to each electrical input signal pulse. This interrogatory pulse travels into the body and is reflected from the features of the body to be imaged as an ultrasonic response signal. This response 25 signal is received by the transducer and converted into an electrical received signal. The depth from which the echo is received can be determined by the time delay between transmission and reception, with echoes from deeper features being received after a longer delay. Since the ultrasound signal attenuates in 30 tissue, the signal from deeper features will be relatively weaker than that from shallower features.

10 The diplexer 311 connects the electrical receive signal to time gain compensation circuit (TGC) 313 via a pre-amp 316. The TGC applies amplification to the received signal. The characteristics of the amplification are selected to compensate for the depth attenuation, giving a compensated 5 receive signal where the intensity is proportional to the reflectiveness of the feature which caused the echo. In general, the amplification characteristics may take any shape. This compensated signal is passed to an analogue to digital converter (ADC) 314, via an anti-aliasing filter 317. The output of the ADC for each input signal 10 pulse is a received signal pulse being a digital data stream representing the intensity of the received echoes over time for a single ultrasonic pulse. The DPU includes a touchscreen user interface device 16. This gives the user control of a user interface which allows parameters for an ultrasound scan to be set. Further user input devices 362 may be provided. These include but are 15 not limited to, a scroll wheel, numeric or alpha numeric keypad and voice recognition means. In use, a user applies the probe unit 10 to a target body to be imaged. The handgrip 15 is depressed to cock the transducer movement mechanism and to store the energy required for movement of the transducer in the torsion 20 member or spring. The actuation button 17 is pressed to initiate a scan. As previously described, this mechanically initiates the movement of the transducer to perform a scan. The button press is also detected by the controller 351 and communicated to the DPU 11 via the message channel 310. 25 The DPU responds with a message which includes any parameters which have been selected for the scan. The controller 351 controls the high voltage driver to produce the required pulse sequence to be applied via the diplexer to the transducer in order to perform a scan according to the parameters set by the user, or set as defaults in the DPU. 30 The speed movement of the transducer will not be constant across the full swing of the transducer movement. However the characteristic change in velocity will be reasonably consistent, and can be known from calibration tests 11 of the transducer movement mechanical assembly or from the physical characteristics of the said mechanical system. In an embodiment, the controller 351 controls the transmission of ultrasound pulses such that the angle of movement of the transducer between pulses is 5 approximately constant and of a known value. The transducer movement assembly can be designed such that, following initial acceleration of the transducer, its rate of movement is relatively constant. In an embodiment, the pulse the received signal pulses received in response to the first few input pulses of a scan are discarded, and the remaining response 10 signal pulses are assumed to be a constant angular distance apart. The scan dataset is the result of a single scan. As illustrated in Fig 4, the scan dataset is a series of scanlines 41, each having a common origin 42, and falling in a common plane, the plane of movement of the transducer within the transducer housing. The distance along the length 43 is the depth of 15 penetration from which the ultrasound echo was returned. Each scanline is a series of values for the intensity of the echo returned from increasing depth into the subject body, along with a value representing the angle from the starting position of the transducer at which that data was received by the transducer. The scan echo intensity values from the ADC are received by the controller 351 20 and assembled into scanlines. As described above, the angle information is either the known value which the controller caused to be the angle traversed by the transducer between consecutive input pulses or the assumed value after the first few received signal pulses are discarded. The scanline data is then passed to a protocol converter to be converted to a 25 protocol suitable for transmission via the data channel. Any suitable protocol may be used. In this embodiment the protocol chosen for use on the data channel is 8blOb, which is well known in the art. The 8b1Ob data is passed to an LVDS transmitter 338 and is transmitted via the data channel 320 to the DPU 11. 30 The LVDS data channel is received by the DPU via LVDS receiver 321 and phase locked loop 322. The 8blOb data is passed to the DPU processor 340.

12 Protocol conversion is performed by processor 340 to recover the original scanline data. An application is now run by the DPU processor 340 to process the scanlines for display as an ultrasound image on the display 16 of the DPU 11. The 5 scanlines are displayed as a sector of a circle. The scanline intensity data is displayed as lines of brightness at the angle included in the scanline data. It is not necessary for the transducer to be moved in an arc. The transducer may also be moved linearly. As shown in Figure 5 there is a probe unit 50, which is connected to a DPU (not shown) by cable 51. The probe unit is 10 rectangular, adapted to be placed against the skin of a patient, covering the area to be scanned. There is a transducer 52, positioned such that it transmits and receives ultrasound signals into and from the body of a patient orthogonal to the long and short axes of the probe unit. 15 The transducer is held by transducer support assembly 53. This assembly is coupled to an internal end wall of the probe unit by a compression member or spring 54. The support assembly holds the transducer in a fixed position relative to the probe unit except that it is free to move linearly along the long axis of the probe unit. 20 There is a cocking member 55 which is coupled to the support assembly 53, and allows a user to move the transducer against the resistance of the spring to a cocked position in which the spring is compressed at one end of the probe unit. It is held in that position by a stop mechanism (not shown). When a user wishes to perform a scan the actuation button 56 is pressed, releasing the 25 spring loaded transducer assembly, and allowing the transducer to be carried linearly along the probe unit. The pressing of the actuation button is also communicated to the electronics. The electronic actions of the device of this embodiment are as described for the embodiment of figure 3. 30 The resulting scanline data set is as shown in figure 6. There are scanlines 61 which are parallel to each other. There is a distance measure associated with 13 each scanline which is a linear displacement from the transducer start position, rather than an angular displacement. The display of the scan on the DPU is of a rectangular area. The cocking mechanism for the device of any embodiment may be 5 implemented in other ways. Any convenient means for storing potential energy by a user mechanical action may be employed. Springs and torsion members have been described. Any convenient arrangement of a spring or springs and a release mechanism may be used. Another method which might be employed is compression of a gas, including air. The required potential energy may also be 10 stored by movement of the transducer support member in a potential field, such as gravity or a magnetic field. The hold and release mechanism may likewise be implemented in a variety of ways. It will be clear to one skilled in the art that, in addition to purely mechanical arrangements, electromagnetic or pneumatic means may be used 15 to allow the actuation button to cause the release of the stored potential energy. Although the invention has been herein shown and described in what is conceived to be the most practical and preferred embodiment, it is recognised that departures can be made within the scope of the invention, which is not to 20 be limited to the details described herein but is to be accorded the full scope of the appended claims so as to embrace any and all equivalent devices and apparatus.

Claims (5)

1. A hand-held ultrasound scanning device including non-motorised mechanical means adapted to move an ultrasound transducer relative to a probe housing in order to scan an area of a target body. 5

2. The device of claim 1 wherein the mechanical means includes a potential energy storage means adapted to provide the energy and force to move the transducer, said potential energy storage means being selected from a spring and a torsion member.

3. The device of claim 2 further including a cocking and actuation mechanism 10 adapted to allow a user to manually move the mechanical means in order to store potential energy in the potential energy storage means and to actuate the mechanical means such that the potential energy is released and the transducer is moved to scan a target area.

4. The device of claim 3 wherein the potential energy storage apparatus is a 15 spring and the cocking mechanism includes a manually moveable member adapted to be moved by a user to move the mechanical means to compress the spring.

5. The device of any one of the preceding claims wherein the mechanical means includes a member supported at a pivot point such that the 20 transducer is substantially constrained to move in an arc in a single plane.