AU2011100156A4 - Improved Imaging Apparatus and Method - Google Patents

Description

IP0321P AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT Invention Title: Improved Imaging Apparatus and Method 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 IMPROVED IMAGING APPARATUS AND METHOD TECHNICAL FIELD The present invention relates to a hand held ultrasound diagnostic apparatus 5 adapted for use in a moving vehicle. 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 B-mode scanning system using a mechanically mounted 30 rotating transducer was introduced.

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. 15 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 single plane, whose spatial relationship was known because the sweep 20 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. A solution to these problems has been sought in electronic beam steering 25 transducers consisting of 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 an array of ultrasonic crystals in the transducer. The early designs used at least 64 30 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. These high cost, high power consumption devices are unsuitable for broad 25 point-of-care application outside of specialist sonography facilities. In particular, these systems are unsuitable for application to hand-held devices. There is a need for hand-held ultrasound systems, of a size and cost which will enable their routine use at point-of-care by practitioners other than trained sonographers. 30 The ability to provide immediate ultrasound diagnosis is particularly valuable in emergency situations. Such emergencies may be accident trauma, where, for 5 instance, direct imaging to detect internal fluid filled cavities allows rapid diagnosis of internal bleeding. Emergencies may also be acute illnesses, where rapid diagnosis of such conditions as kidney stones may be vital. 5 In many emergency cases, intravenous needles must be inserted under difficult conditions. Ultrasound guidance can be invaluable for this procedure, allowing quick, accurate insertion, where the attendant can be immediately confident that the insertion has in fact occurred successfully. Emergency procedures in many cases are undertaken while the casualty is 10 being evacuated. There is therefore a need for such an ultrasound system to function in a moving vehicle, such as an ambulance or an aircraft. It is an object of this invention to provide a hand held diagnostic ultrasound unit which overcomes limitations of the prior art. Other objects and advantages of the present invention will become apparent 15 from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. DISCLOSURE OF THE INVENTION One type of diagnostic ultrasound system, disclosed in patent application 20 PCT/AU2008/001278, which is hereby incorporated by reference in its entirety, uses a single, manually swept beam, where one or more inertial sensors internal to the probe provide data from which the relative spatial orientation of the beam may be calculated. Typically, this information is then used to define display vectors on a screen, each vector being an analogue of the returned 25 ultrasound echo received by the probe. By changing the angle of the probe relative to the patient, and successively acquiring and displaying the returned echo vectors, an ultrasound picture of the underlying tissue can be constructed on a display screen. The function of such a system may, however, be disrupted if the patient and 30 the ultrasound probe are located in a moving (specifically, an accelerating) frame of reference such as an aeroplane or ambulance. In this situation, the inertial sensors inside the ultrasound probe will measure not only the 6 movement of the probe relative to the patient but also a varying and unknown contribution from the acceleration of the vehicle in which they are enclosed. This, in general, will lead to an erroneous calculation for the direction of the probe relative to the patient and hence erroneous positioning of the display 5 vectors on a display screen with concomitant image degradation. It is advantageous for equipment based on the low cost, accelerometer method of determining probe orientation to function within, for example, a moving ambulance, ship or airplane. In one form of this invention although this may not necessarily be the only or 10 indeed the broadest form of this there is proposed a hand held ultrasound diagnostic apparatus adapted for use in a moving vehicle including a probe unit including an ultrasound transducer and a positional inertial sensor adapted to sense changes in the position and/or orientation of the probe unit, 15 the probe unit being adapted to be manually moved in such a manner that ultrasound energy is transmitted to and received from an area or sector of a target to be scanned, a processor adapted to receive ultrasound reflection information from the transducer and to receive positional information from the positional inertial 20 sensor, said positional information including a contribution from the movement of the moving vehicle, further including a reference unit including at least one reference inertial sensor, the reference unit being adapted to be secured in such a manner as to be substantially stationary with respect to the moving vehicle, 25 a processor adapted to process acceleration information from the reference inertial sensor and the positional information from the positional inertial sensor, and to produce modified positional information wherein at least a significant portion of the contribution from the moving vehicle has been removed, said modified positional information being used to associate a position vector 30 with each element of ultrasound reflection information to produce a resultant ultrasound image and a display unit adapted to display the resultant ultrasound image.

7 There is a probe unit containing conventional accelerometers as the positional inertial sensor, the outputs of which are subjected to a double integration, or approximate equivalent, to calculate continuously the orientation change of the device from some fiducial point established when the calculations began. 5 In addition, a sensor which may be a set of accelerometers is contained in a housing that is separate from the ultrasound probe. This reference sensor measures acceleration in at least one and preferably all linear and rotational dimensions and can be attached to the structure, or an extension thereof, of the vehicle in which the patient and the ultrasound scanner are traveling. 10 When scanning, the processor receives signals both from the probe sensor and the reference sensor. The reference sensor signal is used to compensate for the accelerating frame of reference component of the probe sensor. The signals resulting from the compensation calculations then form the modified positional information, resulting in an image that is largely insensitive to vehicle 15 movement. Preferably, data from the positional inertial sensor is used to calculate a first direction vector being the direction vector of the ultrasound energy from the probe unit; data from the reference sensor is used to calculate a second direction vector, being a direction vector of the moving vehicle; the first and 20 second vector being compared to determine a phase angle difference at a point in time, subsequent data from the reference sensor being modified by that phase angle difference and subtracted from subsequent positional inertial sensor data to form a corrected directional vector, being the modified positional data said corrected directional vector being associated with a corresponding 25 element of ultrasound reflection information to produce a scanline, successive scanlines being displayed on a display to produce a resultant ultrasound image. BRIEF DESCRIPTION OF THE DRAWINGS Fig 1 illustrates an ultrasonic scan system including an embodiment of the invention; 30 Fig 2 illustrates a probe unit showing the relationship to the orientation sensor; Fig 3 illustrates a block diagram of a hand held ultrasound system of the invention; 8 BEST MODE FOR CARRYING OUT THE INVENTION Referring now to Fig 1, there is illustrated an ultrasonic scan system according to an embodiment of the invention. There is a hand held ultrasonic probe unit 10, a display and processing unit (DPU) 11 with a display screen 16 and a 5 cable 12 connecting the probe unit to the DPU 11. The probe unit 10 includes an ultrasonic transducer 13 adapted to transmit pulsed ultrasonic signals into a target body 14 and to receive returned echoes from the target body 14. In this embodiment, the transducer is adapted to transmit and receive in only a 10 single direction at a fixed orientation to the probe unit, producing data for a single scanline 15. As shown in Fig 2, the probe unit further includes an orientation sensor 20 capable of sensing orientation or relative orientation about one or more axes of the probe unit. Thus, in general, the sensor is able to sense rotation about any 15 or all of the axes of the probe unit, as indicated by rotation arrows 24, 25, 26. The sensor may be implemented in any convenient form. In an embodiment the sensor consists of three orthogonally mounted gyroscopes. In further embodiments the sensor may consist of two gyroscopes, which would provide information about rotation about only two axes, or a single gyroscope providing 20 information about rotation about only a single axis. Since the distance between the mounting point of the sensor 20 and the tip of the transducer 13 is known, it would also be possible to implement the sensor with one, two or three accelerometers. The patient 14 is placed on a stretcher or other support which is attached to the 25 structure of a vehicle, which may be moving. The attachment may be permanent or temporary, as for a stretcher in an ambulance, but is sufficient to ensure that the patient is substantially at rest with respect to the body of the vehicle. There is also provided a reference unit 3 which is adapted to be clipped or 30 otherwise attached to a member 2 which is substantially at rest with respect to the vehicle, and hence the patient.

9 The reference unit may be incorporated into the DPU, or may be a separate unit. The reference unit 3 includes a reference sensor or sensors 4. This is a sensor which is adapted to measure acceleration in one or more directions. 5 In an embodiment, it consists of one or more accelerometers adapted to measure acceleration in three orthogonal directions. It may also include gyroscopic elements to sense rotational acceleration. A block diagram of the ultrasonic scan system is shown in Fig 3. There is a probe unit 10 and a DPU 11. The probe unit includes a controller 351 which 10 controls all of the functions of the probe. In this embodiment, the controller is implemented as a combination of a field programmable gate array (FPGA) 315 and a microcontroller 330. The DPU includes a main CPU 340 and a communications controller 352. The probe unit 10 communicates with the DPU 11 via a low speed message 15 channel 310 and a high speed data channel 320. The message channel is a low power, always on connection. In an embodiment, it is implemented as a direct connection between the microcontroller 330 on the probe unit and the main CPU 340 of the DPU. In this embodiment, it is implemented using 1 2 C bus technology. 20 The data channel is a higher speed and hence higher power consumption bus which is on only when required to transmit data from the probe unit to the DPU. In this embodiment, it is implemented as a low voltage, differential signal (LVDS) bus. In this embodiment, it is a single channel. Multiple channels may be used in other embodiments, to carry higher data rates or separate sensor 25 channels. 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, 30 which is controlled by controller 351 to provide a pulsed voltage to the transducer 13. The transducer produces an interrogatory ultrasonic pulse in response to each electrical pulse.

10 This interrogatory pulse travels into the body and is reflected from the features of the body to be imaged 14 as an ultrasonic response signal. This response signal is received by the transducer and converted into an electrical received signal. 5 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 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 as shown in Fig 4, to the received signal. This shows a plot of amplification against time to be applied to the returned echo for each pulse. The characteristics of the amplification are selected to compensate for the 15 depth attenuation, giving a compensated 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 is a digital data 20 stream representing the intensity of the received echoes over time for a single ultrasonic pulse. There is an orientation sensor 20 which is adapted to provide information about angular rotation of the probe unit. There is a reference sensor 3, attached to the a member 2 which is at rest with 25 respect to the patient, which is adapted to provide acceleration information about the vehicle in which the patient is travelling. 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 30 not limited to, a scroll wheel, numeric or alpha numeric keypad and voice recognition means.

11 The parameters which may be set may be any variable affecting the ultrasound. They include the sample rate for the ADC, the number of values to be taken, the length of a scan in time or in angle travelled by the probe unit. The set up parameters for the TGC may also be set. 5 Returning to Fig 2, when the ultrasound is to be used in a moving vehicle, the reference unit 3, which may be incorporated in the DPU, is attached to a member 2 which is at rest with respect to the patient 14. This member may be the body of an ambulance or other vehicle. It may be the frame of the stretcher or other support on which the patient is lying. 10 The attachment may be permanent, in the case where the reference unit is separate from the DPU. More usually, the attachment will be temporary, by use of a clip, or a magnetic attachment, or any other convenient method of attachment. The user then applies the probe unit 10 to the patient 14. A scan is initiated by 15 manipulation of the appropriate control on the DPU 11. This control may be a button or other physical control on the DPU, or it may be a soft control on the touchscreen 16. The DPU transmits a message to the probe unit via message channel 310. This message includes the parameters which have been selected for the scan. 20 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. The user rotates the probe as required to sweep the ultrasound beam over the 25 desired area, keeping linear displacement to a minimum. In embodiments where rotation about all axes is not sensed, the user will also keep rotation about unsensed axes, that is axes about which rotation is not detected by the sensor of the embodiment, to a minimum. At the same time, data is received from the orientation sensor 20. This is the 30 rotation about the sensed axes of the probe unit. It may be the angular change in the position of the probe unit since the immediately previous transducer 12 pulse, or since some other transducer pulse, which may be the first of a scan sequence. In a moving (specifically and accelerating) vehicle, the data from orientation sensor 20 will include not only the movement of the probe relative to the patient 5 but also a varying and unknown contribution from the acceleration of the vehicle in which they are enclosed. The data from the orientation sensor is passed to low pass filter 352 to remove high frequency components which are generated by vibrations or other very short term accelerations. 10 The filtered sensor data and the response signal are passed to the controller 351 and in particular the field programmable gate array (FPGA) 315 where they are combined to give a scanline. A scanline is a dataset which comprises a sequential series of intensity values of the response signal combined with a direction vector. 15 The high voltage generator 312 continues to provide the pulsed voltage to the transducer under control of the microcontroller and each pulse results in a scanline. Taken together, these constitute the echo data for some geometric region in the target body. Since only orientation data is collected, the origins of all of the scanlines are co-incident, since no information about any linear 20 displacement which may have occurred is available. They are not, in general, co-planar. In embodiments where rotation about only a single axis is sensed by the sensor, the scanlines will be co-planar, since no information about rotation out of the plane orthogonal to the sensed axis will be available. 25 The scanline is generated in the controller 351. Echo intensity data from the ADC data is combined with low pass filtered orientation data which has come from the orientation sensor 20, via low pass filter 352. The data is then passed to a protocol converter to be converted to a protocol suitable for transmission via the data channel. Any suitable protocol may be used. In this embodiment 30 the protocol chosen for use on the data channel is 8b1Ob, which is well known in the art.

13 The 8blOb data is passed to an LVDS transmitter 338 and is transmitted via the data channel 320 to the DPU 11. Referring to Fig 3, 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 5 FPGA 341. Protocol conversion is performed by controller 352 to recover the original scanline data. An application is now run by the DPU CPU 340 to process the scanlines for display as an ultrasound image on the display 16 of the DPU 11. The scanline data is known to include an unknown error caused by the 10 acceleration (if any) of the vehicle in which the patient is travelling. The processing of the scanlines in the DPU CPU 340 seeks to remove at least a significant portion of this in accuracy. Reference data is received by wireless interface 341 from reference sensor 4 via wireless link 5. The wireless link may be replaced with a wired link. 15 This data is passed to low pass filter 342, to filter out very rapid movement components which are generated by vibrations or other short term accelerations. The reference data is then co-processed with the direction vectors of the scanlines in order to remove the effects of the acceleration of the moving 20 vehicle from the direction vectors. In order for the correct amount of reference signal to be removed from each of the directional components of the direction vectors provided by the probe orientation sensor it is necessary to know the alignment of the acceleration vectors of the probe unit with respect to those of the reference unit. 25 This is effected by continuously calculating as far as possible the three dimensional translational and rotational vectors of the scanline direction vectors and of the reference data signal direction vectors, and determining the difference between their phase angles. When the probe is stationary relative to the patient, then the two vectors will be almost identical in amplitude, there 30 being only a possible small difference in their rotational components under some circumstances. In the general case, though, they will differ in phase angle. Aligning their phase angles and then subtracting the reference values 14 from the probe values will yield a translational value of zero - the correct value for the orientation of the stationary probe relative to the patient. Storing this difference in phase angles allows the relative orientation of the reference unit and the probe unit to be determined immediately prior to scanning the patient. 5 If the probe is now moved in the performance of a scan, the ongoing signals from the reference accelerometers may be geometrically translated by the known angle of orientation relative to the probe measured just prior to scanning and subtracted from the matching probe signals to leave only the vectors of motion relative to the patient. The duration of this accord will be limited both by 10 the rate of change of acceleration of the frame of reference and by the ongoing electrical drift within the accelerometer sensors themselves which are typically of the order of 30 seconds or more. Stopping and restarting the scanner will, again, bring the accelerometers into synchronisation, ready for the next scan. In an embodiment, the probe unit may receive the reference data directly, via a 15 wired or wireless link. The orientation data and the reference data may be co processed, as for the previously described embodiment, to provide corrected orientation data. This corrected orientation data has had a significant portion of the error due to acceleration of the moving vehicle removed. This corrected orientation data is then combined with the ultrasound response signal to give 20 corrected scanlines. These scanlines are then sent to the DPU for display. A further embodiment utilises a mode of operation that reduces reliance on accelerometer data to determine the ultrasound probe position. This is either implemented continuously or invoked during periods where significant acceleration of the common frame of reference of patient and ultrasound 25 scanner are detected, that is, when significant acceleration of the vehicle occurs. The operator of a manually-swept, single beam, ultrasound probe tends to sweep that beam at a relatively constant angular velocity. Therefore, if the timing of the start of the sweep is known, an assumption or estimate can be 30 made about its velocity and that value used to define the direction vectors of each of the scanlines on a screen as described above. An error between the estimated and the actual velocity will only change the angle over which the image is displayed - the "pie slice" appearance of the image will then have a 15 slightly different angle from the correct one but with the displayed components still possessing the correct relative positions to each other, albeit with minor distortions. In this mode of operation, depth/range information will, however, still remain accurate. 5 The start of scan is detected by a sharp reversal in rotation of the probe about its tip - this gross change being detectable above the smaller artefacts generated by the moving frame of reference. The end of scan is either signalled after a fixed time or by the detection of a complementary sharp reversal in rotation of the probe. The probe can, thus, be continuously scanned 10 in one direction then the other, the start of each new scan being signalled by the change in direction of its rotation. Each pass of the probe will generate a new image. An extension of this method continues to take measurements of angular displacement from the probe's accelerometers, calculates the mean, median or 15 mode of the values and uses this to correct the assumed velocity of the probe. In all described embodiments, the device will normally operate in a mode where no motion is expected. The motion resistant mode is either selected manually by the operator or, optionally, is switched on automatically when a certain threshold of external motion is detected by the reference accelerometers. 20 The disclosed methods and apparatus for determining the movement of an ultrasound probe relative to a patient are largely insensitive to the acceleration of their joint frame of reference. The methods may be used separately or in association with each other, with partial, low cost implementations of each being combined to yield a higher accuracy for the assembly as a whole. 25 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 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 30 apparatus.

Claims (5)

1. A hand held ultrasound apparatus adapted for use in a moving vehicle including a probe unit including an ultrasound transducer and 5 a positional inertial sensor adapted to sense changes in the position and/or orientation of the probe unit, the probe unit being adapted to be manually moved in such a manner that ultrasound energy is transmitted to and received from an area or sector of a target to be scanned, 10 a processor adapted to receive ultrasound reflection information from the transducer and to receive corresponding positional information from the positional inertial sensor, said positional information including a contribution from the movement of the moving vehicle, further including a reference unit including at least one reference inertial 15 sensor, the reference unit being adapted to be secured in such a manner as to be substantially stationary with respect to the moving vehicle, a processor adapted to process acceleration information from the reference inertial sensor and the positional information from the positional inertial sensor, and to produce modified positional information wherein at least a 20 significant portion of the contribution from the movement of the moving vehicle has been removed, said modified positional information being associated with the corresponding ultrasound reflection information to produce a scanline and a display unit adapted to display groups of scanlines as an ultrasound 25 image.

2. The hand held ultrasound apparatus of claim 1 wherein the reference sensor includes one or more of an accelerometer and a gyroscope.

3. The hand held ultrasound apparatus of claim 1 wherein the reference unit and the display unit are contained within a common casing. 30

4. The hand held ultrasound apparatus of claim 1 wherein data from the positional inertial sensor is used to calculate a first motion vector being the motion vector the probe unit; data from the reference sensor is used to 17 calculate a second motion vector, being a motion vector of the moving vehicle; the first and second motion vector being compared to determine a phase angle difference at a point in time, 5 subsequent data from the reference sensor being modified by that phase angle difference and subtracted from subsequent positional inertial sensor data to form the modified positional data.

5. A hand held ultrasound apparatus of the type having a probe emitting a single ultrasound beam which is manually swept over an area to be 10 scanned, the probe having an inertial sensor to provide positional data indicating the position of the probe during said manual sweeping, wherein when usage circumstances are identified which would significantly compromise the accuracy of said positional data, the apparatus enters a robust mode in which that positional data is at least partly replaced by 15 estimated probe positional data, the values of the estimated data being estimated from a selected velocity profile which a user is assumed to apply to the probe during said manual sweeping.