WO2009065167A1

WO2009065167A1 - Low power medical scanning method and apparatus

Info

Publication number: WO2009065167A1
Application number: PCT/AU2008/001706
Authority: WO
Inventors: Paul James Hirschausen
Original assignee: Signostics Pty Ltd
Priority date: 2007-11-19
Filing date: 2008-11-17
Publication date: 2009-05-28

Abstract

A hand held ultrasound scanner and a method of operation of such a scanner giving tow power consumption having multiple power up modes Including a stand by mode In which only a first processor Is active providing the function of recognising a user command to initiate an ultrasound scan; a setup mode in which a second processor is also active to receive and process communications which direct the setting of values for set up parameters for an ultrasound scan; a low power pre-charge mode In which a third processor Is active to provide control for analogue circuitry which performs an ultrasound scan, and a high voltage power supply is also activated, to provide power to an ultrasound transducer under the control of the third processor; a high power pre-charge mode In which analogue circuitry for ultrasound scanning is supplied with power and echoes are received and analysed by the analogue circuitry; the stand by, setup, low power pre-charge, high power pre-charge and scanning modes being entered sequentially.

Description

TITLE

LOW POWER MEDICAL SCANNING METHOD AND APPARATUS

TECHNICAL FIELD

Thθ present invention relates to a method and apparatus for minimizing power consumption In a hand held ultrasound scanning system.

BACKGROUND ART

The use of ultrasound scanning of patients for medical diagnostic purposes dates to the mid-20th century. An ultrasound transducer is used to project a beam of ultrasound energy Into a patient. The same or another transducer detects the echoes returned from features within the body. These echoes, called a scanliπe, are then converted to a form suitable for recording or display.

When a series of scanlines, spaced angularly apart, are acquired rapidly and displayed on a display screen, the familiar B-modθ sector scan Is achieved.

This Is a sector of a circle, wherein the brightness of each pixel of the display is proportional to the magnitude of the ultrasound echo received from the corresponding point in the body being imaged.

A method from the prior art for collecting the required series of scanlines which are spaced angularly apart was to provide a single transducer in a handpiece attached to a data processing and display unit by an articulated arm. The articulated arm included means at each Joint for tracking the movement of the joint. Tracking the position of each joint allowed the position and orientation of the handpiece, and hence of the transducer, to be known at all times. An operator would place the handpiece against the body of a patient, and sweep the handpiece in an arc to obtain the required set of angularly spaced scanlines. A further development of this method was to place a motor in the handpiece. This motor moved the transducer, relative to the handpiece. The transducer rotated about an axis parallel to the surface of the body to be scanned. Means were provided within the handpiece for accurately determining thθ position of the transducer relative to the handpiece as the transducer moved. In use, an operator placed thθ handpiece against the body of a patient, and held thθ handpiece still. The rotating transducer was activated to cause the ultrasound beam emitted by the transducer to sweep out a sector of the body. All the scanllnθδ obtained in a single sector sweep were displayed to form a static B- modθ Image.

Since the relative position of the transducer was now known, it was no longer necessary for the exact position and orientation of the handpiece to be known, and the articulated arm was no longer required.

A further method for collecting the required angularly separated scaπliπes came with the advent of transducer arrays consisting of a number of plezo-βlectric crystals where the transmitting pulse can be delayed in sequence to each crystal and thus effect an electronic means to steer the ultrasound beam. An operator uses the system In the same way as for the motor driven transducer. The steered beam sweeps out a sector to produce the static B-mode scan, without the need for a motor to move the transducer.

The motor driven transducer has the disadvantage that the motor and the associated moving parts decrease the reliability and increase maintenance requirements.

The motor also adds cost, and more Importantly, greatly Increases the power consumption of the ultrasound scanning system. The motor will also add significantly to the weight and bulk of the handpiece. Nearly all modern medical ultrasound systems use 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.

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 channel matching and low cross-talk.

The power consumption for such electronic systems is high, and is generally proportional to the number of channels being simultaneously operational. The history of medical ultrasound has been a history of steadily increasing utility and steadily broadening applications. It has become Increasingly to be relied upon by medical staff and Its use to be desired In an Increasing number of situations. Many of these situations are not suitable for deploying expensive, bulky, high power consumption devices.

DISCLOSURE OF THE INVENTION

In order for hand held ultrasound to become as ubiquitous and useful in a doctor's hands as a stethoscope, It is necessary that it should be lightweight and able to be U3θd for extended periods without connection to an external power source. A practical hand held ultrasound device should thus be battery powered.

It is advantageous, given the relatively low energy density of currently available batteries, for the power consumption of the device to be absolutely minimized, within the constraint of providing adequate functionality.

These requirements make the use of array transducers or motor driven transducers unattractive.

It is advantageous to use a transducer with the lowest possible power requirements. This will be a single transducer, or a very small number of transducers.

It is further advantageous to employ a manner of movement of the transducer or the unit containing the transducer which uses little or no battery power.

A lower power method of acquiring a series of scanltnes distributed over a sector is to move a single crystal probe through a planar sector by hand. In one form of the invention although this may not necessarily be the only or indeed the broadest form of this there Is proposed a method for operating a hand held ultrasound scanner having low power consumption wherein a supply of power to circuitry adapted to transmit ultrasound pulses and to receive and process returned echoes Is controlled such that elements of the circuitry are provided with power sequentially in such a manner that substantially only elements performing functions which are in operation at a given time are provided with power at that time.

Preferably the method includes controlling the sequential supply of power such that circuitry performing basic communications functionality is substantially always " provided with power in a first power up stage. The device Is therefore able to receive a request from a user to Initiate an ultrasound scan which is followed by Implementing a second power up stage by controlling the sequential supply of power such that circuitry performing a main processing function is supplied with power. The staged power up then continues by Implementing a second power up stage by controlling the sequential supply of power such that circuitry performing a main processing function is supplied with power.

A third power up stage has the circuitry of a high voltage power supply and transmitter supplied with power, while a fourth power up stage includes analogue componentry adapted to receive and process a returned ultrasound signal being supplied with power. In a fifth power up stage clock signals are supplied to digital circuitry controlling the analogue circuitry. High voltage pulses from the transmitter are provided to an ultrasound transducer to cause ultrasound pulses to be transmitted into a body to be scanned and echoes of said pulses to be received and processed.

The emitting of ultrasound energy by a hand held ultrasound device in order to scan a subject Is clearly a dominant contributor to energy use and draining of a battery. It is advantageous to ensure that the device does not isoπify the subject with more ultrasound pulses than are required, thus saving battery power. In a further form, the invention may be said to lie in a hand held ultrasound apparatus Including a probe unit adapted to emit at least one ultrasound beam at a fixed angle relative to the probe unit; an orientation sensor adapted to sense the relative angle at which successive ultrasound beam pulses are directed into a subject to be scanned and a controller adapted to control a transmitter such that the ultrasound beam pulses are emitted when and only when the orientation sensor Indicates that the probe unit has rotated a selected angle since the transmission of the Immediately preceding pulse.

Other objects and advantages of the present invention will become apparent 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. S

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 1s a hand held ultrasound scanning system incorporating a preferred embodiment of the present Invention.

Figure 2 is a simplified block diagram of the probe unit of the system of Figure 1. Figure 3 shows a plot of current draw over time for an embodiment of the invention.

Figure 4 shows a more detailed block diagram representation of a probe unit of a system embodying the invention.

Figure S shows a block diagram of a multi-clock domain system of the Invention. Figure 6 shows a clock enabling diagram for an embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIg 1, there is illustrated an ultrasound scanning system incorporating 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 cable 12 connecting the probe unit to the DPU 1 1.

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.

The transducer is adapted to transmit and receive In at a fixed orientation to the probe unit, producing data for a single scanline 15. The system is a simple, low cost portable ultrasound scanning system. Additional transducers may be provided, at the expense of increased cost and complexity.

The probe unit further Includes an orientation sensor 16 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 or all of the axes of the probe unit.

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 information about rotation about only a single axis. Since the distance between the mounting point of the sensor 18 and the tip of the transducer 13 is known, it would also be possible to Implement the sensor with one, two or three accelβrometers.

The orientation sensor may also incorporate position sensing, or may be only a position sensor, adapted to sense absolute position or relative position movements of the probe unit In further embodiments, the position and/or orientation sensor may be any combination of gyroscopes and accelerometers mounted In relative position to one another so as to give information about the linear and angular displacement of the probe unit. Full relative position data for the probe unit can be obtained with three orthogonally mounted accelerometers and three orthogonally mounted gyroscopes. This arrangement provides measurement of displacement in any direction and rotation about any axis. This allows for direction Information for a scanllne to be given for all six degrees of freedom. In further embodiments, direction Information for scaπlines may be available for any number of possible degrees of freedom.

In another embodiment, the position and/or orientation sensing means is an electromagnetic spatial positioning system of the type requiring a fixed positioning transmitter separate from the probe unit, which transmits electromagnetic signals which are received by a receiver on the probe unit, the receiver providing Information as to the position and orientation of the probe In the field of the transmitter.

The position and orientation means may be any suitable system or combination of systems which yields sufficient position information to form a useful Image from the received scanlines. Optical positioning systems employing LED's and photodetectors may be used. This has the disadvantage of requiring line of sight access to the probe unit at all times.

Acoustic location systems may also be used combining a sound source on the probe with acoustic sensors at known points. Visual tracking systems using a camera to observe the movement of the probe and translate this into tracking data could also be used. This has the disadvantage of requiring line of sight access to the probe unit at all times. In use, a user initiates a scan by operating a control on either the DPU or the probe unit. The probe unit begins to emit ultrasound pulses and to receive returned echoes. The user then moves the probe unit relative to the body to be scanned in a manner appropriate to the type of scan required, and to the nature of the position/orientation sensor provided for a given embodiment.

In an embodiment where the position/orientation sensor Is a single gyroscope, capable of sensing rotation about a single axis, the sensed axis, the user may perform a B-mode scan by rotating the probe unit about the sensed axis in order to sweep the ultrasound beam through a sector in a plane. Rotation about other axes and translational movement will reduce the accuracy of the position and orientation determination, and are avoided as much as possible.

When scanning In M-mode, orientation Information is Irrelevant, and, in this embodiment, the sensor may be turned off.

In order to reduce power consumption, functional units of the probe circuitry are supplied with power only when required. A staged power up sequence is one method used to implement this requirement.

Referring now to Figure 2, the probe unit of the system of Figure 1 is shown In block diagram form.

There Is a power supply 210 which supplies power to the entire circuit. The energy source for the power supply is a battery. There is a microprocessor 211 which Is permanently powered by the power supply 210. When only the microprocessor is powered by the power supply, the unit is in stand by mode and uses very little power. The microprocessor acts to receive a request form the DPU (not shown in this figure) to initiate a scan. On receipt of a scan request, the microprocessor Initiates a setup mode. It provides a logic signal to gate 212 which gates power to the main digital circuitry 213, which In this embodiment Is realised by use of a field programmable gate array (FPGA).

The main digital processor is now available to communicate with the DPU to establish the values of all necessary parameters for the requested scan. When these are established, the FPGA initiates a low power pre-charge mode. It provides a logic signal to gate 214, gating power to the position and/or orientation sensor, which In this embodiment Is a gyroscope 215. A logic signal is also supplied to gatθ 220, gating power to a high voltage power supply 216. This high voltage power supply provides the necessary high voltage to drive a transmitter 219 which excites the transducer to produce the scanning ultrasound beam. The transmitter 219 is also powered up at this time.

These components are powered up at this stage since they require time to be ready for the scan. In embodiments where the sensor has a low power or stand by mode, it will be powered up Into this state only.

The FPGA now initiates a high power pre-charge mode. The FPGA provides a logic signal to gate 217 which gates power to the analogue component functional block 218. In this mode all analogue componentry necessary for receiving and processing returned ultrasound echoes Is powered up. In embodiments where individual analogue components have a low power or stand by mode, these will be powered up into this state only. In this mode the gyroscope 215 is fully powered, to ensure that it is able to provide orientation information Immediately a scan begins.

All communication links available to the probe unit are active in this mode.

The FPGA now Initiates scanning mode. A scanning ultrasound pulse at a desired frequency is produced by the transducer and echoes received back from the body to be scanned. These are processed by the analogue componentry 218 and the resulting scanllπes, consisting of orientation data from the gyroscope 215 and processed echo intensity data are transmitted to the DPU.

At the completion of the required scanning cycle, the system returns briefly to setup mode. This allows communication between the FPGA and the DPU in order to allow error reporting and status interrogation. The system then returns to stand by mode.

The effect of this staged power up sequence on power consumption Is shown in figure 3. This is a plot of current drawn from the battery overtime. Since the battery Is essentially a fixed voltage supply, the current drawn is directly related to power consumption. The figure is not to scale.

The plot of figure 3 shows five distinct power up stages, each with progressively greater current draw than the previous stage. In other embodiments, more or lass stages may be implemented. The rationale behind the choice of stages is that components should remain unpowered unless they are in use. When power is supplied to particular components must also take Into account any required lead time between power application and the comment being ready for use. At the same time, to reduce complexity of power handling, components requiring power at substantially the same time In the power up sequence are grouped together into stages. Each stage corresponds to an operating mode of the overall system.

In a first stage 301 , the stand by. mode, current draw is very low, typically less than 200 μA and preferably less than 100 μA. In this mode only the most basic communications functions are available, sufficing only to allow the DPU to identify the probe, and for a user to signal that a scan should be initiated.

In a second stage 302, the setup mode, the current draw Increases, but typically remains below 2OmA, and preferably below 10mA. In this mode, communications sufficient to provide all required setup parameters are enabled. The main digital processor is enabled In order to receive and process these communications. All analogue componentry remains off.

In a third stage 303, the low power pre-charge mode, the current draw again increases, typically remaining below 800mA, and preferably not exceeding 40OmA- In this mode, the high voltage parts of the circuit are powered up. This includes a high voltage power supply and a pulse transmitter. These are supplied with power at this stage since they require more time than some other components to be ready for use.

In a fourth stage 304, a high power pre-charge mode, the current draw Increases nearly to maximum, typically remaining below 140OmA₁ preferably remaining below 70OmA. In this mode, all of the analogue circuitry is powered, but not active.

Finally In a fifth stage 305. scanning mode, scanning ultrasound pulses are transmitted and received and processed. Current draw again Increases, but by a relatively modest amount. The increase In current draw between the fourth and fifth stages would typically be less than 2OmA and preferably less than 10mA.

Following completion of a scan, the system returns to setup mode 306, with the current draw falling dramatically. This return to a mode in which communication is available but all other functions are turned off allows power to be saved whilst parameter values and error conditions may still be communicated.

The system then returns to stand by mode 307, with the current draw dropping to very low levels. Figure 4 shows a more detailed block diagram representation of a probe unit of a system embodying the invention.

There is a transducer 450 which is transmits ultrasound energy Into a body to be scanned, and receives the resultant echoes.

The transducer Is connected alternately to transmit and receive circuitry via a diplexer 451. The transmit circuitry includes a high voltage power supply and a high voltage transmitter 453.

The receive circuitry consists of analogue componentry to receive and process the returned echo signals from the transducer, collectively referred to as the analogue path. The analogue path receives the output of the transducer as an Input and provides digital data as an output, for combination with orientation data for transmission to a display and processing unit (DPU) (not shown) for display as an ultrasound image.

The analogue path Includes a low noise amplifier 454 which receives the low amplitude electrical signal corresponding to received echoes which are produced by the transducer and amplifies it significantly.

The amplified signal Is then passed to a time gain amplifier 455, The time gain amplifier acts broadly to compensate for the fact that ultrasound signals are attenuated by the tissue of the body being βcanned. Thus, signals from deeper within the body are relatively weaker than those from shallower regions. In order to show a result which Is proportional to the reflectivity of the feature being scanned rather than Its depth, a generally ramp shaped amplification function is applied by the time gain amplifier to the received signal.

The adjusted signal is then passed to an anti-aliasing filter 456. This is a bandpass filter which ensures that the aliasing Introduced by the next process, which is analogue to digital conversion, is minimized. The signal is then converted to a digital signal by the analogue to digital converter (ADC) 457.

The digital data Is then passed to the main digital processor 403 for processing.

There is also provided a gyroscope 458 for detecting the orientation of the probe S unit. This data is provided to the main digital processor 403 for combination with the received echo intensity data to form a scaπliπe.

There is provided a low power microprocessor 401 which communicates with a display and processing unit (DPU) via a low power, low speed communications channel 402. In this embodiment, the communication channel Is an I2C bus. This0 communication channel and microprocessor are active are powered and active at substantially all times that the system is turned on. The current drawn by the microprocessor and the communications channel components Is less than 100μA.

A command to initiate a scan is received from the DPU via the low speed communications channel 402. The microprocessor provides a signal which gates5 power to a main digital processor, implemented In this embodiment as an FPGA 403.

The FPGA 403 is divided Into a low speed section 404 and a high speed section 405. On Initial power up, only the low speed section is active. This section allows the main digital processor to communicate with the DPU via the low speed0 communications channel 402. The DPU communicates to the main digital processor the required set up parameters for the scan to be performed. The current draw during this process is less than 10mA.

Once setup is complete, the high speed section of the FPGA becomes active. The system now moves into a pre-charge process. The FPGA high speed section 405 includes controllers for the components of the analogue path.

There Is a gyroscope controller 408 which communicates with the gyroscope 458. The gyroscope 458 Is powered up. Initially, the gyroscope controller keeps the gyroscope in a low power, stand by mode. There is an ADC controller 409 which controls ADC 457 and a time gain amplifier controller 407 which controls time gain amplifier 455. These devices are powered up but the controllers Initially control the respective devices to be in a low power stand by modθ.

During this pre-charge process, current draw is less than 40OmA.

There Is a high speed data communications channel 460 for communicating scan data from the probe unit to the DPU. This channel now becomes active.

There is a high voltage power supply 452, which acts to transform the low voltage power supplied from the battery to the high voltage required for driving the ultrasound transducer. This high voltage supply Is now powered up.

The system Is now ready to scan. There is a transmitter controller 406 which controls the transmitter 453 to drive the transducer with the pulse rate and wave pattern required for the scan.

The scan Is now performed. The transducer Is driven to transmit an ultrasound pulse into a body to be scanned and receives the returned echoes. The electrical signals of the returned echoes are passed to the analogue circuitry for processing. The resultant scaπline data is received by th FPGA via a filter 430. The resultant scanllnes are transmitted via the high speed communications link 460 to the DPU for display. During this process, current draw is at peak, but still less than 70OmA.

When the scan is completed, all elements of the circuit are Immediately powered down, with the exception of the low speed section 404 of the main digital processor and the microcontroller 401.

The low speed section 404 remains active for long enough to communicate any error messages to the DPU and to reply to any tear down queries from the DPU. This section is then powered down.

Power consumption of electronic devices increases with increasing clock speed. Further, In the absence of clock pulses, such devices do not perform their function, and hence use very little power, even if powered on.

It is usual In prior art ultrasound scanners to simply provide a clock which runs at the speed required by the fastest device. If other devices require slower clock speeds, a single clock Is used and clock enabling circuitry is employed. Clock Enable signals are supplied to all clocked devices whilst the system Is powered up. In the current invention, the clock distribution is controlled such that all . components run at the lowest practical operating frequency. Where possible, clock signals are provided to components only at such stages of operation as require the operation of that component. This operation is illustrated in block diagram form in Figure 5. A clock signal is supplied to a clock multiplier 501. This provides two clock outputs, a high speed clock 502 at about ten times the input clock speed, and a low speed clock 503 at about twice the Input clock speed.

In combination with gates 504 and 505, these clocks provide three clock domains. The low speed clock is supplied directly to the low power section 506 of the FPGA. This drives a low power communications link which provides continuous basic communication between the probe and the DPU. This is a semi permanent low speed clock domain It is always enabled when the FPGA is powered.

The low speed clock is also supplied to a high power section 510 of the FPGA₁ via gate 505. This is a gated low speed clock domain.

The gated low speed clock domain Includes the control circuitry for each of the analogue components. This includes the ADC controller 541, the TGA controller 542 and the gyroscope controller 543.

The high speed clock Is provided, via gate 504, to the high speed communications channel controller 520 within the high power section of the FPGA. Also within this domain is the digital filter 530 which is applied to the data stream from the ADC prior to further processing In the FPGA.

This is illustrated In the timing diagram of Figure 6. The duration of a single scanllne 601 is shown. This is the period of the transmission of a single pulse burst and the reception of the associated echoes.

The ADC clock plot 602 shows the period for which clock pulses are supplied to the ADC 457. As can be seen, no clock Is provided to the ADC when a scanline acquisition is not In progress.

Clock signals are provided to the gyroscope intermittently as shown in the plot 603. Clock bursts are provided at the gyroscopes refresh rate. The time gain amplifier requires clock signals only during setup and configuration as shown by plot 604. The first clock burst allows configuration of the Initial gain and a second clock burst allows configuration of the gain ramp.

Prior art devices either uniformly move a transducer or uniformly sweep a transducer array in order to provide B-mode scanning. Since the rate of sweep Is mechanically or electronically determined, the transducer need only emit ultrasound bursts at a regular rate with respect to time to ensure that the sector to be scanned is uniformly covered with scanllnes.

When the probe unit Is being manually scanned, significant variation of speed of movement relative to the subject being scanned, within a single scan, is possible. Indeed some variation Is inevitable for even the steadiest handed manual operator.

When the scanllnes are produced regularly in time, this will mean that the sector being scanned Is not evenly covered with scaπlines. In this case, the scan rate will be chosen to ensure that the area which is swept most rapidly is covered by sufficient scanlines to achieve a required lateral resolution. Since this most rapid scan speed will not be known exactly, a high scan rate appropriate to the highest likely sweep speed will be chosen.

This resultant relatively high scan rate means that in most cases, significantly more scanllnes are produced than are necessary. This wastes power. It also increases the exposure of the subject tα ultrasound. Ultrasound is very safe, but there are nonetheless limits set by medical standards bodies as to the lsonificatlon to which a patient may be exposed. Wasted scanlines reduce the Intensity of the iaonϊficatlon which may be employed by the scanner. It is advantageous to link the production of scanlines to the physical movement of the probe unit.

In an embodiment where the βensor Is purely an orientation sensor, for example a single gyroscope, the transmitter is controlled to excite the transducer when and only when the sensor Indicates that the probe unit has been rotated a specified angle. In an embodiment where the sensor senses only translatlonal movement, the transmitter Is controlled to excite the transducer when and only when the probe unit has been moved laterally a specified distance.

The specified angle or distance may be default values or may be specified by a user for a given scan.

This has the effect that the sector to be scanned Is swept with only the required minimum number of scaπlines required to achieve the desired resolution. This reduces the number of scanlinβs produced, which saves power.

The term hand held as used in this specification and appended claims should be taken to encompass any portable device primarily operating disconnected from mains power.

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 apparatus.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS

1. A hand held ultrasound scan apparatus Including a main power supply; and a high voltage power supply; and a transmitter which excites a transducer to transmit ultrasound pulses, s said transducer receiving returned echoes from said pulses and providing an output electrical signal proportional to the magnitude of the returned echoes; analogue circuitry adapted to receive, amplify, filter and digitise said electrical signal; digital circuitry adapted to process the digitised electrical signal and to0 communicate with a user control and display unit to control and to display the results of an ultrasound scan; control circuitry adapted to control the flow of power from the main power supply such that circuit elements of the apparatus are powered up In a sequence said sequence being such that circuit elements are provided with5 power substantially only when performing a required function.

2. The apparatus of claim 1 wherein the control circuitry operates such that the sequence Includes a first power up stage wherein power Is provided only to that part of the digital circuitry providing basic communications with the display device; 0 the sequence including a second power up stage wherein that part of the digital circuitry performing a main processing function is supplied with power; the sequence including a third power up stage wherein the high voltage power supply and the transmitter are supplied with power; the sequence including a fourth power up stage wherein the analogue circuitry is supplied with power, the sequence including a fifth power up stage wherein clock signals are provided to all said digital circuitry and high voltage pulses are sent from the transmitter to the transducer to cause ultrasound pulses to be transmitted Into a body to be scanned and echoes of said pulses are received and processed.

3. Thθ apparatus of claim 2 further including gating circuitry adapted to control the reticulation of clock pulses such that there are at least two clock domains of differing clock speed.

4. The apparatus of claim 2 further including gating circuitry adapted to control the reticulation of clock pulses such that there are at least two clock domains which are active over differing time periods.

5. The apparatus of claim 3 or claim 4 further including clock enable circuitry adapted to ensure clock pulses are supplied to elements of the circuit substantially only during time periods when those circuit elements require clock pulses to perform their function.

β. The apparatus of claim 2 wherein current drain from the main power supply during said first stage Is less than 200 mlcroAmperes; current drain from the main power supply during said second stage Is less than

20 milliAmperas; current drain from the main power supply during said third stage is less than 800 milliAmperβs; current drain from the main power supply during said fourth stage and said fifth stage is less than 1400 mliHAmperes.

7. The apparatus of claim 2 wherein current drain from the main power supply during said first stage is less than 100 mlcroAmperes; current drain from the main power supply during said second stage is less than 10 millϊAmpθrθs; current drain from the main power supply during said third stage is less than 400 mllHAmperes; current drain from the main power supply during said fourth stage and said fifth stage Is less than 700 milNAmperes.

8. A method for operating a hand held ultrasound scanner to achieve low power consumption wherein a supply of power to circuitry adapted to transmit ultrasound pulses and to receive and process returned echoes Is controlled such that elements of the circuitry are provided with power sequentially in such a manner that substantially only elements performing functions which are In operation at a given time are provided with power at that time.

9. The method of claim 8 including controlling the sequential supply of power such that circuitry performing basic communications functionality Is substantially always provided with power in a first power up stage; • receiving a request from a user to Initiate an ultrasound scan; implementing a second power up stage by controlling the sequential supply of power such that circuitry performing a main processing function is supplied with power; implementing a third power up stage by controlling the sequential supply of power such that circuitry of a high voltage power supply and a transmitter are supplied with power; implementing a fourth power up stage by controlling the sequential supply of power such that analogue componentry adapted to receive and process a returned ultrasound signal is supplied with power; implementing a fifth power up stage by providing clock signals to all digital circuitry and providing high voltage pulses from the transmitter to an ultrasound transducer to cause ultrasound pulses to be transmitted Into a body to be scanned and echoes of said pulses to be received and processed.

10. A method for operating a hand held ultrasound scanner having low power consumption Including the steps of providing a stand by mode in which only a first processor is active, said processor providing at least the function of recognising a user command to

Initiate an ultrasound scan; providing a setup mode in which a second processor Is also active, said second processor being adapted to receive and process communications which direct the setting of values for set up parameters for an ultrasound scan; providing a low power pre-charge mode in which a third processor Is active, said third processor being adapted to provide control for analogue circuitry adapted to perform an ultrasound scan, and a high voltage power δupply is also activated, said high voltage power supply being adapted to provide power to an ultrasound transducer under the control of the third processor; . providing a high power pre-charge mode in which said analogue circuitry is supplied with power; providing a scanning mode In which a target to be scanned Is isonlfied and resulting echoes received and analysed by the analogue circuitry; the stand by, setup, low power pre-charge, high power pre-charge and scanning modes being entered sequentially.

11.A hand held ultrasound apparatus Including a probe unit adapted to emit at least one ultrasound beam at a fixed angle relative to the probe unit; an orientation sensor adapted to sense the relative angle at which successive ultrasound beam pulses are directed into a subject to bθ scanned and a controller adapted to control a transmitter such that the ultrasound beam pulses are emitted when and only when the orientation sensor indicates that the probe unit has rotated a selected angle since the transmission of the Immediately preceding pulse.

12.A hand held ultrasound apparatus Including a probe unit adapted to emit at least one ultrasound beam at a fixed angle relative to the probe unit; a position sensor adapted to sense the relative translational position at which successive ultrasound beam pulses are directed Into a subject to be scanned and a controller adapted to control a transmitter such that the ultrasound beam pulses are emitted when and only when the position sensor Indicates that the probe unit has translated a selected distance since the transmission of the Immediately preceding pulse.

13.A hand held ultrasound scan apparatus having low power consumption substantially as described in the specification with reference to and as illustrated by any one or more of the accompanying drawings.

14.A method for operating a hand held ultrasound 3can apparatus with minimal power consumption substantially as described In the specification with reference to and as Illustrated by any one or more of the accompanying drawings.