Patent Description:
Intravenous ultrasound imaging catheters are widely used in a number of different clinical applications. Typically, an ultrasound imaging catheter is fully controlled from a back end processing unit, or console. For each ultrasound transducer element in the ultrasound imaging catheter, it needs to be decided whether the transducer element is active during transmission of an ultrasonic pulse and whether the transducer element should be active during the reception of echoes from the transmitted pulse.

In order to improve the imaging quality of ultrasound imaging catheters, attempts have been made to increase the number of transducer elements that can be located at the tip of the catheter.

By increasing the number of transducer elements, and increasing the number of return channels for the echoes, the full control of the array of transducer elements at the catheter tip by the console causes significant challenges, such as steep signal slopes and high bandwidth requirements, resulting in increased strain on the communication between the console and the catheter.

Typically, communication channels in ultrasound imaging catheter systems are comprised of wires having relatively high resistances and capacitances, due to mechanical requirements, causing interference in the communication signals and degrading the accuracy of the images produced by the ultrasound imaging catheter.

<CIT> discloses an ultrasonic imaging system in which a column-row-parallel architecture is provided at the circuit level of an ultrasonic transceiver. The ultrasonic imaging system includes an N×M array of transducer elements and a plurality of transceiver circuits, where each transceiver circuit is connected to a corresponding one transducer element of the N×M array of transducer elements. A shared pulser gate driver and a shared VGA is provided for each row and column. Selection logic includes row select, column select, and per-element bit select.

<NPL>, discloses the design of an integrated circuit (IC) that is flip-chip bonded to a <NUM> × <NUM>-element CMUT array. The IC provides <NUM> receive channels which are configured to receive along either of the array diagonals or on any single row of the array.

There is therefore a need for an improved means of handling communication between the ultrasound imaging catheter and the control console.

According to examples in the disclosure, there is provided an ultrasound imaging catheter, the ultrasound imaging catheter comprising:.

In this way, the functionality of the front end of the ultrasound imaging catheter may be increased, thereby reducing the amount of communication required between the front end and a back end processing unit, thereby providing for a means of implementing higher frame rates, higher numbers of transducer elements in the transducer array and a higher number of echo return channels. The ultrasound imaging catheter further comprises:.

In this way, an asynchronous communication scheme may be implemented in the ultrasound imaging catheter front end, which would otherwise require a free running clocking signal in order to provide superfluous signal edges in order to initiate the manipulation of the registers.

The local oscillator is adapted to operate outside of the imaging phase of the ultrasound imaging catheter. In this way, potential imaging artifacts due to signal feedthrough or crosstalk from the local oscillator may be avoided.

Alternatively or additionally, the local oscillator is adapted to operate at a frequency that is greater than a bandwidth of the plurality of ultrasound transducers. In this way, imaging artifacts caused by a local oscillator may be reduced, or eliminated.

Alternatively or additionally, the local oscillator is adapted to generate a square wave having a predetermined duty cycle of. The duty cycle is such that components of the local oscillator's frequency spectrum are outside the bandwidth of the plurality of ultrasound transducers. In this way, the harmonics of the local oscillator are made to be outside of the bandwidth of the ultrasound transducers, thereby reducing any imaging artifacts caused by the local oscillator.

In an embodiment, the plurality of registers are arranged into a plurality of register groups, each register group comprising:.

By providing individual registers for each function, a greater flexibility in the activation pattern and its application may be achieved.

In a further embodiment, the ultrasound transducer array comprises a plurality of output channels, and wherein each register group further comprises a third register, comprising a third register bit, and wherein the transducer element is further associated with the third register bit, which is adapted to control which of the plurality of output channels a signal received at the transducer element is output to.

In an embodiment, the plurality of register groups are connected in a daisy chain, wherein each register group is connected in series with an adjacent register group.

In this way, the number of connections required in the catheter front end may be reduced, without negatively impacting the functionality of the ultrasound imaging catheter.

In an embodiment, the ultrasound imaging catheter further comprises a signal conditioning unit provided at the distal end of the ultrasound imaging catheter adapted to apply signal conditioning to the received ultrasound signals.

In this way, the signals may be conditioned before being sent to the back end processing unit, thereby reducing imaging artifacts that may be accentuated during transmission and so increasing the accuracy of the final ultrasound image.

In a further embodiment, the signal conditioning unit comprises a low noise amplifier.

In an embodiment, the signal conditioning unit comprises one or more time gain compensation units.

According to examples in accordance with an aspect of the invention, there is provided an ultrasound imaging system, the system comprising:.

According to examples in the disclosure, there is provided a method for controlling an ultrasound imaging catheter comprising an ultrasound transducer array having a plurality of ultrasound transducers, the method comprising:.

According to examples in the disclosure, there is provided a computer program comprising computer program code means which is adapted, when said computer program is run on a computer, to implement the method described above.

For a better understanding of the invention, and to show more clearly how it may be implemented, reference will now be made, by way of example only, to the accompanying drawings, in which:.

The invention provides an ultrasound imaging catheter comprising an ultrasound transducer array provided at a distal end of the ultrasound imaging catheter and adapted to transmit and receive ultrasound signals, wherein the ultrasound transducer array comprises a plurality of ultrasound transducers. The ultrasound imaging catheter further includes a local memory provided at the distal end of the ultrasound imaging catheter adapted to store a plurality of activation patterns, wherein each activation pattern corresponds to a number of transducer elements of the plurality of transducer elements to be activated and a number of transducer elements of the plurality of transducer elements to be deactivated. In addition, the ultrasound imaging catheter includes a control unit provided at the distal end of the ultrasound imaging catheter adapted to: access the local memory; select any one of the plurality of activation patterns; and generate a control signal to activate or deactivate the plurality of transducer elements of the transducer array according to the selected activation pattern during an imaging phase of the ultrasound imaging catheter, the imaging phase comprising a transmit period and a receive period.

The general operation of an exemplary ultrasound system will first be described, with reference to <FIG>.

The system comprises an array transducer probe <NUM> which has a transducer array <NUM> for transmitting ultrasound waves and receiving echo information. The transducer array <NUM> may comprise CMUT transducers; piezoelectric transducers, formed of materials such as PZT or PVDF; polymer based transducers; or any other suitable transducer technology. In this example, the transducer array <NUM> is a two-dimensional array of transducers <NUM> capable of scanning either a 2D plane or a three dimensional volume of a region of interest. In another example, the transducer array may be a 1D array.

The transducer array <NUM> is coupled to a microbeamformer <NUM> which controls reception of signals by the transducer elements. Microbeamformers are capable of at least partial beamforming of the signals received by sub-arrays, generally referred to as "groups" or "patches", of transducers as described in <CIT>), <CIT>), and <CIT>).

It should be noted that the microbeamformer is entirely optional. Further, the system includes a transmit/receive (T/R) switch <NUM>, which the microbeamformer <NUM> can be coupled to and which switches the array between transmission and reception modes, and protects the main beamformer <NUM> from high energy transmit signals in the case where a microbeamformer is not used and the transducer array is operated directly by the main system beamformer. The transmission of ultrasound beams from the transducer array <NUM> is directed by a transducer controller <NUM> coupled to the microbeamformer by the T/R switch <NUM> and a main transmission beamformer (not shown), which can receive input from the user's operation of the user interface or control panel <NUM>. The controller <NUM> can include transmission circuitry arranged to drive the transducer elements of the array <NUM> (either directly or via a microbeamformer) during the transmission mode.

In a typical line-by-line imaging sequence, the beamforming system within the probe may operate as follows. During transmission, the beamformer (which may be the microbeamformer or the main system beamformer depending upon the implementation) activates the transducer array, or a sub-aperture of the transducer array. The sub-aperture may be a one dimensional line of transducers or a two dimensional patch of transducers within the larger array. In transmit mode, the focusing and steering of the ultrasound beam generated by the array, or a sub-aperture of the array, are controlled as described below.

For each line (or sub-aperture), the total received signal, used to form an associated line of the final ultrasound image, will be a sum of the voltage signals measured by the transducer elements of the given sub-aperture during the receive period. The resulting line signals, following the beamforming process below, are typically referred to as radio frequency (RF) data. Each line signal (RF data set) generated by the various sub-apertures then undergoes additional processing to generate the lines of the final ultrasound image. The change in amplitude of the line signal with time will contribute to the change in brightness of the ultrasound image with depth, wherein a high amplitude peak will correspond to a bright pixel (or collection of pixels) in the final image. A peak appearing near the beginning of the line signal will represent an echo from a shallow structure, whereas peaks appearing progressively later in the line signal will represent echoes from structures at increasing depths within the subject.

In addition, upon receiving the echo signals from within the subject, it is possible to perform the inverse of the above described process in order to perform receive focusing. In other words, the incoming signals may be received by the transducer elements and subject to an electronic time delay before being passed into the system for signal processing. The simplest example of this is referred to as delay-and-sum beamforming. It is possible to dynamically adjust the receive focusing of the transducer array as a function of time.

The structural and motion signals produced by the B mode and Doppler processors are coupled to a scan converter <NUM> and a multi-planar reformatter <NUM>. The scan converter <NUM> arranges the echo signals in the spatial relationship from which they were received in a desired image format. In other words, the scan converter acts to convert the RF data from a cylindrical coordinate system to a Cartesian coordinate system appropriate for displaying an ultrasound image on an image display <NUM>. In the case of B mode imaging, the brightness of pixel at a given coordinate is proportional to the amplitude of the RF signal received from that location. For instance, the scan converter may arrange the echo signal into a two dimensional (2D) sector-shaped format, or a pyramidal three dimensional (3D) image. The scan converter can overlay a B mode structural image with colors corresponding to motion at points in the image field, where the Doppler-estimated velocities to produce a given color. The combined B mode structural image and color Doppler image depicts the motion of tissue and blood flow within the structural image field. The multi-planar reformatter will convert echoes that are received from points in a common plane in a volumetric region of the body into an ultrasound image of that plane, as described in <CIT>). A volume renderer <NUM> converts the echo signals of a 3D data set into a projected 3D image as viewed from a given reference point as described in <CIT>).

The 2D or 3D images are coupled from the scan converter <NUM>, multi-planar reformatter <NUM>, and volume renderer <NUM> to an image processor <NUM> for further enhancement, buffering and temporary storage for display on an image display <NUM>. The imaging processor may be adapted to remove certain imaging artifacts from the final ultrasound image, such as: acoustic shadowing, for example caused by a strong attenuator or refraction; posterior enhancement, for example caused by a weak attenuator; reverberation artifacts, for example where highly reflective tissue interfaces are located in close proximity; and so on. In addition, the image processor may be adapted to handle certain speckle reduction functions, in order to improve the contrast of the final ultrasound image.

In addition to being used for imaging, the blood flow values produced by the Doppler processor <NUM> and tissue structure information produced by the B mode processor <NUM> are coupled to a quantification processor <NUM>. The quantification processor produces measures of different flow conditions such as the volume rate of blood flow in addition to structural measurements such as the sizes of organs and gestational age. The quantification processor may receive input from the user control panel <NUM>, such as the point in the anatomy of an image where a measurement is to be made.

Output data from the quantification processor is coupled to a graphics processor <NUM> for the reproduction of measurement graphics and values with the image on the display <NUM>, and for audio output integrated into the display device <NUM>. The graphics processor <NUM> can also generate graphic overlays for display with the ultrasound images. These graphic overlays can contain standard identifying information such as patient name, date and time of the image, imaging parameters, and the like. For these purposes the graphics processor receives input from the user interface <NUM>, such as patient name. The user interface is also coupled to the transmit controller <NUM> to control the generation of ultrasound signals from the transducer array <NUM> and hence the images produced by the transducer array and the ultrasound system. The transmit control function of the controller <NUM> is only one of the functions performed. The controller <NUM> also takes account of the mode of operation (given by the user) and the corresponding required transmitter configuration and band-pass configuration in the receiver analog to digital converter. The controller <NUM> can be a state machine with fixed states.

<FIG> shows a schematic representation <NUM> of an ultrasound imaging catheter <NUM>.

The ultrasound imaging catheter <NUM> comprises an ultrasound transducer array <NUM> provided at a distal end of the ultrasound imaging catheter comprising a plurality of ultrasound transducers <NUM>.

The ultrasound imaging catheter <NUM> further comprises a local memory (LM) <NUM> provided at the distal end of the ultrasound imaging catheter, which is adapted to store a plurality of activation patterns. Each of the plurality of activation patterns corresponds to a number of transducer elements of the plurality of transducer elements to be activated 125a and a number of transducer elements of the plurality of transducer elements to be deactivated 125b during an imaging phase of the ultrasound imaging catheter.

The imaging phase may be regarded as two distinct periods, a transmit period, where ultrasound signals are generated by the ultrasound transducers and transmitted into the subject, and a receive period, wherein echoes from the transmitted ultrasound transducers are received at the ultrasound transducers.

In addition, the ultrasound imaging catheter <NUM> comprises a control unit (CU) <NUM> provided at the distal end of the ultrasound imaging catheter adapted to access the local memory and select any one of the plurality of activation patterns stored in the local memory.

The control unit then generates a control signal <NUM> to activate or deactivate the plurality of transducer elements of the transducer array according to the selected activation pattern. In the example shown in <FIG>, the LM <NUM> is manipulated by the CU <NUM> in order to pass control signal <NUM> to the transducers, thereby controlling the transducer activity. The CU <NUM> also acts as the communication link between the circuitry at the distal end of the ultrasound imaging catheter <NUM> and the rest of the ultrasound system.

By locating the local memory <NUM> and the control unit <NUM> at the catheter, rather than at a back end processing unit, the required communication between a back end console and the catheter is reduced.

Put another way, operational control features are added to the catheter, such that it may independently perform at least part of the manipulations in transmit element selection, receive element selection and/or return channel selection. This results in significantly reduced communication requirements between a console and the catheter, allowing higher frame rates, a higher number of ultrasound transducer elements, and higher number of echo return channels to be employed in the system.

The ultrasound imaging catheter may act as the ultrasound probe <NUM> described above with reference to <FIG>.

<FIG> shows a schematic representation <NUM> of the ultrasound imaging catheter <NUM> of <FIG> in greater detail.

In the example shown in <FIG>, the ultrasound imaging catheter <NUM> is shown as having two component groups, a digital part <NUM> and an analog part <NUM>.

In the digital part <NUM> there is a two wire serial interface (SI) <NUM>, which may for example be in communication with a console or any other suitable back end processing unit for controlling the ultrasound imaging catheter <NUM>. Signals may be provided through the serial interface to a parameter control unit (P) <NUM> adapted to set and read back parameters for controlling the operation of both the analog part <NUM> and the digital part <NUM> of the ultrasound imaging catheter.

The digital part <NUM> further comprises a transducer selection unit (TSU) <NUM>, which may comprise the local memory <NUM> and control unit <NUM> described above with reference to <FIG>.

The transducer selection unit determines which transducer elements of the transducer array <NUM> should be active during a transmit period, and which transducer elements will be used during a receive period. This is done by way of the control unit accessing the local memory to retrieve one of a plurality of activation patterns.

In the example shown in <FIG>, the transducer selection unit generates a control signal <NUM>, which is provided to a driver unit (D) <NUM> and a receiver unit (R) <NUM>. The driver unit activates ultrasound transducers of the transducer array during the transmit period according to the control signal received from the transducer selection unit. Similarly, the receiver unit activates ultrasound transducers of the transducer array during the receive period according to the control signal received from the transducer selection unit.

In other words, the transducers of the ultrasound transducer array are activated according to a control signal generated by a transducer selection unit, which is based on an activation pattern, during the transmit and receive periods of an imaging phase.

Put another way, the transducer elements of a transducer array located at the distal end of an ultrasound imaging catheter are activated based on an activation pattern stored in a local memory also located at said distal end.

During the transmit phase, the ultrasound transducers selected as active according to the activation pattern are operated to generate an ultrasonic pulse, for example when the ultrasound imaging catheter is located inside a subject, such as within a vessel of the subject.

During the receive phase, the ultrasound transducers receive echo signals <NUM> from the subject's body. The received echo signals may undergo signal conditioning prior to sending the appropriate echo signals to the back end processing system.

In the example shown in <FIG>, the analog part <NUM> of the ultrasound imaging catheter <NUM> comprises a low noise amplifier <NUM> to condition the incoming received echo signals; however, any other signal conditioning unit may be implemented in the analog part, such as a time gain compensation unit.

The conditioned signals are then passed to a signal selector (SS) <NUM>, which may apply selection criteria to the conditioned signals in order to decide which signals may be sent to a back end processing in order to generate an ultrasound image. The selection criteria may, for example, include a given measure of signal quality, such as a signal to noise ratio. The selection criteria may be adjusted, for example by way of a user input, according to an application of the ultrasound imaging catheter.

When the transducer selection unit receives a signal <NUM> to initiate a "give next acquisition" instruction, i.e. an instruction to begin a subsequent imaging phase, the transducer selection unit determines the transducers that will be used for the next imaging actions as transmit and receive elements. More specifically, the instruction may cause the control unit to access the local memory in order to select an activation pattern corresponding to the transducers to be activated or deactivated.

<FIG> shows an example implementation <NUM> of the digital part <NUM> of the ultrasound imaging catheter of <FIG>.

In the example shown in <FIG>, the intelligence level of the transducer selection unit is slightly reduced with respect to the example described with respect to <FIG>. As a result the communication requirements between the back end processing unit, or console, and the ultrasound imaging catheter may be slightly increased, although the communication requirements are still significantly reduced when compared to a standard ultrasound imaging catheter. However, this example may provide for more flexibility in determining the ultrasound elements to be activated or deactivated during the transmit period and the receive period. Further, this example may also increase the flexibility in the return channel selection for sending the received echo signals to the back end processing system.

The example shown in <FIG> operates using two communication mechanisms. The first communication interface <NUM> is a serial interface for setting and reading back parameters for both the analog and digital parts of the ultrasound imaging catheter as described above with reference to <FIG>. The serial interface may be connected to an I<NUM>C interface <NUM>, which operates based on two signals, a serial clock (SCL) signal and a serial data (SDA) signal.

The second communication interface <NUM> may comprise a high-speed serial (HS) interface <NUM>, which is a unidirectional equivalent of the "give next acquisition" instruction described above with respect to <FIG>.

<FIG> shows several dies located in the ultrasound imaging catheter; one master die <NUM> and multiple slave dies <NUM>. The first communication interface <NUM>, which may include an I<NUM>C interface <NUM>, may be implemented such that it is the same for all dies. The die type, master die <NUM> or slave die <NUM>, may be determined by three address pins on the I<NUM>C interface unit. If the address pins read "<NUM>", the die is considered to be the master die <NUM>. If on the other hand the address pins read between "<NUM>" and " <NUM><NUM><NUM>", the die is considered to be a slave die <NUM>. In this example, the maximum allowable number of slave dies <NUM> is seven; however, the number of slave dies may be expanded or reduced according to the application.

The I<NUM>C interface unit <NUM> of the slave dies <NUM> may be connected to analog circuity, which may comprise components such as the low noise amplifier (LNA) and/or the time gain compensation (TGC) as described above with reference to <FIG>, as well as connecting a slave unit <NUM> in each slave die <NUM>. The slave unit <NUM> is a piece of circuitry that provides an indication for each ultrasound transducer <NUM> whether it is to active or inactive during transmit, during receive, and on which output channel the received echo signals should be placed.

In the example shown in <FIG>, each slave die <NUM> can address a maximum of twenty four individual transducers <NUM>, the information relating to: which transducer elements are active during the transmit periods; which transducer elements are active during the receive periods; and which output channel a received echo signal is provided to being held on three twenty four bit registers. Accordingly, with a maximum of seven slaves, catheters with up to one hundred and sixty eight transducer elements may be constructed according to this implementation.

The first communication interface <NUM> and the second communication interface <NUM> are fully asynchronous, means that clock edges in the communication protocols themselves are used to register data. In other words, there is no free running clock in the catheter that can be used to sample the communication interfaces. For several reasons, such as electromagnetic compatibility (EMC) and potential image artefacts, it may be advantageous to not have a free running clock in the catheter during imaging phases. As the number of clock edges in the two communication interfaces is matched with the data being transferred, there are no superfluous edges available for the HS interface <NUM> to manipulate the information in the registers of the slave units, and so apply the information contained in an application pattern to the ultrasound transducers <NUM>.

Accordingly, the ultrasound imaging catheter may further comprise a local oscillator (LO) <NUM> in communication with the plurality of registers and adapted to receive the control signal generated by the control unit and manipulate the plurality of bits in the plurality of registers to activate and/or deactivate the plurality of transducer elements of the transducer array according to the selected activation pattern.

The local oscillator <NUM> may be located on the master die <NUM> that can be started by the HS unit <NUM> in order to perform the required manipulations of the registers. The manipulating of registers by the HS unit, and thus running the local oscillator only occurs outside the imaging phases, thereby preventing potential image artefacts due to, for example, local oscillator feedthrough or crosstalk. Another mechanism employed to prevent image artefacts by the local oscillator is to ensure the lowest frequency of the local oscillator is above the bandwidth of the ultrasonic transducers <NUM>. The local oscillator may be adapted to produce a square wave with a given duty cycle in order to bring the harmonics of the local oscillator outside of the bandwidth of the ultrasonic transducers. For example, the duty cycle may be <NUM>%, or <NUM>%, or indeed any suitable duty cycle that ensures that the spectral components of the oscillator are outside of the bandwidth of the plurality of ultrasound transducers.

<FIG> shows an example <NUM> of interconnections between registers <NUM> of different slave units <NUM> on the slave dies <NUM>. Each register comprises a plurality of bits, wherein each bit is associated with an ultrasound transducer of the plurality of ultrasound transducers in the transducer array of the ultrasound imaging catheter.

In the example shown in <FIG>, each slave unit <NUM> comprises three registers <NUM>, which include: a transmit register Tx adapted to control which of the associated transducer elements are activated or deactivated during the transmit period; a receive register Rx adapted to control which of the associated transducer elements are activated or deactivated during the receive period; and an output channel register Rxmap adapted to control which of the plurality of output channels a signal received at the transducer element is output to. In this case, a given transducer element will be associated with one bit from each of the three registers of a given slave unit.

In order to limit the amount of connections required between the slave dies, the registers for transmit (Tx), receive (Rx), and mapping to an output channel (Rxmap) may be connected via a single connection to the next die.

A single connection between dies, also referred to as a daisy chain connection, means that the manipulation of the transmit register, the receive register and the output channel register must be performed sequentially.

To select the appropriate number of transducer elements, there are two methods available: selecting the number of slave dies in the catheter, with a maximum of seven; and selecting the number of elements controlled per die, with a maximum of twenty four.

In the implementation described above, a slave die can control twenty four transducer elements. It is also possible to connect fewer transducer elements to a slave die. The number of transducer elements that are connected into the register daisy chain as shown in <FIG> may be set by a parameter in the I<NUM>C interface unit <NUM> described in <FIG>. The HS unit <NUM> does not need to be aware of the exact number of transducer elements in the register daisy chain, since the register cells are connected in a daisy chain and no data can may be lost by shift operations. If, for example, a one hundred and fourteen element catheter is required, five slave dies should be used, four of which will control twenty four elements and one of which will control eighteen elements.

<FIG> shows a conceptual representation <NUM> of the transmit Tx register, the receive Rx register and the output channel Rxmap register in relation to the circular catheter circumference, slave die <NUM> boundaries and transducer elements <NUM>. <FIG> shows some example data, and a meaning for the three register chains.

Looking to transducer element <NUM>, as indicated by the arrow, the registers indicate that this element is to be used for transmitting an ultrasonic pulse, as indicated by the <NUM> in the transmit Tx register, used for echo reception, as indicated by the <NUM> in the receive Rx register, and the received echo will be transmitted via channel <NUM>, as indicated by the <NUM> in the output channel Rxmap register. A <NUM> in the transmit register or the receive register would indicate that the element would be inactive for the transmit or receive period, respectively. A <NUM> in the channel output register would indicate that the received echo should be output on channel <NUM>.

It should be noted that the transmit Tx register, the receive Rx register and the output channel Rxmap register, and the combination of the Tx, Rx, and Rxmap bits together, as shown in <FIG> and <FIG> above may be part of the local memory (LM) <NUM> as described with reference to <FIG>.

<FIG> shows a method <NUM> for controlling an ultrasound imaging catheter comprising an ultrasound transducer array having a plurality of ultrasound transducers.

The method begins in step <NUM> by accessing a local memory provided at the distal end of the ultrasound imaging catheter;
In step <NUM>, any one of a plurality of activation patterns stored on the local memory is selected, wherein each activation pattern corresponds to a number of transducer elements of the plurality of transducer elements to be activated and a number of transducer elements of the plurality of transducer elements to be deactivated.

In step <NUM>, a control signal to activate or deactivate the plurality of transducer elements of the transducer array according to the selected activation pattern during an imaging phase of the ultrasound imaging catheter is generated, the imaging phase comprising a transmit period and a receive period.

In step <NUM>, the control signal is provided to a local oscillator.

In step <NUM>, a plurality of bits of a plurality of registers is manipulated to activate and/or deactivate the plurality of transducer elements of the transducer array according to the selected activation pattern, wherein each bit is associated with an ultrasound transducer of the plurality of ultrasound transducer.

Claim 1:
An ultrasound imaging catheter (<NUM>), comprising:
an ultrasound transducer array (<NUM>) provided at a distal end of the ultrasound imaging catheter and adapted to transmit and receive ultrasound signals, wherein the ultrasound transducer array comprises a plurality of ultrasound transducer elements (<NUM>);
a local memory (<NUM>) provided at the distal end of the ultrasound imaging catheter adapted to store a plurality of activation patterns, wherein each activation pattern corresponds to a number of transducer elements of the plurality of transducer elements to be activated and a number of transducer elements of the plurality of transducer elements to be deactivated;
a control unit (<NUM>) provided at the distal end of the ultrasound imaging catheter adapted to:
access the local memory;
select any one of the plurality of activation patterns;
generate a control signal (<NUM>) to activate or deactivate the plurality of transducer elements of the transducer array according to the selected activation pattern during an imaging phase of the ultrasound imaging catheter, the imaging phase comprising a transmit period and a receive period;
wherein the ultrasound imaging catheter further comprises:
a plurality of registers (<NUM>), each register comprising a plurality of bits, wherein each bit is associated with an ultrasound transducer element of the plurality of ultrasound transducer elements;
a local oscillator (<NUM>) in communication with the plurality of registers and adapted to receive the control signal generated by the control unit and manipulate the plurality of bits in the plurality of registers to activate and/or deactivate the plurality of transducer elements of the transducer array according to the selected activation pattern; characterized in at least one of:
the local oscillator being adapted to operate outside of the imaging phase of the ultrasound imaging catheter;
the local oscillator being adapted to operate at a frequency that is greater than a bandwidth of the plurality of ultrasound transducer elements;
the local oscillator being adapted to generate a square wave having a given duty cycle, wherein the given duty cycle is such that components of the local oscillator's frequency spectrum are outside the bandwidth of the plurality of ultrasound transducer elements.