Patent Description:
While offering high resolution, ultrasound image acquisition with focused beam transmissions and dynamic receive beamforming poses a time limit to the real time volumetric imaging. Compared to unfocused beam imaging methods, it takes about an order of magnitude longer for focused beam transmissions to cover a three-dimensional (3D) imaging region-of-interest (ROI), which results in a much slower frame rate. This can be a serious problem for imaging applications where high frame rate is important such as 3D cardiac imaging. For faster imaging, unfocused ultrasound transmissions may be used. Unfocused transmissions may illuminate a much larger portion of the ROI with a single transmission compared to focused beam transmissions. These unfocused transmissions may consist of plane waves or spherically or cylindrically diverging waves.

Ultrasound probes with two-dimensional (2D) transducer arrays may be used for faster and/or higher resolution 3D imaging. However, 2D transducer arrays may have an array of hundreds or thousands of transducer elements which need to be coupled to the imaging system. To avoid a large number of wires between an ultrasound probe and the imaging system base, some ultrasound probes include microbeamformers. A microbeamformer receives signals from the individual transducer elements and performs some preliminary beamforming operations to combine signals from groups of transducer elements (e.g., sub-arrays, patches) into an output signal. The preliminary beamforming operations may include applying delays to the signals from the individual transducer elements and then summing the delayed signals to generate the output signal. The number of output signals may be based on the number of patches the transducer array is divided into. Combining the signals of groups of individual transducer elements into output signals may reduce the number of channels required. For example, an ultrasound probe may have <NUM> output channels coupled to the ultrasound system base. However microbeamformers are typically designed for focused transmit beams and image quality may start to degrade when the receive beam is steered away from the transmit beam main axis. Implementing diverging and plane wave imaging with transducer arrays coupled to microbeamformers may degrade image contrast and introduces grating-lobe artifacts. A technique for combining the potential high speed 3D imaging capabilities of diverging and plane wave imaging with transducer arrays including microbeamformers with reduced image degradation is desired.

"<NPL>, discloses an approach for multiplexing ultrasound signals for reducing a number of coaxial cables required.

Methods and systems for microbeamforming operations that may increase image acquisition speed and quality are disclosed. The microbeamforming and beamforming operations perform encoding and decoding. Instead of constructing an image directly from microbeamformed data, the original data is reconstructed based on a limited number of measurements and image formation is performed based on the reconstruction. A jitter sampling scheme may be used by the microbeamformer to encode data in a manner that is compatible with analog RAM. The microbeamformer encoding may multiplex spatial frequencies over fast time. Based on the output of the coded microbeamformer, the original signal may be reconstructed with a computationally inexpensive inversion method as described herein. An image may be formed from the reconstructed data.

According to examples of the present disclosure, it is provided a system according to claim <NUM>.

According to examples of the present disclosure, it is provided a method according to claim <NUM>.

The following description of certain exemplary embodiments is merely exemplary in nature and is in no way intended to limit the invention or its applications or uses. In the following detailed description of embodiments of the present systems and methods, reference is made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the described systems and methods may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the presently disclosed systems and methods, and it is to be understood that other embodiments may be utilized and that structural and logical changes may be made without departing from the scope of the present system as defined by the appended claims. Moreover, for the purpose of clarity, detailed descriptions of certain features will not be discussed when they would be apparent to those with skill in the art so as not to obscure the description of
the present system. The following detailed description is therefore not to be taken in a limiting sense, and the scope of the present system is defined only by the appended claims.

According to the principles of the present disclosure, rather than using a traditional delay-and-sum approach to combine signals from individual transducer elements, a microbeamformer can be used as an encoder to encode radio frequency (RF) data associated with received echoes and the encoded data may be transmitted from an ultrasound probe to an imaging system base where the encoded data is decoded to reconstruct the original RF data (e.g., signal). An image may then be generated based on the reconstructed data. An image generated from the reconstructed data may have fewer artifacts (e.g., grating lobes) compared to images generated from typical delay-and-sum beamforming. In addition to mitigating the artifacts of microbeamforming, the reconstruction of the original data may allow for more advanced adaptive beamforming algorithms that may require the original channel data.

RF data may be highly correlated and/or compressible (e.g., in fast time) in ultrasound imaging applications. Encoding the RF data may exploit this redundancy and compress the original RF data. However, despite the compression, the original RF data may still be recoverable by decoding the encoded data. This may reduce the amount of data required to be transmitted between the ultrasound probe and the imaging system base.

<FIG> shows simplified diagrams illustrating an imaging system <NUM> with a typical microbeamformer arrangement and an imaging system <NUM> with a microbeamformer arrangement in accordance with examples of the present disclosure. Imaging system <NUM> includes an ultrasound probe <NUM>, which may include a transducer array with individual transducer elements (not shown). The transducer array may transmit ultrasound signals and receive echo signals responsive to the transmitted ultrasound signals. The transducer elements may generate electrical signals (e.g., RF data) responsive to the echo signals. The RF data may be transmitted from the transducer elements to a microbeamformer <NUM>. The microbeamformer may divide the signals from transducer elements into patches. In the example shown in <FIG>, the transducer elements are grouped into two patches P1, P2. The microbeamformer may apply appropriate delays to the signals received from each transducer in a patch and sum the delayed signals into a single output signal OS1, OS2 for each patch P1, P2, respectively. The appropriate delay may be determined, at least in part, on a relative location of a transducer element to other transducer elements in the patch. The output signals OS1 and OS2 may be partially beamformed signals. The output signals OS1 and OS2 may be provided to a main beamformer <NUM> included in a system base <NUM> of the imaging system <NUM>. The main beamformer <NUM> may apply additional delays to the output signals OS1 and OS2 to form a fully beamformed signal BFS used to generate an ultrasound image <NUM>.

Imaging system <NUM> may include ultrasound probe <NUM>, which may include a transducer array with individual transducer elements (not shown), that transmit RF data to a microbeamformer <NUM> that divides the transducer elements into patches P1, P2, similar to system <NUM>. In contrast to system <NUM>, microbeamformer may sample the RF data received from the transducer elements and/or apply delays in a pseudo-random manner then sum the delayed samples of each patch to generate encoded signals ES1, ES2. The encoded signals ES1, ES2 may be provided to a decoder <NUM> located on a system base <NUM>. The decoder <NUM> may reconstruct the original RF data from the encoded signals ES1, ES2. The reconstructed data may be provided to a beamformer <NUM>, which may perform beamforming operations to generate image <NUM>.

According to examples of the present disclosure, a system may include a transducer array including a plurality of transducer elements. The transducer elements may be configured to receive ultrasound echoes and convert the ultrasound echoes into electrical signals (e.g., RF data, RF signals). The system may include a microbeamformer coupled to the plurality of transducer elements. The microbeamformer may include a first delay line coupled to a first transducer element of the plurality of transducer elements. The first delay line may include a first plurality of memory cells configured to store the electrical signals received from the first transducer element. The microbeamformer may further include a second delay line coupled to a second transducer element of the plurality of transducer elements. The second delay line may include a second plurality of memory cells configured to store the electrical signals received from the second transducer element. In some examples, the delay lines may be programmable delay lines. In some examples, the plurality of memory cells are configured as a circular buffer. The microbeamformer may be configured to jitter sample the electrical signal stored in the first plurality of memory cells and the second plurality of memory cells and generate a jitter signal. The system may include a decoder configured to receive the jitter signal and generate a reconstructed signal representative of the electrical signals.

In some examples, the system may include a main beamformer configured to generated a beamformed signal based at least in part on the reconstructed signal. In some examples, the main beamformer may include the decoder. In some examples, the system may include a transmit controller, wherein the transmit controller provides delays to be added to the jitter signal by the microbeamformer to focus or steer a beam associated with the ultrasound echoes.

In some examples, the microbeamformer is configured to generate the jitter signal by pseudo-randomly summing the electrical signals sampled from the first plurality of memory cells and the second plurality of memory cells. In some examples, the decoder is configured to apply a covariance matrix to the jitter signal to generate the reconstructed signal, wherein the covariance matrix is based, at least in part, on the jitter sample of the electrical signal stored in the first and second pluralities of memory cells.

In some examples, the microbeamformer is configured to jitter sample the electrical signal stored in the first and second pluralities of memory cells using a pseudo-random pattern of time sample segments. In some examples, the pseudo-random pattern of time sample segments is configured such that individual memory cells of the first plurality of memory cells and the second plurality of memory cells are sampled no more than once per memory cycle.

In some examples, a first subset of the plurality of transducer elements are grouped into a first patch including the first transducer element and a second subset of the plurality of transducer elements are grouped into a second patch including the second transducer element.

<FIG> shows a block diagram of an ultrasound imaging system <NUM> constructed in accordance with the principles of the present disclosure. An ultrasound imaging system <NUM> according to the present disclosure may include a transducer array <NUM>, which may be included in an ultrasound probe <NUM>, for example an external probe or an internal probe such as an intravascular ultrasound (IVUS) catheter probe. In other embodiments, the transducer array <NUM> may be in the form of a flexible array configured to be conformally applied to a surface of subject to be imaged (e.g., patient). The transducer array <NUM> is configured to transmit ultrasound signals (e.g., beams, waves) and receive echoes responsive to the ultrasound signals. A variety of transducer arrays may be used, e.g., linear arrays, curved arrays, or phased arrays. The transducer array <NUM>, for example, can include a two dimensional array (as shown) of transducer elements capable of scanning in both elevation and azimuth dimensions for 2D and/or 3D imaging. As is generally known, the axial direction is the direction normal to the face of the array (in the case of a curved array the axial directions fan out), the azimuthal direction is defined generally by the longitudinal dimension of the array, and the elevation direction is transverse to the azimuthal direction.

The transducer array <NUM> may be coupled to a microbeamformer <NUM>, which may be located in the ultrasound probe <NUM>, and which may control the transmission and reception of signals by the transducer elements in the array <NUM>. In some embodiments, the microbeamformer <NUM> may control the transmission and reception of signals by active elements in the array <NUM> (e.g., an active subset of elements of the array that define the active aperture at any given time). The transducer elements in the array <NUM> may generate radio frequency (RF) data (e.g., electrical signals) and transmit the RF data to the microbeamformer <NUM>.

In some embodiments, the microbeamformer <NUM> may be coupled, e.g., by a probe cable or wirelessly, to a transmit/receive (T/R) switch <NUM>, which switches between transmission and reception and protects a decoder <NUM> and main beamformer <NUM> from high energy transmit signals. In some embodiments, for example in portable ultrasound systems, the T/R switch <NUM> and other elements in the system can be included in the ultrasound probe <NUM> rather than in the ultrasound system base, which may house the image processing electronics. An ultrasound system base typically includes software and hardware components including circuitry for signal processing and image data generation as well as executable instructions for providing a user interface.

The transmission of ultrasonic signals from the transducer array <NUM> under control of the microbeamformer <NUM> is directed by the transmit controller <NUM>, which may be coupled to the T/R switch <NUM> and a decoder <NUM> coupled to a main beamformer <NUM>. The transmit controller <NUM> may control the direction in which beams are steered. Beams may be steered straight ahead from (orthogonal to) the transducer array <NUM>, or at different angles for a wider field of view. Unfocused beams (e.g., plane waves, diverging waves) may also be transmitted. The transmit controller <NUM> may also be coupled to a user interface <NUM> and receive input from the user's operation of a user control. The user interface <NUM> may include one or more input devices such as a control panel <NUM>, which may include one or more mechanical controls (e.g., buttons, encoders, etc.), touch sensitive controls (e.g., a trackpad, a touchscreen, or the like), and/or other known input devices.

According to the principles of the present disclosure, the microbeamformer <NUM> may receive the RF data from the transducer elements of the transducer array <NUM> to generate an encoded signal. Details of the encoding will be explained in more detail further below. The microbeamformer <NUM> may be coupled to the decoder <NUM> by a probe cable or wirelessly. The encoded signal may be provided by the microbeamformer <NUM> to the decoder <NUM>. The decoder <NUM> may decode the encoded signal provided by the microbeamformer <NUM> to reconstruct the RF data. The reconstructed RF data may be provided by the decoder <NUM> to the main beamformer <NUM>. In some embodiments, the decoder <NUM> may be implemented by one or more processors.

The main beamformer <NUM> may perform beamforming operations (e.g., delay-and-sum or other beamforming operations) to generate a fully beamformed signal. The beamformed signals of beamformer <NUM> are coupled to processing circuitry <NUM>, which may include one or more processors (e.g., a signal processor <NUM>, a B-mode processor <NUM>).

The signal processor <NUM> may be configured to process the received beamformed RF data in various ways, such as bandpass filtering, decimation, I and Q component separation, and harmonic signal separation. The signal processor <NUM> may also perform additional signal enhancement such as speckle reduction, signal compounding, and noise elimination. The processed signals (also referred to as I and Q components or IQ signals) may be coupled to additional downstream signal processing circuits for image generation. The IQ signals may be coupled to a plurality of signal paths within the system, each of which may be associated with a specific arrangement of signal processing components suitable for generating different types of image data (e.g., B-mode image data, Doppler image data). For example, the system may include a B-mode signal path <NUM> which couples the signals from the signal processor <NUM> to a B-mode processor <NUM> for producing B-mode image data.

The B-mode processor can employ amplitude detection for the imaging of structures in the body. The signals produced by the B-mode processor <NUM> may be coupled to a scan converter <NUM> and/or a multiplanar reformatter <NUM>. The scan converter <NUM> may be configured to arrange the echo signals from the spatial relationship in which they were received to a desired image format. For instance, the scan converter <NUM> may arrange the echo signal into a two dimensional (2D) sector-shaped format, or a pyramidal or otherwise shaped three dimensional (3D) format. The multiplanar reformatter <NUM> can convert echoes which are received from points in a common plane in a volumetric region of the body into an ultrasonic image (e.g., a B-mode image) of that plane, for example as described in <CIT>). The scan converter <NUM> and multiplanar reformatter <NUM> may be implemented as one or more processors in some embodiments.

A volume renderer <NUM> may generate an image (also referred to as a projection, render, or rendering) of the 3D dataset as viewed from a given reference point, e.g., as described in <CIT>). The volume renderer <NUM> may be implemented as one or more processors in some embodiments. The volume renderer <NUM> may generate a render, such as a positive render or a negative render, by any known or future known technique such as surface rendering and maximum intensity rendering.

Output (e.g., B-mode images) from the scan converter <NUM>, the multiplanar reformatter <NUM>, and/or the volume renderer <NUM> may be coupled to an image processor <NUM> for further enhancement, buffering and temporary storage before being displayed on an image display <NUM>. A graphics processor <NUM> may generate graphic overlays for display with the images. These graphic overlays can contain, e.g., standard identifying information such as patient name, date and time of the image, imaging parameters, and the like. For these purposes the graphics processor may be configured to receive input from the user interface <NUM>, such as a typed patient name or other annotations. The user interface <NUM> can also be coupled to the multiplanar reformatter <NUM> for selection and control of a display of multiple multiplanar reformatted (MPR) images.

The system <NUM> may include local memory <NUM>. Local memory <NUM> may be implemented as any suitable non-transitory computer readable medium (e.g., flash drive, disk drive). Local memory <NUM> may store data generated by the system <NUM> including B-mode images, executable instructions, inputs provided by a user via the user interface <NUM>, or any other information necessary for the operation of the system <NUM>.

As mentioned previously system <NUM> includes user interface <NUM>. User interface <NUM> may include display <NUM> and control panel <NUM>. The display <NUM> may include a display device implemented using a variety of known display technologies, such as LCD, LED, OLED, or plasma display technology. In some embodiments, display <NUM> may comprise multiple displays. The control panel <NUM> may be configured to receive user inputs (e.g., threshold value, filter type, render type). The control panel <NUM> may include one or more hard controls (e.g., buttons, knobs, dials, encoders, mouse, trackball or others). In some embodiments, the control panel <NUM> may additionally or alternatively include soft controls (e.g., GUI control elements or simply, GUI controls) provided on a touch sensitive display. In some embodiments, display <NUM> may be a touch sensitive display that includes one or more soft controls of the control panel <NUM>.

In some embodiments, various components shown in <FIG> may be combined. For instance, image processor <NUM> and graphics processor <NUM> may be implemented as a single processor. In another example, the scan converter <NUM> and multiplanar reformatter <NUM> may be implemented as a single processor. In some embodiments, various components shown in <FIG> may be implemented as separate components. In some embodiments, one or more of the various processors shown in <FIG> may be implemented by general purpose processors and/or microprocessors configured to perform the specified tasks. In some embodiments, one or more of the various processors may be implemented as application specific circuits. In some embodiments, one or more of the various processors (e.g., image processor <NUM>) may be implemented with one or more graphical processing units (GPU).

<FIG> is a block diagram illustrating an example processor <NUM> according to principles of the present disclosure. Processor <NUM> may be used to implement one or more processors described herein, for example, image processor <NUM> shown in <FIG>. Processor <NUM> may be any suitable processor type including, but not limited to, a microprocessor, a microcontroller, a digital signal processor (DSP), a field programmable array (FPGA) where the FPGA has been programmed to form a processor, a graphical processing unit (GPU), an application specific circuit (ASIC) where the ASIC has been designed to form a processor, or a combination thereof.

The processor <NUM> may include one or more cores <NUM>. The core <NUM> may include one or more arithmetic logic units (ALU) <NUM>. In some embodiments, the core <NUM> may include a floating point logic unit (FPLU) <NUM> and/or a digital signal processing unit (DSPU) <NUM> in addition to or instead of the ALU <NUM>.

The processor <NUM> may include one or more registers <NUM> communicatively coupled to the core <NUM>. The registers <NUM> may be implemented using dedicated logic gate circuits (e.g., flip-flops) and/or any memory technology. In some embodiments the registers <NUM> may be implemented using static memory. The register may provide data, instructions and addresses to the core <NUM>.

In some embodiments, processor <NUM> may include one or more levels of cache memory <NUM> communicatively coupled to the core <NUM>. The cache memory <NUM> may provide computer-readable instructions to the core <NUM> for execution. The cache memory <NUM> may provide data for processing by the core <NUM>. In some embodiments, the computer-readable instructions may have been provided to the cache memory <NUM> by a local memory, for example, local memory attached to the external bus <NUM>. The cache memory <NUM> may be implemented with any suitable cache memory type, for example, metal-oxide semiconductor (MOS) memory such as static random access memory (SRAM), dynamic random access memory (DRAM), and/or any other suitable memory technology.

The registers <NUM> and the cache memory <NUM> may communicate with controller <NUM> and core <NUM> via internal connections 320A, 320B, 320C and 320D. Internal connections may implemented as a bus, multiplexor, crossbar switch, and/or any other suitable connection technology.

Inputs and outputs for the processor <NUM> may be provided via a bus <NUM>, which may include one or more conductive lines. The bus <NUM> may be communicatively coupled to one or more components of processor <NUM>, for example the controller <NUM>, cache <NUM>, and/or register <NUM>. The bus <NUM> may be coupled to one or more components of the system, such as display <NUM> and control panel <NUM> mentioned previously.

The bus <NUM> may be coupled to one or more external memories. The external memories may include Read Only Memory (ROM) <NUM>. ROM <NUM> may be a masked ROM, Electronically Programmable Read Only Memory (EPROM) or any other suitable technology. The external memory may include Random Access Memory (RAM) <NUM>. RAM <NUM> may be a static RAM, battery backed up static RAM, Dynamic RAM (DRAM) or any other suitable technology. The external memory may include Electrically Erasable Programmable Read Only Memory (EEPROM) <NUM>. The external memory may include Flash memory <NUM>. The external memory may include a magnetic storage device such as disc <NUM>. In some embodiments, the external memories may be included in a system, such as ultrasound imaging system <NUM> shown in <FIG>, for example local memory <NUM>.

As previously discussed with reference to <FIG>, a transducer array including multiple transducer elements may be divided into patches, sometimes also referred to as subarrays or simply groups, by the microbeamformer. <FIG> is a block diagram of components of an imaging system <NUM> in accordance with examples of the present disclosure. The imaging system <NUM> may include transducer elements <NUM>, a microbeamformer <NUM>, and a decoder <NUM>. The transducer elements <NUM> may be included in a transducer array in an ultrasound probe (not shown in <FIG>). The transducer elements <NUM> may provide RF signals to respective delay lines <NUM> of the microbeamformer <NUM>. In some examples, such as the one shown in <FIG>, the delay lines <NUM> may be programmable delay lines. The delay lines <NUM> may be coupled to summing nodes <NUM>. All of the delay lines coupled to a same summing node <NUM> may be included in a same patch <NUM>. Outputs from the summing nodes <NUM> of each patch <NUM> may be provided to the decoder <NUM>. The components of imaging system <NUM> may be used to implement one or more of the components of imaging system <NUM> shown in <FIG>. For example, microbeamformer <NUM> may be used to implement microbeamformer <NUM> in <FIG>.

<FIG> is a block diagram of a programmable delay line <NUM> in accordance with examples of the present disclosure. In some examples, programmable delay line <NUM> may be used to implement delay line <NUM> in <FIG>. The delay line <NUM> may receive an input via input line <NUM>. In some examples, such as the one shown in <FIG>, the input line <NUM> may include an input buffer <NUM>. The input line <NUM> may receive an electrical signal (e.g., RF data) from a transducer element (not shown in <FIG>), for example, transducer element <NUM> shown in <FIG>. The delay line <NUM> may include a number of input switches <NUM>. The input switches <NUM> may direct electrical signals from the input line <NUM> to one or more memory cells <NUM> by selectively coupling the memory cells <NUM> to the input line <NUM>. The memory cells <NUM> may be implemented with capacitors in some examples, such as the one shown in <FIG>. The memory cells <NUM> may store the electrical signals received from the input line <NUM>. The delay line <NUM> may include a number of output switches <NUM>. The output switches <NUM> may selectively couple one or more memory cells <NUM> to an output line <NUM>. When coupled to the output line <NUM>, the electrical signals stored in the memory cells <NUM> may be transmitted to the output line <NUM>. The output line <NUM> may transmit the electrical signal to a summing node (not shown in <FIG>) such as summing node <NUM> shown in <FIG>. In some examples, such as the one shown in <FIG>, the output line <NUM> may include an output buffer <NUM>.

The operation of the input switches <NUM> may be controlled by an input controller logic circuit <NUM>. The input controller logic circuit <NUM> may receive a clock signal and change which input switches <NUM> are closed responsive to a rising and/or falling clock edges in the clock signal. In some examples, the input controller logic circuit <NUM> may include a counter and a multiplexer. The input controller logic circuit <NUM> controls which memory cells <NUM> store an electrical signal received via the input line <NUM> each clock cycle. Thus, the delay line <NUM> effectively samples the electrical signal on the input line <NUM> and stores the samples in the memory cells <NUM>. The sampling rate may be based on a frequency of the clock signal. The sampling rate of the delay line <NUM> should be no less than a Nyquist rate of the electrical signal to avoid aliasing the electrical signal.

In some examples, the delay line <NUM> may be configured as a circular buffer. That is, each clock cycle, one input switch <NUM> is closed to couple one memory cell <NUM> to the input line <NUM> to store the electrical signal present on the input line <NUM> during that clock cycle. The input controller logic circuit <NUM> cycles through the input switches <NUM> in a same order. For example, a first memory cell <NUM> (e.g., the top memory cell <NUM> shown in <FIG>) may hold a first time sample, a second memory cell <NUM> may hold a second time sample, etc. After all of the memory cells <NUM> have been written to, the input controller logic circuit <NUM> may repeat the cycle, overwriting any stored data in the memory cells <NUM> during a next memory cycle. For example, if the delay line <NUM> includes eight input switches <NUM> and eight memory cells <NUM>, after eight clock cycles, data in the first memory cell <NUM> will be rewritten with new data received from the input line <NUM>.

The operation of output switches <NUM> may be controlled by an output controller logic circuit <NUM>. The output controller logic circuit <NUM> may receive delay data and change which output switches <NUM> are closed to couple memory cells <NUM> to the output line <NUM>. The delay data may be received from one or more shift registers (not shown) or a transmit controller (not shown in <FIG>), such as transmit controller <NUM> in <FIG>. In other examples, the delay data may be programmed into a memory included in the output controller logic circuit <NUM>. The time between when a sample of the electrical signal is stored on the memory cell <NUM> and when the memory cell <NUM> is coupled to the output line <NUM> may determine the delay of the electrical signal. Providing the sample of the electrical signal to the output line <NUM> may be a destructive read. That is, once the memory cell <NUM> has provided the sample to the output line <NUM>, the memory cell <NUM> no longer stores the electrical signal. Thus, a sample can only be read from a memory cell <NUM> once. Once read, there is no valid data in the memory cell <NUM> until the memory cell <NUM> is again coupled to the input line <NUM> to receive a new sample of the electrical signal.

The delay line <NUM> shown in <FIG> is provided for exemplary purposes, and principles of the present disclosure are not limited to the delay line shown in <FIG>. Examples of other suitable delay lines and/or delay line controls that may be used may be found in <CIT> and <CIT>and <CIT>.

In a typical microbeamformer operation, each sample from each memory cell <NUM> may be appropriately delayed by control of the output switches <NUM> and provided to the output line <NUM> for summing with the outputs of other delay lines of the patch. When the delay line <NUM> is arranged as a circular buffer, the maximum delay may be limited to the length of a memory cycle (e.g., eight cycles in the example described previously). Otherwise, a sample may be overwritten by a newly acquired sample. The summed outputs of the delay lines of the patch may then be provided by the microbeamformer to a main beamformer.

According to principles of the present disclosure, a jitter sampling scheme may be used to control the output switches <NUM>. The jitter sampling scheme, as will be described in more detail with reference to <FIG>, may apply pseudo-random delays to the electrical signals stored in the memory cells <NUM>. Furthermore, not all samples acquired by the memory cells <NUM> may be provided to the output line <NUM>. That is, the jitter sampling scheme may down-sample the electrical signal. The jitter sampling scheme may be provided to the output controller logic circuit <NUM> to control the operation of the output switches <NUM> to perform the jitter sampling operation. The jitter sampling scheme may encode the electrical signal such that the electrical signal may be reconstructed by a decoder.

<FIG> is a graphical illustration of typical delay-and-sum (DAS) beamforming (Aflat) and jitter sampling (Ajitter) in accordance with examples of the present disclosure. For ease of understanding, the jitter sampling scheme is first described in reference to a onedimensional array having fifteen transducer elements grouped into three patches, where each patch includes five transducer elements. In DAS beamforming, samples of electrical signals (e.g., RF data) from transducer elements acquired by delay lines (e.g., delay line <NUM>) are delayed such that signals from the same spatial location are aligned in time (e.g., delayed) and then summed. This is shown in panels <NUM>, <NUM>, and <NUM>. The horizontal axis corresponds to the transducer element and the vertical axis corresponds to the time sample for that transducer element. The time samples may be stored in memory cells, such as memory cells <NUM>. As indicated by the dark blue squares <NUM> for Patch <NUM>, dark blue squares <NUM> for Patch <NUM>, and dark blue squares <NUM> for patch <NUM>, the first time sample from each transducer element are summed together after alignment to obtain the signals for Patch <NUM>, Patch <NUM>, and Patch <NUM>. For example, the first time samples may be stored in the top memory cell <NUM> shown in <FIG>. Next, the second time samples for each transducer element may be aligned and summed. For example, the second time samples may be stored in a memory cell <NUM> below the top memory cell <NUM> shown in <FIG>. This process may continue for every time sample acquired by the delay lines. The signals from five transducer elements from each patch are combined and sent by the microbeamformer to the imaging system base as a single signal. Thus, in the example shown in <FIG>, three rather than fifteen signals are sent to the imaging system base from the ultrasound probe.

In accordance with principles of the present disclosure, the microbeamformer may be used to encode the electrical signal rather than perform typical DAS beamforming. The encoding may use a jitter sampling scheme that pseudo-randomly sums time samples stored in the delay lines for the transducer elements. An example of a jitter sampling scheme is illustrated panels <NUM>, <NUM>, and <NUM>. As shown by the dark blue squares <NUM>, Patch <NUM> combines the second time samples for transducer elements <NUM>, <NUM>, <NUM>, and <NUM> and the first time sample from transducer element <NUM>. As shown by dark blue squares <NUM>, Patch <NUM> combines the second time sample of transducer elements <NUM>, <NUM>, <NUM>, the third time sample of transducer element <NUM> and the first time sample of transducer element <NUM>. As shown by dark blue squares <NUM>, Patch <NUM> combines the second time sample of transducer elements <NUM> and <NUM> and the first time samples of <NUM>, <NUM>, and <NUM>.

The jitter sampling scheme may reduce the amount of data transferred from ultrasound probe to the imaging system base, but may allow the original fully sampled data to be reconstructed. The jitter sampling scheme may access only a few previous samples (e.g., three in the example shown in <FIG>), so delay lines with large numbers of memory cells are not required. The jitter sampling scheme reads each memory cell only once per memory cycle. Furthermore, as seen in <FIG>, the jitter sampling scheme communicates across patches by varying the pseudo-random pattern across patches as well as time.

<FIG> illustrates an example jitter sample grouping <NUM> in accordance with examples of the present disclosure. The example jitter sample grouping <NUM> shows how the jitter sampling scheme may vary across time. Each panel shows a non-overlapping delay grouping for the jitter sampling scheme that is used to generate three sequential output samples from a patch. The light-colored blocks of each panel illustrate the time sample for each transducer element read from a memory cell. In the example jitter sampling scheme shown in <FIG>, three sequential sample patterns are grouped together and then randomly summed across the transduce elements such that each memory cell is read once. Unlike conventional microbeamforming shown in the top panels of <FIG>, the delays are not monotonically increasing. While <FIG> shows three groups that sample a segment of fifteen samples, other numbers may be used. For example, five different sets of time samples groups such that the data is divided into twenty-five time sample segments may be used. In this example, the jitter sampling scheme is repeated periodically for each non-overlapping fifteen sample segment. Other jitter sampling schemes of non-overlapping sampling could also be used.

Heuristically, the jitter sampling acquisition scheme for encoding the RF signal (e.g., electrical signals) by the microbeamformer can be understood as follows: while two consecutive fast time samples of a microbeamformer are very similar and sample identical spatial frequencies (e.g., a first time sample stored in a first memory cell and a sequential second time sample stored in a second memory cell of a delay line), two consecutive jitter samples sample different spatial frequencies. In a sense, the jitter sampling acquisition is multiplexing different spatial frequencies over fast time. This is possible if the microbeamformer clock (e.g., the clock signal controlling the input control logic circuit <NUM> that controls the operation of the input switches <NUM> in <FIG>) is significantly faster than the RF signal sampling requirement. However, jitter sampling may perform better compression compared to simply down-sampling the data to its Nyquist limit.

Both Aflat and Ajitter shown in <FIG> can be written as linear operators acting to down sample the original data (x) consisting of <NUM> data points (<NUM> time samples x <NUM> patches x <NUM> transducer elements per patch) to a reduced number of measurements (y) (<NUM> time samples x <NUM> patch output signals).

In the one dimensional example of <FIG> and <FIG> of microbeamforming the data compression rate is <NUM>% for both Aflat and Ajitter.

The jitter sampling scheme may be extended to two-dimensional (2D) transducer arrays. In 2D, the microbeamformer groups the transducer elements in rectangular patches (e.g., 3x3, 4x4, 5x5). Depending on the type of microbeamformer included in an ultrasound probe, the microbeamformer may impose additional constraints to the delays which can be applied to the transducer elements of each patch. Each patch may be controlled by row-wise and column-wise constant delays (e.g., left-delays and down-delays). The row-wise <NUM> and column-wise delays <NUM> are shown in <FIG>. In the example shown in <FIG>, transducer elements are grouped as 4x4 patches. The delay applied to the electrical signals of each individual transducer element may be the sum of these row-wise delays <NUM> and columnwises delays <NUM>. The control line values for left and down delays may be used to generate a pseudo-random delay pattern of the patch <NUM>. As shown in <FIG>, different colors indicate different delay values fed to the delay lines and resulting delays of transducer elements in the patch <NUM>. Pane <NUM> of <FIG> shows examples of several pseudo random delay patterns which satisfy the microbeamformer control constraint that can be used to implement jitter sampling scheme. Similar to the 1D case shown in <FIG>, three sequential time samples may be grouped together and then randomly summed. Again memory cells are read only once, so the method is not dependent on samples that were destroyed in prior reads.

In some examples five different sets of time sample groups may be used such that the data is divided into fifteen time sample segments. For a simulated 2D array consisting of <NUM> elements (<NUM> x <NUM>), an example of a set of pseudo-random delay patterns 900A over the sixteen <NUM>-element-by-<NUM>-element patches corresponding to these fifteen time sample segments are shown in <FIG>. An example grouping 900B with three sequential time samples is shown in three dimensions is shown in <FIG> illustrate that the samples may be grouped into non-overlapping sets of three similar to the onedimensional array acquisition scheme shown in <FIG>.

The jitter samples are collected by the microbeamformer and combined to generate a jitter signal. The jitter signal may be the encoded RF data sampled from the transducer elements. In some examples, delays may be added to the jitter samples and/or jitter signal for focusing or steering of ultrasound beams. The jitter signal may then be provided to a decoder for reconstruction of the RF data (e.g., original RF data).

The reconstruction of the RF data from the encoded signal (e.g., jitter signal) may be an inverse problem. In reconstructing an estimate of the original (e.g. true) data (x), the compressibility and non-randomness of the RF data may be leveraged to improve reconstructions. To reconstruct the RF data, it may be assumed that the RF data is drawn from a Gaussian distribution with some covariance matrix Σ and an estimate of x (xmap) may be found given the observed data (y) and the prior assumption on the distribution of x, p(x).

This estimate of x (xmap) is known as the maximum a posterior (MAP) estimator as it maximizes the posterior distribution,
<MAT>.

Where p(y|x) is the probability of a measurement y given true data x. For a linear operator A, such as Ajitter , the MAP estimator has a closed form solution,
<MAT>.

Where Σ is the estimated covariance matrix and y is the output the microbeamformer (e.g., jitter signal). The decoder may have the pseudo-random pattern (Ajitter) used by the microbeamformer to generate the jitter signal. Thus, Equation (<NUM>) may be used to reconstruct the original data and perform beamforming. The covariance matrix Σ may be estimated from a single frame of data in some examples and/or from synthetically generated data. The matrix in Equation (<NUM>) can be pre computed such that the inversion only requires a single matrix multiplication and may be extremely fast.

Since both the signal reconstruction and beamforming operations are linear, they could be combined in a single operation that reconstructs the final image from the jitter data. That is, the decoder could be included in a main beamformer (or vice versa) in some examples.

<FIG> is a flow chart of a method <NUM> in accordance with examples of the present disclosure. The flow chart summarizes a microbeamforming encoding method described herein. At block <NUM>, a step of "acquiring a plurality of samples of an electrical signal" may be performed. In some examples, acquiring the plurality of samples of the electrical signal is controlled by a clock signal. A frequency of the clock signal may be higher than a Nyquist rate of the electrical signal.

The electrical signal may be associated with an acoustic signal. For example, the electrical signal may be generated by transducer elements responsive to echoes received. The echoes may be responsive to ultrasound signals transmitted by the transducer elements and/or other transducer elements. The electrical signal may be radio frequency data (e.g., radio frequency signal). For example, prior to block <NUM>, the step of "transmitting an ultrasound signal" may be performed. The transmitting may be performed by a transducer array comprising a plurality of transducer elements in some examples. The ultrasound signal may be a plane wave or a diverging wave in some examples. After transmitting the ultrasound signal, a step of "receiving the acoustic signal responsive to the ultrasound signal," may be performed. The acoustic signal (e.g., echoes) may be received with the transducer array. After receiving the acoustic signal, a step of "generating the electrical signal responsive to the acoustic signal" may be performed. The electrical signal may be generated with the plurality of transducer elements in some examples. In some examples, at least one of the plurality of memory cells is coupled to individual ones of the plurality of transducer elements. In some examples, the plurality of transducer elements are grouped into a plurality of patches and summing the individual samples of the plurality of samples comprises summing individual samples associated with at least two of the plurality of patches.

At block <NUM>, a step of "storing the plurality of samples in a plurality of memory cells" may be performed. The individual memory cells of the plurality of memory cells may store individual samples of the plurality of samples.

At block <NUM>, a step of "pseudo-randomly selecting a subset of the plurality of memory cells" may be performed. The subset may include fewer than the plurality of memory cells. In some examples, pseudo-randomly selecting the subset of the plurality of memory cells may down-sample the electrical signal. In some examples, after block <NUM>, a step of "adding delays to the pseudo-randomly selecting the subset of the plurality of memory cells" may be performed. The delays may focus or steer a beam associated with the acoustic signal.

At block <NUM>, a step of "summing the individual samples of the plurality of samples" may be performed. The individual samples may be stored in the subset of the plurality of memory cells. The summing of the individual samples may generate a jitter signal.

At block <NUM>, a step of "decoding the jitter signal" may be performed. Decoding the jitter signal may generate a reconstructed signal. Decoding may include applying the matrix described in Equation (<NUM>) to the jitter signal. In some examples, the covariance matrix may be based at least in part on the pseudo-randomly selecting.

<FIG> show examples of original signals and reconstructed signals generated in accordance with the examples of the present disclosure.

In <FIG> a simulated per-channel data from S5-<NUM> phased array is shown. Pane <NUM> shows the original "truth image," pane <NUM> shows the reconstruction generated after encoding the truth image with the jitter sample scheme and decoding the jitter signal generated by the jitter sample scheme, and pane <NUM> shows the difference between the truth and reconstruction. All panes are shown with the same dynamic range. This dataset was obtained by simulating a synthetic phantom with various grey levels and point targets, with diverging wave transmissions from a <NUM> virtual apex behind the physical aperture, consisting of <NUM> angles ranging uniformly from -<NUM>° to <NUM>°. The covariance matrix used to calculate the reconstruction was calculated using the data obtained at <NUM>° transmit. Jitter sampling and reconstruction was performed on the data obtained at <NUM>° transmit. Truth and reconstruction data match each other well and the difference data has some content corresponding to the high amplitude and high frequency echoes only.

<FIG> shows simulated channel data from a hypothetical 2D transducer array with <NUM> elements (<NUM> x <NUM>). However, for simplicity, instead of displaying raw data for all the channels, one slice of the 2D array is shown. The x-element index is fixed to channel <NUM> and signals from all y-elements are shown. The full aperture is divided into <NUM>-element-by-<NUM>-element subarrays and jitter sampling technique described herein is applied on each subarray. Similar to <FIG>, true data is presented in pane <NUM>, reconstruction following the compression with jitter sampling scheme is presented in pane <NUM>, and the difference is shown in pane <NUM>. This dataset was obtained by simulating a synthetic speckle phantom with a hyper echoic target in the middle, with a plane wave transmission. Truth and reconstruction data images in <FIG> look similar, however the difference image has a lot more content with relatively large amplitude. Although the reconstructed data does not appear as clean as the reconstruction shown in <FIG>, the down-sampling rate is significantly higher in the 2D case (<NUM>% for the 1D array in <FIG> versus <NUM>% for the 2D array in <FIG>). Despite the significant down-sampling, the reconstruction scheme is able to recover most of the original data as shown in <FIG>.

<FIG> shows images acquired by diverging ultrasound beams in accordance with examples of the present disclosure. The left column (panes <NUM>, <NUM>, and <NUM>) show images acquired by beamforming and displaying B-mode images directly from raw channel signals. That is, the signal from each transducer element was individually processed by a main beamformer with no microbeamforming. The second column (panes <NUM>, <NUM>, and <NUM>) shows images acquired by typical microbeamforming operations with patch size of <NUM>. The third column (panes <NUM>, <NUM>, and <NUM>) show images generated by original signals compressed with the jitter sampling scheme and reconstructed according to principles of the present disclosure. The top row (panes <NUM>, <NUM>, and <NUM>) shows images from a simulated phantom beamformed from one diverging transmit wave. The middle row (panes <NUM>, <NUM>, and <NUM>) shows images from the simulated phantom beamformed from eleven diverging wave transmits (middle row). Both the top row and middle row images were acquired with a <NUM> focus. The bottom row (panes <NUM>, <NUM>, and <NUM>) shows images from an in vivo cardiac dataset generated from <NUM> diverging wave transmits and a <NUM> focus.

The jitter sample scheme for encoding and decoding the RF data significantly improves the final image compared to conventional microbeamforming as illustrated in <FIG>. Both improvements in contrast and reduction in grating lobe artifacts obtained with the jitter sampling reconstruction beamforming. For example, the grating lobe artifacts in circle <NUM> in pane <NUM> do not appear in the reconstructed image of pane <NUM>. In the eleven transmit case these grating lobe artifacts are not as pronounced as single transmit since they are slightly reduced by angular compounding with other transmits. However, in another example of the improvements demonstrated by the principles of the present disclosure, the grey level inside the hypo echoic cysts <NUM> of pane <NUM> are increased and the overall contrast is reduced compared with pane <NUM>. The grating lobes and reduced contrast artifacts of the microbeamformed images are avoided, and an image much closer to the image beamformed from the per-channel data is obtained using the jitter sampling and reconstruction scheme described herein. For all of the jitter reconstructed images shown in <FIG>, the covariance matrix was estimated from synthetic data, including the in vivo cardiac data.

Finally in the cardiac example of the bottom row, even the per-channel beamformed image in pane <NUM> has some clutter in an area corresponding to the chamber. However with the microbeamformered image in pane <NUM>, overall image contrast is lower with a lot of clutter introduced due to microbeamforming processing. The cluttering and reduced contrast are not present in the image generated by the jitter sampling and reconstruction scheme in pane <NUM>.

As described herein, a jitter sampling scheme may be used with a microbeamformer to encode RF data received from transducer elements. The encoded signal may be transmitted to a decoder for reconstruction of the original RF data. The encoding may allow for less data to be transmitted between an ultrasound probe and an imaging system base. The encoding and reconstruction may allow for improved image generation (e.g., via beamforming or other methods) compared to images generated from typical microbeamforming operations. The systems, methods, and apparatuses described herein may allow for the use of unfocused beam imaging (e.g., plane waves, diverging waves) with ultrasound probes that include microbeamformers.

In various embodiments where components, systems and/or methods are implemented using a programmable device, such as a computer-based system or programmable logic, it should be appreciated that the above-described systems and methods can be implemented using any of various known or later developed programming languages, such as "C", "C++", "FORTRAN", "Pascal", "VHDL" and the like. Accordingly, various storage media, such as magnetic computer disks, optical disks, electronic memories and the like, can be prepared that can contain information that can direct a device, such as a computer, to implement the above-described systems and/or methods. Once an appropriate device has access to the information and programs contained on the storage media, the storage media can provide the information and programs to the device, thus enabling the device to perform functions of the systems and/or methods described herein. For example, if a computer disk containing appropriate materials, such as a source file, an object file, an executable file or the like, were provided to a computer, the computer could receive the information, appropriately configure itself and perform the functions of the various systems and methods outlined in the diagrams and flowcharts above to implement the various functions. That is, the computer could receive various portions of information from the disk relating to different elements of the above-described systems and/or methods, implement the individual systems and/or methods and coordinate the functions of the individual systems and/or methods described above.

In view of this disclosure it is noted that the various methods and devices described herein can be implemented in hardware, software, and/or firmware. Further, the various methods and parameters are included by way of example only and not in any limiting sense. In view of this disclosure, those of ordinary skill in the art can implement the present teachings in determining their own techniques and needed equipment to affect these techniques, while remaining within the scope of the invention. The functionality of one or more of the processors described herein may be incorporated into a fewer number or a single processing unit (e.g., a CPU) and may be implemented using application specific integrated circuits (ASICs) or general purpose processing circuits which are programmed responsive to executable instructions to perform the functions described herein.

Of course, it is to be appreciated that any one of the examples, embodiments or processes described herein may be combined with one or more other examples, embodiments and/or processes or be separated and/or performed amongst separate devices or device portions in accordance with the present systems, devices and methods.

Claim 1:
A system (<NUM>, <NUM>) comprising:
a transducer array (<NUM>) including a plurality of transducer elements (<NUM>), wherein the transducer elements are configured to receive ultrasound echoes and convert the ultrasound echoes into electrical signals, wherein the plurality of transducer elements are grouped into a plurality of patches;
a microbeamformer (<NUM>, <NUM>) coupled to the plurality of transducer elements, the microbeamformer including, for each transducer element, a delay line (<NUM>, <NUM>) that comprises a plurality of memory cells (<NUM>), wherein the microbeamformer is configured to:
for each patch of the plurality of transducer elements:
select, from the plurality of memory cells of the delay lines, time samples from a group of consecutive time samples according to a set of pseudo-random sample patterns or jitter sampling schemes such that each selected memory cell is read only once;
sum, for each set of the pseudo-random sample patterns or jitter sampling schemes, the selected time samples to generate a jitter signal; and
a decoder (<NUM>) configured to receive the jitter signals and generate a reconstructed signal representative of the electrical signals.