Patent Description:
<CIT> discloses systems and methods for ultrasound imaging capable of achieving spatial resolutions that can resolve objects smaller than <NUM>.

<CIT> discloses an ultrasound imaging method in which ultrasound signals are transmitted and received with a resolution limit in a first direction, wherein a peak-sharpening operation is applied to image data generated from the received ultrasound signals in order to obtain images having a finer resolution in the first direction than the resolution limit.

<NPL>, discloses the use of deep learning to attain super-resolution ultrasound with challenging contrast-agent densities.

<NPL> discloses the use of ultrasound imaging at ultrafast frame rates to provide an analogue to optical localization microscopy by capturing transient signal decorrelation of contrast agents.

In contrast-enhanced imaging, a contrast agent is provided to an area or volume to be imaged in order to provide a higher signal strength from the area or volume, or selectively enhance signals from areas or volumes with high contrast concentration. For example, in contrast-enhanced ultrasound (CEUS), microbubbles may be injected into a subject's bloodstream and ultrasound images may be acquired of the subject's vasculature. Without the microbubbles, little to no signal may be provided by the blood vessels. In contrast accumulation imaging (CAI), multiple contrast-enhanced images (e.g., multiple image frames) are acquired and combined and/or normalized to form the final image, which can be used to map contrast agent progression and enhance vessel topology and conspicuity. Temporal accumulation imaging of CEUS has been commercialized and widely used for vascularity visualization. However, CEUS has limited spatial resolution due to the large size of the point spread function (PSF) in contrast mode. The PSF is a measure of blurring or spreading of a point source by an imaging system. CEUS may also have strong residual clutter artifacts as well as vulnerability to patient induced motion due to the combining of multiple image frames to form the final image.

<FIG> shows example (a) CEUS and (b) CAI images of a two-branch flow phantom with circulating microbubbles. As can be seen in <FIG>, the CEUS image has "holes" in the visualization of the vasculature because microbubbles are not present at every point in the vasculature during a single image acquisition. A more complete image of the vasculature can be seen in the CAI image of <FIG>. However, the CAI image suffers from low spatial resolution. In principle, CAI has similar spatial resolution to CEUS, however, in practice, its resolution is worse due to tissue motion and clutter artifacts. The clutter artifacts act as false positives for microbubbles and/or vasculature. For example, in the CAI image, there is visible residual clutter appearing as a haze at the left and right boundaries of the image as indicated by arrows <NUM> and <NUM>, respectively. Furthermore, in both the CEUS image and the CAI image, line-shaped residual clutter is present as indicated by white arrows <NUM> and <NUM>, which acts as a false positive for a vessel branch. Accordingly, improved contrast-enhanced accumulated imaging techniques with higher spatial resolution and reduced artifacts are desired.

Systems and methods for performing imaging techniques with adjustable resolution and acquisition times, which may be tailored to different clinical applications intended for the visualization of different vascular levels of organs or diseases. The present disclosure describes a contrast accumulation imaging technique that may provide improved imaging performance that strategically selects multiple pixels to represent one or more microbubbles localized within an image. The systems and methods described herein may particularly localize each microbubble with its more specific characteristics and may provide better spatial resolution than CAI, adjustable spatial resolution, and/or less residual clutter than CAI which may result in higher contrast-to-tissue ratio (CTR). The system and methods described herein may provide contrast enhanced images at regular CEUS frame rates (e.g. <NUM>-<NUM>) with shorter data acquisition times (e.g., approximately <NUM>) compared to Super-resolution imaging.

The following description of certain exemplary examples 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 examples 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 examples in which the described systems and methods may be practiced. These examples 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 examples may be utilized, and that structural and logical changes may be made without departing from the scope of the present system. 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.

Super-resolution imaging (SRI), also known as ultrasound localization microscopy (ULM), is another imaging technique for vasculature imaging and quantification. It has several advantages: (<NUM>) high spatial resolution (up to ~<NUM>×<NUM>, almost close to the size of red blood cells); (<NUM>) same penetration depth as regular CEUS; (<NUM>) quantification of blood flow in both magnitude and direction (also, optionally, speed of propagation); (<NUM>) non-invasive with non-toxic microbubble-based contrast agents; (<NUM>) no hardware modifications to existing clinical scanners. In a common SRI technique, each super-resolved image is obtained by two steps: (<NUM>) localizing the center of each separable microbubble and then (<NUM>) accumulating these centers over thousands of acquisitions. The position of each microbubble is obtained by taking the local maxima of each microbubble intensity profile. This means that the center of each microbubble can be seen and represented as a single-pixel dot. During localization, the center of each microbubble can be obtained also with the following methods: (<NUM>) directly finding the peak (maximum intensity) of each separable microbubble in image domain; or (<NUM>) fitting the microbubble image with a 2D/3D Gaussian function and then finding the peak; or (<NUM>) fitting the microbubble image with the PSF of the imaging system and then finding the peak. The term, "maximum pixel projection technique" is used to refer to the accumulation of center positions from multiple acquisitions (e.g., multiple image frames). The accumulation of the center positions of microbubbles is the probability density mapping of microbubbles, which is the super-resolved image of the microvasculature.

SRI typically requires tens or hundreds of thousands of individual contrast imaging frames, corresponding to a combination of very high imaging frame rates (often ><NUM>) and very long acquisition times (e.g., several minutes) compared to conventional contrast ultrasound scans. It is very challenging to achieve acceptable super-resolved images with regular CEUS frame rate (e.g., <NUM>-<NUM>) and short acquisition time (e.g., <NUM>). High imaging frame rate in SRI is preferable for (<NUM>) good separation of individual microbubbles, (<NUM>) sufficient accumulation of microbubbles, and (<NUM>) adequate motion compensation. SRI with low frame rate (~<NUM>, as in conventional CEUS) is limited by motion artifacts and requires prolonged acquisition times (><NUM>). If the acquisition time is not sufficient, the super-resolved image may not be properly formed due to partial filling and a large number of "holes". Hemodynamically, large blood vessels (diameter><NUM>) get perfused more quickly. Hence, the acquisition time required to reconstruct them may be much shorter than for very small vessels (~<NUM> and smaller). Since SRI is a technique developed to mainly image small structures--for example, capillaries with diameter less than <NUM>--the data acquisition time has to be long enough to reconstruct such microvessels.

Spatial resolution and temporal resolution of SRI may be related to the local concentration of microbubbles, given that this technique reconstructs microvessels based on the localized sources (e.g., microbubbles) within them (e.g., single-pixel dot is used to represent each microbubble for accumulation). For example, a high concentration of microbubbles and an accumulation of <NUM>,<NUM> images (e.g., acquisition time of <NUM> at frame rate of <NUM>), yielding <NUM>,<NUM>,<NUM> events (e.g., microbubbles) may be used to generate one super-resolved image with <NUM> spatial resolution.

The present disclosure is directed to systems and methods for performing imaging techniques with adjustable resolution and acquisition times, which may be tailored to different clinical applications intended for the visualization of different vascular levels of organs or diseases. The present disclosure describes a contrast accumulation imaging technique that strategically selects multiple pixels to represent one or more microbubbles localized within an image, as opposed to a large number of pixels associated with a general PSF of CAI or a single pixel representation of SRI. The pixels representing microbubbles are selected by applying a filter to the image data such that multiple pixels are representative of the microbubbles within the image data. In some examples, the filter may include an intensity threshold of a value between a maximum pixel intensity and a minimum pixel intensity associated with identified microbubbles. In other examples, the filter may select a certain percentage of pixels whose intensity is greater than the mean signal intensity. In yet other examples, the filter may include other thresholds or algorithms to select the pixels representative of the microbubbles. The pixel intensity values for the filter may be preset or estimated based on existing image data. This filtered technique may allow microbubbles of different intensity values to be localized and accumulated in subsequent imaging frames to achieve a high-resolution image (e.g., an enhanced CAI image). The techniques described herein may be referred to as "enhanced CAI.

When a contrast agent, such as microbubbles, are present in the subject, contrast-enhanced images may be generated from the ultrasound signals. In some examples, the ultrasound imaging system may separate the signals to generate contrast images to visualize the contrast agent and tissue images to visualize tissue structures. In some examples, the ultrasound imaging system may include at least one processor configured to identify microbubbles in the ultrasound signals and/or the images. After identification, the at least one processor may localize the microbubbles by representing each identified microbubble by multiple pixels by passing the identified microbubbles through a filter. The number of pixels may depend on a threshold value of a filter. Multiple ultrasound signals (e.g., signals based on echoes received from multiple transmit/receive events) and/or multiple image frames processed by the at least one processor may be combined to form a final enhanced contrast accumulation image. In some examples, the at least one processor may perform motion estimation and compensation prior to accumulating the images. Optionally, in some examples, the at least one processor may pass the ultrasound signals and/or images through one or more clutter rejection filters.

<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 examples, 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 (e.g., received ultrasound signals) responsive to the transmitted 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.

In some examples, 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 examples, 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).

In some examples, 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 the main beamformer <NUM> from high energy transmit signals. In some examples, 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 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. 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.

In some examples, the partially beamformed signals produced by the microbeamformer <NUM> may be coupled to a main beamformer <NUM> where partially beamformed signals from individual patches of transducer elements may be combined into a fully beamformed signal. In some examples, microbeamformer <NUM> is omitted, and the transducer array <NUM> is under the control of the beamformer <NUM> and beamformer <NUM> performs all beamforming of signals. In examples with and without the microbeamformer <NUM>, 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>, a Doppler processor <NUM>, and one or more image generation and processing components <NUM>) configured to produce an ultrasound image from the beamformed signals (i.e., beamformed RF data).

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 electronic 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.

In some examples according to principles of the present disclosure, the signal processor <NUM> may analyze the RF data and/or IQ signals to identify and localize microbubbles in the signals. The processed signals may be provided to the B-mode processor <NUM> and other processing circuitry (e.g., scan converter, <NUM>, image processor <NUM>) for accumulation and generation of an enhanced CAI image. In some examples, the signal processor <NUM> may accumulate the signals over multiple transmit/receive events to generate a combined signal to be further processed into an enhanced CAI image by the B-mode processor <NUM> and other processing circuitry.

The B-mode processor <NUM> can employ amplitude detection for the imaging of structures in the body. According to principles of the present disclosure, the B-mode processor <NUM> may generate signals for tissue images and/or contrast images. Because microbubbles may generate much higher intensity echoes than the surrounding tissue, signals from the microbubbles may be extracted from the B-mode signal for forming a separate contrast image. Similarly, the lower intensity tissue signals may be separated from the microbubble signals for generating a tissue image. 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. In another example of the present disclosure, the scan converter <NUM> may arrange the echo signals into side-by-side contrast enhanced and tissue images. As explained further below, in some examples, the image processor <NUM> performs microbubble identification, localization, and accumulation.

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 examples.

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 examples. 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.

In some examples, the system may include a Doppler signal path <NUM> which couples the output from the signal processor <NUM> to a Doppler processor <NUM>. The Doppler processor <NUM> may be configured to estimate the Doppler shift and generate Doppler image data. The Doppler image data may include color data which is then overlaid with B-mode (i.e. grayscale) image data for display. The Doppler processor <NUM> may be configured to filter out unwanted signals (i.e., noise or clutter associated with non-moving tissue), for example using a wall filter. The Doppler processor <NUM> may be further configured to estimate velocity and power in accordance with known techniques. For example, the Doppler processor may include a Doppler estimator such as an auto-correlator, in which velocity (Doppler frequency) estimation is based on the argument of the lag-one autocorrelation function and Doppler power estimation is based on the magnitude of the lag-zero autocorrelation function. Motion can also be estimated by known phase-domain (for example, parametric frequency estimators such as MUSIC, ESPRIT, etc.) or time-domain (for example, cross-correlation) signal processing techniques. Other estimators related to the temporal or spatial distributions of velocity such as estimators of acceleration or temporal and/or spatial velocity derivatives can be used instead of or in addition to velocity estimators. In some examples, the velocity and power estimates may undergo further threshold detection to further reduce noise, as well as segmentation and post-processing such as filling and smoothing. The velocity and power estimates may then be mapped to a desired range of display colors in accordance with a color map. The color data, also referred to as Doppler image data, may then be coupled to the scan converter <NUM>, where the Doppler image data may be converted to the desired image format and overlaid on the B-mode image of the tissue structure to form a color Doppler or a power Doppler image. For example, Doppler image data may be overlaid on a B-mode image of the tissue structure.

Output (e.g., B-mode images, Doppler 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>.

According to principles of the present disclosure, in some examples, the image processor <NUM> may analyze one or more images to identify and localize one or more microbubbles within an image based on multiple pixels per microbubble. In some examples, identifying microbubbles may include identifying a general microbubble region (e.g. using PSF) and then applying one or more filters to the general microbubble region to identify one or more particular microbubbles. In some examples, pixels with intensities greater than a threshold of the filter are classified as a microbubble. The one or more filters may further be used to localize the microbubbles by representing centers of the microbubbles as multiple pixels. The filters may be preset (e.g., based on exam type and/or contrast agent type). The filters are based on the range of intensities presented in the microbubble region of the image. In other examples, the filters may be set by a user input. The filters apply threshold values and/or may apply other selection algorithms for determining which pixels to visualize. In some examples, the threshold value may be an intensity value. Thus, in some examples, the threshold value is an intensity threshold which is less than the maximum intensity (e.g., <NUM>%, <NUM>%) and greater than the minimum intensity (e.g., <NUM>%, <NUM>%) of the microbubble so that the microbubble representation is a multi-pixel spot which is greater than one pixel, but the extent of the pixels is less than the entire microbubble (e.g. PSF). As the percentage of the maximum intensity increases, the number of pixels representing each microbubble decreases and the resolution increases. By using this technique, a plurality of microbubbles may be localized within the PSF, and each microbubble may have its own intensity or pixel signature in some examples. After localization, the image processor <NUM> may accumulate the localized microbubbles over multiple image frames and/or transmit/receive events.

Optionally the image processor <NUM> may apply clutter rejection filters to the one or more images prior to identifying and localizing the microbubbles. The image processor <NUM> may alternatively or additionally optionally apply other pre-processing steps prior to identifying and localizing the microbubbles including smoothing, detail enhancement, and/or additional noise suppression.

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, masks, 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 examples, display <NUM> may comprise multiple displays. The control panel <NUM> may be configured to receive user inputs (e.g., exam type, filter values for microbubble localization). The control panel <NUM> may include one or more hard controls (e.g., buttons, knobs, dials, encoders, mouse, trackball or others). In some examples, 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 examples, display <NUM> may be a touch sensitive display that includes one or more soft controls of the control panel <NUM>.

According to principles of the present disclosure, in some examples, a user may set a threshold value of the filter for localizing the microbubbles via the user interface <NUM>. As described above, adjusting the threshold value may adjust the resolution of the contrast accumulation image. Thus, by setting the threshold value, the user may have control over the resolution and/or required acquisition time. In some examples, the user may select a desired resolution and/or acquisition time and the imaging system <NUM> may calculate the corresponding threshold value for the filter. In some examples, the threshold value may be pre-set based on exam type, contrast agent type, and/or properties of the image (e.g., dynamic range).

In some examples, 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 examples, various components shown in <FIG> may be implemented as separate components. For example, signal processor <NUM> may be implemented as separate signal processors for each imaging mode (e.g., B-mode, Doppler). In some examples, 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 examples, one or more of the various processors may be implemented as application specific circuits. In some examples, 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 examples, 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 examples the registers <NUM> may be implemented using static memory. The register may provide data, instructions and addresses to the core <NUM>.

In some examples, 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 examples, 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 <NUM> may communicate with controller <NUM> and core <NUM> via internal connections 320A, 320B, 320C and 320D. Internal connections may be 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 examples, the external memories may be included in a system, such as ultrasound imaging system <NUM> shown in <FIG>, for example local memory <NUM>.

<FIG> and <FIG> are flow charts <NUM>, <NUM> that illustrate steps of methods performed by an image processor, such as image processor <NUM> shown in <FIG>, to perform methods in accordance with examples of the present disclosure. The steps in both flow charts <NUM>, <NUM> are the same, but may be performed in different orders as will be described in detail below.

In some examples, a multi-frame loop (formats can be DICOM, AVI, WMV, JPEG, etc.) of conventional side-by-side contrast and tissue images may be used as inputs to the signal processor as indicated by blocks <NUM> and <NUM>. The image-domain-based processing may be implemented as an off-line processing feature in some examples. In some applications, the images may be log-compressed with a limited dynamic range, thus, the image-domain implementation of enhanced CAI may have limited performance. In some examples, enhanced CAI may also be implemented at IQ-domain (input is IQ data) or RF-domain (input is RF data) rather than a multi-frame loop as shown in <FIG> and <FIG>. In some applications, IQ data and/or RF data may provide better performance of microbubble localization and clutter rejection. In examples using IQ and/or RF data, the image processor may receive data from a signal processor and/or beamformer, such as signal processor <NUM> and/or beamformer <NUM> shown in <FIG>. Alternatively, in these examples, the steps shown in <FIG> and <FIG> may be performed by the signal processor.

At blocks <NUM> and <NUM>, the image processor may perform image formatting. In some examples, the multi-frame loops are processed to separate the tissue and contrast images so that they can be processed independently as indicated by blocks <NUM> and <NUM> and blocks <NUM> and <NUM>. The tissue and contrast images may be properly formatted for following processing blocks. For example, red-green-blue (RGB) images may be converted to gray-scale images (or indexed images) with a desired dynamic range (e.g., normalized from <NUM> to <NUM>). In examples where enhanced CAI is performed on RF data and/or IQ data rather than a multi-frame loop, image formatting may include separating signals resultant from the contrast agent and signals resultant from the tissue.

Optionally, at blocks <NUM> and <NUM>, clutter rejection filtering may be performed on contrast images prior to temporal accumulation, which may reduce the effect of stationary echoes (especially in the near field), reverbs, etc. Clutter rejection filters can be implemented as finite impulse response (FIR), infinite impulse response (IIR)-based high-pass filters with sufficient numbers of coefficient delay pairs (e.g., taps), a polynomial least-squares curve fitting filter, and/or singular value decomposition (SVD)-based high-pass filter. Filter parameters may be optimized to suppress most of the residual clutter but preserve most of the contrast signals. In some examples, blocks <NUM> and <NUM> may be omitted.

At blocks <NUM> and <NUM>, microbubble identification is performed. Separable individual microbubbles may be identified in this step. An optional interpolation step can be performed to bring the image pixel size to a desired resolution (e.g. <NUM> × <NUM>) in some examples. Next, an intensity-based thresholding may be performed to remove background noise. For example, normalized intensities less than the threshold (e.g. <NUM>% of maximum intensity) may be considered background noise and set to zero. Additionally, a local maxima search may be performed to find the locations of microbubbles. In some examples, to make sure the identified microbubbles are separable and not clustered, only one microbubble may be identified (e.g., the one with the maximum intensity) within any PSF area (e.g., microbubble region). In some examples, microbubbles may be identified by methods similar to those described above with reference to generating SRI images.

At blocks <NUM> and <NUM>, microbubble localization may be performed. Localization refers to generating the visual representation of each identified microbubble (e.g., multi-pixel spot), which may be established in this step. The identified microbubbles are passed through a filter that applies a threshold value or other algorithm for selecting which pixels of the microbubbles to visualize. In the example of a filter including a threshold value, only pixels of the microbubble above the threshold value may be visualized. A threshold (e.g. <NUM>%, <NUM>%, <NUM>% of maximum intensity of the microbubble) may be pre-defined based on different imaging settings or exam-type based presets. Typically, the threshold is less than <NUM>% and greater than <NUM>% of the maximum intensity of the microbubble. This threshold can be used to adjust the spatial resolution. For a higher spatial resolution (e.g., fewer pixels), a longer acquisition time may be used. For a lower spatial resolution (e.g., more pixels), a shorter acquisition time may be used. Within the microbubble region (e.g., the PSF), if the intensity ratio (e.g., normalized to maximum intensity) is greater than or equal to the threshold, the pixels may be defined as the representation of the microbubble. In other examples, the filter may include other algorithms or operators for selecting pixels for visualization. For example, the filter may select a certain percentage of pixels whose intensity is greater than a mean signal intensity of the microbubble, all microbubbles, or image.

In some examples, different intensity values may be assigned to different pixels of the microbubble representation (e.g., visualization). In some examples, the pixel intensities within the microbubble representation remain unchanged and the rest of the microbubble pixel intensities (e.g., the portions of the microbubbles not visualized) may be set to zero. Different algorithms for value assignment may be implemented in other examples. For example, all of the pixels of the microbubble above the threshold value may be set to a uniform intensity value in some examples. The uniform intensity may be based on an average intensity of the pixels above the threshold value or a maximum intensity of the pixels above the threshold value in some examples.

Motion compensation may be performed before microbubble accumulation. As shown by dashed boxes <NUM> and <NUM>, motion compensation may be provided at different points in the process of enhanced CAI in various examples of the present disclosure. In some examples, the tissue images <NUM> and <NUM> may be used for motion compensation. That is, movement of tissue structures in the tissue images <NUM> and <NUM> may be used to estimate displacements due to motion. In some examples, the motion compensation on contrast images alone may be used. If there is not much motion in the multi-frame loop <NUM>, contrast images may be used alone for enhanced CAI, bypassing the tissue image pathway in box <NUM> as shown in <FIG>. However, in some applications, using only the contrast images may be less reliable.

In the example shown in <FIG>, motion compensation is performed after microbubble localization. At block <NUM>, estimated displacements from the tissue images <NUM> are performed. At block <NUM>, the estimated displacements calculated at block <NUM> may be used to compensate for motion in the outputs of the microbubble localization step shown in block <NUM>.

Alternatively, as shown in <FIG>, motion compensation may be performed prior to microbubble identification. The dashed box <NUM> of <FIG> shows the estimated displacements from the tissue images <NUM> calculated at block <NUM> are used to compensate for motion on the contrast images at block <NUM> before microbubble localization is performed at block <NUM>. The method shown in <FIG> may allow for motion compensated contrast images for display. However, the method shown in <FIG> may reduce the computational cost of motion compensation, but may come at the expense of not providing motion compensated contrast images for display.

After motion compensation, microbubble accumulation is performed at blocks <NUM> and <NUM>. A high-resolution image <NUM> and <NUM> is output from the accumulation step. In some examples, accumulation may be performed by summing multiple image frames from the multi-frame loop, for example, sequential image frames. In some examples, multiple frames may be summed followed by a normalization step. In some examples, multiple frames may be analyzed to determine the maximum pixel intensity for each location in the image may be determined and the maximum pixel intensity values may be used to generate the final image <NUM>. In examples where microbubble identification and localization are performed by processing IQ and/or RF data, the processed ultrasound signals from multiple transmit/receive events may be summed or otherwise combined. The combined ultrasound signals may then be provided to other processing components (e.g., B-mode processor, scan converter) for generating a final image.

<FIG> shows example CAI, enhanced CAI, and SRI images of a flow phantom. The conventional CAI image is shown in pane (a). The enhanced CAI image in accordance with examples of the present disclosure is shown in pane (b), and the SRI is shown in pane (c). The data acquisition time was <NUM> and the frame rate was <NUM>. The enhanced CAI image in pane (b) shows better spatial resolution and better CTR compared to conventional CAI in pane (a). Additionally, due to insufficient number of localized microbubbles accumulated within the data acquisition time, SRI image shown in pane (c) has many "holes" in visualizing the phantom vessels and the phantom vessels are not completely filled.

<FIG> shows example in vivo images of a human liver. Pane (a) shows side-by-side contrast (left side) and tissue images (right side). Pane (b) shows a conventional CAI image, pane (c) shows an enhanced CAI image in accordance with examples described herein, and pane (d) shows an SRI image. The data acquisition time was <NUM> and the frame rate was <NUM>. There was significant respiratory motion of the liver in this example. As seen in pane (c), enhanced CAI image shows better spatial resolution compared to conventional CAI shown in pane (b). Additionally, due to insufficient data acquisition time, SRI image shown in pane (d) is not properly formed due to bad filling with many "holes".

The examples provided in <FIG> and <FIG> demonstrate the potential advantages of the proposed systems and methods described herein (e.g., enhanced CAI): better spatial resolution compared to conventional CAI, ability to use regular CEUS frame rates, and/or shorter data acquisition time relative to SRI. Furthermore, the systems and methods described herein allow uses to adjust the representation of the microbubbles (e.g., the number of pixels) to control the spatial resolution of the images. This may give users more control over the trade-offs between resolution and acquisition time.

In various examples 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.

Another advantage of the present systems and method may be that conventional medical image systems can be easily upgraded to incorporate the features and advantages of the present systems and methods.

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

Claim 1:
An ultrasound imaging system (<NUM>) comprising:
an ultrasound probe (<NUM>) for receiving ultrasound signals for a plurality of transmit/receive events; and
at least one processor in communication with the ultrasound probe, the at least one processor configured to:
identify microbubbles in the ultrasound signals for the plurality of transmit/receive events;
represent individual ones of the identified microbubbles as a multi-pixel spot comprising a plurality of pixels, wherein the number of the plurality of pixels for individual ones of the identified microbubbles is less than a number of pixels representative of the entire extent of the identified microbubble according to a point spread function of the ultrasound imaging system and greater than a single pixel; and
combine the ultrasound signals including the represented microbubbles for the plurality of transmit/receive events to form an enhanced contrast accumulation image, and characterized in that:
the processor is configured to represent the individual ones of the identified microbubbles as multi-pixel spots by passing the identified microbubbles through a filter that applies an intensity threshold value for selecting which pixels of the microbubbles to visualize, wherein the filter is based on the range of intensities presented in each identified microbubble and wherein only pixels of the identified microbubbles above the threshold value are represented in the individual ones of the plurality of ultrasound images.