MULTIPLE APERTURE ULTRASONIC IMAGING SYSTEM AND METHOD - Patent application

Abstract

Systems and methods for ultrasound imaging are provided. In some embodiments, unfocused and diverging ultrasound signals may be transmitted into a target medium from an apparent point source located behind a concave probe surface. Echoes may be received and the location of a reflector within the target medium may be determined. The location may be determined by obtaining element position data describing the location of a spherical center point of the apparent point source r and the positions of the receiving elements, calculating a total path distance as the sum of a first distance between the spherical center point and the reflector and a second distance between the reflector and the receiving elements, and determining a locus of points where the reflector may be located. This may generate a data set for the entire target medium.

Description

[Technical field]

[0001] (Priority Claim) This patent application claims priority to U.S. Provisional Patent Application No. 63 / 306,936, filed February 4, 2022, entitled "MULTIPLE APERTURE ULTRASOUND IMAGING SYSTEMS AND METHODS," which is incorporated herein by reference in its entirety. This application is related to the following U.S. Patents: US9,146,313, US9,883,848, US10,226,234, US10,064,605, and US9,668,714.

[0002] (Incorporated by reference) Unless otherwise stated in this specification, all patents, publications, and patent applications mentioned in this specification are incorporated by reference into this specification as if each individual publication and patent application was specifically and individually indicated to be incorporated by reference.

[0003] (Field) The present invention relates generally to ultrasound imaging, and more particularly to systems and methods for using symmetric and asymmetric synthetic aperture waveforms for use with PMA (Ping Based Multiple Aperture Imaging) or CET (Computed Echo Tomography). [Background technology]

[0004] (background) In conventional ultrasound imaging, a focused beam of ultrasound energy is transmitted into the body tissue to be examined, and the returned echoes are detected and plotted to form an image. Although ultrasound is widely used for diagnostic purposes, conventional ultrasound methods are severely limited by scanning depth, speckle noise, poor lateral resolution, unclear tissue, and other such problems.

[0005] To insonify body tissue at high frequencies, an ultrasound beam is shaped and focused, usually by either a phased array or a shaped transducer. Phased array ultrasound is a commonly used method of steering and focusing narrow ultrasound beams to form images in medical ultrasound examinations. A phased array probe contains many small ultrasound transducer elements, each of which can be pulsed individually. By varying the timing of the ultrasound pulses (e.g., by pulsing the elements one by one along the row), a constructive interference pattern is set up to direct the beam at a selected angle. This is known as beam steering. The ultrasound beam thus steered can then be swept across the tissue or object to be examined. Data from the multiple beams is then combined to form a visual image showing a slice through the object.

[0006] Traditionally, the same transducer or array used to transmit the ultrasound beam is used to detect the returning echoes. This design configuration results in poor lateral resolution, which is one of the most significant limitations at the heart of the use of ultrasound imaging in medical applications. Although lateral resolution could theoretically be improved by increasing the aperture width of the ultrasound probe, practical problems associated with increasing the size of the aperture have led to the aperture being kept small. Undoubtedly, ultrasound imaging is very useful even with this limitation; however, improved resolution would be even more useful.

[0007] Synthetic aperture imaging has long been used in ultrasound imaging. Advantages of using segments of an array to image from multiple separate spatial locations and directions include allowing a "wider" area and angle of view, facilitating ultrasound transmission to and from difficult to access areas, and improving image resolution. The ultrasound return data from the different segments of the array can then be stitched together into a single ultrasound image by beamforming separately, together, or a combination thereof.

[0008] Similarly, transmissions to the medium being imaged are subsequently received at different times. The longer the latency before data collection, the deeper the field of view. Thus, one or more transmissions from the array may result in several data collections that can be combined in memory and used to display a composite image or view by stitching together beamformed images from time-separated data segments. Typically, a transducer (sometimes called a probe) contains an array of transmit / receive / transmit / receive elements arranged in a plane and oriented in the plane. This is usually referred to as a one-dimensional (1D) array and is used to view a plane in the medium being imaged. The element array may be straight, "linear," or may be arranged in a symmetric convex shape, referred to in the industry as "curvilinear" or convex curve. The transducer may contain a square or rectangular array in which the piezoelectric elements are arranged adjacent to each other in both the height and width directions, also referred to as a matrix, with the elements oriented normal to the plane or surface that contains the elements. For example, a matrix array may contain 256 elements, 16 elements in the height direction by 16 elements in the width direction. To construct a collection of piezoelectric Micro-Machined Ultrasound Transducers (pMUT) or capacitive Micro-Machined Ultrasound Transducers (cMUT), a matrix of transducer elements is often "cut" from a substrate of piezoelectric material or formed in a MEMS manufacturing process.

[0009] A significant improvement in the field of ultrasound imaging has been made with the creation of multiple aperture imaging, examples of which are shown and described in applicant's prior patents and patent applications. Multiple aperture imaging methods and systems allow for both transmitting and receiving ultrasound signals through separate apertures. [Brief description of the drawings]

[0010] BRIEF DESCRIPTION OF THE DRAWINGS The novel features of the invention are set forth with particularity in the appended claims. The features and advantages of the present invention will be better understood by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings, which are set forth below.

[0011] [Figure 1] FIG. 1 is a schematic diagram of a multiple aperture imaging probe with three transducer arrays and several points to be imaged.

[0012] [Diagram 2] FIG. 2 shows a diverging beam transmission from a virtual source placed behind a transducer array.

[0013] [Diagram 3] FIG. 3 illustrates converging or focusing ultrasound waves produced by a conventional linear or matrix array by applying specially designed waveforms to the transmit elements of the transducer array.

[0014] [Figure 4] FIG. 4 is a schematic diagram of a data "cube" according to one embodiment of the present disclosure.

[0015] [Diagram 5] FIG. 5 shows a typical unfocused pulse emanating from an element on a transducer array.

[0016] [Figure 6] FIG. 6 shows that one can alternatively or additionally use a virtual point source behind the array with elements fired using waveforms / pulses based on the time delays required to create the desired semicircular diverging or converging wave pattern.

[0017] [Figure 7]FIG. 7 shows how a uniform unfocused transmit waveform can be produced over a particular target area of ​​the medium being imaged, even when there is physical spacing between the arrays and the “view” angles vary due to probe recession.

[0018] [Figure 8] FIG. 8 shows a system that may include three separate arrays with transducer elements used to generate focused waveforms that target specific points.

[0019] [Figure 9] FIG. 9 shows focused wave transmission using multiple elements across two segments of a multi-segment concave probe.

[0020] [Figure 10] FIG. 10 illustrates an embodiment of a smoothly curved concave transducer array including transmit elements configured to generate multiple transmissions that, using appropriate selection of the transmit array elements, can fill multiple sub-areas within a region of interest with sufficiently uniform diverging waves.

[0021] [Figure 11] FIG. 11 shows focused wave transmission using multiple elements in a smooth concave transducer array.

[0022] [Figure 12] FIG. 12 shows an embodiment using multiple transducers to provide diverging wave transmission from an array in a 3D curved probe with a 2D transducer array module.

[0023] [Figure 13] FIG. 13 shows an embodiment similar to FIG. 12, except that the transducer array comprises a sparse transducer array.

[0024] [Figure 14]FIG. 14 is similar to the embodiment of FIG. 12, except that it illustrates focused or convergent wave transmission using multiple elements in a regular 3D curved probe with a 2D transducer array (or a 2D sparse transducer array). [Figure 15] FIG. 15 is similar to the embodiment of FIG. 13, except that it illustrates focused or convergent wave transmission using multiple elements in a regular 3D curved probe with a 2D transducer array (or a 2D sparse transducer array). Summary of the Invention

[0025] (Summary of disclosure) A method for imaging an object using ultrasonic energy, the method comprising the steps of: transmitting an unfocused and diverging ultrasonic signal into a target medium from an apparent point source located behind a concave probe surface; receiving echoes from reflectors in the target medium with omnidirectional receive elements distinct from the apparent point source; determining the location of a reflector in the target medium by obtaining element position data describing the location of a spherical point of the apparent point source r and the positions of the receive elements, calculating a total path distance as the sum of a first distance between the spherical point and the reflector and a second distance between the reflector and the receive elements, and determining a locus of points where the reflector may be located; and generating a data set for the entire target medium.

[0026] In some aspects, the receiving elements of the probe are comprised of a shell of piezoelectric material in the shape of a concave curve, and the locations of the receiving elements are locations on the curved shell.

[0027] In one embodiment, the shape of the concave probe can be either symmetric or asymmetric.

[0028] In one embodiment, the probe is made of a concave piezoelectric, cMTU, or pMUT material.

[0029] In one embodiment, the probe elements or arrays are not physically attached.

[0030] In one embodiment, the elements of the probe are sparsely arranged and in a non-linear pattern.

[0031] In one embodiment, the array or arrays of elements are three-dimensional shapes centered about two or more axes.

[0032] In one embodiment, the array of elements is contained in a flexible material that can move or articulate about two or more axes.

[0033] In one aspect, the method further includes repeating the steps of receiving, determining, and generating with a plurality of receiving elements.

[0034] In one embodiment, the method further includes that multiple receive elements can be used to combine data of a common receive aperture.

[0035] In one aspect, the method further includes repeating the steps of receiving, determining, and generating with elements of a plurality of receive apertures.

[0036] In one embodiment, less than 10 transducers are used simultaneously to transmit unfocused and diverging ultrasound signals.

[0037] A method for imaging an object using ultrasonic energy, the method comprising the steps of: transmitting focused and convergent ultrasonic signals into a target medium toward an apparent point source located in front of a concave probe surface; receiving echoes from reflectors in the target medium with omnidirectional receive elements distinct from the apparent point source; determining a location of a reflector in the target medium by obtaining element position data describing a location of a spherical point of the apparent point source and positions of the receive elements, calculating a total path distance as the sum of a first distance between the spherical point and the reflector and a second distance between the reflector and the receive elements, and determining a locus of points where the reflector may be located; and generating a data set for the entire medium.

[0038] In one embodiment, the receiving elements of the probe are constructed from a shell of piezoelectric material in the shape of a concave curve, and the locations of the receiving elements are locations on the curved shell.

[0039] In one embodiment, the shape of the concave probe can be either symmetric or asymmetric.

[0040] In one embodiment, the probe is made of a concave piezoelectric, cMTU, or pMUT material.

[0041] In one embodiment, the probe elements or arrays are not physically attached.

[0042] In one embodiment, the elements of the probe are sparsely arranged and in a non-linear pattern.

[0043] In one embodiment, the array or arrays of elements are three-dimensional shapes centered about two or more axes.

[0044] In one embodiment, the array of elements is contained in a flexible material that can move or articulate about two or more axes.

[0045] In one aspect, the method further includes repeating the steps of receiving, determining, and generating with a plurality of receiving elements.

[0046] In one embodiment, the method further includes that multiple receive elements can be used to combine data of a common receive aperture.

[0047] In one aspect, the method further includes repeating the steps of receiving, determining, and generating with elements of a plurality of receive apertures. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] (Detailed Description) Various embodiments will now be described in detail with reference to the accompanying drawings, in which: References to specific examples and implementations are for illustrative purposes only and are not intended to limit the scope of the invention or the claims.

[0049] Although various embodiments are described herein with respect to ultrasound imaging of various anatomical structures or implanted medical devices, it will be understood that many of the methods and apparatus shown and described herein can also be used for other applications, such as imaging and evaluation of non-anatomical structures and objects.

[0050] This disclosure describes the use of composite ultrasound transmit waveforms to transducer elements that collectively produce a preferred ultrasound profile in the medium being imaged in combination with ping-based Multiple Aperture Ultrasound (MAUI) transducers used for Computed Echo Tomography (CET). MAUI transmits focused or unfocused pings into the medium, allowing reception at multiple elements, whether or not part of a continuous array. Unlike traditional phased array ultrasound systems, CET can use transmit from only a few transducers. With focused or convergent transmit, as many transducers can be used as needed, but with unfocused or divergent transmit, not many transducers are needed to form an unfocused wave. Often, less than 10 transducers are used simultaneously to form a focused or unfocused transmit. This weak signal can be combined with other methods used in CET to image tissue types with different sound speeds and attenuation.

[0051] The focused and unfocused transmission methods used in CET allow for various types of probe configurations. MAUI transducers are often concave and asymmetric or adjustable in one or more directions. The probes may be adjustable and made of flexible or mesh materials. While linear or matrix arrays can be used in CET, the concave configuration of MAUI probes often provides better data and associated imaging due to closer proximity to the target and access to the tissue from different perspectives along the probe face relative to the target medium. The method of CET, or PMA (Ping Based Multiple Aperture Imaging), as it is also called, is described in U.S. Pat. No. 9,220,478, which also shows the use of several types of concave, 3D, and adjustable ultrasound element array transducers and probes.

[0052] Thus, this disclosure provides and describes the use of synthetic aperture transmit and receive in PMAs using concave, 3D, and tunable or mesh arrays. By generating ultrasound images using either a diverging ultrasound wavefront, a converging ultrasound wavefront, or a combination thereof, significant improvements in image processing capabilities and quality are obtained.

[0053] The present disclosure provides implementation and operation of an ultrasound imaging system with the necessary hardware functionality to transmit an intended ultrasound pulse / ping or sequence of pulses / pings by synthesizing and applying appropriate electrical signals to appropriate elements in a probe / array. Additionally, the present disclosure shows the use of ultrasound reflections received from the medium being imaged, and a method for buffering and processing the converted ultrasound reflection data using the calculations outlined in prior work. The CET data set can be used to form an image for the user, as described in International Application PCT / US2020 / 056652, or analyzed by artificial intelligence without image formation. This includes variations / enhancements of this method, or the use of other beamforming methods. The calculations for processing the received reflection data to render an ultrasound image may be performed using computer software running locally on the system or on a remote system, or may be performed using firmware or electronics.

[0054] The present invention is used to improve image quality obtained with synthetic aperture ping-based imaging using 2D or 3D convex, concave, or linear segmented array or flexible array probes, but is not limited to these probe designs. The present invention allows for the utilization of multiple transmit elements to generate stronger ultrasound transmits / pings, and allows for the direction of transmit energy of these pings to be adjusted to improve image quality. Improvements in image resolution, contrast, signal-to-noise ratio, contrast-to-noise ratio, image field size, image depth, and image speed can be achieved by using multi-element transmits and by appropriately selecting transmit combinations.

[0055] Examples include directing ultrasound energy using converging wave transmissions to improve image quality at greater depths, directing diverging waves to an area of ​​interest to image it from multiple angles, using wide area diverging pings to speed up the imaging process, and positioning and steering transmissions to avoid ultrasound disturbing / attenuating elements in the image field to improve images in their shadows. Imaging different parts of the body or viewing them from a desired viewing angle may require the use of different transmit pings or combinations of pings used to generate the image.

[0056] In operation, a MAUI or PMA ultrasound imaging system is programmed to transmit a series of pings, which may vary in source location, divergence, range, and direction, by applying excitation voltage signals to selected transmit elements with appropriate delays to generate a desired ultrasound wavefront. Each ping and associated received echoes in all selected channels generate a data set or string for that channel. The channel data can be combined to generate a larger data set of the medium being imaged. This larger data set takes advantage of channels that have different perspectives on the medium. Methods are described for resolving variations in the speed of sound so that these data sets can be combined or discussed in prior work. The reflected data received from the series of pings is used to generate a data set frame by processing with beamforming calculations appropriate for the pings. All or a portion of the data set can be selected by the end user for display as an image. Data from individual transmits / pings may be weighted in generating the final image frame to equalize (or accentuate) differences in transmit / ping energy. Images generated from different combinations of pings may also be generated sequentially for display or averaging based on image requirements, with or without weighting factors applied to the images.

[0057] The present disclosure provides for the use of multiple elements, with or without spanning multiple arrays or segments of a multi-aperture or variable geometry probe, to generate strong converging or diverging directional ultrasound transmissions over all or a sub-area of ​​the medium / field being imaged that is sufficiently uniform over that sub-area to enable the generation of good ultrasound images.

[0058] Additionally, the present disclosure provides for combining data acquired from such multiple transmissions and then stitching them together into a single data set or a single image frame.

[0059] In some embodiments, judicious selection and design of such transmissions is provided to provide sufficient coverage of the region of interest while avoiding intervening obstacles that may degrade image quality.

[0060] Additionally, weighting factors may be used in image beamforming to emphasize (de-emphasize) stronger pings / transmitted data.

[0061] The application of these techniques allows the acquisition of images of better quality (resolution, contrast, signal-to-noise ratio, contrast-to-noise ratio) and at greater depths than is achievable with true point-source (single element) ultrasound transmissions using multiple aperture ping techniques in the medium. These techniques can also be used to similarly improve image quality in other obscured parts of the image (due to strong absorbers / reflectors) by judicious design of the ping / transmit pattern, with or without the use of appropriate weighting factors in these transmissions.

[0062] Different combinations of convergent and divergent transmissions are likely to be more effective for certain types of tissues and anatomical features, and optimized transmit sequences can be designed and used to image different target organs and fields of view to produce the best image of the region of interest from a selected field of view / imaging angle. For example, imaging through the skull may require more divergent imaging, while imaging through the lungs may require more convergent imaging.

[0063] (PING-based multiple aperture imaging) Some embodiments of the systems and methods described herein are based on a unique imaging modality called ping-based multiple aperture imaging ("PMA" imaging). A basic description of PMA follows. Further details, examples, embodiments, and applications of methods and structures useful for implementing ping-based multiple aperture imaging are described in applicant's earlier patent applications referenced above.

[0064] Briefly, PMA imaging involves transmitting a series of unfocused two-dimensional or three-dimensional "pings" into a medium from a "transmit aperture" (which may consist of a transducing structure or a group of transducers working in concert), then receiving and storing the echo and / or through-transmission signal of each ping. The signals are received by a number of "receive elements" (each of which consists of one or more transducer structures) grouped into an "aperture". The receive transducers generate a time-varying analog signal having an amplitude proportional to the intensity of the energy impinging on the transducer. This analog signal may be digitally sampled at a sampling rate, and the digital samples may then be stored. Each digital sample value may be proportional to the intensity of the received ultrasound. Each digital sample may represent an "echo" of some reflective or transmissive structure in the medium. The digital samples received by a single receive transducer element may be organized into a "string" of data samples, which may be subdivided into "substrings" as described in some embodiments herein. An image can be formed by mapping the samples to locations in the medium being imaged and assigning each image point (e.g., pixel or voxel) a brightness (and / or color) value proportional to the value of the contributing data sample.

[0065] While terms such as "bright" and "dark" are used herein with respect to image points and data samples, those skilled in the art will recognize that such terms are not absolute, since the brightness or contrast of the displayed image may be adjusted. Instead, these terms are used in a relative sense to distinguish those data samples and image points that represent highly reflective or "echogenic" structures, usually not necessarily referred to as "bright", from those that are least reflective, usually not necessarily referred to as "dark". Of course, some imaging systems may set up the opposite convention, such that samples of greater energy intensity are displayed as dark points, while samples of lower energy intensity are displayed as brighter points. In either convention, in the context of the systems and methods described herein, the term "bright" is intended to represent points of greater received energy intensity (whether that energy is received after reflection from the structure being imaged or after transmission through the structure being imaged), while "darker" points are those of relatively lower received energy intensity.

[0066] (Beamforming images from a PING-based multiple aperture imaging system) An entire sub-image of the medium may be obtained from the signals generated by each receive element. Sub-images obtained from multiple elements of one common aperture may be combined with each other to generate a "first level" image. Sub-images and / or first level images from multiple ping transmissions (transmitted from the same or different transmit apertures) may be combined to generate a "second level" image. Second level images from multiple receive apertures may be combined to generate a "third level" image. Many permutations of the combining order of image layers are possible, so that the sub-, first-, second-, and third level images need not necessarily be formed in the order of their names.

[0067] When the transmit and / or receive elements are spaced apart in two or three dimensions, an "image" (including sub-images) may be a three-dimensional volume made up of three-dimensional voxels. Any two-dimensional cross-section of such a volume can be selected and displayed as a matrix of two-dimensional pixels. The term "image point" can be used to refer to an individual component (e.g., pixel or voxel) of a two- or three-dimensional image.

[0068] Once a signal is received by a transducer element, the signal may be converted into a digital data sequence and stored in a volatile and / or non-volatile memory device. Each entry in this data sequence may be referred to as a "data sample." The term "data sample" may also refer to a value obtained by aggregating multiple data entries (e.g., averaging, taking a minimum or maximum value, etc.) or by interpolating between two or more data entries.

[0069] To form a sub-image from the collected data samples, each sample (individual, aggregated, or interpolated) must be mapped to a possible location in the image through a process referred to herein as "beamforming." Each data sample represents a range of possible locations (trajectories) in the image, determined by the positions of the transmitting and receiving elements, the time difference between when the ping is sent and when the signal is received, and the speed of sound through the medium being imaged.

[0070] In a multi-aperture imaging system where the transmitters are located at different points than the receivers, the locus of possible locations for each sample takes the shape of a two-dimensional ellipse or three-dimensional ellipsoid at the foci of the ellipse or ellipsoid where the transmit and receive elements are located; see U.S. Pat. No. 9,146,313 (entitled "Point Source Transmission and Speed-of-Sound Correction Using Multi-Aperture Ultrasound Imaging"). The term "locus" (and its plural form "loci") may be used to represent either the ellipse or the ellipsoid. The imaging system converges to the correct location for each image point by summing multiple data samples whose loci intersect at the same image point. Each data sample that contributes to an image point is sometimes referred to as a "contributor" to that image point. The point where the ellipse or ellipsoid intersects is enhanced (i.e., its individual contributors also have a large total intensity) and represents the correct location for that point to be displayed or recorded.

[0071] The process is susceptible to a unique form of error referred to herein as adjacent noise. If a particular data sample contains a high degree of noise that makes its trail substantially brighter than other contributors to an image point, larger areas of the adjacent noise samples may be displayed, causing noise artifacts in the shape of its trail. Such individual adjacent noise samples may cause significant distortions in the image, accentuating areas that do not correspond to the physical structure of the medium being imaged. The distortions caused by adjacent noise may be identified by any of a number of techniques, some of which are described below. Once identified, the adjacent noise may be minimized during image formation by one or more of the techniques described herein.

[0072] (Identifying adjacent noise data samples by averaging) Highly echogenic reflectors that are substantially brighter than other contributors to the same image point are problematic because they can cause adjacent noise. In this case, a "too bright" contributor that overwhelms other contributors can generate bright artifacts or other false information. This is particularly problematic at image points that would be relatively "dark" were it not for the strong echogenic reflector located in the data sample. In a related but inverse manner, a lower echogenic reflector can be erroneously displayed as much darker than would be expected because other contributors to the same image point tend to counteract the effect of the "too dark" contributor. Thus, in either case, it would be beneficial to identify data samples (or ellipses) that represent the adjacent noise.

[0073] In general, data samples resulting from different combinations of transmitted pings and receiving elements for a single image point will reveal brighter or dimmer echoes of reflectors due to differences in path length, look angle, obstacles, materials, ping transmission time, or other factors. Nevertheless, under normal conditions, the extent of such variations can be expected to remain within predictable ranges that may be determined based on empirical testing and / or mathematical modeling / simulation. Echo values ​​that fall significantly outside such predicted ranges may be noise or other forms of error. It may therefore be desirable to systematically define an "abnormally bright" value, identify data samples that contribute to the "abnormally bright" value of any image point, and minimize the adverse effects of the abnormally bright samples.

[0074] In some implementations, instead of evaluating all image points in the media for high noise, the set of image points evaluated may be reduced to a candidate set of image points. For example, in some implementations, image points having luminance values ​​less than a preset value (e.g., ≦0.9 on a scale of 0.0 to 1.0) may be selected for analysis to detect adjacent noise contributors. In other implementations, image points having luminance values ​​greater than a preset low value (e.g., 0.1 on a scale of 0.0 to 1.0) but less than a preset high value (e.g., 0.8) may be selected for analysis to detect adjacent noise contributors.

[0075] In some implementations, image points to be evaluated for the presence of adjacent noise data samples may be identified based on an analysis of neighboring image points, or image points within a region. For example, if a particular image point has a substantially higher luminance value than all neighboring image points, or all image points within a region, after applying all contributors, the image point may be selected for contributor evaluation as a possible adjacent noise contributor. In other implementations, image points to be evaluated for the presence of adjacent noise data samples may be identified by evaluating data samples that contribute to a group of image points within a region to detect "boundaries" between relatively darker and brighter image points within the region. Examples of such processes are described in the following sections.

[0076] Regardless of whether all image points or a subset of image points selected by the methods described above are evaluated, various processes can be used to identify neighboring noise contributors to a particular image point. In one exemplary embodiment, such a process may include transmitting pings from a transmit aperture, receiving reflected and / or transmitted signals from the pings, digitizing and storing sampled digital data representative of the received signals, and beamforming the stored data to map the data samples to the image points. Then, for each image point evaluated: determine an aggregate value of the set of data samples that contribute to the image point, and identify nearby noise contributors as data samples whose values ​​vary from the aggregate value by more than the expected variance.

[0077] In various implementations, evaluating the data samples to identify adjacent noise contributors may be performed before and / or after various coherent or incoherent summing steps, as described in the various applications referenced above and incorporated by reference herein. For example, in some implementations, raw data samples may be evaluated before any data summing steps in order to detect boundary regions or other identifiable features with a much higher degree of detail than would be possible after data summation.

[0078] In various embodiments, the "aggregate value" of a data sample set contributing to a particular image point may be the arithmetic mean (simple average), median (the midpoint of all sample values ​​in the set), mode (the most frequently occurring value in the set), maximum (the largest value in the set), minimum (the smallest value in the set), or other value describing or derived from the data sample set.

[0079] In various implementations, the variance from the aggregate value defining the neighboring noise data samples can be defined in many ways, for example, the variance can be a fixed numerical value, a multiple of the aggregate value, a percentage change from the aggregate value, a number of standard deviations above the aggregate value, a percentile of the set of data samples contributing to the image point, or other metric of the variance from the aggregate value.

[0080] In some implementations, neighboring noise contributors to an image point may be defined as samples having intensity values ​​at least N times greater than the mean, median, mode, maximum, or other aggregate value of the set of contributors to that image point, where N may be at least about 1.0 and up to about 2.0 or more in such implementations.

[0081] In other embodiments, adjacent noise contributors may be defined as samples having luminance values ​​that are more than N standard deviations above the mean value of the contributors to an image point. In other embodiments, adjacent noise contributors may be defined as samples having luminance values ​​greater than the maximum value of the contributor set, or N times the maximum value, or more than M% greater than the maximum value. In other embodiments, adjacent noise contributors may be defined as samples having luminance values ​​greater than N times the mode, where the "mode" is defined as the value that occurs most frequently in the set of data samples contributing to that image point. In some embodiments, the mode may be determined based on rounded values ​​of the data samples (e.g., by rounding each value in the set to a pre-set number of digits and then determining the most frequent value).

[0082] (Convergent and divergent beamforming in ping-based multiple aperture imaging) In some implementations, mathematical or other evaluation of raw data samples collected by multiple transducer elements from a PMA system may be performed prior to image beamforming to identify data samples that should be adjusted, and in some implementations, such pre-beamforming evaluation may be used for other analyses, such as object recognition or otherwise.

[0083] FIG. 1 shows a ping-based multi-aperture probe 100 with respect to a skin surface S, having arrays 12, 14, and 16. Subarrays, or often individual elements, within each array are shown as points a, b, c, d, e, f, g, h, and i. However, subarrays may be located across physical gaps between arrays and should not be considered limited to individual elements on individual arrays. The ping transmission is represented by wavefront 13 (dashed wavefront(s)) generated by the transmit aperture at "a" on array 12, shown as multiple wavelets. Point A in medium or tissue 20 is intended to represent a hard structure (e.g., calcium or hardened plaque from atherosclerosis, or other hard objects such as bone), which directly reflects or scatters the transmitted wavefront 13 in multiple directions, represented here as reflected wavefront 15 (solid wavefront(s)). The reflected wavefront emanating from point A will provide a relatively bright signal to the receiving elements of arrays 12, 14, and 16. The transmitted wavefront 13 will also continue through the medium or tissue 20 to point B, which is intended to represent an anechoic structure (e.g., a blood vessel or other soft tissue), which will provide a relatively weak reflected wavefront 17 returning to the elements on arrays 12, 14, and 16.

[0084] Echoes from points A and B are received by the receiver elements in the arrays 12, 14 and 16 and may be used by the probe 100 to generate data sets and frames used to form a multiple aperture ultrasound image or for analysis by an artificial intelligence engine. The electronic controller(s) or processor(s) associated with any probe on a PMA enabled system may initiate the process of analyzing the data within the region of interest. The data collected after analog to digital conversion is stored in a data string for a first receiver element. This receiver element may be part of an array or may be a separate element used as an omni-directional receiver. It does not need to be used in conjunction with other elements to collect and combine data in real time. A second receiver element may be used to generate a second data string resulting from the same ping used to provide the receiver element data to the first receiver element. Similarly, echo data resulting from the same ping transmission may be used by multiple receiver elements (e.g., the third, fourth, fifth, etc. receiver elements).

[0085] A processor in the PMA system, in the probe itself, or in communication with the probe (e.g., wirelessly) may then be configured to perform an average of all data set values ​​for all data strings. In some implementations, the data strings may be collected over the entire region of interest (i.e., a long sample period). In other implementations, data may be collected only for specific pixels (i.e., a specific sample period). The processor may then begin a beamforming process to generate a pixel image of the region of interest. For 3D imaging, the same process can be used to generate a voxel image. This process can be repeated for multiple ping and echo data strings.

[0086] Sending unfocused pings into a medium whose origin is not at the surface of the array becomes more difficult with ping-based multiple aperture probes. US Patent US 9,883,848 teaches some techniques related to virtual point sources. This work makes the formation of divergent and convergent beams using PMA and CET more clear.

[0087] To begin with, FIG. 2 shows a transmitted ultrasound wavefront 5 generated on a conventional linear or matrix array 1 by applying a set of designed excitation waveforms to the transmit elements 7 of the transducer array 1. In this example, the array can include a selected or resulting virtual point source 2 that can be located at a range behind the array by appropriate design of the excitation waveforms. The virtual point source 2 can be configured to transmit a circular (2D) or spherical (3D) virtual transmit wave 5. If the virtual transmit wave is electronically launched from the virtual point 2, each element of the transducer array can be controlled to launch based on delay calculations as the circular (2D) or spherical (3D) virtual transmit wave passes through that element. These launches are then integrated to generate a real physical wave in the medium at the selected virtual point source.

[0088] FIG. 3 shows converging or focused ultrasound waves generated by a conventional linear or matrix array 1 by applying specially designed waveforms to the transmit elements 7 of the transducer array 1. Here, a virtual point source 2 (or focal point) can be electronically synthesized to be any of several positions in front of the array 1. That is, the pulses from each transmit element 7 arriving at one location at a time can form a converging circle or sphere that condenses and gets smaller until it hits the virtual point source 2. When that virtual circle or sphere 5 passes the transducer elements of the array 1, it is time for the transducer elements of the array to fire. The coordination of these impulse firings then creates an actual physical wave in the medium that targets the selected virtual point source 2. This allows the transmissions from multiple transducer elements to be "focused" to a single point in the medium. The echoes returning from the point source 5 are then collected by each receiver.

[0089] Referring to Figure 2-3, at the origin of the coordinate system 6(0, 0), the coordinate (x f , z f The reflection time from an image field point 3 in the imaged medium having a field of 100 Hz is (x m , z m ) to image field point 3(x f , z f ) and from there to the receiving elements 4 of the transducer array. These reflection time information can be used by the system (e.g., electronic controller) to generate an image in a beamforming process. This beamforming process and the calculation of the appropriate transducer excitation voltage waveform requires knowledge of the speed of sound in the medium being imaged, which is typically set to 1540 m / s for soft tissue. (Details are provided in U.S. Patent Application Serial No. 16 / 506,570.)

[0090] For a normal directional transmission from a simple linear aperture / array, the simple beamforming calculation used to generate a pixel-by-pixel ultrasound image with converging or diverging waves is given as follows:

number

[0091] Where:

[0092] s m,i is the reflected signal recorded by the ith receiving element for the mth ping / transmission, and t m,f is the (x f , z f ) is the pulse arrival time delay at the pixel located at t f,i is the reception time delay between that pixel and the reflection from the i-th receiving element in the probe / aperture / array, (x m , z m) is the position of the virtual source (positive for converging sources and negative for diverging sources), L is the width of the linear probe aperture or array, c is the average speed of sound in the medium being imaged, and B(x m , z m ) is the position (x f , z f ), N is the number of receive elements in the probe / array / receive (sub)aperture, and M is the number of distinct transmit / pings used to generate the image frame. H is the Heaviside step function, which is equal to 0 for arguments less than or equal to 0 and 1 for arguments greater than 0. The origin of the spatial coordinates is the center of the linear array.

[0093] FIG. 4 is a schematic diagram of a data "cube" according to one embodiment of the present disclosure. The "cube" is composed of reflected data acquired by a series of transmissions of virtual (and / or real) sources that are beamformed based on the individual virtual source positions and combined or stitched together into a single image. Different transmissions can be targeted to different lateral or depth spatial locations, and only data related to the target region is beamformed and folded into the image. The embodiment of FIG. 4 illustrates the ability to build a data "cube" composed of samples from either diverging ultrasound waveforms, focusing ultrasound waveforms, or a combination of both. The system can receive channel data samples at time t, with the number of samples proportional to the sampling rate and image depth. Samples from transmitting sources / pings along index m (1...M) combined with receiving elements along index i (1...N) can be combined from different transmitting pings to create a data column in the complete data "cube". The data cubes (M,N,t) can then be beamformed and integrated into one image frame.

[0094] The techniques and methods described above can also be extended to segmented or multi-aperture probes to enhance their performance. For example, FIG. 5 shows a standard unfocused pulse 3 emanating from an element 4 on a transducer array 1. Such a pulse can come from any element 2 on any array 1. FIG. 6 proceeds by showing a virtual point source 2 behind the array that can be used alternately or additionally. FIG. 6 also shows additional elements of sub-aperture 4 fired to shape the waveform / pulse based on the time delay required to generate the desired semicircular diverging or converging wave pattern.

[0095] In some embodiments, the elements 4 of the array 1 may be cut from the same substrate. In other embodiments, the elements may be physically formed and shaped using micromachined piezoelectric materials such as capacitive micromachined ultrasonic transducers (cMUTs) or piezoelectric micromachined ultrasonic transducers (pMUTs). In such cases, the elements themselves may be shaped to provide additional benefits for converging or diverging waveform types to provide optimal imaging. For example, a 1D array may require rectangular shaped elements to facilitate in-plane reception of data, whereas a 2D or 3D array may require circular or elliptical elements to transmit and receive data from all angles. The size, shape and location of the elements are described in detail in US Pat. No. 10,586,846.

[0096] When the transmit elements for a virtual source must span physical spacing between elements, arrays, or angles due to recesses or spacing, difficulties arise in generating uniform, unfocused pulses, but transmit positions and orientations that must span such spacing can be designed and utilized to provide adequate wave uniformity over a specific region in the medium being imaged, allowing the entire medium to be imaged without gaps. US Patent US 10,064,605 ​​introduces several methods used to calculate the acoustic center of each element. The element positions can be fixed based on calibration to a phantom, or can be electronically adjusted in real time based on identification of a common landmark imaged by multiple transducer elements. The alignment of a probe with a fixed position does not need to be done in real time, or periodically. The alignment of a flexible or adjustable array and probe can help provide clearer imaging when using multiple aperture ultrasound imaging.

[0097] FIG. 7 illustrates how uniform unfocused transmit waveforms can be generated over a particular target area of ​​the medium being imaged, even when there is a physical spacing between the arrays and the "view" angles are different due to probe recession. As shown in FIG. 7, when there is a physical spacing between the elements or arrays utilized in a multiple aperture ultrasound probe and a diverging virtual point source 2 is located between or directly behind the physical spacing, an "imaging dead zone" 5 may be located in the immediate field in front of the spacing. In this area, due to wave interference effects, there may not be adequate reflections and sufficient data to beamform an acceptable image, compared to areas 6 where the transmit pulse is of good quality and high quality data and images are obtained. The size of the dead zone can be reduced by moving the virtual point source 2 to another location 3, especially when multiple virtual point source transmissions are utilized to collect and generate the image data set. The size of the imaging dead zone may also vary based on the physical size of the spacing and / or the angle of the plane of the separated elements or arrays. For example, even with a wide spacing, the dead zone may be negligible if the angle between the elements or arrays is large. Conversely, if the angle is near zero, the dead zone can be as large as the spacing itself. The method described in US Pat. No. 9,668,714 can be used to apply weighting factors to the data collected and finally assembled into a data set and pixel / voxel.

[0098] In the embodiment of FIG. 8, the system may include three separate arrays 1 with transducer elements 4. As shown, waves may be generated from three different physically separated transducer elements 4. Traditionally, the focal points 2 are located approximately equidistant from each element of each array. In this example, there is an analogy in that the converging waves 3 are formed from sub-apertures 4 focused to the same point. A common converging focal target may be exposed by sub-apertures of transmit elements from any array 1 in the probe, as long as they are substantially equidistant. However, FIG. 8 illustrates that the focal points need not be equidistant from each element or array. In this example, a converging / focused wave exposure region 3 is shown bounded by the intersection of three converging waves. As shown, the focal points may favor one side of the targeted tissue region. Then, by using this technique thousands of times, focal points may be located throughout the targeted tissue region, and images from each targeted region may be stitched together into a single image. When using MAUI imaging to image at deeper depths, it may be necessary to use only a portion of the probe to transmit to the target in order to obtain sufficient transmit strength to the target while avoiding strong reflectors at shallow depths.

[0099] FIG. 9 illustrates focused wave transmission using multiple elements 4 across two segments 1 of a multi-segment concave probe. In the embodiment of FIG. 9, only a portion of the multi-aperture probe is used to transmit focused energy to a deep focal target to the left of the region of interest, resulting in a convergent / focused wave 3. A virtual point source 2 is shown. In this embodiment, region 5 indicates an area of ​​poor transmit pulse quality and region 6 indicates an area of ​​good transmit pulse quality. Moving the virtual point source 2 to another location within the medium can reduce the size of the dead zone, especially when multiple virtual point source transmissions are utilized to collect and generate an image dataset. The size of the imaging dead zone can also vary based on the physical size of the spacing and / or the angle of the plane of the separating elements or arrays. For example, even with a wide spacing, the dead zone may be negligible if the angle between the elements or arrays is large. Conversely, if the angle is near zero, the dead zone can be as large as the spacing itself. The method described in US Pat. No. 9,668,714 can be used to apply weighting factors to the data collected and ultimately assembled into a dataset and pixel / voxel.

[0100] FIG. 10 shows an embodiment of a smoothly curved concave transducer array 1 including transmit elements 4 configured to generate multiple transmissions that can fill multiple sub-areas in the region of interest with sufficiently uniform diverging waves 5 using appropriate selection of transmit array elements 2. Multiple images can be stitched together to generate a final image. The probe does not necessarily need to be symmetric. In this embodiment, a virtual point source 3 is placed behind the array 1. Ping-based MAUI transmission can generate uniform and unfocused transmissions if element positions are known prior to waveform generation.

[0101] FIG. 11 shows focused wave transmission using a subset of elements 4 from within a smooth concave transducer array 1 with many more elements 2. In this embodiment, a uniform focused transmit wave can be created from the transducer array by a virtual point source 3 located at the focal point (e.g., in front of the array). The probe does not necessarily need to be symmetric. Ping-based MAUI transmission can generate uniform and focused transmissions if element positions are known prior to waveform generation.

[0102] FIG. 12 shows an array 1 with transducers arranged in an array that is concavely curved about multiple axes. In some embodiments, the same effect can be achieved using flat 2D rectangular transducers. These arrays are described in detail in US Patent US 10,835,208. This embodiment can be used to generate divergent wave transmissions by using multiple transducer elements 2 from the array 1. Furthermore, the array 1 does not have to be fixed or stationary. It can be adjustable and can be a flexible mesh. Calibration of such adjustable arrays is described in US Patent US 9,510,806. A 3D curved probe 1 can be constructed in multiple ways. In one embodiment, a 3D probe can be made of multiple flat segments of a 2D planar array to approximate a 3D curvature. In another embodiment, a custom curved array can be constructed in a molded substrate using cMUT or pMUT transducers. As described herein, the transducer array 1 can be configured to generate an ultrasonic wavefront. In the illustrated example, a subgroup 4 of transmit elements 2 is configured to generate diverging waves at a virtual source point 3 located behind the transmit elements, resulting in an exposure region 5 as shown. FIG. 13 shows an embodiment similar to FIG. 12, except that the transducer array consists of a sparse transducer array 2. In a PMA system using computed echo tomography, the elements do not have to be adjacent to each other or even coplanar. The elements do not have to be in the same array, but their positions must be known, as described in US Patent US 9,510,806. The elements may be sparse, random, physically separated, or out of plane with each other and may be effectively used within the same PMA transmit and receive sequence. Methods relating to these types of arrays are further described in US Patent US 10,854,846.

[0103] Figures 14 and 15 are similar to the embodiments of Figures 12 and 13, respectively, except that they show convergent or focused wave transmission using multiple elements in a 3D curved probe array that is concavely curved about multiple axes. In some embodiments, the same effect can be achieved using a flat 2D rectangular transducer. In these embodiments, a virtual point source 3 is placed at the focal position of the transducer array, as shown, resulting in exposure regions 5 both in front of and behind the virtual point source.

[0104] Additional geometric corrections may be required when transmissions are directed or received in directions other than normal to the array, or when the probe geometry is non-rectilinear, but the principles of determining transmit and receive path lengths and times and beamforming the received data into an image remain the same.

[0105] Regardless of the array type used in the PMA system, 1D, 2D or 3D, each ping and associated received echoes of all selected channels will generate a data set or string for that channel. The channel data can be combined to generate a larger data set of the medium being imaged. Those skilled in the art will appreciate that optimal image quality may be obtained by using a combination of virtual point sources during transmissions, including both converging and diverging transmissions, and then collecting and combining the channel data into a larger data set. This larger data set will take advantage of channels that have different perspectives on the medium. Methods are described to resolve variations in the speed of sound so that these data sets can be combined or discussed in prior work. All or a portion of the data set can be selected by the end user to display as an image. Data from individual transmits / pings may be weighted in generating the final image frame to equalize (or accentuate) differences in transmit / ping energy.

[0106] Any of the above embodiments may be used in combination with a multiple aperture imaging probe of any desired configuration. Examples of multiple aperture ultrasound imaging probes are provided in Applicant's prior patent applications referenced herein.

[0107] The above described system and method embodiments may also be advantageously applied to multiple aperture ultrasound imaging systems that utilize focused phased array transmit pulses rather than point source transmit pulses (pings). Similarly, the above described system and method embodiments may also be advantageously applied to single aperture imaging systems that use multiple sub-apertures for ping transmission. In yet further embodiments, the above described methods may also be applied to conventional ultrasound systems that use phased array transmission from a single aperture probe.

[0108] Although the present invention has been disclosed in the context of certain preferred embodiments and examples, those skilled in the art will appreciate that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and / or uses of the present invention and obvious modifications and equivalents thereof. Various modifications of the above-described embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments without departing from the spirit or scope of the present invention. Thus, the scope of the invention disclosed herein should not be limited by the specific disclosed embodiments above, but should be determined solely by a proper interpretation of the following claims.

[0109] In particular, materials and manufacturing techniques are within the level of ordinary skill in the art. Furthermore, reference to a singular item includes the possibility of a plurality of the same items. More specifically, the singular forms "a," "and," "said," and "the" as used herein and in the appended claims include plural referents unless the context clearly dictates otherwise. Unless expressly stated otherwise, the term "or" as used herein includes all alternatives presented and essentially means the same as the commonly used phrase "and / or." It is further noted that the claims may be drafted to exclude any or all elements. This statement is therefore intended to serve as a preliminary basis for the use of exclusive terms such as "solely" and "only" in connection with the description of elements of the claims, or the use of "negative" limitations. Unless otherwise stated herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains.

Claims

1. 1. A method for imaging an object using ultrasound energy, comprising: transmitting an unfocused and diverging ultrasonic signal into the target medium from an apparent point source located behind a concave probe surface; receiving echoes from reflectors within the target medium with omnidirectional receiving elements distinct from the apparent point source; determining a location of the reflector within the target medium by obtaining element position data describing a location of a spherical center point of the apparent point source r and the locations of the receiving elements, calculating a total path distance as a sum of a first distance between the spherical center point and the reflector and a second distance between the reflector and the receiving elements, and determining a locus of points where the reflector may be located; and generating a data set for the entire target medium; The method comprising:

2. The method of claim 1 , wherein the receiving elements of the probe are comprised of a shell of piezoelectric material in the shape of a concave curve, and the locations of the receiving elements are locations on the curved shell.

3. The method of claim 2 , wherein the shape of the concave probe can be either symmetric or asymmetric.

4. The method of claim 2 , wherein the probe is made of a concave piezoelectric material, a cMTU material, or a pMUT material.

5. The method of claim 2 , wherein the probe elements or arrays are not physically attached.

6. The method of claim 2 , wherein the elements of the probe are sparsely arranged in a non-linear pattern.

7. The method of claim 2 , wherein the array or arrays of elements are three-dimensional shapes centered about two or more axes.

8. The method of claim 2 , wherein the array of elements is comprised in a flexible material that can move or articulate about two or more axes.

9. The method of claim 1 , further comprising repeating the steps of receiving, determining, and generating with a plurality of receiving elements.

10. The method of claim 1 further comprising: multiple receive elements can be used to combine data of a common receive aperture.

11. The method of claim 1 , further comprising repeating the receiving, determining and generating steps with the elements of a plurality of receive apertures.

12. The method of claim 1 , wherein less than 10 transducers are used simultaneously to transmit the unfocused and diverging ultrasonic signals.

13. 1. A method for imaging an object using ultrasound energy, comprising: transmitting focused and convergent ultrasonic signals into the target medium toward an apparent point source located in front of a concave probe surface; receiving echoes from reflectors within the target medium with omnidirectional receiving elements distinct from the apparent point source; determining a location of the reflector within the target medium by obtaining element position data describing a location of a spherical center point of the apparent point source and the locations of the receiving elements, calculating a total path distance as a sum of a first distance between the spherical center point and the reflector and a second distance between the reflector and the receiving elements, and determining a locus of points where the reflector may be located; and generating a data set for the entire medium; The method comprising:

14. 14. The method of claim 13, wherein the receiving elements of the probe are comprised of a shell of piezoelectric material in the shape of a concave curve, and the locations of the receiving elements are locations on the curved shell.

15. The method of claim 14, wherein the shape of the concave probe can be either symmetric or asymmetric.

16. The method of claim 14 , wherein the probe is made of a concave piezoelectric material, a cMTU material, or a pMUT material.

17. The method of claim 14 , wherein the probe elements or arrays are not physically attached.

18. The method of claim 14 , wherein the elements of the probe are sparsely arranged in a non-linear pattern.

19. The method of claim 14, wherein the array or arrays of elements are three-dimensional shapes about two or more axes.

20. The method of claim 14 , wherein the array of elements is comprised in a flexible material that can move or articulate about two or more axes.

21. The method of claim 13 , further comprising repeating the steps of receiving, determining, and generating with a plurality of receiving elements.

22. The method of claim 13 further comprising: multiple receive elements can be used to combine data of a common receive aperture.

23. The method of claim 13 , further comprising repeating the receiving, determining and generating steps with the elements of a plurality of receive apertures.

Images