Systems and methods for imaging through varying tissue types using computed echo tomography

Abstract

Diagnostic ultrasound imaging systems and methods are provided, that can include transmitting ultrasound pulses into tissue that includes multiple tissue types and or tissue densities. The tissue densities and / or tissue thicknesses can be calculated to assign speed of sound values for each tissue type. The systems and methods can beamform received echoes based on the varying tissue types and / or tissue densities. In some examples the tissue types or densities can be determined based on patient information, or based on a location of the imaging probe. In other embodiments, the tissue densities can be computed with shear wave elastography.

Description

SYSTEMS AND METHODS FOR IMAGING THROUGH VARYING TISSUE TYPES USING COMPUTED ECHO TOMOGRAPHYPRIORITY CLAIM

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 685,217, titled “IMAGING TRAUMA INSIDE THE SKULL USING COMPUTED ECHO TOMOGRAPHY,” filed August 20, 2024; U.S. Provisional Patent Application No. 63 / 685,620, filed August 21, 2024, titled “SIMULTANEOUS IMAGING OF GAS FILLED TISSUE AND SOFT TISSUE USING COMPUTED ECHO TOMOGRAPHY,”; and U.S. Provisional Patent Application No. 63 / 685,626, titled “DYNAMIC IMAGING OF ABDOMINAL AND RIB TISSUE USING COMPUTED ECHO TOMOGRAPHY,” filed August 21, 2024, each of which are herewith incorporated by reference in their entirety.INCORPORATION BY REFERENCE

[0002] Unless otherwise specified herein, all patents, publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.FIELD

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

[0004] In conventional ultrasonic imaging, a focused beam of ultrasound energy is transmitted into body tissues to be examined and the returned echoes are detected and plotted to form an image. While ultrasound has been used extensively for diagnostic purposes, conventional ultrasound has been greatly limited by depth of scanning, speckle noise, poor lateral resolution, obscured tissues, and other such problems.

[0005] To insonify body tissues, an ultrasound beam is typically formed and focused either by a phased array or a shaped transducer. Phased array ultrasound is a commonly used method of steering and focusing a narrow ultrasound beam for forming images in medical ultrasonography. A phased array probe has many small ultrasonic transducer elements, each- 1 -SG Docket No. 10622-728.600of which can be pulsed individually. By varying the timing of ultrasound pulses (e.g., by pulsing elements one by one in sequence along a row), a pattern of constructive interference is set up that results in a beam directed at a chosen angle. This is known as beam steering. Such a steered ultrasound beam may then be swept through the tissue or object being examined. Data from multiple beams are then combined to make a visual image showing a slice through the object.

[0006] Traditionally, the same transducer or array used for transmitting an ultrasound beam is used to detect the returning echoes. This design configuration lies at the heart of one of the most significant limitations in the use of ultrasonic imaging. Imaging from behind barriers such as bone or gas filled tissue (e.g. lung, stomach) causes interference in the transmit waveform pathway which causes phase aberration in the receive beamforming that cannot be resolve. This causes what is commonly called “shadowing” where tissue behind the obstruction cannot be resolved or “seen.” Unquestionably, ultrasonic imaging has been very useful even with this limitation, but it could be more effective if it could image all tissue types. That is, image the tissue causing the obstruction as well as the tissue behind it.

[0007] In trauma, identifying areas of either pooling or pooled fluid can be especially important for quick and accurate diagnosis of chronic conditions such as subdural hematoma or inflamed ventricles. However, not only is the soft tissue of the brain not identifiable using conventional ultrasound, identifying areas of fluid or other pathology is not possible. Some conventional ultrasound systems provide physiological information on fluid movement using transcranial ultrasound; however, that tool does not provide B-Mode or anatomical imaging.

[0008] Imaging the parenchyma in the lung in real time is necessary for both diagnosis and for guidance during treatment. At present, ultrasound systems do not have adequate signal return beyond the pleura, and an entire body of science around what “A lines” and “B lines’ mean has evolved; where actual tissue beyond the pleura and into the lung is not visualized. Therefore, providers conducting therapy must rely on CT, MRI and Fluoroscopy for diagnosis and guidance in most conditions where treatment of the lung is needed.

[0009] Some tissue such as the heart and upper quadrant of the liver are often covered or obscured by the lung. Sometimes, technicians can use conventional ultrasound to effectively image the heart or upper quadrant of the liver, but cannot complete their study because one or more portions of the organ are obscured due to lung shadowing.

[0010] Synthetic aperture imaging has long been utilized in ultrasound imaging. However, it is often limited to “near field” imaging due to the weak strength of its transmissions. Computed Echo Tomography or sometimes referred to as Ping Based Imaging or Multiple Aperture Imaging uses systems and methods to conduct receive side- 2 -SG Docket No. 10622-728.600beamforming that accommodates variations in the speed-of-sound of tissue types along a path between a transmit apertures and one or more receive apertures as described in US 9,146,313. The benefits of utilizing individual receive elements or sometimes segments of an array to image from multiple separate spatial locations when combined with the speed-of-sound algorithms enables a “wider” areal and angular field of view that can facilitate the ultrasound illumination of and reception from otherwise difficult to access regions now including the tissue which was causing the obstruction like bone and lung. The reflected ultrasound data from the different segments of the array can then be stitched together into a single ultrasound image by beamforming it separately or together, or combinations thereof.

[0011] Imaging inside the skull is essential for identifying life threatening injuries and conditions such as inflamed ventricles or subdural hematoma. Ultrasound is commonly used on infants to detect such conditions up until 6 to 8 months of age, when the fontanels close. At that point, the skull becomes fully osseous tissue and a barrier to conventional imaging. Not only is the soft tissue of the brain not identifiable using conventional ultrasound, identifying areas of fluid or other pathology is also not possible. Some conventional ultrasound systems provide physiological information on fluid movement using transcranial ultrasound; however, that tool does not provide B-Mode or anatomical imaging. Similarly, lesions, bone breaks and fluid buildup in the epidural space can threaten or injure the spinal cord and nerve roots. Therefore, care takers require immediate diagnostic and navigation imaging assistance in providing care during these situations. The methods and apparatus described in this application address how Computed Echo Tomography overcomes these barriers and identify pathology therein.

[0012] Significant improvements have been made in the field of ultrasound imaging with the creation of Computed Echo Tomography (previously referred to as Ping Based Imaging or Multiple Aperture Imaging), examples of which are shown and described in Applicant's prior patents and applications. Multiple aperture imaging methods and systems allow for ultrasound signals to be both transmitted and received via separate apertures.SUMMARY

[0013] A method of ultrasound imaging in tissue is provided, comprising transmitting one or more unfocused ultrasound pulses from a transmit aperture of an ultrasound probe towards a reflector through at least two tissue types having different tissue densities; receiving echoes from the reflector with one or more receive apertures of the ultrasound probe; determining a first speed of sound value corresponding to a first tissue type; determining a second speed of sound value corresponding to a second tissue type; and beamforming the received echoes- 3 -SG Docket No. 10622-728.600with the first speed of sound value and the second speed of sound value to produce images of the reflector in the tissue.

[0014] In some aspects, the first tissue type comprises bone and the second tissue type comprises soft tissue.

[0015] In another aspect, transmitting the one or more unfocused ultrasound pulses through the first tissue type causes a propagation speed of the one or more unfocused ultrasound pulses to increase.

[0016] In some embodiments, the method includes receiving an input from a user corresponding to patient demographics.

[0017] In some aspects, the method includes receiving an input from a user corresponding to patient age.

[0018] In one aspect, the method includes receiving an input from a user corresponding to an anatomical location of the ultrasound probe.

[0019] In some aspects, the method comprises determining the first speed of sound value based on the input.

[0020] In some aspects, the first speed of sound value is different than the second speed of sound value.

[0021] In other aspects, the first speed of sound value corresponds to a first time of flight of the one or more unfocused ultrasound pulses from the transmit aperture to the reflector.

[0022] In some aspects, the second speed of sound value corresponds to a second time of flight of the echoes from the reflector to the one or more receive apertures.

[0023] In one aspect, beamforming is further based on the first time of flight and the second time of flight.

[0024] In some aspects, the method includes determining the first speed of sound value comprises: dynamically adjusting one or more parameters of the ultrasound probe; and evaluating subsequent image frames to optimize an image parameter of the image frames.

[0025] In some aspects, the image parameter comprises contrast, sharpness, and / or focus.

[0026] In some aspects, the method includes displaying the images on a display.

[0027] An ultrasound imaging system is provided, comprising: an ultrasound array comprising: at least one transmit aperture configured to transmit one or more unfocused ultrasound pulses towards a reflector through at least two tissue types having different tissue densities; at least one receive aperture configured to receive echoes from the reflector; one or more processors configured to: determine a first speed of sound value corresponding to a first tissue type; determine a second speed of sound value corresponding to a second tissue type;- 4 -SG Docket No. 10622-728.600and beamform the received echoes with the first speed of sound value and the second speed of sound value to produce images of the reflector in the tissue.

[0028] In some aspects, the first tissue type comprises bone and the second tissue type comprises soft tissue.

[0029] In another aspect, transmitting the one or more unfocused ultrasound pulses through the first tissue type causes a propagation speed of the one or more unfocused ultrasound pulses to increase.

[0030] In some embodiments, the system is configured to receive an input from a user corresponding to patient demographics.

[0031] In some aspects, the system is configured to receive an input from a user corresponding to patient age.

[0032] In one aspect, the system is configured to receive an input from a user corresponding to an anatomical location of the ultrasound probe.

[0033] In some aspects, the system is configured to determine the first speed of sound value based on the input.

[0034] In some aspects, the first speed of sound value is different than the second speed of sound value.

[0035] In other aspects, the first speed of sound value corresponds to a first time of flight of the one or more unfocused ultrasound pulses from the transmit aperture to the reflector.

[0036] In some aspects, the second speed of sound value corresponds to a second time of flight of the echoes from the reflector to the one or more receive apertures.

[0037] In one aspect, beamforming is further based on the first time of flight and the second time of flight.

[0038] In some aspects, the system is configured to determine the first speed of sound value comprises: dynamically adjusting one or more parameters of the ultrasound probe; and evaluating subsequent image frames to optimize an image parameter of the image frames.

[0039] In some aspects, the image parameter comprises contrast, sharpness, and / or focus.

[0040] In some aspects, the system is configured to display the images on a display.

[0041] A method of using unfocused transmissions through osseosis tissue to insonify anatomic imaging an object inside the skull with ultrasound energy is provided, the method comprising the steps of: transmitting an un-focused and diverging ultrasound signal through a skull into a target medium including brain tissue from a transmit aperture of an ultrasound transducer array; receiving echoes from reflectors inside the skull and brain tissue with at least one receive aperture that is different than the transmit aperture; determining a thickness- 5 -SG Docket No. 10622-728.600of the skull adjacent to the transmit aperture; and beamforming images from the echoes based on the thickness of the skull.

[0042] A method of identifying tissue edges below osseosis tissue by: transmitting a first unfocused ultrasound pulse into a tissue region of interest including one or more tissue edges; transmitting a second unfocused ultrasound pulse into the tissue region of interest; receiving echoes of the second unfocused ultrasound pulse; identifying one or more speckle noise patterns associated with the one or more tissue edges in the received echoes; assigning fiducial markers to the one or more tissue edges; transmitting a third unfocused ultrasound pulse into the tissue region of interest; measuring a movement of the fiducial markers; computing a tissue density of at least one tissue near the one or more tissue edges; and producing ultrasound images using the computed tissue density.

[0043] A method of identifying tissue density of tissues located below an ultrasound transducer and optimizing transmit and receive signals, comprising: transmitting an unfocused and diverging ultrasound signal into a target medium; receiving echoes from a reflectors in the target medium from multiple tissue types; determining speed of sound values for each of the multiple tissue types; and beamforming images with the received echoes using the speed of sound values.BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained 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 of which:

[0045] FIG. l is a schematic illustration of a multiple aperture imaging probe with three transducer arrays and several points to be imaged.

[0046] FIG. 2 is a schematic diagram of an embodiment of a concave curvilinear transducer demonstrating how transmit and receive apertures can be widened around a desired view angle to achieve greater resolution of the target area.

[0047] FIG. 2A is a schematic diagram of an embodiment of a concave transducer where the transmit aperture and multiple receive apertures can be electronically controlled to operate in different positions.

[0048] FIG. 3 is a schematic diagram of an embodiment of a concave transducer located over osseosis tissue to demonstrate the affects of bone on transmit and receive waveforms.- 6 -SG Docket No. 10622-728.600

[0049] FIG. 4 is a schematic diagram of an embodiment of a concave transducer located over osseosis tissue to demonstrate the affects of bone on transmit and receive waveforms using multiple receive apertures.

[0050] FIG. 5 is a schematic diagram of an embodiment of a concave transducer located over osseosis tissue to demonstrate the affects of bone on transmit and receive waveforms using multiple transmit and receive apertures.

[0051] FIG. 6 is a schematic diagram of an embodiment a concave curvilinear matrix with curvature in two orthogonal directions, also referred to as a Three Dimensional (3D) array. Each element in a 3D array is displaced relative to adjacent elements in all of x, y, and z axes. In this illustration, an element or elements of a transmit aperture is designated to insonify the medium. Multiple targets in the medium are illustrated for the purpose of demonstrating how volumetric data may be gathered. Multiple receive apertures are illustrated to demonstrated how simultaneous gathering of data may involve timing and tissue speed of sound adjustments.

[0052] FIG. 6A is a schematic diagram of an embodiment a concave curvilinear matrix with curvature in two orthogonal directions, also referred to as a Three Dimensional (3D) array. Each element in a 3D array is displaced relative to adjacent elements in all of x, y, and z axes. In this illustration, an transmit elements or apertures are designated to insonify the medium from throughout the array. Multiple targets in the medium are illustrated for the purpose of demonstrating how volumetric data may be gathered. Multiple receive apertures are illustrated to larger segments to demonstrate how simultaneous gathering of data may be advantageous when using designated coherence windows.

[0053] FIG. 7 is a schematic diagram of an embodiment of a concave curvilinear transducer demonstrating how transmit and receive apertures can be widened around a desired view angle to achieve greater resolution of the target area.

[0054] FIGS. 8A-8D are diagrams of a transducer array having transmit and / or receive apertures positioned over different tissue types having different tissue densities and therefore different speeds of sound in tissue.

[0055] FIGS. 9A-9C are diagrams of a transducer array having transmit and / or receive apertures transmitting ultrasound pulses into soft tissue and / or ribs having different tissue densities and therefore different speeds of sound in tissue.

[0056] FIG. 10 is a flowchart describing a method of performing ultrasound imaging through two or more tissue types having different tissue densities.

[0057] FIG. 11 is another flowchart describing a method of performing ultrasound imaging through two or more tissue types having different tissue densities.- 7 -SG Docket No. 10622-728.600DETAILED DESCRIPTION

[0058] The various embodiments will be described in detail with reference to the accompanying drawings. References made to particular examples and implementations are for illustrative purposes, and are not intended to limit the scope of the invention or the claims.

[0059] The present disclosure provides systems and methods for utilizing artificial intelligence to analyze raw data produced by Computed Echo Tomography (CET) or pingbased multiple aperture imaging (“PMA” imaging) systems The resultant data can be used to improve image quality and to conduct quantitative or qualitative analysis of both visual and non-visual diagnostic conditions.

[0060] As described in more detail below and in Applicant’s prior patents and applications, PMA imaging involves transmission of ultrasound “pings,” which can be unfocused or omnidirectional ultrasound pulses that insonify a tissue region of interest. In the case of omnidirectional unfocused pulses, the entire tissue region of interest is insonified with a single ping. Echoes of the ping(s) may be received by receive elements located at some distance from the transmitter. Each received echo signal lies along an ellipse defined by the transmitter and receiver positions and the time interval between ping transmission and echo reception. A data element can be created virtually anywhere in a 2D grid or 3D volume. Typically, ellipses crossing at a location in a 2D grid is known as a pixel. Ellipses crossing in a 3D volume are known as a voxel. An image may be formed by combining such pixels or voxels (i.e., data elements) in a way that their intersections become emphasized. Each intersection may be an image point in a two-dimensional or three-dimensional image. Concurrently and separately, groupings of data elements known as data sets may be evaluated for quantitative and or qualitative indications of diagnostic conditions.

[0061] FIG. 1 demonstrates a ping based multiple aperture probe 100 S, with arrays 12, 14, and 16. Subarrays or often individual elements within each array are indicated as points a, b, c, d, e, f, g, h and i. However, sub-arrays can be located across physical gaps between arrays and should not be considered limited to individual elements on an individual array. A ping transmission is represented by the wavefront 13 (dashed wavefront(s)) generated by a transmit aperture at ‘a’ on array 12 and is indicated by wavelets. Point A in the medium or tissue 20 is meant to represent a hard structure (e.g., calcium or hardened plaque from atherosclerosis, or other hard objects such as bone), which would immediately reflect or scatter the transmitted wavefront 13 in multiple directions represented here as reflected wavefront 15 (solid wavefront(s)). The reflected wavefront emanating from point A may provide a relatively bright signal to the receive elements in arrays 12, 14, and 16. The transmitted wavefront 13 may also continue on through the medium or tissue 20 to point B, - 8 -SG Docket No. 10622-728.600which is meant to represent an anechoic structure (e.g., a blood vessel or other soft tissue) that would provide a relatively weaker reflected wavefront 17 back to the individual transducer elements on arrays 12, 14, and 16.

[0062] Echoes from points A and B can be received by receive elements in arrays 12, 14, and 16 and used by the probe 100 to create data sets and frames used to form multiple aperture ultrasound images or for analysis by artificial intelligence engines. An electronic controller(s) or processor(s) associated with any probe on a PMA enabled system can begin the process of analyzing the data in the region of interest. Data being collected after Analog to Digital conversion is stored into data strings for a first receiver element. This receiver element may be part of an array, or it may be an independent element used as an omnidirectional receiver. It need not be used in conjunction with other elements to collect and compound data in real time. A second receiver element can be used to produce a second string of data coming off of the same ping utilized to provide receiver element data to the first receiver element. Similarly, echo data coming off of the same ping transmission can be used by a plurality of receive elements (e.g., third, fourth, fifth, etc. receiver elements).

[0063] Transducers may be contiguous in some embodiments or may configured using multiple arrays in other embodiments. No matter the type of array, transducer elements operate independently and can be utilized to form any number of either transmit or receive apertures within the structure. As used in the embodiment in FIG. 1, the terms "transducer array" or "array" generally refers to a collection of transducer elements mounted to a common backing plate. Such arrays may have one dimension (ID), two dimensions (2D), 1.5 dimensions (1.5D) or three dimensions (3D). Other dimensioned arrays as understood by those skilled in the art may also be used. Transducer arrays may also be collections of pMUT or cMUT transducer elements. An element of a transducer array may be the smallest discretely functional component of an array. For example, in the case of an array of piezoelectric transducer elements, each element may be a single piezoelectric crystal or a single machined section of a piezoelectric crystal.Imaging Inside the Skull

[0064] Computed Echo Tomography In the embodiment illustrated in FIG. 2 data reflected by reflector 170 within a region of interest 190 collected at the receiver aperture Ri is coming from a single transmit source Ti, and therefore will have a singular consistent speckly noise pattern. By itself, this is the same limiting factor of conventional ultrasound today. However, data from the transmission Ti may also be collected at aperture R2 at the same time. The channel data collected has a different aspect angle on the target, and when compounded with the aperture data at Ri will provide higher resolution data collection for the - 9 -SG Docket No. 10622-728.600pixels at the target location. The subject of how to combine pixel data for receivers located along different physical pathways at different apertures and sometime on different arrays altogether, is the subject of US Patent 9,146,313 titled "Point Source Transmission and Speed-of- Sound Correction Using Multi -Aperture Ultrasound Imaging.” In FIG. 2A, the receiver aperture Ri from FIG. 2 is now a transmit aperture TIR, which can transmit ultrasound signals into a reflector 170 within a region of interest 190. Echoes off the reflector 170 can be received by receiver aperture RIR, as shown.

[0065] In the embodiment illustrated in FIG. 3 the array of elements 150 is located over the scalp 155 and osseosis tissue, namely skull 160. The skull added here is typically fairly consistent in depth / thickness, however, the method works equally well on bone or skull with variable thicknesses. The unfocused CET transmission initially travels through the scalp on transmission line or vector 180, However, once the signals pass through the bone, the speed- of-sound of the transmission naturally accelerates from 1540 m / s to match the speed-of-sound of the bone tissue which is typically closer to 3000 m / s. The new vector for the unfocused transmit pulse may be now closer to transmission line or vector 185. This speed change is annotated in FIG. 3 by the distance between transmit lines becoming further apart. Thus, the pulse is affected by Snell’s law, both normalizes and accelerates. However, that single pulse, represented by vector 185, still insonifies more or all of the target region as if the bone / skull segment was not there. Computed Echo Tomography does not need the transmission to be precisely aimed at a target, so this change in vector and speed of the pulse is material only in that the sample collection period may be shortened due to the change in speed of sound.

[0066] Reflector 170 in the target medium then provides echos in return back towards the array of elements. This echo response then travels at the normal tissue speed-of-sound of the surrounding tissue until it reaches the skull barrier 160 again. The majority of the return trip to the transducer is therefore in the “soft tissue” of the brain which has a speed-of-sound near 1540 m / s.

[0067] In FIG 4, this sequence of transmitting from transmit aperture Ti to reflector 170 with echoes returning to receive apertures Ri and R2 is shown, where the echoes will arrive at the receive apertures at different times, and likely out of phase with each other. In this example, the transmitted pulse insonifies the target at the increased transmission speed as a result of passing through the skull (e.g., at 3000 m / s), and then reflects back to the receive apertures at the normal tissue speed for soft tissue (e.g., of 1540 m / s). This naturally causes an aberration in timing for reflected data for conventional ultrasound where trigonometry is used to try and determine a pre-designated point based on a common speed-of-sound for- 10 -SG Docket No. 10622-728.600tissue. However, CET channel data is collected for a period of n, where n is the time of flight for the target area tissue density. Meaning that if the target is located in soft tissue such as brain inside the skull, then the time-of-flight used to collect sample data is period n. However, if the target is located inside of bone, such as bone marrow inside the iliac bone, where the majority of tissue is cancellous tissue, then the time-of-flight n should be the speed of sound of cancellous tissue.

[0068] Referring to FIG. 5, a first data set is created at a first time from R1 collected from transmit T1 combined with second and third data sets collected at a second time from R2 and a third time from R3. In addition to echoes now being combined to identify soft tissue inside the skull, the aggregated data set will benefit from the constructive interference of the speckle noise patterns emanating from the different transmit locations described in PCT Pat. App. No. PCT / US2024 / 046953, incorporated herein by reference.

[0069] Now, multiple receive apertures Ri, R2 and R3 collect data from Ti at a first time. Subsequently, all receive apertures collect additional data from the transmission at T2 at a second time, and the transmission at T3 at a third time. One natural benefit of this process is to create wider and wider apertures which improved resolution. This process of improving lateral resolution using CET systems is described in US Patent No. 8,007,439, incorporated herein by reference. The curvature of the concave probe also improves trans lateral (or resolution measured diagonally from the center of the transducer) and axial resolution (measured vertically from the center of the transducer. These improvements are in part due to the reduction in angular offset and associated “view angle” by receiving elements, and in part due to being physically closer to the image targets. Further, different transmission frequencies can be interlaced into the different transmit and receive apertures, can be utilized to further create higher resolution data sets.

[0070] The exact time at which reflector 170 is insonified is not critical. What is critical is that that channel be collected for the period of the preponderance of tissue as described above. Much like the aperture of a camera remains open for fill the matrix of arrays data sets, CET systems collect, assemble and use weighting factors to build data sets from the receive data collected from multiple insonifications and subsequently directions of interrogation for the target region. These methods are described more fully in US 9,668,714, incorporated by reference herein.

[0071] While beamforming / imaging can be performed with the systems described herein using a single assumed speed of sound corresponding, generally, to the speed of sound in soft tissue, the present disclosure provides systems and methods that can increase imaging resolution and accuracy by using two-speed of sound values to correct for distortion of the - 11 -SG Docket No. 10622-728.600ultrasound signals resulting from passing through other tissue types, such as bone (e.g., the skull, ribs, etc.), or other tissue regions or types with different speeds of sound (e.g., organs or gassy tissue regions like the lungs or stomach). The first speed of sound value can be used to calculate transmission times from the array to the reflector through the other tissue type, which, such as when the signal passes through bone, is typically faster than it would be if only transmitted through normal soft tissue. The second speed of sound value can be used to calculate transmission times from the reflector back to the array, or to each of the receive apertures of the array (e.g., to Ri, R2, R3, etc.). The second speed of sound value may correspond to normal (e.g., soft tissue).

[0072] In one example, the first (increased) speed of sound value can be determined based on assumptions made by or input into the system about the bone or other tissue the transmission signals are passing through that would affect the transmission speed. The assumptions can be input into the imaging probe or system, such as by a user. For example, a user may input patient information, such as age, gender, disease state, or other factors that may be useful for determining the thickness or depth of the tissue that the transmitted pulses are passing through. The user may also input the transmission location (e.g., the skull, ribs, etc.), or specifics on the transmission location. For example, the skull is typically thinner near the temples than it is on the top or back of the skull, so knowledge of the transmission location is important to make the most accurate assumptions about the bone or skull thickness. Therefore, the system may include input settings allowing the user to input not only the general location (e.g., the skull), but also specific sub-locations relevant to the anatomy for more accurate estimates of the tissue thickness.

[0073] In some embodiments, the system can automatically determine the location of the probe, and use that information to make assumptions about the thickness of the tissue of interest. For example, the system may obtain images using a single speed of sound, analyze the images, and determine that the images are obtained, for example, by passing transmission signals through a specific tissue type such as the skull, ribs, lungs, spine, etc. In other examples, the system may include optical tracking sensors, accelerometers, or other sensors which, in combination with other information such as sensors positioned on the body, or images of the probe on the body of the patient, may determine the location of the probe relative to specific patient anatomy.

[0074] In some examples, the probe or system can automatically calculate the thickness of a tissue region of interest, such as with image processing algorithms that analyze images obtained with the system and measuring or calculating the width or depth of the tissue region or structure of interest directly from the images.- 12 -SG Docket No. 10622-728.600

[0075] Alternatively, the system can automatically determine the first speed of sound of the tissue region of interest by obtaining a series of images in which the first speed of sound value is iteratively adjusted, and the images can be compared to another until the sharpest images are produced. The system can evaluate any number of parameters of the images to obtain the best resolution, including but not limited to sharpness or contrast. If subsequent images get sharper before then becoming less sharp, then the system knows the optimal first speed of sound value to use based on the value used for the sharpest (or most contrasty) image. That first speed of sound value can then be used for all subsequent images taken at that anatomical location.

[0076] In other embodiments, the probe itself may be specifically suited or tailored for a specific anatomy. For example, if the probe is only used for imaging through the skull, then the probe can be preprogrammed with assumptions that assume the first speed of sound value is for the thickness of the skull. The assumptions can be for an average patient. While these assumptions may not be perfect, and therefore may not result in the most optimal image quality, the image quality will be improved compared to systems that use only a single speed of sound in the beamforming.

[0077] In some examples, the system is able to estimate or calculate the thickness or depth of the target tissue of interest to an accuracy of at least 100 microns. This accuracy allows for precise speed of sound values to be used to optimize images and / or increase resolution, sharpness, or contrast.

[0078] It is noted that the ultrasound probes or arrays described herein can have very wide apertures that span large distances, typically having far wider apertures than conventional imaging probes. As such, the depth or width of a target tissue of interest, such as the skull, may vary even between different transmit or receive apertures on the probe of the present disclosure (e.g., a skull thickness at Ti in FIG. 5 may be thinner / thicker than the skull thickness at R3). Therefore, it is an object of this disclosure to determine tissue thickness / widths at multiple points or apertures along a given ultrasound probe. The techniques described above can be repeated for multiple transmit apertures along the probe. Assuming the probe remains stationary, separate “first” speed of sound values can be used depending on the transmit aperture used.

[0079] FIGS. 6-6 A are presented here to represent a 3D array used with a PMA system to create 3D volumetric data sets. In FIG. 6, a snapshot of multiple aperture data collection is depicted enroute to building an image of an entire volume 310. Here, an element or elements of a transmit aperture Ti transmit a pulse into the volume that includes scatterers such as 321 and 332. Receive echoes returning to receive apertures R2 and R3 are shown in FIG. 6 A. The- 13 -SG Docket No. 10622-728.600elements making up receive aperture R2 may be assembled in a variety of shapes. Here, a square of elements makes up the receive apertures R2 and R3. As mentioned above, the speed of sound along the path from the transmit aperture Ti to the reflector 321 or 332 is irrelevant to the coherent addition of the received signals as long as a single aperture is used to receive, however, speed of sound corrections can be made to improve image quality when using multiple receive apertures Ri and R2.

[0080] In some embodiments, the size of the receive aperture R2 may be as large as for a conventional phased array (e.g., about 2cm). But unlike a conventional array, the total aperture 340 determining the lateral and transverse resolution of the system is much larger comprising the distance from the transmitter Ti to the group of receiver elements R2, and could be as wide as the entire array 300 or wider if a transmitter was located on another array within the probe (or in a separate probe in electronic communication). The elements located in the receive aperture R2 each collect volumetric data from the Ti transmit pulse.Identifying Trauma Within the Skull

[0081] Collecting data through varying tissue types naturally requires the accommodation of differing tissue acoustic impedance with differing speeds-of-sound. Pixel and voxel computations can only be accurate when these accommodations are made. US Patent 9,146,313 titled "Point Source Transmission and Speed-of-Sound Correction Using MultiAperture Ultrasound Imaging" covers these methods in detail.

[0082] A processor in the PMA system, in the probe itself or in communication with the probe (e.g., wirelessly) may then be configured to conduct calculations using all data set values for all data strings. In some implementations, the data string may be collected for an entire region of interest (i.e., large sample period). In other implementations, the data may be collected for only a specific pixel and voxel (i.e. specific sample period).

[0083] The processor can then initiate the beamforming process to create digital values at a pixel location in the region of interest. In the case of 3D diagnostics and imaging, the same process can be utilized to create data values by voxel. The process can be repeated for multiple ping transmissions and echo data strings collected for multiple receivers.

[0084] As a result of the beamforming process, two key pieces of data are collected for each pixel or voxel. The first is frequency. Peak frequency is determined as a function of the bandwidth selected in the system settings. Larger receiver bandwidth, selectable by the end user, enables more dynamic range and therefore each pixel can have a more accurately determined frequency value. Smaller bandwidth settings will not offer as much information on frequency per pixel or voxel.- 14 -SG Docket No. 10622-728.600

[0085] The second key piece of data collected is value or amplitude at that pixel or voxel location. The pixel or voxel value is determined by the strength of the return in milli-volts.

[0086] MAUI Assigned Acoustic Impedance (MAAI) can be a value generated from lab testing of all body tissues (e.g. bone, blood, muscles, organs, etc.) and assigned using preset controls used by the operator. That is, if imaging liver and ribs, a preset control would be assigned for that condition so that those types of tissue speed-of-sound would be ideally included in beamforming This method analyzes multiple tissue types simultaneously within the data set (see US 63 / 583,103 Imaging Skull, Bone and Lung Imaging Using Multiple Aperture Ultrasound) and subsequently in the beamformed imaging. Therefore, preset values need not be assigned during imaging or data collection, rather the operator need only place the probe over the area of interest and MAAI will be automatically assigned.

[0087] A second, and preferred method of determining subsets of traumatic tissue in real time using the methods described in No.PCT / US2013 / 027120 Determining Material Stiffness in Multiple Aperture Ultrasound. CET or PMA systems may use a combination of speckle noise edge detection either off axis shear waves to determine tissue stiffness in real time. This unique enables identifying and tracking traumatic tissue inside the cranial vault.

[0088] The lab generated MAAI values may be stored locally on a PMA system, PMA base station or in the cloud, and are regularly updated.

[0089] Pixel or voxel data will be assigned MAAI values by comparison to the lab generated table. The assigned value will be relative to data energy level. The higher the energy level, the higher MAAI value will be. In certain embodiments, data can be classified based on density because the higher MAAI value is the harder tissue the target it.The speed of sound associated with a pixel location, when grouped with like tissue, may be an important indicator of that type of tissue. The table below is a listing of acoustic impedance collected with a PMA system:

[0090] Using the methods and apparatus described herein, it therefore becomes possible to both collect data and beamform images of trauma within the cranial vault. When imaging through the skull, the bulk of channel data collected by the transducers represents either soft tissue with a typically at 1540 m / s or cancellous bone tissue with a typically speed-of-sound value of 3000 m / s.

[0091] B-Mode and Doppler or Flow images can be produced of all types of all tissue types and implanted devices inside the cranial vault as described above and in (insert motion detection patent number).

[0092] Tissue affected by trauma can be further identified using MAAI methods as described herein. Trauma physiology such as subdural hematomas, ruptured or inflamed- 15 -SG Docket No. 10622-728.600ventricles, or even the patency of a ventricular shunt may be imaged and identified using edge detection from either CET elastography or the use of MAAI. Hence a fluid filled suspected trauma region, such as a subdural hematoma, may be automatically identified by the CET system.

[0093] While edge detection can often be done by the system automatically, in cases where the operator may want to mark the tissue experiencing trauma, the use of manually set fiducial marks is also possible with the system. Not only does the system manually allow these marks, but per US (insert motion tracking) those fiducial marks may be tracked automatically by the system after manual placement.

[0094] Using fiducial marks can also be beneficial for recording size, shape and volume of the tissue experiencing trauma. For instance, a subdural hematoma may spread out in a long oval type structure directly below the skull (like a squished pancake). This would be hard to meause and identify the volume of fluid that is present. However, by using a PMA system with 3D probe and fiducial marks, the volume of fluid could be easily calculated.Using CET to Image Tissue with Different Acoustic Impedance

[0095] Computed Echo Tomography In the embodiment illustrated in FIG. 7 data collected at the receiver aperture Ri is coming from a single transmit source Ti, and therefore will have a singular consistent speckly noise pattern. By itself, this is the same limiting factor of conventional ultrasound today. However, data from the transmission Ti may also be collected at aperture R2 at the same time. The channel data collected has a different aspect angle on the target, and when compounded with the aperture data at Ri will provide higher resolution data collection for the pixels at the target location. The subject of how to combine pixel data for receivers located along different physical pathways at different apertures and sometime on different arrays altogether, is the subject of US Patent No. 9,146,313, incorporated herein by reference.

[0096] In the embodiment illustrated in FIG. 8 A two fundamentally different organ tissues are represented under a CET array of elements 150: Lung 165 and Liver 160. The transmitter Ti is located directed over the liver 160. Ti is transmitting through the skin, adipose tissue, and into the liver; all tissues roughly having a first speed of sound of 1540 m / s. While receive aperture Ri is also located directly over the liver tissue. Therefore, the receive aperture Ri will receive data from the same tissue density consideration as the transmitted data at 1540 m / s. The data received on R2, which is positioned over the lung 165, will receive echoes through a completely different type of tissue, in this case lung 165, with a different tissue density than that of the tissue adjacent to the transmit aperture (e.g., liver). Lung tissue has a speed of sound coefficient of roughly 700 m / s, while liver tissue has a- 16 -SG Docket No. 10622-728.600speed of sound of roughly 1540 m / s. Therefore, echoes arriving a R2 will out of phase with those arriving at Ri. This is similar to the issue described above with respect to transmitting through bone such as the skull.

[0097] In order to ensure that channel data is captured for the entire data target region when the array is over significantly different types of tissue, the period of data collection can be either manually or automatically adjusted. CET channel data is collected for a period of n where n is the time of flight for the target area tissue density. Meaning that if the target is located in air filled tissue such as lung, then the time-of-flight used to collect sample data is period n. Or, if the target is located primarily in soft tissue like the liver, then the time-of- flight n should be the speed of sound of liver tissue.

[0098] Tissue density can be automatically determined by CET systems in a few ways. MAUI Assigned Acoustic Impedance (MAAI) can be a value generated from lab testing of all body tissues (e.g. bone, blood, muscles, organs, etc.) and assigned using preset controls used by the operator. This method analyzes multiple tissue types simultaneously within the data set and subsequently in the beamformed imaging. Presuming that the majority of tissue being imaged is of the same density, then preset values need not be assigned during imaging or data collection, rather the operator need only place the probe over the area of interest and MAAI will be automatically assigned.

[0099] A second, and preferred method includes determining tissue subsets in real time. CET or PMA systems may use a combination of speckle noise edge detection from off axis shear waves to determine tissue stiffness in real time. This unique capability enables identifying and tracking tissue types, such as organs, inside the same target region or field of view.

[0100] A primary obstacle in all types of ultrasound based imaging is when there is a large differential in tissue density that either causes diminished (shadowed out behind an obstacle) or over saturated data (bright reflection off of an obstacle obscuring view of other tissue).

[0101] In the embodiment illustrated in FIG. 8B, two fundamentally different organ tissues are represented under a CET array of elements 150: Lung 165 and Liver 160. The transmitter Ti is now located directed over the lung in a different aperture altogether from receive aperture R2. In this example, Ti is transmitting through the skin, adipose tissue, and into the lung. Receive aperture Ri is directly over the lung 165, therefore data collection and imaging are conducted normally using CET. However, there are two complications. First, the unfocused transmit is now proceeding at two different speeds: 700 m / s inside the lung, and 1540 m / s inside the liver. Therefore, transmissions will arrive at reflectors 170 and 180- 17 -SG Docket No. 10622-728.600with different intensities and speeds (reflective of tissue density and associated speed-of sound). The transmission time of flight is not of primary concern using CET for the reasons described here. However, the fact that two different times of flight on the receive beamforming is of concern. Echoes arriving a R2 will be out of phase with those arriving at Ri.

[0102] A primary obstacle in all types of ultrasound-based imaging is when there is a large differential in tissue density that either causes diminished (shadowed out behind an obstacle). Additionally, transmissions can be deflected off of swaths of tissue with large speed-of-sound differentials from the surrounding tissue. In this case, the pleura 167 may may serve as such a barrier. A portion of the transmission from Ti therefore may be deflected off of the pleura 167 and hit Ri causing an over saturation the normal tissue data due to the immediate collection of such a strong pulse. Such an oversaturation has the appearance of a bright light obscuring the tissue data behind it.

[0103] A further complication is the respiration of the patient during imaging. For instance, during exhalation the lung may make up only a small portion of the imaged area as in FIG. 8A. However, during inhalation FIG. 8B may be a more accurate representation of the type of tissues below the probe. This affects all organs and tissue around the lungs including the heart, spinal column, great vessels, and spleen to name just a few. Therefore, all of the complications of diminished signal and oversaturated signal mentioned above can be subject to the respiration rate of the patient depending on probe location. In order to collect volumetric 2D and 3D data sets, it would be ideal to overcome these limitations and collect complete and coherent data sets as described herein.Accommodating Differentiated Tissue in the Same Image Using CET

[0104] What’s unique in CET is that the transmit energy is unfocused. All CET system must identify the time and location of the transmit, however, diffraction on transmit pulse and speed cause by tissue differences accommodated by the received side beamforming of CET. That is the pulse is affected by Snell’s law, normalizes and accelerates. However, that single pulse still insonifies more or all of the target region even as is transfers between tissue types. The speed-of-sound of the transmission at the point of impact with the reflectors 170 and 180 does not significantly affect data collection or beamforming. The amplitude of the insonification of the target is of more consequence, so that the returning echo will have strength to reach the probe surface. Tissue with high acoustic impedance naturally degrade transmission signal strength or amplitude with depth; however, that effect has no affect on the receive side beamforming process. The data which is collected will be beamformed as long as there is adequate signal strength the reach the probe’s surface. Those familiar with CET- 18 -SG Docket No. 10622-728.600and PMA systems know that weak signal strength on the return signal is less of a factor on image quality than with conventional ultrasound systems since CET systems are able to compound data from distant or disparate elements of a large probe. This compounding of weak signal strength often provides more than enough signal to beamform a very good image or data set.

[0105] To compensate for tissue with high acoustic impedance, it is preferred to use unfocused transmissions using a larger number of wavefronts. Using a virtual point source as described in both US Application 18 / 165,276 and US 9,883,848, 3, 5, 7, 9 or more elements as unfocused transmissions are helpful in overcoming tissue impedance at depth. In one embodiment, using a 9-element unfocused ping transmission provides adequate lung insonification to receive echoes through the CET array from the lung tissue. Conversely, to image soft tissue such as the liver, a single element unfocused ping transmission provides adequate signal strength throughout insonifying the liver and even tissue below (e.g. IVC) because of the low acoustic impedance of the liver.

[0106] The exact time at which reflector 170 is insonified is not critical. What is critical is that that channel be collected for the period of the preponderance of tissue as described above. Much like the aperture of a camera remains open for fill the matrix of arrays data sets, CET systems collect, assemble and use weighting factors to build data sets from the receive data collected from multiple insonifications and subsequently directions of interrogation for the target region.

[0107] In a preferred embodiment, therefore, dynamically adjusting transmit configuration is desired. As described above, tissue density can be automatically determined by CET systems in a few ways. MAUI Assigned Acoustic Impedance (MAAI) can be a value generated from lab testing of all body tissues (e.g. bone, blood, muscles, organs, etc.) and assigned using preset controls used by the operator. This method analyzes multiple tissue types simultaneously within the data set and subsequently in the beamformed imaging.

[0108] The second, and preferred method includes determining tissue subsets in real time. FIGS. 8C and FIG. 8D demonstrate the respiration process between inhalation and exhalation. This embodiment utilizes shear wave elastography to identify the tissue stiffness and therefore density. In FIG. 8C the shear wave is sent from transmit Aperture T1 181 causing wave forms 182. Using Young’s modulus, therefore, the speed of the progression of the waveforms can be utilized to determine tissue density. In this case, organ 160 is likely liver. FIG. 8D then illustrates another point in the respiration cycle, where shear wave 181 also enters the tissue from Tl. Waveforms 182 also progress outward and tissue stiffness can be determined as above.- 19 -SG Docket No. 10622-728.600

[0109] The edge between tissue types can be identified by speckle patterns as described above. This edge can be logged into memory. An alternate embodiment enables the user to manually place fiducial marks to identify the edge between the organs. It’s also important to note that the edge need not proceed vertically to the surface, but could be horizontal and define an edge at depth. Edges need not be straight or long to be defined. They can be curved or even non-liner with breaks between segments. The complete edge may be interpolated and added in software.

[0110] Once the edge of the organs has been defined, then one or more processors can be utilized to dynamically and in real time change two fundamental variables to improve image quality. First, the transmission variables (e.g. more or less elements utilized) will be adjusted based on the acoustic impedance of the tissue being transmitted into. Second, the data collection period n, can be adjusted to accommodate the time of flight for the type of image. Put another way, more than one speed of sound value can be used in beamforming the images based on the detected edges of the organs or various tissues, and the associated speed of sound values for each tissue between the detected edges.

[0111] In a preferred embodiment, data collected on either side of the edge will be weighted. Data received from the segment of elements over one type of tissue should be weighted more strongly, while data received from the other type of tissue could also be weighted.

[0112] CET or PMA systems may use a combination of speckle noise edge detection from off axis shear waves to determine tissue subsets inside the larger organ stiffness in real time. This unique capability enables identifying and tracking tissue types, such as organs, inside the same target region or field of view. The use of elastography in tissue definition can be of further advantage to define lesions or pathology.Using CET to Image Through the Ribs

[0113] In the embodiment illustrated in FIG. 9A, transmit aperture Ti is the source of the transmit ping (single or small group of elements) creating an unfocused pulse toward reflector 170. For reference, the path 180 is from the element(s) to reflector 170. The echo off of the reflector 170 and toward receiver Ri is annotated by vector 190. Ribs or bone are represented by structures 150. Ti is located over and transmitting through the skin, adipose tissue, and into soft tissue beneath. Similarly, receiver Ri is located over and receiving echoes from reflector 170 located in the soft tissue (organ) and then through the adipose tissue, and skin. Therefore, Ri will receive data echoes by using roughly the same tissue density consideration as the transmitted Ti at 1540 m / s.- 20 -SG Docket No. 10622-728.600

[0114] In the embodiment illustrated in FIG. 9B, transmit aperture T1 remains located over and transmitting through the skin, adipose tissue, and into soft tissue beneath. Receive aperture R2 is located directly behind a rib or bone 150. The echo coming off of reflector 170 has a contiguous wave shape while remaining in tissue of the same density. In this case, a liver or other similar soft tissue organ. However, once the echo reaches rib 150 it normalizes and accelerates due to Snell’s law. The wave shape now breaks up. The original wave shape 160 coming from 170 continues on paths to both R1 and R3. The portion of the wave transitioning the rib or bone now accelerates to attempt to match the speed-of-sound of the rib, roughly 3000 m / s. Hence new wavelets 165 emerge slightly ahead of the original waveform 160. These wavelets will also change their vector away from the original vector 190 depending on the angle of incidence and shape of the bone. The acceleration and deflection of the different return wavefronts are compensated for by CET so that an entire data set can be constructed.

[0115] CET is concerned with receive side beamforming, and the fact that multiple tissues are in the return path of the echo are commonly accommodated during CET beamforming as is the case represented in FIG. 9B.

[0116] The primary problem of imaging through and around ribs or bone, is when the transmission is directly through the rib. FIG. 9C illustrates transmit aperture T2 being located directly over rib or bone 150. The normal transmission is initiated from the element(s) at aperture T2 as illustrated. However, upon reaching rib 150 the waveform is affected by two physical effects. First, the waveform encounters large difference in acoustic impedance between the soft tissue (skin and adipose tissue) followed by much higher acoustic impedance of the rib. A portion of the transmission then bounces off as represented by waveforms 187 or is immediately reflected back toward the CET array. Some of the transmit waveform 185 continues on its normal trajectory past rib 150. The remainder of the waveform actually transits through rib 150. This portion of the transmission is affected by Snell’s law. That is, the transmission accelerates to attempt to match the new speed-of-sound of the rib or bone closer to 3000 m / s. The waveform direction is also altered when it normalizes. The resultant transmit energy 190 on the distal side of the rib is now traveling faster, in a new direction and may be further fragmented oval and non-uniform shape of the probe. Therefore, the transmit energy is not sufficient out of phase and scattered, that reflected energy may not be captured or be sufficiently dislocated during the receive period that channel data will contribute more noise than meaningful signal during for this frame collection. While perhaps a small portion of the transmit energy from T2 may be utilized, presumably most of the data collected will add “noise” to the data set and subsequent image.- 21 -SG Docket No. 10622-728.600

[0117] While CET elements can be used to transmit both focused and unfocused waves, the preferred embodiment is to use small numbers of element to create unfocused “ping.” After a single ping is initiated, all elements on the array are used to collect data. For instance, in one embodiment a single element transmits an unfocused pulse, then the remaining elements collect echo data from reflectors in the medium. CET transmitter elements, therefore, use a small number of elements that can be easily turned on and off since they are not used as phase transmitters.

[0118] This advantage of turning off transmitters without degrading the amount of energy utilized during transmission is unique to CET and PMA systems. Turning off transmitter elements that are directly in front of ribs or bone then enables the use of transmitters that provide the greatest and most coherent signal strength to be placed into the area of the body. That is, CET beamforming is done on the receive side only, so the more transmit energy that makes into the abdomen without interference from the ribs on transmit, the more energy that will be returned to the array and contribute to strong signal detection. Remember, with CET systems energy coming back to receivers through differing types of tissue including through the ribs, will be beamformed completely and presented in the image.

[0119] Adding a proximity detector then to CET and PMA systems enables dynamic echo location when the probe is located over ribs. In FIG. 9C, for instance, when a fully saturated signal is detected in channel data from element(s) located at R4, immediately after the T2 ping transmit, it can be determined that there is a rib adequately in front of the transmit aperture T2 to interfere with the transmit signal. Therefore, transmit aperture T2 would be skipped in the transmit cycle so that other transmit apertures may be utilized which don’t have ribs directly in front of them. The result would be to further use data from unobscured transmitters rather than dilute the strong signal strength data with noise from obscured transmit sequences. In a non-intuitive way, the transmissions coming back through the ribs will actually be stronger and more coherent, and in light of the receive side beamforming of CET, will provide more clear images of the ribs themselves.

[0120] CET systems typically fire multiple pings per data frame collected, and operated at over 25 frames per second. A typical sequence of 48 pings are fired for each frame, and from locations all across the face of the transducer array. Therefore, the cycle time on dynamically turning off transmissions located directly in front of ribs can be refreshed in almost real time in conjunction with normal CET beamforming. Therefore, operators can move the probe over the ribs without restriction on speed of angle.- 22 -SG Docket No. 10622-728.600

[0121] According to aspects of the disclosure provided above, methods of ultrasound imaging are included. FIG. 10 is a flowchart 1000 that describes one such method of forming ultrasound images using the technique described above.

[0122] At step 1002 of flowchart 1000, the method can include transmitting unfocused ultrasound pulses towards a reflector and through at least two tissue types having different tissue densities. For example, ultrasound pulses transmitted from a transmit aperture may pass through bone or other dense tissue as they propagate towards a reflector in a subject. The bone or dense tissue may comprise, for example, skull, ribs, spine, or other bones. In some examples, the tissue may instead be gaseous or filled with air, such as lungs or the stomach. Regardless, the pulses pass through at least one tissue having a different speed of sound value than typical soft tissue. If the pulses pass through dense tissues such as skull or bone, the increased density can cause the speed of the pulses to increase towards the reflector.

[0123] At step 1004 of flowchart 1000, the method can included receiving echoes from the reflector with one or more receive apertures. As described herein, receive apertures may include groupings of transducer elements that are separate or distinct from the transducer elements of the transmit aperture. The receive apertures may be physically separated from the transmit aperture, or spaced apart from the transmit aperture.

[0124] Next, at step 1006 of flowchart 1000, the method can include determining, calculating, or estimating a first speed of sound value corresponding to the first tissue type. If the first tissue type is bone, for example, then the speed of sound value can be based on the thickness and / or location of the bone. The thickness can be estimated in a number of ways, including but not limited the system making assumptions about the tissue, or receiving input / assumptions from a user that can include but not be limited to patient data, demographic data, patient age, disease state, or precise anatomical location of the imaging probe or transmit array. With this information or assumptions, the system can estimate the thickness of the first tissue type (e.g., the thickness of the skull at the location of the transmit aperture). In other embodiments, the system can automatically adjust the speed of sound value by obtaining a series of images and iteratively adjusting the speed of sound value, then evaluating each image frame to optimize resolution, contrast, focus, or sharpness.

[0125] Similarly, at step 1008 of flowchart 1000, the method can include determining, calculating, or estimating a second speed of sound value corresponding to the second tissue type. Typically the second speed of sound value is the general speed of sound in soft tissue. For example, if imaging through the skull, then echoes returning from a reflector to the probe will pass through the skull at the very end of their propagation, prior to being received or- 23 -SG Docket No. 10622-728.600detected by the probe. Therefore, changes in propagation speed of the waves will not affect imaging as much as they do on the transmit side.

[0126] At step 1010 of flowchart 1000, the method can included beamforming the received echoes to produce images of the reflector. The beamforming can use the first speed of sound value for the transmission time from the probe to the reflector, and the second speed of sound value for the return time from the reflector to the probe. The resulting images can be displayed on a display of the system at step 1012.

[0127] FIG. 11 is a flowchart 1100 that describes another method of forming ultrasound images using the technique described above.

[0128] At step 1102 of flowchart 1100, the method can include transmitting one or more shear wave pulses into tissue to determine tissue edges and / or tissue densities of two or more tissue types. The edge between tissue types can be identified by speckle patterns as described above.

[0129] At step 1104 of flowchart 1100, once the edges have been defined, the system can dynamically and in real time determine speed of sound values for the different tissue types. This can be accomplished in a number of ways as described above, including but not limited to dynamically adjusting beamforming parameters, such as a speed of sound value for each tissue type, to optimize the image quality, sharpness, contrast, or resolution.

[0130] At step 1106 of flowchart 1100, the method can include transmitting unfocused ultrasound pulses towards a reflector and through at least two tissue types having different tissue densities. For example, ultrasound pulses transmitted from a transmit aperture may pass through bone or other dense tissue as they propagate towards a reflector in a subject. The bone or dense tissue may comprise, for example, skull, ribs, spine, or other bones. In some examples, the tissue may instead be gaseous or filled with air, such as lungs or the stomach. Regardless, the pulses pass through at least one tissue having a different speed of sound value than typical soft tissue. If the pulses pass through dense tissues such as skull or bone, the increased density can cause the speed of the pulses to increase towards the reflector.

[0131] At step 1108 of flowchart 1100, the method can include receiving echoes from the reflector with one or more receive apertures. As described herein, receive apertures may include groupings of transducer elements that are separate or distinct from the transducer elements of the transmit aperture. The receive apertures may be physically separated from the transmit aperture, or spaced apart from the transmit aperture.

[0132] At step 1010 of flowchart 1100, the method can included beamforming the received echoes to produce images of the reflector. The beamforming can use speed of sound- 24 -SG Docket No. 10622-728.600values and / or the dynamically adjusted parameters as discussed above in step 1104. The resulting images can be displayed on a display of the system at step 1112. of flowchart 1100.

[0133] Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and / or uses of the invention and obvious modifications and equivalents thereof. Various modifications to the above embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.

[0134] In particular, materials and manufacturing techniques may be employed as within the level of those with skill in the relevant art. Furthermore, reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms "a," "and," "said," and "the" include plural referents unless the context clearly dictates otherwise. As used herein, unless explicitly stated otherwise, the term “or” is inclusive of all presented alternatives, and means essentially the same as the commonly used phrase “and / or.” It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as "solely," "only" and the like in connection with the recitation of claim elements, or use of a "negative" limitation. Unless defined otherwise 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 this invention belongs.- 25 -SG Docket No. 10622-728.600

Claims

1. CLAIMSWhat is claimed is:

1. A method of ultrasound imaging in tissue, comprising: transmitting one or more unfocused ultrasound pulses from a transmit aperture of an ultrasound probe towards a reflector through at least two tissue types having different tissue densities; receiving echoes from the reflector with one or more receive apertures of the ultrasound probe; determining a first speed of sound value corresponding to a first tissue type; determining a second speed of sound value corresponding to a second tissue type; and beamforming the received echoes with the first speed of sound value and the second speed of sound value to produce images of the reflector in the tissue.

2. The method of claim 1, wherein the first tissue type comprises bone and the second tissue type comprises soft tissue.

3. The method of claim 2, wherein transmitting the one or more unfocused ultrasound pulses through the first tissue type causes a propagation speed of the one or more unfocused ultrasound pulses to increase.

4. The method of claim 1, further comprising receiving an input from a user corresponding to patient demographics.

5. The method of claim 1, further comprising receiving an input from a user corresponding to patient age.

6. The method of claim 1, further comprising receiving an input from a user corresponding to an anatomical location of the ultrasound probe.

7. The method of any of claims 4-6, further comprising determining the first speed of sound value based on the input.

8. The method of claim 1, wherein the first speed of sound value is different than the second speed of sound value.- 26 -SG Docket No. 10622-728.6009. The method of claim 1, wherein the first speed of sound value corresponds to a first time of flight of the one or more unfocused ultrasound pulses from the transmit aperture to the reflector.

10. The method of claim 9, wherein the second speed of sound value corresponds to a second time of flight of the echoes from the reflector to the one or more receive apertures.

11. The method of claim 10, wherein beamforming is further based on the first time of flight and the second time of flight.

12. The method of claim 1, wherein determining the first speed of sound value comprises: dynamically adjusting one or more parameters of the ultrasound probe; and evaluating subsequent image frames to optimize an image parameter of the image frames.

13. The method of claim 12, wherein the image parameter comprises contrast.

14. The method of claim 12, wherein the image parameter comprises sharpness.

15. The method of claim 12, wherein the image parameter comprises focus.

16. The method of claim 1, further comprising displaying the images on a display.

17. An ultrasound imaging system, comprising: an ultrasound array comprising: at least one transmit aperture configured to transmit one or more unfocused ultrasound pulses towards a reflector through at least two tissue types having different tissue densities; at least one receive aperture configured to receive echoes from the reflector; one or more processors configured to: determine a first speed of sound value corresponding to a first tissue type; determine a second speed of sound value corresponding to a second tissue type; and beamform the received echoes with the first speed of sound value and the second speed of sound value to produce images of the reflector in the tissue.- 27 -SG Docket No. 10622-728.60018. The system of claim 17, wherein the first tissue type comprises bone and the second tissue type comprises soft tissue.

19. The system of claim 2, wherein transmission of the one or more unfocused ultrasound pulses through the first tissue type causes a propagation speed of the one or more unfocused ultrasound pulses to increase.

20. The system of claim 1, further comprising a user-input device configured to receive an input from a user corresponding to patient demographics.

21. The system of claim 1, further comprising a user-input device configured to receive an input from a user corresponding to patient age.

22. The system of claim 1, further comprising a user-input device configured to receive an input from a user corresponding to an anatomical location of the ultrasound probe.

23. The system of any of claims 20-22, wherein the one or more processors are configured to determine the first speed of sound value based on the input.

24. The system of claim 1, wherein the first speed of sound value is different than the second speed of sound value.

25. The system of claim 1, wherein the first speed of sound value corresponds to a first time of flight of the one or more unfocused ultrasound pulses from the transmit aperture to the reflector.

26. The system of claim 25, wherein the second speed of sound value corresponds to a second time of flight of the echoes from the reflector to the one or more receive apertures.

27. The system of claim 26, wherein the one or more processors are further configured to beamform based on the first time of flight and the second time of flight.

28. The system of claim 1, wherein the one or more processors are further configured to determine the first speed of sound value by: dynamically adjusting one or more parameters of the ultrasound probe; and- 28 -SG Docket No. 10622-728.600evaluating subsequent image frames to optimize an image parameter of the image frames.

29. The system of claim 28, wherein the image parameter comprises contrast.

30. The system of claim 28, wherein the image parameter comprises sharpness.

31. The system of claim 28, wherein the image parameter comprises focus.

32. A method of using unfocused transmissions through osseosis tissue to insonify anatomic imaging an object inside the skull with ultrasound energy, the method comprising the steps of: transmitting an un-focused and diverging ultrasound signal through a skull into a target medium including brain tissue from a transmit aperture of an ultrasound transducer array; receiving echoes from reflectors inside the skull and brain tissue with at least one receive aperture that is different than the transmit aperture; determining a thickness of the skull adjacent to the transmit aperture; and beamforming images from the echoes based on the thickness of the skull.

33. A method of identifying tissue edges below osseosis tissue by: transmitting a first unfocused ultrasound pulse into a tissue region of interest including one or more tissue edges; transmitting a second unfocused ultrasound pulse into the tissue region of interest; receiving echoes of the second unfocused ultrasound pulse; identifying one or more speckle noise patterns associated with the one or more tissue edges in the received echoes; assigning fiducial markers to the one or more tissue edges; transmitting a third unfocused ultrasound pulse into the tissue region of interest; measuring a movement of the fiducial markers; computing a tissue density of at least one tissue near the one or more tissue edges; and producing ultrasound images using the computed tissue density.

34. A method of identifying tissue density of tissues located below an ultrasound transducer and optimizing transmit and receive signals, comprising:- 29 -SG Docket No. 10622-728.600transmitting an un-focused and diverging ultrasound signal into a target medium; receiving echoes from a reflectors in the target medium from multiple tissue types; determining speed of sound values for each of the multiple tissue types; and beamforming images with the received echoes using the speed of sound values.- 30 -SG Docket No. 10622-728.600

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