KR102322776B1 - Method of constructing an ultrasound image and multi-aperture ultrasound imaging system therefor - Google Patents

Abstract

Any number of features are provided in multiple aperture ultrasound imaging systems and methods of use. In some embodiments, the multi-aperture ultrasound imaging system is configured to transmit ultrasound energy to, and receive ultrasound energy from, respective physical ultrasound apertures. In some embodiments, the transmit aperture of the multi-aperture ultrasound imaging system is configured to transmit an omni-directional, non-coherent ultrasound waveform proximate the first point source through the target region. In some embodiments, the ultrasound energy is received with a single receiving aperture. In other embodiments, ultrasonic energy is received with multiple receiving apertures. Algorithms capable of combining echoes received by one or more receiving apertures to form high resolution ultrasound images are described. Additional algorithms can account for changes in tissue speed of sound, allowing the ultrasound system to be used virtually anywhere in or on the body.

Description

METHOD OF CONSTRUCTING AN ULTRASOUND IMAGE AND MULTI-APERTURE ULTRASOUND IMAGING SYSTEM THEREFOR

This application claims priority to U.S. Provisional Patent Application Serial No. 61/305,784, filed February 18, 2010, entitled "Alternative Method for Medical Multi-Aperture Ultrasound Imaging."

This application is also entitled "Method and Apparatus to Produce Ultrasonic Images Using Multiple Apertures," and U.S. Patent Application Serial No. 11/865,501, filed October 1, 2007, and "Method and Apparatus to Visualize the Coronary Arteries Using Ultrasound." to U.S. Patent Application Serial No. 11/532,013, filed September 14, 2006, entitled

All publications, including patents and patent applications, mentioned herein are hereby incorporated by reference in their entirety to the same extent as if each individual publication were expressly and individually indicated to be incorporated by reference.

In conventional ultrasonic imaging, a focused beam of ultrasound energy is transmitted to body tissues to be examined, and the returned echoes are detected and plotted to form an image. The basic principles of conventional ultrasonic imaging are well described in the first chapter of "Echocardiography" by Harvey Feigenbaum (Lippincott Williams & Wilkins, 5th ed., Philadelphia, 1993).

To project a high frequency wave into body tissues, an ultrasound beam is typically formed and focused by either a phased array or a shaped transducer. Phased array ultrasound is a commonly used method of steering and focusing a narrow ultrasound beam to form images in medical ultrasound examination. A phased array probe has a number of small ultrasonic transducer elements, each of which can be individually pulsed. By varying the timing of the ultrasound pulses (eg, by pulsing elements one after another along a row), a pattern of constructive interference is established that results in a beam directed at a selected angle. This is known as beam steering. Such a steered ultrasound beam may then be swept through the object or tissue being inspected. Data from multiple beams is combined to create a visual image showing the slice through the object.

Traditionally, the same transducer or array used to transmit the ultrasound beam is used to detect the returning echoes. This design configuration is at the heart of one of the most important limitations in the use of ultrasound imaging for medical purposes. Theoretically, the latter solution could be improved by increasing the width of the aperture of the ultrasonic probe, but the practical problems involved with aperture size make the apertures smaller. Obviously, ultrasound imaging has been very useful with this limitation, but it can be more efficient to use better resolution.

In the practice of cardiology, for example, the limitation on the size of a single opening is dictated by the space between the ribs (intercostal space). Such intercostal openings are typically limited to only one to two centimeters. For scanners intended for abdominal and other use, the limitation on aperture size is a smaller problem with physical constraints and a bigger problem with difficulties in image processing. The problem is that it is difficult to keep elements of a large aperture array in phase because the ultrasound transmission rate varies with the type of tissue between the probe and the region of interest. According to the book by Wells (mentioned above), the rate varies by +/- 10% in soft tissues. When the aperture remains small (eg, less than about 2 cm), in the first order of estimation, the intermediate tissues are all identical, and any changes are ignored. When the size of the aperture is increased to improve lateral resolution, additional elements of the phased array may be out of phase and may actually degrade the image rather than enhance it.

US Patent Application Publication 2008/0103393 to Specht teaches embodiments of ultrasound imaging systems that utilize multiple apertures that can be separated by greater distances, thereby resulting in significant improvements in the lateral resolution of ultrasound images.

One embodiment of the method describes a method of constructing an ultrasound image, the method comprising: an omni-directional, non-coherent ultrasound waveform approximating a first point source within a transmission opening on a first array through a target region. transmitting a directional unfocused ultrasound waveform, receiving ultrasound echoes from a target area with first and second receiving elements disposed on a first receiving opening on a second array, wherein the first array is physically separated by - determine, for a first receive element, a first time for the waveform to propagate from a first point source to a first pixel location in a first target region, and for a second receive element, determine a first time for the waveform to propagate at the first point determining a second time for propagation from the source to a first pixel location in the target area, and comparing the echo received by the first receiving element at the first time with the echo received by the second receiving element at the second time by combining, forming a first ultrasound image of the first pixel.

In some embodiments, the method further comprises repeating the determining and forming steps for additional pixel locations of the target region. In one embodiment, the additional pixel positions are located on a grid without scan-conversion.

In one embodiment, determining the first time and the second time comprises estimating a uniform speed of sound.

In another embodiment, the method includes transmitting a second omni-directional uncoherent ultrasound waveform proximate to a second point source within a transmitting opening through a target region, first and second receiving elements disposed on the first receiving opening receiving ultrasound echoes from a target area with the beams, determining, for a first receiving element, a third time for a second waveform to propagate from a second point source to a first pixel location of the target area, and a second receiving element for , determining a fourth time for the second waveform to propagate from the second point source to a first pixel location in the target region, and at a fourth time an echo received by the first receiving element at a third time forming a second ultrasound image of the first pixel by combining with the echo received by the second receiving element.

In some embodiments, the method further comprises combining the first ultrasound image with the second ultrasound image. The combining may include coherent addition. In another embodiment, the combining may include incoherent addition. In another embodiment, the combining may include a combination of coherent addition and incoherent addition.

In some embodiments, the method comprises receiving ultrasound echoes from the target region with third and fourth receiving elements disposed on a second receiving opening on a third array, wherein the third array comprises the first and first physically separated from the two arrays—determining, for a third receive element, a third time for the waveform to propagate from the first point source to the first pixel location in the target region, and for a fourth receive element, the waveform is determining a fourth time for propagation from the first point source to a first pixel location in the target area, and receiving an echo received by the third receiving element at a third time by the fourth receiving element at a fourth time The method may further include forming a second ultrasound image of the first pixel by combining it with the echo.

In some embodiments, the method further comprises repeating the determining and forming steps for additional pixel locations of the target region. In some embodiments, additional pixel positions are located on the grid without scan-transform.

In one embodiment, the method comprises: transmitting a second omni-directional, non-coherent ultrasound waveform proximate to a second point source within a transmitting opening through a target region, first and second receiving elements disposed on the first receiving opening receiving ultrasonic echoes from the target region into the poles and with third and fourth receiving elements disposed on the second receiving opening, for the first receiving element, a second waveform from a second point source to a second of the target region determine a fifth time to propagate to the first pixel location; determine, for the second receive element, a sixth time for the second waveform to propagate from the second point source to the first pixel location in the target region; determine, for the receive element, a seventh time for the second waveform to propagate from the second point source to the first pixel location of the target area, and for the fourth receive element, the second waveform from the second point source to the target area determining an eighth time to propagate to a first pixel location of , and combining an echo received by the first receiving element at a fifth time with an echo received by the second receiving element at a sixth time; forming a third ultrasound image of the pixel, and combining the echo received by the third receiving element at the seventh time with the echo received by the fourth receiving element at the eighth time, thereby a fourth ultrasound image of the first pixel It further comprises the step of forming.

In some embodiments, the method further comprises combining the first, second, third and fourth ultrasound images. In some embodiments, the combining comprises a coherent addition. In other embodiments, the combining comprises incoherent addition. In additional embodiments, the combining comprises a combination of a coherent addition and an incoherent addition.

In some embodiments, the method further comprises combining the first ultrasound image with the second ultrasound image. The combining may include coherent addition. In another embodiment, the combining may include incoherent addition. In another embodiment, the combining may include a combination of coherent addition and incoherent addition.

In some embodiments, the method comprises converting the first ultrasound image to a second, third and fourth ultrasound image to determine displacements of the second, third and fourth ultrasound images with respect to the first ultrasound image. It further comprises a step of comparing them.

In another embodiment, the method comprises correcting for displacements of the second, third and fourth ultrasound images with respect to the first ultrasound image and then combining the first, second, third and fourth ultrasound images. further includes

In a further embodiment, the method uses third, fourth, fifth, sixth, seventh and eighth times to correct for displacements of the second, third and fourth ultrasound images with respect to the first ultrasound image. including adjusting.

In some embodiments, the method further comprises comparing the first ultrasound image to the second ultrasound image to determine a displacement of the second ultrasound image with respect to the first ultrasound image.

The method may further comprise correcting a displacement of the second ultrasound image with respect to the first ultrasound image, and then combining the first and second ultrasound images.

In another embodiment, the method comprises adjusting the third time and the fourth time to correct for a displacement of the second ultrasound image with respect to the first ultrasound image.

In some embodiments, the first pixel is disposed outside the plane defined by the point source, the first receive element, and the second receive element. In other embodiments, the first pixel is disposed in a plane defined by the point source, the first receive element, and the second receive element.

Various embodiments of a multi-aperture ultrasound imaging system are also provided, wherein the multi-aperture ultrasound imaging system is configured to transmit an omni-directional, non-coherent ultrasound waveform proximate a first point source through a target region on a first array. a first receive aperture on a second array having a transmit aperture, first and second receive elements, the second array being physically separated from the first array, the first and second receiving elements receiving ultrasound echoes from the target area configured to: a control system coupled to the transmit aperture and the first receive aperture, wherein the control system comprises, for the first receive element, a first time for the waveform to propagate from the first point source to a first pixel location in the target area. and determine, for the second receiving element, a second time for the waveform to propagate from the first point source to the first pixel location of the target region, and the control system is further configured to: configured to form a first ultrasound image of the first pixel by combining the echo received by the receiving element with the echo received by the second receiving element at a second time.

In some embodiments of the system, there are no transducer elements disposed between the physical separation of the first receive aperture and the transmit aperture.

In one embodiment of the system, the transmit aperture and the first receive aperture are separated by at least twice a minimum transmit wavelength from the transmit aperture. In another embodiment, the transmit aperture and the receive aperture include an overall aperture ranging from 2 cm to 10 cm.

In some embodiments, the ultrasound system further comprises a second receive aperture on a third array having third and fourth receive elements, the third array being physically separated from the first and second arrays; The third and fourth receiving elements are configured to receive ultrasound echoes from the target region.

In another embodiment of the multi-aperture ultrasound imaging system, a control system is coupled to the transmit aperture and the first and second receive apertures, wherein the control system, for a third receive element, determines that, for a third receive element, the waveform is directed from the first point source to the target. and determine, for a fourth receive element, a fourth time for the waveform to propagate from the first point source to the first pixel location in the target region; and the control system is further configured to form a second ultrasound image of the first pixel by combining the echo received by the third receiving element at the third time with the echo received by the fourth receiving element at the fourth time. .

In some embodiments, the control system is configured to correct a displacement of the second ultrasound image relative to the first ultrasound image due to a change in the speed of sound.

In a multi-aperture ultrasound imaging system, the transmit aperture, the first receive aperture, and the second receive aperture are not necessarily all in a single scan plane.
In another embodiment of the method of constructing an ultrasound image, the method generates an omni-directional unfocused ultrasound waveform approximating a first point source in a transmission opening on a first array through a target area. transmitting, wherein the omni-directional non-coherent ultrasound waveform is transmitted from a transmission aperture comprising at least one transducer element; receiving ultrasound echoes from the target region with first and second receive elements disposed on a first receive opening on a second array, the first array physically separated from the second array; retrieving position data describing the acoustic location of each of the at least one transducer element, the first receive element, and the second receive element of the transmit aperture with respect to a common reference point; using the position data to determine, for the first receive element, a first time for the waveform to propagate from the first point source to a first pixel location in the target area, for the second receive element , determining a second time for the waveform to propagate from the first point source to the first pixel location in the target area; and combining a first echo received by the first receiving element at the first time with a second echo received by the second receiving element at the second time; comprising the step of forming
In another embodiment of a multi-aperture ultrasound imaging system, the system is configured to transmit an omni-directional, non-coherent ultrasound waveform proximate a first point source through a target region, wherein the transmitting aperture is at least one comprising a transducer element of ; a first receive aperture on a second array having first and second receive elements, the second array being physically separated from the first array, the first and second receiving elements receiving ultrasound echoes from the target area configured to receive — ; a location memory comprising positional data describing an acoustic position of each of the at least one transducer element, the first receive element, and the second receive element of the transmit aperture with respect to a common reference point; a control system coupled to the transmit aperture and the first receive aperture, wherein the control system retrieves the location data from the location memory and uses the location data for the first receive element. , configured to determine a first time for the waveform to propagate from the first point source to a first pixel location in the target region, and for the second receive element, the waveform is configured to propagate from the first point source to the target. and determine a second time to propagate to the first pixel location of a region, wherein the control system is further configured to determine a first echo received by the first receiving element at the first time at the second time. 2 configured to form a first ultrasound image of the first pixel location by combining with a second echo received by the receiving element.

1A shows a two-aperture system.
1B shows equidistant time delay points forming an ellipse around a transmit transducer element and a receive transducer element.
1C shows the trajectories of points with respect to equidistant time delays for different receive transducer elements.
2 shows a three-aperture system.
3 shows a grid for the display and coordinate system.
4 shows a fat layer model using a three-aperture system.
5 shows a configuration for estimation of a point spread function.

Greatly improved lateral resolution in ultrasound imaging can be achieved by using multiple separate apertures for transmit and receive functions. The systems and methods herein provide transmit functions from point sources and the speed of sound of ultrasonic pulses traveling through potentially various tissue types along a path between one or more receive apertures and a transmit aperture. It can provide all compensation for changes in Such velocity compensation may be performed by a combination of image comparison techniques (eg, cross-correlation) and coherent and/or incoherent averaging of multiple received image frames.

The terms “ultrasonic transducer” and “transducer” as used herein may have their ordinary meanings as understood by those skilled in the art of ultrasound imaging techniques, including, but not limited to, converting an electrical signal into an ultrasonic wave. may refer to any single component capable of converting to a signal and/or vice versa. For example, in some embodiments, the ultrasonic transducer may include a piezoelectric device. In some alternative embodiments, the ultrasound transducers may include capacitive micromachined ultrasound transducers (CMUT). Transducers often consist of arrays of multiple elements. An element of a transducer array may be the smallest discrete component of the array. For example, in the case of an array of piezoelectric transducer elements, each element may be a single piezoelectric crystal.

As used herein, the terms “transmitting element” and “receiving element” may have their ordinary meanings as understood by one of ordinary skill in the art of ultrasound imaging techniques. The term “transmitting element” may refer to, but is not limited to, an ultrasonic transducer that performs a transmitting function of converting an electrical signal into an ultrasonic signal for at least a short time. Similarly, the term “receiving element” may refer to, but is not limited to, an ultrasonic transducer element that performs a receiving function in which an ultrasonic signal affecting the element is converted into an electrical signal for at least a short time. Transmission of ultrasound to a medium may also be referred to herein as “insonifying”. An object or structure that reflects ultrasonic waves may be referred to as a “reflector” or “scatterer”.

The term “aperture” as used herein, without limitation, refers to one or more ultrasound transducer elements that collectively perform a common function at a given instant of time. For example, in some embodiments, the term opening may refer to a group of transducer elements that perform a transmit function. In alternative embodiments, the term aperture may refer to a number of transducer elements that perform a receiving function. In some embodiments, the group of transducer elements forming the aperture may be re-established at different points in time. 3 shows multiple apertures used in a multiple aperture ultrasound probe. The opening of the probe has as many as three distinct features. First it is physically separated from other transducers, which are often located in different openings. In FIG. 3 , distance 'd' physically separates opening 302 from opening 304 . The distance 'd' may be the minimum distance between the transducer elements on the opening 302 and the transducer elements on the opening 304 . In some embodiments, no transducer elements are disposed along the distance 'd' between the physical separation of openings 302 and 304 . In some embodiments, distance 'd' may be equal to at least twice the minimum wavelength of transmission from the transmission aperture. Second, the transducer elements of the aperture need not be in the same rectangular or horizontal plane. In FIG. 3 , all elements of opening 304 have a different vertical position 'j' from any element of opening 302 . Third, the apertures do not share a common line of sight to the region of interest. In FIG. 3 , aperture 302 has a line of sight 'a' to point (i, j), while aperture 304 has line of sight 'b'. The aperture may include any number of individual ultrasound elements. The ultrasound elements defining the aperture are not necessarily, but often adjacent to each other in the array. During operation of the multi-aperture ultrasound imaging system, the size of the aperture (eg, number and/or size and/or location of ultrasound elements) may be dynamically changed by re-assigning elements.

The term “point source transmission” as used herein may refer to the introduction of transmitted ultrasonic energy into a medium from a single spatial location. This can be accomplished using a single ultrasound transducer element or a combination of adjacent transducer elements transmitting together. A single transmission from the element(s) approximates a uniform spherical wavefront, or in the case of imaging a 2D slice, this produces a uniform circular wavefront within the 2D slice. This point source transmission differs in its spatial characteristics from a “phased array transmission,” which focuses energy in a specific direction from the array of transducer elements. Phased array transmission in turn processes the phase of a group of transducer elements to enhance or steer an insonifying wave to a particular region of interest. A short duration point source transmission is referred to herein as a “point source pulse”. Similarly, a short duration phased array transmission is referred to herein as a "phased array pulse".

As used herein, the terms "receive aperture", "high frequency emitting aperture" and/or "transmit aperture" may have their ordinary meanings as understood by those skilled in the art of ultrasound imaging, and It may refer to an individual element, a group of elements in an array, or even entire arrays within a common housing, that at a given time perform the desired transmit or receive function from an opening or desired physical viewpoint. In some embodiments, these various openings may be created as physically discrete components with a dedicated function. In alternative embodiments, the function may be designated or changed electronically as needed. In still further embodiments, the aperture function may involve a combination of both fixed and deformable elements.

In some embodiments, the aperture is an array of ultrasound transducers separate from other transducer arrays. Such multiple aperture ultrasound imaging systems provide greatly increased lateral resolution. According to some embodiments, a multi-aperture imaging method comprises: emitting a high-frequency ultrasound pulse from a first aperture to a target object, detecting echoes returned to a second aperture positioned at a distance from the first aperture; determining the relative positions of the second aperture with respect to the first aperture, and processing the returned echo data to combine the images while correcting for changes in the speed of sound through the target object.

In some embodiments, the distance and orientation between adjacent openings may be fixed relative to each other, such as by use of a rigid housing. In alternative embodiments, the distances and orientations of the openings relative to each other may be variable, such as using a movable linkage. In further alternative embodiments, the apertures may be defined as groups of elements on a single large transducer array, wherein the groups are separated by at least a specified distance. For example, embodiments of such a system are shown and described in US Provisional Patent Application Serial No. 61/392,896, filed Oct. 13, 2010, entitled "Multiple Aperture Medical Ultrasound Transducers." In some embodiments of a multi-aperture ultrasound imaging system, the distance between adjacent apertures may be the width of at least one transducer element. In alternative embodiments, the distance between the apertures may be as large as possible within the constraints of the particular application and probe design.

Multi-aperture ultrasound imaging systems with large effective apertures (total aperture of multiple sub apertures) can be successful by compensating for changes in the speed of sound in the target tissue. This may be accomplished in one of several ways for the increased aperture to be effective rather than destructive, as described below.

1A illustrates one embodiment of a simplified multi-aperture ultrasound imaging system 100 including two apertures (aperture 102 and aperture 104 ). Each of the openings 102 and 104 may include a number of transducer elements. In the two-aperture system shown in FIG. 1A , the aperture 102 may comprise transmitting elements T1 ... Tn to be used exclusively for transmit functions, and the aperture 104 to be used exclusively for receive functions. It may include elements R1 ...Rm. In alternative embodiments, transmit elements may be collocated with receive elements, or some elements may be used for both transmit and receive functions. The multi-aperture ultrasound imaging system 100 of FIG. 1A may be configured to be positioned on the skin surface of a patient to image a target object or internal tissue T with ultrasound energy. As shown in FIG. 1A , opening 102 is positioned at distance “a” from tissue T, and opening 104 is positioned at distance “b” from tissue T. As also shown in FIG. 1A , MAUI electronics may be coupled to transmit and receive openings 102 and 104 . In some embodiments, the MAUI electronics may include a processor, control system, or computer system, including software and hardware configured to control the multi-aperture imaging system 100 . In some embodiments, the MAUI electronics may be configured to control the system to transmit an omnidirectional unfocused ultrasound waveform from the aperture. As will be described in further detail below, the MAUI electronics may be configured to control and effectuate any of the methods described herein.

The ultrasound elements and arrays described herein may also be multi-functional. That is, the designation of transducer elements or arrays as transmitters in one case does not preclude their intermediate re-designation as receivers in the next case. In addition, embodiments of the control system described herein include capabilities for making such assignments electronically based on user inputs or pre-set scan or resolution criteria.

Another embodiment of a multi-aperture ultrasound imaging system 200 is shown in FIG. 2 and includes transducer elements aligned to form open apertures 202 , 204 and 206 . In one embodiment, the transmit elements T1 ... Tn of the opening 202 may be used for transmitting, and the receive elements R _R 1 ... R _R m of the openings 204 and 206 . can be used to receive. In alternative embodiments, elements of all openings may be used for both transmit and receive. The multi-aperture ultrasound imaging system 200 of FIG. 2 may be configured to image the tissue T with ultrasound energy. As also shown in FIG. 2 , MAUI electronics may be coupled to transmit and receive openings 202 and 204 . In some embodiments, the MAUI electronics may include a processor, control system, or computing system, including software and hardware configured to control the multi-aperture imaging system 200 . In some embodiments, the MAUI electronics may be configured to control the system to transmit an omni-directional unfocused ultrasound waveform from the aperture, receive echoes on the aperture, and form images from the transmitted waveform and the received echoes. have. As will be described in further detail below, the MAUI electronics may be configured to control and effectuate any of the methods described herein.

The multi-aperture ultrasound imaging systems described herein may be configured to use transducers of any desired configuration. For example, 1D, 1.5D, 2D, CMUT or any other transducer arrays may be used in multi-aperture configurations to improve overall resolution and field of view.

point source transmission

In some embodiments, acoustic energy may be transmitted in a two-dimensional slice as wide as possible by using point source transmission. For example, in some embodiments, a transmit opening, such as transmit openings 102 or 202 in FIGS. 1A and 2 , respectively, may contain acoustic energy in the form of a point source pulse from a single substantially omni-directional transducer element of the array. can be sent. In alternative embodiments, multiple transducer elements may be provisioned to transmit a relatively wide point source pulse in three dimensions for high frequency firing at objects in three-dimensional space. In such embodiments, all beamforming may be accomplished by firmware or software associated with the transducer arrays acting as receivers. By transmitting as point source pulses rather than phased array pulses, there are a number of advantages to using multi-aperture ultrasound imaging techniques. For example, when using a phased array pulse, tight focusing on the transmit side is problematic because it must be focused at a certain depth but will be somewhat out of focus at all other depths. In contrast, with point source transmission an entire two-dimensional slice or three-dimensional volume can be high-frequency fired with a single point source transmission pulse.

Each echo detected at a receive aperture, such as receive apertures 104 or 204/206 of FIGS. 1A and 2 , may each be individually stored. If the echoes detected by the elements of the receiving aperture are stored separately for every point source pulse from the high-frequency emission or transmit aperture, then a full two-dimensional image can be formed from the information received by only one element. Additional copies of the image may be formed by additional receive apertures collecting data from the same set of high frequency firing point source pulses. Ultimately, multiple images may be simultaneously generated and combined from one or more apertures to achieve a comprehensive 2D or 3D image.

Several point source pulses are typically used to produce a high quality image, but fewer point source pulses are required than if each pulse was focused on a particular scan line. Because the number of pulses that can be transmitted at any given time is strictly limited by the speed of ultrasound in the tissue, this yields a practical advantage that more frames can be generated every second by using a point source pulse. This is very important when imaging moving organs, especially the heart.

In some embodiments, a spread spectrum waveform may be introduced on a transmit aperture comprised of one or more ultrasound transducer elements. A spread spectrum waveform is a sequence of frequencies, e.g., a chirp (e.g., frequencies going from low to high or vice versa), random frequency sequences (also called frequency hops). ), or a signal (PN sequence) generated by a pseudo-random waveform. These techniques may be collectively referred to as pulse compression. Pulse compression provides longer pulses for greater depth penetration without loss of depth resolution. In fact, depth resolution can be greatly improved in the process. Spread spectrum processing typically involves much more signal processing in the form of matched filtering of each of the received signals prior to delay and summation steps. The above examples of transmit pulse shapes are provided for illustration only. The techniques taught herein can be applied regardless of the shape of the transmit pulse.

Basic image rendering

1a comprises a first opening 102 with ultrasound transmitting elements T1 , T2 , ... Tn and a second opening 104 with ultrasound receiving elements R1 , R2 , ... Rm One embodiment of a multi-aperture ultrasound imaging system 100 is illustrated. This multi-aperture ultrasound imaging system 100 is configured to be positioned on a surface of an object or body (such as a human body) to be examined. In some embodiments, both apertures may be sensitive to the same scan plane. In other embodiments, one of the openings may be in a different scan plane. The mechanical and acoustic positions of each transducer element of each aperture must be known precisely with respect to a common reference point or with respect to each other.

In one embodiment, the ultrasound image is transmitted to an internal tissue or target object T (eg, a heart, organ, tumor, or other part of the body) to a transmitting element (eg, transmitting element T1 of opening 102 ). It can be generated by high-frequency emitting to the entire area to be imaged, such as a plane through the part, and then receiving echoes from the entire imaged plane on a receiving element (eg, receiving element R1 of aperture 104 ). . In some embodiments, receive functions may be performed by all elements of the receive probe (eg, R1 through Rm). In alternative embodiments, the echoes are received on only one element or several elements of the receiving aperture. Using each of the elements on the transmit aperture 102 (eg, T2, ... Tn), in turn high-frequency emitting the entire area to be imaged with each of the transmitting elements, and the receiving aperture after each high-frequency firing pulse By receiving echoes on the phase, the method proceeds. The transmitting elements are actuated in any desired sequential order, and may not necessarily follow a prescribed pattern. Individually, the images obtained after high-frequency emission by each transmitting element may not be sufficient to provide a high-resolution image, but the combination of all images may provide a high-resolution image of the entire imaged area. For a scanning point represented by the coordinates (i,j) as shown in Figure 1a, the total distance "a" from a particular transmitting element Tx to an element of the internal tissue or target object T and said point It is a simple problem to compute the distance "b" from to a particular receiving element. These calculations can be performed using basic trigonometry. The sum of these distances is the total distance traveled by one ultrasonic wave.

When the velocity of ultrasound in the tissue is assumed to be uniform through the tissue, it is possible to calculate the time delay from the start of the transmit pulse to the time at which the echo is received at the receiving element. (Uniform speed of sound in tissue is not discussed below.) One such fact means that the scatterer (ie, the point of reflection within the target object) is a point in the medium where a+b = a given time delay. The same method can be used to calculate delays for any point in the desired tissue to be imaged, creating a trajectory of the points. 1b shows that all of the points (g,h), (i,j), (k,m), (n,p), (q,r), (s,t) are a transmit element (T1) and a receive element shows that it has the same time delay for (R1). A map of scatter locations and amplitudes can be rendered by tracking the echo amplitude for all points on the trajectory of the same-time-delay points. This trajectory takes the form of an ellipse 180 with foci at the transmit and receive elements. 1B also illustrates a MAUI electronic device, which may include the MAUI electronic device described above with reference to FIGS. 1A and 2 .

The fact that all points on the ellipse 180 are returned with the same time delay presents a challenge for display, as it is impossible to distinguish the points along the ellipse from each other in a single image. However, by combining images obtained from multiple receiving points, the points can be more easily distinguished, since the same-time-delay ellipses defined by the multiple receiving apertures will be slightly different.

Figure 1c shows, with a transmit pulse from element T1, that echoes from a single scatterer (n,p) are received at different times by different receiving elements such as R1, R2 and R3. Trajectories of the same scatterer may be represented by ellipses 180 , 185 and 190 of FIG. 1C . The location where these ellipses intersect (points n, p) represents the true location of the scatterer. Beamforming hardware, firmware, or software can combine the echoes from each receiving element to produce an image, effectively augmenting the image at the intersection of the ellipses. In some embodiments, multiple receiver elements, more than the three shown, may be used to obtain a desired signal-to-noise ratio for the image. 1C also illustrates a MAUI electronic device, which may include the MAUI electronic device described above with reference to FIGS. 1A and 2 .

A method of rendering the positions of all scatterers of the target object and thus forming a two-dimensional cross-section of the target object will now be described with reference to the multi-aperture ultrasound imaging system 300 of FIG. 3 . 3 illustrates a grid of points to be imaged by openings 302 and 304 . A point on the grid is given by rectangular coordinates (i,j). A complete image would be a two-dimensional array called "echo". In the grid of Figure 3, mh is the maximum horizontal dimension of the array, and mv is the maximum vertical dimension. 3 also illustrates a MAUI electronic device, which may include the MAUI electronic device described above with reference to FIGS. 1A and 2 .

In one embodiment, the following pseudo code is received by one receiving element of the arrangement of FIG. 3 (eg, one of R1 ...Rm from opening 304 ). It can be used to accumulate all information to be collected from the resulting echoes and the transmit pulse from one transmit element (eg, one of T1 ... Tn from aperture 302 ).

for (i = 0; i < mh; i++){

for (j = 0;j < mv; j++){

compute distance a

compute distance b

compute time equivalent of a+b

echo[i][j] = echo[i][j]+stored received echo at the computed time delay

* }

}

The fixed delay is primarily the time from the transmit pulse until the first echoes are received. As will be discussed later, increments can be added or subtracted to compensate for the fat layers.

A complete two-dimensional image may be formed by repeating this process for all receiving elements (eg, R1 ... Rm) of aperture 304 . In some embodiments, it is possible to implement such code in parallel hardware resulting in real-time image formation.

Combining similar images resulting from pulses from different transmitting elements can improve the quality of the image (eg, in terms of signal-to-noise ratio). In some embodiments, the combination of images may be performed by simple summation (eg, coherent addition) of single point source pulse images of single point source pulse images of single point source pulse images. Alternatively, combining may involve first taking the absolute value of each element of the single point source pulse images prior to weighting (eg, incoherent addition). In some embodiments, the first technique (coherent addition) may be best used to improve lateral resolution, and the second technique (incoherent addition) may be best applied for reduction of speckle noise. In addition, the incoherent technique can be used with the lower precision required in the measurement of the relative positions of the transmit and receive apertures. A combination of the two techniques can be used to provide an optimal balance of improved lateral resolution and reduced speckle noise. Finally, in the case of coherent addition, the final summation has to be replaced by the absolute value of each element, and in both cases some form of compression of dynamic range shows that both important and more subtle features display the same It can be used to appear on the In some embodiments, additional pixel positions are located on the grid without scan-transform.

In some embodiments, compression schemes may include taking the log (eg, 20 log ₁₀ or “dB”) of each element prior to display or the nth root of each element (eg, prior to display). for example, taking the fourth root). Other compression schemes may also be used.

Still referring to FIG. 3 , any number of receive probes and transmit probes may be combined to enhance the image of the scatterer (i,j), as long as the relative positions of the transducer elements are known to a specified degree of accuracy, All elements are in the same scan plane and focused on either the receive energy propagating in the scan plane or the transmit energy into the scan plane. Any element of any probe may be used for transmission or for reception or for both transmission and reception.

The speed of sound in various soft tissues through the body can vary by +/- 10%. Using conventional ultrasound techniques, it is commonly assumed that the speed of sound is constant in the path between the transducer and the organ of interest. This estimate is valid for narrow transducer arrays in systems that use one transducer array for both transmit and receive. However, as the ultrasound pulses pass through more tissue and possibly different types of tissue, such as fat, muscle, blood vessels, etc., the constant velocity estimate is broken as the aperture of the transducer becomes wider. The tissue diversity below the width of the transducer array affects both transmit and receive functions.

When the scatterer is high-frequency emitted by a point source pulse from a single transmitting element, it reflects the echo back to all of the elements in the receiver group. The coherent addition of the images collected by the elements of this receiving aperture is +/-180 degrees out of phase with respect to one path selected as reference where the speed of sound changes in the paths from the scatterer (i,j) to each of the receiver elements are selected as reference. It can be effective if the shift is not exceeded. Referring to FIG. 3 , the maximum size of the receive aperture for which coherent addition can be effective depends on tissue changes within the patient and may not be pre-calculated. However, the practical maximum for a particular transmission frequency can be determined from experience.

In high frequency emission using non-coherent point source pulses, the aperture size of the transmit group is very It's not important. For example, a change that results in a phase shift of 180 degrees in the receive paths results in complete phase cancellation when using coherent addition, whereas the same change on the transmit paths only results in half the wavelength (typically about 0.2 mm). will result in a displayed position error of , and the distortion will not be noticed.

Thus, in a multi-aperture imaging system having one aperture used only for transmission and the other aperture used only for reception during a single transmit/receive cycle, as illustrated in FIG. 1A , very little additional compensation for sound velocity variations I need this. Although the aperture has been increased from elements T1 to Rm, which may be several times the width of a conventional sector scanner probe, concerns regarding destructive interference of signals from the scatterers (i,j) may be related to the separation of apertures or the size of the transmit aperture. Regardless of the width, it only depends on the width of the receiving apertures (elements R1 to Rm). The standard width for which the speed of sound variation actually presents a minimal problem is about 16-20 mm for 3.5 MHz systems (and smaller for higher frequencies). Thus, if the receiving aperture has a width equal to or smaller than the standard apertures, explicit compensation for the speed of sound change is not necessary.

Substantial improvements in lateral resolution are achieved with a receive aperture the same width as a conventional single array 1D, 1.5D, or 2D ultrasound probe used for both transmit and receive, with nearby cells presenting a scatterer (i.e., a target object). This is because the energy received when imaging regions of When the transmit pulses are generated from the same array used for reception, the time difference is small. However, when the transmit pulses originate from the second array at a distance from the receive array, the time difference is larger and thus out of phase with the signal to the correct cell. Eventually fewer nearby cells will have enough signals in phase to falsely represent the true scatterer.

Referring to FIG. 4 , consider a signal received at a single element (eg, one of the receiving elements R1 ... Rm) of the receiving aperture 404 from the scatterer at “S”. If both transmit and receive functions were performed on the same element, the time for the ultrasound to propagate to "S" and return would be 2a/C (where C is the speed of sound in the tissue). When the reconstruction algorithm evaluates the received signal for a possible scatterer at aperture 404 "S" separated by a distance "c" from the true scatterer "S'", the expected time of arrival is 2(sqrt(a ² +c) ² )/C). When “c” is small, this time is almost the same, so the signal from “S” will degrade only slightly when estimating the size of the scatterer “S′” of aperture 404 . 4 also illustrates a MAUI electronic device, which may include the MAUI electronic device described above.

Consider now the transmit aperture 402 moving away from the receive aperture 404 by an angle theta (“θ”). For convenience of comparison, the distance “b” from the opening 402 to the scatterer “S” is assumed to be the same as the distance “a” from the opening 404 to the scatterer “S”. The time for the ultrasonic wave to propagate from the transmit aperture 402 to "S" and return to the receive aperture 404 will still be (a+b)/C = 2a/C (where a=b), but the signal " The expected time to propagate to S'" is (d+sqrt(a ² +c ² ))/C=(sqrt((a sinθ-c) ² +(a cosθ) ² )+sqrt(a ² +c ² ) ) will be /C. The difference between the expected arrival time and the actual will be Diff=(sqrt((a sinθ-c) ² +(a cosθ) ² )+sqrt(a ² +c ² )-2a)/C.

To put some numbers into this equation, assume that the separation of opening 402 and opening 404 is only 5 degrees, distance a = 400 cells, and distance c = 1 cell. Then, the ratio of the difference of the arrival time for θ = 5 degrees to the arrival time for θ = 0 degrees is 33.8. That is, the drop off of display amplitude to adjacent cells is 33 times faster than using θ = 5 degrees. Larger differences in arrival times greatly simplify the ability to uniquely distinguish echo information from adjacent cells. Thus, with high theta angles, the display of a point will be less visible as noise in adjacent cells, resulting in a higher resolution of the actual image. With multiple aperture transmitters and receivers, we can make the angle as high as necessary to improve the resolution.

Simulations for a real ultrasound system with multiple reflectors in multiple cells show that the effect is still significant, but not as dramatic as above. For a system comprising a receive aperture of 63 elements, a θ of 10 degrees, and a transmit pulse from a point-source transmit aperture extending for 5 cycles with cosine modulation, the lateral spread of the point spread function improves by a factor of 2.3. became

Clear compensation for speed of sound changes

A single image can be formed by coherent averaging of all signals arriving at the receiver elements as a result of a single point source pulse for high frequency emission. The weighting of these images resulting from multiple point source pulses may be achieved by coherent addition, incoherent addition, or a combination of coherent addition by groups and incoherent addition of images from groups. can Coherent addition (which involves phase information prior to addition) can maximize resolution, while incoherent addition (which uses magnitude of signals rather than phase) minimizes the effects of registration errors and averages speckle noise. do. Some combination of the two modes may be preferred. Coherent addition can be used to average point source pulse images resulting from transmitting elements that are close to each other and thus generate pulses that are transmitted through very similar tissue layers. Incoherent addition can then be used where phase cancellation is an issue. In the extreme case of transmission time variation due to speed of sound variations, 2D image correlation can be used to align the images prior to addition.

When the ultrasound imaging system includes a second aperture, using the second aperture for receiving as well as transmitting produces much better resolution. In a combination of images from two or more receiving arrays, it is possible and desirable to use an explicit compensation for the speed of sound change.

Consider a tissue layer model for a three-aperture ultrasound imaging system 500 as shown in FIG. 5 , illustrating the effects of varying the thicknesses of different types of tissue, such as fat or muscle. Fat layer “F” is shown in FIG. 5 , wherein the thickness of tissue layers f1 , f2 , and f3 under each opening 502 , 504 , and 506 are respectively different and unknown. The tissue layer at aperture 506 will be the same as at aperture 504 , so it is not reasonable to assume that coherent addition of signals from all receive elements is usually not possible. In one example, if the tissue layer at aperture 504 is larger than the tissue layer at aperture 506 by 3 cm, this corresponds to a displacement of about 3 wavelengths (at 3.5 MHz) of signals, but this is a representation of deep tissues. of 1.3 mm displacement. For such small displacements, only a very small amount of geometric distortion of the image will be observed. Thus, although coherent addition is not possible, incoherent addition using the displacement of one image with respect to another image is possible.

Image comparison techniques may be used to determine the amount of displacement required to align image frames from the left and right apertures (eg, apertures 506 and 504, respectively). In one embodiment, the image comparison technique may be cross-correlation. Cross-correlation involves evaluating the similarity of an image or image sections to identify regions with a high degree of similarity. Regions having at least a threshold value of similarity may be assumed to be identical. Thus, by identifying regions within images that have a high degree of similarity, one image (or a section of an image) can be shifted such that regions with substantial similarity overlap and improve overall image quality. 5 also exemplifies MAUI electronics, which may include the MAUI electronics described above.

Additionally, these image comparison techniques can also be used by applying sub-image analysis, which can be used to determine the displacement of the sub-images and accommodate for localized changes in the speed of sound in the underlying tissue. . In other words, by breaking down the image into smaller segments (eg, bisect, third, quart, etc.), small portions of the first image may be compared with corresponding smaller portions of the second image. can The two images can then be combined by warping to confirm alignment. Warping is a technique understood by one of ordinary skill in the art and is described, for example, in US 7,269,299 by US 7,269,299.

The same technique of incoherent addition of images from multiple receive transducer arrays can be applied to any number of apertures. The same idea can be applied even to single element arrays that are too wide to be used for coherent addition all together. An ultrasound imaging system with a single wide array of elements can be divided into sections (openings), each of which is small enough for addition, and then images resulting from these sections (with displacement if necessary) They may be combined in an incoherent manner.

Even slight distortion of the image can be compensated for with sufficient computational power. Image renderings may be computed for one receive array using a variable amount of delay in the rendering algorithm (echo[ i ] [ j ] = echo[ i ][ j ]+stored receive echo at the computed time+delay). The best match of these (by cross-correlation or some other measure of acuity) can then be added incoherently to the image from the other receiving array(s). A faster technique involves computing a cross-correlation network for a non-corrected pair of images and feeding it into a trained neural network to pick a correction delay.

Because the multi-aperture ultrasound systems capable of correcting for sound velocity incongruences allow for significantly larger apertures, some embodiments of the multi-aperture ultrasound systems described herein allow for openings located 10 cm away from each other. can have Since the resolution is proportional to 2λ/D, this larger aperture results in a higher resolution of tissues located well below the surface of the skin. For example, renal arteries are often located 10 cm to 15 cm below the skin and are 4 mm to 6 mm in size near the abdominal aorta. Phased array, linear array and synthetic aperture ultrasound systems are usually unable to detect this physiology in most patients; In particular this is because the aperture size is not large enough to have a suitable lateral resolution. Typically, phased array systems have aperture sizes of approximately 2 cm. Increasing the aperture size from greater than 2 cm to approximately 10 cm in multi-aperture ultrasound systems can increase the resolution by 5x.

3D imaging

In some embodiments, three-dimensional information may be obtained by moving the two-dimensional imaging system and acquiring 2D slices at multiple positions or angles. From this information, and using interpolation techniques, a 3D image at any position or angle can be reconstructed. Alternatively, a 2D projection of all data in the 3D volume may be created. A third alternative is to use the information directly in the 3D display.

Since multi-aperture ultrasound imaging systems can result in wider probe devices, the easiest way to use them to acquire 3D data is not to move them on the patient's skin, but only so that the 2D slices expand into the 3D volume to be imaged. to rock them. In some embodiments, a mechanical rotor mechanism that records position data may be used to aid in the collection of 2D slices. In other embodiments, a freely operating ultrasound probe with precision position sensors (such as gyroscope sensors) positioned in the head of the probe may be used instead. Such a device allows full freedom of movement while collecting 2D slices. Finally, intravenous and intracavity probes can also be fabricated to accommodate wide apertures. Such probes can be processed in similar ways to collect 2D slices.

This combination is particularly desirable for 3D cardiac imaging using a multi-aperture ultrasound imaging system. Most patients have superior acoustic windows between the two intercostals next to the sternum. A multi-aperture imaging system is ideal in this case because the intervening ribs would render the flattened probe obsolete, whereas a probe with at least two widely spaced apertures would have a transmit aperture and a receive aperture aligned with separate intercostal spaces. It can be positioned as much as possible. Once the probe with multiple apertures is in place, the probe cannot be rotated, but can be locked to obtain 3D information. Multi-aperture probes can also be used in the same intercostal space but across the sternum.

3D information can also be obtained directly with multi-aperture imaging systems with apertures that are not all in the same scan plane. In this case, the elements made up of the transmit aperture preferably propagate spherical waveforms (rather than circular waveforms confined to one scan plane). Elements made up of receive apertures may be sensitive to energy arriving from all directions (rather than being sensitive only to the ultrasonic energy of a single scan plane). The reconstruction pseudo code provided above can be extended to three dimensions.

As for additional details pertaining to the present invention, the materials and manufacturing techniques may be employed at the level of those skilled in the relevant art. The same holds true for the method-based aspects of the present invention in terms of additional operations commonly or logically used. It is also contemplated that any optional features of the variations of the invention described may be independently stated or claimed in combination with, or independently of, any one or more of the features described herein. Similarly, reference to a single item includes the possibility that there are multiple identical items presented. More specifically, as used in this specification and the appended claims, the singular forms "a," "and," "said" and "the" refer to pluralities, unless the context clearly dictates otherwise. Includes referents. It is further noted that claims may be written to exclude any optional element. Likewise, this statement is intended to serve as an antecedent basis for the use of such exclusive terms such as "solely", "only", etc. or the use of a "negative" limitation in conjunction with the recitation of claim elements. 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. The breadth of the invention is not limited by this specification, but rather only by the literal meaning of the claim terms used.

Claims (41)

A method of constructing an ultrasound image, comprising:
transmitting an omni-directional unfocused ultrasound waveform approximating a first point source within a transmission aperture on a first array through a target area, the omni-directional unfocused ultrasound waveform comprising at least one transmitted from a transmission aperture comprising a transducer element;
receiving ultrasound echoes from the target region with first and second receive elements disposed on a first receive opening on a second array, the first array physically separated from the second array;
retrieving position data describing the acoustic location of each of the at least one transducer element, the first receive element, and the second receive element of the transmit aperture with respect to a common reference point;
using the position data to determine, for the first receive element, a first time for the waveform to propagate from the first point source to a first pixel location in the target area, for the second receive element , determining a second time for the waveform to propagate from the first point source to the first pixel location in the target area; and
a first ultrasound image of the first pixel location by combining a first echo received by the first receiving element at the first time with a second echo received by the second receiving element at the second time step to form
comprising, a method of constructing an ultrasound image. According to claim 1,
and repeating the determining and forming for additional pixel locations of the target region. 3. The method of claim 2,
wherein the additional pixel positions are located on a grid without scan-conversion. According to claim 1,
and determining the first time and the second time includes estimating a uniform speed of sound. 3. The method of claim 2,
transmitting a second omni-directional, non-coherent ultrasound waveform proximate to a second point source within the transmission aperture through the target region;
receiving ultrasound echoes from the target region with first and second receiving elements disposed on the first receiving opening;
determine, for the first receiving element, a third time for the second omni-directional, non-coherent ultrasound waveform to propagate from the second point source to the first pixel location in the target area; determining a fourth time for the second omni-directional unfocused ultrasound waveform to propagate from the second point source to the first pixel location in the target region; and
a second ultrasound image of the first pixel position by combining a third echo received by the first receiving element at the third time with a fourth echo received by the second receiving element at the fourth time step to form
Further comprising, a method of constructing an ultrasound image. 6. The method of claim 5,
and combining the first ultrasound image with the second ultrasound image. 7. The method of claim 6,
wherein the combining comprises coherent addition. 7. The method of claim 6,
wherein the combining comprises incoherent addition. 7. The method of claim 6,
wherein the combining comprises combining a coherent addition and an incoherent addition. According to claim 1,
receiving ultrasound echoes from the target region with third and fourth receive elements disposed on a second receive opening on a third array, the third array being physically separated from the first and second arrays; ;
determine, for the third receive element, a third time for the waveform to propagate from the first point source to the first pixel location in the target area; determining a fourth time to propagate from a one point source to the first pixel location in the target area; and
a second ultrasound image of the first pixel position by combining a third echo received by the third receiving element at the third time with a fourth echo received by the fourth receiving element at the fourth time step to form
Further comprising, a method of constructing an ultrasound image. 11. The method of claim 10,
and repeating the determining and forming for additional pixel locations of the target region. 12. The method of claim 11,
wherein the additional pixel positions are located on a grid without scan-transformation. 12. The method of claim 11,
transmitting a second omni-directional, non-coherent ultrasound waveform proximate to a second point source within the transmission aperture through the target region;
receiving ultrasound echoes from the target region with first and second receiving elements disposed on the first receiving opening and with the third and fourth receiving elements disposed on the second receiving opening;
determine, for the first receiving element, a fifth time for the second omni-directional, non-coherent ultrasound waveform to propagate from the second point source to the first pixel location in the target area; , determine a sixth time for the second omni-directional non-coherent ultrasound waveform to propagate from the second point source to the first pixel location in the target region, and for the third receiving element, determine a seventh time for a directional unfocused ultrasound waveform to propagate from the second point source to the first pixel location in the target region, wherein, for the fourth receiving element, the second omni-focused ultrasound waveform is determining an eighth time to propagate from the second point source to the first pixel location in the target area; and
forming a third ultrasound image of the first pixel location by combining a fifth echo received by the first receiving element at the fifth time with a sixth echo received by the second receiving element at the sixth time and combining a seventh echo received by the third receiving element at the seventh time with an eighth echo received by the fourth receiving element at the eighth time to obtain a fourth position of the first pixel location. forming an ultrasound image
Further comprising, a method of constructing an ultrasound image. 14. The method of claim 13,
and combining the first, second, third and fourth ultrasound images. 15. The method of claim 14,
wherein the combining comprises coherent addition. 15. The method of claim 14,
wherein the combining comprises incoherent addition. 15. The method of claim 14,
wherein the combining comprises combining a coherent addition and an incoherent addition. 11. The method of claim 10,
and combining the first ultrasound image with the second ultrasound image. 19. The method of claim 18,
wherein the combining comprises coherent addition. 19. The method of claim 18,
wherein the combining comprises incoherent addition. 19. The method of claim 18,
wherein the combining comprises combining a coherent addition and an incoherent addition. 14. The method of claim 13,
comparing the first ultrasound image to the second, third and fourth ultrasound images to determine displacements of the second, third and fourth ultrasound images with respect to the first ultrasound image; Further comprising, a method of constructing an ultrasound image. 23. The method of claim 22,
correcting the displacements of the second, third and fourth ultrasound images with respect to the first ultrasound image and then combining the first, second, third and fourth ultrasound images , how to construct an ultrasound image. 23. The method of claim 22,
adjusting the third, fourth, fifth, sixth, seventh and eighth times to correct for the displacements of the second, third and fourth ultrasound images with respect to the first ultrasound image A method of constructing an ultrasound image, comprising: 11. The method of claim 10,
and comparing the first ultrasound image to the second ultrasound image to determine a displacement of the second ultrasound image with respect to the first ultrasound image. 26. The method of claim 25,
The method of constructing an ultrasound image, further comprising correcting the displacement of the second ultrasound image relative to the first ultrasound image, and then combining the first and second ultrasound images. 26. The method of claim 25,
and adjusting the third time and the fourth time to correct for the displacement of the second ultrasound image with respect to the first ultrasound image. According to claim 1,
and the first pixel location is disposed outside a plane defined by the point source, the first receiving element, and the second receiving element. According to claim 1,
wherein the first pixel location is disposed within a plane defined by the point source, the first receiving element, and the second receiving element. 11. The method of claim 10,
and the first pixel location is disposed outside a plane defined by the point source, the first receiving element, and the second receiving element. 11. The method of claim 10,
wherein the first pixel location is disposed within a plane defined by the point source, the first receiving element, and the second receiving element. 11. The method of claim 10,
and the first pixel location is disposed outside a plane defined by the point source, the third receiving element, and the fourth receiving element. 11. The method of claim 10,
wherein the first pixel location is disposed within a plane defined by the point source, the third receiving element, and the fourth receiving element. A multi-aperture ultrasound imaging system comprising:
a transmit aperture on a first array configured to transmit an omni-directional, non-coherent ultrasound waveform proximate a first point source through a target region, the transmit aperture comprising at least one transducer element;
a first receive aperture on a second array having first and second receive elements, the second array being physically separated from the first array, the first and second receiving elements receiving ultrasound echoes from the target area configured to receive — ;
a location memory comprising position data describing an acoustic position of each of the at least one transducer element, the first receive element, and the second receive element of the transmit aperture with respect to a common reference point;
a control system coupled to the transmit aperture and the first receive aperture, wherein the control system retrieves the location data from the location memory and uses the location data for the first receive element. , determine a first time for the waveform to propagate from the first point source to a first pixel location in the target region, and for the second receive element, the waveform is configured to propagate from the first point source to the target. and determine a second time to propagate to the first pixel location of a region, wherein the control system is further configured to determine at the second time a first echo received by the first receiving element at the first time. 2 configured to form a first ultrasound image of the first pixel location by combining with a second echo received by a receiving element;
A multi-aperture ultrasound imaging system comprising: 35. The method of claim 34,
wherein there are no transducer elements disposed between the first receiving aperture and a physical separation of the transmitting aperture. 35. The method of claim 34,
wherein the transmit aperture and the first receive aperture are separated by at least twice a minimum transmit wavelength from the transmit aperture. 35. The method of claim 34,
wherein the transmit aperture and the receive aperture comprise an overall aperture in a range of 2 cm to 10 cm. 35. The method of claim 34,
a second receive opening on a third array having third and fourth receive elements, the third array physically separate from the first and second arrays, the third and fourth receive elements are configured to receive ultrasound echoes from the target region. 39. The method of claim 38,
The control system is coupled to the transmit aperture and to the first and second receive apertures, wherein the control system is configured such that, for the third receive element, the waveform is transmitted from the first point source to a first of the target area. and determine, for the fourth receive element, a fourth time for the waveform to propagate from the first point source to the first pixel location in the target region. wherein the control system is further configured to: combine a third echo received by the third receiving element at the third time with a fourth echo received by the fourth receiving element at the fourth time to thereby A multi-aperture ultrasound imaging system configured to form a second ultrasound image of a pixel location. 40. The method of claim 39,
and the control system is configured to correct a displacement of the second ultrasound image relative to the first ultrasound image due to a change in the speed of sound. 39. The method of claim 38,
wherein the transmit aperture, the first receive aperture, and the second receive aperture are not all necessarily in a single scan plane.

Images