High-quality high-frame-rate ultrasound imaging using diverging transmit beams

Abstract

An ultrasound system produces high quality images at a high display frame rate. The plane or volume to be imaged is scanned by different divergent transmit beams to acquire a series of different subframes, the number of subframe acquisitions comprising the total number of transmit beams that will produce a high quality image. The echoes received in response to the transmit beams of the subframes are coherently combined with the echoes received in the other subframes. A complete image is produced each time the echoes of a new subframe have been coherently combined with the echoes of all other different subframes. After the entire series of subframes has been received and the echoes are combined, another series of subframe acquisitions begins and a new series of subframes is acquired. As each new subframe is acquired, it is coherently combined with all other different and most recently acquired subframes. The technology produces new images at the subframe scan rate, rather than waiting for a completely new series of subframes before forming a new image.

Description

Technical Field

[0001] The present invention relates to ultrasound imaging systems, and in particular to three-dimensional (3D) ultrasound imaging systems that utilize diverging transmit beams to produce high quality, high frame rate images. Background Art

[0002] High quality two-dimensional (2D) ultrasound imaging is usually produced by scanning a planar image field using a one-dimensional (1D) array transducer. Beams are emitted adjacent to each other within the image field, and echoes are collected in response to each emission. The received echoes are beamformed by a delay and sum beamformer to form scan lines of coherent echo signals across the image field. The typical number of scan lines for an image can be 128-196 scan lines. The scan lines are processed by B-mode or Doppler processing to form a planar image of tissue and / or flow in the planar image field. Such images have high quality because each scan line in the image is formed by a focused transmit beam and a coaxially focused receive beam. However, the disadvantage of this imaging is the time required to collect the echo signals used to form the image, which is limited by the speed of sound of the transmit beam and the return echo signal in the object. The time required to form an image can be improved by emitting fewer transmit beams, which improves the acquisition time and therefore the display frame rate, but the cost of doing so is reduced image quality.

[0003] The frame rate problem is even more serious when performing three-dimensional (3D) imaging. In 3D scanning, the transmit beam must be transmitted in both the azimuth and elevation dimensions to scan the entire volumetric area. This requires transmitting not a hundred or so beams as required for 2D imaging but thousands of transmit beams. This situation can be achieved by acquiring multiple scan lines in response to each transmit beam, but the time required to scan the entire volume and therefore the display frame rate is typically even slower than the time and display frame rate of 2D imaging. Therefore, it is desirable to be able to improve the display frame rate of both 2D and 3D imaging while maintaining high image quality. Summary of the invention

[0004] According to the principles of the present invention, an ultrasound imaging system that produces high-quality images at a high display frame rate is described. The plane or volume to be imaged is scanned by different divergent transmit beams to acquire a series of different subframes, and the number of subframes includes the total number of transmit beams that will produce high-quality images. The echoes received in response to the transmit beams of the subframes are coherently combined with the echoes received in other subframes. Whenever the echoes of a new subframe have been coherently combined with the echoes of all other different subframes, a complete image is generated. After the entire series of subframes has been received and the echoes are combined, another series of subframe acquisitions begins and a new series of subframes is acquired. When each new subframe is acquired, it is coherently combined with all other different and most recently acquired subframes. The technology produces new images at the subframe scanning rate, rather than waiting for a completely new series of subframes before forming a new image. According to another aspect of the present invention, motion in the image field can be detected, and the presence of detected motion is used to change the scanning sequence or correct motion artifacts. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] In the attached picture:

[0006] Figure 1a , 1b , 1c and 1d illustrate a scanning sequence of four subframes for 2D image scanning according to the principles of the present invention.

[0007] Figure 2a and 2b A scanning sequence of two subframes for 3D image scanning according to the principles of the present invention is illustrated.

[0008] Figure 3a and 3b Another diverging beam scanning sequence for 3D image scanning according to the principles of the present invention is illustrated.

[0009] Figure 4 An ultrasound imaging system for 2D imaging constructed in accordance with the principles of the present invention is illustrated in block diagram form.

[0010] Figure 5 An ultrasound imaging system for 3D imaging constructed in accordance with the principles of the present invention is illustrated in block diagram form. DETAILED DESCRIPTION

[0011] Figure 1a-1dFour subframe scanning sequences for scanning a 2D image plane according to the principles of the present invention are illustrated. The illustrated sequences each include the transmission of five different transmit beams and the corresponding echo reception, and are four of eight such sequences and the resulting subframes are used to scan the entire 2D image plane and produce a high-quality image. This means that a total of forty transmit beams are used in the eight sequences. Each scanning sequence for a different subframe includes five different transmit beams distributed across the complete image hole 12. In FIG. 1 , the transmit beam arrows are numbered to indicate their position in the full sequence of forty beams covering the entire image field. Figure 1a The scan sequence of is considered to include transmit beams 1, 9, 17, 25, and 33. Each transmit beam is a divergent beam containing multiple receive scan line positions, as indicated by the divergent beam profile 50 around transmit beam #1. In this example, the divergent beam insonifies eight receive scan line positions 1-8 so that echoes for eight scan lines can be received from these positions in response to the transmission of divergent beam #1. After beam #1 is transmitted and its echoes are received, beam #9 is transmitted and echoes for another set of scan lines insonified by beam #9 are received. The process continues with the transmission and reception of divergent beams 17, 25, and 33.

[0012] The scan line echoes acquired from this five-beam sequence are then coherently combined with the echoes received from other different sequences. The echoes can even be used to form an image. However, the image will be low in quality due to the low number of transmit beams and receive lines, and may even show gaps due to lack of echo reception from different areas of the image field. However, the image formed by the subframes of the eight different sequences and the full scan will be a high quality image.

[0013] Additional subframes are collected by transmitting different sequences, such as Figure 1b , 1c and 1d. Figure 1b , a sequence of divergent beams 5, 13, 21, 29 and 37, which is considered to be intermediate the beam positions of the first sequence. Beam #5 is considered to be insonified and results in the acquisition of echoes for scan lines 9-16 of the eighty scan line image field. After the acquisition with the second sequence is completed, a complete image field of eighty scan lines has been acquired. Figure 1cThe third sequence shown in transmits divergent beams 2, 10, 18, 26, and 34. The scan lines acquired during this scan will all be used for scan lines that have been previously acquired, resulting in coherent combinations at twenty scan line locations across the aperture. For example, transmit beam #2 will result in acquisition for scan lines 3-10, which will coherently combine with the scan lines acquired during the two previous sequences. After the third sequence has been transmitted and the scan lines received and combined, a fourth sequence of divergent beams 6, 14, 22, 30, and 38 is transmitted and echoes are received. This sequence also receives echoes from scan lines that have been previously acquired in the previous sequence, and therefore the echoes it receives will coherently combine with the previously acquired scan line echoes.

[0014] The process continues for four more sequences of transmission and reception of subframes from beams 3, 11, 19, 27, and 35; beams 7, 15, 23, 31, and 39; beams 4, 12, 20, 28, and 36; and beams 8, 16, 24, 32, and 40. In addition, except for the most lateral edges, each scan line of the image field has been scanned and acquired four times. Therefore, the resulting image data is produced by the coherent combination of four scan line samples at each point in the image field, resulting in the desired high quality image.

[0015] Now, the process repeats, and Figure 1a The first divergent beam sequence of is transmitted again, and the echo is received. But instead of waiting for the other seven sequences to be completed to form the second image, the second image is now formed by coherently combining the echoes from the sequence with the echoes collected from the previous seven sequences. In fact, the first image is now updated by providing a second image, wherein the echo signal data from the first sequence has been replaced by the echo signal data from the second repetition of the first sequence. This means that the new image is displayed to the user within one eighth of the time required to acquire and process a completely new image. The second image has the same quality as the first image because it consists of eight component subframes that have been coherently combined, just like the first image. The newly updated image is continuously generated in this way. After the acquisition of the new subframe, the scan line of the new subframe is coherently combined with the scan line data of the seven previously acquired subframes. This produces continuous high-quality images at a high display frame rate. It will be appreciated that the number of subframes, the number of transmit beams of the subframe, and the divergent beam profile of each transmit beam can be changed and adjusted to produce a wide range of scanning possibilities. Differently steered plane waves are also possible implementations for diverging beams.

[0016] Figure 2a and 2bThe diverging beam transmission and scanline echo reception for an embodiment of the present invention for 3D (volume) scanning is illustrated. In these figures, a diverging beam in the form of a volume plane wave 60 is transmitted from the aperture 12 of a two-dimensional array of transducer elements. The illustrated plane wave is not focused in one dimension (either azimuth or elevation), but is slightly focused in another dimension. An incompletely focused plane wave would require a large number of simultaneously operating receive channels and processing. The illustrated plane wave slightly focused in one dimension requires a smaller number of receive channels and processors due to the smaller number of receive scan lines in the slightly focused dimension. Figure 2a In the example of , each plane wave 60a spans only four scan lines in elevation. Figure 2b The same is true for plane wave 60b, except that the focus is slightly more in the azimuth dimension. In FIG2 , a subframe may include one or several plane waves 60a, 60b, as indicated by the small dots extending from the plane waves. Although the parallel plane waves are not shown as overlapping, in constructed embodiments, the overlap can extend to any desired extent. Figure 2a and 2b An embodiment is illustrated in which the volume is first scanned by four different scans in the lateral direction and then again by four different plane waves along the transverse direction. Figure 2a Plane wave 60a includes transmissions for two subframes, one subframe including the first and third plane waves, and the other subframe including the second and fourth plane waves. Figure 2b Also shown is the transmission for two subframes including the first and third and second and fourth plane waves. The echoes acquired for each subframe are coherently combined with the echoes acquired for the three previous subframes. Instead of generating an image after all eight plane waves have been transmitted and their echoes acquired and processed, a new image is generated after acquiring each new subframe from two plane wave transmissions, which is three times faster than is usually the case. The display frame rate is thus improved.

[0017] FIG3 shows another embodiment of the present invention for scanning a 3D volume, this time wherein each subframe comprises a divergent beam scan of a different angle of the entire target volume. In the example of these figures, there are eighty-one such volume subframes, each of which is transmitted with its virtual apex located differently in a grid 90 of positions behind the two-dimensional array aperture 12. Figure 3b A nine-by-nine grid 90 of virtual vertex positions is shown in , where the virtual vertex positions are located at the intersection of each vertical and horizontal line of the grid, as shown by the small dots. Figure 3a The volume scanned by the diverging beam of two enlarged dots AV1 and AV2 on the reference grid is shown in perspective in FIG. Due to the beam divergence and the fact that the apex of each pyramid scan is behind the hole, the holes 12 in the two-dimensional array surface emit diverging beams downward in the form of truncated pyramids. Figure 3b As shown, virtual vertex AV1 is located on the grid centrally relative to the 2D aperture, and thus the truncated pyramid diverging beam takes the form of an upright symmetrical pyramid, as shown by edge line 92. If a center line is drawn downward from the vertex of pyramid 92, it will be orthogonal to and extend from the center of aperture 12. The scan volume includes one subframe in a series of eighty-one subframes.

[0018] The second volume subframe generated with reference to the virtual apex AV2 is tilted at a different angle from the first pyramid volume, as illustrated by its dashed edge line 94. Since the virtual apex AV2 is behind and to the left of the center point AV1 on the grid, this truncated pyramid of transmitted energy is tilted backward and to the left. If the center line is drawn downward from the apex of the pyramid 92, it will extend from the aperture 12 at an angle that is tilted in azimuth (Az) and elevation (El). Therefore, the scanning of the full volume below the aperture by this second diverging beam will collect different echo information due to its different angles of the target volume.

[0019] Eighty-one such scans are performed using eighty-one different divergent transmit beams to collect volume echo signal data for eighty-one different volume subframes. The echo signals of these subframes are coherently combined on a spatial point-by-point basis for the position of the return echo in the volume. Most of the point (pixel or voxel) positions in the target volume will therefore be sampled eighty-one times, which gives the resulting 3D image its high image quality. The series of eighty-one scans is then repeated, wherein each new acquisition is coherently combined with eighty previous and subframes of echo signal data at different angles to produce a new 3D image. Therefore, the volume frame rate is eighty times faster than when a new volume image is produced only after the acquisition of the entire set of eighty-one new scans.

[0020] Reference now Figure 4, an ultrasonic diagnostic imaging system constructed according to the principles of the present invention is shown in block diagram form. A two-dimensional array of transducer elements 12 is provided in an ultrasound probe 10 for transmitting ultrasound waves and receiving echo information. The transducer array 12 can be a one or two-dimensional array of transducer elements that can be scanned in two or three dimensions (e.g., in both azimuth and elevation) for 3D scanning. The transducer array 12 is coupled to a microwave beamformer 14 in the probe, which controls the transmission and reception of signals through the array elements. The microwave beamformer is a probe integrated circuit that is capable of transmitting beam steering and at least partially beamforming signals received by a group or "patch" of transducer elements, as described in U.S. Patents US 5997479 (Savord et al.), US 6013032 (Savord), US 6623432 (Powers et al.), and US 8177718 (Savord). The microwave beamformer is coupled by the probe cable to a transmit / receive (T / R) switch 16 which switches between transmit and receive and protects the system beamformer from high energy transmit signals. Transmission of a plane wave or diverging ultrasound beam from the transducer array 12 under the control of the microwave beamformer 14 is directed by a beamformer controller 18 coupled to the T / R switch and the main beamformer 20, which receives user operated input from a user interface or control panel 38. Among the transmit characteristics controlled by the transmit controller are the focus, number, spacing, amplitude, shape, angle, phase, frequency, polarity and diversity of the transmit waveform. The beam formed in the direction of beam transmission can be steered straight ahead from the transducer array or at different angles on either side of the unsteered beam for a wider sector field of view. For the techniques described above, a plane wave or diverging beam is used for transmission. Most one-dimensional array probes of relatively small array lengths (e.g., 128-element arrays) do not use a microbeamformer, but are driven to and respond directly to the main system beamformer. A two-dimensional array transducer can be operated as a one-dimensional array by scanning with only a single column or row of transducer elements.

[0021] The echoes received by adjacent groups of transducer elements are beamformed by appropriately delaying them and then combining them. The partially beamformed signals produced by the microbeamformer 14 from each tile are coupled to a receiver in the form of a main beamformer 20, where the signals from individual transducer elements or partially beamformed signals from individual tiles of transducer elements are combined into received scan lines from fully beamformed coherent echo signals throughout the scanned target area. Preferably, the beamformer 20 is a multiple beamformer that produces multiple receive scan lines from echoes received after a transmit event. For example, the main beamformer 20 may have 128 channels, each of which receives partially beamformed signals from a tile of 12 transducer elements or from individual elements. In this way, the signals received by a row of transducer elements or more than 1500 transducer elements of a two-dimensional array transducer can efficiently contribute to a single beamformed signal, and the signals received from the image plane are combined.

[0022] The coherent echo signals of the scan lines received from each plane wave or diverging beam scan are coupled to the subframe compound circuit 22, where they are combined on a spatial basis with the echo signals received from the previous scan of the target area. When the scan lines of one subframe are aligned with the scan lines of other subframes, as in the example of FIG. 1, they can be compounded on a scan line basis, and can even be given a synthetic beam focus by the scan lines according to the phase alignment of their different transmit beam origins, as described and shown in U.S. Pat. No. 8,137,272 (Cooley et al.). When the received scan lines of each transmit volume of the 3D scan are in a common spatial distribution relative to the dimensions of its insonification pyramid volume (which facilitates beamformer programming), the scan lines from different scans will actually all be at different spatial angles from each other and the echoes from the intersection points will be combined on a point-by-point spatial basis. Since the flight time of each echo determines its spatial position in the volume, echoes with the same x, y, z coordinates in the target volume are compounded by the subframe compound circuit. As echoes from each different scan volume are received, they are added to the echo data previously received from the same x, y, z position of the target volume and stored in memory.

[0023] The composite coherent echo signals from the entire set of subframes undergo signal processing through a signal processor 26, which includes filtering through a digital filter and noise or speckle reduction such as through frequency compounding. The filtered echo signals also undergo orthogonal bandpass filtering in the signal processor 26. This operation performs three functions: band limiting the RF echo signal data, generating in-phase and orthogonal pairs (I and Q) of the echo signal data, and decimating the digital sampling rate. The signal processor can also shift the frequency band to a lower or baseband frequency range. For example, the digital filter of the signal processor 26 can be a filter of the type disclosed in U.S. Pat. No. 5,833,613 (Averkiou et al.).

[0024] The composite and processed coherent echo signals are coupled to a B-mode processor 30, which generates a signal for a B-mode image (such as a tissue image) of a structure in the object. The B-mode processor calculates (I 2 +Q 2 ) 1 / 2 The amplitude (envelope) detection of the I and Q signal components of the orthogonal demodulation is performed using the amplitude of the echo signals in the form of a quadrature signal. The quadrature echo signal components are also coupled to the Doppler processor 34. The Doppler processor 34 stores an ensemble of echo signals from discrete points in the image field, which is then used to estimate the Doppler shift at the point in the image using a fast Fourier transform (FFT) processor. The rate at which the ensemble is acquired determines the range of velocities of motion that the system can accurately measure and depict in the image. The Doppler shift is proportional to the motion (e.g., blood flow and tissue motion) at the point in the image field. For color Doppler images, the estimated Doppler flow value at each point in the vessel is wall filtered and converted to a color value using a lookup table. The wall filter has an adjustable cutoff frequency, above or below which motion, such as low-frequency motion of the vessel wall, will be rejected when imaging flowing blood. The B-mode image signals and Doppler flow values ​​are coupled to a multi-planar reformatter 32, which extracts the image signals of the desired planes of the 3D image data set when a planar image of the scanned volume is desired. The extraction is performed on the basis of the x, y, z coordinates of the 3D data set of tissue and flow signals, and the extracted signals or planar image data in the case of 2D scanning are then formatted for display in the desired display format (e.g., a linear display format or a sector display format). The B-mode image or the Doppler image can be displayed separately, or both can be shown together in an anatomically registered manner, wherein a color Doppler overlay shows the tissue in the blood vessels and the blood flow in the vessels of the B-mode tissue image. Another display possibility is to display images of the same anatomical structure that have been processed differently side by side. This display format is useful when comparing images.

[0025] The image data is coupled to an image memory 36, wherein the image data is stored in a memory location addressable according to the spatial location from which the image value was acquired. The image data from the 3D scan can be accessed by a volume renderer 42, which converts the echo signals of the 3D data set into a 3D image as a projection viewed from a given reference point, as described in U.S. Pat. No. 6,530,885 (Entrekin et al.). The 3D images produced by the volume renderer 42 and the 2D images produced by the multiplanar reformatter 32 from the planes of the scanned volume or from the scan of a single plane are coupled to a display processor 48 for further enhancement, buffering and temporary storage for display on the image display 40.

[0026] According to yet another aspect of the present invention, Figure 4 Embodiments include a motion detector 24. Because embodiments of the present invention are able to combine data from the most recently acquired subframe with data from subframes acquired many subframe intervals earlier, it is possible that motion artifacts such as blurring will occur. This is possible when the probe moves or there is motion in the scanned anatomical structure (such as a moving heart valve). The echo signal data will not be in registration when being compounded, thus producing artifacts in the image. The motion detector will detect when motion has occurred and take action to minimize or eliminate the artifact. Any known or later developed motion detection technology can be used. One possible embodiment is to use subframe data for motion analysis. When the scan lines of different subframes are axially aligned, one or more scan lines of the current subframe can be processed using spatially corresponding scan lines of one or more earlier acquired subframes and processed for motion detection. Echo data from an ensemble of temporally different but axially aligned scan lines can be processed by standard Doppler phase shift analysis to detect motion laterally or axially. Speckle tracking of image data from spatially common but temporally distinct groups of pixels can be used to detect any motion of the speckle as described in US Pat. No. 8,187,186 (Salgo et al.). Spatial analysis of spatially common, temporally distinct image regions or volumes, such as minimum sum of absolute differences (MSAD) calculations, can be used as described in US Pat. No. 6,442,289 (Olsson et al.). Other image-based tracking techniques, such as registration based on gradient descent or optical flow, can be employed. Instead of using data from subframes, special scan lines selectively spaced across the image plane or volume and dedicated only to motion detection can be acquired between subframes and analyzed using any of the aforementioned techniques. Motion detection can be performed using 1D, 2D, or 3D echo times.

[0027] The motion detector can be programmed to take various actions when motion is detected during a series of subframes. One possibility is to compensate for motion by realigning the subframes into registration, as performed in extended field of view imaging and described in the aforementioned patent of Olsson et al. Another way to align the subframes is to apply time delay correction to the received signal or distortion of the subframes (interpolation between subframes). Once registered, the subframes can be compounded with little or no motion artifacts. Another possibility is that the motion detector modifies the transmit parameters so that the entire set of subframes can be collected using fewer transmit beams. For example, the divergence of the divergent beam can be increased to collect a larger number of scan lines or a larger volume with each transmission, which requires fewer transmissions to scan the complete image target. Yet another possibility is to end the high frame rate technology of the present invention and cause the ultrasound system to return to standard scanning technology.

[0028] The inventors have discovered that static off-axis signals and moving objects have similar characteristics, which can cause false motion detection of static targets in the image field. This is because the round-trip point spread function of the acquired signal rotates when the transmit direction changes. The main beam lobe is the same, but the side lobes are shifted, resulting in apparent motion of off-axis scatterers. To prevent this, the receive aperture is shifted in the opposite direction to the transmit aperture, causing the round-trip point spread function to remain the same. For example, if the transmit direction is rotated by +1 degree, the receive aperture is shifted so that the receive direction is rotated by -1 degree, which does not cause the round-trip point spread function to remain rotated.

[0029] exist Figure 5 A second embodiment of the ultrasound imaging system of the present invention is illustrated in block diagram form in FIG. Figure 5 In the implementation mode Figure 41D array or a patch of elements of a 2D array transducer, storing them in correspondence with their point locations in the target plane or volume being scanned. After all echo signals have been received from the image plane or target volume in accordance with the transmission of a plane wave or diverging beam, the 2D or 3D volume of subframe data is combined on a spatial basis by a synthetic focusing processor 122 with the 2D or 3D data received from the previous subframe acquisition. Adding all the echoes received from the plane wave or diverging transmission events on a spatial basis achieves synthetic focusing, whereby image data at points throughout the plane or volume is fully focused. See, for example, U.S. Pat. No. 4,604,697 (Luthra et al.) for a description of synthetic focusing. Similar to the previous embodiments, the combination of data by the synthetic focus processor provides a composite of 3D data sets from multiple plane wave or diverging scans of the target volume.

[0030] It should be noted that the ultrasound system suitable for use in embodiments of the present invention and in particular Figure 4 and 5 The component structure of the ultrasound system can be implemented in hardware, software or a combination thereof. Various embodiments of the ultrasound system and / or components and their controllers, or components and controllers therein, can also be implemented as part of one or more computers or microprocessors. The computer or processor may include a computing device, an input device, a display unit and an interface, for example, for accessing the Internet. The computer or processor may include a microprocessor. The microprocessor may be connected to a communication bus, for example, to access a PACS system or a data network for importing training images. The computer or processor may also include a memory. Memory devices (such as scanning composite circuit memory, image memory 36 and multi-channel memory 120) may include random access memory (RAM) and read-only memory (ROM). The computer or processor may also include a storage device, which may be a hard drive or a removable storage drive, such as a floppy disk drive, an optical drive, a solid-state thumb drive, etc. The storage device may also be other similar modules for loading computer programs or other instructions into a computer or processor.

[0031] As used herein, the term "computer" or "module" or "processor" or "workstation" may include any processor-based or microprocessor-based system, including systems using microcontrollers, reduced instruction set computers (RISC), ASICs, logic circuits, and any other circuits or processors capable of performing the functions described herein. The above examples are exemplary only, and are therefore not intended to limit the definition and / or meaning of these terms in any way.

[0032] The computer or processor executes an instruction set stored in one or more storage elements to process input data. The storage element may also store data or other information as desired or required. The storage element may be in the form of an information source or physical memory element within a processing machine. The instruction set of an ultrasound system including instructions for controlling the acquisition, processing and display of ultrasound images as described above may include various commands that instruct a computer or processor as a processing machine to perform specific operations, such as the methods and processes of various embodiments of the present invention. The instruction set may be in the form of a software program. The software may take various forms, such as system software or application software, and may be embodied as a tangible and non-transient computer-readable medium. The operation of the scan line compound circuit and the synthetic focusing processor is typically performed by or under the direction of a software routine. In addition, the software may take the form of a collection of separate programs or modules within a larger program or a portion of a program module. The software may also include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to an operator command, or in response to the results of a previous process, or in response to a request from another processing machine.

[0033] Furthermore, the following claim limitations are not written in a means-for-function format and are not to be interpreted based on 35 U.S.C. 112, sixth paragraph, unless and until such claim limitations expressly use the phrase "means for..." followed by a description of functionality without further structure.

Claims

1. An ultrasound imaging system for producing an image of a target area at a high display frame rate, comprising: an ultrasound probe comprising an array of transducer elements adapted to transmit different sequences of one or more divergent beams to the target volume and to collect ultrasound echo signals returned from the target area, wherein each sequence of the one or more divergent beams is further adapted to collect a different subframe of the echo signal from the target area as a subframe of the series of different subframes; a receiver coupled to receive the echo signal from each transmission and adapted to process the echo signal returned from the target area; a sub-frame compounding circuit coupled to said receiver and adapted to coherently compound said echo signals of a series of sub-frames on a spatial basis, wherein the echo signal of each newly acquired subframe is composited with the echo signals of all said subframes in the current and previous acquired series except for the subframes of the previous series that are not different from those of the current series; an image processor coupled to receive the composite image data and adapted to generate an ultrasound image; and A display is adapted to display the ultrasound image.

2. The ultrasound imaging system according to claim 1, wherein: Each sequence of the series of one or more diverging beams also includes a plurality of diverging beams steered in different directions.

3. The ultrasound imaging system according to claim 2, wherein: Each sequence of one or more diverging beams in the series further comprises a plurality of diverging beams steered in a plurality of directions different from the directions of the plurality of diverging beams of each other sequence in the series.

4. The ultrasound imaging system according to claim 3, wherein: The echo signals of each newly acquired subframe are composited with the echo signals of all most recently acquired subframes having different divergent beam steering directions.

5. The ultrasound imaging system according to claim 4, wherein: The ultrasound probe is further adapted to repeat the acquisition of the series of different subframes; and The subframe compounding circuit is further adapted to compound the most recently acquired subframe with all the subframes in the series that are most recently acquired and repeated twice and are different from each other.

6. The ultrasound imaging system according to claim 1, wherein: The receiver further comprises a multi-line beamformer adapted to process the received echo signals by beamforming.

7. The ultrasound imaging system according to claim 6, wherein: The ultrasound probe further includes a two-dimensional array transducer; and A microbeamformer is coupled to the elements of the two-dimensional array and is adapted to perform partial beamforming of echo signals received by a patch of array elements.

8. The ultrasound imaging system according to claim 1, wherein: The sub-frame composite circuit further includes a memory adapted to store the composited echo signals on a spatial basis.

9. The ultrasound imaging system according to claim 1, wherein: The receiver also includes a synthetic focusing processor.

10. The ultrasound imaging system according to claim 9, wherein: The synthetic focusing processor is further adapted to coherently combine on a spatial basis echo signals received from points in the target volume and generated by the multiple diverging beam transmissions on a spatial basis.

11. The ultrasound imaging system of claim 1 , further comprising a motion detector adapted to detect the presence of motion in the image field and to alter operation of the imaging system in response thereto.

12. The ultrasound imaging system according to claim 11, wherein: The motion detector is further adapted to detect motion using one of an echo signal from a different subframe or an echo received from the transmission of a beam dedicated to motion detection.

13. The ultrasound imaging system according to claim 12, wherein: The motion detector is further adapted to detect the presence of motion by one of: Doppler processing, speckle tracking or spatial analysis of spatially identical but temporally different echo or image signals.

14. The ultrasound imaging system according to claim 11, wherein: The motion detector is further adapted to change the operation of the imaging system by one of: re-registering subframe data, reducing the number of divergent beams transmitted in a series of different subframes, or changing the imaging procedure to a standard imaging technique.

15. The ultrasound imaging system according to claim 12, wherein: The motion detector is further adapted to shift the receiving aperture in the opposite sense of the transmission aperture rotation when receiving echoes from the beam dedicated to motion detection.

Images