Ultrasonic imaging using elevation-complexed acoustic attenuation coefficients

Abstract

An ultrasound system produces a map of acoustic attenuation coefficients from B-mode image signals. Multiple maps are produced in different parallel and elevationally separated planes (A, B, C, D, E) and then compounded in the elevation direction. A confidence map can also be produced for one or more of the attenuation coefficient maps and the confidence map or a measure thereof is displayed or used to determine weighting for the compounding process. Compounding of elevationally separated planes improves attenuation coefficient estimation in the presence of estimated blood vessels affecting one or more of the planes.

Description

TECHNICAL FIELD

[0001] The present application relates to ultrasound imaging systems, and in particular to imaging of acoustic attenuation coefficient maps with 1.75D and 2D array transducers. BACKGROUND

[0002] Pulse-echo ultrasound imaging systems transmit beams of acoustic energy over an image field. As each transmitted beam encounters acoustic reflectors and tissue boundaries, some of the transmitted energy is reflected back to the transmitting transducer and is received as an echo. In this way, as the ultrasound beam energy travels deeper into the body, a sequence of echoes is received from increasingly deeper tissue. The amplitudes of the echoes are detected and displayed in correspondence with their time of receipt, which corresponds to their depth of receipt. The display thereby reveals the characteristics of the tissue structures within the body. However, as the beam energy travels through the tissue and encounters acoustic absorption and scattering along the path of the beam, it is continuously attenuated. This attenuation will result in typically stronger echoes being received from tissue in the near field, and typically weaker echoes from tissue at deeper depths. Without compensation for this effect, the resulting image will appear brighter in the near field (from the higher amplitude echoes), and darker in the far field due to the lower echo amplitudes being received. A common compensation for this effect is time gain control (TGC), whereby the receiver increases the amplification of the echo signal as it receives the echo signal from increasingly greater depths. The ultrasound system is equipped with TGC settings which enable the user to select the gains applied at different depths, from which the ultrasound system calculates the TGC curve for the continuous gain variation during echo reception. The ultrasound system is also typically equipped with predetermined TGC curves which have been empirically shown to be typical for various tissue types. Thus, the user can invoke a pre-calculated TGC curve for the liver for an abdominal exam, or a different pre-calculated TGC curve when imaging a breast. The typical curves are exactly that, because the attenuation characteristics of tissue vary from one person to another due to tissue density variations, composition, location differences, and other properties. It would therefore be desirable to know the attenuation characteristics of the particular tissue being diagnosed, rather than relying on typical or average characteristics. Thus, efforts have been made to measure the attenuation characteristics of a subject in vivo by estimating and displaying the degree of attenuation for each point in the ultrasound image field. See, for example, Walach et al., "Local Tissue Attenuation Images Based on Pulsed-Echo Ultrasonic Scans," IEEE Trans. On Biomedical Engineering, vol. BME-33, no. 7, July 1986 at pp 637-43. Walach et al. suggest that such local attenuation maps in the image field can be used to pinpoint tissue pathologies because of their different attenuation characteristics from healthy tissue. An example of this property is the diagnosis of fatty liver disease. Since fat is more attenuating than normal liver tissue, the acoustic attenuation characteristics can potentially be used to stage fatty liver disease.

[0003] However, the estimates used to produce such attenuation maps often depend on specific assumptions made about the tissue, such as local homogeneity of the tissue, which can not be true throughout the image field. Tissues such as liver tissue contain a network of blood vessels throughout the parenchyma. The presence of a vascular system adjacent to the image plane that is not visible in the image can affect the sound attenuation estimates in the image plane. Other error sources include effects of frequency dependent sound diffraction caused by aberrations, speckle, aperture blockage, clutter, or other adverse conditions. It would be desirable to produce a map of sound attenuation in the image field that suffers less from such error sources. SUMMARY

[0004] According to the principles of the present invention, an ultrasound imaging system, method, and technique for more accurately estimating the sound attenuation coefficients over an ultrasound image field are described. Instead of acquiring echo signal data only in a plane of interest, the echo signals used for sound attenuation estimation are acquired from a plurality of planes that differ in elevation angle. Thus, echo signal data is acquired adjacent to the main plane of interest. The sound attenuation estimates from the plurality of planes are compounded, reducing the effects of inaccurate in-plane estimates. According to another aspect of the present invention, less accurate or less reliable data points can be removed from the compounding, or less heavily weighted, when combined with other elevation angle varied values. BRIEF DESCRIPTION OF DRAWINGS

[0005] In the drawings:

[0006] Figure 1 An ultrasound system configured according to the principles of the present invention is illustrated in block diagram form.

[0007] Figure 2 A perspective view of the plane of the scout image and several elevation angle different regions for which sound attenuation coefficients are estimated for subsequent compounding is illustrated.

[0008] Figure 2a A scout image of a region of interest with a sound attenuation coefficient map containing anatomical registration is illustrated.

[0009] Figure 3 is the ultrasound beam used to scan Figure 2 An axial view of the ultrasound beam for sound attenuation estimation of the scout image and plane shown.

[0010] Figure 4 is the axial view of the ultrasound beam used to scan two orthogonal scout images and used to scan planes separated in elevation angle for sound attenuation compounding in either of the scout image planes.

[0011] Figure 5 A time interleaving of the scout image acquisition and the acquisition of echo signal data for sound attenuation estimation is illustrated.

[0012] Figure 6is a flowchart of a method for creating and displaying a composite attenuation coefficient map. DETAILED DESCRIPTION

[0013] Referring to Figure 1 An ultrasound diagnostic imaging system constructed in accordance with the principles of the present application is shown in block diagram form. A transducer array 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 capable of scanning in two or three dimensions, for example, in both elevation (3D) and azimuth. The preferred transducer array for scanning in accordance with the present application is a 1.75D array with limited beam steering in elevation, or a 2D array with full electronic steering capability in both elevation and azimuth. The transducer array 12 is coupled to a microbeamformer 14 in the probe, which controls the transmission and reception of signals by the array elements. The microbeamformer can at least partially beamform signals received by groups or "tiles" of transducer elements, as described in U.S. Patents 5,997,479 (Savord et al.), 6,013,032 (Savord), and 6,623,432 (Powers et al.). The microbeamformer is coupled through a probe cable to a transmit / receive (T / R) switch 16, which switches between transmission and reception and protects the main beamformer 20 from high-energy transmit signals. Transmission of ultrasound beams from the transducer array 12 under the control of the microbeamformer 14 is directed by a beamformer controller 18 coupled to the T / R switch and the main beamformer 20, which receives input from user operation of a user interface or control panel 38. Transmit characteristics controlled by the transmit controller are the number, spacing, amplitude, phase, frequency, polarity, and diversity of the transmit waveforms. Beams formed in the direction of transmission can be steered straight ahead from the transducer array, or steered at different angles on either side of the unsteered beam to obtain a wider sector field of view. For some applications, unfocused plane waves can be used for transmission. Most ID array probes, for example, 128-element arrays, do not use a microbeamformer, but are driven and respond directly to the main beamformer.

[0014] The echoes received by the contiguous groups of transducer elements are beamformed by appropriately delaying and then combining them. The partial beamformed signals produced by the microbeamformer 14 from each tile are coupled to the main beamformer 20, where the partial beamformed signals from individual tiles of transducer elements are combined into a full beamformed coherent echo signal. For example, the main beamformer 20 can have 128 channels, with each receiving a partial beamformed signal from a tile of 12 transducer elements. In this way, the signals received by over 1500 transducer elements of a two-dimensional array transducer can be effectively constructed into a single beamformed signal, and the signals received from an image plane are combined.

[0015] The microbeamformer 14 or the beamformer 20 also includes amplifiers that amplify the signals received from each element or tile of the transducer array 12. These amplifiers have controllable gain characteristics that are controlled by TGC curves stored in the ultrasound system, TGC controls on the user interface 38, or a combination of both. See, for example, U.S. Patent 5,482,045 (Rust et al.). Thus, the beamforming by delaying and summing the signals from individual transducer elements or tiles is performed with the echo signals compensated by time gain control.

[0016] The coherent echo signals undergo signal processing by the signal processor 26, which includes filtering by digital filters and noise or speckle reduction as by spatial or frequency compounding. The filtered echo signals can be coupled to a quadrature bandpass filter (QBP) 28. The QBP performs three functions: band limiting the RF echo signal data, producing an in-phase and quadrature pair (I and Q) of the echo signal data, and decimating the digital sampling rate. The QBP includes two separate filters, one producing in-phase samples and the other producing quadrature samples, with each filter formed by a plurality of multiplier accumulator (MAC) that implement FIR filters. The signal processor can also shift the frequency band to a lower or baseband frequency range, as the QBP is capable of doing. For example, the digital filters of the signal processor 26 can be of the type disclosed in U.S. Patent 5,833,613 (Averkiou et al.).

[0017] The beamformed and processed coherent echo signals are coupled to a B-mode processor 30 which creates the signal for the B-mode image of the body structure, such as tissue. The B-mode processor performs amplitude (envelope) detection of the I and Q signal components of the quadrature demodulated echo signals by computing the echo signal magnitude in the form (I2+Q2)1 / 2. The quadrature echo signal components are also coupled to a 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 of points in the image with a fast Fourier transform (FFT) processor. The rate at which the ensemble is collected determines the range of motion velocities the system can accurately measure and depict in the image. The Doppler shift is proportional to the motion of the points in the image field, for example, blood flow and tissue motion. For color Doppler images, the estimated Doppler flow values for each point in the blood vessels are wall filtered and converted to color values using a lookup table. The wall filter has an adjustable cutoff frequency above or below which motion such as the low frequency motion of the walls of the blood vessels will be rejected when imaging flowing blood. The B-mode image signals and the Doppler flow values are coupled to a scan converter 32 which converts the B-mode and Doppler samples from their R-theta coordinates in which they were acquired to Cartesian (x,y) coordinates for display in the desired display format, for example, a linear display format or a sector display format. The B-mode image or the Doppler image can be displayed separately or both together in an anatomic registration in which the color Doppler overlays the blood flow in the tissue and blood vessels in the image. Another display possibility is to display side-by-side images of the same anatomy which have been processed differently or, in the case of a multiplanar acquisition, images of different planes. This display format is useful when comparing images.

[0018] The scan converted images are coupled to an image data memory 36 where they are stored in memory locations which are addressable from the spatial locations from which the image values were acquired. The image data from a 3D scan can be accessed by a volume renderer 42 which converts the echo signals of the 3D data set to a projected 3D image as viewed from a given reference point as described in U.S. Patent 6,530,885 (Entrekin et al.). The 3D images produced by the volume renderer 42 and the 2D images produced by the scan converter 32 are coupled to a display processor 48 for further enhancement, buffering, and temporary storage for display on an image display 40.

[0019] In accordance with the principles of the present application, Figure 1An ultrasound system includes a subsystem that produces an image map of sound attenuation coefficient estimates. The subsystem includes an attenuation coefficient estimator 50 that receives B-mode echo signals, preferably from the QBP 28, prior to detection. The attenuation coefficient estimator is capable of producing an attenuation coefficient map from echo signals acquired from a scan plane, and according to the present application, is capable of producing multiple attenuation coefficient maps from multiple scan planes separated in the elevation dimension, as more fully described in the subsequent figures and description. The attenuation coefficient estimator 50 operates on the organized values of the I, Q data prior to detecting the pixel values of the B-mode image, and processes the tissue values in conjunction with reference value maps, such as attenuation coefficient measurements implemented by a homogeneous tissue phantom, a theoretical model of the attenuation coefficient, or a numerical simulation of the attenuation coefficient. Various reference value maps are stored in the attenuation coefficient estimator 50 or in a memory accessible by the attenuation coefficient estimator 50. A matching reference value map will be accessed by the attenuation coefficient estimator for system correlation compensation according to the user's real-time selection of the transmit / receive acoustic settings.

[0020] The different attenuation coefficient maps produced by the attenuation coefficient estimator are coupled to a confidence measure estimator 52 that produces a spatially corresponding map of estimated confidence, i.e. reliability, either of a single attenuation coefficient map or one attenuation coefficient map relative to another. The results of the attenuation coefficient maps and the confidence estimates are coupled to an attenuation coefficient map compositor 54 that composites, i.e. combines, the coefficient map values in the elevation dimension on a pixel-by-pixel basis, for example by a weighted average where the weighting is determined by the confidence estimate. The result is a final attenuation coefficient map that is not produced by a single estimation method but from the combination of multiple spatially distinct attenuation coefficient maps. Thus, the technique will include the benefits of nearby estimates that can be more accurate than some of the attenuation coefficient estimates in a given plane of interest, e.g. less affected by in-plane blood vessels. The final attenuation coefficient map is coupled to the scan converter 32 for scan conversion and then to the graphics processor 44 that formats the map for display, such as by color encoding the coefficient values of the map relative to a scaled range of color values. The attenuation coefficient map is coupled to the display processor 48 for display on the image display 40. Optionally, the confidence estimate map obtained from the confidence measure estimator 52 can be composited and displayed in the same manner so that the user can assess the reliability of the attenuation estimates made in a particular region of interest (ROI) of the image field. Another way to present the attenuation coefficient estimate results is to display only the attenuation image in the central plane (superimposed with the echo plane) but use all the attenuation images in the calculation of the average attenuation coefficient. In either display option, the system can allow the user to view the attenuation images in different planes during review.

[0021] The processor of the attenuation coefficient estimator 50 can use any of a variety of techniques for estimating the values of the acoustic attenuation coefficient over the image field, such as the spectral difference method, the spectral log difference method, and the maximum likelihood method. The estimation of the acoustic attenuation coefficient (in dB / cm or its equivalent units) or the acoustic attenuation coefficient slope (in dB / cm / MHz or its equivalent units) from the pulse echo signal can be based on the following expressions:

[0022] S s (f,z) = P(f)D s (f,z)A s (f,z0)B s (f,z)exp[-4a s (f)(z-z0)], [1]

[0023] and

[0024] S r (f,z) = P(f)D r (f,z)A r (f,z0)B r (f,z)exp[-4a r (f)(z-z0)], [2]

[0025] where the subscripts s and r refer to the tissue sample and the reference, respectively; f is the frequency; z is the depth in the image field; S(f,z) is the measured power spectrum from a region of interest (ROI) centered at depth z; P(f) is the combination of the sensor response and the frequency spectrum of the transmitted pulse; D(f,z) is the diffraction effect; z0is the starting depth of the ROI; A(f,z0) is the cumulative attenuation effect from the transducer surface to depth z0; B(f,z) is the influence of acoustic scattering; and a(f) is the attenuation coefficient in the ROI. By using S r (f,z) from a homogeneous reference phantom and assuming the same acoustic speed of the tissue sample and the reference, P(f) and D s (f,z) are suppressed, and the following expression will hold:

[0026]

[0027] Starting from these relations, the spectral difference method can be executed as follows. The spectral difference method assumes that the term in the above expression [3] is independent of z. Thus,

[0028]

[0029] where and a s (f) at a given frequency f can be estimated by estimating Obtained with respect to the slope of z. Note that the reference attenuation coefficient a r (f) is known. In soft tissue, a can be modeled as:

[0030] a(f) = βf n . [5]

[0031] When assuming n = 1, then a r (f) = β r f, and a s (f) = β s f, and

[0032]

[0033] The attenuation coefficient slope β s can then be estimated as

[0034]

[0035] where w(f) is a weighting function. Note that the assumption that the scattering effect B s is independent of the depth z, the effect of G(f) disappears after differentiation with respect to z. When the assumption of depth independence of the scatterer is valid, the spectral difference method is generally superior to other methods, such as the maximum likelihood (ML) method. Additional details regarding the above three sound attenuation coefficient techniques can be found in commonly assigned U.S. Provisional Patent Application US 62 / 796372, which is incorporated herein by reference.

[0036] According to another aspect of the present invention, the expressions and assumptions of the attenuation coefficient estimation techniques are used to produce spatially corresponding maps of confidence factors of the attenuation coefficient estimates for each of the elevation angle distinct planes. Confidence factor maps for different attenuation coefficient maps are computed by the confidence metric estimator 52 and are used to display the confidence of the attenuation coefficients across the image field, or to compound into different attenuation coefficient maps according to their trustworthiness. Another option is to compound the confidence factor maps in the elevation dimension in the same way as the compounded attenuation coefficient maps. For example, in order for the spectral difference method of attenuation coefficient estimation to be valid for accurate coefficient slope estimates, the following expression is required:

[0037]

[0038] is independent of f. It will be whether

[0039]

[0040] Whether this is the case can be determined by computing:

[0041]

[0042] The confidence of the coefficient slope estimate is greater when u is small and less when u is large. A map of the u values calculated for each pixel of the attenuation coefficient map calculated by the spectral difference method would thus inform the user of the trustworthiness of the attenuation coefficient map and the accuracy of the coefficient estimates at points throughout the attenuation coefficient map in this way. The difference between the original attenuation coefficient map and its smoothed version (e.g., the version that has been median filtered) can also be used to indicate confidence, with higher confidence values assigned to pixels with lower differences. Other methods or metrics for deriving a confidence measure include texture analysis, flow measurements, tissue response to acoustic radiation force, and coherence of pre-beamsum channel data.

[0043] The attenuation coefficient map compositor 54 produces a final attenuation coefficient map by composing the attenuation coefficient maps that are different in elevation. During composition, the coefficient values of the attenuation coefficient maps that have higher confidence factors and / or higher agreement with other maps will be given greater weight in the combination process. For example, if the attenuation coefficient from one map for a given pixel has a higher confidence factor than the coefficients from the other maps, that coefficient value will be given greater weight than the other coefficient values in the combination process. If the attenuation coefficients from two of the maps have higher agreement than the attenuation coefficient from a third map, e.g., are within 5% of each other, while the value from the third map differs by 20% from the values from the other maps, then the coefficients from the first two maps will be given greater weight in the combination process. The composition of the different maps proceeds in this way on a pixel-by-pixel basis in the elevation dimension until a final attenuation map is produced for display to the user. As previously mentioned, the final map can be displayed alone, or in combination with one or all of the confidence maps, or preferably in combination with the merged confidence map.

[0044] Figure 2 is a perspective view of the elevation composition technique of the present application. Plane 60 is the plane of the ultrasound image for the image-guided acquisition of the procedure. Positioned in correspondence with this image plane are planes A, B, C, D, and E that are different in elevation, from which echo signals are acquired for the computation of the acoustic attenuation coefficient values in each plane. Plane C is in the plane of the guide image plane 60, and defines the region of interest in plane 60 for acoustic attenuation estimation. Planes A and B are in front of plane 60 in the elevation dimension, and planes D and E are behind plane 60. After the acoustic attenuation coefficient maps have been computed for each of the five planes using the expressions given above, the five acoustic attenuation maps are composed on a pixel-by-pixel basis in the elevation direction to produce a composite acoustic attenuation map of the region of interest in plane 60. The composition can be performed with or without confidence weighting as described above. Figure 2aThree image panels formed in accordance with the present application are illustrated, an image panel 82 showing an echo image with a designated ROI, an image panel 86 with the ROI having color-coded attenuation coefficient values, and an image panel 84 with the confidence factor color-coded in the ROI.

[0045] Figure 3 is the echo signal data from the transducer array for acquiring Figure 2 An axial view of some of the beams of the echo signal data illustrated for the guidance image and the composite acoustic attenuation map. Beams 62 in plane 60 are used to acquire echo signals for the guidance image, while beams 72 are used to acquire echo signals for the acoustic attenuation coefficient maps in five elevationally separated planes A-E. Echo signal data from the acoustic attenuation map planes A-E can be acquired one plane at a time and coupled to the attenuation coefficient estimator 50 for computation of the attenuation coefficient map for one plane before acquiring echo signal data for another attenuation coefficient map plane using a 1.75D or 2D array transducer. When using a 2D array transducer with full electronic steering in the elevation dimension in a multi-line mode, as described in U.S. Patent US 8137272 (Cooley et al.), echo along scan lines of each elevation plane can be acquired simultaneously in response to a single pulse transmission. The transmission and reception proceed in this manner so that all of the different elevation planes can be acquired in the same time required to scan a single plane with a 1D array by using multi-line acquisition. After all of the echo signals for all of the planes have been acquired in this manner, the different elevation plane acoustic attenuation maps are computed by the attenuation coefficient estimator 50 and then compounded by the attenuation coefficient map compounding to produce the final attenuation coefficient map for the ROI.

[0046] The locations of the transmissions for attenuation imaging can vary from volume to volume and need not stay on a regular grid in the lateral elevation plane.

[0047] Figure 4 Another embodiment of the present application is illustrated using a 2D array to acquire two orthogonal guidance images, one in plane 60 and the other in orthogonal direction 64. As described above, echo signal data for the attenuation coefficient map planes is acquired along beams 72. This echo signal data can be processed in one of two ways, either by processing the rows of the echo signal (A) to produce attenuation coefficient maps in the elevation dimension as described in U.S. Patent US 8137272 (Cooley et al.) or by producing attenuation coefficient maps for the columns of the echo signal (A') to produce a composite attenuation coefficient map for the ROI in the orthogonal guidance image for plane 64. In the latter case, the elevation and azimuthal dimensions are reversed for the orthogonal guidance image of plane 64 and its attenuation coefficient map. The user can toggle back and forth between the two guidance images of planes 60 and 64 and their attenuation coefficient maps, or both can be displayed simultaneously. Figure 3 ​

[0048] In Figure 5 a timing diagram for acquiring echo signal data from the guide planes and for Figure 4 attenuation coefficient maps. As the timing diagram illustrates, scanning of the image guide planes is interleaved with acquisition of echo signal data for the attenuation coefficient maps. Initially frame 1 (plane 60) and then frame 2 (plane 64) are scanned, and guide images are produced from the two frames of echo signal data. Then, volume 1 is scanned with beam 72 to acquire a volume of echo signal data for an attenuation coefficient map. As explained above, this data can be processed in one direction in the plane to produce an attenuation coefficient map that differs in elevation for one of the guide images, and / or processed in the orthogonal direction to produce an attenuation coefficient map that differs in elevation for the other orthogonal guide image. The scan sequence then continues in this manner, updating the guide images with echo signal from frames 3 and 4, and then updating the attenuation coefficient map by processing acquired echo signal data from volume 2 echo signal.

[0049] Figure 6 A method flowchart is illustrated for a method 600 of automatically producing attenuation coefficient maps in an ultrasound image field. The method generally incorporates the ultrasound diagnostic imaging system described above and the functions and features as Figures 1 to 5 shown. The method 600 begins at a start step 602, for example, with obtaining and initializing the system for acquiring ultrasound echo signals. In an acquisition step 604, ultrasound echo signals are received from the image field, with the signals preferably acquired in both azimuth and elevation dimensions. The system produces coherent echo signals from the raw received signals from the acquisition step 604 at a production step 606. An estimation step 608 then estimates attenuation coefficient values based on the coherent echo signals. Optionally, a B-mode guide image can also be derived from the coherent echo signals produced at step 606 in a B-mode image creation step 620.

[0050] The system uses the attenuation coefficients from the estimation step 608 to automatically create attenuation coefficient maps at a creation step 610. The maps are created for at least two elevation planes, but the present invention contemplates creating maps for more than two planes. Then, the system composites the two or more attenuation maps to obtain a composite attenuation coefficient map at step 612, according to the previously described technique. The advantages of the composite attenuation coefficient map were also previously described.

[0051] The obtained composite attenuation map from step 612 can then be used for various purposes, including further analysis or automatic adjustment of system settings. For example, a display step 618 can also provide a visual display of the obtained composite attenuation coefficient map. In an optional embodiment, the B-mode guide image created at step 620 can be displayed at step 618 in an anatomic registration with the region of interest of the guide images, for example, with the composite attenuation coefficient map. Figure 1It was displayed.

[0052] A second composite attenuation coefficient map can also be obtained from multiple planes with orientations different from the elevation plane. For example, step 614 automatically creates multiple such attenuation coefficient maps with attenuation coefficient values ​​in the azimuth dimension. The azimuth dimension is, of course, orthogonal to the elevation dimension, but other angular orientations fall within the scope of this invention. Then, according to the previously described technique, the system composites two or more attenuation maps at step 616 to obtain a second composite attenuation coefficient map in different planes.

[0053] The second composite attenuation plot from step 616 can then be used for various purposes, including further analysis or automatic adjustment of system settings. The second composite attenuation plot can be displayed at step 618, or it can be combined with the composite attenuation coefficient from step 612. Figure 1 It was displayed.

[0054] Optionally, multiple confidence factor plots corresponding to the attenuation coefficients of different planes can be created at creation step 622. The confidence factor plots preferably correspond to values ​​associated with the attenuation coefficient plots created in step 610 or 614. Then, multiple plots can be used at creation step 624 to create a composite confidence factor plot of the attenuation coefficients. Each composite confidence value there is preferably associated with a corresponding composite attenuation coefficient value. The composite confidence factor plot can be displayed at display step 618 and can be associated with the composite attenuation coefficients from step 612 or 616. Figure 1 Start displaying.

[0055] It should be noted that the ultrasonic system applicable to embodiments of the present invention, in particular Figure 1 The component structure of an ultrasound system can be implemented using hardware, software, or a combination thereof. Various embodiments and / or components of the ultrasound system and its controller, or components and controllers therein, can also be implemented as part of one or more computers or microprocessors. The computer or processor may include computing devices, input devices, display units, and interfaces, such as 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 data network to import training images. The computer or processor may also include memory. Memory devices, such as memory for a reference value map for the attenuation coefficient estimator 50, may include random access memory (RAM) and read-only memory (ROM). The computer or processor may also include storage devices, which may be hard disk drives or removable storage drives, such as floppy disk drives, optical disk drives, solid-state thumb drives, etc. Storage devices may also be other similar means for loading computer programs or other instructions into the computer or processor.

[0056] As used herein, the term "computer" or "module" or "processor" or "workstation" can include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), ASICs, logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and / or meaning of these terms.

[0057] The computer or processor executes a set of instructions that are stored in one or more storage elements, in order to process input data. The storage elements can also store data or other information as desired or needed. The storage element(s) can be in the form of an information source or physical memory element within a processing machine. The set of instructions for the ultrasound system as described above, including those that control the acquisition, processing, and display of ultrasound images, can include various commands that instruct the computer or processor as a processing machine to perform specific operations such as the methods and processes of the various embodiments of the application. The set of instructions can be in the form of a software program. The software can be in various forms such as system or application software and can be embodied as tangible and non-transitory computer readable media. The formulas given above for the different methods of attenuation coefficient estimation and mapping, as well as the calculations for producing the confidence map described above, are typically computed by or under the direction of software routines. Further, the software can take the form of a single program or a collection of separate programs or modules, such as an attenuation coefficient computation module, or an attenuation coefficient mapping program module or portion of a program module. The software can also include modular programming in the form of object-oriented programming. The processing of input data by the processing machine can be in response to operator commands, or in response to a previous output, or in response to another machine processing.

[0058] Further, the limitations of the following claims are not written in the format of a FET module architecture, and are not intended to be interpreted in accordance with 35 U.S.C. 112, paragraph 6, unless and until such claim limitation explicitly recites the phrase "means for" followed by a structural identification, without the structural identification being parenthetically expressed.

Claims

1. An ultrasound imaging system for generating an attenuation coefficient map of an image field, comprising: An ultrasonic probe (10) having a 1.75D or 2D transducer array (12) adapted to acquire ultrasonic echo signals from an image field in both azimuth and elevation dimensions. Beamformer (20) adapted to process the ultrasonic echo signal to generate a coherent echo signal for an ultrasonic image of the image field; An attenuation coefficient estimator (50), coupled to the beamformer, is adapted to estimate attenuation coefficient values ​​for an attenuation coefficient map. The attenuation coefficient estimator is also adapted to generate multiple attenuation coefficient maps in different planes along the elevation angle dimension; An attenuation coefficient map compositer (54), coupled to the attenuation coefficient estimator, and adapted to composite the plurality of attenuation coefficient maps in the elevation direction; and Display (40) adapted to display the attenuation coefficient diagram generated by the attenuation coefficient diagram compositer.

2. The ultrasound imaging system of claim 1 further includes a mode-B processor, the mode-B processor being coupled to receive the coherent echo signal and adapted to generate a mode-B image signal for the attenuation coefficient estimator.

3. The ultrasound imaging system according to claim 2, wherein, The mode B processor is also adapted to generate echo signals for the guide image. The composite attenuation coefficient map generated by the attenuation coefficient map compositer is anatomically registered with the region of interest of the guided image.

4. The ultrasound imaging system according to claim 1, wherein, The attenuation coefficient map compositer is also adapted to composite two or more attenuation coefficient maps generated by the attenuation coefficient estimator pixel by pixel in the elevation direction.

5. The ultrasound imaging system of claim 1 further includes a confidence estimator adapted to generate a corresponding graph of confidence factors related to the corresponding attenuation coefficient value of each attenuation coefficient graph in response to the generation of the attenuation coefficient graph.

6. The ultrasound imaging system according to claim 5, wherein, The attenuation coefficient map compositer is also adapted to combine two or more attenuation coefficient maps generated by the attenuation coefficient estimator by weighted averaging.

7. The ultrasound imaging system according to claim 6, wherein, The attenuation coefficient map compositer is further adapted to combine two or more attenuation coefficient maps using weights determined by confidence factor estimation; and / or The attenuation coefficient map compositer is further adapted to use weights determined by the consistency of the attenuation coefficients of the composited maps to composite two or more attenuation coefficient maps.

8. The ultrasound imaging system according to claim 1, wherein, The transducer array is a 2D array suitable for simultaneously acquiring ultrasonic echo signals for multiple attenuation coefficient maps with different elevation angles via multi-line acquisition.

9. The ultrasound imaging system according to claim 8, wherein, The beamformer is also adapted to generate coherent echo signals for two orthogonal ultrasound images.

10. The ultrasound imaging system according to claim 9, wherein, The attenuation coefficient estimator is also adapted to estimate the attenuation coefficient value of the attenuation coefficient map in the azimuth dimension or the elevation dimension.

11. The ultrasound imaging system according to claim 10, wherein, The attenuation coefficient map compositer is also adapted to composite multiple attenuation coefficient maps in the elevation direction of two orthogonally oriented ultrasound images.

12. The ultrasound imaging system of claim 1, further comprising a memory suitable for storing a graph of reference values, in, The reference values ​​include the measurement results of the attenuation coefficient of the tissue phantom, the theoretical model of the attenuation coefficient, or the numerical simulation of the attenuation coefficient.

13. The ultrasound imaging system according to claim 9, wherein, The transducer array is also adapted to acquire echo signal data for ultrasound images and echo signal data for attenuation coefficient mapping in a time-staggered manner.

14. A method for automatically generating an attenuation coefficient map in an ultrasound image field, comprising the following steps: Acquire ultrasonic echo signals from the ultrasonic image field in both azimuth and elevation dimensions; A coherent echo signal is generated based on the ultrasonic echo signal; Estimate the attenuation coefficient value corresponding to the coherent echo signal; Automatically create multiple attenuation coefficient maps for attenuation coefficient values ​​in multiple different planes along the elevation angle dimension; The multiple attenuation coefficient maps are combined to obtain a composite attenuation coefficient map; and The composite attenuation coefficient diagram is shown.

15. A computer program product residing in a non-transient computer-readable medium and containing instructions for implementing the method of claim 14 when run by a computer communicating with an ultrasound imaging system.

Images