Fat percentage estimation using ultrasound with shear wave propagation

Abstract

Method for estimating fat content based on shear wave propagation, wherein the method comprises the following: the transmission (30) of an acoustic radiation force excitation to a patient; the measurement (32), using ultrasound, of tissue displacements at tissue locations within a patient in response to a shear wave resulting from acoustic radiation force excitation; the calculation (36), by a processor (18), of the damping of the shear wave from the displacements; calculating (37) a center frequency, a bandwidth or a center frequency and a bandwidth of the displacements as a function of time; the estimation (40) by the processor (18) of the fat content of the tissue as a function of the shear wave damping, wherein the estimation (40) of the fat content comprises the estimation (40) of the fat content as a function of the center frequency, the bandwidth or the center frequency and the bandwidth; and the display (42) of an indication of the fat content.

Description

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[0001] This patent document claims the benefit of the filing date pursuant to 35 USC §119(e) of the preliminary US patent application serial no. 61 / 799,616, filed on March 15, 2013, which is hereby incorporated by reference into this document. BACKGROUND

[0002] The present embodiments relate to ultrasound imaging. In particular, the fat content in tissue is estimated using ultrasound. Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease in American adults and children. NAFLD is characterized by excessive hepatic fat accumulation and hepatic fibrosis. Magnetic resonance imaging (MRI) accurately measures the proton density fat fraction (PDFF) as a biomarker for hepatic fat content. However, MRI is not widely available and is also expensive. An ultrasound-based method for quantifying liver fat can advance clinical treatment.

[0003] From WO 2013 / 025 798 A1, an ultrasound-based method for determining liver fat using interfering shear waves is known. Shear waves are generated at multiple positions within the tissue using at least two actuators. The interfering shear waves are detected by an ultrasound transducer and analyzed by a processor, whereby the dispersion and attenuation of the shear waves are determined. Based on the dispersion or attenuation, the liver fat content is determined.

[0004] From 'Nightingale, Kathryn, et al., “Acoustic radiation force impulse imaging: ex vivo and in vivo demonstration of transient shear wave propagation”, IEEE International Symposium on Biomedical Imaging Proceedings, 2002, pp. 525-528', the use of acoustic radiation force impulse imaging (AFE) for determining the mechanical properties of tissue, e.g., stiffness, from tissue displacements is known. In this technique, shear waves are generated by acoustic radiation force impulses, which are then used to determine the mechanical properties.

[0005] US 2008 / 0249408 A1 describes a method for determining mechanical properties, such as stiffness or shear modulus of liver tissue, using acoustic radiation force impulse imaging. BRIEF SUMMARY

[0006] The preferred embodiments described below comprise methods, instructions, and systems for estimating fat content based on shear wave propagation. Acoustic radiation force is used to generate a shear wave in the tissue of interest. Attenuation, center frequency, bandwidth, or other non-velocity-related characteristics of the shear wave are calculated and used to estimate the fat content.

[0007] In the first aspect, a method for estimating fat content based on shear wave propagation is provided. An acoustic radiation force excitation is transmitted into the patient. Ultrasound is used to measure tissue displacements within the patient in response to a shear wave resulting from the acoustic radiation force excitation. A processor calculates the shear wave attenuation from the displacements and a center frequency, bandwidth, or center frequency and bandwidth of the displacements as a function of time. Alternatively, the processor calculates only a center frequency, bandwidth, or center frequency and bandwidth of the displacement as a function of time. The processor estimates the fat content of the tissue as a function of the shear wave attenuation and as a function of the center frequency, bandwidth, or center frequency and bandwidth.Alternatively, the processor estimates the tissue fat percentage based solely on the center frequency, bandwidth, or both. The fat percentage is then displayed.

[0008] A second aspect involves storing data on a non-transient, computer-readable storage medium, representing instructions that can be executed by a programmed processor for fat percentage estimation based on shear wave propagation.The storage medium includes instructions for generating an acoustic radiation force focused on a location in the tissue, for measuring the shear wave propagation resulting from the acoustic radiation force, for calculating a property of shear wave propagation other than velocity, and for estimating the fat content of the tissue as a function of this property, wherein the calculation includes calculating a center frequency of shear wave propagation and / or calculating a bandwidth of shear wave propagation, or wherein the calculation includes calculating an attenuation of shear wave propagation and calculating a center frequency of shear wave propagation and / or calculating a bandwidth of shear wave propagation.

[0009] A third aspect involves providing a system for estimating body fat percentage based on shear wave propagation. A transducer is configured to transmit an acoustic pulse excitation to a patient and is further configured to scan a region of the patient with ultrasound. A receiving beamformer is configured to generate data representing the region at different times following the acoustic pulse excitation. This data is generated from the ultrasound scan. A processor is configured to estimate the tissue displacement caused by a shear wave induced by the acoustic pulse excitation in order to calculate attenuation, center frequency, bandwidth of the tissue displacements, or combinations thereof, and to perform the body fat percentage estimation based on the attenuation, center frequency, bandwidth, or combinations thereof.The processor is also configured to calculate the center frequency and bandwidth from a spectrum of tissue displacements over a specific time for each of several locations, and to determine the fat percentage estimate from the center frequencies and bandwidths at a single location or across multiple locations.

[0010] The present invention is defined by the following claims, and nothing in this section should be construed as limiting those claims. Further aspects and advantages of the invention are discussed below in connection with the preferred embodiments and may, if appropriate, be claimed independently or in combination at a later date. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The components and figures are not necessarily shown to scale; rather, the focus is on illustrating the principles of the present invention. Furthermore, identical reference numbers in the figures denote the corresponding parts in the different views. Fig. Figure 1 shows a flowchart of an embodiment of a method for estimating fat content using shear wave propagation; Fig. Figure 2 is a graphical representation showing two exemplary shifts as a function of time; The Fig. 3 and Fig. 4 are graphical representations showing exemplary damping calculations; Fig. Figure 5 is a graphical representation of spectra for calculating a center frequency and / or bandwidth; Fig. Figure 6 shows an example filter bank applied to displacements; and Fig. Figure 7 shows a block diagram of an embodiment of a system for estimating fat content based on shear wave propagation. DETAILED DESCRIPTION OF THE DRAWINGS AND CURRENTLY PREFERRED EXECUTION METHODS

[0012] One or more shear wave propagation parameters induced by an acoustic radiation force impulse (ARFI) are used to estimate the fat content of tissue. Hepatic fat accumulation alters the shear wave propagation in tissue. Measuring the shear wave attenuation difference or the frequency response (e.g., center frequency and / or bandwidth) provides an indication of the extent or amount of fat accumulation.

[0013] In the following example, the fat content in the patient's liver is measured. The fat content is estimated to aid in the diagnosis of NAFLD. In other embodiments, the fat content is measured in a different tissue.

[0014] Fig. Figure 1 shows a method for estimating fat content based on shear wave propagation. The method is performed by the system consisting of Fig. 7 or another system is implemented. Additional, different, or fewer actions can be provided. For example, actions 36, 37, and 38 are examples. One, two, all three, or none of actions 36, 37, and 38 can be used. Other types of additional information can be used. In another example, action 42 is not performed. The estimated body fat percentage is stored or transmitted instead of being displayed. The actions are performed in the order described or shown, but can also be performed in a different order.

[0015] In action 30, an acoustic excitation is transmitted to a patient. The acoustic excitation acts as an impulse excitation to cause displacement. For example, a 400-cycle transmit waveform with power or peak amplitude levels similar to or higher than B-mode transmissions for tissue imaging is transmitted as an acoustic beam. In one embodiment, the transmission is a shear wave generation sequence applied to the field of view. Any acoustic radiation force impulse (ARFI) or shear wave imaging sequence can be used.

[0016] The transfer is configured by power, amplitude, timing, or other characteristics to exert pressure on the tissue sufficient to displace it at one or more locations. For example, a transfer focus of the beam is positioned near a lower, mid-range portion of the field of view or region of interest (ROI) to cause displacement across the entire field of view. The transfer can be repeated for different subregions or ROIs.

[0017] The excitation is transmitted by an ultrasound transducer. This excitation is acoustic energy. The acoustic energy is focused, resulting in a three-dimensional beam profile. The excitation is focused using a phased array and / or mechanically. The excitation may be unfocused in one dimension, for example, the height dimension. The excitation is then delivered to the patient's tissue.

[0018] Impulse excitation generates a shear wave at a specific location. Where the excitation is sufficiently strong, a shear wave is generated. The shear wave propagates through the tissue more slowly than the longitudinal wave propagates along the emission direction of the acoustic wave. This timing difference is used to isolate the shear wave from the longitudinal wave, for example, by taking localized samples at specific times. The shear wave propagates in various directions, including one perpendicular to the direction of the applied pressure. The shear wave displacement is greater at locations closer to where the shear wave is generated. As the shear wave propagates longitudinally, its magnitude is attenuated.

[0019] In action 32, a displacement response to the shear wave is detected in the patient. For example, in Fig. Figure 2 demonstrates the displacement profiles for two locations. The excitation causes tissue displacement. A shear wave is generated and propagates from the focal region. As the shear wave travels through the tissue, the tissue is displaced. Timing and / or lateral location are used to distinguish the shear wave from other generated waves. Longitudinal waves or other displacement causes can be used instead of shear. The tissue is forcibly displaced within the patient's body.

[0020] The displacement caused by the force or pressure is measured. The displacement is measured at one or more locations over a specific period of time. The displacement measurement can begin before the pressure or impulse ends, for example, by using a different frequency or coding. Alternatively, the displacement measurement begins after the impulse ends. Because the shear wave, longitudinal wave, or other wave that causes tissue displacement away from the point or region of pressure takes time to travel, the displacement can be measured from a relaxed or partially contracted state to maximum displacement and then back to a relaxed state, which is described in Fig. Figure 2 shows a temporal displacement profile. Alternatively, the displacement is measured only while the tissue is relaxed from its maximum position.

[0021] The measurement corresponds to the amount or magnitude of the displacement. The tissue is moved in any direction. The measurement can be taken along the direction of greatest movement. The magnitude of the movement vector is determined. Alternatively, the measurement can be taken along a given direction, for example, perpendicular to the scanning line, regardless of whether the tissue is displaced more or less in other directions.

[0022] The displacement is detected by ultrasound examination. Ultrasound data is acquired. At least some of the ultrasound data represents a response to the shear wave. A region, for example, a region of interest, an entire field of view, or a subregion of interest, is scanned with ultrasound. The region is monitored to detect the shear wave. The region can be of any size, for example, 5 mm laterally and 10 mm axially. B-mode scans, for example, are performed to detect tissue displacement caused by the shear wave. Doppler, color flow, or other ultrasound modes can be used to monitor the shear wave.

[0023] For a specific period of time, ultrasound is transmitted to the tissue or region of interest. Any currently known or subsequently developed displacement imaging technique can be used. For example, pulses with a duration of 1-5 cycles and an intensity of less than 720 mW / cm² are used. 2Pulses of other intensities can also be used. Monitoring is performed for any number of scan lines. For example, four or eight receive beams are formed in response to each transmission. After the excitation is transmitted to generate the shear wave, B-mode transmissions are repeatedly performed along a single transmit scan line, and receive operations are performed along four or eight adjacent receive scan lines. In other embodiments, only a single receive beam or another number of receive beams is formed in response to each transmission. Additional transmit scan lines and corresponding receive scan lines can be used. Any number of repetitions can be used, for example, about 120 times. Some of the ultrasonic data, for example, at the beginning or end of the repetitions, may not be a response to the shear wave.

[0024] As the shear wave propagates through the scan lines, the B-mode intensity can vary due to tissue displacement. A data sequence representing a time profile of the tissue movement resulting from the shear wave is provided for the monitored scan lines. Echoes or reflections from the transmission are received. The echoes are beamshaped, and the beamshaped data represents one or more locations. To detect displacement, ultrasound energy is transmitted to the tissue to be displaced, and reflections of this energy are received. Any transmit and receive sequence can be used.

[0025] By repeatedly transmitting and receiving data, representing a one-, two-, or three-dimensional region at different times, data is received. The transmission and reception are repeated several times to detect changes due to displacement. Repeated ultrasound scans determine the tissue position at different times.

[0026] The displacement is detected from the differences for each spatial location. For example, velocity, variance, shift in the intensity pattern (e.g., speckle tracking), or other information from the received data are recognized as displacement.

[0027] In one embodiment using B-mode data, data from different samples are correlated over time. For each depth or spatial location, a correlation is performed across multiple depths or spatial locations (e.g., a core of 64 depths, where the center depth is the point for which the profile was calculated). For example, a current dataset is correlated multiple times with a reference dataset. The location of a subset of data centered at a given location in the reference dataset is identified in the current dataset. Various relative translations and / or switches between the two datasets are performed.

[0028] The reference data is an initial set of data or data from a different sample. The reference set originates from before the ARFI pulse, but can also originate from after the ARFI pulse. The same reference data is used for the entire displacement detection, or the reference data changes within a continuous or moving window.

[0029] The correlation can be one-, two-, or three-dimensional. For example, correlation is used along a sampling line away from and towards the converter, or along a line perpendicular to the sampling line. In another example, translation is performed along two axes with or without rotation. In yet another example, translation is performed along three axes with or without rotation over three or fewer axes. The degree of similarity or correlation of the data at each of the different offset positions is calculated. The translation and / or rotation with the highest correlation represents the motion vector or offset for time, which is coupled to the current data compared with the reference data.

[0030] Any currently known or subsequently developed correlation can be used, such as cross-correlation, pattern matching, or minimum sum of absolute differences. Tissue structure and / or speckle are correlated. Using Doppler detection, a clutter filter forwards information about the moving tissue. The tissue velocity is derived from multiple echoes. This velocity is used to determine displacement toward or away from the transducer. Alternatively, the relative velocity or the difference between velocities at different locations can indicate pressure or displacement.

[0031] Fig. Figure 2 shows two example displacement profiles. The distance of the motion vector over time relative to the reference data is shown. The analysis period is approximately 8 milliseconds, but can also be longer or shorter (e.g., 12 milliseconds at a sampling rate of 4.8 kHz). Other displacement profiles are also possible. Displacements can be measured at any number of locations, for example, by measuring every millimeter in the 10 x 5 mm region of interest. The displacement for each location and for each sampling time is measured.

[0032] In action 33, the transducer's movement relative to the patient is taken into account during the measurement. The shear wave causes local displacements in a region of interest. The region of interest is a subset of a larger field of view. The B-mode data, or other data from the larger field of view, or even just the entire region of interest, can show movements caused by sources other than the shear wave. For example, the patient's breathing causes the patient or the region of interest to shift relative to the transducer. In another example, voluntary movement by the patient or shifting of the transducer causes the region of interest to shift relative to the transducer.

[0033] Global motion is determined by measuring motion as a displacement of the region of interest and / or the larger field of view in one, two, or three dimensions. The same data used to measure shear wave displacements, or data acquired through nested sampling, are employed. Translation and / or rotation between time points are determined. The locations represented by the data are shifted to counteract the global motion. This shift, achieved by selecting data points, changing coordinates, or changing locations, represents data results from different time points that are more likely to represent the same tissue locations despite the global motion. Alternatively, the global displacement is subtracted from each of the local or site-specific displacement measurements.

[0034] In step 34, one or more shear wave characteristics are calculated. The shear wave characteristics include various possible parameters or properties, such as velocity, attenuation, center frequency, or bandwidth. In one embodiment, the property is other than the velocity. Steps 36, 37, and 38 represent some example characteristics. Only one, two, all three, or different types of characteristics are calculated.

[0035] A processor performs the calculation. The displacement information is used to determine the property without user input. Once the displacements have been recorded, the processor automatically calculates the property for each location and / or time.

[0036] The shear wave property is detected from the displacements. These displacements over time and / or space are used. In one embodiment, the displacements for different depths are combined so that the displacements are spaced apart in the azimuth direction or along the propagation direction of the shear wave. For example, the displacements for a given scan line or lateral location are averaged over depth. Alternatively, instead of averaging, a maximum or other selection criterion is used to determine the displacement for a given lateral location.

[0037] In step 36, the attenuation property of shear wave propagation is calculated from the displacements. The maximum displacement over time for each location is determined. The shear wave magnitudes (peak values) at several locations along the propagation direction are calculated and used to derive the attenuation. Other attenuation measurements can also be used.

[0038] The magnitude of the displacement caused by the shear wave is determined. This magnitude can be derived from the displacement profile over time, for example, by identifying a maximum displacement. The magnitude of the maximum displacement is determined. The maximum displacement is calculated from the displacement profile. The peak or highest amount of movement or displacement magnitude of the tissue along a line, within a plane, or within a three-dimensional spatial region is calculated for the peak. The smoothed or filtered displacement curve is used to calculate the maximum. In other embodiments, the raw or unfiltered displacement curve can be used. The maximum value over the entire profile or a portion of the profile is identified or determined. In the example from Fig. 2. The maximum displacement of 1.45 micrometers occurs at approximately 0.9 milliseconds for one location, and the maximum displacement of 1.65 micrometers occurs at approximately 1.2 milliseconds for the other location. Alternatively, the magnitude can be derived from a given time based on the distance between the focal region and the monitored location.

[0039] The time profile for a given location indicates the detection of the shear wave at that location. The profile is analyzed for a noise-free or single instance of deviation. A peak in the profile, with or without time-based low-pass filtering, indicates the passage of the shear wave front. The largest displacement is selected, but the average, a first noise-free displacement, or other displacement parameters can also be used to indicate the passage.

[0040] In other embodiments, the energy or power for each location is calculated and used to derive the damping. The power of the displacement corresponds to the square of the quantity. The energy of the displacement corresponds to the integral over time. The quantity, energy, and / or power of the displacement can be used.

[0041] The damping is given by the slope of the maxima of the displacements across each location. To calculate the damping, the ratios of adjacent maximum values ​​are calculated. Fig. 3 and Fig. Figure 4 shows an example line across the maxima of tissue movements to indicate the attenuation for each of the different narrow-bench components of the displacements. Each curve represents a detection position in the direction of propagation. Alternatively, the ratios of non-adjacent maximum values ​​are calculated (e.g., ratios from a reference to each of the locations). The logarithms of these ratios provide the attenuations. An average attenuation across the azimuthally spaced locations can be used. Alternatively, the attenuation at each location separately is used. Other attenuation calculations can also be employed.

[0042] In step 37, the center frequency, bandwidth, or center frequency and bandwidth of the displacements are calculated. These spectral features are derived from the shear wave propagation represented by displacements. For each location, a Fourier transform of the displacement is determined as a function of time. From the resulting spectrum, a center frequency and / or bandwidth is calculated. Any measure for center frequencies or bandwidths can be used. For example, the center frequency could be the frequency corresponding to the peak value of the power spectrum, and the bandwidth could be a frequency range or a difference over a region 3 dB or another value below the power spectrum peak, or it could be a value (e.g., 2 / 3) of the region under the spectrum curve that is integrated. Fig. Figure 5 shows example spectra with a horizontal line plotted for the location 3 dB lower in the spectrum. The peaks are shown for the center frequency. The center frequency can also be calculated as an average or weighted value within the frequency bandwidth. Each spectrum is taken from a detection position in the direction of propagation.

[0043] The center frequency and / or bandwidth of the shear wave are provided for each location. The center frequencies and / or bandwidths can be used separately for each location. Alternatively, the center frequencies and / or bandwidths can be combined for the ROI. For example, the average or mean center frequency and bandwidth can be calculated for the ROI. Other combinations can also be used.

[0044] In action 38, the shear wave dispersion is calculated from the displacements. Dispersion is a measure of velocity as a function of frequency. Any dispersion measure can be used, for example, the derivative of velocity as a function of frequency or the slope of a regression line (e.g., linear regression fit) for velocity as a function of frequency.

[0045] In one embodiment, the displacement data are filtered as a function of time. The same data are filtered with different passbands. For example, to obtain a shear wave dispersion, a filter bank with ten or another number of center frequencies, evenly distributed within a range, for example from 50 to 275 Hz, is applied to the shear wave displacement data. The filters are temporary, so the process is repeated separately for each location. Fig. Figure 6 represents this filter bank approach, where each curve represents a detection position in the direction of propagation. In this example, each filter has a bandwidth of 32 Hz, in increments of 11.25 Hz between 50 Hz and 275 Hz, using a second-order elliptical filter with a ripple of 0.5 dB and a stopband attenuation of 40 dB. Other filters can also be used.

[0046] The filtered displacement data for each passband are used to estimate the shear rate. For example, the maximum filtered displacement indicates the passage of the shear wave. For location, the time or duration required for the shear wave to travel from the origin (e.g., the transmit focal region) to that location is determined. The maximum displacement, or another part of the displacement profile, indicates the arrival time of the shear wave. Using the timing from shear wave generation to arrival, the travel time is calculated. This time is known from the relative time between shear wave generation and detection. The travel time may be non-linear.

[0047] The shear wave velocity is calculated from the timing information. The travel time is the inverse of the velocity. Using the distance and the travel time, the velocity is calculated. The distance is known from the scanning line spacing (i.e., the transmitting beam position for generating the shear wave and the receiving beam position for detecting the shear wave).

[0048] Other techniques can be used to identify the peak in the profile, along with its corresponding time and velocity. For example, regression is applied. Since the shear wave velocity is linear, robust linear regression with automatic outlier detection can reveal the shear wave velocity. The ultrasonic data for all sampling points in the region of interest are plotted as a function of distance over time or as a function of time and distance. Linear regression is applied to the plot or data, providing a regression line for the data. The slope of the line indicates the shear wave velocity.

[0049] Since velocities are provided for different frequency bands, the dispersion of the shear rate with respect to frequency is provided. A derivative or other feature of this dispersion curve or line indicates the dispersion.

[0050] In step 40, the fat content of the tissue is estimated. The fat content depends on the calculated shear wave property. Any function can be used. In one embodiment, an experimentally determined relationship between the property and the fat content is used. Based on MRI-PDFF and / or liver biopsy measurements, the actual value of the fat content in the liver is determined. The relationship of an ultrasound-measured shear wave property (e.g., attenuation) to the actual fat content is determined. This relationship is used to determine the fat content based on the property in subsequent measurements. In other embodiments, a theoretical or manually set function is used.

[0051] The processor calculates a fat content value for each location and / or for the ROI. Using a lookup table, the property is mapped to a fat content value. Alternatively, another mapping method can be used, such as calculating the fat content using the property in a curve representing the relationship. Statistics, a machine-learned function, fuzzy logic, or other mapping methods can be employed.

[0052] Each of these properties can be used individually to estimate the fat content. For example, damping can be used to estimate the fat content. Center frequency, bandwidth, or both can be used to estimate the fat content. Any feature of a curve or other measure can be used.

[0053] A combination of properties can be used. For example, the fat content, estimated separately from two or more properties, is averaged. In another example, the representation of the fat content depends on the two or more properties.

[0054] Values ​​other than fat content can also be estimated. For example, the degree of fibrosis in the liver can be estimated. A velocity or velocity characteristic as a function of location can indicate the amount of fibrosis. In another example, a combination of shear wave properties, such as velocity and damping, can be used to estimate fat and the degree of fibrosis. Both properties are used to estimate fat and fibrosis. An iterative solution can be provided where fat and fibrosis are related to each other.

[0055] In action 42, an image of the body fat percentage is generated. A value representing the estimated body fat percentage is displayed on a screen. Alternatively or additionally, a graphic representing the estimated body fat percentage (e.g., a curve or a symbol) is displayed. A reference to a scale or other references may be shown. In other embodiments, the body fat percentage is displayed in a two-dimensional representation according to color, brightness, hue, luminance, or some other modulation of display values, depending on the location.

[0056] The percentage of fat is reported alone or with other shear wave information. For example, shear wave imaging is performed. The shear wave velocity, modulus, or other information determined from the tissue response to a shear wave is displayed. Any shear wave imaging can be used. The displayed image represents shear wave information for the region of interest or for the entire imaging region. In cases where, for example, shear velocity values ​​are determined for all grid points in a region of interest or field of view, the pixels of the display represent the shear wave velocities for that region. The display grid can differ from the scanning grid and / or the grid for which displacements are calculated.

[0057] Shear wave information is used for color overlay or other modulation of display values. Color, brightness, luminance, hue, or other display characteristics are modulated depending on the shear wave characteristic, such as the shear wave velocity. The image represents a two- or three-dimensional region of location. The shear data is in a display format or can be converted into a display format during scanning. The shear data is color or grayscale data; however, it can also be data prior to mapping with a grayscale or color scale. The information can be mapped to the display values ​​linearly or non-linearly.

[0058] The image can include other data. For example, shear wave information is displayed over or with B-mode information. B-mode data, or other data representing tissue, fluid, or contrast agent in the same region, can be included, for example, when displaying B-mode data for any location with a shear wave velocity below a threshold or of poor quality. The other data assists the user in determining the location of the shear information. In other embodiments, the shear wave feature is displayed as an image without any other data.

[0059] The additional fat content is displayed essentially simultaneously with the shear wave imaging. This essentially takes into account the visual perception of the view. Displaying two images consecutively at a sufficient frequency can allow the viewer to perceive the images as if they were being displayed at the same time.

[0060] Any format for essentially simultaneous display can be used. In one example, the shear wave image is a two-dimensional image. The fat percentage is represented as text, a graphic, a two-dimensional image, or another indicator of the fat percentage estimate. A cursor or other location selection can be positioned relative to the shear wave image. The cursor indicates the selection of a location linked to the shear wave velocity information. For example, the user selects a pixel linked to an internal region of a lesion, cyst, deposit, or other structure. The fat percentage for the selected location is then displayed as a value, a pointer along a scale, or some other indication.

[0061] In another embodiment, shear wave and fat content images are displayed essentially simultaneously. For example, a display with two screen areas is used. The shear wave image (e.g., the shear wave velocity) is displayed in one area of ​​the screen. The fat content as a function of location is displayed in another area of ​​the screen. The user can view the different images on the screen for diagnostic purposes. The additional information aids the user in diagnosing the region.

[0062] Fig. Figure 7 shows an embodiment of a system 10 for estimating fat content based on shear wave propagation. The system 10 implements the method from Fig. 1 or other methods. System 10 comprises a transmit beamformer 12, a converter 14, a receive beamformer 16, an image processor 18, a display 20, and a memory 22. Additional, different, or fewer components may be provided. For example, user input is provided for user interaction with the system.

[0063] System 10 is an ultrasound imaging system for medical diagnosis. In alternative embodiments, System 10 is a personal computer, a workstation, a PACS station, or another arrangement in the same location or a network-distributed arrangement for real-time or post-acquisition imaging.

[0064] The transmit beamformer 12 is an ultrasonic transmitter, a storage device, a pulse generator, an analog circuit, a digital circuit, or a combination thereof. The transmit beamformer 12 can be used to generate waveforms for multiple channels with different or relative amplitudes, delays, and / or phases. When acoustic waves are transmitted from the transducer 14 in response to the generated electrical waveforms, one or more beams are formed. A sequence of transmit beams is generated to scan a two- or three-dimensional region. Sector scanning, Vector® scanning, linear scanning, or other scanning formats can be used. The same region is scanned multiple times. In flow imaging, Doppler imaging, and shear wave imaging, a sequence of scans along the same line or lines is used.In Doppler imaging, the sequence can include multiple beams along the same scan line before an adjacent scan line is sampled. In shear wave imaging, scan or frame nesting can be used (i.e., the entire region is sampled before re-scanning). Line or line group nesting can also be used. In alternative embodiments, the transmit beamformer 12 generates a plane wave or a diverging wave to achieve faster scanning.

[0065] The same transmit beamformer 12 generates pulse excitations or electrical waveforms to produce acoustic energy in order to cause displacement. Electrical waveforms for acoustic radiation force pulses are generated. In alternative embodiments, a different transmit beamformer is provided for generating the pulse excitation. The transmit beamformer 12 causes the transducer 14 to generate pressure pulses or acoustic radiation force pulses.

[0066] Transducer 14 is an array for generating acoustic energy from electrical waveforms. In an array, relative delays focus the acoustic energy. A given transmission event corresponds to the transfer of acoustic energy through different elements at essentially the same time due to the delays. The transmission event provides a pulse of ultrasound energy for tissue displacement. This pulse is either a pulse excitation or a tracking pulse. Pulse excitation involves waveforms with many cycles (e.g., 500 cycles), but this occurs in a relatively short time to cause tissue displacement over a longer period. A tracking pulse can be a B-mode transmission, for example, using 1–5 cycles. Tracking pulses are used to scan a region of a patient.

[0067] The transducer 14 is a 1-, 1.25-, 1.5-, 1.75-, or 2-dimensional array of piezoelectric or capacitive membrane elements. The transducer 14 comprises several elements for converting acoustic and electrical energy. Received signals are generated in response to ultrasonic energy (echoes) striking the elements of the transducer 14. The elements are connected to channels of the transmit beamformer 12 and the receive beamformer 16. Alternatively, a single element with mechanical focusing is used.

[0068] The receive beamformer 16 comprises multiple channels with amplifiers, delays, and / or phase shifters, as well as one or more buzzers. Each channel is connected to one or more transducer elements. The receive beamformer 16 is configured by hardware or software to apply relative delays, phases, and / or apodization to form one or more receive beams in response to each imaging or tracking transmission. Receive operation may not occur for echoes from the pulse excitation used to displace tissue. The receive beamformer 16 outputs data representing spatial locations using the received signals. Relative delays and / or phases, and the summation of signals from different elements, provide the beamforming.In alternative embodiments, the receiving beamformer 16 is a processor for generating samples using the Fourier method or other transformation methods.

[0069] The receiving beamformer 16 can include a filter, for example, a filter for isolating information in a second harmonic frequency band or another frequency band relative to the transmission frequency band. Such information is more likely to contain the desired tissue, contrast agent, and / or flow information. In another embodiment, the receiving beamformer 16 includes a memory or buffer and a filter or adder. Two or more receiving beams are combined to isolate information in a desired frequency band, for example, a second harmonic frequency band, a cubic fundamental frequency band, or another frequency band.

[0070] In coordination with the transmit beamformer 12, the receive beamformer 16 generates data representing the region at different times. Following acoustic pulse excitation, the receive beamformer 16 generates beams representing locations along multiple lines at different times. By scanning the region of interest with ultrasound, data (e.g., beam-shaped samples) are generated. By repeating the scanning process, ultrasound data representing the region at different times after pulse excitation are acquired.

[0071] The receive beamformer 16 outputs beam-summed data representing spatial locations. Data for a single location, multiple locations along a line, multiple locations for a region, or multiple locations for a three-dimensional area are output. Dynamic focusing can be provided. The data can serve various purposes. For example, different scans are performed for B-mode or tissue data than for displacements. Alternatively, the B-mode data can also be used to determine a displacement. In another example, data for fat percentage estimation and shear wave imaging are acquired using a set of common scans, and the B-mode or Doppler scan is performed separately or using some of the same data.

[0072] The processor 18 is a B-mode detector, a Doppler detector, a pulsed Doppler detector, a correlation processor, a Fourier transform processor, an application-specific integrated circuit, a general-purpose processor, a control processor, an image processor, a field-programmable gate array, a digital signal processor, an analog circuit, a digital circuit, combinations thereof, or other devices known or subsequently developed for detecting and processing information for displaying beam-shaped ultrasonic samples. In one embodiment, the processor 18 comprises one or more detectors and a separate processor.The separate processor is a control processor, a general-purpose processor, a digital signal processor, an application-specific integrated circuit, a field-programmable gate array, a network, a server, a group of processors, a data path, combinations thereof, or other devices already known or subsequently developed for determining displacements, identifying the magnitude of a displacement, calculating travel time, calculating shear wave velocity, calculating one or more other properties of shear wave propagation, and / or estimating fat content. For example, the separate processor is configured by hardware and / or software to perform any combination of one or more of the following: Fig. performs the actions shown in point 1.

[0073] Processor 18 is configured to estimate tissue displacement induced by acoustic pulse excitation. Using correlation, tracking, motion detection, or other displacement measurements, the value of the tissue's positional shift is estimated. This estimation is performed multiple times over a specific period, for example, from the time before tissue movement due to the pulse until the time after the tissue has largely or completely returned to its relaxed state (e.g., when the tissue has recovered from the pressure caused by the pulse excitation).

[0074] Processor 18 is configured to calculate a shear wave characteristic, such as the attenuation, center frequency, bandwidth, and / or dispersion of the shear wave. The attenuation, center frequency, bandwidth, or combinations thereof are calculated from tissue displacements. For example, the attenuation is calculated from the slope of the distribution of a maximum shear wave magnitude along a propagation direction. Processor 18 is configured to find the maximum displacement of the displacement profile. In another example, the center frequency and bandwidth are calculated from a spectrum of tissue displacements over time for each of several locations. Processor 18 applies a Fourier transform to the displacements over time.In yet another example, a filter bank or a memory and programmable filter can be implemented by or used with the processor 18 to determine a shear rate characteristic as a function of frequency.

[0075] Processor 18 determines the fat percentage estimate from the damping, center frequency, bandwidth, or another shear wave property, or combinations thereof. For example, damping is used to locate a fat percentage based on an empirically determined relationship. Damping can show an 83% to 85% correlation with MRI-based measurements of fat percentage. Similarly, bandwidth can show an approximately 75% correlation with MRI-based measurements of fat percentage. Larger or smaller correlations can also be provided.

[0076] The shear wave velocity and / or modulus can also be calculated. For the velocity, the maximum or another displacement is used to determine the shear wave's travel time. The velocity is calculated using the distance and travel time. The velocity can be determined for any number of locations.

[0077] Processor 18 is configured to generate one or more images. For example, an image for the shear wave velocity is generated. The shear wave velocity image is displayed as a superimposition or region of interest within a B-mode image. The shear wave velocity modulates the color at locations within the region of interest. In cases where the shear wave velocity is below a certain threshold, the B-mode information can be displayed without modulation by the shear wave velocity.

[0078] Other information is incorporated into the image or displayed sequentially or essentially simultaneously. For example, an image of the fat percentage estimate is displayed at the same time as the shear wave velocity. Each of these images is generated as a color overlay in the region of interest in B-mode images. The velocity and fat percentage can be combined as a single overlay on a B-mode image. Alternatively, the fat percentage can be displayed as text or a numerical value alongside or as an overlay on an image for B-mode or shear wave imaging. The Processor 18 can be configured to generate other displays. For example, the shear wave velocity image can be displayed alongside a graph, text, or graphical indicators of the fat percentage and / or the degree of fibrosis.The information is presented in addition to the shear wave velocity for one or more locations in the region of interest, without being displayed in a separate two- or three-dimensional representation.

[0079] Processor 18 operates according to instructions stored in memory 22 or in another memory for fat percentage estimation based on shear wave propagation. Memory 22 is a non-transient, computer-readable storage medium. The instructions for implementing the processes, procedures, and / or techniques discussed herein are provided on computer-readable storage media or on memory, such as a cache, buffer, RAM, removable media, a hard disk drive, or other computer-readable storage media. Computer-readable storage media include various types of volatile and non-volatile storage media. The functions, actions, or tasks depicted in the figures or described herein are executed in response to one or more sets of instructions stored in or on computer-readable storage media.The functions, actions, or tasks are independent of the specific type of instruction set, storage medium, processor, or processing strategy and can be executed by software, hardware, integrated circuits, firmware, microcode, and the like, either alone or in combination. Similarly, the processing strategies can include simultaneous processing, multiprocessing, parallel processing, and the like. In one embodiment, the instructions are stored on a removable media device for retrieval by local or non-local systems. In other embodiments, the instructions are stored at a remote location for transmission over a computer network or telephone lines. In still other embodiments, the instructions are stored in a given computer, CPU, GPU, or system.

[0080] Display 20 is a cathode ray tube (CRT), a liquid crystal display (LCD), a projector, a plasma display, or another type of display for showing two-dimensional images or three-dimensional representations. The two-dimensional images represent a spatial distribution within a region. The three-dimensional representations are output based on data representing the spatial distribution within a three-dimensional area. Display 20 is configured by processor 18 or another device by inputting the signals to be displayed as an image. Display 20 shows an image representing the shear for different locations within a region of interest or an entire image. Display 20 displays information about the fat content.

[0081] Although the present invention is described above by reference to various embodiments, it should be noted that many changes and modifications can be made without departing from the scope of the present invention. It is therefore intended that the preceding detailed description be regarded as explanatory rather than limiting, and it should be noted that the following claims, including all equivalents, are intended to define the spirit and scope of the present invention.

Claims

[1] Method for estimating fat content based on shear wave propagation, the method comprising: the transmission (30) of an acoustic radiation force excitation to a patient; the measurement (32), using ultrasound, of tissue displacements at tissue locations within a patient in response to a shear wave resulting from acoustic radiation force excitation; the calculation (36), by a processor (18), of the damping of the shear wave from the displacements; calculating (37) a center frequency, a bandwidth or a center frequency and a bandwidth of the displacements as a function of time; the estimation (40) by the processor (18) of the fat content of the tissue as a function of the shear wave damping, wherein the estimation (40) of the fat content comprises the estimation (40) of the fat content as a function of the center frequency, the bandwidth or the center frequency and the bandwidth; and the display (42) of an indication of the fat content. [2] Method according to claim 1, wherein the measurement (32) of the displacements comprises repeated scanning of the locations with ultrasound. [3] Method according to claim 1, wherein the calculation (34) of the shear wave damping comprises determining a maximum of the displacements over time for each of the locations and calculating (34) a slope of the maxima of the displacements over the locations. [4] Method according to claim 1, wherein the estimation (40) of the fat content comprises looking up the fat content based on the damping. [5] Method according to claim 1, wherein the measuring (32) comprises measuring (32) in the liver of the patient. [6] Method according to claim 1, wherein the display (42) of the indication comprises the display (42) of a value of the fat content. [7] Method according to claim 1, wherein the display (42) of the indication comprises the display (42) of an image which represents the fat content at the locations. [8] Method for estimating fat content based on shear wave propagation, the method comprising: the transmission (30) of an acoustic radiation force excitation to a patient; the measurement (32), using ultrasound, of tissue displacements at tissue locations over a certain time within a patient in response to a shear wave resulting from acoustic radiation force excitation; the calculation (37) by a processor (18) of a center frequency, a bandwidth or a center frequency and a bandwidth of the shifts as a function of time; the estimation (40), by the processor (18), of the fat content of the tissue as a function of the center frequency, the bandwidth or the center frequency and the bandwidth of the shear wave; and the display (42) of an indication of the fat content. [9] Non-transitory computer-readable storage medium containing data representing instructions that can be executed by a programmed processor (18) for fat content estimation based on shear wave propagation, wherein the storage medium includes instructions for: the generation (30) of an acoustic radiation force focused on a location in the tissue; the measurement (32) of a shear wave propagation resulting from the acoustic radiation force; calculating (34) a property of shear wave propagation other than the velocity, wherein the calculation (34) includes calculating (37) a center frequency of the shear wave propagation and / or calculating (37) a bandwidth of the shear wave propagation; and estimating (40) the fat content of the tissue depending on the property. [10] Non-transient computer-readable storage medium according to claim 9, wherein the measurement (32) of the shear wave propagation comprises measuring (32) a displacement over a certain time and at different locations. [11] Non-transient computer-readable storage medium according to claim 9, wherein the calculation (34) comprises the calculation (36) of a damping of the shear wave propagation. [12] Non-transitory computer-readable storage medium according to claim 9, wherein the estimation (40) of the fat content comprises the assignment of the property to a value of the fat content. [13] Non-transient computer-readable storage medium according to claim 9, wherein the measuring (32) further comprises taking into account the movement of a transducer (14) relative to the patient. [14] System for estimating fat content based on shear wave propagation, comprising: a transducer (14) configured to transmit an acoustic impulse excitation to a patient and further configured to scan a region of the patient with ultrasound; a receiving beamformer (16) configured to generate data representing the region at different times after acoustic pulse excitation, the data being generated from ultrasound scanning; a processor (18) configured to estimate the tissue displacement caused by a shear wave induced by acoustic impulse excitation in order to calculate an attenuation, a center frequency, a bandwidth of the tissue displacements or combinations thereof, and to estimate the fat percentage based on the attenuation, the center frequency, the bandwidth or combinations thereof, wherein the processor (18) is configured to calculate the center frequency and the bandwidth from a spectrum of the tissue displacements over a certain time for each of several locations, and is configured to determine the fat percentage estimate from the center frequencies and the bandwidths at a single location or over several locations. [15] System according to claim 14, wherein the processor (18) is configured to calculate the damping from a distribution slope of a quantity of the shear wave along a propagation direction.

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