Adaptive Image Optimization in Induced Wave Ultrasound Imaging

Abstract

Adaptive image optimization (34) is provided in induced wave ultrasound imaging (30-33). The values ​​for the various transmission and reception parameters can be adapted (34). Based on feedback (36) from use with a given patient, the values ​​are adjusted (34) to better optimize a signal-to-noise ratio, interruption time, tracking accuracy, or other consideration. A transmission frequency, numerical aperture, line spacing, tracking pulse repetition rate, line sampling count, and / or push pulse amplitude values ​​can be adapted (34).

Description

BACKGROUND These embodiments relate to induced wave ultrasound imaging. In particular, shear wave and / or radiation force ultrasound imaging can be enhanced. Acoustic Radiation Force Imaging (ARFI) generates a longitudinal wave in tissue with acoustic energy. Wave propagation characteristics indicate tissue characteristics, such as elasticity. Similarly, shear wave velocity information can be useful for diagnosis. Rather than a longitudinal wave, the shear wave generated by acoustic energy is monitored. Shear wave information can indicate tissue characteristics in addition to acoustic impedance imaging (e.g., B-mode) and Doppler imaging (e.g., flow mode).However, acoustic wave-induced imaging is subject to limitations related to the transducer and tissue heating, causing interruption times during imaging. These acoustic wave-induced imaging techniques may provide less information than is available due to setup limitations. BRIEF SUMMARY As an introduction, the preferred embodiments described below include methods, instructions, and systems for adaptive image optimization in acoustic wave-induced ultrasound imaging. The values ​​of various transmission and reception parameters can be set adaptively. Based on feedback from use with a given patient, the values ​​are set to best optimize signal-to-noise ratio, interruption time, tracking accuracy, and other considerations.A transmission frequency, numerical aperture, line spacing, tracking pulse repetition frequency, line sampling count, and values ​​for the thrust pulse length and / or thrust pulse amplitude can be adapted. In a first aspect, a method is provided for adaptive image optimization in wave-induced ultrasound imaging. Acoustic energy is transmitted into a patient. A wave is generated in response to the transmission. A region of the patient is scanned with ultrasound. From the 5th scan onward, tissue displacement caused by the wave is detected. A transmission frequency, line spacing, numerical aperture, pulse repetition frequency, line sampling count, acoustic energy amplitude, acoustic energy pulse length, or combinations thereof, are adapted as a function of the displacement.In a second aspect, a non-transient, computer-readable storage medium has data stored on it representing instructions executable by a processor programmed for adaptive image optimization in induced-wave ultrasound imaging. The storage medium 15 includes instructions for imaging by acoustic radiation force or shear wave of a region of a patient, and an adaptation of a transmission frequency, line spacing, numerical aperture, pulse repetition rate, line sampling count, acoustic energy amplitude, acoustic energy pulse length, or combinations thereof, of the imaging as a function of information derived from the imaging.BRIEF DESCRIPTION OF THE DRAWINGS 25 The components and figures are not necessarily to scale, the emphasis being instead on illustrating the principles of the invention. Furthermore, in the figures, identical reference numbers designate corresponding parts in the different views. Figure 1 is a flowchart of an embodiment of a method for adaptive image optimization in induced wave ultrasound imaging; and Figure 2 is a functional diagram of a system embodiment for adaptive image optimization in induced wave ultrasound imaging. DETAILED DESCRIPTION OF CURRENTLY PREFERRED DESIGNS AND EMBODIMENTS: ARFI and shear wave imaging modes are adaptively optimized for the tissue type and patient being scanned. The optimization improves the imaging of elasticity or other tissue characteristics without specific classification of the imaged tissue. One or more of various parameters can be tailored to a given patient and the tissue being examined.For example, transmission frequency, line spacing, digital aperture, pulse repetition frequency (PRF), interlaced PRF (line sampling count), and / or thrust pulse amplitude are adaptively optimized in radiation force imaging or shear wave tracking. Optimization can produce greater displacement amplitude, improved tracking signal-to-noise ratio (SNR), image uniformity, and / or reduced cooling time compared to using a generic imaging modality configuration and / or a generalized application. Optimization can improve imaging even for transmission and reception configurations specific to a tissue type, but not to a given patient. Optimization can use a single instance of feedback, such as tuning a parameter based on a measured displacement value. Alternatively, the optimization of the value(s) can be based on the results of iterative interrogations. Different settings are tested. A sufficient setting, or the best among the test settings, can then be selected and used. Interpolation or extrapolation can be used to calculate a value for a parameter other than a tested value. The results of sequential interrogations are interpolated or extrapolated to select a setting that differs from one of the settings used during the interrogation phase. Adaptive optimization is applied before capturing a single static image.The adaptive process can be implemented after or during the capture of a test image, but before the acquisition of an image intended for diagnostic use. Once the optimization is performed, the diagnostic image is acquired. Multiple diagnostic images, using the same settings, can be acquired. In other embodiments, the optimization is repeated during real-time induced-wave imaging. Periodically, in response to a trigger, or for each image, the settings or values ​​of one or more parameters are adapted. Figure 1 shows a method for adaptive image optimization in induced-wave ultrasound imaging. The method is implemented by the system in Figure 2 or a different system. Additional actions, either different or fewer, can be performed. For example, any combination of one or more of actions 38 to 48 is not executed.As another example, action 30 is not performed, and a source of constraint to generate a wave is provided by the body, manually, using a striker, or by another mechanism. The actions 20 are performed in the order described or shown, but can be performed in other orders. The method is implemented for each of one or more locations. In one embodiment, the method is implemented for each of the sample locations for B-mode or other scanning within an entire field of view or region of interest. More or less dense sampling 25 can be used for induced wave imaging other than B-mode or other imaging. Actions 30 to 33 (transmission, generation, scanning, and detection) correspond to induced wave imaging. Acoustic energy is used to induce a wave in a region of a patient. The acoustic energy is a 30-push impulse to move the tissue.The region is scanned to track or detect the wave. Tissue displacement due to the wave propagating through the region indicates the presence of the wave. The timing associated with the displacement can be used to determine the wave velocity. Other tissue characteristics, such as tissue modulus, can be determined from the displacement and / or velocity information. Different types of waves can be generated and / or tracked. Longitudinal waves are tracked for acoustic radiation force imaging, such as elastography or stress imaging. Shear waves are tracked for shear wave or shear wave velocity imaging. In Action 30 of Figure 1, acoustic energy is transmitted into a patient. The acoustic energy acts as a voltage-raising excitation.For example, a 400-cycle transmission waveform with power or peak amplitude levels similar to or greater than those of B-mode transmissions is transmitted to image tissue. In one embodiment, the transmission is a radiation force sequence applied to the field of view. Any ultrasound radiation force imaging (RFI) sequence can be used. Any number of cycles can be used. The transmission is configured by power, amplitude, timing, or other characteristics to cause sufficient stress on tissue to displace the tissue in one or more locations. For example, a transmission focus is positioned near a lower center of the field of view to cause displacements throughout the field of view. The transmission can be repeated for different subregions.Acoustic energy is focused, resulting in a three-dimensional beam profile. Excitation is focused using phase control 25 and / or mechanical focusing. Excitation can be defocused in one dimension, such as the elevation dimension. Excitation is transmitted into a patient's tissue. In action 31, a wave is generated in response to the transmission of acoustic energy. The tissue is forced to move within the patient. The transmitted excitation 30 causes tissue displacement. At the focal point or region, a longitudinal, shear, or other type of wave is generated in the tissue. For example, a shear wave is generated and propagates from the focal region. As the shear wave travels through the tissue, the tissue is displaced. Longitudinal waves or other causes of displacement can be used. In action 32, a region of the patient is scanned with ultrasound.Displacement is detected with an ultrasonic scan. The entire field of view of a region, such as a region of interest (ROI) or a subregion of interest, is scanned with ultrasound. For a specified duration, ultrasound is transmitted to the tissue or region of interest. Any displacement imaging technique known today or developed in the future can be used. For example, pulses with durations of 1 to 5 cycles are used with an intensity of less than 720 mW / cm². Pulses with other intensities can be used. Echoes or reflections of the transmission are received. The echoes are beamformed, and the beamformed data represent one or more locations. To detect displacement, ultrasonic energy is transmitted to the displaced tissue, and reflections of the energy are received. Any transmission and reception sequence can be used.By performing transmission and reception a multiple number of times, data representing a region in one, two, or three dimensions at different times are received. The frequency of this repetition is the pulse repetition frequency. Transmission and reception are performed a multiple number of times to determine a change due to displacement. By repeatedly scanning with ultrasound, the position of the tissue at different times is determined. For shear wave imaging, voltage-lift excitation generates a shear wave at a spatial location. When the excitation is sufficiently strong, a shear wave is generated. The shear wave propagates through the tissue more slowly than the longitudinal wave in the direction of acoustic wave emission.The shear wave 30 propagates in various directions, including a direction perpendicular to the direction of the applied stress. The displacement of the shear waves is greater at points closer to the location where the shear wave is generated. Ultrasound data are acquired. At least some of the ultrasound data are responses to the shear wave. A region of interest is monitored for the shear wave. The region of interest can be of any size, such as 6 mm laterally and 10 mm axially. This detection region is monitored by ultrasound. For example, B-mode scans are performed to detect tissue displacement caused by the shear wave. A Doppler mode, color coding, or other ultrasound mode can be used to monitor the shear wave. Monitoring is performed for any number of 10 scan lines. For example, four receive beams are formed in response to each transmission. After the excitation is transmitted to generate the wave, B-mode transmissions are performed repeatedly on a single scan line, and receptions are performed on four adjacent scan lines.In other embodiments, a single receiving beam or up to 15 receiving beams are formed in response to each transmission. Any number of repetitions can be used, such as approximately 120 times. Some of the ultrasound data, such as at the beginning or end of the repetitions, may not be a response to the shear wave. In action 33, tissue displacement caused by the wave is detected in response to the scan. Echoes are detected using B-mode or Doppler detection. Displacement is detected from the differences for each spatial location over time. For example, velocity, variance, intensity shift pattern (e.g., followed by coherent granulation), or other information is detected from the received data such as displacement. For velocity-based wave imaging, a displacement response profile in the patient is determined.For example, displacement profiles for different locations are determined. The displacement caused by the force or stress is measured. The displacement can be measured over time at one or more locations. The displacement measurement can begin before the end of the stress or impulse, such as by using a different frequency or encoding. Alternatively, the displacement measurement can begin after the end of the impulse. Since the shear, longitudinal, or other wave causing displacement in the tissue spaced from the point or region of stress takes time to propagate, the displacement from a resting or partially stressed state to a maximum displacement and then back to a resting state can be measured. Alternatively, the displacement is measured only when the tissue returns to the resting state to form the maximum. The measurement is that of the quantity or magnitude of the displacement. The fabric is displaced in any direction. The measurement can be taken in the direction of the greatest displacement. The magnitude of the motion vector is determined. Alternatively, the measurement is taken in a given direction, such as perpendicular to the scan line, regardless of whether the fabric is displaced to a greater or lesser extent in other directions. In an embodiment using B-mode data, data from different scans are correlated. For example, a current dataset is correlated a multiple of times with a reference dataset. Various relative translations and / or rotations between the two datasets are performed. The location of a subset of data centered at a given location in the reference dataset is identified in the current dataset. The reference is either a first dataset or data from another scan.The same reference is used for the entire displacement detection, or the reference data changes within a continuous or moving window. The correlation is one-, two-, or three-dimensional. For example, a correlation on a scan line to and from the transducer is used. For a two-dimensional scan, the translation occurs along two axes, with or without rotation. For a three-dimensional scan, the translation occurs along three axes, with or without rotation around three or fewer axes. The level 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 the time associated with the current data compared to the reference.Any correlation known today or developed in the future can be used, such as cross-correlation, shape matching, or a minimum sum of absolute differences. A tissue structure and / or speckle pattern is correlated. Using Doppler detection, a noise filter transmits information associated with moving tissue. The tissue velocity is obtained from multiple echoes. The velocity is used to determine displacement toward or away from the transducer. Alternatively, the relative difference in velocities at different locations can indicate stress or displacement. As the wave propagates along the scan lines, the intensity in B-mode may vary due to tissue displacement. For the monitored scan lines, a data sequence is provided, representing a time profile of the tissue motion resulting from the wave.For example, data from a plurality of spatial locations (e.g., on scan lines) are correlated as a function of time. Any velocity or shear detection can be used. For each depth or spatial location, a correlation is performed over a plurality of depths or spatial locations (e.g., a kernel of 64 depths with the central depth being the point for which the profile is calculated). A two- or three-dimensional displacement in space can be used. A one-dimensional displacement in a direction different from the scan lines or beams can be used. The spatial offset with the highest correlation, or a sufficient correlation at a given time, indicates the amount of displacement. Displacements can be determined for a given location at different times. The time profile for a given location indicates wave detection.The profile is examined for a noise-free or single instance of variation. A peak in the profile, with or without time-low-pass filtering, indicates the passage of the wavefront. The largest displacement is selected, but the mean or other displacement statistic can be used. The maximum displacement at a given location is detected. Alternatively, a mean or other shear is detected. In other embodiments, the displacement, whether maximum or not, at a given time (for example, 10 milliseconds after generation or X milliseconds per unit distance from the focal region) is used. The displacement profile can be smoothed or filtered for the calculation of the maximum. In other embodiments, the raw or unfiltered displacement curve can be used. The maximum value over the whole or part of the profile is identified or determined. The above discussion relates to depth.The sampling can be arranged to provide a grid covering the entire axial extent of the region of interest. In another embodiment, samples are obtained at multiple depths for each receiving beam. A separate time profile is provided for each axial depth as well as each lateral location. Any number of depths can be used, such as approximately 200 for 5 mm or 400 for 10 mm. Ultrasonic data representing different locations within the region of interest are obtained. The ultrasonic data are acquired in real time with the scan or retrieved from memory. For each location, the motion information represents the response at different times. Another scan, another monitoring, or other techniques can be used to obtain ultrasonic data to estimate a displacement magnitude.A shear or longitudinal velocity can be detected for different spatial locations within the tissue. For each location, the displacement as a function of time is determined. The velocity is obtained by determining the time from wave generation to wave detection at a different location. The time and distance to the location determine the velocity. The distance is known from the scan line spacing (i.e., the position of the transmitting beam to generate the wave and the position of the receiving beam to detect the wave). The time is known from the relative time between wave generation and detection. Other techniques can be used to detect the peak in the profile. For example, regression is applied.Since wave velocity is linear, a robust linear regression with automated outlier detection can determine the wave velocity. Ultrasonic data for all sample points in the region of interest are plotted for distance as a function of time or as time and distance. Linear regression is applied to the graph or data, yielding a line fit. The slope of the line indicates the shear wave velocity. Various aspects of transmission, scanning, and detection can be controlled. Values ​​for different parameters are set. In one embodiment, the values ​​are set based on a selected configuration. For example, the user selects shear wave imaging or ARFI. In response, predetermined parameters are loaded to operate the system.The predetermined parameters are the same for every application of that imaging type or mode. Alternatively, other selections, such as liver or other tissue type imaging, for a given mode may result in a configuration with different values. Examples of parameter types for which values ​​can be set include a transmission frequency for action 30, a transmission frequency for action 32, a line spacing for action 32, a numerical aperture for action 30, a numerical aperture for action 32, a pulse repetition rate for action 30, a pulse repetition rate for action 32, a line sampling count for action 30, a line sampling count for action 32, an acoustic energy amplitude (e.g., a push pulse) for action 30, or combinations thereof.Different, additional, or fewer parameters can be set with different values. Parameter values ​​can be adaptively optimized. Using data received from a scan of a given region of a given patient, values ​​can be adapted to better image the region. Rather than relying on predetermined values ​​for a given scan situation, one or more values ​​can be modified to take into account any aspect of the imaging. An optimization can be an improved value for one or more criteria, even if it is not the best value for the given criterion. Adaptation takes place during ARFI, shear wave, or other induced wave imaging. Adaptive optimization can be applied before static image acquisition or continuously during real-time imaging.For example, values ​​are determined using feedback from the scan or displacement before an image is presented to the user for diagnosis. Subsequent images use these same settings, at least during a given patient examination for an ultrasound session. As another example, adaptation is prolonged or performed at different times during the examination. Periodic or triggered adaptation can be used. The adaptation in action 34 is a function of any feedback, such as a data amplitude. In one embodiment shown in action 36, the feedback is displacement data or data derived from the displacement. For example, velocity can be obtained from the displacement information. The feedback, such as displacement, is used directly.For example, a value is set based on the amount of displacement for a location or region. Alternatively, the displacement or other feedback information is used to obtain a value. For example, a signal-to-noise ratio, a displacement difference, a velocity, or a determination of displacement thresholds is used to set a value. In one embodiment, the signal-to-noise ratio of the displacement is calculated. The noise value may be measured, such as measuring an average displacement over a region when it is not subjected to the acoustic energy of action 30. Alternatively, the noise value is assumed or based on empirical data, such as a displacement of 1 micrometer or less being considered noise. The signal level for the displacement is the magnitude of the displacement.The quantity can be in a given dimension (e.g., one-dimensional quantity) or can be from a plane or a volume (e.g., two- or three-dimensional quantity). For the signal-to-noise ratio, the signal is divided by the noise. When the noise is 1 micrometer, the displacement in micrometers is the signal-to-noise ratio. Other combinations of signal and noise can be used. The resulting signal-to-noise ratio can be used to fit a parameter. In another embodiment, a wave distance and / or a wave velocity is calculated from the displacement. The wave distance can be a distance from the focal region of the transmission action 30 at which the wave is above a threshold level, such as the noise floor. For example, the wave may cause tissue displacement greater than 1 micrometer over 4 mm, but not greater than 1 micrometer for greater distances.The distance of 4 mm or other is measured from the displacements for the different locations. The velocity can be calculated as discussed above. In yet another embodiment, the interruption time for the transmission of action 30 is used. The displacement or other feedback information may indicate an excessive amplitude or length of transmission. Based on this excess, the acoustic power delivered to the region can be reduced. Since ultrasonic transmissions are limited by the transducer and tissue temperatures, transmissions may need to cease for a period. By adjusting based on the excess, the interruption time can be shortened. A shorter interruption time can result in shorter cooling times.In addition to, or instead of, adaptive optimization to improve the SNR or shear wave tracking accuracy, the cooling time can be adaptively optimized. The feedback or data obtained from the feedback is / are used directly to set the value. A lookup table or calculation (e.g., applying the feedback as a variable in a function) is used to determine the value. For example, an average SNR above a threshold results in a value of X, while the average SNR between the threshold and another threshold results in a value of Y. Any resolution (e.g., binary with three or more ranges) for setting the value can be used. In another embodiment, the value is set based on a plurality of samples.The transmission, generation, scanning, and detection actions 30 to 33 are repeated with different settings or values ​​for one or more parameters. Feedback, such as wave amplitude, displacement amplitude, minimum cooling, wave velocity, or combinations thereof, is obtained for each repetition. The setting or value associated with the sufficient or most optimal result is selected. For example, five different values ​​are used. Of the five, the fourth value brings the displacement quantity to a desired level (e.g., above the noise floor but below an excessive level). Based on the iterative settings for imaging, this value is selected. The value can be interpolated or extrapolated. In the five example values ​​tested discussed above, a curve can be fitted to the feedback results.The curve may indicate an optimum value different from any of the five tested, such as a value between the third and fourth values. The value may be based on one or more criteria. For example, the SNR is used to set a transmission frequency. As in another example, the transmission amplitude and velocity are both used to set the PRF and the line sampling count. Adaptation can be performed for each parameter sequentially. Alternatively, more than one value is changed based on feedback at any given time. Adaptation can be iterative to obtain a combination of values ​​for different parameters. Any matrix or other solution to the iterative approach can be used. Actions 38 to 48 give some examples of adaptation. In action 38, the transmission frequency is adapted to the imaging of a given region of a patient.The transmission of the action 30 is repeated at different frequencies. As an alternative, broadband transmission (e.g., wavelength fluctuation) is provided with fewer repetitions or no repetitions. The transmission frequency associated with the highest or greatest displacement magnitude is selected for subsequent use. The thrust pulse transmission frequency is optimized adaptively by sequentially transmitting several different primary pulses with different transmission frequencies and determining which transmission frequency produces the greatest displacement or wave amplitude at the depths of interest. For broadband transmission, a Fourier analysis of the displacement change or another time-displacement profile characteristic may indicate a particular frequency associated with the greatest response.In another embodiment, the transmission and / or reception frequency used for the sweep of action 32 is adapted. The sweep is repeated at different sweep frequencies, such as different tracking pulse transmission frequencies (e.g., 1.5 to 4.5 MHz in 1 MHz increments). The transmission and / or reception frequency is different for each repetition associated with different transmissions of action 30. Within the repetitions for a sweep in response to a wave, the frequency is the same. A given repetition may include multiple scans, such as those associated with wave detection after each transmission of action 30. The same frequency is used for scanning and detection after a given transmission of action 30, but is changed for subsequent scans and detections after another transmission of action 30. Alternatively, the transmission and / or reception frequency of the action 32 scan is changed for different scan lines or frames (region scans) but in response to the same wave (transmission action 30). To adapt the scan frequency, displacements are detected for each repetition. The signal-to-noise ratios of the displacements are calculated. The scan frequency associated with an optimal signal-to-noise ratio, such as the highest or sufficient, is selected for the next scan.The selected frequency can be extrapolated or interpolated based on the signal-to-noise ratios of other scan frequencies. In action 40, the line spacing is matched. The line spacing is the density or lateral extent of the receive scan lines in the scan of action 32. For example, samples on 4 or 16 lines are received in response to a given scan transmission where the lines are spaced 1 mm, 2 mm, or some other distance apart. As another example, only 3 or 13 scan lines are used for receiving, where the overlap distance by the scan is less. In other embodiments, the line spacing is the density of the region spacing or the density of the focal regions of the transmission of action 30. In one embodiment, the line spacing is matched as a function of the wave velocity. The wave velocity is calculated from the displacement.Line spacing is denser, or the scan lines are closer together, for lower speeds. Waves propagating at higher speeds can be tracked more effectively by increasing the window size or decreasing the spatial resolution. Less dense line spacing can limit or prevent overheating of the transducer and / or tissue. In another embodiment, the line spacing for radiation force imaging can be adaptively optimized by sequentially acquiring images or data using different line spacings. Spatial variance is calculated from the displacement information. The line spacing associated with the least amount of spatial variance in the displacement can provide the best uniformity. In yet another embodiment, the line spacing is fixed for a lateral distance.The displacement level at a given point, or the range of locations where the displacement is above a threshold (e.g., the noise floor or a value greater than the noise), indicates a spatial extent at which detection can be expected. The lateral distance 15 for the lines is fixed based on the lateral extent at which the wave can be detected. For example, the spacing of tracking pulse lines, or the number of lines for shear wave imaging, can be adaptively optimized by using multiple starting points to determine the greatest achievable lateral shear wave tracking distance and then placing subsequent tracking lines within the maximum distance. At step 42, the numerical aperture value is adjusted.The numerical aperture is controlled by the aperture size, element spacing, apodization, delay / phase profile, or other characteristic that modifies the amount or size of focus. The numerical aperture for the transmission of the thrust or stress impulse of action 30 is fixed. The numerical aperture adjusts as a function of the displacement. A larger focus is intended for a smaller displacement, and a smaller focus is intended for a larger displacement. A larger focus 30 may result in a larger displacement but a smaller region for which the wave is generated at action 31. This can modify the wave range. For hard / rigid or rigid tissues or structures, a larger focus may be desirable.For softer or more elastic tissue with greater attenuation, a lower focus but a correspondingly larger wave-generating region may be desired. The absolute value of a measured displacement can be used to determine the numerical aperture, such as via a lookup table. Alternatively, steps 30 to 33 are repeated for different numerical aperture settings of the acoustic energy of step 30. The numerical aperture associated with the desired, highest, or sufficient displacement is selected. In step 44, the pulse repetition frequency (PRF) is adjusted. The scan rate of step 32 is fixed. For example, the shear wave tracking PRF is adaptively optimized. The PRF for longitudinal wave scanning can be adaptively optimized. The PRF is adjusted based on the maximum wave velocity.The maximum wave velocity is the highest velocity in the scanned region. Fifteen displacements and synchronization for different sample points are acquired and used to determine the maximum velocity. The maximum wave velocity dictates a sampling frequency for adequate information. The PRF is at or above the Nyquist frequency. The Nyquist frequency is calculated from the maximum velocity. The PRF that adequately samples the maximum velocity is selected. In other embodiments, different PRFs are tried, and the lowest PRF associated with no aliasing is selected. In action 46, the line sampling count is adjusted. If the maximum PRF cannot be achieved due to the round-trip propagation time of the 25 tracking pulses, interleaved primary pulses and time-shifted tracking pulses at the maximum permissible PRF or another lower PRF may be used.To increase the sampling rate, the line sampling count is adjusted. For example, a region is scanned to track the wave. Due to the depth and maximum velocity, 30 scans may not be sufficient for a given wave. The line sampling count is increased by scheduling repetitions of actions 30 through 33 for the same region. A repetition acquires samples for the region on the receiving lines at an initial time offset from the transmission of action 30 (for example, every 10 milliseconds, starting 5 milliseconds after the transmission of action 30 began or ended).Another repetition acquires samples for the same region on the same receiving lines but at a different time offset from a subsequent transmission of action 30 (for example, every 0 milliseconds starting 10 milliseconds after the transmission of action 30). The data acquired from the different repetitions are interleaved to represent a higher-frequency acquisition. The number of repetitions, or the line sampling count, is set based on the maximum velocity. If the maximum velocity results in a PRF that is not achievable, the line sampling count is increased to provide data at the desired PRF or better, but acquired by one repetition. Adjusting the line sampling count can provide better imaging or detection of high-velocity waves or other waves and / or wave detection at greater depths.To monitor a larger area, additional receive beams are formed in response to the monitoring transmission beam (for example, a change in line spacing). Alternatively, another wave is generated, and the transmit and receive beams are positioned at different distances from the wave generation point. In the 6 mm x 10 mm example above, 36 receive scan lines can be positioned. With four receive beams per transmit beam, the process is repeated nine times for different lateral spacings. For each receive beam location, a time-domain motion information profile is provided, represented by the ultrasonic data.Transmissions on different scan lines to monitor the same wave are avoided during time profile formation to provide higher temporal resolution, but interlaced or offset scan positions can be expected. At action 48, the acoustic energy amplitude of the transmission from action 30 is matched. The transmission, generation, scanning, and detection of actions 30 to 33 are repeated with different amplitudes for the acoustic energy of action 30. The different amplitudes cause different wave amplitudes and corresponding amounts of displacement over a given distance. A thrust pulse transmission amplitude is adaptively optimized by sequentially triggering primary pulses with different transmission amplitudes. The thrust pulse amplitude that produces an adequate signal-to-noise ratio (SNR) is determined.Adequate can be above one level but below another. Lowering the transmission voltage can reduce the cooling time between acquisitions. Alternatively, a displacement is determined without repetition, and the amplitude is changed based on whether the displacement is above or below a desired displacement range. In another embodiment, the pulse length of the thrust pulse or acoustic energy transmitted to action 30 is adjusted. Longer pulses generally produce a greater amount of thrust or stress. Greater displacement can be caused by longer pulses, at least over a range of possible pulse lengths 15. Longer pulses correspond to a greater number of cycles, such as 100 cycles instead of 50 cycles. The greater length may result in more heating and / or a longer cooling time. The pulse length can be adjusted to the amount of displacement so that sufficient displacement is created without excess. Combinations of any two or more of actions 38 to 48 can be provided. Combinations of different possible values ​​can be determined iteratively.Different combinations are tried, and feedback trends can be analyzed to determine a possible next combination. Alternatively, the value for each of the 25 parameters is determined sequentially. A priority can be assigned to any parameter so that it is fitted first or last. In step 50, wave-induced imaging is performed. The imaging is performed based on the optimized parameter values. Using the 30 optimized parameter values, with or without other predetermined or user-defined values, steps 30 through 33 are repeated to determine wave information, such as velocity, displacement, or tissue characteristics (e.g., modulus). An image or sequence of images is generated to display the wave information. Any shear imaging or ARFI technique can be used.Waveform information is used for color overlay or other modulation of display values. Color, brightness, luminance, tone, or other characteristics are modulated as a function of displacement. For example, waveform information is displayed over or alongside B-mode information. Displacement data is in a display format or can be scanned into a display format. Displacement data is either color or grayscale data, but it can also be pre-mapping data with either grayscale or color scale. The information can be mapped linearly or non-linearly to the display values. The image represents the displacement information, such as shear or moduli (e.g., shear moduli), for the various locations.When values ​​are determined for all grid points in a region of interest or field of view, the display pixels represent the wave information for that region. The display grid may differ from the scanning grid and / or the grid for which displacements are calculated. Scanning conversion, nearest neighbor selection, interpolation, and / or extrapolation may be used to bring the wave information resolution into conformance with the display resolution. The image may include other data. For example, B-mode or other data representing tissue, fluid, or contrast agents in the same region are included. The displacement data is used for overlay or combination with the other data. The other data helps the user determine the beam's location relative to the tissue to be treated.Figure 2 shows an embodiment of a system 10 for adaptive optimization of induced wave imaging. The system 10 implements the method of Figure 1 or other methods. The system 10 includes a transmit beam former 12, a transducer 14, a receive beam former 16, an image processor 18, a display 20, and a memory 22. Additional, different, or fewer components may be provided. For example, a user input is provided for user interaction with the system. The system 10 is a medical diagnostic ultrasound imaging system. In other embodiments, the system 10 is a personal computer, a workstation, a PACS station, or other arrangement in a single location or distributed over a network for real-time or post-acquisition imaging.The transmission beam former 12 is an ultrasound transmitter, a memory, a pulser, an analog circuit, a digital circuit, or a combination thereof. The transmission beam former 12 can be used to generate waveforms for a plurality of channels with different or relative amplitudes, delays, and / or phasing. Upon transmission of acoustic waves from the transducer 14 in response to the generated waveforms, one or more beams are formed. A sequence of transmission beams is generated to scan a two- or three-dimensional region. Sector, Vector, linear, or other scanning formats can be used. The same region is scanned a multiple number of times. For flow or Doppler imaging and for induced wave imaging, a scan sequence is used.In Doppler imaging, the sequence may include multiple beams on the same scan line before scanning an adjacent scan line. For induced wave imaging, a scan or frame interleaving may be used (i.e., scanning the entire region before a new scan). In other embodiments, the transmission beam former generates a plane wave or a diverging wave for faster scanning. The same transmission beam former generates pulsed excitations or electrical waveforms to generate acoustic energy to cause displacement. In other embodiments, a different transmission beam former is provided to generate the voltage lift excitation. The transmission beam former causes the transducer to generate high-intensity focused ultrasonic waveforms.Transducer 14 is an array for generating acoustic energy from electrical waveforms. For an array, relative delays focus the acoustic energy. A given transmission event corresponds to the transmission of acoustic energy through different elements at approximately the same time, taking into account the delays. The transmission event delivers an ultrasonic energy pulse to displace the tissue. The pulse is a voltage-lift excitation. Voltage-lift excitation includes waveforms with many cycles (e.g., 500 cycles) but which occur over a relatively short time to cause tissue displacement over a longer time. Transducer 14 is an array in 1, 1.25, 1.5, 1.75, or 2 dimensions of piezoelectric or capacitive membrane elements. Transducer 14 includes a plurality of elements for transduction between acoustic and electrical energies.Receive signals are generated in response to ultrasonic energy (echoes) striking the transducer elements 14. The elements are connected to channels of the transmit and receive beamformers 12, 16. Alternatively, a single element with mechanical focusing is used. The receive beamformer 16 includes a plurality of channels with amplifiers, delays, and / or phase rotators, and one or more summing elements. 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 image transmission. A receive operation cannot occur for echoes originating from the voltage-lift excitation used to move the tissue. The receive beamformer 16 outputs data representing spatial locations using the received signals. Relative delays and / or phasing and summation of signals from different elements result in beamforming. In other embodiments, the receive beamformer 16 is a processor for generating samples using a Fourier transform or other transforms. The receive beamformer 16 includes a filter, such as a filter for isolating second-harmonic or other frequency band information from the transmission frequency band. Such information may include tissue, contrast agent, and / or desired flow information. In another embodiment, the receive beamformer 16 includes memory or a buffer and a filter or a summer.Two or more receive beams are combined to isolate information at a desired frequency band, such as a second harmonic, a cubic fundamental frequency, or another band. The receive beamformer 16 can isolate information at the fundamental frequency or at the transmission frequencies. In coordination with the transmission beamformer 12, the receive beamformer 16 generates data representing the region at 10 different times. After acoustic excitation by voltage boosting, the receive beamformer 16 generates beams representing different lines or locations at different times. By scanning the region of interest with ultrasound, data (e.g., beamformed samples) are generated. The receive beamformer 16 outputs beam-summed data representing spatial locations.Data for a single location, locations along a line, locations for an area, or locations for a volume are output. Dynamic focusing can be performed. The data can be used for various purposes. For example, different scans are performed for B-mode or tissue data depending on the displacement. Alternatively, B-mode data are also used to determine displacement. As another example, data for displacement-based classification and induced wave imaging are performed with a series of shared scans, and a B-mode or Doppler scan is performed separately or using some of the same data.The processor 18 is a B-mode detector, a Doppler detector, a pulsed-wave Doppler detector, a correlation processor, a Fourier transform processor, an application-specific integrated circuit, a general-purpose processor 30, a control processor, an image processor, a user-programmable pre-scatter matrix, a digital signal processor, an analog circuit, a digital circuit, combinations thereof, or any other device known now or developed in the future for detecting and processing information for display from beamformed ultrasonic samples. In one embodiment, the processor 18 includes one or more detector(s) 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 user-programmable pre-diffused matrix, a network, a server, a group of processors, a data path, combinations thereof, or any other device known today or developed in the future for determining displacement and calculating displacement profile properties. For example, the separate processor is configured by hardware and / or software to perform any combination of one or more of the actions shown in Figure 1. Processor 18 is configured to estimate tissue displacement induced by acoustic voltage lift excitation. Using correlation, tracking, motion detection, or other displacement measurement, the amount of positional displacement of the tissue is estimated.The estimation is performed a multiple number of times over a period, such as from before the tissue displacement due to the impulse until after the tissue has substantially or completely returned to a resting state (e.g., has recovered from the stress caused by the voltage rise excitation). The processor 18 can derive at least one parameter describing a characteristic of the tissue and / or the displacement. For example, the signal-to-noise ratio of the displacement is derived. As another example, the maximum displacement and / or the velocity is / are derived. The processor 18 can calculate other parameters, such as a distance, a cooling time, or an interruption time. Using the displacement or other detected information, the values ​​of one or more parameters are determined by the processor 18 or another controller.Any transmission, reception, or scanning parameter can be adapted to the scanned region based on feedback. Processor 18 can be configured to classify tissue within the region. The fabric can be a fluid fabric or a solid fabric. The classification can be between fabric types, between a fabric and a fluid, or between fabric types and one or more other classes. In one embodiment, the processor 18 classifies the material at a location as fluid / fluid fabric, solid fabric, and other / non-determining. The processor 18 operates according to instructions stored in memory 22 or other memory for adaptive image optimization in induced wave ultrasound imaging. The processor 18 is programmed to provide feedback for adapting shear or ARFI imaging. Memory 22 is a non-transient computer-readable storage medium. Instructions for implementing the processes, methods, and / or techniques discussed herein are provided on computer-readable storage media or memories, such as a cache, buffer, RAM, removable media, hard disk drive, or other computer-readable storage medium. Computer-readable storage media includes various types of volatile and non-volatile storage media.The functions, actions, or tasks illustrated in the figures or described herein are executed in response to one or more sets of instructions stored on or in computer-readable storage media. These functions, actions, or tasks are independent of any particular type of instruction set, storage medium, processor, or processing strategy and may be executed by software, hardware, integrated circuits, firmware, microcode, and the like, operating alone or in combination. Similarly, processing strategies may include multiprocessing, multitasking, parallel processing, and the like. In one embodiment, the instructions are stored on a removable storage device for reading by local or remote systems.In other embodiments, the instructions are stored at a remote location for transfer via a computer network or telephone lines. In still other embodiments, the 25 instructions are stored within a computer, CPU, GPU, or other given system. The display 20 is a CRT, LCD, projector, plasma, or other display for showing two-dimensional images or three-dimensional representations. The display 20 is configured by the processor 18 or other device 30 by inputting the signals to be displayed as an image. The display 20 shows an image representing shear, elasticity, or other wave information for different locations within a region of interest or the entirety of an image. Although the invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made without departing from the scope of the invention. It is therefore understood that the foregoing detailed description should be considered illustrative rather than limiting, and that the following claims, including all equivalents, are intended to define the spirit and scope of this invention.

Claims

Claims 1. A method for adaptive image optimization in induced wave ultrasound imaging, the method comprising: transmitting (30), from a transducer of an ultrasound imaging system, acoustic energy into a patient, said acoustic energy being capable of causing tissue displacement; generating (31) a wave in response to the transmission (30); scanning (32) a region of the patient with an ultrasound; detecting (33), from the scan (32), a tissue displacement caused by the wave; and adapting (34), by the ultrasound imaging system, at least one transmission parameter of the ultrasound imaging system before acquiring one or more images for diagnosis, said at least one transmission parameter being chosen from: a transmission frequency, a line spacing, a numerical aperture, a pulse repetition frequency, a line sampling count, an acoustic energy amplitude, an acoustic energy pulse length, and combinations thereof, said at least one transmission parameter being adapted to take a value depending on the displacement.

2. Method according to claim 1 in which the wave comprises a longitudinal wave, the actions of transmission (30), generation (31), scanning (32) and detection (33) composing an acoustic radiation force imaging.

3. The method of claim 1 wherein the wave comprises a shear wave, the actions of transmitting (30), generating (31), scanning (32) and detecting (33) composing shear wave imaging.

4. Method according to claim 1 in which the adaptation (34) comprises: the calculation of a signal-to-noise ratio of the displacement; and adaptation (34) as a function of the signal-to-noise ratio.

5. The method of claim 4 wherein calculating the signal-to-noise ratio comprises calculating a magnitude of the displacement as the signal-to-noise ratio.

6. The method of claim 1 wherein the adaptation (34) comprises: calculating a wave distance or a wave speed from the displacement; and adaptation (34) as a function of wave distance or wave speed.

7. The method of claim 1 wherein the adaptation (34) comprises the adaptation (34) as a function of interruption time of the transmission (30).

8. The method of claim 1 wherein the adaptation (34) comprises: repeating the transmission (30), the generation (31), the scanning (32), and detection (33) with different settings; and the selection of one of the different settings.

9. The method of claim 1 wherein the adaptation (34) comprises: repeating the transmission (30) at different frequencies; adjusting (38) the transmission frequency of the acoustic energy as a function of a highest of displacements caused by repetition at the different frequencies.

10. The method of claim 1 wherein the adaptation (34) comprises: repeating the scanning (32) at different scanning frequencies (32); calculating signal-to-noise ratios from the displacements detected from the scan repetitions (32); and adjusting (38) the transmission frequency of the sweep (32) as a function of the signal-to-noise ratios.

11. Method according to claim 1 in which the adaptation (34) comprises: the calculation of a shear wave velocity as a function of displacement; adjusting (40) a line spacing as a line density for the scan (32), the line spacing being a function of the shear wave velocity.

12. The method of claim 1 wherein the adapting (34) comprises adjusting (40) the line spacing for a lateral distance, the lateral distance being a function of the displacement.

13. The method of claim 1 wherein the adaptation (34) comprises adjusting (42) the numerical aperture as a function of displacement such that a greater focus is created for less displacement and a lesser focus is created for greater displacement.

14. The method of claim 1 wherein the adaptation (34) comprises: calculating a maximum wave speed; and adjusting (44) the pulse repetition frequency of the sweep (32) as a function of the maximum speed.

15. The method of claim 14 wherein adjusting comprises adjusting (44, 46) the pulse repetition frequency and the line sampling count as a function of the maximum speed, the line sampling count being a number of repetitions of the transmission (30), generation (31), scanning (32), and detection (33) for each scanning line.

16. The method of claim 1 wherein the adaptation (34) comprises: repeating the transmission (30), generation (31), scanning (32) and detection (33) with different amplitudes for the acoustic energy; and adjusting (48) the acoustic energy amplitude as a function of the displacements caused by the different amplitudes.

17. The method of claim 1 wherein the adaptation (34) comprises an interpolation or an extrapolation of a setting.

18. A non-transitory computer-readable storage medium (22) having stored thereon data representing instructions executable by a processor (18) programmed for adaptive image optimization in induced wave ultrasound imaging, the storage medium (22) comprising instructions for: acoustic radiation force or shear wave imaging of a region of a patient; and an adaptation (34) of at least one transmission parameter of the ultrasound imaging system before the acquisition of one or more images for diagnosis, said at least one transmission parameter being chosen from: a transmission frequency, a line spacing, a numerical aperture, a pulse repetition frequency, a line sampling count, an acoustic energy amplitude, a pulse length, or combinations thereof; said at least one transmission parameter being adapted according to information coming from the imaging.

19. The non-transitory computer-readable storage medium (22) of claim 18 wherein the information from the imaging comprises displacement, and wherein the adaptation (34) comprises adjustment as a function of the displacement.

20. The non-transitory computer-readable storage medium (22) of claim 18 wherein the adaptation (34) comprises the adaptation (34) as a function of wave amplitude, displacement amplitude, minimal cooling, wave velocity, or combinations thereof based on iterative adjustments for imaging.

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