Quantitative ultrasound using fundamental and harmonic signals

Abstract

A system and method includes storing an echo signal power spectrum of a reference phantom of a fundamental frequency band and an echo signal power spectrum of a reference phantom of a harmonic frequency band; obtaining an echo signal power spectrum of the tissue area of the fundamental wave frequency band and an echo signal power spectrum of the tissue area of the harmonic wave frequency band; determining a first backscattering coefficient based on the echo signal power spectrum of the tissue region of the fundamental frequency band and the echo signal power spectrum of the reference phantom of the fundamental frequency band; determining a second backscattering coefficient based on the echo signal power spectrum of the tissue region of the harmonic band and the echo signal power spectrum of the reference phantom of the harmonic band; and determining a non-linearity of the tissue region based on the first backscattering coefficient and the second backscattering coefficient.

Description

This case is a divisional application. The invention name of the parent case is “Quantitative Ultrasound Using Fundamental and Harmonic Signals”, the application date is February 6, 2020, and the application number is 202080022296.0. Background Art

[0001] Conventional ultrasound imaging systems create images of the interior of a volume (i.e., B-mode images) by detecting acoustic impedance discontinuities within the volume. More specifically, conventional ultrasound imaging involves transmitting an ultrasound beam into the volume and detecting return signals reflected from acoustic impedance discontinuities within the volume. Since different materials typically exhibit different acoustic impedances, the detected acoustic impedance discontinuities represent the locations of different materials within the volume.

[0002] The B-mode images described above depict qualitative features in tissue, but do not directly provide quantitative information about the tissue. On the other hand, a quantitative ultrasound system can determine the attenuation coefficient (AC) and backscatter coefficient (BSC) of a region of interest (ROI). AC is a measure of the ultrasonic energy lost in the tissue, and BSC is a measure of the ultrasonic energy returned from the tissue. Quantitative ultrasound values ​​such as these help characterize the properties of the tissue, such as hardness and fat fraction. Additional quantitative ultrasound measurements will further assist these characterizations.

[0003] The determination of AC and BSC requires compensation for the system effects of the acquisition ultrasound system. These effects include transmit pulse power, transducer sensitivity, beam focusing pattern, and depth-dependent receiver gain. Conventionally, compensation involves dividing the echo signal power spectrum of the tissue sample in the fundamental frequency band by the echo signal power spectrum of a well-characterized reference phantom in the fundamental frequency band from the same depth. The resulting quotient is a normalized spectrum, which depends on the attenuation and backscattering properties of the tissue sample and the reference phantom. Since the properties of the reference phantom are known, the AC and BSC of the tissue sample can be derived from the normalized spectrum.

[0004] One drawback of the aforementioned determination is the need to acquire reference phantom data at the time of clinical scanning. This additional acquisition hinders workflow and patient throughput. Furthermore, the accuracy of such determination has been found to be lacking in many scenarios. The aforementioned determination also fails to provide other potentially useful quantitative measures, such as tissue nonlinearity. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The construction and use of the embodiments will become apparent from consideration of the following description as illustrated in the accompanying drawings, in which like reference numerals designate like parts, and in which: Figure 1 is a block diagram of a quantitative ultrasound system according to some embodiments; Figure 2 is a flow chart of a process for determining a quantitative ultrasound value according to some embodiments; Figure 3 is a block diagram of an ultrasound system for acquiring reference phantom calibration data according to some embodiments; Figure 4 is a tabular representation of data used to determine reference phantom calibration data according to some embodiments; Figure 5 is an ultrasound image including quantitative ultrasound values ​​according to some embodiments; and Figure 6 is a block diagram of an ultrasound system according to some embodiments. DETAILED DESCRIPTION

[0006] The following description is provided to enable any person skilled in the art to make and use the described embodiments and sets forth the best mode contemplated for practicing the described embodiments. However, various modifications will still be apparent to those skilled in the art.

[0007] Some embodiments provide efficient and accurate determination of quantitative ultrasound values. More specifically, some embodiments provide an inventive system for determining AC and BSC based on echo signal power spectra from harmonic frequency bands. Using harmonic frequency bands is more clinically desirable. The clinical benefit of using harmonic signals is the improved repeatability and reproducibility of QUS estimation due to reduced reverberation, clutter noise and phase aberrations.

[0008] Such an embodiment may utilize pre-stored echo signal power spectra (or RF or IQ signal data from which the power spectra may be calculated) of a well-characterized reference phantom in harmonic frequency bands, thereby eliminating the need to acquire calibration data at or near the time of clinical data acquisition.

[0009] Some embodiments advantageously determine a quantitative value for tissue non-linearity.In contrast, the conventional systems described above assume that the non-linearity of the reference phantom is substantially equal to the non-linearity of the tissue in the ROI.

[0010] Figure 1 1. The system 100 includes an ultrasound unit 110, an ultrasound transducer 120, and a display 130. The volume 140 may include a human body, but the embodiments are not limited thereto. The ultrasound transducer 100 may include any suitable ultrasound transducer, such as, but not limited to, a phased array, a linear, or a convex ultrasound transducer.

[0011] Generally, the processing unit 112 of the unit 110 can execute program code to control the transducer 120 to transmit an ultrasound beam into the volume 140 and receive an acoustic radio frequency signal therefrom. The processing unit 112 of the unit 110 can execute program code to generate an image and / or determine a quantitative ultrasound value based on the received signal. The image and / or the determined value can be displayed to the technician on the display 130.

[0012] According to some embodiments, a technician operates the system 100 to acquire a power spectrum of an echo signal in a harmonic frequency band from a ROI of the volume 140. The acquisition may include acquiring an RF or IQ signal and calculating the power spectrum of the echo signal in the harmonic frequency band therefrom. The acquisition is performed using a first scan setting, which may include specific values ​​of frequency, F number / aperture size, focusing, and apodization function parameters. The transducer 120 operates in conjunction with the transmitting unit 116 to transmit an ultrasound beam into the ROI, and the receiver unit 118 operates in conjunction with the transducer 120 to receive a reflected signal in the harmonic frequency band from the ROI according to the scan setting.

[0013] Next, the harmonic calibration data corresponding to the first scanning setting is retrieved from the storage device 114. The harmonic calibration data may include an echo signal power spectrum of a harmonic frequency band acquired from a reference phantom using a scanning setting that is the same as or substantially similar to the first scanning setting (or data from which the echo signal power spectrum can be derived). The acquisition and storage of the harmonic calibration data are described in detail below.

[0014] The echo signal power spectrum acquired from the volume 140 is normalized by dividing the echo signal power spectrum acquired from the volume 140 by the stored echo signal power spectrum. The result is a normalized spectrum that depends only on the attenuation and backscattering properties of the ROI tissue and the reference phantom. Since the attenuation and backscattering properties of the reference phantom are known, the AC and BSC of the tissue can be derived from the normalized spectrum, as will be described in detail below.

[0015] According to some embodiments, an echo signal power spectrum of a fundamental frequency band is also acquired from the ROI of the volume 140. The acquisition is performed using a second scan setting, which may or may not be different from the first scan setting mentioned above. Fundamental calibration data corresponding to the second scan setting is retrieved from the storage device 114. The fundamental calibration data includes an echo signal power spectrum of a fundamental frequency band acquired from a reference phantom using a scan setting that is the same as or substantially similar to the second scan setting (or, similarly, RF or IQ data from which the echo power signal spectrum can be derived).

[0016] The fundamental frequency band echo signal power spectrum acquired from the volume 140 is normalized by dividing it by the fundamental calibration data, thereby obtaining another normalized spectrum that depends only on the attenuation and backscattering properties of the ROI tissue and the reference phantom. The AC and BSC of the tissue can also be derived from this normalized spectrum.

[0017] According to some embodiments, the nonlinearity of the ROI may be determined based on the BSC derived from the harmonic band data and the BSC derived from the fundamental band data. This determination provides improved ROI characterization compared to conventional systems that assume that the nonlinearity of the reference phantom and the ROI are equivalent.

[0018] Figure 2 200 is a flow chart of a process 200 for determining a quantitative ultrasound value according to some embodiments. The process 200 may be performed by elements of the system 100, but the embodiments are not limited thereto. The process 200 and all other processes mentioned herein may be embodied in a processor executable program code read from one or more non-transitory computer readable media (such as a hard disk, a volatile or non-volatile random access memory, a DVD-ROM, a flash drive, and a tape), and then stored in a compressed, uncompiled, and / or encrypted format. In some embodiments, hard-wired circuits may be used instead of program code or in combination with program code to implement the process according to some embodiments. Therefore, the embodiments are not limited to any particular combination of hardware and software.

[0019] Initially, at S210, a reference phantom is scanned to acquire RF or IQ data, and echo signal power spectra of fundamental and harmonic frequency bands are determined therefrom. The reference phantom is scanned using a specific scan setting. In some embodiments, additional echo signal power spectra of fundamental and harmonic frequency bands are acquired at S210 using other scan settings.

[0020] Figure 3 A system 300 for performing S210 according to some embodiments is illustrated. The system 300 may be operated by an ultrasound system provider, a phantom provider, or other non-clinical entity. The processing unit 312 of the ultrasound unit 310 executes a scanning program of the storage device 314 to control the transducer 320 to transmit signals to and receive signals from the phantom 340. The phantom 340 represents an intended ROI (e.g., an adult male torso), and the ultrasound unit 310 and the transducer 320 may include production equivalent versions of the ultrasound unit and the transducer that are intended to be used in scanning the intended ROI. The storage device 314 stores the acquired power spectrum.

[0021] Next, at S220, the acquired echo signal power spectra of the fundamental frequency band and the harmonic frequency band are stored in the ultrasound system. In some embodiments, the stored data includes data from which the echo signal power spectra of the fundamental frequency band and the harmonic frequency band can be derived. In some examples, the spectrum is stored as the above-mentioned fundamental and harmonic calibration data of the ultrasound system to be shipped to the customer. According to some embodiments, the spectrum is stored in association with the scanning settings used to acquire the corresponding spectrum.

[0022] Figure 4 is a tabular representation of the data stored at S220 according to some embodiments. Table 400 associates each acquired power spectrum with the scan settings and reference phantom used to acquire the power spectrum. As shown, at S210, more than one type of reference phantom may be scanned. Each reference phantom / scan settings pair is associated with fundamental band power spectrum data and harmonic band power spectrum data. The value of the spectral data column may consist of the file name of the file that includes the corresponding spectral data.

[0023] In some embodiments, S210 and S220 are performed during a time period long before the data acquired therein are used clinically (e.g., before the ultrasound system is shipped to the clinic). Therefore, the dashed arrow between S220 and S230 indicates a significantly longer time lapse than the time between other adjacent steps of process 200.

[0024] At S230, for example in a clinical setting, an ultrasound system in which the spectrum is stored is operated to acquire echo signal power spectra of fundamental and harmonic frequency bands from the ROI. The acquisition uses a first scan setting, which is used to generate calibration data corresponding to the reference phantom at S210. In some embodiments, the first scan setting is set as a default scan setting of the ultrasound system.

[0025] According to some embodiments of S230, the ultrasound system transmits a signal with a center frequency of 3 MHz and a frequency bandwidth from 2 to 4 MHz. Then, the fundamental signal is received within the range of 2-4 MHz. In order to obtain a signal in a harmonic frequency band, a signal is transmitted with a center frequency of 1.5 MHz, and the signal has a bandwidth between 1-2 MHz. The resulting received harmonic signal can exhibit, for example, twice the center frequency or a frequency band between 2-4 MHz. Therefore, the subsequent calculation of the QUS value is associated with a frequency between 2-4 MHz.

[0026] Next, at S240, the stored calibration data corresponding to the first scan setting is determined. The determined calibration data consists of echo signal power spectra of fundamental and harmonic frequency bands acquired using a reference phantom corresponding to the ROI and the first scan setting. For example, S240 may include: identifying an appropriate reference phantom and scan setting in a row of table 400, and acquiring a stored fundamental and harmonic calibration data file identified in the same row of table 400.

[0027] At S250, a first AC and a first BSC are determined. The determination is based on the echo signal power spectrum of the fundamental frequency band acquired at S230 and the calibration echo signal power spectrum of the fundamental frequency band determined at S240. The embodiment is not limited to the following description of the determination at S250.

[0028] Initially, each RF echo line of the ROI is divided into several overlapping time-gated windows. A Fourier transform is applied to each window, and the power spectra of windows corresponding to the same depth are averaged. The same process is performed on the corresponding ROI of the reference phantom. In standard pulse-echo imaging, the measured power spectrum in the fundamental frequency band of the windowed region in statistically homogeneous tissue is given by equation (1):

[0029] The subscript s refers to the sample (i.e., the tissue of the ROI). The distance from the transducer surface to the center of a specific time-gated window within the ROI is denoted by z. The frequency is denoted by f. T(f) represents the transfer function of the transmitted pulse. E tx (f) and E rx (f) represents the transducer electric-acoustic and acoustic-electric transfer functions, respectively. D(f,z) denotes the diffraction effect, which is related to the transducer geometry and the transmit and receive focus. s (f) and BSC s (f) are the frequency-dependent AC and BSC values ​​of the samples, respectively.

[0030] Similarly, the power spectrum of the backscattered signal from the reference phantom is:

[0031] Dividing the power spectrum of the sample by the power spectrum of the reference phantom yields:

[0032] Compensating for the known attenuation and backscattering properties of the reference phantom, equation (3) becomes:

[0033] Computing the natural logarithm yields: ln(RS′(f,z))=ln(BSCs (f))-4α s (f)z (5).

[0034] Then, the slope of the line (-4α) of Eq. (5) can be fitted from the alignment depth z s (f)) and intercept (ln(BSC s (f))) The attenuation coefficient α is derived s (f)(np / cm) and backscatter coefficient BSC s (1 / cm-str).

[0035] At S260 , a second AC and a second BSC are determined. The determination at S260 is based on the echo signal power spectrum of the harmonic frequency band acquired at S230 and the calibration echo signal power spectrum of the harmonic frequency band determined at S240 . The embodiment is not limited to the following description of the determination at S260 .

[0036] Using harmonic frequency bands to estimate AC and BSC requires a new model that accounts for tissue nonlinearity. The second harmonic pressure from a plane wave P0 at the fundamental frequency f is given by: where α f (f) and α h (2f) are the attenuation coefficients (np / cm) of the fundamental and harmonic signals, respectively, and K is a constant proportional to the nonlinearity parameter B / A.

[0037] The ratio term in equation (6) can be further simplified using the Taylor series of the exponential function: The last step uses the common assumption α h (2f) = 2α f (f) and the Taylor series approximation.

[0038] In the case of focused transmission using a clinical transducer array, P0(f) is modeled as: P0(f)=T(f)E tx (f)D tx (f) (8), Where T(f) is the transfer function of the transmitted pulse, E tx (f) is the electro-mechanical transfer function during emission, and D tx (f) is the diffraction pattern at emission. Using equations (7) and (8):

[0039] The power spectrum of the received second harmonic signal is given by: Where E rx (f) is the electromechanical transfer function at reception, and D rx (f) is the diffraction pattern upon reception, BSC(2f) is the backscatter coefficient at the second harmonic frequency (np / cm-str), and Taking into account the attenuation of the return harmonic signal, we combine equations (9) and (10):

[0040] In tissue harmonic imaging (THI) mode, the radio frequency signals from two pulses 180° out of phase are summed to obtain a harmonic signal.

[0041] Each RF echo line of the ROI is divided into several overlapping time-gated windows. Fourier transform is applied to each window, and the power spectra of windows corresponding to the same depth are averaged. The same process is performed on the corresponding ROI of the reference phantom.

[0042] The power spectra of the sample and reference in the ROI are given by equation (11). It is assumed that the terms in brackets are the same for both the sample and the reference. By calculating the ratio of the power spectra from the sample and the reference, we obtain an equation similar to equation (3):

[0043] Compensating for the known attenuation, backscatter, and nonlinearity of the reference phantom, equation (12) becomes:

[0044] Computing the natural logarithm yields:

[0045] The attenuation coefficient α at frequency 2f can be derived from the slope of the line fitted to equation (14) versus depth z: s (dB / cm). The intercept of the line fitted to equation (14) versus depth z gives the nonlinear term Bias ln(BSC s (2f)).

[0046] Returning to process 200, at S270, the nonlinearity of the ROI is determined based on the first BSC determined at S250 and the second BSC determined at S260. Continuing with the above example, ln(BSC) can be measured using the fundamental frequency band based on equation (5). s(2f)) (where the fundamental frequency is now 2f) and substituting the result into equation (14), the nonlinearity term in equation (14) is estimated

[0047] At S280, an image of the ROI is generated and displayed. As known in the art, the image may be generated based on one or both of the spectra acquired at S230. The image may also indicate nonlinearity and any other values ​​determined based on the received signal.

[0048] Figure 5 An image 500 generated and displayed at S280 according to some embodiments is shown. As shown, the determined values ​​of shear wave velocity (Vs), elasticity (E), AC, BSC, ultrasound-derived fat fraction (UDFF), and nonlinearity (K) are displayed simultaneously with the ultrasound B-mode image data. These quantitative measurements can improve the diagnostic capabilities of medical ultrasound by removing the qualitative interpretation of the B-mode images and by reducing system-related factors.

[0049] The estimates of AC based on the fundamental band and the harmonic band should be equivalent. Therefore, the image 500 can display either the average or the estimated value of the two. In some embodiments, the variability can be reduced by determining and displaying a weighted average of the two AC estimates.

[0050] In the case of BSC, the BSC value determined at S260 based on the harmonic band is biased by the nonlinearity term. Therefore, the BSC displayed at S280 may be the BSC value determined at S250 based on the fundamental band. If it is assumed that the nonlinearity term is negligible, the average of these two BSC values ​​may be displayed.

[0051] Figure 6 600 according to some embodiments. The system 600 may implement one or more of the processes described herein. The system 600 is a phased array ultrasound imaging system, but the embodiments are not limited thereto. A typical phased array system utilizes 64 to 256 receive channels and a comparable number of transmit channels. For clarity, Figure 6 A single transmit and receive channel is shown.

[0052] The system 600 includes a transducer element 605 and a transmit / receive switch 610. The transducer element 605 may include elements of a 1-D, 1.25-D, 1.5-D, 1.75-D, or 2-D array of piezoelectric or capacitive film elements. The transmit / receive switch 610 is operated to allow transmission of ultrasonic energy via the element 605 (e.g., in response to application of a voltage across the element 605), or to allow reception of a voltage generated by the element 605 in response to received ultrasonic energy (i.e., an echo).

[0053] The transmit beamformer 615 is operable in conjunction with the digital-to-analog converter 620 and the high voltage transmitter 625 to generate waveforms for multiple channels, where each waveform may exhibit a different amplitude, delay, and / or phase. The receive beamformer 630 receives signals from multiple channels, each of which may be subjected to amplification 635, filtering 640, analog-to-digital conversion 645, delay and / or phase rotators, and one or more summers. The receive beamformer 630 may be configured by hardware or software to apply relative delays, phases, and / or apodization in response to each transmit beam to form one or more receive beams. The receive beamformer 630 may provide dynamic receive focusing as known in the art, as well as fixed focus reception.

[0054] The receive beam formed by the receive beamformer 630 represents the material through which the transmit beam and the receive beam have passed. The receive beam is output to the processor 650 for processing. For example, the processor 650 may generate an image based on the receive beam.

[0055] The processor 650 may execute processor-executable program code stored in the memory 660 to execute and / or control other components of the system 600 to perform the processes described herein. The processor 650 may include 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, a control processor, an image processor, a field programmable gate array, a digital signal processor, an analog circuit, a digital circuit, a combination thereof, or other currently known or later developed devices for generating data (e.g., image data) based on beamformed ultrasound samples.

[0056] The memory 660 may include a non-transitory computer-readable storage medium, such as a random access memory and / or a non-volatile memory (e.g., flash memory, hard disk storage). The memory 660 may store program code, calibration data, B-mode images, and / or any other suitable data. The display 655 may include a cathode ray tube display, a liquid crystal display, a light emitting diode display, a plasma display, or other types of displays for displaying images and / or measurements.

[0057] Those skilled in the art will appreciate that various adaptations and modifications of the above-described embodiments may be configured without departing from the scope and spirit of the claims.It is therefore to be understood that the claims may be practiced other than as specifically described herein.

Claims

1. An ultrasound system, comprising: a memory storing an echo signal power spectrum of a reference phantom of a fundamental frequency band and an echo signal power spectrum of a reference phantom of a harmonic frequency band, wherein a center frequency of the harmonic frequency band is substantially similar to a center frequency of the fundamental frequency band; and Transducers for: transmitting a first ultrasound beam into a tissue region and receiving a first acoustic radio frequency signal representing a power spectrum of an echo signal of the tissue region in a fundamental frequency band; as well as transmitting a second ultrasound beam into the tissue region and receiving a second acoustic radio frequency signal representing a power spectrum of an echo signal of the tissue region in a harmonic frequency band; A processing unit for: determining a first backscatter coefficient based on an echo signal power spectrum of the tissue region in a fundamental frequency band and an echo signal power spectrum of a reference phantom in a fundamental frequency band; determining a value representing a second backscatter coefficient and a nonlinearity term associated with the tissue region based on an echo signal power spectrum of the tissue region in a harmonic frequency band and an echo signal power spectrum of a reference phantom in the harmonic frequency band; as well as determining a nonlinearity term associated with the tissue region based on the first backscatter coefficient and the value; as well as The display is used to display the second backscatter coefficient, the nonlinearity term, and the B-mode image of the tissue region. 2 . The ultrasound system according to claim 1 , wherein the echo signal power spectrum of the reference phantom in the fundamental frequency band and the echo signal power spectrum of the tissue region in the fundamental frequency band are acquired using substantially similar scanning settings. 3 . The ultrasound system according to claim 2 , wherein the echo signal power spectrum of the reference phantom in the harmonic frequency band and the echo signal power spectrum of the tissue region in the harmonic frequency band are acquired using substantially similar scanning settings.

4. The system according to claim 1, wherein the memory stores the echo signal power spectrum of the second reference phantom in the fundamental frequency band and the echo signal power spectrum of the second reference phantom in the harmonic frequency band, and The processing unit further determines an echo signal power spectrum of the reference phantom using a fundamental frequency band for determining a first backscatter coefficient and an echo signal power spectrum of the reference phantom using a harmonic frequency band for determining a second backscatter coefficient based on correlation between the tissue region and the reference phantom.

5. The system according to claim 4, wherein the echo signal power spectrum of the reference phantom in the fundamental frequency band and the echo signal power spectrum of the reference phantom in the harmonic frequency band have been acquired using the first scanning setting, The memory stores a second echo signal power spectrum of a reference phantom in a fundamental frequency band and a second echo signal power spectrum of a reference phantom in a harmonic frequency band, wherein the second echo signal power spectrum is acquired using a second scanning setting. wherein a third scanning setting is used to acquire an echo signal power spectrum of the tissue region in a fundamental frequency band and an echo signal power spectrum of the tissue region in a harmonic frequency band, and The processing unit is used to determine the echo signal power spectrum of the reference phantom using the fundamental frequency band and the echo signal power spectrum of the reference phantom using the harmonic frequency band based on the correlation between the first scanning setting and the third scanning setting, so as to determine the first backscatter coefficient and determine the second backscatter coefficient.

6. The system according to claim 1, wherein the processing unit is further configured to: The attenuation coefficient of the tissue region is determined based on the echo signal power spectrum of the tissue region in the harmonic frequency band, the echo signal power spectrum of the reference phantom in the harmonic frequency band, and the attenuation coefficient of the reference phantom.

7. The system according to claim 6, further comprising: The display is used to simultaneously display the second backscatter coefficient, the attenuation coefficient of the tissue region, the nonlinearity term, and the B-mode image of the tissue region.

8. A method comprising: controlling the ultrasound system transducer to acquire an echo signal power spectrum of a fundamental frequency band of the tissue region and an echo signal power spectrum of a harmonic frequency band of the tissue region, wherein a center frequency of the harmonic frequency band is substantially similar to a center frequency of the fundamental frequency band; determining a first backscatter coefficient based on an echo signal power spectrum of the tissue region in a fundamental frequency band and an echo signal power spectrum of a reference phantom in a fundamental frequency band; determining a value representing a second backscatter coefficient and a nonlinearity term associated with the tissue region based on an echo signal power spectrum of the tissue region in a harmonic frequency band and an echo signal power spectrum of a reference phantom in the harmonic frequency band; determining a nonlinearity term associated with the tissue region based on the first backscatter coefficient and the value; as well as The second backscatter coefficient, the nonlinearity term, and a B-mode image of the tissue region are displayed. 9 . The method according to claim 8 , wherein the echo signal power spectrum of the reference phantom in the fundamental frequency band and the echo signal power spectrum of the tissue region in the fundamental frequency band are acquired using substantially similar scanning settings. 10 . The method according to claim 9 , wherein the echo signal power spectrum of the reference phantom in the harmonic frequency band and the echo signal power spectrum of the tissue region in the harmonic frequency band are acquired using substantially similar scanning settings.

11. The method according to claim 8, further comprising: storing the echo signal power spectrum of the second reference phantom in the fundamental frequency band and the echo signal power spectrum of the second reference phantom in the harmonic frequency band, and An echo signal power spectrum of a reference phantom using a fundamental frequency band is determined based on correlation between the tissue region and the reference phantom for determining a first backscatter coefficient, and an echo signal power spectrum of a reference phantom using a harmonic frequency band is determined for determining a second backscatter coefficient.

12. The method according to claim 11, wherein the echo signal power spectrum of the reference phantom in the fundamental frequency band and the echo signal power spectrum of the reference phantom in the harmonic frequency band have been acquired using the first scanning setting, further comprising: storing a second echo signal power spectrum of the reference phantom in the fundamental frequency band and a second echo signal power spectrum of the reference phantom in the harmonic frequency band, wherein the second echo signal power spectrum is acquired using the second scanning setting, wherein a third scanning setting is used to acquire an echo signal power spectrum of the tissue region in a fundamental frequency band and an echo signal power spectrum of the tissue region in a harmonic frequency band, and Further comprising: determining an echo signal power spectrum of a reference phantom using a fundamental frequency band for determining a first backscatter coefficient and an echo signal power spectrum of a reference phantom using a harmonic frequency band for determining a second backscatter coefficient based on correlation between the first scanning setting and the third scanning setting.

13. The method according to claim 8, further comprising: The attenuation coefficient of the tissue region is determined based on the echo signal power spectrum of the tissue region in the harmonic frequency band, the echo signal power spectrum of the reference phantom in the harmonic frequency band, and the attenuation coefficient of the reference phantom.

14. The method according to claim 13, further comprising: The second backscatter coefficient, the attenuation coefficient of the tissue region, the nonlinearity term, and the B-mode image of the tissue region are displayed simultaneously.

15. An ultrasound imaging system, for: a transducer for acquiring an echo signal power spectrum of a fundamental frequency band of the tissue region and an echo signal power spectrum of a harmonic frequency band of the tissue region, wherein a center frequency of the harmonic frequency band is substantially similar to a center frequency of the fundamental frequency band; Processor unit for: determining a first backscatter coefficient based on an echo signal power spectrum of the tissue region in a fundamental frequency band and an echo signal power spectrum of a reference phantom in a fundamental frequency band; determining a value representing a second backscatter coefficient and a nonlinearity term associated with the tissue region based on an echo signal power spectrum of the tissue region in a harmonic frequency band and an echo signal power spectrum of a reference phantom in the harmonic frequency band; as well as determining a nonlinearity term associated with the tissue region based on the first backscatter coefficient and the value; as well as The display is used to display the second backscatter coefficient, the nonlinearity term, and the B-mode image of the tissue region. 16 . The system according to claim 15 , wherein the echo signal power spectrum of the reference phantom in the fundamental frequency band and the echo signal power spectrum of the tissue region in the fundamental frequency band are acquired using substantially similar scanning settings.

17. The system according to claim 15, wherein the processor unit is used to determine the echo signal power spectrum of the reference phantom using the fundamental frequency band for determining the first backscatter coefficient, and the echo signal power spectrum of the reference phantom using the harmonic frequency band for determining the second backscatter coefficient based on the correlation between the tissue region and the reference phantom.

18. The system according to claim 17, wherein the first scanning setting is used to acquire the echo signal power spectrum of the reference phantom in the fundamental frequency band and the echo signal power spectrum of the reference phantom in the harmonic frequency band, wherein the second scanning setting is used to acquire the echo signal power spectrum of the tissue region in the fundamental frequency band and the echo signal power spectrum of the tissue region in the harmonic frequency band, and The processor unit is used to determine the echo signal power spectrum of the reference phantom using the fundamental frequency band for determining the first backscatter coefficient and the echo signal power spectrum of the reference phantom using the harmonic frequency band for determining the second backscatter coefficient based on the correlation between the first scanning setting and the second scanning setting.

Images