Method and system for compensating for depth-dependent attenuation in ultrasonic signal data of a medium

Abstract

The present invention relates to a method for compensating for depth-dependent attenuation in ultrasonic signal data of a medium, wherein the method is implemented by a processing system (8), and the method comprises the following steps: a processing step (c), wherein the ultrasonic signal data is processed by a processing unit to provide in-phase and quadrature phase IQ data of the medium; and an attenuation compensation step (f), wherein the attenuation of the medium is compensated according to a plurality of different depths (z 1 , z 2 , z n ) is used to compensate the phase of the IQ data according to the corresponding frequency shift amount at each depth of the plurality of different depths, so that the IQ data spectrum returns to the center position at the plurality of different depths. The present invention also relates to a corresponding system.

Description

Technical Field

[0001] The present invention relates to an imaging method and a device for implementing the method, in particular for medical imaging.

[0002] The present disclosure relates to a method for compensating for depth-dependent attenuation in ultrasound signal data of a medium. The method may be implemented by a processing system, for example, associated with a plurality of (eg, a row or array) transducers associated with the medium. Background Art

[0003] Conventional ultrasound imaging involves insonifying a medium with one or more ultrasound pulses (or waves) emitted by a transducer, and collecting ultrasound signal data in response to the echoes of these pulses, for example by using the same transducer.

[0004] Using the backscattered echoes from a single insonification, a complete line of images can be calculated using a dynamic receive beamforming process. To build a complete image, the process is repeated by sending a set of focused waves that scan along a lateral line (called the focal plane) at a given depth. For each focused wave, dynamic beamforming is performed and the complete image is built up line by line. Dynamic beamforming ensures uniform focusing in receive mode, while in transmit mode the focus is fixed at a given depth. The final image is optimal in the focal plane and in a limited region of the medium corresponding to the axial focal length. However, outside this region imposed by the diffraction laws, the image quality degrades rapidly at other depths (in the near and far fields of the focused beam).

[0005] To overcome this limitation, one approach is to perform multi-focus imaging: using different transmit focal depths to obtain uniform quality throughout the image. Each transmit at a given focal depth is able to obtain a partial image within the region defined by the axial focal depth. The final image is obtained by reassembling these partial images corresponding to various depths. It is conceivable to improve the image quality by performing synthetic dynamic transmit focusing. This approach involves resynthesizing the dynamic transmit focusing (i.e., as many focal depths as there are pixels in the image) by beamforming, and then combining a set of different insonifications.

[0006] Based on the above techniques, a B-mode image (intensity) can be prepared which shows the acoustic impedance of a two-dimensional cross section of the imaging medium.

[0007] However, another phenomenon in ultrasound imaging is the attenuation of ultrasound in the examined medium, which must preferably be taken into account in some applications. When ultrasound propagates in tissue, it is subject to attenuation effects as a function of depth and tissue properties. This results in spectral deformation of the received signal at different depths.

[0008] Attenuation thus constitutes a subtle frequency- and depth-dependent phenomenon. It is therefore desirable to compensate for any effects of attenuation on the resulting computed image, just as tissue attenuation is traditionally accounted for by, for example, time gain compensation.

[0009] In addition, US5879303A describes an ultrasonic diagnostic imaging method, which generates an ultrasonic image based on harmonic echo components of the transmitted fundamental frequency. The proposed attenuation compensation includes mixing the fundamental and harmonic signals. That is, different frequency response filters are proposed according to the depth.

[0010] Thus, the known methods either lack precision, for example because nonlinearities of attenuation are neglected, or are complex, for example because they necessitate a plurality of different filters to compensate for the attenuation effects. Summary of the invention

[0011] There is still a desire to overcome the above problems, and in particular to provide a method and system for reliably compensating for depth-dependent attenuation in ultrasonic signal data of a medium. Advantageously, the method and system may be fast and less complex, for example in terms of required filters and computational complexity. Furthermore, the method and system may preferably improve image quality, for example in terms of reducing speckle / clutter and / or improving clarity.

[0012] Therefore, according to an embodiment of the present disclosure, a method for compensating for depth-related attenuation in ultrasonic signal data of a medium is provided. The method is implemented by, for example, a processing system associated with at least one ultrasonic transducer (which may be associated with the medium). The method comprises the following steps:

[0013] - a processing step, wherein the ultrasonic signal data is processed by a processing system to provide in-phase and quadrature-phase IQ data of the medium;

[0014] as well as

[0015] - an attenuation compensation step, wherein the phase of the IQ data is compensated according to the corresponding frequency shift amount at each of a plurality of different depths in the medium, so that the IQ data spectrum (i.e., the compensated IQ data spectrum) returns to a center position at the plurality of different depths.

[0016] That is, the attenuation compensation step may result in a spectral shift at different depths in the medium, which compensates for any shift caused by attenuation effects. For example, the shift and bandwidth of the low-pass filter may be automatically estimated as a function of the depth.

[0017] By providing such a method, attenuation effects in the ultrasound signal data may be compensated (ie corrected) by corresponding signal data processing. Hence, there is no need to adapt any filters applied to the processed signal data in terms of depth.

[0018] For example, the present disclosure achieves better B-mode image quality in terms of noise reduction and image clarity. At the same time, the method of the present disclosure allows the use of a single conventional filter in the subsequent filtering step. That is, since the method of the present disclosure implements a depth-dependent spectrum shift for compensating for attenuation effects, there is no need to adapt the filter for different depths or use several separately adapted filters (e.g., non-center filters) to match the misaligned spectrum of the input data. Advantageously, this simplifies the filter design.

[0019] Furthermore, the methods and systems of the present disclosure are general and thus applicable to any attenuation and are not limited to linear attenuation.

[0020] Thus, the present disclosure allows for improved image quality (e.g., image quality of B-mode images) in terms of reduced speckle / clutter and clarity, while being a more computationally efficient approach than conventional techniques that use specific filters to correct for depth-dependent attenuation.

[0021] In particular, because depth-dependent attenuation compensation is best performed in the time domain rather than the spectral domain, the method of the present disclosure is more computationally efficient (ie, requires less computation).

[0022] Different depths may mean different depth levels (eg, discrete values) or different depth regions (eg, a range or interval between two adjacent depth levels).

[0023] The compensated IQ data spectrum may be returned to a center position at a predefined reference frequency (eg, zero frequency or another predetermined positive or negative value).

[0024] After the processing step and before the attenuation compensation step, the method of the present disclosure may further include the following steps: an offset determination step, in which a frequency shift amount is determined based on a predefined offset map for each of a plurality of different depths.

[0025] Furthermore, the shift map may also be predetermined according to one or several different ultrasonic transducer types and / or one or several different medium types. For example, the shift map may include one or several different coefficients for each transducer type and / or each medium type.

[0026] The shift map may be derived from a single predefined attenuation coefficient or multiple attenuation coefficients at multiple different depths, respectively. For example, the attenuation coefficient may specify the reduction in ultrasound amplitude in the ultrasound signal data according to the frequency per unit distance (dB / cm / MHz) in the depth direction of the medium.

[0027] That is, in one embodiment, the offset map may include only one attenuation coefficient, based on which a linear offset function may be determined. For example, the coefficient may define the gradient of the linear function.

[0028] However, the offset map may also comprise a plurality of coefficients, for example each coefficient corresponding to a respective depth range in the medium. In this case, the separately obtained linear functions may be combined.

[0029] After the processing step and before the attenuation compensation step, the method of the present disclosure may further include the following steps:

[0030] - a function determination step, in which an autocorrelation function of the IQ data is determined for each of a plurality of different depths in the medium; and

[0031] - a center estimation step, in which for each of a plurality of different depths, the center spectral position ω is estimated from the phase of the autocorrelation function c (z),

[0032] In the attenuation compensation step, for each different depth, according to the corresponding center spectrum position ω c (z) Determine the amount of frequency shift.

[0033] Therefore, the offset is not necessarily based on predetermined data (eg, a predefined offset map or table), but it may also be automatically determined by the method of the present disclosure.

[0034] The autocorrelation function may be, for example, a first order autocorrelation function.

[0035] The attenuation compensation step may be performed in the time domain through each of a plurality of different depths to a maximum depth z max The complex phase of the attenuation compensation step is multiplied by the input data. k The complex phase at can depend, for example, on the depth z k The total offset of the maximum depth z max can be the maximum depth in the ultrasound data. Therefore, the data can be corrected at each depth up to a predefined maximum depth z max . Only the maximum depth z max This is preferably defined (in advance) by the probe, the system or the user. This means that the depths z1, z2, z nThe data at can be multiplied by z1, z2, z n The phase of z1, z2 and z n Can be 0 and z max Discrete depth data between .

[0036] For example, the maximum depth may correspond to a user selected value or may be predefined by the system, representing the maximum depth of a region in a medium scanned in an ultrasound imaging method. In general, the depth may be any kind of predefined or preselected value.

[0037] Therefore, since the compensation step can be performed in the time domain, the method of the present disclosure is advantageously more computationally efficient than performing compensation in the spectral domain.

[0038] After the processing step, the method may further include the following steps:

[0039] - a bandwidth estimation step, wherein for each of a plurality of different depths, a corresponding spectral standard deviation is estimated based on the autocorrelation coefficient of the IQ data; and

[0040] - a bandwidth determination step, wherein for each of a plurality of different depths, a frequency bandwidth of a filter (e.g., a low-pass or band-pass filter) is determined according to the spectral standard deviation, so that the IQ data is adaptively filtered at the plurality of different depths, and

[0041] - The attenuation compensation step is followed by a filtering step, in which a filter is applied to the compensated IQ data.

[0042] Thus, in addition to the spectrum shift during the attenuation compensation step, the bandwidth of the spectrum may be adapted to compensate for any effect of the bandwidth on the ultrasound signal data.

[0043] The ultrasonic signal data generally includes data of a plurality of ultrasonic lines of at least one ultrasonic transducer. A center estimation step and / or a bandwidth estimation step may then be performed for each of the plurality of ultrasonic lines. In addition, the output data of the steps may optionally be smoothed (e.g., averaged) on the ultrasonic line according to predefined rules and parameters.

[0044] That is, the data of each line obtained through the center estimation step and / or the bandwidth estimation step may be combined to smooth the combined data, for example, by determining an average value between the data of each line.

[0045] Therefore, the accuracy of attenuation compensation and / or bandwidth correction can be improved.

[0046] Furthermore, the output data may optionally be smoothed on the ultrasound lines according to other predefined rules and parameters (eg the number of ultrasound lines and / or the transducer type and / or the medium of the transducer used).

[0047] The output data of the center estimation step and / or the bandwidth estimation step may be regularized in the depth direction by a regularization step.

[0048] Therefore, smoother depth-dependent changes can be obtained and the stability of filtering can be improved.

[0049] The robustness of the output data of the center estimation step and / or the bandwidth estimation step can be enhanced by performing hypothesis testing on a pure noise model. Only statistically significant points can be included in the output data, so that the output data is less affected by noise. For example, the hypothesis H0:|ρ1|=0 can be tested, where ρ1 represents the first-order autocorrelation coefficient. Under the pure noise assumption, a threshold T for the value of |ρ1| can be derived so that the probability of observing |ρ1| above T does not exceed a predefined significance level or p-value (typically selected values ​​are 5% or 1%). In this case, only estimates from statistically significant points (according to the predefined significance level) can be included in the output data, so that the output data is less affected by noise.

[0050] This step (especially the hypothesis testing step) may be performed before the center estimation step and / or the bandwidth estimation step, for example, may also be performed before the processing step of the present disclosure, and may provide predetermined data used in the center estimation step and / or the bandwidth estimation step.

[0051] The above steps (especially the step for smoothing the combined output data between the lines, the step for regularizing the output data and the step for enhancing the robustness of the output data) may be arbitrarily combined.

[0052] By fitting a piecewise attenuation function (eg, a linear or nonlinear function) of adjacent depths (ie, a depth range or region in the depth direction) to the offset map, a frequency shift map over depth may be generated based on the frequency shift amounts at different depths.

[0053] The method of the present disclosure may preferably be part of a scattering or backscattering process, in particular a beamforming process method, such as a synthetic beamforming process.

[0054] For example, the in-phase and quadrature-phase IQ data IQ may be scattered and / or backscattered IQ data, and in particular may be beamformed IQ data.

[0055] Alternatively or additionally, the method of the present disclosure may include a beamforming step, wherein the IQ data is processed by a beamforming process to provide beamformed acquisition data of the medium. The processing step, the attenuation compensation step, and any steps between these steps may be performed in the beamforming process.

[0056] Due to the beamforming process, diffraction patterns in the acquired data may be reduced. The beamforming process may be, for example, a synthetic beamforming process. Advantageously, this may further reduce the diffraction patterns.

[0057] Furthermore, the processing of ultrasound data in the method of the present disclosure may be performed in a processing step of the beamforming process including IQ data re-phasing. Therefore, the method of the present disclosure does not imply any significant additional computational cost.

[0058] The method may be implemented by a processing system associated or coupled to at least one ultrasonic transducer. Prior to the processing step, the method may further include the following steps:

[0059] - a transmitting step, in which at least one pulse is transmitted in the medium by the transducer; and

[0060] - A receiving step, wherein in response to the pulse, ultrasonic signal data is acquired by the transducer.

[0061] The method may further comprise at least one of the following steps:

[0062] - a filtering step, wherein a low pass filter is applied to the compensated IQ data spectrum, and the same filter is applied to a plurality of different depths; and / or

[0063] - An envelope detection step, wherein the envelope of the filtered compensated IQ data is output.

[0064] The filtering step may include using a single low pass filter and / or a band pass filter. The filtering step may also include using a plurality of low pass filters and / or band pass filters. It may be desirable to use only one filter applied to a plurality of different depths, since the input signal data input to the filter already has a spectrum back to the center position (i.e., the attenuation has been compensated by the spectrum shift in the input signal data). However, several filters, for example with different bandwidths for each depth level, may also be used.

[0065] Thus, only one filter (e.g., a low-pass or band-pass filter) may be used which is not itself used to compensate for the depth-dependent spectral shift of the attenuation effect. This is also not necessary, since the signal data input to the filter is already compensated (i.e., corrected) for the attenuation effect. The filter may be predefined, or may be selected from a predefined list depending on the transducer and / or medium, or may be adaptive when the method is performed (e.g., the filter may be determined to have an average value of the bandwidth estimated by the method).

[0066] However, as mentioned above, the filters used can be adapted for depth-dependent bandwidth adaptation. That is, there can also be multiple filters for multiple depths, respectively. Each filter can have an adapted and possibly different bandwidth. However, the centers of the filters can be aligned. Therefore, the filters do not have to have different center frequencies, because the spectrum shift has been achieved in the attenuation compensation step.

[0067] The present disclosure also relates to a computer program, comprising computer-readable instructions, which, when executed by a data processing system, cause the data processing system to perform the method for compensating for depth-dependent attenuation in ultrasonic signal data of a medium as described above.

[0068] The present disclosure may further relate to a method for imaging an ultrasound image, wherein in the image processing, the attenuation effect has been compensated as described above.The image may then be displayed on any associated local or remote display at the same or similar time period and / or position.

[0069] The present disclosure also relates to a system for compensating for depth-dependent attenuation in ultrasonic signal data of a medium, comprising a processing system for:

[0070] -processing the ultrasonic signal data to provide in-phase and quadrature-phase IQ data of the medium,

[0071] - compensating the phase of the IQ data according to a corresponding frequency shift at each of a plurality of different depths in the medium,

[0072] The IQ data spectrum is returned to the center position at the multiple different depths.

[0073] Optionally, the system may also include an ultrasonic data acquisition system, for example including at least one transducer. However, the system of the present disclosure may also not be limited to this option. The system may also be used to receive ultrasonic signal data from an external acquisition system, which may be connected to the system of the present disclosure, for example, via the Internet, the "cloud", 4G or 5G protocols, WIFI, any local network or any other data contact or contactless connection.

[0074] The at least one transducer may be a single transducer for emitting pulses and receiving tissue responses, such as a focused transducer, for example having a concave shape or a corresponding lens. Furthermore, the single transducer may be scanned.

[0075] Multiple transducers and / or a transducer array may also be used. For example, a linear array may be provided, typically including dozens of transducers (e.g., 100 to 300) juxtaposed along the X-axis (horizontal or array direction X). A 3D probe or any other probe may also be used to implement the present disclosure.

[0076] The same transducer may be used to transmit the pulse and receive the response, or different transducers may be used for transmitting and receiving.

[0077] The present disclosure may also relate to a computer program, comprising instructions, and when the program is executed by a computer, the instructions are used to perform the steps of at least one of the above methods.

[0078] The present disclosure may also relate to a computer-readable recording medium having a computer program recorded thereon, including instructions. When the program is executed by a computer, the instructions are used to execute the steps of at least one of the above methods.

[0079] The present disclosure and its embodiments may be used in the context of medical devices specifically for humans and animals, but may also be used in any contemplated material, such as sheet metal, gravel, pebbles, and the like.

[0080] It is intended that the elements described above and in this specification can be combined unless otherwise incompatible.

[0081] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are provided for purposes of illustration only and are not restrictive of the disclosure, as claimed.

[0082] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to support and explain the principles thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] Figure 1 Shown is a schematic diagram illustrating an ultrasonic device according to an embodiment of the present disclosure;

[0084] Figure 2 Shown is a diagram showing Figure 1 A block diagram of a portion of the apparatus;

[0085] Figure 3Shown is a flow chart of a method for compensating for depth-dependent attenuation in ultrasonic signal data of a medium according to the present disclosure;

[0086] Figure 4 Shown is a schematic diagram of a first exemplary embodiment of a method according to the present disclosure (using predefined coefficients / maps);

[0087] Figure 5 Shown is a schematic diagram of a second exemplary embodiment of the method according to the present disclosure (using automatic offset determination);

[0088] Figure 6 Shown is a schematic diagram of a third exemplary embodiment of the method according to the present disclosure (in addition, automatic bandwidth correction is employed);

[0089] Figure 7a Shown is a first example of a depth-dependent frequency spectrum of an ultrasound image without attenuation compensation;

[0090] Figure 7b Shown is a first example in which attenuation compensation is performed;

[0091] Figure 8a Shown is a second example of a depth-dependent frequency spectrum of an ultrasound image without attenuation compensation; and

[0092] Figure 8b Shown is a second example in which attenuation compensation is performed. DETAILED DESCRIPTION

[0093] Reference will now be made in detail to exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0094] Figure 1 The device shown is suitable for imaging an area 1 of a medium, for example, living tissue of a patient, animal or plant, in particular human tissue. The device may correspond to a system of the present disclosure. The device may, for example, comprise:

[0095] · (Optionally) at least one transducer, such as a single transducer for transmitting pulses and receiving tissue responses. In addition, multiple transducers and / or a transducer array 2 may be used. For example, a linear array may be provided, as is known in conventional probes, typically comprising dozens of transducers (e.g., 100 to 300) juxtaposed along the X-axis (horizontal or array direction X). In this case, the array 2 is adapted for two-dimensional (2D) imaging of the region 1, but the array 2 may also be a two-dimensional array adapted for three-dimensional imaging of the region 1. The transducer array 2 may also be a convex array, comprising multiple transducers arranged along a curve. The same transducer may be used for transmitting pulses and receiving responses, or different transducers may be used for transmitting and receiving;

[0096] Electronics cabin 3, which controls the transducer array and collects signals from it;

[0097] A microcomputer 4 for controlling the electronics cabin 3 and for viewing, for example, images obtained from the electronics cabin (in a variant, a single electronic device may perform all the functions of the electronics cabin 3 and of the microcomputer 4). The microcomputer may be, for example, a personal computer (PC).

[0098] However, the transducer can be outside the electronics compartment 3 and / or microcomputer 4. For example, the transducer can be remotely connected to the electronics compartment 3 and / or microcomputer 4. In an exemplary embodiment, the transducer is an Internet of Things (IOT) device and / or can be connected to an IOT device and / or a smartphone. The transducer can be connected to the electronics compartment 3 and / or microcomputer 4 via the Internet, the "cloud", 4G or 5G protocols, WIFI, any local network, or any other data contact or remote connection.

[0099] The electronics compartment 3 and the microcomputer 4 may also be connected remotely, for example via the Internet, the “cloud”, 4G or 5G protocols, WIFI, any local network or any other data contact or remote connection.

[0100] The device may also include a display for displaying the ultrasound image. The display may be connected to or consist of the microcomputer 4. The display may also be remotely connected to the electronics compartment 3 and / or the microcomputer 4, for example via the Internet, the "cloud", 4G or 5G protocols, WIFI, any local network or any other data contact or remote connection.

[0101] Figure 1 The Z axis is the axis perpendicular to the X axis and is usually the direction of the ultrasound beam generated by the transducer of the array, for example in the depth direction of the medium being inspected. This direction is designated as the vertical or axial direction in this document.

[0102] like Figure 2 As shown, the electronics compartment 3 may include, for example:

[0103] L analog / digital converters 5 (A / Di-A / DL), respectively connected to L transducers (Tl-TL) of the transducer array 2;

[0104] L buffer memories 6 (Bi-Bn), respectively associated with n analog / digital converters 5;

[0105] A processing system 8, including, for example, a central processing unit 8a (CPU) communicating with a buffer memory 6 and a microcomputer 4

[0106] and / or a graphics processing unit 8b (GPU);

[0107] Memory 9 (MEM), connected to the central processing system 8; and

[0108] A digital signal processor 10 (DSP), connected to the central processing system 8.

[0109] The apparatus disclosed herein is a device for ultrasonic imaging, the transducer is an ultrasonic transducer, and the implemented method estimates the ultrasonic attenuation parameter of the region 1 , and optionally can generate an ultrasonic image of the region 1 .

[0110] However, the device may be any imaging equipment using other waves than ultrasound (waves having a wavelength different from that of ultrasound), to which the transducer and the electronics compartment components are then adapted.

[0111] Figure 3 FIG. 1 is a flow chart of a method for compensating for depth-dependent attenuation in ultrasonic signal data of a medium according to the present disclosure. The method may be Figure 1 is implemented in the device.

[0112] The steps of the method may be mainly controlled by a processing system 8, for example including a central processing unit 8a and / or a graphics processor 8b, and ultimately facilitated by a digital signal processor 10 or any other device. The method comprises the following main steps:

[0113] - an optional emission step (a), in which at least one pulse is emitted in the medium by a transducer;

[0114] - an optional receiving step (b), wherein in response to the pulse, ultrasonic signal data is collected by the transducer;

[0115] - a processing step (c), wherein the ultrasonic signal data is processed by a processing system to provide in-phase and quadrature-phase IQ data of the medium;

[0116] oOptional offset determination step (d1), as in Figure 5 described in the context of;

[0117] or

[0118] o an optional function determination step (d2) and an optional center estimation step (e2), as in Figure 6 described in the context of;

[0119] o an optional bandwidth estimation step (d2') and an optional bandwidth determination step (e2'), as described in the context of Figure 7;

[0120] - an attenuation compensation step (f), wherein the attenuation compensation step is performed according to a plurality of different depths (z1, z2, z n ) so that the IQ data spectrum returns to the center position at the multiple different depths;

[0121] - an optional (e.g. low-pass) filtering step (g), wherein a (e.g. single) filter is applied to the corrected compensated IQ data spectrum, the same filter being applied to a plurality of different depths (z1, z2, z n );as well as

[0122] - an optional envelope detection step (h), wherein the envelope of the filtered compensated IQ data is output.

[0123] The method may also include an optional beamforming step (cf), including a processing step (c), an attenuation compensation step (f), and any steps between (c) and (f), wherein in the optional beamforming step, the IQ data is processed by a beamforming process to provide beamforming acquisition data of the medium.

[0124] The method can be repeated, for example, by looping back from step (h) to step (a). In this way, repeated ultrasound data acquisition and / or ultrasound imaging in real time or quasi-real time is possible.

[0125] Figure 4 Shown is a schematic diagram of a first exemplary embodiment of the method according to the present disclosure (using predefined coefficients / maps). Figure 4 As shown, the method may include an optional offset determination step (d1), wherein for a plurality of different depths (z1, z2, z n), the amount of frequency shift is determined based on a predefined offset map and, for example, also based on the probe type. For example, by user input or by estimation, a predefined offset map (e.g., attenuation coefficient) can be obtained to calculate the amount of frequency shift based on depth. The frequency shift is applied to the input IQ data. Correction can be performed in the time domain by complex phase multiplication of the input data corresponding to the offset. The corrected data is then low-pass filtered to reduce noise before being sent to envelope detection.

[0126] Figure 5 Shown is a schematic diagram of a second exemplary embodiment of the method according to the present disclosure (using automatic offset determination). Figure 5 As shown, the method may include an optional function determination step (d2), wherein for a plurality of different depths (z1, z2, z n ), determining the autocorrelation function of the IQ data. Furthermore, the method may comprise a subsequent optional center estimation step (e2), wherein for a plurality of different depths (z1, z2, z n ) at each depth, the central spectrum position ω is estimated based on the phase of the autocorrelation function c (z). In this exemplary embodiment, for each different depth (z1, z2, z n ) is used as the attenuation compensation step (f), according to the corresponding center spectrum position ω c (z) Determine the amount of frequency shift.

[0127] In addition, the frequency shift can be automatically estimated by the first-order autocorrelation on the IQ data. The first-order autocorrelation function R1(z) and the coefficient ρ1(z) can be calculated based on the IQ at each depth. The central spectral position ω at each depth z is estimated by the phase of R1 c (z):

[0128]

[0129] The estimated position can be used to compensate (correct) the IQ data phase at each depth so that the corrected data spectrum returns to the center position at zero frequency.

[0130] Figure 6 Shown is a schematic diagram of a third exemplary embodiment of the method according to the present disclosure (in addition, automatic bandwidth correction is employed). Figure 6 As shown, the method may further include an optional bandwidth estimation step (e2'), wherein for a plurality of different depths (z1, z2, z n ), the corresponding spectral standard deviation is estimated according to the autocorrelation coefficient of the IQ data. The method may further include a subsequent optional bandwidth determination step (f2″), wherein for a plurality of different depths (z1, z2, zn ), the frequency bandwidth of the filter is determined according to the spectral standard deviation, so that the IQ data is adaptively filtered at multiple different depths. After the attenuation compensation step (f), a filtering step (g) can be performed, in which the filter is applied to the compensated IQ data.

[0131] Therefore, the filter bandwidth can also be estimated by the same autocorrelation function to adapt the filter bandwidth. The standard deviation of the spectrum can be estimated at each depth z in the following way:

[0132]

[0133] The accuracy of both estimates (frequency shift and bandwidth) can be further improved by smoothing the estimates from multiple ultrasound lines. Both estimates can also be regularized with respect to depth to obtain smoother variations depending on depth, thereby improving the stability of the filtering. The robustness of both estimates can be improved by hypothesis testing a pure noise model (i.e., H0:|ρ1|=0). Only statistically significant points are included in the estimation, making the estimates less affected by noise.

[0134] Figure 7a Shown is a first example of a depth-dependent frequency spectrum of an ultrasound image without attenuation compensation. Figure 7b Shown is the same first example with attenuation compensation performed, which is an example of automatic spectral correction as a function of depth for a phantom with a linear attenuation coefficient.

[0135] In the example, the spectrum of the ultrasonic signal is distorted due to attenuation when propagating in the depth direction. The method according to the present disclosure allows automatic estimation of the frequency center and bandwidth at each depth. This brings the spectrum back to the center position and adaptively low-pass filters the ultrasonic signal data to compensate for the attenuation distortion. The method is also applicable to nonlinear attenuation. Figure 7b In FIG. 1 , it is exemplarily and schematically shown that a single low-pass filter can be used for each depth level in the spectrum. This is possible because the depth-dependent spectrum shift for attenuation compensation is already performed by the method of the present disclosure.

[0136] Figure 8a A second example of a depth-dependent spectrum of an ultrasound image without attenuation compensation is shown, wherein Figure 8b Another example of attenuation compensation is shown. As shown in the second example, the attenuation is not necessarily linear. The example illustrates an in vivo example and the results of the disclosed automatic correction. Figure 8bIn the figure, it is exemplarily and schematically shown that multiple filters with matching bandwidth can be used for corresponding multiple depth levels in the spectrum. In the illustrated example, only two filters are shown, but more than two filters, for example 10 or 20 filters, can be used. The filter can be a low-pass filter. The center thereof can be the same. That is, the filter may not need to match any spectral offset of the ultrasonic signal data. This is not necessary because the depth-dependent spectral offset (i.e., returning to the center position) for attenuation compensation has been performed by the method of the present invention. However, the bandwidth of the filter may be different. That is, the filter can have different bandwidths at depth. Therefore, filters with different matching bandwidths can be used at different depths. The bandwidth can be calculated, for example, in steps d2' and e2' as described above.

[0137] Throughout the specification (including claims), unless otherwise stated, the term "comprising a" should be understood as being synonymous with "comprising at least one". In addition, unless otherwise stated, any ranges set forth in this specification (including claims) should be understood to include their end values. The specific values ​​of the elements described should be understood to be within acceptable manufacturing or industrial tolerances known to those skilled in the art, and any use of the terms "substantially" and / or "approximately" and / or "generally" should be understood to fall within such acceptable tolerances.

[0138] Although the present disclosure has been described herein in conjunction with specific embodiments, it should be understood that these embodiments are merely illustrative of the principles and applications of the present disclosure.

[0139] It is intended that the specification and examples be considered as exemplary only, with the true scope of the disclosure being indicated by the following claims.

[0140] In summary, the method according to the present disclosure as described above allows for a more accurate attenuation estimation and implies less computational cost, which improves in particular the real-time computation mode. Furthermore, due to the increased accuracy, the variance can be reduced, thereby improving reproducibility.

Claims

1. A method for compensating for depth-dependent attenuation in ultrasonic signal data of a medium, wherein the method is implemented by a processing system (8), the method comprising the following steps: Processing step (c), wherein the ultrasonic signal data is processed by the processing system to provide in-phase and quadrature-phase IQ data of the medium; as well as The offset determination step (d1) comprises: for a plurality of different depths (z1, z2, z n ), determining a frequency shift amount based on a predefined offset map for each depth in the ; Attenuation compensation step (f), wherein the attenuation compensation step is performed according to a plurality of different depths (z1, z2, z n ) is used to compensate the phase of the IQ data according to the corresponding frequency shift amount at each depth in the plurality of different depths, so that the spectrum of the IQ data returns to the center position at the plurality of different depths.

2. The method according to claim 1, The IQ data spectrum is returned to the center position at a predefined reference frequency.

3. The method according to claim 1 or 2, The shift map is derived from a single predefined attenuation coefficient or a plurality of attenuation coefficients at the plurality of different depths, respectively, the attenuation coefficient specifying a reduction in ultrasonic wave amplitude in the ultrasonic signal data according to a frequency per unit distance in a depth direction of the medium.

4. The method according to claim 1 or 2, After the processing step (c) and before the attenuation compensation step (f), the method further comprises the following steps: Function determination step (d2), wherein for a plurality of different depths (z1, z2, z n ), determining an autocorrelation function of the IQ data; as well as Center estimation step (e2), wherein for the plurality of different depths (z1, z2, z n ) in each depth, the central spectrum position ω is estimated according to the phase of the autocorrelation function c (z), In the attenuation compensation step (f), for each different depth (z1, z2, z n ), according to the corresponding center spectrum position ω c (z) Determining the frequency shift amount.

5. The method according to claim 1 or 2, wherein the attenuation compensation step (f) is performed in the time domain through the plurality of different depths (z1, z2, z n ) to the maximum depth (z max ) is multiplied by the complex phase of the attenuation compensation step (f) to perform the attenuation compensation at depth (z k ) depends on the complex phase up to the depth (z k )'s total offset.

6. The method according to claim 4, After the processing step (c), the method further comprises the following steps: Bandwidth estimation step (d2'), wherein for the plurality of different depths (z1, z2, z n ), estimating a corresponding spectrum standard deviation according to an autocorrelation coefficient of the IQ data; as well as The bandwidth determination step (e2') comprises: for the plurality of different depths (z1, z2, z n ), determining a frequency bandwidth of a filter according to the spectrum standard deviation, so that the IQ data is adaptively filtered at the plurality of different depths, and The attenuation compensation step (f) is followed by a filtering step (g), wherein the filter is applied to the compensated IQ data.

7. The method according to claim 6, The ultrasonic signal data includes data of multiple ultrasonic lines of the ultrasonic transducer, wherein The center estimation step (e2) and / or the bandwidth estimation step (d2') are performed for each of the plurality of ultrasound lines, and output data of the steps (e2, d2') are smoothed on the ultrasound line.

8. The method according to claim 6, The output data of the center estimation step (e2) and / or the bandwidth estimation step (d2') are regularized in the depth direction through a regularization step.

9. The method according to claim 6, The robustness of the output data of the center estimation step (e2) and / or the bandwidth estimation step (d2') is enhanced by performing hypothesis testing on a pure noise model, wherein the pure noise model is H0:|ρ1|=0, wherein ρ1 is the first-order autocorrelation coefficient of the IQ data, and wherein the output data only includes statistically significant points, so that the output data is less affected by noise.

10. The method according to claim 1 or 2, The attenuation function of adjacent depths (z1, z2) is fitted to the offset map, based on the different depths (z1, z2, z n ) to generate a frequency shift map over depth.

11. The method according to claim 1 or 2, The in-phase and quadrature-phase IQ data are scattered and / or backscattered IQ data and / or beamformed IQ data.

12. The method according to claim 1 or 2, Also included is a beamforming step (cf), wherein the IQ data is processed by a beamforming process to provide beamformed acquisition data of the medium, wherein The processing step (c), the attenuation compensation step (f) and any steps between (c) and (f) are performed in the beamforming process.

13. The method according to claim 1 or 2, The method is implemented by a processing system (8) associated with at least one ultrasonic transducer, and before the processing step (c), the method further comprises the following steps: a transmitting step (a), wherein at least one pulse is transmitted in the medium by a transducer; as well as The receiving step (b) comprises collecting ultrasonic signal data by the transducer in response to the pulse.

14. The method according to claim 1 or 2, The following steps are also included: A filtering step (g), wherein a filter is applied to the compensated IQ data spectrum, and the same filter is applied to the plurality of different depths (z1, z2, z n ); and / or An envelope detection step (h), wherein the envelope of the filtered compensated IQ data is output.

15. A computer-readable medium having a computer program stored thereon, the computer program comprising computer-readable instructions, which, when executed by a data processing system, causes the data processing system to execute the method according to any one of claims 1 to 14.

16. A system for compensating for depth-dependent attenuation in ultrasonic signal data of a medium, comprising a processing system (8) for: processing the ultrasonic signal data to provide in-phase and quadrature-phase IQ data of the medium, For multiple different depths (z1, z2, z n ), determining the frequency shift amount based on a predefined offset map, To compensate for the depth-dependent attenuation, the media is configured to have a plurality of different depths (z1, z2, z n ) is used to compensate the phase of the IQ data according to the corresponding frequency shift amount at each depth in the plurality of different depths, so that the spectrum of the IQ data returns to the center position at the plurality of different depths.

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