Ultrasound systems and methods

Abstract

The present disclosure relates to an ultrasound transducer configured to transmit a plurality of ultrasound signals from a plurality of elements in a transducer array into a region of interest, the ultrasound transducer further configured to receive and sample a plurality of backscattered ultrasound signals from the region of interest; a processing unit configured to calculate a local phase parameter in a time domain for each of the plurality of backscattered ultrasound signals, the processing unit configured to calculate a center frequency for each of the local phase parameters of the backscattered ultrasound signals in the time domain; and a beamformer configured to perform receiver beamforming by summing the center frequencies, the ultrasound system further configured to generate at least one parameter representative of a physical property of the region of interest based on the summed center frequencies. The present disclosure further relates to an ultrasound method for generating at least one parameter representative of a physical property of the region of interest.

Description

[Technical field]

[0001] The present disclosure relates to ultrasound systems, particularly ultrasound imaging systems, and ultrasound methods, particularly ultrasound imaging methods. The disclosed ultrasound systems and methods include improvements in the ability to calculate and / or extract parameters representative of physical properties of a region of interest, such as characterizing atherosclerotic plaque in an arterial wall of a subject. [Background technology]

[0002] Medical ultrasound is an imaging technique based on ultrasound. The technique can be used to create images of body structures. The purpose is often to find the source of disease, but it is also used for other purposes, such as testing pregnant women. Ultrasound is a sound wave with a frequency higher than that which humans can hear. Ultrasound images, also known as sonograms, are created using a transducer with elements arranged in a transducer array. The elements in the transducer array propagate ultrasound waves into the medium. When the ultrasound waves are reflected by objects or other variations in the medium, the reflected ultrasound waves are received by the transducer. The received signals can then be processed to create an image.

[0003] In ultrasound processing, beamforming can be applied to both transmission and reception, improving the directionality and sensitivity of the resulting data. In general, beamforming can be referred to as a technique that controls the electronic parameterization and signal transformation for the generation of ultrasound signals (transmit beamforming) and the processing of reflected ultrasound signals (receive beamforming).

[0004] Backscattered ultrasound energy depends on tissue properties, such as size, shape and density of cells / structures / components, which are related to the wavelength and propagation direction of sound. As a result, the frequency content of the backscattered pulse depends on the properties of the tissue microstructure. However, the transducer excitation and geometry determine the transmitted ultrasound field and therefore also have a large effect on the frequency of the backscattered ultrasound. It is therefore important to introduce some kind of normalization to remove the transducer effect in the analysis of the frequency spectrum of the backscattered ultrasound data. This can be achieved in several ways. Typically, the spectrum is divided by the spectrum from a reference phantom or mirror plate placed in water at the same investigation depth, received by the same transducer. Using these normalizations in the right way effectively removes the transducer effect from the frequency spectrum. The result is a spectrum that can give the clinician tissue-specific information.

[0005] Despite recent advances in the application of ultrasound techniques in the assessment of tissue structure by spectral analysis, this technique still suffers from relatively poor signal-to-noise ratio and image resolution. Summary of the Invention

[0006] The present disclosure relates to an ultrasound system and method that introduces improvements in terms of accuracy compared to conventional ultrasound systems. A first aspect of the disclosure is an ultrasound system comprising: an ultrasound transducer configured to transmit a plurality of ultrasound signals from a plurality of elements in a transducer array into a region of interest, the ultrasound transducer being further configured to receive and sample a plurality of backscattered ultrasound signals from the region of interest; A processing unit comprising: calculating a local phase parameter in the time domain for each or group of the plurality of backscattered ultrasound signals; the processing unit configured to calculate a center frequency for each local phase parameter of the backscattered ultrasound signal in the time domain; a beamformer configured to perform receiver beamforming by summing center frequencies; The ultrasound system is further configured to generate at least one parameter indicative of a physical property of the region of interest based on the summed center frequencies.

[0007] In frequency measurement and spectrum analysis of ultrasound, it is usually difficult to achieve a good signal-to-noise ratio, especially while simultaneously achieving high spatial resolution. The inventors have recognized that in ultrasound systems using beamforming, accuracy can be improved by calculating local phase parameters in the time domain of each or group of multiple backscattered ultrasound signals, and by calculating the center frequency still operating in the time domain before any receive beamforming is performed. In ultrasound systems, there are usually transmit and receive beamforming sections. During transmit beamforming, the ultrasound transmitted by each element of the transducer array is usually delayed individually to obtain a sum beam at the focal point. The transducer then switches to receive mode. The backscatter pressure impinging on the elements is generated by the scatterers in the region of interest. The pressure is converted into a signal in the transducer. The signal is then delayed and averaged to create one radio frequency (RF) line in the form of a vibrating ultrasound line. This operation is generally referred to as receive beamforming. In the ultrasound system disclosed herein, the raw ultrasound signal is directly used in the receive processing. A local phase parameter is calculated in the time domain for each of the multiple backscattered ultrasound signals. This can be done, for example, by converting the multiple backscattered ultrasound signals to a complex representation of the backscattered ultrasound signals, for example by calculating a Hilbert transform. Based on the complex representation, a center frequency can then be calculated for each of the local phase parameters of the backscattered ultrasound signals in the time domain. Figure 1B shows this additional step in the form of a processing unit (106) configured to operate on the individual backscattered ultrasound signals as described above. The additional processing can be performed before or after the time delay. Receive beamforming can then be applied to the calculated center frequencies.

[0008] In further frequency analysis, the model can be used to estimate the size of structures (e.g., cells) in the region of interest. The above-described method has been found to provide improved accuracy in subsequent analysis of frequencies. Figures 3A-3C show an example of a frequency image of a region. Figure 3A shows theoretical frequency responses for structures of different sizes. Region 301 shows a well-defined region with structures of different sizes, which causes a well-defined frequency shift in the image. Figure 3B shows a frequency image of a conventional ultrasound system. Figure 3C shows a frequency image of an ultrasound system disclosed herein.

[0009] The present disclosure further relates to Transmitting a plurality of ultrasound signals from a plurality of elements of a transducer array into a region of interest; receiving and sampling a plurality of backscattered ultrasound signals from a region of interest; Calculating a local phase parameter in the time domain for each of the plurality of backscattered ultrasound signals; Calculating a center frequency for each of the local phase parameters of the backscattered ultrasound signal in the time domain; performing receiver beamforming by summing center frequencies; and generating at least one parameter representative of a physical property of the region of interest based on the summed center frequencies.

[0010] Those skilled in the art will recognize that the ultrasound methods disclosed herein may be performed using any embodiment of the ultrasound system disclosed herein, and thus the methods may perform any steps that the ultrasound system disclosed herein is configured to perform.

[0011] BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the ultrasound systems and methods disclosed herein are provided in the following drawings, which are exemplary and intended to illustrate some of the features of the ultrasound systems and methods of the present disclosure and should not be construed as limiting the invention of the present disclosure. [Brief description of the drawings]

[0012] [Figure 1A] 1 illustrates an embodiment of a transmit side with a transmit beamformer according to one embodiment of an ultrasound system disclosed herein. [Figure 1B] 1 illustrates an embodiment of a receive side with a receive beamformer according to one embodiment of an ultrasound system disclosed herein. [Diagram 2] 1 illustrates an embodiment of an ultrasound method disclosed herein. [Figure 3A] A comparison of theoretical backscatter frequencies for structural changes (A) and backscatter frequencies measured using a conventional ultrasound system (B) and the backscatter frequencies measured using the ultrasound system disclosed herein is shown. [Figure 3B] A comparison of theoretical backscatter frequencies for structural changes (A) and backscatter frequencies measured using a conventional ultrasound system (B) and the backscatter frequencies measured using the ultrasound system disclosed herein is shown. [Figure 3C] A comparison of theoretical backscatter frequencies for structural changes (A) and backscatter frequencies measured using a conventional ultrasound system (B) and the backscatter frequencies measured using the ultrasound system disclosed herein is shown. [Figure 4A] 1 shows a comparison of ultrasound images of carotid artery plaque using a conventional ultrasound system (A) and the ultrasound system disclosed herein (B). [Figure 4B] 1 shows a comparison of ultrasound images of carotid artery plaque using a conventional ultrasound system (A) and the ultrasound system disclosed herein (B). [Diagram 5] A diagram of the center frequency shift for different scatterer sizes is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present disclosure provides an ultrasound system comprising: The ultrasound system includes an ultrasound transducer configured to transmit a plurality of ultrasound signals from a plurality of elements in a transducer array into a region of interest, the ultrasound transducer further configured to receive and sample a plurality of backscattered ultrasound signals from the region of interest.

[0014] Preferably, the ultrasound system comprises a transmit beamformer. Those skilled in the art will generally know how to implement transmit beamforming. FIG. 1A shows an embodiment of the transmit side with a transmit beamformer according to one embodiment of the ultrasound system (100) disclosed herein. Multiple parallel pulses are generated. The pulses can be generated typically at 1-20 MHz, for example 10 MHz, but any suitable frequency is possible. The parallel pulses are individually delayed. Multiple elements (102) in the transducer array (101) are configured to transmit ultrasound signals (104) to obtain a sum beam at a focal point (103). The relative delay between the pulses can be constructed such that the ultrasound pulses arrive at the focal point (103) simultaneously with their phase aligned. Preferably, the ultrasound system further comprises a receive beamformer. Those skilled in the art will generally know how to implement receive beamforming. However, the receive side of the ultrasound system disclosed herein includes further processing. FIG. 1B shows an embodiment of the receiving side with a receive beamformer according to one embodiment of the ultrasound system (100) disclosed herein. Backscattered ultrasound waves (105) from one point (103) impinge on an element (102) in the transducer array (101). The signal is then delayed. The delay at the receiver may correspond to the time difference of the received signals at the element (102). The ultrasound system may further include a processing unit (106), which may be integrated or connected to the transducer in any suitable manner. The processing unit may be configured to calculate a local phase parameter in the time domain for each of the multiple backscattered ultrasound signals. The processing unit may be further configured to calculate a center frequency for each of the local phase parameters of the backscattered ultrasound signals in the time domain. More specifically, the local phase parameter and the center frequency may be calculated for each sample at each element. If the transducer includes, for example, 64 elements and 2048 samples are received, the processing unit may be configured to calculate 2048×64 local phase parameters and centre frequencies.In one embodiment, the processing unit is configured to calculate a local phase parameter in the time domain for each sample in each of the plurality of backscattered ultrasound signals. The processing unit may be further configured to calculate a center frequency for all of the calculated phase parameters. The ultrasound system may further comprise a receive beamformer (107) configured to perform receiver beamforming by summing the center frequencies. The beamformer may be implemented in hardware, software or a combination thereof. Based on the summed center frequencies and preferably a model of the region of interest, the processing unit may be further configured to generate at least one parameter representative of a physical property of the region of interest.

[0015] Although it may be said to break common practice in ultrasound systems, by calculating the center frequency before receive beamforming is performed, the frequency data is more accurate than if the frequency calculation is performed after receive beamforming. Thus, the ultrasound system may be configured to calculate the local phase parameters and calculate the center frequency before performing receiver beamforming. "Center frequency" is to be interpreted broadly to encompass scenarios in which the center frequency is multiplied by a factor. It may be assumed that the local phase parameters in the time domain for each of the multiple backscattered ultrasound signals are calculated before beamforming, whereas the center frequency for each local phase parameter is calculated after beamforming. Thus, the processing unit may be configured to calculate the local phase parameters in the time domain for each of the multiple backscattered ultrasound signals.

[0016] The beamformer can be configured to perform receiver beamforming by summation of local phase parameters. The processing unit can then calculate a center frequency for the summed local phase parameters. In one embodiment, the samples summed in the beamforming process are weighted according to the amplitude of the backscattered ultrasound signal before the center frequency is calculated from the phase parameters.

[0017] In one embodiment, the ultrasound system is configured to calculate or compute a variance of the summed center frequencies over at least a portion of the region of interest. The inventors have found that if the center frequencies are calculated before performing receive beamforming, the variance of the summed center frequencies can be used to characterize tissue in the region of interest.

[0018] Preferably, the processing unit is configured to calculate a center frequency for each of the local phase parameters of the backscattered ultrasound signal in the time domain. Thus, the processing unit may be configured to calculate the center frequency based on the backscattered ultrasound signal without frequency transformation. The beamformer can then sum the center frequencies, preferably only the center frequencies. The system and method may be based on the assumption that the backscattered pulse is Gaussian shaped.

[0019] According to one embodiment, the ultrasound system is an ultrasound system for characterizing tissue, where the ultrasound transducer is configured to transmit a plurality of ultrasound signals from a plurality of elements in a transducer array to a region of interest in the tissue, and the system is further configured to characterize the tissue based on a summed center frequency. Backscattered ultrasound energy depends on tissue properties, such as cell / structure size, shape, and density, related to the wavelength and propagation direction of the sound. As a result, the frequency content of the backscattered pulse depends on the properties of the tissue microstructure. Therefore, the ultrasound system may be further configured to estimate structure size using the backscattered center frequency.

[0020] According to a further embodiment, the ultrasound system is an ultrasound system for characterizing arterial walls and atherosclerotic plaques, the ultrasound transducer is configured to transmit a plurality of ultrasound signals from a plurality of elements in a transducer array to a region of interest in at least one arterial wall, and the ultrasound system is further configured to characterize atherosclerotic plaques in the at least one arterial wall based on the summed center frequency. Other applications are possible, including, but not limited to, characterization of myocardium, characterization of breast lesions, thyroid lesions, prostate lesions, detection of micrometastases in resected lymph nodes, as well as quantification of hepatic steatosis and detection of cervical ripening.

[0021] The ultrasound system is configured to generate at least one parameter representing a physical characteristic of the region of interest based on the summed center frequency and a model of the region of interest. The model of the region of interest may be a physical model that includes information about backscattering for different structures in the region of interest. A person skilled in the art would be able to implement such a model, which may be a physical model of the structure that includes a mathematical description of how the material and / or size of the structure scatters ultrasound, in particular how the backscattered center frequency correlates with the radius of the scatterer. Figure 5 shows examples of center frequency shifts for structures (108) of various sizes. The transducer (101) is configured to transmit ultrasound signals and receive backscattered ultrasound signals.

[0022] The ultrasound system may be an ultrasound imaging device. A useful method of presenting the center frequency, or the center frequency shift, or other parameters generated from the center frequency, may use images, such as frequency images, in which colors or grayscales represent different frequencies. In such an embodiment, the ultrasound system may further comprise a display for displaying at least one image of the region of interest. The at least one image may include a representation of the size of structures in the region of interest that reflect multiple ultrasound signals. The processing unit may further be configured to calculate and / or extract the size of the structures based on the summed center frequencies. It may not be necessary to present an image to the user. Alternatively, the system may be configured to generate the frequencies, for example, in the form of a list, table, or database, from which further parameters may be derived. Furthermore, the image may include a representation in which arterial plaque is characterized, the image including a translated representation of the structure or composition of atherosclerotic plaque and / or risks associated with arterial plaque, for example represented as a color map. FIG. 4 shows a comparison of ultrasound images of plaque using a conventional ultrasound system, where frequency analysis / processing is performed after beamforming (A) and after using the ultrasound system of the present disclosure (B). As can be seen, the ultrasound system of the present disclosure provides greater accuracy, which may be perceived as improved spatial resolution. The processing unit may be configured to estimate the size of cells or components, such as fibers and / or non-cellular material, in the region of interest based on the summed center frequencies.

[0023] In one embodiment, the ultrasound system is configured to determine tissue composition, preferably carotid plaque composition, based on the summed central frequency. The tissue composition or carotid plaque composition may include a quantitative value of a physical property of the arterial wall, such as a percentage or proportion of the arterial wall, a size of cells and / or structures, or a quantified diagnostic value, such as a calculated plaque risk score. The ultrasound system may be configured to detect plaque components associated with a risk of plaque rupture. It has been found that a correlation exists between the central frequency shift and the amount of collagen and smooth muscle cells (in positive cases) and macrophages and core size (in negative cases). These plaque characteristics are consistent with the description of stable plaque and vice versa.

[0024] The elements arranged in the array of the transducer are typically configured to generate one line of an image. Thus, the ultrasound system can be configured to generate a line of an image based on the summed center frequency and a model of the region of interest. If this process is repeated, i.e., multiple ultrasound signals are transmitted, local phase parameters and center frequencies are calculated, and receiver beamforming is performed, a full image including multiple lines can be generated. The transducer probe in the example of FIG. 1A includes seven elements (102) configured to transmit ultrasound signals. A typical transducer may have, for example, 64, 192, 256 or 512 elements arranged in a row. The transducer may also have elements arranged in an array of m×n elements, i.e., m elements in one direction and n elements in the other direction. These elements may be piezoelectric elements configured to convert electrical signals into ultrasound signals and backscattered ultrasound signals into received electrical signals that are further processed by a processing unit. FIG. 1B shows the receiver side, where the seven elements (102) are configured to convert ultrasound into electrical signals. Additionally, the ultrasound system can be configured to repeat the processes of transmitting multiple ultrasound signals, receiving multiple backscattered ultrasound signals, and processing the received multiple backscattered ultrasound signals for multiple focal lengths.

[0025] The local phase parameters may typically be calculated by converting the multiple backscattered ultrasound signals into a complex representation of the backscattered ultrasound signals, for example by computing a Hilbert transform or quadrature demodulation. Using the complex data, the time domain phase difference between samples in the backscattered data can be obtained and used to estimate the center frequency. One method is to measure the phase derivative, usually referred to as the instantaneous frequency. Another commonly used method to derive the phase difference is the complex autocorrelation method.

[0026] Center Frequency Calculation Example The center frequency can be calculated according to the following example: A number of samples are collected at each element of the transducer array, for example a vector of n=1 to m. sampleHT = Hilbert transform of the sample, sampleComplex(n) = sample(n) + i*sampleHT(n), sampleConj(n)=sampleComplex(n)*conj(sampleComplex(n-1)), where conj is the conjugate [each sample in sampleConj may be averaged with several adjacent samples], Phase difference between samples = PD = arctan(IMAG(sampleConj) / REAL(sampleConj)), where arctan is the four-quadrant arctangent, IMAG is the imaginary part, and REAL is the real part. Center frequency=PD / (2*pi)*Fs, where Fs is the sampling frequency of the samples.

[0027] ultrasound method The present disclosure further relates to an ultrasound method for generating at least one parameter representative of a physical property of a region of interest. Figure 2 illustrates an embodiment of an ultrasound method (200) disclosed herein. In an embodiment, the ultrasound method (200) includes: Transmitting a plurality of ultrasound signals from a plurality of elements of a transducer array into a region of interest (201); Receiving and sampling a plurality of backscattered ultrasound signals from a region of interest (202); Calculating (203) a local phase parameter in the time domain for each of the plurality of backscattered ultrasound signals; Calculating (204) a center frequency for each of the local phase parameters of the backscattered ultrasound signal in the time domain; performing receiver beamforming by summing center frequencies (205); and generating (206) at least one parameter representative of a physical characteristic of the region of interest based on the summed center frequencies.

[0028] Preferably, the step of calculating the centre frequency occurs prior to the step of performing receiver beamforming. The steps of the method may be performed sequentially. Preferably, the method includes the step of performing transmit beamforming.

[0029] Further details of the invention 1. An ultrasound system comprising: an ultrasound transducer configured to transmit a plurality of ultrasound signals from a plurality of elements in a transducer array into a region of interest, the ultrasound transducer being further configured to receive and sample a plurality of backscattered ultrasound signals from the region of interest; A processing unit comprising: calculating a local phase parameter in the time domain of each or group of the plurality of backscattered ultrasound signals; the processing unit configured to calculate a center frequency for each of the local phase parameters of the backscattered ultrasound signal in the time domain; a beamformer configured to perform receiver beamforming by summing the center frequencies; The ultrasound system is further configured to generate at least one parameter indicative of a physical characteristic of the region of interest based on the summed center frequencies.

[0030] 2. The ultrasound system of item 1, wherein the ultrasound system is an ultrasound system for characterizing tissue, the ultrasound transducer is configured to transmit multiple ultrasound signals from multiple elements in a transducer array to a region of interest in the tissue, and the system is further configured to characterize the tissue based on the summed center frequency.

[0031] 3. The ultrasound system of any one of the preceding items, wherein the ultrasound system is an ultrasound system for characterizing atherosclerotic plaque, the ultrasound transducer being configured to transmit multiple ultrasound signals from multiple elements in a transducer array to a region of interest in at least one arterial wall, and the ultrasound system is further configured to characterize the atherosclerotic plaque in the at least one arterial wall based on the summed center frequency.

[0032] 4. An ultrasound system as described in any one of the preceding items, wherein the ultrasound system is configured to generate at least one parameter representative of a physical property of the region of interest based on the summed center frequency and a model of the region of interest.

[0033] 5. The ultrasound system of item 4, wherein the model of the region of interest is a physical model that includes information about backscattering for different structures in the region of interest.

[0034] 6. The ultrasound system of any one of the preceding claims, wherein the ultrasound system is further configured to generate lines of an image based on the summed center frequencies.

[0035] 7. The ultrasound system of item 6, wherein the ultrasound system is configured to repeat the transmission of multiple ultrasound signals and the calculation of local phase parameters and center frequencies, and to perform receiver beamforming to generate an image including multiple lines.

[0036] 8. The ultrasound system of any one of the preceding items, wherein the ultrasound system is configured to calculate the local phase parameters and calculate the center frequency before performing the receiver beamforming.

[0037] 9. The ultrasound system of any one of the preceding claims, wherein the ultrasound system is further configured to determine plaque composition, such as carotid plaque composition, based on the summed central frequencies.

[0038] 10. The ultrasound system of item 9, wherein the carotid artery plaque composition comprises a quantitative value of a physical property of the arterial wall, such as a percentage or proportion of the arterial wall, a size of cells and / or structures, or a quantified diagnostic value, such as a calculated plaque risk score.

[0039] 11. The ultrasound system of any one of the preceding items, wherein the ultrasound transducer includes a piezoelectric element configured to convert an electrical signal into an ultrasound signal and to convert the backscattered ultrasound signal into a received electrical signal, further processed by the processing unit.

[0040] 12. The ultrasound system of any one of the preceding claims, further comprising a display for displaying at least one image of the region of interest.

[0041] 13. The ultrasound system of any one of the preceding items, wherein the at least one image includes a representation of a size of structures within the region of interest that reflect the multiple ultrasound signals.

[0042] 14. The ultrasound system of claim 13, wherein the processing unit is further configured to calculate and / or extract a size of the structure based on the summed center frequencies.

[0043] 15. An ultrasound system according to any one of the preceding items, wherein the processing unit is configured to estimate a size of cells or components, e.g., fibers and / or non-cellular material, in the region of interest based on the summed central frequencies.

[0044] 16. The ultrasound system of any one of the preceding items, wherein the processing unit is configured to calculate the center frequency based on the backscattered ultrasound signal without frequency conversion.

[0045] 17. The ultrasound system of any one of the preceding claims, wherein the beamformer is configured to sum only the center frequencies.

[0046] 18. An ultrasound system as described in any one of the preceding items, wherein the ultrasound system is configured to repeat the processes of transmitting the plurality of ultrasound signals, receiving the plurality of backscattered ultrasound signals, and processing the received plurality of backscattered ultrasound signals for a plurality of focal lengths.

[0047] 19. An ultrasound system according to any one of the preceding items, wherein the local phase parameters are calculated by converting the plurality of backscattered ultrasound signals into a complex representation of the backscattered ultrasound signals, preferably by calculating a Hilbert transform.

[0048] 20. The ultrasound system of claim 19, wherein the center frequency is calculated based on the complex representation.

[0049] 21. An ultrasound method comprising: Transmitting a plurality of ultrasound signals from a plurality of elements of a transducer array into a region of interest; receiving and sampling a plurality of backscattered ultrasound signals from the region of interest; calculating a local phase parameter in the time domain for each of the plurality of backscattered ultrasound signals; calculating a center frequency for each of the local phase parameters of the backscattered ultrasound signal in the time domain; performing receiver beamforming by summing said center frequencies; generating at least one parameter representative of a physical property of the region of interest based on the summed center frequencies.

[0050] 22. The ultrasound method of claim 21, wherein the steps are continuous.

[0051] 23. The ultrasound method according to any one of items 21 to 22, wherein the step of calculating the central frequency is performed before the step of performing receiver beamforming.

[0052] 24. An ultrasound system comprising: an ultrasound transducer configured to transmit a plurality of ultrasound signals from a plurality of elements in a transducer array into a region of interest, the ultrasound transducer being further configured to receive and sample a plurality of backscattered ultrasound signals from the region of interest; a processing unit configured to calculate a local phase parameter in the time domain for each of the plurality of backscattered ultrasound signals; a beamformer configured to perform receiver beamforming by summing the local phase parameters; The processing unit includes: and further configured to calculate a center frequency for each of the local phase parameters of the backscattered ultrasound signal in the time domain; The ultrasound system is further configured to generate at least one parameter indicative of a physical characteristic of the region of interest based on the summed center frequencies.

Claims

**Claim 1** An ultrasonic system, an ultrasonic transducer configured to transmit a plurality of ultrasonic signals from a plurality of elements in a transducer array to a region of interest, the ultrasonic transducer further configured to receive and sample a plurality of backscattered ultrasonic signals from the region of interest, a processing unit, calculating a local phase parameter in the time domain for each of the plurality of backscattered ultrasonic signals, calculating a center frequency for each of the local phase parameters of the backscattered ultrasonic signals in the time domain configured processing unit, a beamformer, An ultrasonic system comprising, the beamformer is configured to perform receiver beamforming by summing the center frequencies, the ultrasonic system is further configured to generate at least one parameter representing a physical characteristic of the region of interest based on the summed center frequencies characterized in that, the ultrasonic system is configured to calculate the local phase parameter and calculate the center frequency before performing the receiver beamforming. **Claim 2** The ultrasonic system according to any one of the preceding claims, wherein the ultrasonic system is configured to calculate or compute a dispersion of the summed center frequencies over at least a portion of the region of interest. **Claim 3** The ultrasonic system is an ultrasonic system for characterizing atherosclerotic plaques, the ultrasonic transducer is configured to transmit a plurality of ultrasonic signals from a plurality of elements in a transducer array to a region of interest within at least one arterial wall, and the ultrasonic system is based on the summed center frequencies and / or based on a dispersion of the summed center frequencies. The ultrasonic system according to any one of the preceding claims, further configured to characterize the atherosclerotic plaque within the at least one arterial wall. **Claim 4** The ultrasonic system is an ultrasonic system for characterizing tissue, the ultrasonic transducer being configured to transmit a plurality of ultrasonic signals from a plurality of elements in a transducer array to a region of interest in the tissue, the ultrasonic system being further configured to characterize the tissue based on the summed center frequency and / or based on the variance of the summed center frequency, the ultrasonic system according to any one of the preceding claims.

5. The ultrasonic system is configured to generate at least one parameter representing a physical characteristic of the region of interest based on the summed center frequency and a model of the region of interest, the model of the region of interest being a physical model comprising information regarding backscattering for different structures within the region of interest, the ultrasonic system according to any one of the preceding claims.

6. The ultrasonic system is further configured to determine a plaque composition, such as a carotid plaque composition, based on the summed center frequency and / or based on the variance of the summed center frequency, the ultrasonic system according to any one of the preceding claims.

7. The at least one image comprises a representation of the size of a structure within the region of interest that reflects the plurality of ultrasonic signals, the ultrasonic system according to any one of the preceding claims.

8. The processing unit is further configured to calculate and / or extract the size of the structure based on the summed center frequency, the ultrasonic system according to claim 7.

9. The processing unit is configured to calculate the center frequency based on the backscattered ultrasonic signals without frequency conversion, the ultrasonic system according to any one of the preceding claims.

10. The beamformer is configured to sum only the center frequency, the ultrasonic system according to any one of the preceding claims.

11. The ultrasonic system is configured to repeat a process of transmitting the plurality of ultrasonic signals, a process of receiving the plurality of backscattered ultrasonic signals, and a process of processing the received plurality of backscattered ultrasonic signals with respect to a number of focal distances, the ultrasonic system according to any one of the preceding claims.

12. The local phase parameter is calculated by converting the plurality of backscattered ultrasonic signals into a complex representation of the backscattered ultrasonic signals, preferably by calculating a Hilbert transform, according to any one of the preceding claims, for an ultrasonic system.

13. An ultrasonic method, comprising: transmitting a plurality of ultrasonic signals from a plurality of elements of a transducer array to a region of interest; receiving and sampling a plurality of backscattered ultrasonic signals from the region of interest; calculating a local phase parameter in the time domain for each of the plurality of backscattered ultrasonic signals; calculating a center frequency for each of the local phase parameters of the backscattered ultrasonic signals in the time domain; performing receiver beamforming by summing the center frequencies; generating at least one parameter representing a physical characteristic of the region of interest based on the summed center frequencies; An ultrasonic method, comprising: The steps of calculating the local phase parameter and calculating the center frequency are performed before the step of performing the receiver beamforming.

14. An ultrasonic system, comprising: an ultrasonic transducer configured to transmit a plurality of ultrasonic signals from a plurality of elements in a transducer array to a region of interest, the ultrasonic transducer being further configured to receive and sample a plurality of backscattered ultrasonic signals from the region of interest; a processing unit, configured to calculate a local phase parameter in the time domain for each of the plurality of backscattered ultrasonic signals; A processing unit configured as such; a beamformer configured to perform receiver beamforming by summing the local phase parameters; Comprising: The processing unit, is further configured to calculate a center frequency for each of the local phase parameters of the backscattered ultrasonic signals in the time domain; Further configured as such; The ultrasonic system is further configured to generate at least one parameter representing a physical characteristic of the region of interest based on the summed center frequencies. The ultrasonic system is configured to calculate the local phase parameter and calculate the center frequency before performing the receiver beamforming. An ultrasonic system, characterized by...

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