METHOD AND SYSTEM FOR EVALUATING AN ASSUMED WAVE PROPAGATION SPEED IN A MEDIUM

Abstract

The invention relates to a method of evaluating an assumed wave propagation speed in a medium, the medium being associated with spatio-temporal signal data, wherein the method comprises:

evaluating (e) the assumed wave propagation speed based on phase properties of the spatio-temporal signal data.

Claims

1. A method of evaluating an assumed wave propagation speed in a medium, the medium being associated with spatio-temporal signal data, the method comprising: evaluating assumed wave propagation speed based on phase properties of the spatio-temporal signal data.

2. The method according to claim 1, wherein the spatio-temporal signal data comprises one of pre-beamformed spatio-temporal signal data and radiofrequency data.

3. The method according to claim 1, wherein the phase properties comprise at least one of: signs, phases, a sign proportion, phase intervals, phase evolution states, and proportions of phase properties.

4. The method according to claim 1, further comprising: determining a figure of merit of the assumed wave propagation speed based on the phase properties, wherein evaluating the assumed wave propagation speed is based on the figure of merit.

5. The method according to claim 4, wherein the figure of merit is determined by using a predefined function G, the predefined function G being at least one of: a function G(x) that is symmetric about the axis x=50%, configured to one of maximize at x=50% and minimize at x=0% and x=100%, and to minimize at x=50% and maximize at x=0% and x=100%. a bell-shaped function, a normal distribution function, and a negative Shannon entropy function.

6. The method according to claim 1, wherein the spatio-temporal signal data are associated with a predefined spatial region in the medium.

7. The method according to claim 1, further comprising: determining a subset of the spatio-temporal signal data as a function of a predefined spatial region in the medium and the assumed wave propagation speed, wherein the assumed wave propagation speed is evaluated based on the subset.

8. The method according to claim 7, wherein the subset comprises sections of the oscillating signals, wherein the sections are selected with respect to each other as a function of the spatial region and the assumed wave propagation speed.

9. The method according to claim 6, wherein the method is iterated, in parallel or in series, for a plurality of subsets, each one being associated with a different spatial region in the medium, wherein the assumed wave propagation speed is evaluated based on figures of merit of the plurality of subsets.

10. The method according to claim 9, wherein at least one of: the assumed wave propagation speed is evaluated based on figures of merit of selected subsets which are above a predefined threshold, and the assumed wave propagation speed is evaluated based on weighted figures of merit according to a predefined weighting function.

11. The method according to claim 1, wherein the method is carried out for a plurality of different assumed wave propagation speeds, and wherein the method further comprises: estimating an actual wave propagation speed in the medium based on the assumed wave propagation speed having the best figure of merit.

12. The method according to claim 1, further comprising: adjusting the assumed wave propagation speed, as a function of the figure of merit, wherein the method is iterated, such that the figure of merit is increased, wherein the method comprises in each iteration an adjusted wave propagation speed.

13. The method according to claim 12, wherein at least one of: evaluating the assumed wave propagation speed comprises comparing the figure of merit with a predefined threshold, the method is iterated until the figure of merit is above a predefined threshold, and the method further comprises: estimating an actual wave propagation speed in the medium, based on the assumed wave propagation speed having the best figure of merit.

14. The method according to claim 1, wherein the plurality of signals is received by a respective plurality of transducer elements.

15. The method according to claim 1, further comprising before determining one of the subset the figure of merit: transmitting a pulse into the medium, and receiving in response the plurality of signals from the medium.

16. A method of estimating a wave propagation speed in a medium, comprising a method according to claim 11.

17. A computer program comprising computer-readable instructions which when executed by a data processing system cause the data processing system to carry out the method according to claim 1.

18. A system for evaluating an assumed wave propagation speed in a medium, the medium being associated with spatio-temporal signal data, wherein the system comprises a processing unit configured to: evaluate the assumed wave propagation speed based on the spatio-temporal signal data.

19. The method of claim 2, wherein the spatio-temporal signal data comprises at least one of a plurality of oscillating signals and periodic signals received from the medium.

20. The method of claim 2, wherein the spatio-temporal signal data comprises sections of the plurality of oscillating signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] FIG. 1 shows a schematic drawing showing an ultrasound system according to examples of the present disclosure; and

[0072] FIG. 2 shows a diagram of a method of evaluating an assumed wave propagation speed in a medium according to the present disclosure, the method may be implemented in the system of FIG. 1;

[0073] FIG. 3 shows a first example of evaluating an assumed wave propagation speed based on phase properties, which may for example be implemented in the system of FIG. 1 and/or according to the method of FIG. 2;

[0074] FIG. 4 shows figures of merit determined as a function of a plurality of assumed wave propagation speeds according to an example of the present disclosure; and

[0075] FIG. 5 shows a plurality of different phase properties that may be used according to examples of the present disclosure.

DESCRIPTION OF THE DRAWINGS

[0076] Reference will now be made in detail to examples of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. The system 100 shown on FIG. 1 is adapted for evaluating an assumed wave propagation speed in a medium 10, for instance living tissues and in particular human tissues of a person, for example a sporty professional and/or a patient. The system may include for instance:

[0077] A plurality of transducer elements 21. The transducer elements may be configured to transmit (a) a pulse into the medium and/or to receive (b) a plurality of signals from the medium, optionally in response to transmitting (a) the pulse into the medium. A transducer array comprising a plurality of transducer elements 21 may be used. For example, a linear array 20 may be provided typically including a few tens of transducer elements (for instance 100 to 300) juxtaposed along an axis X (horizontal or array direction X) as already known in usual probes. In this example, the array 20 is adapted to perform a bidimensional (2D) imaging of the medium 10, but the array 20 could also be a bidimensional array adapted to perform a 3D imaging of the medium 10. The transducer array 20 may also be a convex array including a plurality of transducer elements aligned along a curved line. The same transducer element(s) may be used to transmit a pulse and receive the response, or different transducer elements are used for transmission and reception. There may be one or more emitting transducer elements and a plurality of receiving transducer elements. In a further alternative, only a single transducer element may be used which receives a plurality of signals which have different spatial properties (for example originating from different spatial regions). The transducer element may for instance be electronically or physically moveable; an electronic bay 30 controlling the transducer array and acquiring signals therefrom. The system may further include a microcomputer (not shown) for controlling the electronic bay 30 and/or for example for sending data to a server, to an artificial intelligence (AI) entity, to a dedicated workstation, presenting data, displaying/viewing images obtained from the electronic bay (in a variant, a single electronic device could fulfil all the functionalities of the electronic bay 30 and the microcomputer).

[0078] The transducer elements 21 may comprise piezo-crystals and/or other components that may be configured to generate and/or record and/or receive signals. The terms transducer and transducer elements may be used synonymously throughout this disclosure unless denoted differently.

[0079] Transducer elements 21 may be configured to generate and/or record and/or receive signals, optionally ultrasonic signals. Transducer elements 21 and/or electronic bay 30 and/or the microcomputer may be configured to determine phase properties of spatio-temporal signal data.

[0080] The axis Z on FIG. 1 is an axis perpendicular to the axis X, for example in the depth direction of the examined medium. This direction is designated in the present document as a vertical or axial direction.

[0081] The medium 10 may comprise a spatial region 40. The spatial region 40 may be predefined and/or may be selected during operation of methods according to examples of the present disclosure. The medium 10 may comprise a plurality of spatial regions 40.

[0082] The medium 10 may optionally comprise one or more regions of interest 42. Spatial regions 40 optionally may be comprised only in one or more regions of interest 42. Spatial regions 40 may be located in the medium at various positions not necessarily restricted to specific regions of interest 42. The whole medium or a part of the medium may be the region of interest 42. For example, only regions corresponding to regions in beamformed image data corresponding to the medium and/or the region corresponding to the entire beamformed image data may be regions of interest 42. For example, in case of a tumor, it may be most interesting to evaluate an assumed wave propagation speed in the supposed tumor region while the remaining tissue may be of minor interest.

[0083] The system herein disclosed is a device for ultrasound imaging, the transducer elements are ultrasound transducer elements, and the implemented method evaluates an assumed wave propagation speed in the medium 10 based on phase properties of spatio-temporal signal data. The medium 10 is associated with the spatio-temporal signal data. The method optionally may produce ultrasound images of the medium 10 and/or of spatial regions 40 of the medium 10 and/or may send data to a dedicated server or working station.

[0084] However, the system may be any imaging or sensor device using other waves than ultrasound waves (for example waves having a wavelength different than an ultrasound wavelength and/or waves being no sound waves), the transducer elements and the electronic bay components and related elements being then adapted to said waves.

[0085] FIG. 2 shows a diagram of a method of evaluating an assumed wave propagation speed in a medium according to the present disclosure. The method may be implemented in the system of FIG. 1.

[0086] The method may comprise an optional operation of transmitting (a) a pulse into the medium. For example, the transmission operation may comprise insonification of the medium with a cylindrical wave that focuses on a given point and/or plane waves of different angles. More in particular, during the transmission operation a plurality of ultrasonic waves may be transmitted into a spatial region 40.

[0087] Generally, in the present disclosure a pulse may correspond to an acoustic and/or electrical signal emitted by a transducer element. The pulse may for example be defined by at least one of: the pulse duration, the frequency of the resulting wave, the number of cycles at the given frequency, the polarity of the pulse, etc. A wave may correspond to the wavefront generated by one or several transducer elements (i.e. by respectively emitted pulses). The wave may be controlled by means of emission delay between the different used transducer elements. Examples comprise a plane wave, a focused wave and a divergent wave. A beam may correspond to the physical area insonified by the wave (for example in the medium). Hence, the beam may be related to the wave but may have less or no temporal notion. For example, it may be referred to a beam when the depth of field of a focused beam is of interest.

[0088] In an optional operation (b), a plurality of signals may be received, optionally in response, from the medium by the plurality 20 of transducer elements 21. The plurality of signals may comprise backscattered echoes of the transmission of operation (a). The response sequence may also be referred to as spatio-temporal data and/or signal data, in particular ultrasound signal data and/or RF and/or IQ signal data. The signal data may be in the time domain, more in particular in a spatio-temporal domain, as for example described in more detail below. In one example, the response sequence may be processed by bandpass filtering, in order to keep only one or several frequency ranges.

[0089] It is noted that operations (a) to (b) are optional, as they may also be carried out by any other system than the system used for operation (e) and optional operations (c), (d), (f), (g) and/or at another time. Data may also be provided by other functionalities such as simulation devices, insonification on a phantom, etc. It is also possible that the spatio-temporal signal data are pre-stored, and for example provided by/read on a data storage, a communication interface, etc.

[0090] In an optional operation (c), a subset of the spatio-temporal signal data may be determined as a function of a predefined spatial region 40 in the medium 10 and as a function of the assumed wave propagation speed. For example, data in the subset corresponding to a specific spatial region 40 in the medium 10 may be determined based on the assumed propagation time of a signal between the spatial region 40 and respective transducer elements 10. The assumed propagation times may be determined based on the location of the spatial region 40 and the location of the plurality of transducers and/or each respective transducers, optionally in relation to the location of the spatial region 40, and the assumed wave propagation speed. Determining a subset of the spatio-temporal signal data as a function of a predefined spatial region 40 in the medium 10 and as a function of the assumed wave propagation speed may be based on the geometry of the plurality 20 of transducers 21. It is noted that the spatial region may be associated with a pixel or a plurality of pixels in beamformed image data. The optional beamforming process may be done in an optional operation after operation (g).

[0091] As described above, spatial regions 40 optionally may be comprised only in one or more regions of interest 42. Spatial regions 40 may be located in the medium at various positions not restricted to specific regions of interest 42. The whole medium or a part of the medium may be the region of interest 42. For example, only regions corresponding to regions in beamformed image data corresponding to the medium and/or the region corresponding to the entire beamformed image data may be regions of interest 42. For example, in case of a tumor, it may be most interesting to evaluate an assumed wave propagation speed in the supposed tumor region while the remaining tissue may be of minor interest.

[0092] Methods of the present disclosure may also be used for estimating a spatial extent of a region of interest, for example a tumor. One or more regions of interest may be indicated by a user and/or selected automatically (for example by an artificial intelligence), optionally based on historic data that for example may have been generated during earlier examinations.

[0093] In an optional operation (d), a figure of merit of an assumed wave propagation speed may be determined, based on the phase properties. For example, an entropy of phase properties may be computed, for example a negative Shannon entropy of sign proportions.

[0094] In operation (e), the assumed wave propagation speed is evaluated based on phase properties of the spatio-temporal signal data. The operation (e) may be based on the figure of merit optionally determined in operation (d). Operation (e) may be performed after one or several iterations of operation (d) (for example, each operation (d) may be carried out for a different subset).

[0095] It may be desirable to evaluate an assumed wave propagation speed as a function of a plurality of predefined spatial regions. For example, some spatial regions 40 may not constitute good reflectors and may therefore not be well suited for evaluating an assumed wave propagation speed. Furthermore, using a plurality of predefined spatial regions may allow to decrease the uncertainty of the propagation speed evaluation due to better statistics. In examples of the invention, a pre-defined spatial region may correspond to a pixel and/or a plurality of pixels in beamformed image data corresponding to the medium 10. Accordingly, operation (e) and optional operations (c) and (d) may be repeated in a first loop L1. As such, another spatial region in the medium 10 may be chosen in each iteration or in some iterations.

[0096] It may also be desirable to evaluate a plurality of assumed wave propagation speeds, for example to estimate an actual wave propagation speed in the medium. In an optional operation (f), the assumed wave propagation speed may be adjusted. The assumed wave propagation speed may be adjusted as a function of the figure of merit.

[0097] Operations (e) and optional operations (c), (d) and (f) may be repeated in a second loop L2. A different wave propagation speed may be assumed in each iteration and/or in some iterations.

[0098] It should be noted that various combinations of loops L1 and L2 may be possible. For example, loops L1 and L2 may performed in arbitrary order. For example, it is possible to first assume a wave propagation speed and to then perform loop L1, for example iterating operation (e) and optionally optional operations (c) and (d) for a plurality of (optionally predefined) spatial regions. Loop L2 may be performed subsequently, for example operation (e) and optional operations (c) and (d) may be iterated for a plurality of (optionally predefined) spatial regions in loop L1, then a different wave propagation speed may be assumed, for example in operation (f), for example in loop L2, and operation (e) and optional operations (c) and (d) may then be iterated again for a plurality of (optionally predefined) spatial regions in L1. Loop L2 may then be iterated for a plurality of assumed wave propagation speeds.

[0099] It is also possible to first perform operation (e) and optionally optional operations (c), (d), and (f) for a predetermined spatial region for a plurality of assumed wave propagation speeds in loop L2. Loop L1 may be performed afterwards, for example operations (e) and optional operations (c), (d), and (f) may be repeated for a different spatial region in loop L2 and for a plurality of assumed wave propagation speeds in loop L1. Loop L1 may be iterated for a plurality of spatial regions in the medium.

[0100] For example, it is possible to vary assumed wave propagation speeds in iterations while remaining at one predetermined spatial region, to then select another predetermined spatial region and to vary assumed wave propagation speeds again in iterations. It is also possible to remain at one assumed wave propagation speed, to select different spatial regions in iterations, to then assume a different wave propagation speed and to select different spatial regions again in iterations.

[0101] Various more combinations of loops L1 and L2 of the respective optional operations (c), (d), and (f) and the operation (e) are readily apparent for the skilled person. The skilled person may combine above operations as appropriate, optionally for example as a function of figures of merit, without deviating from the present disclosure.

[0102] The terms “repeat” and “iterate” may be used synonymously throughout this disclosure unless denoted differently.

[0103] In optional operation (g), an actual wave propagation speed in the medium may be estimated, optionally based on the assumed wave propagation speed having the best figure of merit and/or the best evaluation of the assumed wave propagation speeds. For example, the assumed wave propagation speed having the best figure of merit and/or the best evaluation of the assumed wave propagation speeds may be the estimated actual wave propagation speed.

[0104] An optional beamforming process may be performed after operation (g) and may be based on the propagation speed estimated in operation (g).

[0105] FIG. 3 shows a first example of evaluating (e) an assumed wave propagation speed based on phase properties, which may be implemented in the system of FIG. 1 and/or according to the method of FIG. 2. A plurality 20 of transducer elements 21 are displayed on the top. Spatio-temporal signal data 50 are indicated below. The spatio-temporal signal data comprise a plurality of signals respectively received by the plurality of transducer element elements 21 during a period of time. Specific subsets 51 of each signal are schematically illustrated. The subsets 51 are located along a dotted line 60. The dotted line 60 may be theoretical line and/or an imaginary line and/or may be understood as an illustration, for example as an illustration of operation (c) of determining a subset of spatio-temporal signal data as a function of a predefined spatial region 40 in the medium 10. The shape of the dotted line is related to an actual wave propagation speed in the medium. The shape of the dotted line 60 may be related to the location of a spatial region in the medium reflecting a transmitted ultrasonic pulse. The dotted line 60 may be precomputed. In other words, the sections of the signals covered by the dotted line may be associated with the spatial region. Based on said sections, a pixel of beamformed image data may be calculated in an optional beamforming operation.

[0106] Operation (c) of determining a subset of the spatio-temporal signal data as a function of a predefined spatial region in the medium and the assumed wave propagation speed may be understood as corresponding to drawing/determining/building the dotted line 60 in FIG. 3. Accordingly, by changing the assumed wave propagation speed, also the shape of the dotted line (and hence the covered signal sections) is changed. Phase properties of the respective individual signals along the dotted line may be compared to each other in the optional operation (d) of determining a figure of merit of the assumed wave propagation speed and/or the operation (e) of evaluating the assumed wave propagation speed based on phase properties of the spatio-temporal signal data.

[0107] For example, spatial temporal signal data, which may be RF data or pre-beamformed data, may comprise n signals from n transducer elements 21. Spatial temporal signal data 50 lying below (i.e. covered by) the dotted line 60 may correspond to sections of a plurality of oscillating signals, for example of the spatio-temporal signal data. Spatial temporal signal data 50 lying below the dotted line 60 may correspond to a subset of the spatio-temporal signal data 50 that may be associated with a predefined spatial region 40 in the medium 10. The subset may comprise one instance in time of a corresponding signal, for example of a signal corresponding to a respective transducer, and/or of a plurality of instances in time of a signal corresponding to a respective transducer. A figure of merit may be determined in operation (d) based on phase properties of the subset. For example, a sign proportion may be used as a figure of merit. For example, out of 100 signals corresponding to 100 respective transducers, 70 signals may exhibit a positive sign and 30 may exhibit a negative sign. A corresponding sign proportion of for example 70% may then be determined. An assumed wave propagation speed may then be evaluated based on the determined figure of merit, for example based on the sign proportion of 70%.

[0108] In other words, FIG. 3 may be interpreted as showing a dotted line 60 corresponding to a delay of signals from a predefined spatial region 40 in the medium 10, assuming an assumed wave propagation speed in the medium. An assumed wave propagation speed that is close or identical to an actual wave propagation speed in the medium 10 may result in similar and/or identical phase properties of individual signals of respective transducers 21 that correspond to areas indicated by the dotted line 60. A figure of merit may be determined based on comparing phase properties of respective individual signals corresponding to respective transducers 21.

[0109] FIG. 4 shows figures of merit determined as a function of a plurality of assumed wave propagation speeds according to an example of the present disclosure. For example, a sign proportion may be used as a figure merit. The best and/or highest figure of merit may then be determined for the assumed wave propagation speed at which most signals have the same sign, i. e. the highest number of signals being either positive or negative.

[0110] For determining the figures of merit in FIG. 4, the operations described with respect to FIG. 3, i. e. for example operation (e) and optionally optional operations (c) and (d), may be repeated for a plurality of assumed wave propagation speeds. Accordingly, the imaginary/hypothetical dotted line 60 may be determined based on the plurality of assumed wave propagation speeds.

[0111] The figures of merit may be maximized for an assumed wave propagation speed that may be close and/or closest to an actual wave propagation speed, as in such case phase properties of spatio-temporal signal data may for example exhibit a highest similarity.

[0112] In the optional operation (g), an actual wave propagation speed in the medium may be estimated, optionally based on the assumed wave propagation speed having the best figure of merit, for example the best figure of merit out of a plurality of figures of merit determined during iterations of operation (d). For example, an actual wave propagation speed in the medium may be estimated by the assumed wave propagation speed v1 having the best figure of merit in FIG. 4 and/or based on the assumed wave propagation speed v1 having the best figure of merit in FIG. 4. The best figure of merit may for example be determined by interpolating between respective figures of merits as a function of assumed wave propagation speeds and selecting the maximum interpolation value.

[0113] FIG. 5 shows a plurality of different phase properties of periodic signals that may be used for evaluating an assumed wave propagation speed according to examples of the present disclosure.

[0114] For example, the first diagram a) shows that signs of signal data may be used for evaluating an assumed wave propagation speed. Transducers 21 may comprise piezo-crystals and/or other objects that record and/or receive signals. Determining phase properties may require knowledge of only a single instance in time of respective signals. Thus, a fast, robust and cheap method of evaluating an assumed wave propagation speed in a medium may advantageously be provided according to examples.

[0115] The second diagram b) shows that finer categories than signs may be used. For example, positive and negative signs may be grouped according to whether the signal is ascending or descending. Corresponding categories are denoted by subscripts “asc” and “dsc” as appropriate. This may allow for a more precise evaluation of an assumed wave propagation speed and/or a more precise estimation of an actual wave propagation speed in a medium. Determining whether a signal is ascending or descending may require a knowledge of a plurality of instances in time of respective signals.

[0116] The third diagram c) shows that chosen intervals p1, p2, p3, p4 do not necessarily have to have the same size. Furthermore, they also do not need to be symmetric with respect to certain points of a signal, for example maximum/minimum points, inflection points and/or the rest position. For instance, any appropriate phase interval may be chosen. Phases of signals may be determined for example also by interpolation of recorded and/or received signals for example with periodic functions, such as sums of complex exponential functions and/or Fourier series. This may allow for an even more precise evaluation of an assumed wave propagation speed and/or a more precise estimation of an actual wave propagation speed in a medium.

[0117] According to the method of the present disclosure, a fast and automatic estimator of an actual wave propagation speed in a medium is provided. The estimation may be based on evaluating figures of merit of assumed wave propagation speeds, for examples entropies of sign proportions. Figures of merit may be determined based on spatio-temporal signal data associated with the medium. The spatio-temporal signal data may comprise per-channel samples of one or more or all pixels and/or spatial regions in beamformed image data corresponding to the medium. The figures of merit may be evaluated across the spatio-temporal signal data, for example across the per-channel samples. The figure of merit, for example an entropy of sign proprtions, may provide a quality measure of the alignment of delay wavefront which is optionally insensitive to wave shape or apodization. By minimizing entropy and/or maximizing the figure of merit, better alignment of delay wavefront may be achieved, from which an actual wave propagation speed may be estimated.

[0118] Examples of the present disclosure do not require specific types of emitted ultrasonic pulses. For example, a single planewave emission may be sufficient for carrying out optional operation (a).

[0119] Examples of the present disclosure may bear a light computational burden and may thus be used during real-time operations.

[0120] Examples of the present disclosure may advantageously be insensitive to wave shape or apodization. Example methods of the present disclosure may be performed in an automatic way.

[0121] Examples of the present disclosure may not rely on cross-correlation operators but may be based on phase properties of spatio-temporal signal data associated with the medium, for example sign proportions of spatio-temporal signal data, for example delay wave front. The computation burden may be much reduced accordingly.

[0122] Examples of the present disclosure may be insensitive to apodization, since the evaluation is based on phase properties, such as for example signs of signals, and may for example not be based on exact wave shapes.

[0123] Examples of the present disclosure may be extensible to depth-layer dependent speed estimation. Examples of the present disclosure may for example be able to work with any type of pulse transmitted into the medium during operation (a), for example focused beams.

[0124] More precise estimations of an actual wave propagation speed allow for a higher quality of beamformed image data which may be obtained by beamforming using the estimated actual wave propagation speed. A more precise estimation of an actual wave propagation speed may thus provide a higher signal-to-noise ratio (SNR) and/or a higher contrast and/or a higher spatial resolution.

[0125] Various other phase properties are known to the skilled person from the general knowledge of the skilled person. The present disclosure shall be construed as not being limited to the phase properties discussed above.

[0126] Furthermore, also various combinations of phase properties may be used. Methods described above may also be iterated, wherein different phase properties may for example be used in subsequent iterations. For example, one might start with broad categories, such as signs (cf. first diagram a), and iteratively apply finer categories, such as signs in combination with descending signals/ascending signals (cf. second diagram b) and/or appropriately chosen phase intervals (cf. third diagram c).

[0127] Throughout the description, including the claims, the term “comprising a” should be understood as being synonymous with “comprising at least one” unless otherwise stated. In addition, any range set forth in the description, including the claims should be understood as including its end value(s) unless otherwise stated. Specific values for described elements should be understood to be within accepted manufacturing or industry tolerances known to one of skill in the art, and any use of the terms “substantially” and/or “approximately” and/or “generally” should be understood to mean falling within such accepted tolerances.

[0128] The terms “record” and “receive” may be used synonymously throughout this disclosure unless denoted differently.

[0129] Although the present disclosure herein has been described with reference to particular examples, it is to be understood that these examples are merely illustrative of the principles and applications of the present disclosure.

[0130] It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims.

[0131] A reference herein to a patent document or any other matter identified as prior art, is not to be taken as an admission that the document or other matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.

[0132] In summary the method according the present disclosure as described above provides a method and system of evaluating an assumed wave propagation speed in a medium, which advantageously is faster, more reliable, more robust, computationally less expensive and thus requires less processing power. This implies less computational costs what in particular improves a real time computation mode. Further, due to the increased preciseness a decreased variance and thus an increased reproducibility can advantageously be achieved.