CN115308656A

CN115308656A - Method and device for determining B0 field map, electronic equipment and storage medium

Info

Publication number: CN115308656A
Application number: CN202210951927.8A
Authority: CN
Inventors: 刘楠; 张涛; 王燕燕
Original assignee: Shanghai Electric Holding Group Co ltd Zhihui Medical Equipment Branch
Current assignee: Shanghai Electric Holding Group Co ltd Zhihui Medical Equipment Branch
Priority date: 2022-08-09
Filing date: 2022-08-09
Publication date: 2022-11-08
Anticipated expiration: 2042-08-09
Also published as: CN115308656B

Abstract

The invention provides a method, a device, electronic equipment and a storage medium for determining a B0 field map, wherein the method comprises the following steps: acquiring an original phase diagram of a B0 field, and separating a foreground region from the original phase diagram; taking the non-edge points in the foreground region as initial seed points, starting with the initial seed points, sequentially performing phase unwrapping on other points in the foreground region in a direction away from the initial seed points, and determining a phase unwrapped intermediate phase map; and performing fitting correction on singular points of the phase wrap until a B0 field map containing no singular points is generated. By the method, the device, the electronic equipment and the storage medium for determining the B0 field diagram, the selected initial seed points are less influenced by magnetic sensitivity, the B0 field is more uniform, the stability is higher, the overall calculated amount in the phase unwrapping process can be reduced, the processing efficiency is improved, and complete unwrapping can be realized.

Description

Method and device for determining B0 field map, electronic equipment and storage medium

Technical Field

The invention relates to the technical field of magnetic resonance imaging, in particular to a method and a device for determining a B0 field map, electronic equipment and a storage medium.

Background

The nuclei spin in an applied magnetic field, and their spin produces a magnetic moment as the nuclei are charged. When atomThe nuclei are placed in a static magnetic field, and the bipolar magnets, which are originally randomly oriented, are subjected to a magnetic field force and oriented in the same direction as the magnetic field. Taking the proton, i.e. the main isotope of hydrogen, as an example, it can only have two basic states: the orientations "parallel" and "antiparallel," which correspond to the low and high energy states, respectively. Accurate analysis shows that the spins do not exactly align with the magnetic field, but are tilted by an angle θ. In this way, the dipole magnet begins to precess around the magnetic field. The frequency of precession depends on the magnetic field strength. And also with the type of nucleus. The relationship between them satisfies the larmor relationship: omega ₀ ＝γB ₀ I.e. precessional angular frequency ω ₀ (also known as Larmor frequency) is the magnetic field strength B ₀ Product with the spin ratio γ. γ is a basic physical constant for each species. The main isotope of hydrogen, proton, is abundant in the human body, and its magnetic moment is easy to detect, so it is most suitable for obtaining nuclear magnetic resonance image from it.

The larmor frequency is proportional to the magnetic field strength, and if the magnetic field is varied in a gradient along the X-axis, the resulting resonance frequency is also clearly related to the location of the voxel on the X-axis. To obtain signals projected on two coordinate axes X-Y simultaneously, a gradient magnetic field GX is added, the obtained signals are collected and converted, then the magnetic field GY is used for replacing GX, and the process is repeated. In practical cases, signals are collected from a large number of spatial location points, the signals being composed of many frequency complexes. By means of mathematical analysis methods, such as fourier transformation, not only the respective resonance frequency, i.e. the corresponding spatial position, but also the corresponding signal amplitude can be determined, which is proportional to the spin density at the particular spatial position. All magnetic resonance imaging methods are based on this principle.

In a magnetic resonance apparatus, an external magnetic field is generated by a magnet, which is called a static field or B0 field. The uniformity of the B0 field has a crucial impact on the image quality. For measuring the B0 field, a fast gradient echo sequence is usually used to acquire two images with different echo times, and the phase difference between the two images contains the information of the B0 field. Specifically, it can be described by the following formula:

where ω is Larmor frequency, Δ TE is the echo time difference between the two images, Δ B ₀ Is the B0 field deviation that needs to be measured. When Δ B ₀ Or Δ TE is large, the generated phase may exceed the (-pi, pi) range, thereby generating a wrap around (or wrap around) on the phase map. Phase unwrapping is the reduction of the phase value to the actual phase value at the point in the phase map where phase wrapping occurs. Phase deconvolution is also referred to as phase deconvolution, phase unwrapping, and the like.

In order to solve the phase map convolution problem, the prior art generally adopts a phase gradient minimum two-norm method to perform phase deconvolution, but the method is quite heavy in computation, especially for processing a 3-dimensional B0 field map. Partial scheme adopts a method of removing the low-order field and then removing the convolution, and although the method can improve the efficiency to a certain degree, the data volume is large, and the calculation speed still needs to be improved; and after deconvolution by the method, singular points which cannot be completely deconvoluted can still be included, so that the deconvolution is incomplete.

Disclosure of Invention

In order to solve the existing technical problems, embodiments of the present invention provide a method and an apparatus for determining a B0 field map, an electronic device, and a storage medium.

In a first aspect, an embodiment of the present invention provides a method for determining a B0 field map, including:

acquiring an original phase diagram of a B0 field, and separating a foreground region from the original phase diagram;

taking the non-edge points in the foreground region as initial seed points, starting with the initial seed points, sequentially performing phase unwrapping on other points in the foreground region in a direction away from the initial seed points, and determining a phase unwrapped intermediate phase map;

performing fitting correction operation on singular points of the phase convolution until a B0 field map which does not contain the singular points is generated;

the operation of fitting and correcting the singular points of the phase convolution comprises:

and determining singular points of phase convolution in the intermediate phase diagram, performing high-order fitting in a neighborhood on the singular points, and taking phases determined by the high-order fitting as the phases of the singular points.

In a second aspect, an embodiment of the present invention further provides an apparatus for determining a B0 field map, including:

the acquisition module is used for acquiring an original phase diagram of the B0 field and separating a foreground region from the original phase diagram;

the unwrapping module is used for sequentially carrying out phase unwrapping on other points in the foreground region in a direction away from the initial seed points by taking the initial seed points as the initial seed points and taking the non-edge points in the foreground region as the initial seed points, so as to determine a middle phase diagram after the phase unwrapping;

the correction module is used for performing fitting correction operation on singular points of the phase convolution until a B0 field map which does not contain the singular points is generated;

the operation of fitting and correcting the singular points of the phase convolution by the correction module comprises the following steps:

In a third aspect, an embodiment of the present invention provides an electronic device, including a bus, a transceiver, a memory, a processor, and a computer program stored on the memory and executable on the processor, where the transceiver, the memory, and the processor are connected via the bus, and the computer program, when executed by the processor, implements the steps in the method for determining a B0 field map according to any one of the foregoing methods.

In a fourth aspect, the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps in the method for determining a B0 field map according to any one of the above.

According to the method, the device, the electronic equipment and the storage medium for determining the B0 field diagram, provided by the embodiment of the invention, the non-edge points in the foreground area are selected as the initial seed points, the area growth is carried out on the basis of the initial seed points, and the initial phase unwrapping can be quickly realized; and then, performing high-order fitting on the singular points with the phase convolution still existing, and finally generating a B0 field map without the singular points. According to the method, non-edge points are selected as initial seed points, so that the selected initial seed points are less influenced by magnetic sensitivity, a B0 field is more uniform, and the stability is higher; all points are subjected to initial and rapid phase unwrapping based on a region growing mode, and then a small number of singular points are subjected to high-order fitting, so that the overall calculated amount in the phase unwrapping process can be reduced, the processing efficiency is improved, and complete unwrapping can be realized.

Drawings

In order to more clearly illustrate the technical solutions in the embodiments or the background art of the present invention, the drawings required to be used in the embodiments or the background art of the present invention will be described below.

FIG. 1 is a flow chart illustrating a method of determining a B0 field map provided by an embodiment of the present invention;

fig. 2 is a schematic diagram illustrating a foreground region in the method for determining a B0 field map according to the embodiment of the present invention;

FIG. 3 is a flow chart illustrating another method for determining a B0 field map provided by an embodiment of the present invention;

FIG. 4 is a schematic structural diagram of an apparatus for determining a B0 field map according to an embodiment of the present invention;

fig. 5 is a schematic structural diagram of an electronic device for performing a method for determining a B0 field map according to an embodiment of the present invention.

Detailed Description

The embodiments of the present invention will be described below with reference to the drawings.

Fig. 1 shows a flowchart of a method for determining a B0 field map according to an embodiment of the present invention. As shown in fig. 1, the method includes:

step 11: an original phase map of the B0 field is acquired and the foreground region is separated from the original phase map.

In the embodiment of the present invention, the B0 field map to be unwrapped, that is, the original phase map, may be determined based on the existing magnetic resonance imaging technology, and the process of determining the original phase map is not limited in this embodiment. The original phase diagram includes a background and a foreground, the background is generally a noise region, and the foreground refers to a signal region of an image. The foreground region may be extracted based on a threshold method, and the like, which is not limited in this embodiment.

Optionally, in the process of extracting the foreground region, some image morphological processing, such as dilation etching or hole filling, may be performed on the discontinuous region, so that the selected foreground region is connected. For example, foreground selection of Volume can be adopted to separate a 3D foreground, and in addition to morphological processing, basically, it can be ensured that a selected foreground region is a connected domain, so that occurrence of a disconnected region or a region with a very low signal-to-noise ratio can be effectively avoided.

Step 12: and taking the non-edge points in the foreground region as initial seed points, starting with the initial seed points, sequentially performing phase unwrapping on other points in the foreground region in a direction away from the initial seed points, and determining a phase unwrapped intermediate phase diagram.

In the embodiment of the invention, the foreground area is an image signal area of human tissues, and the edge of the foreground area is a human tissue boundary. The part with larger magnetic sensitivity influence is the part for tissue connection, so that the part far away from the tissue connection is relatively smaller in magnetic sensitivity theoretically, the B0 field is more uniform, and the stability is higher. Therefore, in the foreground region, the farther a point is from the boundary of the human tissue, the more likely it is a non-convolved point, and the embodiment selects a non-edge point as the initial seed point, so that the initial seed point is as non-convolved as possible. Optionally, since the human tissue is generally convex (the shape of the human tissue is substantially the same as the convex hull of the human tissue), in the foreground region, the centroid of the foreground region is farther from the edge point, and the centroid of the foreground region can be used as the initial seed point, so that the influence of the magnetic sensitivity on the initial seed point can be weakened to the greatest extent. For example, the foreground region includes a connected region, and the centroid of the connected region is used as an initial seed point; or, the foreground region includes a plurality of connected regions, and the centroid of the largest connected region may be used as the initial seed point.

Starting from the initial seed point, phase unwrapping is performed gradually outward on other seed points in the foreground region, that is, phase unwrapping is performed gradually toward the edge of the foreground region from the initial seed point, so that all points in the foreground region can be traversed, and the original phase diagram after all points are phase unwrapped is called as an "intermediate phase diagram".

For example, as shown in fig. 2, if the foreground region is a9 × 9 two-dimensional region, the foreground region includes 81 pixels, i.e., pixels A1 to I9. In this embodiment, the middle pixel E5 is used as the initial seed point O, and the initial seed point O is used as the start point to gradually perform phase unwrapping on other pixels from the inside to the outside. For example, phase unwrapping is performed on 8 pixel points D4, E4, F4, D5, F5, D6, E6, and F6 closest to the initial seed point O, and then phase unwrapping is performed on more peripheral pixel points (e.g., pixel points C3 and G7, etc.) \ 8230 \ 8230and so on until phase unwrapping is performed on the outermost edge points (e.g., pixel points A1, A9, I1, I9, etc.), thereby traversing all the pixel points in the foreground region from inside to outside.

Those skilled in the art will appreciate that the original phase map may be two-dimensional, where the points are specifically pixel points; alternatively, the original phase map may also be three-dimensional, and the separated foreground region may also be three-dimensional, where the points are specifically voxel points. For convenience of description, the embodiments of the present invention mainly use pixel points as an example for illustration.

Step 13: and performing fitting correction on singular points of the phase wrap until a B0 field map containing no singular points is generated.

The operation of fitting and correcting singular points of the phase convolution includes:

step 131: and determining singular points of phase convolution in the intermediate phase diagram, performing high-order fitting in a neighborhood on the singular points, and taking the phases determined by the high-order fitting as the phases of the singular points.

In the embodiment of the present invention, the step 12 is to perform preliminary phase unwrapping on the original phase diagram, and the phase unwrapping can be simply and quickly implemented in a region growing manner. But only a preliminary phase unwrapping is performed, there may still be singularities of the phase wrap, i.e. the ones in the intermediate phase map where there is a phase wrap. For example, a point whose phase difference with another adjacent point exceeds a certain threshold (for example, pi) may be used as the singular point, or the singular point may be determined in another manner, which is not limited in this embodiment.

In the embodiment of the present invention, after the step 12, fitting correction is further performed on the intermediate phase map to remove singular points in the intermediate phase map, so as to finally obtain a phase map without singular points, that is, a phase map without phase convolution, thereby obtaining the required B0 field map.

The embodiment of the invention corrects the phase of the singular point by adopting a high-order fitting mode. Specifically, a neighborhood of the singular point is selected, high-order fitting of a local field is performed in the neighborhood of the singular point, so that a phase value after the high-order fitting can be determined, the phase value replaces the original phase value of the singular point, and therefore the correction of the phase of the singular point is achieved. The neighborhood size of the singular point needs to satisfy the condition that the number of pixels in the neighborhood is larger than the spherical harmonic coefficient. For example, a 2 nd order spherical harmonic fit requires a local field neighborhood size of 6 x 6.

It will be appreciated by those skilled in the art that the above-described process of fitting correction is also a phase unwrapping process. In the present embodiment, "high order" refers to more than 1 order, for example, 2 order, 3 order, and the like. The existing mature technology may be adopted to implement high-order fitting of the local field, for example, fitting a 2-order field phase map based on the scan phase map to further determine a 2-order fitting phase at the singular point, and other high-order fitting manners may also be adopted, which is not limited in this embodiment.

Optionally, when performing high-order fitting on the singular point, the neighborhood of the selected singular point is an area close to the initial seed point. In particular, at least one boundary in the neighborhood of singular points, which is distant from the initial seed point, contains the singular point. For example, the neighborhood of the singular point is a 4 × 4 region, as shown in fig. 2, if the pixel B2 is a singular point, the pixel B2 can be used as the vertex of the selected neighborhood, that is, the 4 × 4 region determined by the pixels B2, E2, B5, and E5 (i.e., the initial seed point O) is used as the neighborhood of the singular point.

Because the intermediate phase diagram may contain a plurality of singular points, the embodiment of the invention selects a region close to the initial seed point as a neighborhood of the singular point, and preferentially performs high-order fitting in the neighborhood on the singular point closest to the initial seed point (the point closer to the initial seed point is not the singular point), so that the neighborhood of the singular point is effectively ensured not to have other singular points, high-order fitting can be more accurately realized, and the influence of other singular points is avoided.

According to the method for determining the B0 field map, provided by the embodiment of the invention, the non-edge points in the foreground region are selected as the initial seed points, and the region growth is carried out on the basis of the initial seed points, so that the initial phase unwrapping can be quickly realized; and then, performing high-order fitting on the singular points with the phase convolution still existing, and finally generating a B0 field map without the singular points. According to the method, non-edge points are selected as initial seed points, so that the selected initial seed points are less influenced by magnetic sensitivity, a B0 field is more uniform, and the stability is higher; all points are subjected to initial and rapid phase unwrapping based on a region growing mode, and then a small number of singular points are subjected to high-order fitting, so that the overall calculated amount in the phase unwrapping process can be reduced, the processing efficiency is improved, and complete unwrapping can be realized.

Alternatively, when phase unwrapping is implemented, the conventional region growing method needs to use a threshold value, the signal strength (phase value) is directly compared with the threshold value, the points with the signal strength lower than the threshold value are noise points, and the noise points do not perform phase unwrapping any more; the reliability of the method depends on the selection of the threshold, the too small threshold can cause the premature termination of the unwrapping process, and the too large threshold can cause the inaccurate unwrapping result. The embodiment of the invention carries out phase prediction based on the phase values of other points in the neighborhood, thereby realizing phase unwrapping. Specifically, the step 12 "sequentially phase-unwrapping other points in the foreground region in a direction away from the initial seed point starting from the initial seed point, and determining the intermediate phase map after phase unwrapping" includes:

step A1: and starting from the initial seed point, sequentially performing first phase unwrapping operation on other points in the foreground region in a direction away from the initial seed point until all the points in the foreground region are traversed, and generating a phase unwrapped intermediate phase map.

In the embodiment of the invention, the first phase unwrapping operation is performed on other points except the initial seed point in the foreground area, and the execution sequence is in a direction far away from the initial seed point. Wherein the above-mentioned "first phase unwrapping operation" includes steps a11-a14:

step A11: and taking a point which is adjacent to the first growth point in the foreground region and does not execute the first phase unwrapping operation as a first target point, wherein the first growth point is a point executing the first phase unwrapping operation, and the initial seed point is a first growth point.

In the embodiment of the present invention, the points in the foreground region may be divided into two types: a point at which the first phase unwrapping operation is performed (i.e., a point that has been unwrapped), and a point at which the first phase unwrapping operation is not performed (i.e., a point that has not been unwrapped); for convenience of description, the present embodiment refers to a point at which the first phase unwrapping operation is performed as a "first growth point" at which phase unwrapping is required for a point at which the first phase unwrapping operation is not performed. Wherein the initial seed point is a point which does not need to be unwound, and the initial seed point can be directly used as a first growing point.

In the embodiment of the present invention, a point adjacent to the first growing point in the foreground region and not performing the first phase unwrapping operation is taken as a point at which the first phase unwrapping operation needs to be performed, that is, a first target point. The first target point thus selected enables phase unwrapping in a direction away from the initial seed point. For example, a point that is closest to the initial seed point and at which the first phase unwrapping operation is not performed may be taken as the first target point.

For example, referring to fig. 2, at the beginning, only the initial seed point O in the foreground region is the first growth point, and the remaining pixel points are all the points that do not execute the first phase unwrapping operation, and at this time, the pixel points D4, E4, F4, D5, F5, D6, E6, and F6 can all be used as the first target points. After the first phase unwrapping operation is performed on the pixel points D4, E4, F4, D5, F5, D6, E6, and F6, the 8 pixel points are the first growth points. Then, the more peripheral pixels C3 and G7 and the like can be used as new first target points, and the first phase unwrapping operation is continuously executed until all the pixels in the target area are phase unwrapped.

It should be noted that, since there may be a plurality of points in the foreground region that are adjacent to the first growing point and have not performed the first phase unwrapping operation, that is, there may be a plurality of first target points currently, the first phase unwrapping operation may be performed on the plurality of first target points one by one in sequence; alternatively, the first phase unwrapping operation may be performed on all the first target points determined at this time at the same time, which is not limited in this embodiment.

Step A12: and predicting the phase value of the first target point according to the phase values of all the first growing points in the neighborhood of the first target point, and determining the predicted phase value of the first target point.

In an embodiment of the present invention, after determining the first target point, phase unwrapping is performed by using a difference between the predicted phase value of the first target point and the original phase value (i.e. the current phase value) of the first target point. Specifically, firstly, determining a neighborhood of the first target point; the neighborhood of the first target point refers to a part of a connected region including the first target point, such as a 3 × 3 region, a 4 × 4 region, and the like. The first target point may be a center of the neighborhood, or the first target point is located at a boundary of the neighborhood, which is not limited in this embodiment, but at least one first growing point needs to exist in the neighborhood. As shown in fig. 2, if the first target point is the pixel D4, the 3 × 3 area corresponding to 8 surrounding pixels (C3, E3, C5, E5, etc.) can be used as the neighborhood of the pixel D4.

If the first target point is located at the boundary position of the neighborhood, the first target point can be taken as the boundary (or the vertex) and the area close to the initial seed point is selected as the neighborhood of the first target point; in other words, at least one boundary in the neighborhood of the first target point, which is distant from the initial seed point, contains the first target point. As shown in fig. 2, if the first target point is the pixel D4, it can be used as a vertex, and the 3 × 3 area corresponding to the pixels D4, F4, D6, and F6 is used as the neighborhood of the pixel D4.

In the embodiment of the present invention, the neighborhood of the first target point includes at least one first growth point, and the phase value of the first target point is predicted based on the phase values of all the first growth points in the neighborhood, so that the predicted phase value of the first target point can be determined; for example, the average value of the phase values of all the first growing points in the neighborhood is used as the predicted phase value of the first target point. In the embodiment of the present invention, the first increasing point is a point subjected to phase unwrapping, and the phase wrap is probably absent, so that the phase value of the first target point when the phase wrap is absent, that is, the predicted phase value, can be predicted based on the phase value of the first increasing point.

Alternatively, the predicted phase value may be determined by means of weighted summation. In an embodiment of the present invention, the predicted phase value of the first target point is a weighted sum of phase values of all first growing points in a neighborhood of the first target point. For example, if the neighborhood of the first target point i includes n first growing points, the predicted phase value of the first target point i

Can be expressed as:

wherein,

representing the phase value, ω, of a first growth point j in the neighborhood of the first object point i _j Representing the weight of the first growth point j in the neighborhood of the first target point i. If all the weights are the same, it is equivalent to take the mean value of the phase values of all the first growing points in the neighborhood as the average valueThe predicted phase value of the first target point.

Optionally, the weight corresponding to the first increasing point and the distance from the first increasing point to the first target point are in a negative correlation relationship, that is, the larger the distance from the first increasing point to the first target point is, the smaller the weight corresponding to the first increasing point is. And the sum of the weights of all first accretion points in the neighbourhood of the first target point is 1. For example, referring to fig. 2, for the first target point E3, three first growing points D4, E4, and F4 are included in the neighborhood, wherein the distances from the first target point E3 to D4 and F4 are the same and greater than the distance from E3 to E4; thus, in the vicinity of the first target point E3, the weight ω of the first growth point E4 _E4 A weight ω greater than the first growth point D4 _D4 And the weight ω of the first growth point F4 _F4 And ω is _E4 ＞ω _D4 ＝ω _F4 。

In the embodiment of the invention, the phase value of the first target point can be predicted simply and quickly in a manner of weighting and summing the phase values of the first growing points in the neighborhood, so that quick phase unwrapping is realized conveniently.

Step A13: and under the condition that the difference value between the current phase value of the first target point and the predicted phase value of the first target point exceeds a preset threshold value, performing phase unwrapping on the phase of the first target point.

Step A14: and keeping the phase of the first target point unchanged under the condition that the difference value between the current phase value of the first target point and the predicted phase value of the first target point does not exceed a preset threshold value.

In the embodiment of the present invention, under normal conditions, the phase value of the first target point is not much different from the phase values of its neighboring points (other points neighboring the first target point), so the phase value of the first target point (i.e. the current phase value) is not much different from the predicted phase value. Therefore, if the difference between the current phase value of the first target point and the predicted phase value of the first target point does not exceed the preset threshold, it can be determined that no phase wrap exists in the first target point, i.e., the phase of the first target point is kept unchanged, i.e., the phase value of the first target point is still the current phase value. Conversely, if the difference between the current phase value of the first target point and the predicted phase value of the first target point exceeds the preset threshold, it can be considered that the phase of the first target point is abnormal, and there is a problem of phase wrapping, and at this time, phase unwrapping needs to be performed on the phase of the first target point.

For example, a 3 × 3 region centered on the first target point is selected as the neighborhood of the first target point. Referring to fig. 2, if only the initial seed point O is the first increasing point, when the pixel D4 is the first target point, the neighborhood thereof only includes one first increasing point O, so that the predicted phase value of the pixel D4 is determined based on the phase value of the first increasing point; if the difference between the current phase value of the pixel point D4 and the predicted phase value (i.e., the current phase value of the initial seed point O) is not large, the phase of the pixel point D4 is kept unchanged; otherwise, the phase of the pixel point D4 needs to be unwrapped.

Optionally, the preset threshold is pi, and the phase value after the first target point is unwrapped satisfies:

wherein,

representing the current phase value of the first target point i,

representing the phase value after unwrapping the first target point i,

represents the predicted phase value of the first target point i, sign () represents a sign function. I.e. when x>Sign (x) =1 when 0, when x<At 0, sign (x) = -1.

In the embodiment of the invention, the preset threshold value is set as pi, and the phase unwrapping is realized in a mode of +/-2 pi of the phase value, so that the difference value between the unwrapped phase value and the predicted phase value is smaller than the preset threshold value pi. Specifically, the first target is neededWhen phase unwrapping is performed on the phase of the point, if the current phase value of the first target point is

Greater than predicted phase value

Subtracting 2 pi from the current phase value; conversely, if the current phase value of the first target point

Less than the predicted phase value

Then 2 pi is added to the current phase value.

On the basis of any of the above embodiments, the operation of "performing fitting correction on singular points of phase convolution" in step 13 includes, in addition to step 131, step B1:

step B1: after the phase determined by the high-order fitting is used as the phase of a singular point, starting with the singular point, and sequentially performing second phase unwrapping operation on the relevant points in the intermediate phase diagram in the direction away from the initial seed point until all the relevant points in the intermediate phase diagram are traversed; the relevant point is a point that directly or indirectly takes the singular point as a first growing point in the neighborhood during the execution of the first phase unwrapping operation.

In the embodiment of the present invention, since the fitting correction is performed on the phase value of the singular point, it may affect the phase unwrapping of other points after the singular point, for example, in the above steps a13 and a14, it may affect whether the other points need to be phase unwrapped. Therefore, after "the phase determined by the high-order fitting is taken as the phase of the singular point" in the above step 131, the embodiment of the present invention re-performs the phase unwrapping operation, which is similar to the above-described first phase unwrapping operation, starting from the singular point; for convenience of description, the present embodiment refers to the phase unwrapping operation at this time as the "second phase unwrapping operation". Since the singular point only affects the point that is used as the first growing point in the neighborhood during the first phase unwrapping operation, the second phase unwrapping operation is only required to be performed on the points, and the points are referred to as "relevant points".

Here, the "second phase unwrapping operation" in the above step B1 includes steps B11 to B14, similar to the "first phase unwrapping operation":

step B11: regarding a point in the intermediate phase map, which is adjacent to the second growth point and on which the second phase unwrapping operation is not performed, as a second target point, the second growth point is a point on which the second phase unwrapping operation is performed, and the singular point is a second growth point.

In the embodiment of the present invention, similarly to the process of determining the first target point in step a11 described above, the second target point at which the second phase unwrapping operation needs to be performed may be determined. Here, since only the relevant point needs to be phase unwrapped at this time, only the relevant point on which the second phase unwrapping operation is not performed needs to be set as the second target point. Similar to the initial seed point, since the singular point is a point subjected to fitting correction, it can be considered that there is no problem of phase wrap of the singular point, and thus the singular point can be directly used as the second growing point.

Step B12: predicting the phase value of the second target point according to the phase values of all effective growth points in the neighborhood of the second target point, and determining the predicted phase value of the second target point; the effective growth point includes the second growth point, or the effective growth point includes the first growth point and the second growth point.

Similar to the process of determining the predicted phase value of the first target point in step a12, the phase prediction is still performed by using the phase value of the growing point in the neighborhood of the second target point. In the above step B12, the phase prediction may be performed based on only the second growth points in the neighborhood, that is, the effective growth point only includes the second growth point; alternatively, the phase prediction may be performed based on the first growth point and the second growth point in the neighborhood, that is, the effective growth point includes the first growth point and the second growth point.

Optionally, similar to the process of step a12, the predicted phase value may also be determined by means of weighted summation, that is, the predicted phase value of the second target point is a weighted sum of phase values of all effective growth points in the neighborhood of the second target point. And the weight of the effective growth point and the distance from the effective growth point to the second target point are in a negative correlation relationship.

Optionally, the neighborhood of the second target point is a region centered on the second target point. Alternatively, similar to the neighborhood of the singular point, the neighborhood of the second target point is a region close to the initial seed point, i.e. at least one boundary of the neighborhood of the second target point, which is far from the initial seed point, contains the second target point. In the case where the effective growing points include a first growing point and a second growing point, a region close to the initial seed point is preferentially taken as a neighborhood of the second target point.

Step B13: and under the condition that the difference value between the current phase value of the second target point and the predicted phase value of the second target point exceeds a preset threshold value, performing phase unwrapping on the phase of the second target point.

Step B14: in the case that the difference between the current phase value of the second target point and the predicted phase value of the second target point does not exceed the preset threshold, the phase of the second target point is kept unchanged.

In the embodiment of the present invention, similar to the above steps a13-a14, it may also be determined whether phase unwrapping is required based on whether a difference between the current phase value of the second target point and the predicted phase value of the second target point exceeds a preset threshold. In step B13, the phase unwrapping process performed on the phase of the second target point may also adopt a phase unwrapping method similar to that in step a13, which is not described in detail in this embodiment.

In the embodiment of the invention, after fitting and correcting the singular points, the second phase unwrapping operation is continuously carried out on the relevant points of the singular points, so that the phase unwrapping can be carried out on the relevant points more accurately, and finally, a perfect wrapping-free phase diagram can be obtained.

Optionally, the step 13 is executed in a loop, that is, the operation of fitting and correcting the singular points of the phase convolution is executed in a loop; the "operation of fitting and correcting singular points of a phase wrap" further includes:

and step B2: after traversing all relevant points in the intermediate phase map, a new intermediate phase map is generated.

In the embodiment of the present invention, after traversing all the relevant points in the intermediate phase map in step B1, the intermediate phase map is updated, that is, the intermediate phase map after traversing all the relevant points is used as a new intermediate phase map, and step 13 is executed again until no singular point exists in the current intermediate phase map.

Those skilled in the art can understand that there are a plurality of points in the foreground region, and the same point may correspond to different states at different times or need to perform different processing, and for convenience of distinguishing and description, description manners such as "initial seed point", "growing point", "target point", "singular point", "related point" are introduced in this embodiment. For a point, different description modes may be referred to in different processing procedures to refer to the point; for example, for a certain point a, it may be a "first growth point" in step a11 and a "singular point" or a "correlation point" in step B1.

The flow of the method of determining the B0 field map is described in detail below by one embodiment.

Referring to fig. 3, the method for determining the B0 field map includes:

step 301: an original phase map of the B0 field is acquired and the foreground region is separated from the original phase map.

For example, a threshold may be used to separate the image foreground and obtain a phase mask (mask) of the foreground, thereby obtaining the foreground region.

Step 302: the centroid in the foreground region is taken as the initial seed point.

Step 303: taking a point adjacent to the first growing point in the foreground region and not performing the first phase unwrapping operation as a first target point; the first growth point is a point at which the first phase unwrapping operation is performed.

The initial value of the first growth point is the initial seed point, that is, the initial seed point is used as the initial first growth point, thereby determining the first target point.

Step 304: and predicting the phase value of the first target point according to the phase values of all the first growing points in the neighborhood of the first target point, and determining the predicted phase value of the first target point.

Step 305: and judging whether the difference value between the current phase value and the predicted phase value of the first target point is greater than a preset threshold value, if so, executing a step 306, otherwise, executing a step 307.

Step 306: the phase of the first target point is phase unwrapped before step 308 is performed.

Step 307: the phase of the first target point is kept unchanged, after which step 308 is performed.

Step 308: if all points in the foreground region have been traversed, step 309 is executed, otherwise step 303 is executed again, i.e. the first target point is determined again.

Step 309: an intermediate phase map is generated.

Step 310: and judging whether the intermediate phase diagram has singular points, if so, executing step 311, otherwise, executing step 318.

Step 311: and determining singular points of phase convolution in the intermediate phase diagram, performing high-order fitting in a neighborhood on the singular points, and taking the phases determined by the high-order fitting as the phases of the singular points.

Step 312: taking a relevant point which is adjacent to the second increasing point in the intermediate phase diagram and is not subjected to the second phase unwrapping operation as a second target point; the relevant point is a point that directly or indirectly takes a singular point as a first growth point in the neighborhood during the execution of the first phase unwrapping operation, and the second growth point is a point at which the second phase unwrapping operation is executed.

The initial value of the second growth point is a singular point, that is, the singular point is the initial second growth point.

Step 313: and predicting the phase value of the second target point according to the phase values of all second growing points in the neighborhood of the second target point, and determining the predicted phase value of the second target point.

Step 314: and judging whether the difference value between the current phase value and the predicted phase value of the second target point is greater than a preset threshold value, if so, executing a step 315, otherwise, executing a step 316.

Step 315: the phase of the second target point is phase unwrapped before step 317 is performed.

Step 316: the phase of the second target point is kept unchanged, after which step 317 is performed.

Step 317: if all relevant points in the intermediate phase map have been traversed, step 309 is executed if yes, otherwise step 312 is executed again, i.e. the second target point is re-determined.

Step 318: a B0 field map is generated that does not contain singularities.

The method for determining the B0 field map provided by the embodiment of the present invention is described above in detail, and the method can also be implemented by a corresponding apparatus, and the apparatus for determining the B0 field map provided by the embodiment of the present invention is described below in detail.

Fig. 4 is a schematic structural diagram of an apparatus for determining a B0 field map according to an embodiment of the present invention. As shown in fig. 4, the apparatus for determining the B0 field map includes:

an obtaining module 41, configured to obtain an original phase map of the B0 field, and separate a foreground region from the original phase map;

a unwrapping module 42, configured to take a non-edge point in the foreground region as an initial seed point, start with the initial seed point, perform phase unwrapping on other points in the foreground region in sequence in a direction away from the initial seed point, and determine a phase unwrapped intermediate phase map;

a correction module 43, configured to perform an operation of fitting and correcting singular points of the phase convolution until a B0 field map containing no singular points is generated;

the correction module 43 includes:

a fitting unit 431, configured to determine singular points of the phase convolution in the intermediate phase map, perform high-order fitting in a neighborhood on the singular points, and use a phase determined by the high-order fitting as a phase of the singular points.

In one possible implementation, the initial seed point is a centroid of the foreground region.

In one possible implementation, the unwrapping module 42 includes:

a first unwrapping unit, configured to start with the initial seed point, sequentially perform a first phase unwrapping operation on other points in the foreground region in a direction away from the initial seed point until all points in the foreground region are traversed, and generate a phase unwrapped intermediate phase map;

wherein the first phase unwrapping operation comprises:

taking a point which is adjacent to a first growing point in the foreground region and has not performed the first phase unwrapping operation as a first target point, wherein the first growing point is a point at which the first phase unwrapping operation has been performed, and the initial seed point is a first growing point;

predicting the phase value of the first target point according to the phase values of all first growing points in the neighborhood of the first target point, and determining the predicted phase value of the first target point;

performing phase unwrapping on the phase of the first target point under the condition that a difference value between the current phase value of the first target point and the predicted phase value of the first target point exceeds a preset threshold value;

and keeping the phase of the first target point unchanged under the condition that the difference value between the current phase value of the first target point and the predicted phase value of the first target point does not exceed a preset threshold value.

In one possible implementation, the predicted phase value of the first target point is a weighted sum of phase values of all first growth points within a neighborhood of the first target point.

In a possible implementation manner, the weight corresponding to the first growing point and the distance from the first growing point to the first target point are in a negative correlation relationship.

In a possible implementation manner, the preset threshold is pi, and the phase value after the first target point is unwrapped satisfies:

wherein,

representing the current phase value of the first target point i,

representing the phase value after unwrapping the first target point i,

represents the predicted phase value of the first target point i, sign () represents a sign function.

In one possible implementation, a higher-order fitting in the neighborhood is preferentially performed on singular points closest to the initial seed point; and at least one boundary in the neighborhood of singular points, distant from the initial seed point, contains the singular point.

In a possible implementation manner, the modification module 43 further includes:

a second unwrapping unit configured to perform, after the phase determined by the high-order fitting is taken as the phase of the singular point, second phase unwrapping operations on the relevant points in the intermediate phase map in sequence in a direction away from the initial seed point starting from the singular point until all the relevant points in the intermediate phase map are traversed; the correlation point is a point which directly or indirectly takes the singular point as a first growing point in the neighborhood during the execution of the first phase unwrapping operation;

wherein the second phase unwrapping operation comprises:

regarding a point in the intermediate phase map, which is adjacent to a second growth point and is not subjected to the second phase unwrapping operation, as a second target point, where the second growth point is a point at which the second phase unwrapping operation is performed, and the singular point is a second growth point;

predicting the phase value of the second target point according to the phase values of all effective growth points in the neighborhood of the second target point, and determining the predicted phase value of the second target point; the effective growth point comprises the second growth point, or the effective growth point comprises the first growth point and the second growth point;

phase unwrapping the phase of the second target point in case the difference between the current phase value of the second target point and the predicted phase value of the second target point exceeds a preset threshold;

and keeping the phase of the second target point unchanged under the condition that the difference value between the current phase value of the second target point and the predicted phase value of the second target point does not exceed a preset threshold value.

In one possible implementation, the predicted phase value of the second target point is a weighted sum of the phase values of all valid growth points in the neighborhood of the second target point.

In addition, an embodiment of the present invention further provides an electronic device, including a bus, a transceiver, a memory, a processor, and a computer program stored in the memory and capable of running on the processor, where the transceiver, the memory, and the processor are respectively connected through the bus, and when the computer program is executed by the processor, the processes of the method embodiment for determining a B0 field diagram are implemented, and the same technical effects can be achieved, and are not described herein again to avoid repetition.

Specifically, referring to fig. 5, an embodiment of the present invention further provides an electronic device, which includes a bus 1110, a processor 1120, a transceiver 1130, a bus interface 1140, a memory 1150, and a user interface 1160.

In an embodiment of the present invention, the electronic device further includes: a computer program stored on the memory 1150 and executable on the processor 1120, the computer program when executed by the processor 1120 performs the processes of the method embodiments of determining the B0 field map described above.

A transceiver 1130 for receiving and transmitting data under the control of the processor 1120.

In embodiments of the invention in which a bus architecture (represented by bus 1110) is used, bus 1110 may include any number of interconnected buses and bridges, with bus 1110 connecting various circuits including one or more processors, represented by processor 1120, and memory, represented by memory 1150.

Bus 1110 represents one or more of any of several types of bus structures, including a memory bus, and memory controller, a peripheral bus, an Accelerated Graphics Port (AGP), a processor, or a local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include: an Industry Standard Architecture (ISA) bus, a Micro Channel Architecture (MCA) bus, an Enhanced ISA (EISA) bus, a Video Electronics Standards Association (VESA), a Peripheral Component Interconnect (PCI) bus.

Processor 1120 may be an integrated circuit chip having signal processing capabilities. In implementation, the steps of the above method embodiments may be performed by integrated logic circuits in hardware or instructions in software in a processor. The processor described above includes: general purpose processors, central Processing Units (CPUs), network Processors (NPs), digital Signal Processors (DSPs), application Specific Integrated Circuits (ASICs), field Programmable Gate Arrays (FPGAs), complex Programmable Logic Devices (CPLDs), programmable Logic Arrays (PLAs), micro Control Units (MCUs) or other Programmable Logic devices, discrete gates, transistor Logic devices, discrete hardware components. The various methods, steps, and logic blocks disclosed in the embodiments of the present invention may be implemented or performed. For example, the processor may be a single core processor or a multi-core processor, which may be integrated on a single chip or located on multiple different chips.

Processor 1120 may be a microprocessor or any conventional processor. The steps of the method disclosed in connection with the embodiments of the present invention may be directly performed by a hardware decoding processor, or may be performed by a combination of hardware and software modules in the decoding processor. The software modules may be located in a Random Access Memory (RAM), a Flash Memory (Flash Memory), a Read-Only Memory (ROM), a Programmable ROM (PROM), an Erasable Programmable ROM (EPROM), a register, and other readable storage media known in the art. The readable storage medium is located in a memory, and a processor reads information in the memory and completes the steps of the method in combination with hardware of the processor.

The bus 1110 may also connect various other circuits such as peripherals, voltage regulators, or power management circuits to provide an interface between the bus 1110 and the transceiver 1130, as is well known in the art. Therefore, the embodiments of the present invention will not be further described.

The transceiver 1130 may be one element or a plurality of elements, such as a plurality of receivers and transmitters, providing a means for communicating with various other apparatus over a transmission medium. For example: the transceiver 1130 receives external data from other devices, and the transceiver 1130 transmits data processed by the processor 1120 to other devices. Depending on the nature of the computer system, a user interface 1160 may also be provided, such as: touch screen, physical keyboard, display, mouse, speaker, microphone, trackball, joystick, stylus.

It is to be appreciated that in embodiments of the invention, the memory 1150 may further include memory located remotely with respect to the processor 1120, which may be coupled to a server via a network. One or more portions of the aforementioned networks may be an ad hoc network (ad hoc network), an intranet (intranet), an extranet (extranet), a Virtual Private Network (VPN), a Local Area Network (LAN), a Wireless Local Area Network (WLAN), a Wide Area Network (WAN), a Wireless Wide Area Network (WWAN), a Metropolitan Area Network (MAN), the Internet (Internet), a Public Switched Telephone Network (PSTN), a plain old telephone service network (POTS), a cellular telephone network, a wireless fidelity (Wi-Fi) network, and a combination of two or more of the aforementioned networks. For example, the cellular telephone network and the wireless network may be a global system for Mobile Communications (GSM) system, a Code Division Multiple Access (CDMA) system, a Worldwide Interoperability for Microwave Access (WiMAX) system, a General Packet Radio Service (GPRS) system, a Wideband Code Division Multiple Access (WCDMA) system, a Long Term Evolution (LTE) system, an LTE Frequency Division Duplex (FDD) system, an LTE Time Division Duplex (TDD) system, an advanced long term evolution (LTE-a) system, a Universal Mobile Telecommunications (UMTS) system, an enhanced Mobile Broadband (eMBB) system, a mass Machine Type Communication (mtc) system, an Ultra Reliable Low Latency Communication (urrllc) system, or the like.

It is to be understood that the memory 1150 in embodiments of the present invention can be either volatile memory or nonvolatile memory, or can include both volatile and nonvolatile memory. Wherein the nonvolatile memory includes: read-Only Memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), electrically Erasable PROM (EEPROM), or Flash Memory.

The volatile memory includes: random Access Memory (RAM), which acts as an external cache. By way of example, and not limitation, many forms of RAM are available, such as: static random access memory (Static RAM, SRAM), dynamic random access memory (Dynamic RAM, DRAM), synchronous Dynamic random access memory (Synchronous DRAM, SDRAM), double Data Rate Synchronous Dynamic random access memory (Double Data Rate SDRAM, DDRSDRAM), enhanced Synchronous DRAM (ESDRAM), synchronous Link DRAM (SLDRAM), and Direct memory bus RAM (DRRAM). The memory 1150 of the electronic device described in connection with the embodiments of the invention includes, but is not limited to, the above-described and any other suitable types of memory.

In an embodiment of the present invention, memory 1150 stores the following elements of operating system 1151 and application programs 1152: an executable module, a data structure, or a subset thereof, or an expanded set thereof.

Specifically, the operating system 1151 includes various system programs such as: a framework layer, a core library layer, a driver layer, etc. for implementing various basic services and processing hardware-based tasks. Applications 1152 include various applications such as: media Player (Media Player), browser (Browser), for implementing various application services. A program implementing a method of an embodiment of the invention may be included in application program 1152. The application programs 1152 include: applets, objects, components, logic, data structures, and other computer system executable instructions that perform particular tasks or implement particular abstract data types.

In addition, an embodiment of the present invention further provides a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the processes of the method for determining a B0 field map in the embodiment, and can achieve the same technical effects, and in order to avoid repetition, the details are not repeated here.

The computer-readable storage medium includes: permanent and non-permanent, removable and non-removable media may be tangible devices that retain and store instructions for use by an instruction execution apparatus. The computer-readable storage medium includes: electronic memory devices, magnetic memory devices, optical memory devices, electromagnetic memory devices, semiconductor memory devices, and any suitable combination of the foregoing. The computer-readable storage medium includes: phase change memory (PRAM), static Random Access Memory (SRAM), dynamic Random Access Memory (DRAM), other types of Random Access Memory (RAM), read Only Memory (ROM), non-volatile random access memory (NVRAM), electrically Erasable Programmable Read Only Memory (EEPROM), flash memory or other memory technology, compact disc read only memory (CD-ROM), digital Versatile Discs (DVD) or other optical storage, magnetic tape cartridge storage, magnetic tape disk storage or other magnetic storage devices, memory sticks, mechanically encoded devices (e.g., punched cards or raised structures in a groove having instructions recorded thereon), or any other non-transmission medium useful for storing information that may be accessed by a computing device. As defined in embodiments of the present invention, a computer-readable storage medium does not include transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission medium (e.g., optical pulses traveling through a fiber optic cable), or electrical signals transmitted through a wire.

In the several embodiments provided in the present application, it should be understood that the disclosed apparatus, electronic device and method may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the modules or units is only one logical division, and there may be other divisions in actual implementation, for example, multiple units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may also be an electrical, mechanical or other form of connection.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on multiple network units. Some or all of the units can be selected according to actual needs to solve the problem to be solved by the embodiment of the invention.

In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solutions of the embodiments of the present invention may substantially or partially contribute to the prior art, or all or part of the technical solutions may be embodied in the form of a software product stored in a storage medium, and including several instructions for causing a computer device (including a personal computer, a server, a data center or other network devices) to execute all or part of the steps of the methods according to the embodiments of the present invention. And the storage medium includes various media that can store the program code as listed in the foregoing.

In the description of the embodiments of the present invention, it should be apparent to those skilled in the art that the embodiments of the present invention may be embodied as methods, apparatuses, electronic devices, and computer-readable storage media. Thus, embodiments of the invention may be embodied in the form of: entirely hardware, entirely software (including firmware, resident software, micro-code, etc.), a combination of hardware and software. Furthermore, in some embodiments, embodiments of the invention may also be embodied in the form of a computer program product in one or more computer-readable storage media having computer program code embodied in the medium.

The computer-readable storage media described above may take any combination of one or more computer-readable storage media. The computer-readable storage medium includes: an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples of the computer readable storage medium include: a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only Memory (ROM), an erasable programmable read-only Memory (EPROM), a Flash Memory (Flash Memory), an optical fiber, a compact disc read-only Memory (CD-ROM), an optical storage device, a magnetic storage device, or any combination thereof. In embodiments of the invention, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, device, or apparatus.

The computer program code embodied on the computer readable storage medium may be transmitted using any appropriate medium, including: wireless, wire, fiber optic cable, radio Frequency (RF), or any suitable combination thereof.

Computer program code for carrying out operations for embodiments of the present invention may be written in assembly instructions, instruction Set Architecture (ISA) instructions, machine related instructions, microcode, firmware instructions, state setting data, integrated circuit configuration data, or in one or more programming languages, including an object oriented programming language, such as: java, smalltalk, C + +, and also include conventional procedural programming languages, such as: c or a similar programming language. The computer program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the case of a remote computer, the remote computer may be over any of a variety of networks, including: a Local Area Network (LAN) or a Wide Area Network (WAN), which may be connected to the user's computer, may be connected to an external computer.

The method, the device and the electronic equipment are described through the flow chart and/or the block diagram.

It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer readable program instructions. These computer-readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer-readable program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing apparatus to function in a particular manner. Thus, the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The above description is only a specific implementation of the embodiments of the present invention, but the scope of the embodiments of the present invention is not limited thereto, and any person skilled in the art can easily think of the changes or substitutions within the technical scope of the embodiments of the present invention, and should be covered by the scope of the embodiments of the present invention. Therefore, the protection scope of the embodiments of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method of determining a B0 field map, comprising:

the operation of fitting and correcting singular points of the phase wrap comprises:

2. The method of claim 1, wherein the initial seed point is a centroid of the foreground region.

3. The method of claim 1, wherein the determining the phase unwrapped intermediate phase map by sequentially phase unwrapping other points in the foreground region starting from the initial seed point in a direction away from the initial seed point comprises:

starting with the initial seed point, sequentially performing first phase unwrapping operation on other points in the foreground region in a direction away from the initial seed point until all points in the foreground region are traversed, and generating a phase unwrapped intermediate phase map;

wherein the first phase unwrapping operation comprises:

4. A method according to claim 3, wherein the predicted phase value for the first target point is a weighted sum of the phase values of all first growth points within the neighborhood of the first target point.

5. The method of claim 4, wherein the weight corresponding to the first growth point is inversely related to the distance from the first growth point to the first target point.

6. The method of claim 3, wherein the predetermined threshold is pi, and the phase value after unwrapping the first target point satisfies:

wherein,

representing the current phase value of the first target point i,

representing the phase value after unwrapping of the first target point i,

7. The method of any of claims 3-6, wherein the operation of fitting corrections to the singularities of the phase wrap further comprises:

after the phases determined by the high-order fitting are used as the phases of the singular points, starting with the singular points, sequentially performing a second phase unwrapping operation on the relevant points in the intermediate phase diagram in a direction away from the initial seed points until all the relevant points in the intermediate phase diagram are traversed; the correlation point is a point which directly or indirectly takes the singular point as a first growing point in the neighborhood during the execution of the first phase unwrapping operation;

wherein the second phase unwrapping operation includes:

regarding a point in the intermediate phase map, which is adjacent to a second growth point and on which the second phase unwrapping operation has not been performed, as a second target point, where the second growth point is a point on which the second phase unwrapping operation has been performed, and the singular point is a second growth point;

8. The method of claim 7, wherein the predicted phase value of the second target point is a weighted sum of phase values of all valid growth points within a neighborhood of the second target point.

9. The method of claim 1, wherein higher order fits in the neighborhood are preferentially made to singular points closest to the initial seed point; and at least one boundary in the neighborhood of singular points, distant from the initial seed point, contains the singular point.

10. An apparatus for determining a B0 field map, comprising:

the correction module comprises:

and the fitting unit is used for determining singular points of the phase convolution in the intermediate phase diagram, performing high-order fitting in a neighborhood on the singular points, and taking the phases determined by the high-order fitting as the phases of the singular points.

11. An electronic device comprising a bus, a transceiver, a memory, a processor and a computer program stored on the memory and executable on the processor, the transceiver, the memory and the processor being connected via the bus, characterized in that the computer program realizes the steps in the method of determining a B0 field map as claimed in any one of claims 1 to 9 when executed by the processor.

12. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method of determining a B0 field map as claimed in any one of claims 1 to 9.