Image phase calculation method and image phase processing system for magnetic resonance phase difference imaging and high-density phase array coil

Abstract

The invention provides an image phase calculation method and an image phase processing system for magnetic resonance phase difference imaging and a high-density phase array coil, and belongs to the field of magnetic resonance phase difference blood flow measurement. The image phase calculation method comprises the following steps: S1, collecting original complex images SFC and SFE of n coil channels; s2, performing complex number division on the original complex number images SFC and SFE of each coil channel to eliminate the influence of the coil sensitivity phase and the coil element, and obtaining a result after complex number division of each coil channel; s3, summing the results obtained by dividing the complex numbers of all coil channels to obtain the phase sum of each channel of the original complex image; and S4, obtaining the phase difference of the combined phase image according to the phase sum of each channel of the original complex image. The method can effectively remove the influence of coil phase sensitivity and magnetic field nonuniformity, and is especially suitable for low-field application with poor magnetic field uniformity.

Description

Technical Field

[0001] The present invention relates to the field of magnetic resonance phase difference blood flow measurement, and particularly relates to an image phase calculation method and an image phase processing system for magnetic resonance phase difference imaging and a high-density phase array coil. Background Art

[0002] In magnetic resonance cine phase contrast (PC) imaging technology, image phase has been used to quantify the spatio-temporal distribution of blood flow volume and blood flow velocity within the vascular lumen and cardiac cycle. In the PC magnetic resonance blood flow imaging sequence, a pair of gradient pulses with equal magnitudes and opposite directions are applied. In stationary tissues, these two reverse gradient pulses cancel each other out, and the spin phase displacement of the stationary tissues out of phase is zero. However, for moving tissues (such as blood), since the spin protons have moved in position, after being excited by this pair of gradient fields with equal magnitudes and opposite directions, their phase changes cannot return to zero. Therefore, the phase change of the flowing proton group is retained, resulting in a phase difference from the stationary tissues. PC-MRI utilizes this phase difference proportional relationship of the velocity phase shift for quantitative measurement of blood flow velocity. People usually acquire two magnetic resonance images of flow compensation (FC) and flow encoding (FE), and subtract the phase signals of this group of images to obtain information directly related to blood flow.

[0003] In quantitative analysis of phase contrast blood flow volume, clinical applications such as high spatial and temporal resolutions and parallel imaging often require high-density multi-phase array receiving coils. The reconstruction technique selected for synthesizing the final image from the signals of each coil channel will have an important impact on the image reconstruction speed, image quality, and sensitivity to various artifacts. [1][2] 。

[0004] Bernstein, M.A. et al. [3] studied the magnetic resonance image phase problem and expressed it as: Phase of each coil channel = Magnetization phase + Receiving coil phase sensitivity. General PC-MRI first calculates the combined signals of each coil channel, and then calculates the phase difference of the magnetic resonance complex signals S FC and S FE from the original complex image encodings of the flow compensation (FC) and flow encoding (FE) in the signals of the same coil elements to obtain blood flow information. However, this method is difficult to remove the influence of coil phase sensitivity and magnetic field inhomogeneity, resulting in inaccurate and unstable blood flow-related information.

[0005] References

[0006] 1. Robinson, S. and J. Jovicich, B0 mapping with multi-channel RF coils at high field. Magn Reson Med, 2011. 66(4): p. 976-88.

[0007] 2. Parker, D. L., et al., Phase reconstruction from multiple coil data using a virtual reference coil. Magn Reson Med, 2014. 72(2): p. 563-9.

[0008] 3. Bernstein, M. A., et al., Reconstructions of phase contrast, phased array multi-coil data. Magn Reson Med, 1994. 32(3): p. 330-4. Summary of the Invention

[0009] The present invention is made to solve the problems of motion, phase overlap, image noise, and ambiguity in the coil signal combination introduced by unknown phase offsets between coils in the above-mentioned magnetic resonance phase difference blood flow measurement. For high-density phased array coils, the present invention provides an image phase calculation method and an image phase processing system for magnetic resonance phase difference imaging and high-density phased array coils.

[0010] The present invention provides an image phase calculation method for magnetic resonance phase difference imaging and high-density phased array coils, which has the following characteristics, including the following steps: Step S1, collecting the original complex images S from flow compensation FC and flow encoding FE of n coil channels FC and S FE ; Step S2, respectively performing complex division on the original complex images S of each coil channel FC and S FE to eliminate the influence of the coil sensitivity phase and the coil elements, and obtaining the results after complex division of each coil channel; Step S3, summing the results after complex division of all coil channels to obtain the phase sum of each channel of the original complex image; Step S4, obtaining the phase difference of the combined phase image according to the phase sum of each channel of the original complex image.

[0011] In the image phase calculation method for magnetic resonance phase difference imaging and high-density phased array coils provided by the present invention, it may also have the following characteristics: wherein, in step S1, the original complex images S of n coil channels FC and S FE are respectively denoted as

[0012]

[0013] In the image phase calculation method for magnetic resonance phase difference imaging and high-density phased array coils provided by the present invention, it may further have the following feature: wherein, in step S2, the result after complex division of a single coil channel is denoted as

[0014] where conj is the conjugate complex conjugate operation.

[0015] In the image phase calculation method for magnetic resonance phase difference imaging and high-density phased array coils provided by the present invention, it may further have the following feature: wherein, in step S3, the phase sum of each channel of the original complex image is denoted as S com ,

[0016]

[0017] In the image phase calculation method for magnetic resonance phase difference imaging and high-density phased array coils provided by the present invention, it may further have the following feature: wherein, the phase difference of the combined phase image is denoted as Δθ, and Δθ = angle(S com ), and Angle represents calculating the phase angle of a complex number by the Angle function.

[0018] The present invention also provides an image phase processing system, which has the following features, including: an original image acquisition and obtaining unit that acquires the original complex images S FC and S FE from flow compensation FC and flow encoding FE of n coil channels; an image processing unit that performs complex division on the original complex images S FC and S FE of each coil channel respectively to eliminate the influence of the coil sensitivity phase and the coil elements, and obtains the results after complex division of each coil channel; a phase sum calculation unit that sums up the results after complex division of all coil channels to obtain the phase sum of each channel of the original complex image; a phase difference calculation unit that obtains the phase difference of the combined phase image according to the phase sum of each channel of the original complex image.

[0019] In the image phase processing system provided by the present invention, it may further have the following feature: wherein, in step S1, the original complex images S FC and S FE of n coil channels are respectively denoted as

[0020]

[0021] In the image phase processing system provided by the present invention, it may further have the following feature: wherein, in step S2, the result after complex division of a single coil channel is denoted as

[0022] wherein, conj is the conjugate operation of the conjugate complex number.

[0023] In the image phase processing system provided by the present invention, it may further have the following feature: wherein, in step S3, the sum of the phases of each channel of the original complex image is denoted as S com ,

[0024]

[0025] In the image phase processing system provided by the present invention, it may further have the following feature: wherein, the phase difference of the combined phase image is denoted as Δθ, and Δθ = angle(S com ), where Angle represents calculating the phase angle of a complex number by the Angle function.

[0026] Functions and effects of the invention

[0027] According to the image phase calculation method and the image phase processing system for magnetic resonance phase difference imaging and high-density phase array coils involved in the present invention, since the phase differences of the original complex images S FC and S FE of each coil channel are calculated first to obtain the result after complex division of each coil channel, and then the results after complex division of all coil channels are summed, thereby obtaining the phase difference of the combined phase image. In this way, the influence of coil phase sensitivity and magnetic field inhomogeneity can be more effectively removed.

[0028] In addition, the present invention is particularly suitable for low-field applications with poor magnetic field uniformity. Description of the drawings

[0029] Figure 1 is a schematic diagram of an n-channel magnetic resonance coil in Embodiment 1 of the present invention;

[0030] Figure 2 is a flowchart of the image phase calculation method for magnetic resonance phase difference imaging and high-density phase array coils in Embodiment 1 of the present invention;

[0031] Figure 3 is a result diagram of magnetic resonance imaging experiments on a water phantom and a volunteer using the image phase calculation method of Embodiment 1 in combination with a high-density phase array coil in Embodiment 2 of the present invention, wherein, Figure 3The upper left panel shows the water phantom phase difference image between the 8 coil channels FC and FE scans. The lower left panel shows the process of gradually adding phases from all coil channels, and the right side shows the resulting phase (upper right) and magnitude images (lower right). Detailed implementation mode

[0032] In order to make the technical means, creative features, achieved purposes and effects of the present invention easy to understand, the following embodiments will specifically elaborate on the image phase calculation method and image phase processing system for magnetic resonance phase difference imaging and high-density phase array coils of the present invention in conjunction with the accompanying drawings.

[0033] Embodiment 1

[0034] Embodiment 1 provides an image phase calculation method and an image phase processing system for magnetic resonance phase difference imaging and high-density phase array coils.

[0035] Figure 1 is a schematic diagram of an n-channel coil for magnetic resonance in Embodiment 1 of the present invention; Figure 2 is a flowchart of an image phase calculation method for magnetic resonance phase difference imaging and high-density phase array coils in Embodiment 1 of the present invention.

[0036] As shown in Figure 1 and Figure 2 The image phase calculation method for magnetic resonance phase difference imaging and high-density phase array coils includes the following steps:

[0037] Step S1, collect the original complex images S from flow compensation (FC) and flow encoding (FE) of n coil channels FC and S FE , and the original complex images S of n coil channels FC and S FE are respectively denoted as

[0038]

[0039] n≥2, preferably n≥4.

[0040] Step S2, perform complex division on the original complex images S of each coil channel FC and S FE respectively to eliminate the influence of the coil sensitivity phase and the coil elements, and obtain the results after complex division of each coil channel. The result after complex division of a single coil channel is denoted as

[0041]

[0042] where conj is the conjugate complex conjugate operation.

[0043] According to the corresponding relationship in the original complex image space, the phase difference of the image = complex division. Therefore, the phase difference Δθ of the combined phase image is calculated through the following steps S3 and S4.

[0044] Step S3: Sum the results after the complex division of all coil channels to obtain the phase sum S of each channel of the original complex image com ,

[0045]

[0046] Step S4: Obtain the phase difference Δθ of the combined phase image according to the phase sum of each channel of the original complex image

[0047] Δθ = angle(S com ) = arctan(S com ),

[0048] Angle represents calculating the phase angle of a complex number by the Angle function.

[0049] The image phase processing system of this embodiment includes an original image acquisition and obtaining unit, an image processing unit, a phase sum calculation unit, and a phase difference calculation unit.

[0050] Among them, the original image acquisition and obtaining unit acquires the original complex images S from the flow compensation FC and the flow encoding FE of n coil channels according to the above step S1 FC and S FE .

[0051] The image processing unit performs complex division on the original complex images S of each coil channel according to the above step S2 respectively to eliminate the influence of the coil sensitivity phase and the coil elements, and obtains the results after the complex division of each coil channel. FC and S FE

[0052] The phase sum calculation unit sums the results after the complex division of all coil channels according to the above step S3 to obtain the phase sum of each channel of the original complex image.

[0053] The phase difference calculation unit obtains the phase difference of the combined phase image according to the phase sum of each channel of the original complex image according to the above step S4.

[0054] The image phase processing system can automatically implement the generation process of the phase difference of the above combined phase image with the aid of a computer.

[0055] Embodiment 2

[0056] Example 2 is a specific application of Example 1. Specifically, the image phase calculation method for magnetic resonance phase difference imaging and high-density phased array coils in Example 1 was used in combination with a high-density phased array coil to conduct magnetic resonance imaging experiments on a water phantom and volunteers.

[0057] Cross-plane phase contrast imaging with electrocardiogram gating was performed using a 1.5T magnetic resonance system, and an 8-channel head coil was used for the water phantom. The imaging sequence parameters are as follows: imaging range: 270mm x 360mm, slice thickness 6 mm, TE 4.8 ms, TR 9.7 ms, flip angle 20°, VENC 70 cm / s, and FC and FE acquisitions are interleaved.

[0058] Figure 3 It is a result diagram of the magnetic resonance imaging experiment on the water phantom and volunteers in Example 2 of the present invention using the image phase calculation method in Example 1 in combination with a high-density phased array coil. Among them, Figure 3 the upper left panel in the figure is the phase difference image of the water phantom between the FC and FE scans of 8 coil channels, and the lower left panel shows the process of gradually adding phases from all coil channels. The resulting phase (upper right) and amplitude image (lower right) are shown on the right.

[0059] An example of the phase combination of the water phantom is as Figure 3 shown. The upper panel of the 8-phase difference image between the FC and FE scans is a single coil element; the lower panel of the 8-phase combined image shows the process of gradually adding phases from all coil elements; the resulting amplitude and phase images are shown on the right.

[0060] The magnetic resonance imaging experiments on the water phantom and volunteers using the image phase calculation method for magnetic resonance phase difference imaging and high-density phased array coils in Example 1 in combination with a high-density phased array coil show that this is a fast and reliable method that can be applied to areas with severe motion artifacts, low signal-to-noise ratio, and heavy susceptibility artifacts, improving the stability and accuracy of magnetic resonance blood flow analysis technology. It is particularly suitable for low-field permanent magnet applications with poor magnetic field uniformity.

[0061] Those skilled in the art of this industry should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for calculating image phase for magnetic resonance phase difference imaging and high-density phase array coils, characterized in that: The following steps are involved: Step S1, collecting the original complex image S from the flow compensation FC and flow encoding FE of n coil channels FC and S FE ; Step S2, the original complex image S of each coil channel FC and S FE Performing complex number division respectively to eliminate the influence of coil sensitivity phase and coil elements, and obtaining the result of complex number division of each coil channel; Step S3, summing the results of the complex number division of all coil channels to obtain the phase sum of each channel of the original complex image; Step S4, obtaining the phase difference of the combined phase image according to the phase sum of each channel of the original complex image.

2. The image phase calculation method for magnetic resonance phase difference imaging and high-density phase array coil according to claim 1, characterized in that: in, In step S1, the original complex image S of n coil channels FC and S FE Recorded as 3. The image phase calculation method for magnetic resonance phase difference imaging and high-density phase array coil according to claim 2, characterized in that: in, In step S2, the result of complex division of a single coil channel is recorded as Where conj is the conjugate complex conjugation operation.

4. The image phase calculation method for magnetic resonance phase difference imaging and high-density phase array coil according to claim 3, characterized in that: in, In step S3, the phase sum of each channel of the original complex image is denoted as S com , 5. The image phase calculation method for magnetic resonance phase difference imaging and high-density phase array coil according to claim 4, characterized in that: in, The phase difference of the combined phase image is denoted as Δθ, Δθ=angle(S com ), Angle means that the Angle function calculates the phase angle of a complex number.

6. An image phase processing system, characterized in that: include: The original image acquisition unit acquires the original complex image S from the flow compensation FC and flow encoding FE of n coil channels. FC and S FE ; The image processing unit processes the original complex image S of each coil channel. FC and S FE Performing complex number division respectively to eliminate the influence of coil sensitivity phase and coil elements, and obtaining the result of complex number division of each coil channel; The phase sum calculation unit sums the results of the complex number division of all coil channels to obtain the phase sum of each channel of the original complex image; The phase difference calculation unit obtains the phase difference of the combined phase image according to the phase sum of each channel of the original complex image.

7. The image phase processing system according to claim 6, characterized in that: in, In step S1, the original complex image S of n coil channels FC and S FE Recorded as 8. The image phase processing system according to claim 7, characterized in that: in, In step S2, the result of complex division of a single coil channel is recorded as Where conj is the conjugate complex conjugation operation.

9. The image phase processing system according to claim 8, characterized in that: in, In step S3, the phase sum of each channel of the original complex image is denoted as S com , 10. The image phase processing system according to claim 9, characterized in that: in, The phase difference of the combined phase image is denoted as Δθ, Δθ=angle(S com ), Angle means that the Angle function calculates the phase angle of a complex number.

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