Diffusion imaging method, apparatus and magnetic resonance imaging system

Abstract

This invention discloses a diffusion imaging method, apparatus, and magnetic resonance imaging system. The method includes: in a single-excitation diffusion-weighted echo planar imaging process, exciting the target tissue with a radio frequency pulse while simultaneously applying a first slice-selective gradient pulse; after the first slice-selective gradient pulse is applied, performing a first radio frequency pulse refocusing on the target tissue while simultaneously applying a second slice-selective gradient pulse and a diffusion gradient pulse; after the diffusion gradient pulse is applied, acquiring imaging data based on the excited echo; after the imaging data acquisition, performing a second radio frequency pulse refocusing on the target tissue while simultaneously applying a third slice-selective gradient pulse; after the third slice-selective gradient pulse is applied, acquiring navigation data based on the excited echo; and reconstructing the image from the acquired imaging data using the acquired navigation data to obtain a magnetic resonance imaging image of the target tissue. This invention improves the quality and robustness of image reconstruction in diffusion imaging.

Description

Technical Field

[0001] This invention relates to the field of MRI (Magnetic Resonance Imaging) technology, and in particular to diffusion imaging methods, devices and MRI systems. Background Technology

[0002] In traditional SS-DW-EPI (single-shot Diffusion Weighted Echo Planar Imaging), parallel imaging (PI) typically reduces distortion by increasing the effective bandwidth along the PE (Phase Encoding) direction. Distortion can be reduced proportionally to the acceleration factor in the PE direction. Typically, a separate ACS (Auto Calibration Signal) is required to compute the kernel reconstruction of GRAPPA (GeneRalized Autocalibrating Partially Parallel Acquisitions) or the coil sensitivity map reconstruction of Sensitivity Encoding (SENSE). Previous research has shown that ideal ACS data must match the imaging data in terms of phase error and geometric distortion, rather than tissue contrast, to provide the highest quality GRAPPA reconstruction. Therefore, segmented EPI acquisition with matched echo spacing is widely used to accelerate SS-DW-EPI, but breathing or body movement during scanning can increase phase errors between different segments, thus affecting subsequent image reconstruction.

[0003] Furthermore, DWI is highly sensitive to phase changes. Conventional averaging in diffusion imaging is performed on amplitude images, which is robust but alters the noise distribution. Therefore, the averaged image will have a noise shift, which manifests as a hazy background in low-signal regions. This can be avoided by complex averaging, in which appropriate local phase calibration is performed between different diffusion images from repeated scans before averaging. Similar to multi-excitation EPI sequences, to compensate for this phase change, pilot echo acquisition can be used to monitor excitation-to-excitation phase changes and perform 2D image-domain phase calibration on the data.

[0004] Unlike ACS data acquired using multi-excitation EPI, FLEET (Fast Low-angle Excitation Echo planar Technique) rearranges ACS segments to ensure that all segments of any given slice are acquired sequentially in time, minimizing motion effects between segments. The FLEET-ACS method has been shown to provide higher tSNR (Temporal Signal-to-Noise Ratio) and lower sensitivity to motion compared to traditional segmented EPI scans. However, FLEET-ACS is based on FLASH (Fast Low Angle SHot) acquisition, which is better suited for gradient echo EPI, such as BOLD (Blood Oxygenation Level Dependent) imaging. While it can be extended to spin echo EPI with matched distortion, in-plane astigmatism cannot be avoided if the slice is not thin enough. Furthermore, it is difficult to ensure the patient is in the same position during calibration and imaging scans. Incorrect registration between ACS data and imaging data can also lead to artifacts in the reconstructed image.

[0005] In non-EPI sequences, integrated calibration scans are typically used to reduce this motion effect, but because conventional integrated calibration scans in EPI acquisitions violate echo interval consistency, they are not easily extended to EPI applications.

[0006] For complex averaging in diffusion applications, a combination of images from local blocks can be performed without explicitly performing phase calibration between the individual averages. This method assumes that the phase changes within individual image local blocks are constant, where the block size plays a significant role. The optimized block size may vary in different diffusion applications and depends on the imaging parameters. Summary of the Invention

[0007] In view of this, the present invention provides both a diffusion imaging method and a diffusion imaging device and MRI system to improve the quality and robustness of image reconstruction in diffusion imaging.

[0008] A diffusion imaging method, comprising:

[0009] In the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process, the target tissue is first excited by radio frequency pulses, and at the same time, the first layer-selection gradient pulse is applied to the target tissue in the layer-selection coding direction.

[0010] After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to the first radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction.

[0011] After the diffusion gradient pulse is applied, imaging data is acquired based on the excited echo;

[0012] After the imaging data acquisition is completed, a second radio frequency pulse refocusing is performed on the target tissue, and a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction.

[0013] After the second radio frequency pulse refocusing and the third layer selection gradient pulse are applied, navigation data are acquired based on the excited echo;

[0014] Based on the acquired navigation data, the acquired imaging data is reconstructed to obtain magnetic resonance imaging (MRI) images of the target tissue.

[0015] The first radiofrequency pulse refocusing of the target tissue includes:

[0016] Based on the current diffusion gradient application method, determine the number and / or pulse angle of the refocusing pulses included in the first radio frequency pulse refocusing, and use the determined number and / or pulse angle of the refocusing pulses to perform the first radio frequency pulse refocusing on the target tissue.

[0017] The step of reconstructing the image from the acquired imaging data based on the acquired navigation data includes:

[0018] In parallel imaging, for repeated scans, the kernel of the generalized self-calibrated parallel acquisition GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The reconstructed repeated images are then averaged to obtain the MRI image of the target tissue.

[0019] Or, including:

[0020] During parallel imaging, image reconstruction is performed on all imaging data acquired by repeated scans to obtain the corresponding images. Navigation data is used to perform phase calibration on the reconstructed repeated images. Complex averaging is performed on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0021] Or, including:

[0022] In parallel imaging, for repeated scans, the kernel of GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The phase of the reconstructed repeated image is calibrated using navigation data. The complex average of all phase-calibrated repeated images is then performed to obtain the MRI image of the target tissue.

[0023] The acquired imaging data for the excitation echo includes:

[0024] Based on the preset acceleration factor in the PE direction of the phase encoding, the acquisition interval of the imaging data in the PE direction is determined, and the imaging data is acquired sequentially using the acquisition interval.

[0025] The navigation data acquired from the excitation echo includes:

[0026] Navigation data is collected at the center segment of K space in the frequency coding direction, and the number of collected points is equal to the quotient obtained by dividing the total number of collectable navigation data points by the acceleration factor in the PE direction.

[0027] After the diffusion gradient pulse is applied and before the acquisition of imaging data from the excitation echo, the process further includes:

[0028] Routine phase calibration data for excited echo acquisition imaging data;

[0029] After the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, and before the navigation data acquisition based on the excitation echo, the process further includes:

[0030] Routine phase calibration data for navigation data acquired from excited echoes;

[0031] Furthermore, the step of acquiring navigation data from the excited echo and before reconstructing the image from the acquired imaging data based on the acquired navigation data further includes:

[0032] Phase calibration is performed on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data, and phase calibration is performed on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data.

[0033] A diffusion imaging method, comprising:

[0034] In the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process, the target tissue is first excited by radio frequency pulses, and at the same time, the first layer-selection gradient pulse is applied to the target tissue in the layer-selection coding direction.

[0035] After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to the first radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction.

[0036] After the diffuse gradient pulse is applied, navigation data is collected based on the excitation echo;

[0037] After the navigation data acquisition is completed, a second radio frequency pulse refocusing is performed on the target tissue, and a third layer selection gradient pulse is applied to the target tissue in the layer selection coding direction.

[0038] After the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, imaging data are acquired based on the excited echo;

[0039] Based on the acquired navigation data, the acquired imaging data is reconstructed to obtain magnetic resonance imaging (MRI) images of the target tissue.

[0040] The first radiofrequency pulse refocusing of the target tissue includes:

[0041] Based on the current diffusion gradient application method, determine the number and / or pulse angle of the refocusing pulses included in the first radio frequency pulse refocusing, and use the determined number and / or pulse angle of the refocusing pulses to perform the first radio frequency pulse refocusing on the target tissue.

[0042] The step of reconstructing the image from the acquired imaging data based on the acquired navigation data includes:

[0043] In parallel imaging, for repeated scans, the kernel of the generalized self-calibrated parallel acquisition GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The reconstructed repeated images are then averaged to obtain the MRI image of the target tissue.

[0044] Or, including:

[0045] During parallel imaging, image reconstruction is performed on all imaging data acquired by repeated scans to obtain the corresponding images. Navigation data is used to perform phase calibration on the reconstructed repeated images. Complex averaging is performed on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0046] Or, including:

[0047] In parallel imaging, for repeated scans, the kernel of GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The phase of the reconstructed repeated image is calibrated using navigation data. The complex average of all phase-calibrated repeated images is then performed to obtain the MRI image of the target tissue.

[0048] The acquired imaging data for the excitation echo includes:

[0049] Based on the preset acceleration factor in the PE direction of the phase encoding, the acquisition interval of the imaging data in the PE direction is determined, and the imaging data is acquired sequentially using the acquisition interval.

[0050] The navigation data acquired from the excitation echo includes:

[0051] Navigation data is collected at the center segment of K space in the frequency coding direction, and the number of collected points is equal to the quotient obtained by dividing the total number of collectable navigation data points by the acceleration factor in the PE direction.

[0052] After the diffusion gradient pulse is applied and before the navigation data is acquired from the excitation echo, the process further includes:

[0053] Routine phase calibration data for navigation data acquired from excited echoes;

[0054] After the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, and before the acquisition of imaging data from the excitation echo, the process further includes:

[0055] Routine phase calibration data for excited echo acquisition imaging data;

[0056] Furthermore, the step of acquiring navigation data from the excited echo and before reconstructing the image from the acquired imaging data based on the acquired navigation data further includes:

[0057] Phase calibration is performed on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data, and phase calibration is performed on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data.

[0058] A diffusion imaging method, comprising:

[0059] In the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process, the target tissue is first excited by radio frequency pulses, and at the same time, the first layer-selection gradient pulse is applied to the target tissue in the layer-selection coding direction.

[0060] After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction.

[0061] After the diffusion gradient pulse is applied, imaging data is acquired based on the excited echo;

[0062] After the imaging data acquisition is completed, navigation data is acquired based on the emitted echoes;

[0063] Based on the acquired navigation data, the acquired imaging data is reconstructed to obtain magnetic resonance imaging (MRI) images of the target tissue.

[0064] The radiofrequency pulse refocusing of the target tissue includes:

[0065] Based on the currently used diffusion gradient application method, determine the number and / or pulse angle of the refocusing pulses included in the radio frequency pulse refocusing, and use the determined number and / or pulse angle of the refocusing pulses to perform radio frequency pulse refocusing on the target tissue.

[0066] The step of reconstructing the image from the acquired imaging data based on the acquired navigation data includes:

[0067] In parallel imaging, for repeated scans, the kernel of the generalized self-calibrated parallel acquisition GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The reconstructed repeated images are then averaged to obtain the MRI image of the target tissue.

[0068] Or, including:

[0069] During parallel imaging, image reconstruction is performed on all imaging data acquired by repeated scans to obtain the corresponding images. Navigation data is used to perform phase calibration on the reconstructed repeated images. Complex averaging is performed on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0070] Or, including:

[0071] In parallel imaging, for repeated scans, the kernel of GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The phase of the reconstructed repeated image is calibrated using navigation data. The complex average of all phase-calibrated repeated images is then performed to obtain the MRI image of the target tissue.

[0072] The acquired imaging data for the excitation echo includes:

[0073] Based on the preset acceleration factor in the PE direction of the phase encoding, the acquisition interval of the imaging data in the PE direction is determined, and the imaging data is acquired sequentially using the acquisition interval.

[0074] The navigation data acquired from the excitation echo includes:

[0075] Navigation data is collected at the center segment of K space in the frequency coding direction, and the number of collected points is equal to the quotient obtained by dividing the total number of collectable navigation data points by the acceleration factor in the PE direction.

[0076] After the diffusion gradient pulse is applied and before the acquisition of imaging data from the excitation echo, the process further includes:

[0077] Routine phase calibration data for excited echo acquisition imaging data;

[0078] After the imaging data acquisition is completed and before the navigation data acquisition based on the excited echo is completed, the process further includes:

[0079] Routine phase calibration data for navigation data acquired from excited echoes;

[0080] Furthermore, the step of acquiring navigation data from the excited echo and before reconstructing the image from the acquired imaging data based on the acquired navigation data further includes:

[0081] Phase calibration is performed on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data, and phase calibration is performed on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data.

[0082] A diffusion imaging device, comprising:

[0083] The first acquisition module is used in the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process to first excite the target tissue with a radio frequency pulse, and simultaneously apply a first layer-selective gradient pulse to the target tissue in the layer-selective coding direction; after the radio frequency pulse excitation and the first layer-selective gradient pulse are applied, the target tissue is subjected to a first radio frequency pulse refocusing, and simultaneously a second layer-selective gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer-selective coding direction; after the diffusion gradient pulse is applied, imaging data is acquired based on the excited echo; after the imaging data is acquired, the target tissue is subjected to a second radio frequency pulse refocusing, and simultaneously a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction; after the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, navigation data is acquired based on the excited echo.

[0084] The first reconstruction module is used to reconstruct images from the acquired imaging data based on the acquired navigation data, thereby obtaining magnetic resonance imaging (MRI) images of the target tissue.

[0085] A diffusion imaging device, comprising:

[0086] The second acquisition module is used in the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process to first excite the target tissue with a radio frequency pulse, and simultaneously apply a first layer-selective gradient pulse to the target tissue in the layer-selective coding direction; after the radio frequency pulse excitation and the first layer-selective gradient pulse are applied, the target tissue is subjected to a first radio frequency pulse refocusing, and simultaneously a second layer-selective gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer-selective coding direction; after the diffusion gradient pulse is applied, navigation data is acquired based on the excited echo; after the navigation data is acquired, the target tissue is subjected to a second radio frequency pulse refocusing, and simultaneously a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction; after the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, imaging data is acquired based on the excited echo.

[0087] The second reconstruction module is used to reconstruct images from the acquired imaging data based on the acquired navigation data, thereby obtaining magnetic resonance imaging (MRI) images of the target tissue.

[0088] A diffusion imaging device, comprising:

[0089] The third acquisition module is used in the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process to first excite the target tissue with radio frequency pulses, and simultaneously apply a first layer-selective gradient pulse to the target tissue in the layer-selective coding direction; after the radio frequency pulse excitation and the first layer-selective gradient pulse are applied, radio frequency pulse refocusing is performed on the target tissue, and simultaneously a second layer-selective gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer-selective coding direction; after the diffusion gradient pulse is applied, imaging data is acquired based on the excitation echo; after the imaging data acquisition is completed, navigation data is acquired based on the excitation echo.

[0090] The third reconstruction module is used to reconstruct images from the acquired imaging data based on the acquired navigation data, thereby obtaining magnetic resonance imaging (MRI) images of the target tissue.

[0091] A magnetic resonance imaging system includes a diffusion imaging device as described in any of the above.

[0092] In this embodiment of the invention, by acquiring navigation data after acquiring imaging data in a single excitation, the phase error caused by motion is made consistent in the navigation data and imaging data, thereby improving the quality and robustness of image reconstruction in diffusion imaging. Attached Figure Description

[0093] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which will make the above and other features and advantages of the present invention more apparent to those skilled in the art. In the drawings:

[0094] Figure 1 This is a flowchart of the diffusion imaging method provided in the first embodiment of the present invention;

[0095] Figure 2 This is an example diagram of the SS-DW-EPI scanning sequence used in the first embodiment of the present invention;

[0096] Figure 3 This is an example diagram of conventional phase calibration data for acquiring imaging data and navigation data in the first embodiment of the present invention;

[0097] Figure 4 This is a flowchart of the diffusion imaging method provided in the second embodiment of the present invention;

[0098] Figure 5 This is an example diagram of the SS-DW-EPI scanning sequence used in the second embodiment of the present invention;

[0099] Figure 6 This is an example diagram of conventional phase calibration data for acquiring imaging data and navigation data in the second embodiment of the present invention;

[0100] Figure 7 This is a flowchart of the diffusion imaging method provided in the third embodiment of the present invention;

[0101] Figure 8 This is an example diagram of the SS-DW-EPI scanning sequence used in the third embodiment of the present invention;

[0102] Figure 9 This is an example diagram of conventional phase calibration data for acquiring imaging data and navigation data in the third embodiment of the present invention;

[0103] Figure 10 This is a schematic diagram of the diffusion imaging device provided in the first embodiment of the present invention;

[0104] Figure 11 This is a schematic diagram of the diffusion imaging device provided in the second embodiment of the present invention;

[0105] Figure 12 This is a schematic diagram of the diffusion imaging device provided in the third embodiment of the present invention.

[0106] The reference numerals in the attached figures are as follows:

[0107]

[0108]

[0109]

[0110] Detailed Implementation

[0111] To make the objectives, technical solutions, and advantages of the present invention clearer, the following embodiments are provided to further illustrate the present invention in detail.

[0112] Figure 1 The flowchart of the diffusion imaging method provided in the first embodiment of the present invention is as follows:

[0113] Step 101: In the SS-DW-EPI process, the target tissue is first excited by radio frequency pulses, and at the same time, the first layer selection gradient pulse is applied to the target tissue in the layer selection coding direction.

[0114] Step 102: After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to the first radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction.

[0115] In one optional embodiment, the first radio frequency pulse re-convergence of the target tissue in this step includes: determining the number and / or pulse angle of the re-convergence pulses included in the first radio frequency pulse re-convergence based on the currently adopted diffusion gradient application method, and performing the first radio frequency pulse re-convergence of the target tissue using the determined number and / or pulse angle of the re-convergence pulses.

[0116] Step 103: After the diffusion gradient pulse is applied, imaging data is acquired based on the excitation echo.

[0117] Step 104: After the imaging data acquisition is completed, the target tissue is subjected to a second radio frequency pulse refocusing, and at the same time, a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction.

[0118] Step 105: After the second RF pulse refocusing and the third layer selection gradient pulse are applied, navigation data is acquired based on the excitation echo.

[0119] The second radio frequency pulse refocusing only requires the transmission of one refocusing pulse.

[0120] Step 106: Reconstruct the images from the collected navigation data to obtain MRI images of the target tissue.

[0121] In the above embodiments, by acquiring navigation data after acquiring imaging data in a single excitation, it can be ensured that the phase error caused by motion is consistent in the navigation data and imaging data, thereby improving the quality and robustness of image reconstruction in diffusion imaging.

[0122] Figure 2This is an example image of the SS-DW-EPI scanning sequence used in the first embodiment of the present invention. In this example, a monopolar diffusion mode is used.

[0123] RF refers to the radio frequency pulse emitted towards the target tissue, where 211 is the excitation pulse, and 212 and 213 are the refocusing pulses;

[0124] Gs is the gradient field applied to the target tissue in the layer-selective coding direction, where 221, 224 and 226 are layer-selective gradient pulses; 223 and 225 are diffuse gradient pulses; and 222 is the convergence gradient pulse of the layer-selective gradient.

[0125] Gr represents the gradient field applied to the target tissue in the readout direction, where 2311 is the pre-dephasing gradient pulse of the imaging echo in the readout direction, 2312-2327 are the readout gradient pulses of the imaging echo, 2328 is the phase convergence gradient pulse of the imaging echo in the readout direction, 2329 is the pre-dephasing gradient pulse of the navigation echo in the readout direction, 2330-2338 are the readout gradient pulses of the navigation echo, and 2316 and 2334 are the readout gradient pulses of the spin echo.

[0126] Gp represents the gradient field applied to the target tissue in the phase encoding direction, where 2411 is the pre-dephasing gradient pulse of the imaging echo in the phase encoding direction, 2412-2426 are the phase encoding gradient pulses of the imaging echo, 2427 is the phase convergence gradient pulse of the imaging echo in the phase encoding direction, 2428 is the pre-dephasing gradient pulse of the navigation echo in the phase encoding direction, and 2429-2436 are the phase encoding gradient pulses of the navigation echo.

[0127] In one optional embodiment, step 106, image reconstruction of the acquired imaging data based on the acquired navigation data, includes: during parallel imaging, for repeated scans, calculating the kernel of GRAPPA using navigation data, reconstructing all imaging data acquired during repeated scans based on the kernel of GRAPPA to obtain the corresponding image, and performing a complex average on the reconstructed repeated images to obtain the MRI image of the target tissue.

[0128] Alternatively, it may include: during parallel imaging, performing image reconstruction on all imaging data acquired by repeated scans to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0129] Alternatively, it may include: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of GRAPPA, performing image reconstruction on all imaging data acquired during repeated scans based on the kernel of GRAPPA to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0130] In one optional embodiment, step 103, acquiring imaging data for the excited echo, includes: determining the acquisition interval of imaging data in the PE direction according to a preset acceleration factor in the PE direction, and acquiring imaging data sequentially using the acquisition interval.

[0131] In step 105, navigation data is acquired for the excited echo, including: acquiring navigation data at the center segment of K space in the frequency coding direction, and the number of acquired points is equal to the quotient obtained by dividing the total number of acquireable navigation data points by the acceleration factor in the PE direction.

[0132] For example, if the acceleration factor in the PE direction is n (n≥1), then when acquiring imaging data, one line is acquired every n-1 lines in the PE direction; when acquiring navigation data, if there are m points in the readout direction, then the point at the center of K space is acquired in the frequency coding direction. One point, This is the floor operator.

[0133] The above embodiments can make the echo intervals of imaging data and navigation data consistent, thereby further improving the robustness of image reconstruction and the quality of reconstructed images.

[0134] In one optional embodiment, step 103, after the diffusion gradient pulse is applied and before acquiring imaging data for the excited echo, further includes: conventional phase calibration data for the acquired imaging data of the excited echo.

[0135] In step 105, after the second RF pulse refocusing and the third layer selection gradient pulse are applied, and before the navigation data is acquired for the excitation echo, the following is further included: conventional phase calibration data for the navigation data acquired for the excitation echo.

[0136] Furthermore, in step 106, before performing image reconstruction on the acquired imaging data based on the acquired navigation data, the process further includes: performing phase calibration on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data, and performing phase calibration on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data.

[0137] The above embodiments can calibrate Nyquist artifacts in images, further improving image quality.

[0138] Figure 3 This is an example diagram of conventional phase calibration data for acquiring imaging data and navigation data in the first embodiment of the present invention, as shown below. Figure 3 As shown, with Figure 2 In contrast, before acquiring imaging data, two echoes 331 and 332 with alternating readout polarities are acquired to calibrate Nyquist artifacts in the imaging data; and before acquiring navigation data, two echoes 333 and 334 with alternating readout polarities are acquired to calibrate Nyquist artifacts in the navigation data.

[0139] Figure 4 The flowchart of the diffusion imaging method provided in the second embodiment of the present invention is as follows:

[0140] Step 401: In the SS-DW-EPI process, the target tissue is first excited by radio frequency pulses, and at the same time, a first layer selection gradient pulse is applied to the target tissue in the layer selection coding direction.

[0141] Step 402: After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to the first radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction.

[0142] In one optional embodiment, the first radio frequency pulse re-convergence on the target tissue in this step includes: determining the number and / or pulse angle of the re-convergence pulses included in the first radio frequency pulse re-convergence based on the currently adopted diffusion gradient application method, and performing the first radio frequency pulse re-convergence on the target tissue using the determined number and / or pulse angle of the re-convergence pulses.

[0143] Step 403: After the diffusion gradient pulse is applied, navigation data is acquired based on the excitation echo.

[0144] Step 404: After the imaging data acquisition is completed, the target tissue is subjected to a second radio frequency pulse refocusing, and at the same time, a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction.

[0145] Step 405: After the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, imaging data is acquired based on the excited echo.

[0146] Step 406: Reconstruct the images from the collected navigation data to obtain MRI images of the target tissue.

[0147] In the above embodiments, by acquiring navigation data before acquiring imaging data in a single excitation, it can be ensured that the phase error caused by motion is consistent in the navigation data and imaging data, thereby improving the robustness of image reconstruction in diffusion imaging.

[0148] Figure 5 This is an example image of the SS-DW-EPI scanning sequence used in the second embodiment of the present invention. In this example, a monopolar diffusion mode is used.

[0149] RF refers to the radio frequency pulse emitted towards the target tissue, where 511 is the excitation pulse, and 512 and 513 are the refocusing pulses;

[0150] Gs is the gradient field applied to the target tissue in the layer-selective coding direction, where 521, 524, and 526 are layer-selective gradient pulses; 523 and 525 are diffuse gradient pulses; and 522 is the convergence gradient pulse of the layer-selective gradient.

[0151] Gr represents the gradient field applied to the target tissue in the readout direction, where 5311 is the pre-dephasing gradient pulse of the navigation echo in the readout direction, 5312-5320 are the readout gradient pulses of the navigation echo; 5321 is the phase convergence gradient pulse of the navigation echo in the readout direction, 5322 is the pre-dephasing gradient pulse of the imaging echo in the readout direction, 5323-5338 are the readout gradient pulses of the imaging echo, and 5316 and 5327 are the readout gradient pulses of the spin echo.

[0152] Gp represents the gradient field applied to the target tissue in the phase encoding direction, where 5411 is the pre-dephasing gradient pulse of the navigation echo in the phase encoding direction, 5412-5419 are the phase encoding gradient pulses of the navigation echo, 5420 is the phase convergence gradient pulse of the navigation echo in the phase encoding direction, 5421 is the pre-dephasing gradient pulse of the imaging echo in the phase encoding direction, and 5422-5436 are the phase encoding gradient pulses of the imaging echo.

[0153] In one optional embodiment, step 406, image reconstruction of the acquired imaging data based on the acquired navigation data, includes: during parallel imaging, for repeated scans, calculating the kernel of GRAPPA using navigation data, reconstructing the image of all imaging data acquired in repeated scans based on the kernel of GRAPPA to obtain the corresponding image, and performing a complex average on the reconstructed repeated images to obtain the MRI image of the target tissue.

[0154] Alternatively, it may include: during parallel imaging, performing image reconstruction on all imaging data acquired by repeated scans to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0155] Alternatively, it may include: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of GRAPPA, performing image reconstruction on all imaging data acquired during repeated scans based on the kernel of GRAPPA to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0156] In one optional embodiment, step 405, acquiring imaging data for the excited echo, includes: determining the acquisition interval of imaging data in the PE direction according to a preset acceleration factor in the PE direction, and acquiring imaging data sequentially using the acquisition interval.

[0157] In step 403, navigation data is acquired for the excited echo, including: acquiring navigation data at the center segment of K space in the frequency coding direction, and the number of acquired points is equal to the quotient obtained by dividing the total number of acquireable navigation data points by the acceleration factor in the PE direction.

[0158] For example, if the acceleration factor in the PE direction is n (n≥1), then when acquiring imaging data, one line is acquired every n-1 lines in the PE direction; when acquiring navigation data, if there are m points in the readout direction, then the point at the center of K space is acquired in the frequency coding direction. One point, This is the floor operator.

[0159] The above embodiments can make the echo intervals of imaging data and navigation data consistent, thereby further improving the robustness of image reconstruction and the quality of reconstructed images.

[0160] In one optional embodiment, step 403, after the diffusion gradient pulse is applied and before acquiring navigation data for the excited echo, further includes: conventional phase calibration data for acquiring navigation data for the excited echo.

[0161] In step 405, after the second radio frequency pulse refocusing and the third layer selection gradient pulse are applied, and before the navigation data is acquired for the excitation echo, it further includes: conventional phase calibration data for the imaging data acquired for the excitation echo.

[0162] Furthermore, in step 406, before performing image reconstruction on the acquired imaging data based on the acquired navigation data, the process further includes: performing phase calibration on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data, and performing phase calibration on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data.

[0163] The above embodiments can calibrate Nyquist artifacts in images, further improving image quality.

[0164] Figure 6 This is an example diagram of conventional phase calibration data for acquiring imaging data and navigation data in the second embodiment of the present invention, as shown below. Figure 6 As shown, with Figure 5 In contrast, before acquiring navigation data, two echoes 631 and 632 with alternating readout polarities are acquired to calibrate Nyquist artifacts in the navigation data; and before acquiring imaging data, two echoes 633 and 634 with alternating readout polarities are acquired to calibrate Nyquist artifacts in the imaging data.

[0165] Figure 7 The flowchart of the diffusion imaging method provided in the third embodiment of the present invention is as follows:

[0166] Step 701: In the SS-DW-EPI process, the target tissue is first excited by radio frequency pulses, and at the same time, a first layer selection gradient pulse is applied to the target tissue in the layer selection coding direction.

[0167] Step 702: After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction.

[0168] In one optional embodiment, the step of performing radio frequency pulse refocusing on the target tissue includes: determining the number and / or pulse angle of the refocusing pulses included in the radio frequency pulse refocusing according to the currently adopted diffusion gradient application method, and performing radio frequency pulse refocusing on the target tissue using the determined number and / or pulse angle of the refocusing pulses.

[0169] Step 703: After the diffusion gradient pulse is applied, imaging data is acquired based on the excited echo.

[0170] Step 704: Imaging data acquisition is complete. Navigation data is then acquired based on the excited echoes.

[0171] Step 705: Reconstruct the acquired imaging data based on the acquired navigation data to obtain the magnetic resonance imaging (MRI) image of the target tissue.

[0172] In the above embodiments, by acquiring navigation data after acquiring imaging data in a single excitation, it can be ensured that the phase error caused by motion is consistent in the navigation data and imaging data, thereby improving the robustness of image reconstruction and the quality of the reconstructed image.

[0173] Figure 8 This is an example image of the SS-DW-EPI scanning sequence used in the third embodiment of the present invention. In this example, a monopolar diffusion mode is used.

[0174] RF refers to the radio frequency pulse emitted towards the target tissue, where 811 is the excitation pulse and 812 is the refocusing pulse;

[0175] Gs represents the gradient field applied to the target tissue in the layer-selective coding direction, where 821 and 824 are layer-selective gradient pulses; 823 and 825 are diffuse gradient pulses; and 822 is the convergence gradient pulse of the layer-selective gradient.

[0176] Gr represents the gradient field applied to the target tissue in the readout direction, where 8311 is the pre-dephasing gradient pulse of the imaging echo in the readout direction, 8312-8327 are the readout gradient pulses of the imaging echo, 8328 is the phase convergence gradient pulse of the imaging echo in the readout direction, 8329 is the pre-dephasing gradient pulse of the navigation echo in the readout direction, and 8330-8338 are the readout gradient pulses of the navigation echo.

[0177] Gp represents the gradient field applied to the target tissue in the phase encoding direction, where 8411 is the pre-dephasing gradient pulse of the imaging echo in the phase encoding direction, 8412-8426 are the phase encoding gradient pulses of the imaging echo, 8427 is the phase convergence gradient pulse of the imaging echo in the phase encoding direction, 8428 is the pre-dephasing gradient pulse of the navigation echo in the phase encoding direction, and 8429-8436 are the phase encoding gradient pulses of the navigation echo.

[0178] In one optional embodiment, step 705, image reconstruction of the acquired imaging data based on the acquired navigation data, includes: during parallel imaging, for repeated scans, calculating the kernel of GRAPPA using navigation data, reconstructing the image of all imaging data acquired in repeated scans based on the kernel of GRAPPA to obtain the corresponding image, and performing a complex average on the reconstructed repeated images to obtain the MRI image of the target tissue.

[0179] Alternatively, it may include: during parallel imaging, performing image reconstruction on all imaging data acquired by repeated scans to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0180] Alternatively, it may include: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of GRAPPA, performing image reconstruction on all imaging data acquired during repeated scans based on the kernel of GRAPPA to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0181] In one optional embodiment, step 703, acquiring imaging data for the excited echo, includes: determining the acquisition interval of imaging data in the PE direction according to a preset acceleration factor in the PE direction, and acquiring imaging data sequentially using the acquisition interval.

[0182] In step 704, navigation data is acquired for the excited echo, including: acquiring navigation data at the center segment of K space in the frequency coding direction, and the number of acquired points is equal to the quotient obtained by dividing the total number of acquireable navigation data points by the acceleration factor in the PE direction.

[0183] For example, if the acceleration factor in the PE direction is n (n≥1), then when acquiring imaging data, one line is acquired every n-1 lines in the PE direction; when acquiring navigation data, if there are m points in the readout direction, then the point at the center of K space is acquired in the frequency coding direction. One point, This is the floor operator.

[0184] The above embodiments can make the echo intervals of imaging data and navigation data consistent, thereby further improving the robustness of image reconstruction and the quality of reconstructed images.

[0185] In one optional embodiment, step 703, after the diffusion gradient pulse is applied and before acquiring imaging data for the excited echo, further includes: conventional phase calibration data for the acquired imaging data of the excited echo.

[0186] In step 704, after the imaging data acquisition is completed and before the navigation data acquisition for the excited echo is completed, it further includes: conventional phase calibration data for the navigation data acquisition for the excited echo;

[0187] Furthermore, in step 705, before performing image reconstruction on the acquired imaging data based on the acquired navigation data, the process further includes: performing phase calibration on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data, and performing phase calibration on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data.

[0188] The above embodiments can calibrate Nyquist artifacts in images, further improving image quality.

[0189] Figure 9 This is an example diagram of conventional phase calibration data for acquiring imaging data and navigation data in the third embodiment of the present invention, as shown below. Figure 9 As shown, with Figure 8 In contrast, before acquiring imaging data, two echoes 931 and 932 with alternating readout polarities are acquired to calibrate Nyquist artifacts in the imaging data; and before acquiring navigation data, two echoes 933 and 934 with alternating readout polarities are acquired to calibrate Nyquist artifacts in the navigation data.

[0190] As can be seen from the first, second, and third embodiments of the present invention:

[0191] In the first embodiment, the navigation scan, as the second EPI readout, is inserted after each excited imaging scan, wherein navigation data is formed by the second spin echo, and the signal loss caused by B0 inhomogeneity matches the imaging data formed by the first spin echo. In this embodiment, since a longer TE is required to form the second spin echo, this means a significant increase in scan time;

[0192] In the second embodiment, the navigation scan, which is the first EPI readout, is inserted before each excited imaging scan, wherein navigation data is rapidly formed by the first spin echo. The signal loss caused by B0 inhomogeneity is matched with the imaging data formed by the second spin echo. Compared to the first embodiment, the TE can be very short in the first spin echo. Therefore, the imaging data can have a TE equivalent to or greater than that of the imaging data in the first embodiment, the TE of the imaging data specifically depending on the resolution of the navigation data;

[0193] In the third embodiment, the navigation scan, as a second EPI readout, is inserted after each excited imaging scan, but gradient echo is used instead of spin echo. Since the GRAPPA technique is insensitive to contrast variations between the ACS and imaging data, parallel imaging reconstruction can also be achieved using ACS data acquired via gradient echo. Signal loss caused by B0 inhomogeneity differs between the ACS and imaging data, potentially leading to residual artifacts and noise under high acceleration factors.

[0194] Figure 10 This is a schematic diagram of the structure of the diffusion imaging device 100 provided in the first embodiment of the present invention. The device 100 mainly includes: a first acquisition module 101 and a first reconstruction module 102, wherein:

[0195] The first acquisition module 101 is used in the SS-DW-EPI process to first excite the target tissue with a radio frequency pulse, and simultaneously apply a first layer-selective gradient pulse to the target tissue in the layer-selective coding direction; after the radio frequency pulse excitation and the application of the first layer-selective gradient pulse are completed, the target tissue is subjected to a first radio frequency pulse refocusing, and simultaneously a second layer-selective gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer-selective coding direction; after the diffusion gradient pulse is applied, imaging data is acquired based on the excitation echo; after the imaging data is acquired, the target tissue is subjected to a second radio frequency pulse refocusing, and simultaneously a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction; after the second radio frequency pulse refocusing and the application of the third layer-selective gradient pulse are completed, navigation data is acquired based on the excitation echo.

[0196] The first reconstruction module 102 is used to reconstruct images from the imaging data acquired by the first acquisition module 101 based on the navigation data acquired by the first acquisition module 101, so as to obtain MRI images of the target tissue.

[0197] In one optional embodiment, the first acquisition module 101 performs a first radio frequency pulse re-aggregation on the target tissue, including: determining the number and / or pulse angle of the re-aggregation pulses included in the first radio frequency pulse re-aggregation according to the currently adopted diffusion gradient application method, and performing the first radio frequency pulse re-aggregation on the target tissue using the determined number and / or pulse angle of the re-aggregation pulses.

[0198] In one optional embodiment, the first reconstruction module 102 performs image reconstruction on the acquired imaging data based on the acquired navigation data, including: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of the generalized self-calibrated parallel acquisition GRAPPA, performing image reconstruction on all imaging data acquired in repeated scans based on the kernel of GRAPPA to obtain the corresponding image, and performing complex averaging on the reconstructed repeated images to obtain the MRI image of the target tissue.

[0199] Alternatively, it may include: during parallel imaging, performing image reconstruction on all imaging data acquired by repeated scans to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0200] Alternatively, it may include: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of GRAPPA, performing image reconstruction on all imaging data acquired during repeated scans based on the kernel of GRAPPA to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0201] In one optional embodiment, the first acquisition module 101 acquires imaging data for the excited echo, including: determining the acquisition interval of imaging data in the PE direction according to a preset acceleration factor in the PE direction, and acquiring imaging data sequentially using the acquisition interval.

[0202] The first acquisition module 101 acquires navigation data for the excited echo, including: acquiring navigation data at the center segment of K space in the frequency coding direction, and the number of acquired points is equal to the quotient obtained by dividing the total number of acquireable navigation data points by the acceleration factor in the PE direction.

[0203] In one optional embodiment, after the diffusion gradient pulse is applied and before acquiring imaging data of the excited echo, the first acquisition module 101 further includes: conventional phase calibration data for acquiring imaging data of the excited echo.

[0204] After the second RF pulse refocusing and the third layer selection gradient pulse are applied, and before the navigation data is acquired from the excitation echo, the first acquisition module 101 further includes: conventional phase calibration data for the navigation data acquired from the excitation echo.

[0205] Furthermore, after the first acquisition module 101 acquires navigation data from the excited echo and before performing image reconstruction on the acquired imaging data based on the acquired navigation data, it further includes: performing phase calibration on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data, and performing phase calibration on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data.

[0206] Figure 11 This is a schematic diagram of the structure of the diffusion imaging device 110 provided in the second embodiment of the present invention. The device 110 mainly includes: a first acquisition module 111 and a first reconstruction module 112, wherein:

[0207] The second acquisition module 111 is used in the SS-DW-EPI process to first excite the target tissue with a radio frequency pulse, and simultaneously apply a first layer-selective gradient pulse to the target tissue in the layer-selective coding direction; after the radio frequency pulse excitation and the first layer-selective gradient pulse are applied, the target tissue is subjected to a first radio frequency pulse refocusing, and simultaneously a second layer-selective gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer-selective coding direction; after the diffusion gradient pulse is applied, navigation data is acquired based on the excitation echo; after the navigation data is acquired, the target tissue is subjected to a second radio frequency pulse refocusing, and simultaneously a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction; after the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, imaging data is acquired based on the excitation echo.

[0208] The second reconstruction module 112 is used to reconstruct images from the imaging data acquired by the second acquisition module 111 based on the navigation data acquired by the second acquisition module 111, so as to obtain MRI images of the target tissue.

[0209] In one optional embodiment, the second acquisition module 111 performs a first radio frequency pulse re-aggregation on the target tissue, including: determining the number and / or pulse angle of the re-aggregation pulses included in the first radio frequency pulse re-aggregation according to the currently adopted diffusion gradient application method, and performing the first radio frequency pulse re-aggregation on the target tissue using the determined number and / or pulse angle of the re-aggregation pulses.

[0210] In one optional embodiment, the second reconstruction module 112 performs image reconstruction on the acquired imaging data based on the acquired navigation data, including: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of the generalized self-calibrated parallel acquisition GRAPPA, performing image reconstruction on all imaging data acquired in repeated scans based on the kernel of GRAPPA to obtain the corresponding image, and performing complex averaging on the reconstructed repeated images to obtain the MRI image of the target tissue.

[0211] Alternatively, it may include: during parallel imaging, performing image reconstruction on all imaging data acquired by repeated scans to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0212] Alternatively, it may include: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of GRAPPA, performing image reconstruction on all imaging data acquired during repeated scans based on the kernel of GRAPPA to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0213] In one optional embodiment, the second acquisition module 111 acquires imaging data for the excited echo, including: determining the acquisition interval of imaging data in the PE direction according to a preset acceleration factor in the PE direction, and acquiring imaging data sequentially using the acquisition interval.

[0214] The second acquisition module 111 acquires navigation data for the excited echo, including: acquiring navigation data at the center segment of K space in the frequency coding direction, and the number of acquired points is equal to the quotient obtained by dividing the total number of acquireable navigation data points by the acceleration factor in the PE direction.

[0215] In one optional embodiment, after the diffusion gradient pulse is applied and before acquiring navigation data for the excited echo, the second acquisition module 111 further includes: conventional phase calibration data for acquiring navigation data for the excited echo.

[0216] After the second radio frequency pulse refocusing and the third layer selection gradient pulse are applied, and before the acquisition of imaging data for the excited echo, the second acquisition module 111 further includes: conventional phase calibration data for the acquisition of imaging data for the excited echo.

[0217] Furthermore, after acquiring navigation data from the excited echo and before reconstructing the image from the acquired imaging data based on the acquired navigation data, the second acquisition module 111 further includes: performing phase calibration on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data, and performing phase calibration on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data.

[0218] Figure 12 This is a schematic diagram of the diffusion imaging device 120 provided in the third embodiment of the present invention. The device 120 mainly includes: a third acquisition module 121 and a third reconstruction module 122, wherein:

[0219] The third acquisition module 121 is used in the SS-DW-EPI process to first excite the target tissue with radio frequency pulses, and simultaneously apply a first layer-selective gradient pulse to the target tissue in the layer-selective coding direction; after the radio frequency pulse excitation and the first layer-selective gradient pulse are applied, radio frequency pulse refocusing is performed on the target tissue, and simultaneously a second layer-selective gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer-selective coding direction; after the diffusion gradient pulse is applied, imaging data is acquired based on the excitation echo; after the imaging data is acquired, navigation data is acquired based on the excitation echo.

[0220] The third reconstruction module 122 is used to reconstruct images from the imaging data acquired by the third acquisition module 121 based on the navigation data acquired by the third acquisition module 121, so as to obtain MRI images of the target tissue.

[0221] In one optional embodiment, the third acquisition module 121 performs radio frequency pulse refocusing on the target tissue, including: determining the number and / or pulse angle of the refocusing pulses included in the radio frequency pulse refocusing according to the currently adopted diffusion gradient application method, and performing radio frequency pulse refocusing on the target tissue using the determined number and / or pulse angle of the refocusing pulses.

[0222] In one optional embodiment, the third reconstruction module 122 performs image reconstruction on the acquired imaging data based on the acquired navigation data, including: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of the generalized self-calibrated parallel acquisition GRAPPA, performing image reconstruction on all imaging data acquired in repeated scans based on the kernel of GRAPPA to obtain the corresponding image, and performing complex averaging on the reconstructed repeated images to obtain the MRI image of the target tissue.

[0223] Alternatively, it may include: during parallel imaging, performing image reconstruction on all imaging data acquired by repeated scans to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0224] Alternatively, it may include: during parallel imaging, for repeated scans, using navigation data to calculate the kernel of GRAPPA, performing image reconstruction on all imaging data acquired during repeated scans based on the kernel of GRAPPA to obtain the corresponding image, using navigation data to perform phase calibration on the reconstructed repeated images, and performing complex averaging on all phase-calibrated repeated images to obtain the MRI image of the target tissue.

[0225] In one optional embodiment, the third acquisition module 121 acquires imaging data for the excited echo, including: determining the acquisition interval of imaging data in the PE direction according to a preset acceleration factor in the PE direction, and acquiring imaging data sequentially using the acquisition interval;

[0226] The third acquisition module 121 acquires navigation data for the excited echo, including: acquiring navigation data at the center segment of K space in the frequency coding direction, and the number of acquired points is equal to the quotient obtained by dividing the total number of acquireable navigation data points by the acceleration factor in the PE direction.

[0227] In one optional embodiment, after the diffusion gradient pulse is applied and before acquiring imaging data of the excited echo, the third acquisition module 121 further includes: conventional phase calibration data for acquiring imaging data of the excited echo.

[0228] After the imaging data acquisition is completed and before the navigation data acquisition for the excited echo is completed, the third acquisition module 121 further includes: conventional phase calibration data for the navigation data acquisition for the excited echo.

[0229] Furthermore, after the third acquisition module 121 acquires navigation data from the excited echo and before performing image reconstruction on the acquired imaging data based on the acquired navigation data, it further includes: performing phase calibration on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data, and performing phase calibration on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data.

[0230] The magnetic resonance imaging system proposed in the embodiments of the present invention may include the diffusion imaging device 100, 110 or 120 provided in the above embodiments.

[0231] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A diffusion imaging method, characterized in that, include: In the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process, the target tissue is first excited by radio frequency pulses, and at the same time, the first layer-selection gradient pulse is applied to the target tissue in the layer-selection coding direction. After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to the first radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction. After the diffusion gradient pulse is applied, imaging data is acquired based on the excited echo; After the imaging data acquisition is completed, a second radio frequency pulse refocusing is performed on the target tissue, and a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction. After the second radio frequency pulse refocusing and the third layer selection gradient pulse are applied, navigation data are acquired based on the excited echo; Based on the acquired navigation data, the acquired imaging data is reconstructed to obtain magnetic resonance imaging (MRI) images of the target tissue.

2. The method according to claim 1, characterized in that, The first radiofrequency pulse refocusing of the target tissue includes: Based on the current diffusion gradient application method, determine the number and / or pulse angle of the refocusing pulses included in the first radio frequency pulse refocusing, and use the determined number and / or pulse angle of the refocusing pulses to perform the first radio frequency pulse refocusing on the target tissue.

3. The method according to claim 1, characterized in that, The step of reconstructing the image from the acquired imaging data based on the acquired navigation data includes: In parallel imaging, for repeated scans, the kernel of the generalized self-calibrated parallel acquisition GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The reconstructed repeated images are then averaged to obtain the MRI image of the target tissue. Or, including: During parallel imaging, image reconstruction is performed on all imaging data acquired by repeated scans to obtain the corresponding images. Navigation data is used to perform phase calibration on the reconstructed repeated images. Complex averaging is performed on all phase-calibrated repeated images to obtain the MRI image of the target tissue. Or, including: In parallel imaging, for repeated scans, the kernel of GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The phase of the reconstructed repeated image is calibrated using navigation data. The complex average of all phase-calibrated repeated images is then performed to obtain the MRI image of the target tissue.

4. The method according to claim 1, characterized in that, The acquired imaging data for the excitation echo includes: Based on the preset acceleration factor in the PE direction of the phase encoding, the acquisition interval of the imaging data in the PE direction is determined, and the imaging data is acquired sequentially using the acquisition interval. The navigation data acquired from the excitation echo includes: Navigation data is collected at the center segment of K space in the frequency coding direction, and the number of collected points is equal to the quotient obtained by dividing the total number of collectable navigation data points by the acceleration factor in the PE direction.

5. The method according to claim 1, characterized in that, After the diffusion gradient pulse is applied and before the acquisition of imaging data from the excitation echo, the process further includes: Routine phase calibration data for excited echo acquisition imaging data; After the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, and before the navigation data acquisition based on the excitation echo, the process further includes: Routine phase calibration data for navigation data acquired from excited echoes; Furthermore, the step of acquiring navigation data from the excited echo and before reconstructing the image from the acquired imaging data based on the acquired navigation data further includes: Phase calibration is performed on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data, and phase calibration is performed on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data.

6. A diffusion imaging method, characterized in that, include: In the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process, the target tissue is first excited by radio frequency pulses, and at the same time, the first layer-selection gradient pulse is applied to the target tissue in the layer-selection coding direction. After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to the first radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction. After the diffuse gradient pulse is applied, navigation data is collected based on the excitation echo; After the navigation data acquisition is completed, a second radio frequency pulse refocusing is performed on the target tissue, and a third layer selection gradient pulse is applied to the target tissue in the layer selection coding direction. After the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, imaging data are acquired based on the excited echo; Based on the acquired navigation data, the acquired imaging data is reconstructed to obtain magnetic resonance imaging (MRI) images of the target tissue.

7. The method according to claim 6, characterized in that, The first radiofrequency pulse refocusing of the target tissue includes: Based on the current diffusion gradient application method, determine the number and / or pulse angle of the refocusing pulses included in the first radio frequency pulse refocusing, and use the determined number and / or pulse angle of the refocusing pulses to perform the first radio frequency pulse refocusing on the target tissue.

8. The method according to claim 6, characterized in that, The step of reconstructing the image from the acquired imaging data based on the acquired navigation data includes: In parallel imaging, for repeated scans, the kernel of the generalized self-calibrated parallel acquisition GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The reconstructed repeated images are then averaged to obtain the MRI image of the target tissue. Or, including: During parallel imaging, image reconstruction is performed on all imaging data acquired by repeated scans to obtain the corresponding images. Navigation data is used to perform phase calibration on the reconstructed repeated images. Complex averaging is performed on all phase-calibrated repeated images to obtain the MRI image of the target tissue. Or, including: In parallel imaging, for repeated scans, the kernel of GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The phase of the reconstructed repeated image is calibrated using navigation data. The complex average of all phase-calibrated repeated images is then performed to obtain the MRI image of the target tissue.

9. The method according to claim 6, characterized in that, The acquired imaging data for the excitation echo includes: Based on the preset acceleration factor in the PE direction of the phase encoding, the acquisition interval of the imaging data in the PE direction is determined, and the imaging data is acquired sequentially using the acquisition interval. The navigation data acquired from the excitation echo includes: Navigation data is collected at the center segment of K space in the frequency coding direction, and the number of collected points is equal to the quotient obtained by dividing the total number of collectable navigation data points by the acceleration factor in the PE direction.

10. The method according to claim 6, characterized in that, After the diffusion gradient pulse is applied and before the navigation data is acquired from the excitation echo, the process further includes: Routine phase calibration data for navigation data acquired from excited echoes; After the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, and before the acquisition of imaging data from the excitation echo, the process further includes: Routine phase calibration data for excited echo acquisition imaging data; Furthermore, the step of acquiring navigation data from the excited echo and before reconstructing the image from the acquired imaging data based on the acquired navigation data further includes: Phase calibration is performed on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data, and phase calibration is performed on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data.

11. A diffusion imaging method, characterized in that, include: In the single-excitation diffusion-weighted echo planar imaging (SS-DW-EPI) process, the target tissue is first excited by radio frequency pulses, and at the same time, the first layer-selection gradient pulse is applied to the target tissue in the layer-selection coding direction. After the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to radio frequency pulse refocusing, and at the same time, the second layer selection gradient pulse and the diffusion gradient pulse are applied to the target tissue in the layer selection coding direction. After the diffusion gradient pulse is applied, imaging data is acquired based on the excited echo; After the imaging data acquisition is completed, navigation data is acquired based on the emitted echoes; Based on the acquired navigation data, the acquired imaging data is reconstructed to obtain magnetic resonance imaging (MRI) images of the target tissue.

12. The method according to claim 11, characterized in that, The radiofrequency pulse refocusing of the target tissue includes: Based on the currently used diffusion gradient application method, determine the number and / or pulse angle of the refocusing pulses included in the radio frequency pulse refocusing, and use the determined number and / or pulse angle of the refocusing pulses to perform radio frequency pulse refocusing on the target tissue.

13. The method according to claim 11, characterized in that, The step of reconstructing the image from the acquired imaging data based on the acquired navigation data includes: In parallel imaging, for repeated scans, the kernel of the generalized self-calibrated parallel acquisition GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The reconstructed repeated images are then averaged to obtain the MRI image of the target tissue. Or, including: During parallel imaging, image reconstruction is performed on all imaging data acquired by repeated scans to obtain the corresponding images. Navigation data is used to perform phase calibration on the reconstructed repeated images. Complex averaging is performed on all phase-calibrated repeated images to obtain the MRI image of the target tissue. Or, including: In parallel imaging, for repeated scans, the kernel of GRAPPA is calculated using navigation data. Based on the kernel of GRAPPA, image reconstruction is performed on all imaging data acquired in repeated scans to obtain the corresponding image. The phase of the reconstructed repeated image is calibrated using navigation data. The complex average of all phase-calibrated repeated images is then performed to obtain the MRI image of the target tissue.

14. The method according to claim 11, characterized in that, The acquired imaging data for the excitation echo includes: Based on the preset acceleration factor in the PE direction of the phase encoding, the acquisition interval of the imaging data in the PE direction is determined, and the imaging data is acquired sequentially using the acquisition interval. The navigation data acquired from the excitation echo includes: Navigation data is collected at the center segment of K space in the frequency coding direction, and the number of collected points is equal to the quotient obtained by dividing the total number of collectable navigation data points by the acceleration factor in the PE direction.

15. The method according to claim 11, characterized in that, After the diffusion gradient pulse is applied and before the acquisition of imaging data from the excitation echo, the process further includes: Routine phase calibration data for excited echo acquisition imaging data; After the imaging data acquisition is completed and before the navigation data acquisition based on the excited echo is completed, the process further includes: Routine phase calibration data for navigation data acquired from excited echoes; Furthermore, the step of acquiring navigation data from the excited echo and before reconstructing the image from the acquired imaging data based on the acquired navigation data further includes: Phase calibration is performed on the acquired imaging data based on the conventional phase calibration data of the acquired imaging data, and phase calibration is performed on the acquired navigation data based on the conventional phase calibration data of the acquired navigation data.

16. A diffusion imaging device (100), characterized in that, include: The first acquisition module (101) is used to first excite the target tissue with radio frequency pulses during the single excitation diffusion-weighted echo plane imaging (SS-DW-EPI) process, and simultaneously apply a first layer-selection gradient pulse to the target tissue in the layer-selection coding direction; after the radio frequency pulse excitation and the first layer-selection gradient pulse are applied, the target tissue is subjected to the first radio frequency pulse refocusing, and simultaneously a second layer-selection gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer-selection coding direction; After the diffusion gradient pulse is applied, imaging data is acquired based on the excited echo; After the imaging data acquisition is completed, a second radio frequency pulse refocusing is performed on the target tissue, and a third layer-selective gradient pulse is applied to the target tissue in the layer-selective coding direction. After the second radio frequency pulse refocusing and the third layer selection gradient pulse are applied, navigation data are acquired based on the excited echo; The first reconstruction module (102) is used to reconstruct the acquired imaging data based on the acquired navigation data to obtain the magnetic resonance imaging (MRI) image of the target tissue.

17. A diffusion imaging device (110), characterized in that, include: The second acquisition module (111) is used to first excite the target tissue with radio frequency pulses during the single excitation diffusion-weighted echo plane imaging (SS-DW-EPI) process, and simultaneously apply a first layer selection gradient pulse to the target tissue in the layer selection coding direction; after the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is subjected to the first radio frequency pulse refocusing, and simultaneously a second layer selection gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer selection coding direction; After the diffuse gradient pulse is applied, navigation data is collected based on the excitation echo; After the navigation data acquisition is completed, a second radio frequency pulse refocusing is performed on the target tissue, and a third layer selection gradient pulse is applied to the target tissue in the layer selection coding direction. After the second radio frequency pulse refocusing and the third layer-selective gradient pulse are applied, imaging data are acquired based on the excited echo; The second reconstruction module (112) is used to reconstruct the acquired imaging data based on the acquired navigation data to obtain the magnetic resonance imaging (MRI) image of the target tissue.

18. A diffusion imaging device (120), characterized in that, include: The third acquisition module (121) is used to first excite the target tissue with radio frequency pulses during the single excitation diffusion-weighted echo plane imaging (SS-DW-EPI) process, and simultaneously apply a first layer selection gradient pulse to the target tissue in the layer selection coding direction; after the radio frequency pulse excitation and the first layer selection gradient pulse are applied, the target tissue is refocused with radio frequency pulses, and simultaneously a second layer selection gradient pulse and a diffusion gradient pulse are applied to the target tissue in the layer selection coding direction; After the diffusion gradient pulse is applied, imaging data is acquired based on the excitation echo; after the imaging data is acquired, navigation data is acquired based on the excitation echo. The third reconstruction module (122) is used to reconstruct the acquired imaging data based on the acquired navigation data to obtain the magnetic resonance imaging (MRI) image of the target tissue.

19. A magnetic resonance imaging system, characterized in that, Includes the diffusion imaging apparatus (100, 110, 120) as described in any one of claims 16 to 18.

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