MAGNETIC RESONANCE IMAGING (MRI) SYSTEM AND METHOD INTEGRATING MULTI-NUCLIDE SYNCHRONOUS IMAGING AND SPECTRAL IMAGING

Abstract

A magnetic resonance imaging (MRI) system and method integrating multi-nuclide synchronous imaging and spectral imaging is provided. The MRI system includes a spectral imaging module, a multi-nuclide synchronous imaging module, and a spectral reconstruction and image fusion module, where the spectral imaging module is configured to acquire a spectrum of a nuclide Nuc; the multi-nuclide synchronous imaging module is configured to perform synchronous imaging of nuclides Nuc1 . . . . Nucn, where when n=1, Nucl is .sup.1H; and when n>1, Nucn is a non-.sup.1H nuclide; and the spectral reconstruction and image fusion module is configured to receive the spectrum of the nuclide Nuc and images of the nuclides Nuc1 . . . . Nucn, and acquire spatial distribution information of compounds of the nuclide Nuc and spatial distribution information of the non-.sup.1H nuclide through fusion. The system and method can synchronously acquire MR signals of different nuclides, and reconstruct and fuse non-.sup.1H nuclide images.

Claims

1. A magnetic resonance imaging (MRI) system integrating multi-nuclide synchronous imaging and spectral imaging, comprising a spectral imaging module, a multi-nuclide synchronous imaging module, and a spectral reconstruction and image fusion module, wherein the spectral imaging module is configured to acquire a spectrum of a nuclide Nuc; the multi-nuclide synchronous imaging module is configured to perform synchronous imaging of nuclides Nuc1 . . . Nucn, wherein n is an integer, and n?1; when n=1, Nuc1 is .sup.1H; when n>1, Nucn is a non-.sup.1H nuclide; and Nuc and Nuc1 . . . Nucn are different nuclides; the spectral reconstruction and image fusion module is configured to receive the spectrum of the nuclide Nuc and images of the nuclides Nuc1 . . . Nucn, and acquire spatial distribution information of compounds of the nuclide Nuc and spatial distribution information of the non-.sup.1H nuclide through fusion; and specifically, the spectral reconstruction and image fusion module is configured to reconstruct the spectrum and target compound images of the nuclide Nuc, reconstruct the images of the nuclides Nuc1 . . . Nucn, interpolate each of the target compound images of the nuclide Nuc in an image domain to a same size as a .sup.1H image, integrate the target compound images of the nuclide Nuc and a non-.sup.1H nuclide image into the .sup.1H image, and acquire spatial distribution information of target compounds of the nuclide Nuc and spatial distribution information of the non-.sup.1H nuclide; and the spectral imaging performed by the spectral imaging module and the multi-nuclide synchronous imaging performed by the multi-nuclide synchronous imaging module are completed within a same repetition time; and in terms of timing, the multi-nuclide synchronous imaging is performed after the spectral imaging.

2. An MRI method integrating multi-nuclide synchronous imaging and spectral imaging, comprising the following steps: step 1: spectral imaging: selectively exciting a slice of a nuclide Nuc; distinguishing voxels within the slice through phase encoding of two dimensions; and acquiring a free induction decay (FID) signal; step 2: multi-nuclide synchronous imaging: selectively exciting slices of nuclides Nuc1 . . . Nucn through different radio frequency (RF) pulses; distinguishing voxels within each of the slices through phase encoding and frequency encoding; and acquiring echo signals ECHO1 . . . ECHOn while performing frequency encoding, wherein n denotes an n-th nuclide; n is an integer, and n?1; when n=1, Nuc1 is .sup.1H; and when n?1, Nucn is a non-.sup.1H nuclide; and step 3: spectral reconstruction and image fusion: reconstructing a spectrum and target compound images of the nuclide Nuc; reconstructing images of the nuclides Nuc1 . . . Nucn; interpolating each of the target compound images of the nuclide Nuc in an image domain to a same size as a .sup.1H image; integrating the target compound images of the nuclide Nuc and a non-.sup.1H nuclide image into the .sup.1H image; and acquiring spatial distribution information of target compounds of the nuclide Nuc and spatial distribution information of the non-.sup.1H nuclide; wherein, the spectral imaging in step 1 and the multi-nuclide synchronous imaging in step 2 are completed within a same repetition time; and in terms of timing, the multi-nuclide synchronous imaging in step 2 is performed after the spectral imaging in step 1.

3. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 2, wherein in step 1, the spectral imaging comprises: 1.1: combining an RF pulse p1 with a slice selection gradient g1 and a slice selection refocusing gradient g2 applied to a slice selection gradient channel Gs, and selectively exciting the nuclide Nuc for spectral imaging; and adjusting a slice thickness of the nuclide Nuc by adjusting an intensity of the slice selection gradient g1 through a parameter ap1, wherein the nuclide Nuc is a non-.sup.1H nuclide different from Nucn; 1.2: performing phase encoding through gradient channels Gp and Gr of two spatial dimensions orthogonal to a direction of the slice selection gradient; labeling phase encoding gradients as g3 and g4, respectively, wherein g3 is applied to the gradient channel Gp, and g4 is applied to the gradient channel Gr; and adjusting a resolution within the slice of the nuclide Nuc by adjusting intensities of the phase encoding gradients g3 and g4 respectively through parameters ap2 and ap3; 1.3: acquiring the FID signal of the nuclide Nuc; and 1.4: applying phase encoding gradients g5 and g6 to the gradient channels Gp and Gr respectively to refocus phase dispersion effects of the phase encoding gradients g3 and g4.

4. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 2, wherein in step 2, the multi-nuclide synchronous imaging comprises: 2.1: combining RF pulses p2 . . . pn+1 with a slice selection gradient g7 and a slice selection refocusing gradient g8 applied to the slice selection gradient channel Gs, and selectively exciting the nuclides Nuc1 . . . Nucn for imaging; 2.2: performing phase encoding and frequency encoding respectively through gradient channels Gp and Gr of two spatial dimensions orthogonal to a direction of the slice selection gradient; and applying a phase encoding gradient g9 to the gradient channel Gp and a frequency encoding preparation gradient g10 to the gradient channel Gr; and applying a frequency encoding gradient g11 to the gradient channel Gr while synchronously acquiring the echo signals ECHO1 . . . ECHOn of the nuclides, wherein ECHO1 . . . ECHOn sampling time windows are center-aligned; and 2.3: applying a phase encoding gradient g12 to the gradient channel Gp to refocus a phase dispersion effect of the phase encoding gradient g9.

5. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 2, wherein in step 3, the reconstructing a spectrum and target compound images of the nuclide Nuc specifically comprises: performing zero-filling on the FID signal of the nuclide Nuc, performing two-dimensional Fourier transform on the two spatial dimensions, and performing Fourier transform on a time dimension of the FID signal to acquire a spectrum of compounds of the nuclide Nuc in each voxel; and processing the spectrum, assigning peaks in the processed spectrum to different target compounds, integrating the peaks to acquire contents of the target compounds, and labeling a pixel intensity corresponding to the voxel, thereby reconstructing the target compound images.

6. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 2, wherein in step 3, the reconstructing images of the nuclides Nuc1 . . . Nucn specifically comprises: filling the echo signals ECHO1 . . . ECHOn into k-spaces of the nuclides Nuc1 . . . Nucn, respectively; zero-filling each of the k-spaces according to a ratio of a gyromagnetic ratio of the nuclide to a gyromagnetic ratio of .sup.1H, thereby ensuring that each nuclide and .sup.1H maintain a same imaging field of view; and performing two-dimensional Fourier transform to acquire the images of the nuclides Nuc1 . . . Nucn.

7. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 3, wherein step 1.2 further comprises: simultaneously applying and center-aligning the phase encoding gradients g3, g4, and the slice selection refocusing gradient g2.

8. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 4, wherein step 2.1 further comprises: center-aligning the RF pulses p2 . . . pn and the slice selection gradient g7; and adjusting slice thicknesses of different nuclides through different pulse shapes and pulse widths.

9. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 4, wherein step 2.2 further comprises: simultaneously applying and center-aligning the slice selection refocusing gradient g8, the phase encoding gradient g9, and the frequency encoding preparation gradient g10.

10. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 3, wherein in step 3, the reconstructing a spectrum and target compound images of the nuclide Nuc specifically comprises: performing zero-filling on the FID signal of the nuclide Nuc, performing two-dimensional Fourier transform on the two spatial dimensions, and performing Fourier transform on a time dimension of the FID signal to acquire a spectrum of compounds of the nuclide Nuc in each voxel; and processing the spectrum, assigning peaks in the processed spectrum to different target compounds, integrating the peaks to acquire contents of the target compounds, and labeling a pixel intensity corresponding to the voxel, thereby reconstructing the target compound images.

11. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 4, wherein in step 3, the reconstructing a spectrum and target compound images of the nuclide Nuc specifically comprises: performing zero-filling on the FID signal of the nuclide Nuc, performing two-dimensional Fourier transform on the two spatial dimensions, and performing Fourier transform on a time dimension of the FID signal to acquire a spectrum of compounds of the nuclide Nuc in each voxel; and processing the spectrum, assigning peaks in the processed spectrum to different target compounds, integrating the peaks to acquire contents of the target compounds, and labeling a pixel intensity corresponding to the voxel, thereby reconstructing the target compound images.

12. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 3, wherein in step 3, the reconstructing images of the nuclides Nuc1 . . . Nucn specifically comprises: filling the echo signals ECHO1 . . . ECHOn into k-spaces of the nuclides Nuc1 . . . Nucn, respectively; zero-filling each of the k-spaces according to a ratio of a gyromagnetic ratio of the nuclide to a gyromagnetic ratio of .sup.1H, thereby ensuring that each nuclide and .sup.1H maintain a same imaging field of view; and performing two-dimensional Fourier transform to acquire the images of the nuclides Nuc1 . . . Nucn.

13. The MRI method integrating multi-nuclide synchronous imaging and spectral imaging according to claim 4, wherein in step 3, the reconstructing images of the nuclides Nuc1 . . . Nucn specifically comprises: filling the echo signals ECHO1 . . . ECHOn into k-spaces of the nuclides Nuc1 . . . Nucn, respectively; zero-filling each of the k-spaces according to a ratio of a gyromagnetic ratio of the nuclide to a gyromagnetic ratio of .sup.1H, thereby ensuring that each nuclide and .sup.1H maintain a same imaging field of view; and performing two-dimensional Fourier transform to acquire the images of the nuclides Nuc1 . . . Nucn.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] To describe the technical solutions in the embodiments of the present disclosure or in the prior art more clearly, the following briefly describes the drawings required for describing the embodiments or the prior art. Apparently, the drawings in the following description show merely some embodiments of the present disclosure, and those skilled in the art may still derive other drawings from these drawings without creative efforts.

[0041] FIG. 1 shows an overall solution for .sup.31P spectral imaging and .sup.1H-.sup.19F-.sup.23Na synchronous imaging; and

[0042] FIG. 2 is a pulse sequence diagram of .sup.31P spectral imaging and .sup.1H-.sup.19F-.sup.23Na synchronous imaging, where the diagram shows an MRI pulse sequence timing diagram for one scanning period (TR), with a horizontal axis representing a time axis.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0043] The technical solutions of the embodiments of the present disclosure are clearly and completely described below with reference to the drawings in the embodiments of the present disclosure. Apparently, the described embodiments are merely a part rather than all of the embodiments of the present disclosure. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts should fall within the protection scope of the present disclosure.

[0044] An MRI system integrating multi-nuclide synchronous imaging and spectral imaging includes a spectral imaging module, a multi-nuclide synchronous imaging module, and a spectral reconstruction and image fusion module. The spectral imaging module is configured to acquire a spectrum of a nuclide Nuc. The multi-nuclide synchronous imaging module is configured to perform synchronous imaging of nuclides Nuc1 . . . . Nucn, where n is an integer, and n?1; when n=1, Nuc1 is .sup.1H; and when n>1, Nucn is a non-.sup.1H nuclide. The spectral reconstruction and image fusion module is configured to receive the spectrum of the nuclide Nuc and images of the nuclides Nuc1 . . . . Nucn, and acquire spatial distribution information of compounds of the nuclide Nuc and spatial distribution information of the non-.sup.1H nuclide through fusion

[0045] The present disclosure is described below with the nuclide Nuc being .sup.31P and Nuc1, Nuc2 . . . . Nucn being .sup.1H-.sup.19F-.sup.23Na, respectively.

[0046] FIG. 1 shows an overall solution of .sup.31P spectral imaging and .sup.1H-.sup.19F-.sup.23Na synchronous MRI, which includes .sup.31P spectral imaging, .sup.1H-.sup.19F-.sup.23Na synchronous imaging, and spectral reconstruction and image fusion. .sup.31P spectral imaging and .sup.1H-.sup.19F-.sup.23Na synchronous imaging are completed within a same repetition time. .sup.31P spectral imaging achieves chemical shift imaging (CSI), and .sup.1H-.sup.19F-.sup.23Na synchronous imaging achieves multi-nuclide synchronous imaging. During spectral reconstruction and image fusion, a .sup.31P spectrum of each voxel is first reconstructed and processed. Then, peaks in the spectrum are assigned to target compounds such as adenosine triphosphate (ATP), adenosine diphosphate (ADP), creatine phosphate (PCr), and inorganic phosphorus (Pi). The peaks are integrated to acquire the contents of the target compounds, which are converted into corresponding pixel intensities to reconstruct images of the target phosphorus compounds ATP, ADP, PCr, and Pi. The compound images and non-proton images are fused into a proton image to acquire spatial distribution information of different .sup.31P compounds as well as .sup.19F and .sup.23Na.

[0047] Specifically:

[0048] The pulse sequence shown in FIG. 2 is loaded in the MRI system that supports four RF channels for transmission and reception. The four RF channels respectively correspond to the four nuclides .sup.31P, .sup.1H, .sup.19F, and .sup.23Na, and are labeled as .sup.31P channel, .sup.1H channel, .sup.19F channel, and .sup.23Na channel, respectively. The encoding gradients in three directions in space are labeled as Gs, Gp, and Gr.

[0049] As shown in FIG. 2, an MRI method integrating .sup.31P spectral imaging and .sup.1H-.sup.19F-.sup.23Na synchronous imaging includes the following steps.

[0050] 1. .sup.31P spectral imaging

[0051] 1.1. RF pulse p1 of the .sup.31P channel is combined with slice selection gradient g1 and slice selection refocusing gradient g2 applied to slice selection gradient channel Gs to selectively excite .sup.31P for spectral imaging. An intensity of the slice selection gradient g1 is adjusted through parameter ap1, thereby adjusting a slice thickness of the .sup.31P. As shown in FIG. 2, the RF pulse selected for p1 is a SINC pulse with 5 side-lobes.

[0052] 1.2. Phase encoding is performed through the gradient channels Gp and Gr of two spatial dimensions orthogonal to the direction of the slice selection gradient. The phase encoding gradients are labeled as g3 and g4, respectively, where g3 is applied to the gradient channel Gp, and g4 is applied to the gradient channel Gr. Intensities of the phase encoding gradient g3 and g4 are adjusted respectively through parameters ap2 and ap3, thereby adjusting a resolution within the slice of 31P. The phase encoding gradients g3, g4, and the slice selection refocusing gradient g2 are simultaneously applied and center-aligned.

[0053] 1.3. The FID signal of .sup.31P is acquired.

[0054] 1.4. After the FID acquisition of .sup.31P is completed, phase encoding gradients g5 and g6 are applied to the gradient channels Gp and Gr respectively to refocus phase dispersion effects of the phase encoding gradients g3 and g4, where g5 and g3 have a same area and are applied to opposite directions; and g6 and g4 have a same area and are applied to opposite directions.

[0055] 2. After the .sup.31P spectral imaging, the .sup.1H-.sup.19F-.sup.23Na synchronous imaging is performed. The .sup.1H-.sup.19F-.sup.23Na synchronous imaging includes the following steps.

[0056] 2.1. RF pulses p2, p3, and p4 are applied to .sup.1H, .sup.19F, and .sup.23Na channels, respectively. The three RF pulses are combined with slice selection gradient g7 and slice selection refocusing gradient g8 applied to the slice selection gradient channel Gs to selectively excite the nuclides .sup.1H .sup.19F, and .sup.23Na for imaging. The RF pulses p2, p3, and p4 are center-aligned with the slice selection gradient g7. As shown in FIG. 2, the .sup.1H channel uses a SINC pulse with 5 side-lobes; the .sup.19F channel a uses Hermite pulse; and the .sup.23Na channel uses a Gaussian pulse.

[0057] 2.2. Phase encoding and frequency encoding are performed respectively through gradient channels Gp and Gr of two spatial dimensions orthogonal to a direction of the slice selection gradient.

[0058] A phase encoding gradient g9 is applied to the gradient channel Gp, a frequency encoding preparation gradient g10 is applied to the gradient channel Gr, and a frequency encoding gradient g11 is applied to the gradient channel Gr. The echo signals ECHO1, ECHO2, and ECHO3 of .sup.1H, .sup.19F, and .sup.23Na are synchronously acquired, where ECHO1, ECHO2, and ECHO3 sampling time windows are center-aligned; and the slice selection refocusing gradient g8, the phase encoding gradient g9, and the frequency encoding preparation gradient g10 are simultaneously applied and center-aligned.

[0059] 2.3. A phase encoding gradient g12 is applied to an opposite direction to the gradient channel Gp to refocus a phase dispersion effect of the phase encoding gradient g9, where g12 and g9 have a same area.

[0060] 3. As shown in FIG. 1, .sup.31P spectral reconstruction and image fusion includes the following steps.

[0061] 3.1 Reconstruction of .sup.31P spectra and compound images

[0062] Zero-filling is performed on the .sup.31P FID signal, two-dimensional Fourier transform is performed on the two spatial dimensions, and Fourier transform is performed on the time dimension of the FID signal to acquire a .sup.31P compound spectrum in each voxel. The spectrum is subjected to phase correction, baseline correction, calibration, and peak fitting. The peaks in the spectrum are assigned to different target compounds, such as ATP, ADP, PCr, and Pi. Further, the assigned peaks are integrated to acquire the contents of the target compounds. The pixel intensity corresponding to the voxel is labeled to reconstruct images of the target compounds such as ATP, ADP, PCr, and Pi.

[0063] 3.2. Reconstruction of .sup.1H, .sup.19F, and .sup.23Na images

[0064] Echo signals ECHO1, ECHO2, and ECHO3 of .sup.1H, .sup.19F, and .sup.23Na are filled in the k-spaces of .sup.1H, .sup.19F, and .sup.23Na, respectively. According to ratios of gyromagnetic ratios of .sup.19F and .sup.23Na to the gyromagnetic ratio of .sup.1H, the k-spaces are zero-filled to ensure that .sup.19F and .sup.23Na remain the same imaging field of view as .sup.1H. Then two-dimensional Fourier transform is performed to acquire images of .sup.1H, .sup.19F, and .sup.23Na.

[0065] 3.3. The images of the .sup.31P compounds are interpolated in an image domain to the same size as the .sup.1H image, and the .sup.31P compound images are fused with the .sup.19F .sup.23Na and images into the .sup.1H image to acquire the spatial distribution information of different compounds (ATP, ADP, PCr, and Pi) and exogenous .sup.19F and .sup.23Na probes.

[0066] The above described are merely preferred embodiments of the present disclosure, and not intended to limit the present disclosure. Any modifications, equivalent replacements and improvements made within the spirit and principle of the present disclosure should all fall within the scope of protection of the present disclosure.