B1-MAPPING AND B1L-SHIMMING FOR MRI

• US 20110156704A1
• Filed: 09/10/2009
• Published: 06/30/2011
• Est. Priority Date: 09/17/2008
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Katscher, Ulrich, Graesslin, Ingmar, Boernert, Peter, Nehrke, Kay, Koken, Peter
• Granted Patent: US 8,736,265 B2
• Time in Patent Office: Days
• US Class Current: 324/309
• CPC Class Codes: G01R 33/246 Spatial mapping of the RF magnetic field B1
• CPC Class Codes: G01R 33/3415 comprising arrays of sub-coils , i.e. phased-array coils with flexible receiver channels
• CPC Class Codes: G01R 33/4838 using spatially selective suppression or saturation of MR signals
• CPC Class Codes: G01R 33/5612 Parallel RF transmission, i.e. RF pulse transmission using a plurality of independent transmission channels
• CPC Class Codes: G01R 33/5659 caused by a distortion of the RF magnetic field, e.g. spatial inhomogeneities of the RF magnetic field G01R33/56509, G01R33/56518, G01R33/56536 take precedence
• CPC Class Codes: G01R 33/583 Calibration of signal excitation or detection systems, e.g. for optimal RF excitation power or frequency G01R33/246 takes precedence
• CPC Class Codes: G01R 33/586 for optimal flip angle of RF pulses

Abstract

The invention relates to a method of acquiring MRI image data comprising the following steps: performing a 3-dimensional B1 mapping of a first volume using a first voxel size, selecting an MRI protocol, performing the B1-shim in accordance with the MRI protocol, performing the MRI protocol to acquire MRI imaging data of a second volume using a second voxel size, wherein the first voxel size is larger than the second voxel size, wherein the first volume is larger than the second volume, and wherein the second volume is contained within the first volume.

Claims

1. A method of acquiring MRI image data comprising the following steps:

performing a 3-dimensional B1 mapping of a first volume using a first voxel size,

selecting an MRI protocol,

performing the B1-shim in accordance with the MRI protocol,

performing the MRI protocol to acquire MRI imaging data of a second volume using a second voxel size,

wherein the first voxel size is larger than the second voxel size, wherein the first volume is larger than the second volume, and wherein the second volume is contained within the first volume.

2. The method of claim 1, wherein the B1 mapping is performed with an Actual Flip-angle Imaging (AFI) pulse sequence that has a modified gradient timing sequence, wherein the modified timing gradient sequence has had the gradient pulses replaced with Echo Pulse Imaging (EPI) gradient pulses.

3. The method of claim 1, wherein the B1 mapping is integrated with a prescan MRI sequence.

4. The method of claim 1, wherein the B1 mapping is integrated with a B0 mapping.

5. The method of claim 1, wherein the B1 mapping is used for a B1-shim during scan preparation pulse sequences or magnetization preparation pulse sequences during the MRI protocol including regions outside said second volume, but within the first volume.

6. The method of claim 1, wherein the B1 mapping is used for the B1-shimming of a MRI technique selected from the group consisting of:

magnetization preparation pulses, fat suppression pulses, motion sensing, Arterial Spin Labeling (ASL), Regional Saturation Technique (REST), Spectral Presaturation Inversion Recovery (SPIR), and Inversion.

7. A computer program product comprising a set of computer executable instructions for performing the method of claim 1.

8. An apparatus for acquiring MRI images data comprising:

means for performing a 3-dimensional B1 mapping of a first volume using a first voxel size,

means for selecting an MRI protocol,

means for performing a B1-shim in accordance with said MRI protocol,

means for performing the MRI protocol to acquire MRI imaging data of a second volume or slice using a second voxel size,

wherein the first voxel size is smaller than the second voxel size, wherein the first volume or slice is contained within the first volume.

9. The apparatus of claim 8, further comprised of one or more transmit channels and a means for minimizing a first cost function, wherein the solution to minimizing the first cost function provides a set of complex amplitudes, wherein there is an element of the set of complex amplitudes for each transmit channel, wherein the element specifies the amplitude and phase to be used by its corresponding transmit channel, wherein the first cost function is comprising an SAR term and a second cost function, wherein the second cost function is calculated using the spatial transmit sensitivity distributions for all of the transmit channels and the set of complex amplitudes, wherein the SAR term is calculated using the set of complex amplitudes, the averaged total transmit sensitivity, and a regularization parameter operable for adjusting the trade-off between SAR and B1 field homogeneity, wherein the SAR term is weighted with the regularization parameter, and wherein the SAR term is inversely proportional to the averaged total transmit sensitivity.

10. The apparatus of claim 9, further comprising a user interface which is adapted to allow an operator to enter a parameter, wherein the parameter adjusts the trade-off between the B1 homogeneity and the total forward power used during the examination.

11. The apparatus of claim 8, wherein the means for performing the B1 mapping is operable to integrate the B1 mapping with a prescan MRI sequence.

12. The apparatus of claim 8, wherein the means for performing the B1 mapping is operable to integrate the B1 mapping with a B0 mapping.

13. The apparatus of claim 8, wherein the means for performing a B1-shim is operable for the purpose of B1 shimming during scan preparation pulse sequences or magnetization pulses during the MRI protocol including regions outside said second volume, but within the first volume.

14. The apparatus of claim 8, wherein the means for performing a B1-shim is operable for the purpose of B1-shimming during an MRI technique selected from the group consisting of:

magnetization preparation pulses, fat suppression pulses, motion sensing, arterial spin labeling (ASL), Regional Saturation Technique (REST), Spectral Presaturation Inversion Recovery (SPIR), and Inversion.

15. The apparatus of claim 8, wherein the means for performing the B1-shim is operable to allow one or more additional B1-shims of one or more additional MRI protocols, wherein the one or more additional MRI protocols may acquire images of a one or more additional volumes using one or more additional voxel sizes, wherein the one or more additional voxel sizes are smaller than the first voxel size, and wherein the one or more additional volumes are contained within the first volume.