Distortion-free magnetic resonance imaging near metallic implants
View Patent ↗A method for 3D magnetic resonance imaging (MRI) with slice-direction distortion correction is provided. One or more selective cross-sections with a thickness along a first axis is excited using a RF pulse with a bandwidth, wherein a selective cross-section is either a selective slice or selective slab. A refocusing pulse is applied to form a spin echo. One or more 2D encoded image signals are acquired with readout along a second axis and phase encoding along a third axis. Slice-direction distortion is corrected by resolving the position by resolving the frequency offset.
1. A method for 3D magnetic resonance imaging (MRI) with slice-direction distortion correction for distortion caused by field inhomogeneities, comprising:
a) exciting one or more selective cross-sections with a thickness along a first axis using a RF pulse with a bandwidth, wherein a selective cross-section is either a selective slice or selective slab;
b) applying a refocusing pulse to the excited one or more selective cross-sections to form a spin echo;
c) acquiring one or more 2D encoded image signals from the spin echo with readout along a second axis and phase encoding along a third axis; and
d) correcting slice-direction distortion of the one or more 2D encoded image signals by resolving the position by resolving the frequency offset.
2. The method, as recited in claim 1 , further comprising correcting readout distortion.
3. The method, as recited in claim 2 , wherein the correcting readout distortion comprises using spectral information combined with readout bandwidth and pixel size to correct in-plane distortion.
4. The method, as recited in claim 2 , wherein correcting readout distortion comprises applying view angle tilting.
5. The method, as recited in claim 4 , wherein step d comprises encoding and resolving spectral information, and using a cross-section thickness and RF bandwidth to undo slice-direction distortion.
6. The method, as recited in claim 5 , wherein the encoding is a Fourier encoding.
7. The method, as recited in claim 6 , wherein excited cross-section thickness varies to maintain a relatively constant frequency variation within the excited cross-section.
8. The method, as recited in claim 7 , further comprising measuring the frequency spectrum to predict distortion using a spectral prescan.
9. The method, as recited in claim 8 , wherein the excitation-refocusing pulses are a matched-phase pulse pair with individual pulses not necessarily having linear phase.
10. The method, as recited in claim 9 , wherein the encoding comprises using cross-section excitation profile imaging with view angle tilting.
11. The method, as recited in claim 10 , wherein the encoding of frequency offset information comprises using echo-planar spectroscopic imaging.
12. The method, as recited in claim 1 , wherein step d comprises applying additional phase encoding along the first axis to correct slice-direction distortion by resolving an actual location.
13. The method, as recited in claim 1 , wherein step d comprises encoding and resolving spectral information, and using the slice thickness and RF bandwidth to undo slice-direction distortion.
14. The method, as recited in claim 13 , wherein the encoding is a Fourier encoding.
15. The method, as recited in claim 13 , wherein the encoding comprises using slab excitation profile imaging.
16. The method, as recited in claim 13 , wherein the encoding comprises using echo-planar spectroscopic imaging.
17. The method, as recited in claim 1 , wherein excited cross-section thickness varies to maintain a relatively constant frequency variation within the excited slab.
18. The method, as recited in claim 1 , wherein the correcting slice-direction by resolving position, resolves position directly.
19. The method, as recited in claim 1 , wherein the correcting slice-direction by resolving position, resolves position indirectly.
20. An apparatus for providing 3D magnetic resonance imaging with slice-direction distortion compensation for distortion caused by field inhomogeneities, comprising:
a magnetic resonance imaging excitation and detection system; and
a controller electrically connected to the magnetic resonance imaging excitation and detection system, comprising:
a display;
at least one processor; and
non-transitory computer readable media, comprising:
computer readable code for causing the apparatus to excite one or more selective cross-sections with a thickness along a first axis using a RF pulse with a bandwidth, wherein a selective cross-section is either a selective slice or selective slab;
computer readable code for causing the apparatus to apply a refocusing pulse to the excited one or more selective cross-sections to form a spin echo;
computer readable code for causing the apparatus to acquire one or more 2D encoded image signals from the spin echo with readout along a second axis and phase encoding along a third axis;
computer readable code for causing the apparatus to correct slice-direction distortion of the one or more 2D encoded image signals by resolving the position by resolving the frequency offset; and
computer readable code for causing the apparatus to display a 3D magnetic resonance image with slice-direction distortion correction on the display.