High resolution magnetic resonance imaging with reduced distortion based on reduced-field-of-view and generalized parallel imaging
A method for magnetic resonance imaging is provided that includes using a magnetic resonance imaging system to excite a field of view (FOV) for a target being imaged, using an excitation plan to limit the excited FOV to a relatively narrow band of magnetization, exciting multiple bands of magnetization simultaneously, applying phase encoding along a shortest FOV dimension, acquiring a signal from said simultaneously excited bands of magnetization, and reconstructing and outputting a target image from the acquired signal.
1. A magnetic resonance imaging method comprising:
a) using a magnetic resonance imaging system to excite a field of view (FOV) for a target being imaged;
b) using an excitation plan to limit said excited FOV to selected bands of magnetization;
c) simultaneously exciting multiple said selected bands of magnetization within a single slice;
d) applying phase encoding along a shortest FOV dimension;
e) simultaneously acquiring a signal from each said excited selected band of magnetization; and
f) combining different strips of said magnetization into a composite image to reconstruct and output a target image from said acquired signal.
2. The method according to claim 1 further comprises sweeping across a plurality of multiband excitation patterns in a phase-encoded direction, wherein said sweeping fills in coverage of gaps within a single said multiband pattern.
3. The method according to claim 2 , wherein a corresponding signal is received only by a subset of coil elements that are proximal to said excited FOV band, wherein reconstruction of said image is performed using a generalized parallel imaging reconstruction method and a calibration method.
4. The method according to claim 1 further comprises limiting said FOV to reduce an echo train length (ETL), wherein a faster k-space traversal is obtained, wherein said faster k-space traversal is capable of reducing image distortion, wherein T2*-induced blurring is reduced.
5. The method according to claim 4 comprises using a 2D RF pulse to limit said FOV.
6. The method according to claim 5 , wherein said 2D RF pulse has an echo-planar trajectory, wherein a fast echo-planar direction during said excitation corresponds to a phase-encode direction, wherein a slow echo-planar direction during said excitation is a slice-select direction during said imaging, wherein multiple said slices are simultaneously excited, wherein a fat tissue excitation profile is shifted in said slice-select direction with respect to a water signal.
7. The method according to claim 4 further comprises using an outer-volume suppression approach to limit said FOV, wherein a signal from outside a desired said FOV is suppressed using saturation pulses.
8. The method according to claim 6 , wherein in-plane multiband excitation patterns are obtained by summing multiple said 2D RF pulses after a linear phase modulation of individual said 2D RF sub pulses sub-pulse.
9. The method according to claim 8 , wherein a 2D echo-planar RF excitation pulse and an RF refocusing pulse are configured to ensure refocusing of a main lobe of a periodic 2D excitation in a slice-select direction while suppressing a fat tissue excitation signal for each planar simultaneously excited band.
10. The method according to claim 9 , wherein said 2D RF and a multiband refocusing RF pulse are configured to simultaneously refocus said main lobe and additional side lobes in said slice-select direction.
11. The method according to claim 9 where said refocusing RF pulse is up to a 180° pulse.
12. The method according to claim 1 further comprises using parallel imaging to resolve said multiple bands.
13. The method according to claim 1 further comprises steps selected from the group consisting of sweeping a pattern to excite a space between said multiple bands, and using parallel imaging to resolve said multiple bands.
14. The method according to claim 13 , wherein a phase encoded FOV is selected to alias said multiple bands directly onto each other.
15. The method according to claim 13 wherein a phase-encoded FOV is selected to alias said multiple bands imperfectly.
16. The method according to claim 13 , wherein diffusion weighting is applied.
17. The method according to claim 1 , wherein said excitation plan comprises exciting multiple arbitrary 2D volumes both in plane and through plane.
18. The method according to claim 17 , wherein said excitation plan follows a grid pattern.
19. The method according to claim 17 , wherein imaging comprises using parallel imaging.
20. The method according to claim 17 , wherein said excitation plan follows an arbitrary pattern.