Methods and apparatus for scan time reductions in magnetic resonance imaging using outer volume supression
Methods for fast magnetic resonance imaging (“MRI”) using a combination of outer volume suppression (“OVS”) and accelerated imaging, which may include simultaneous multislice (“SMS”) imaging, data acquisitions amenable to compressed sensing reconstructions, or combinations thereof. The methods described here do not introduce fold-over artifacts that are otherwise common to reduced field-of-view (“FOV”) techniques.
1. A method for acquiring images from multiple different slices in a subject using a magnetic resonance imaging (MRI) system, the steps of the method comprising:
(a) controlling the MRI system to acquire data in a plurality of different slices in the subject using a multiband pulse sequence that includes:
an outer volume suppression (OVS) module containing at least one multiband radio frequency (RF) pulse that suppresses magnetic resonance signals in one or more outer volume regions in the plurality of different slices;
an accelerated imaging module containing at least one multiband RF excitation pulse performed after the OVS module, wherein the accelerated imaging module provides an accelerated data acquisition along at least one direction; and
(b) reconstructing images of the plurality of slices from the acquired data.
2. The method as recited in claim 1 , wherein the OVS module simultaneously suppresses magnetic resonance signals in the one or more outer volume regions in the plurality of different slices.
3. The method as recited in claim 2 , wherein the at least one multiband radio frequency (RF) pulse that simultaneously saturates magnetic resonance signals in one or more outer volume regions is applied along a dimension that is aligned with a phase-encoding direction.
4. The method as recited in claim 1 , wherein the at least one multiband RF pulse in the OVS module comprises at least one adiabatic RF pulse that suppresses magnetic resonance signals in one or more outer volume regions in the plurality of different slices.
5. The method as recited in claim 1 , wherein the at least one multiband RF pulse in the OVS module comprises at least one non-selective adiabatic RF pulse that tips down magnetization in the plurality of different slices and at least one selective RF pulse that tips up magnetization in a central region of the plurality of different slices that excludes one or more outer volume regions.
6. The method as recited in claim 1 , wherein the at least one multiband RF pulse in the OVS module comprises at least one spatially selective RF pulse and the at least one multiband RF excitation pulse in the accelerated imaging module includes at least one RF excitation pulse that is a non-selective RF excitation pulse.
7. The method as recited in claim 6 , wherein the non-selective RF excitation pulse is an adiabatic non-selective RF excitation pulse.
8. The method as recited in claim 1 , wherein the OVS module comprises a magnetization preparation module that contains at least one magnetization preparation RF pulse in addition to the at least one multiband radio frequency (RF) pulse that suppresses magnetic resonance signals in the one or more outer volume regions in the plurality of different slices.
9. The method as recited in claim 8 , wherein the magnetization preparation RF pulse is a T2-preparation RF pulse.
10. The method as recited in claim 1 , wherein the accelerated imaging module is a simultaneous multislice (SMS) imaging module having an accelerated data acquisition along a slice direction that simultaneously excites the plurality of different slices.
11. The method as recited in claim 10 , wherein the accelerated imaging module is a parallel imaging module having an accelerated data acquisition along at least one in-plane direction by undersampling k-space along the at least one in-plane direction.
12. The method as recited in claim 1 , wherein the accelerated imaging module is a compressed sensing imaging module having an accelerated data acquisition along the at least one direction by sparsely sampling a subset of k-space.
13. The method as recited in claim 12 , wherein sparsely sampling the subset of k-space comprises randomly sampling the subset of k-space.
14. The method as recited in claim 12 , wherein reconstructing the images includes using a compressed sensing algorithm.
15. The method as recited in claim 14 , wherein the accelerated imaging module further comprises a simultaneous multislice (SMS) imaging module having an accelerated data acquisition along a slice direction by containing at least one multiband RF excitation pulse that simultaneously excites the plurality of different slices.
16. The method as recited in claim 1 , wherein the pulse sequence comprises interleaving the OVS module and the accelerated imaging module for a plurality of repetitions.
17. The method as recited in claim 1 , wherein reconstructing the images includes using a parallel image reconstruction algorithm.
18. The method as recited in claim 17 , wherein the parallel image reconstruction algorithm includes an algorithm based at least in part on one of a sensitivity encoding (SENSE) or generalized autocalibrating partial parallel acquisition (GRAPPA).
19. The method as recited in claim 1 , wherein controlling the MRI system to acquire data in a plurality of different slices includes simultaneously acquiring at least a first slice and a second slice.
20. The method as recited in claim 19 , wherein the at least one multiband RF pulse in the OVS module suppresses magnetic resonance signals in one or more outer volume regions of each of the first slice and the second slice and is configured such the suppressed magnetic resonance signals in the one or more outer volume regions of the second slice are aliased into a region-of-interest (ROI) of the first slice, and the suppressed magnetic resonance signals in the one or more outer volume regions of the first slice are aliased into an ROI of the second slice.