System and method for variable-flip-angle 3D spiral-in-out TSE/space using echo-reordering and concomitant gradient compensation
Acquiring 3D MRI data using spiral-in-out encoding trajectories includes calculating a variable flip angle RF series for use as refocusing pulses, wherein the RF series includes a plurality of refocusing RF pulses. A spoiler gradient waveform is applied along the spoiler gradient direction, wherein the computer alternately adds and subtracts partition encoding waveforms to the spoiler gradient waveform. The method reads MRI data from each encoding step during an MRI sequence. The MRI sequence inserts a spiral-in gradient before a first refocusing RF pulse from the RF sequence, overlaps a pre-winder lobe for the encoding trajectory with the spoiler gradient waveform having the partition encoding waveforms added therein, and overlaps a rewinder lobe for the encoding trajectory with the spoiler gradient waveform having the partition encoding waveforms subtracted there from.
1 . A computer implemented method of gathering three-dimensional (3D) magnetic resonance imaging (MRI) data using spiral-in-out encoding trajectories from a k-space encoding orientation and a spoiler gradient direction, the method comprising:
using a computer having a processor and computer memory to implement steps comprising:
calculating a variable flip angle radio frequency (RF) series for use as refocusing pulses, wherein the RF series comprises a plurality of refocusing RF pulses;
applying a spoiler gradient waveform along the spoiler gradient direction, wherein the computer alternately adds and subtracts partition encoding waveforms to the spoiler gradient waveform;
reading MRI data with the computer for each encoding step associated with the k-space encoding orientation during an MRI sequence further comprising:
inserting a spiral-in gradient before a first refocusing RF pulse from the RF sequence;
overlapping a prewinder lobe for the encoding trajectory with the spoiler gradient waveform having the partition encoding waveforms added therein; and
overlapping a rewinder lobe for the encoding trajectory with the spoiler gradient waveform having the partition encoding waveforms subtracted there from.
2 . The computer implemented method of claim 1 , further repeating the MRI sequence for a selected number of total partition encodings to obtain data for a 3D MRI acquisition.
3 . The computer implemented method of claim 1 , wherein calculating the RF series comprises identifying a target signal curve having an asymptotic pseudo-steady state stabilization.
4 . The computer implemented method of claim 3 , further comprising identifying the variable flip angle radio frequency (RF) series to meet the target signal curve and selected parameters for the MRI sequence.
5 . The computer implemented method of claim 4 , wherein the selected parameters are selected from the group consisting of field of view, echo spacing, effective TE, readout time, a target number of shots during the MRI sequence, a total number of echoes per shot, an acceleration ratio, a spatial resolution, a k-space center location relative to a selected number of total partition encodings, or a target signal-to-noise ratio.
6 . The computer implemented method of claim 1 , wherein each of the refocusing pulses corresponds to a respective variable flip angle used in the MRI sequence.
7 . The computer implemented method of claim 1 , further comprising using the MRI sequence to extend a useable duration of an echo train by increasing the refocusing flip angles to slow signal decay due to T2 relaxation.
8 . The computer implemented method of claim 1 , further comprising applying the MRI sequence at a low static magnetic-field strength.
9 . The computer implemented method of claim 1 , wherein the low static magnetic-field strength is less than or equal to 1 Tesla.
10 . The computer implemented method of claim 1 , wherein the MRI sequence comprises a turbo-spin-echo imaging sequence.
11 . The computer implemented method of claim 1 , wherein the spiral-in-out encoding trajectories comprise either constant density spirals or variable density spirals.
12 . The computer implemented method of claim 1 , further comprising reading the MRI data with a time symmetric spiral-in-out sampling scheme.
13 . The computer implemented method of claim 1 , further comprises forming an MRI output by fully sampling the MRI data or by under-sampling the MRI data.
14 . The computer implemented method of claim 1 , further comprising accelerating the reading of MRI data by utilizing parallel imaging and/or compressed sensing techniques, wherein the parallel imaging comprises 1D or 2D acceleration.
15 . The computer implemented method of claim 1 , further comprising applying trajectory correction to the MRI data.
16 . The computer implemented method of claim 15 , wherein the trajectory correction is a gradient impulse response function (GIRF).
17 . The computer implemented method of claim 16 , further comprising applying sequence-based concomitant field compensation.
18 . The computer implemented method of claim 1 , further comprising applying echo re-ordering to the MRI data prior to image reconstruction.
19 . The computer implemented method of claim 18 , wherein echo re-ordering comprises reversing an echo order during a measurement.
20 . A computerized system for gathering three-dimensional (3D) magnetic resonance imaging (MRI) data using spiral-in-out encoding trajectories from a k-space encoding orientation and a spoiler gradient direction, the system comprising:
a source of a magnetic gradient connected to a computer having a processor and computer memory to implement steps comprising:
calculating a variable flip angle radio frequency (RF) series for use as refocusing pulses, wherein the RF series comprises a plurality of refocusing RF pulses;
applying a spoiler gradient waveform along the spoiler gradient direction, wherein the computer alternately adds and subtracts partition encoding waveforms to the spoiler gradient waveform;
reading MRI data with the computer for each encoding step associated with the k-space encoding orientation during an MRI sequence further comprising:
inserting a spiral-in gradient before a first refocusing RF pulse from the RF sequence;
overlapping a prewinder lobe for the encoding trajectory with the spoiler gradient waveform having the partition encoding waveforms added therein; and
overlapping a rewinder lobe for the encoding trajectory with the spoiler gradient waveform having the partition encoding waveforms subtracted there from.