Merlin J Fair1 and Kawin Setsompop1,2
1Radiological Sciences Laboratory, Stanford University, Stanford, CA, United States, 2Electrical Engineering, Stanford University, Stanford, CA, United States
1Radiological Sciences Laboratory, Stanford University, Stanford, CA, United States, 2Electrical Engineering, Stanford University, Stanford, CA, United States
The time-resolved PEPTIDE approach is investigated for use as a fast (<30s) calibration scan for the estimation of eddy current induced phase evolutions. Simulation, phantom and in vivo work demonstrates the potential accuracy of such a technique, including up to a b-value of 5000s/mm2.
Figure 5 – (a) Single-shot data: phantom & in-vivo. The low SNR of b=5000 in-vivo data is apparent in both EPI and PEPTIDE (PEP), but image phase across time is still measurable. (b) Estimated phantom eddy fields, measured by FSL and PEPTIDE. First 3 directions for PEPTIDE are direct estimates (red square), while others are calculated using a linear model. (c) Estimated in-vivo eddy fields (with same diffusion-directions and acq. params as in phantom). “Phantom PEP-ref”: PEPTIDE-estimated field in the phantom, masked by the in-vivo brain FOV, for reference with the in-vivo results.
Figure 1 - a) EPTI/PEPTIDE uses a zig-zag sampling trajectory to cover a large ky-t section per acquisition shot, with B0-informed-GRAPPA used to fill-in the missing data. PEPTIDE acquires rotated EPTI shots (blades) to cover the full k-t space. With full k-t data, each time-point has consistent phase and signal decay, so the images in the resolved time-series are free from typical-EPI distortion and blurring. b) The phase of the time-series images for a DWI acquisition can be compared with that of a diffusion-free (b=0) acquisition, to estimate eddy current induced phase changes.