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Abstract:
1H MR Spectroscopy is a promising tool for investigating
heart disease. To achieve a good spectral quality, challenges like cardiac and respiratory motion and complex B0-field inhomogeneities must be addressed.
The combination of image-based B0-shimming[1], ECG-triggering and navigator-gating[2] along with frequency-alignment and phase-correction of metabolite-cycled )[3], non-water-suppressed MRS[4] data, is used to demonstrate the feasibility of metabolite-cycling in the heart.
Measurements were performed in five volunteers(21y-
39y) on an Achieva 3T system with a 6-element cardiac coil (Philips Healthcare,Best,NL). Navigator-gated bSSFP cine images (fig.(1)) were used for positioning the spectroscopy voxel (40x20x10mm3) in the interventricular septum and establishing the trigger delay.
For B0-shimming an image-based ‘ShimTool’[1,5] was employed. Calibration and PRESS sequences (min.TR=2500ms,TE=41ms,acq.time=512ms) were ECG-triggered to end-systole and navigator-gated, with a large gating-window during acquisitions. To mitigate spectral contamination from outside the VOI, a previously implemented[6] inner-volume-saturation (IVS)[7] scheme was
used. For comparison MC PRESS was performed with 256NSA in 4 volunteers and with 512NSA in a fifth volunteer, in whom a 256NSA WS PRESS spectrum was also acquired. The MC FIDs from the 512 NSA acquisition were post-processed in 3 different ways using MRecon(Gyrotools,Zurich,CH): (i)
frequency-aligned, phase- and navigator-corrected; (ii)navigator-corrected only; (iii)not corrected. All other acquisitions were fully motion-corrected. Fig.(2) demonstrates the effect of frequency-alignment and phase-correction.
