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Abstract:
Introduction
Cardiac 1H MR-spectroscopy (MRS) is a promising tool for investigating heart disease. However, addressing cardiac and respiratory motion as well as B0 inhomogeneity compensation is crucial in order to obtain good spectral quality. This work presents the combination of image-based B0-shimming1, ECG-triggering and navigator-gating2 along with retrospective frequency-alignment and phase-correction of metabolite-cycled (MC)3, non-water-suppressed MRS4 data for obtaining high quality MRS data.
Methods
Measurements were performed at a 3T Achieva whole body system with a six channel cardiac coil (Philips Healthcare, Best, NL). For initial validation of the method, spectra were obtained from the hearts of two healthy volunteers. Navigator-gated bSSFP cine images were used for positioning the spectroscopy voxel (9.2x6.1x18.7mm3) in the interventricular septum and establishing the trigger delay. Prior to any spectroscopy acquisition, a linear shim for the heart was calculated using an image-based Shimtool1. The 1H PRESS sequence (min. TR=min 3 heart beats, TE=32 ms, 512 averages) was ECG-triggered to end systole and the navigator position was recorded. In addition, a previously implemented5 inner volume saturation6 scheme was used to mitigate spectral contamination from outside the VOI. MRecon (Gyrotools, Zurich, CH) was used to get access to each FID of the measurement. Navigator data was used to dismiss FIDs which were recorded during inspiration (gating window 5mm). Afterwards FIDs were zero filled to twice the original size, phase corrected, frequency-aligned and truncated and zero filled after 100 ms. Resulting spectra were fitted with LCModel7.
Results
Figure 1 demonstrates the effect of phase correction and frequency alignment.
The spectrum and fit are displayed in figure 2. Intramyocellular lipids (IMCL) and extramyocellular lipids (EMCL) around 1.3ppm can be resolved separately for the first time with CRLB of 2 and 15, respectively. Additionally, unsaturated fatty acids, TMA, Taurine can be detected with CRLBs <15.
Conclusions
It was demonstrated that the introduced technique for cardiac 1H MRS allows for very high spectral data quality, which enables the separate analysis of IMCL and EMCL, as well as Taurin and unsaturated fatty acids for the first time.
