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Abstract:
Purpose/Introduction: Cardiac 1H MR-spectroscopy (MRS) is a
promising tool for investigating human heart disease1. Previous MRS measurements localized in the human skeletal muscle allow a separation of intramyocellular lipids (IMCL)2 and extramyocellular lipids (EMCL)2 and it was shown that IMCL levels are related to insulin sensitivity (for a review3). In contrast, EMCL signal can change
dramatically depending on the localization of the voxel e.g. due to inclusion of fascia, which might compromise the reproducibility of the measurement3. Therefore, for cardiac MRS an independent quantification of IMCL and EMCL would be ideal. However, spectral quality of cardiac MRS can be severely impaired by cardiac and respiratory motion, as well as by static field inhomogeneities making the separation difficult. This work presents the combination of imagebased B0-shimming4, ECG-triggering and navigator-gating along with retrospective frequency-alignment and phase-correction of metabolite-cycled (MC)5, non-water-suppressed MRS6,7 data, and demonstrates the feasibility for obtaining high quality spectroscopic information from the heart.
Subjects and Methods: Measurements were performed at a 3 T
Achieva system with a 32 channel cardiac coil (Philips Healthcare, Best, NL) in 8 healthy female volunteers. Navigator-gated bSSFP cine images were used for positioning the spectroscopy voxel (9.2 9 6.1 9 18.7 mm3) (Fig. 1) in the interventricular septum. Fig. 1 Measurement position in the human heart A linear shim for the heart was calculated using an image-based Shimtool8. The inner-volume saturated9 MC PRESS sequence6 (min. TR = min 3 heart beats, TE = 32 ms, C 512 averages) was ECGtriggered to end systole and the navigator position was recorded. MRecon (Gyrotools, Zurich, CH) was used to get access to raw data and for SVD coil combination. FIDs were zero filled to twice the original
size, phase corrected, frequency-aligned and truncated and zero filled after 100 ms (Fig. 2). Resulting spectra were fitted with LCModel12. Results: Quantification results and an exemplary spectrum and fit are displayed in Fig. 3. The SNR of all measurements is 25 ± 11 and the line width is 21 ± 5 Hz (FWHM). IMCL and EMCL around 1.3 ppm can be resolved separately for the first time with CRLB of 2 and 15 , respectively. Additionally, creatine, trimethyl-ammonium
compounds (TMA) and taurine can be detected with CRLBs\15 .
