Abstract
Purpose/Introduction: Spinal cord MRS has rarely been applied in clinical work due to technical challenges, including strong susceptibility changes in the region and the small diameter of the cord, which limit the attainable signal to noise ratio (SNR) and lead to lineshape distortions (1). Therefore, a reliable detection (Cramér–Rao lower bounds (CRLB) <20) of just four metabolites (tNAA, Cr and tCho and mI) has been reported (1,2). However, a detection of further metabolites would improve the value of MRS, but this requires better
spectral quality. Non-water-suppressed MRS with the metabolite cycling (MC) technique (3) enables frequency alignment of every FID even with the very low
SNR available in the spinal cord, improving the spectral quality of measurements in the human spinal cord. In this work, MC was used together with a very high number of averages measured in one volunteer to optimize spectral
quality in the spinal cord and to identify further quantifiable metabolites.
Subjects and Methods: After approval from the local ethics committee, one female volunteer was measured four times within one month using the MC technique (3) at 3T (Achieva, Philips Healthcare, Best, TE/TR = 30/2000 ms, voxel size = 1.2 ml) at the cervical level C3-4 (Fig.1). Each measurement
comprised 512 FIDs (Fig.2, top), thus a total number of 2048 FIDs (Fig.2, bottom) was available for averaging. All MRS data were quantified using LCModel (4) as in (3).
Results: Fig. 2 shows the LCModel fit of spectra. In addition, table 1 shows the LCModel quantification results, the SNR, and the full width at half maximum (FWHM) calculated by LCModel of the measurements toghether with results of 13 healthy volunteers reported earlier (3). Besides the metabolites tNAA, Cr, tCho and mI, Scyllo-Inositol (sI) could be identified reliably.
Discussion/Conclusion: Non-water-suppressed MRS with the metabolite cycling (MC) technique enables spinal cord measurements with improved spectral quality compared to the spinal cord measurements published earlier (1,2). In addition, using this technique it was possible to gain SNR by constructive averaging of 2048 FIDs to investigate the spectral fingerprint of the human spinal cord. However, there might be physiological changes of the metabolite
concentrations within the measurement period (one month). In conclusion, besides the metabolites tNAA, Cr, and tCho, sI can also be reliably quantified due to the increased spectral quality with MC in the spinal cord.
