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Abstract:
PURPOSE: Proton MR spectroscopy (MRS) of the spinal cord can provide valuable diagnostic information in a completely noninvasive way. Although MRS of the spinal cord remains challenging, first results in the healthy cerebral spinal cord as well as in cord lesions have been promising (1, 2). In this work we demonstrate an improvement of spectral quality by combining improved outer-volume suppression bands, based
on quadratic-phase (QPP) and higher-order-phase (HOPP) saturation pulses, with localized higher-order shimming,
based on high-resolution cardiac-triggered B0 mapping.
MATERIALS & METHODS: Single voxel spectroscopy was performed in the cerebral
spinal cord of a patient with multiple sclerosis and in the thoracic spinal cord of a patient with a metastasis and were
compared to spectra from corresponding healthy cord regions. Measurements were performed on a 3 T Philips Achieva system with a dedicated spine coil. PRESS localization was slightly over-prescribed with outer volume QPP and HOPP suppression bands (3), resulting in effective voxel sizes of 0.7 ml and 1.134 ml, respectively. Localized secondorder shimming based on high-resolution ECG-triggered B0 mapping was applied prior to the MRS measurement. ECG triggering also was performed during the MRS acquisition. Five hundred and twelve averages were acquired with a TR
≥ 2000 ms and TE = 43 ms in the MS case and TE = 144 ms in the tumor case.
RESULTS: The improved shimming technique as well as the new saturation bands allowed to obtain reproducible water linewidths of 7 to 10 Hz. Additional saturation bands at the top and bottom of the voxel helped to saturate signal stemming from pulsatile flow. Figure1a shows the voxel placement and spectrum from the patient with multiple sclerosis, demonstrating slightly reduced NAA as well as increased myoinositol and lactate compared to a healthy spectrum from this region. Note that the MS plaque did not cover the whole volume of interest. Figure 1b shows the spectrum obtained in a cord volume covering a metastasis from a glioblastoma, demonstrating almost complete loss of NAA, high levels of alanine and lactate, as well as slightly elevated choline levels.
CONCLUSION: Peak linewidth in MRS of the spinal cord can be improved significantly by localized higher-order shimming using highresolution ECG-triggered B0-maps. In addition, using higher-order-phase and quadratic-phase saturation bands surrounding the volume of interest in all dimensions further improves the spectral quality.
