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changes were seen in these patients in the brain using conventional MRI. However,
MRS measurements were performed in the spinal cord in patients with idiopathic
epilepsy. Nevertheless, the relatively high Glx peak may reflect an effect of seizure
activity as Glx is known to be increased in the postictal phase in dogs. 28 Marliani et
al. 19 applied a similar experimental design in humans as performed in the current
study. The aim of Marliani et al. 19 were to establish spectroscopic measurements
using a 3 Tesla MRI for clinical routine diagnostic. Measurements in the spinal cord
were compared to measurements in the brainstem region. Values of NAA, Cho and
Cr were similar in both locations, 19 however, the standard deviation (SD) revealed
higher values in the spinal cord. These results are similar to our findings and we
agree with the postulation of Marliani et al., 19 that these divergences may be caused
by differences in the signal to noise ratio (SNR). The low signal to noise ratio is
related with difficulties in shimming in the spinal cord.
In the current study, a small voxel size led to increased noise thereby diminishing the
spectral resolution that exacerbates the assessment. Therefore, we enlarged the
voxel size to evaluate the increase of spectral resolution proven by the decreasing
number of unreliable peaks (decrease of interrogation marks in the Extended MR
workspace with the special application tool SpectroView) and were able to confirm
this hypothesis (Tab.2). However, the enlargement of the voxel, which was only
possible in the head to feet direction, prevents measurements of smaller focal
lesions, because a contamination with healthy tissue cannot be avoided. Moreover,
recent studies have shown, that unremarkable tissue in conventional MRI located
next to the lesion may reveal metabolic changes in MRS. 7 However, in one study a
relation between distortion of the B 0 field and the interface between the interspinous
connective tissue and vertebral spinous processes has been detected. Large voxel,
extended beyond more than one intervertebral disc space, exacerbates the shimming
potential and thereby leads to loss of signal. 29 According to these previous findings
and the results of the current study, it is not feasible to measure metabolites in small
focal spinal cord lesions but an extended area can be evaluated.
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