Francisco, Medicine, 400 Parnassus Avenue, San Francisco, CA USA;. Introduction. Most spectroscopic imaging studies of temporal lobe epilepsy (TLE).
Frontal Lobe NAA Reductions in Temporal Lobe Epilepsy by 1H MRSI Joyce SUHY1, Kenneth D. LAXER2, Derek Lee Flenniken1, Jana Axelrad1, Aristides Andres Capizzano1, Michael W WEINER1
1University of California, San Francisco, Medicine, Dept. of Radiology, MR Unit 114M, San Francisco, CA USA; 2University of California, San Francisco, Medicine, 400 Parnassus Avenue, San Francisco, CA USA; Introduction Most spectroscopic imaging studies of temporal lobe epilepsy (TLE) have not accounted for brain tissue composition. However, gray, white and cerebrospinal fluid (CSF) partial volume effects do affect 1HMRSI data in TLE1. In a previous multislice 1HMRSI study of TLE we found reduced NAA in the frontal lobes of TLE patients2. This finding was significant because the frontal lobes are distant from the seizure focus in the hippocampus; thus this finding suggested a widespread affect of TLE. However, the metabolite concentrations of gray and white matter are different and previously it has been shown that TLE is associated with generalized structural brain change3,4, raising the possibility that the frontal lobe NAA reductions we observed were secondary to changes of gray and white matter. Therefore, the goals of this work were to determine if the previously found changes in frontal lobe NAA in TLE were due to differences in gray matter and white matter composition, or to changes of NAA concentrations in gray and white matter. Methods MRI and 1HMRSI were performed on 16 patients with TLE and 12 age matched controls as previously described2. A multi-slice SI sequence (TR=1,800 ms, TE=135 ms) consisting of three 15-mm thick slices was measured oriented parallel to the roof of the orbits to reduce lipid contamination from orbital fat. Lipid contamination of the metabolite spectra was reduced by using a slice selective inversion pulse, with TI=170ms that resulted in nulling of the lipid signal. Spectra were fitted using an automated curve-fitting program. Metabolite values were corrected for coil loading, receiver gain, and other instrumental factors and normalized to the CSF intensity in the MRI to account for scanner instabilities. The composition of MRSI voxels in terms of gray matter, white matter, and CSF of the frontal lobe was estimated from coregistered segmented MRIs The metabolite data was fitted to a linear regression model with GM and WM as independent variables using the method of least squares. Frontal lobe left and right "pure" gray and "pure" white matter coefficients for metabolite concentrations (e.g. [NAA]) were determined for each frontal lobe of each subject and are expressed in the table. Results The table shows that [NAA] was significantly (p=0.03) reduced in the gray matter of the frontal lobe in TLE bilaterally. There was also a non-significant trend for [NAA] to be decreased in white matter. No significant differences in [NAA] were detected between ipsilateral and contralateral sides in the frontal lobe. In contrast, there were nonsignificant trends for [Cr] and [Cho] to be increased in frontal lobes of TLE. The data in the table is expressed as mean ± SD. Control results represent an average of the left and right hemispheres. Ipsi or Contra vs. Control, p = 0.03 in 1-tailed, unpaired t-test. Discussion Our main finding is that frontal gray matter [NAA] concentrations, corrected for partial volume effects are reduced in TLE compared with controls. This finding in both the ipsilateral and contralateral sides of the frontal lobe is evidence of widespread neuronal damage or dysfunction well beyond the seizure focus, which is in the hippocampus. These [NAA] changes may represent secondary metabolic alterations due to seizures; in this case successful treatment of seizures should reverse these changes. Alternatively, these findings may represent a generalized brain abnormality, which contributes to the pathogenesis of TLE; in this case successful treatment of seizures should not affect these changes. These results demonstrate that the findings of our previous voxel selected data (not corrected for changes in tissue composition), are not due to differences in gray/white matter composition, but are due to changes in tissue metabolite concentrations in gray matter. In conclusion, these new findings demonstrating reduced [NAA] in frontal lobe gray matter of TLE demonstrate generalized brain changes outside the seizure focus. Furthermore, the results emphasize the importance of correcting MRS and MRSI data for tissue composition.
References 1. Chu, W.J., et al., Mag. Reson. Med. 43:359-367, 2000. 2. Capizzano, A.A., et al., submitted Epilepsia, 2000. 3. Marsh, L., et al., Epilepsia 38(5): 576-587, 1997. 4. Woermann, F.G., et al., NeuroImage 10:373-384, 1999 Metabolites in Gray and White Matter of TLE and Controls IPSI CONTRA CONTROL NAA gray 75.0±9.8 75.5±8.5 81.4±7.9 NAA white 83.2±9.8 83.7±9.9 89.2±9.5 Cr gray 36.0±3.2 34.9±3.1 34.1±4.4 Cr white 33.4±4.0 33.6±4.7 34.1±2.7 Cho gray 8.9±1.5 8.3±1.3 7.9±1.8 Cho white 11.6±2.1 11.9±1.9 12.1±1.7
Proc. Intl. Soc. Mag. Reson. Med 9 (2001)
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Proc. Intl. Soc. Mag. Reson. Med 9 (2001)
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