Abstracts

Rationale: To explore the utility of oxygen-enhanced MRI, a novel technique of assessing regional brain metabolism, in a set of normal adult volunteers and temporal lobe epilepsy patients. To assess the sensitivity and specificity of the method in the diagnosis and lateralization of disease in MRI-lesional and nonlesional patients. Methods: Six right-handed adult normal volunteers and eight right-handed patients with temporal lobe epilepsy were studied. Four patients had lesions concordant with their epilepsy on high-resolution structural MRI. Four patients were nonlesional. Oxygen enhancement (OE) was carried out by administering 100% O2 in two discrete 5-minute epochs within a 25-minute period, during which T2* (blood oxygen level dependent, BOLD) signal was recorded in continuously acquired gradient-recalled echo-planar images. Data from nine temporal lobe subregions were subjected to spectral analysis and statistical testing. Results: OE resulted in unambiguous concordant positive T2* signal change in all temporal lobe subregions, in all subjects. Overall BOLD response to OE, assessed by Fourier spectral power peak, was significantly less in patients than normals (p < 0.025). This was statistically significant individually in four patients; in two, there was a trend to left-right asymmetry concordant with the laterality of the epilepsy. Analysis of the distribution of spectral power within the temporal lobe revealed significant differences from normals in five patients (p < 0.01 in all, corrected for multiple comparisons), concordant with epilepsy laterality in every case. Two of the latter patients were nonlesional on structural MRI. Conclusions: Echo-planar MRI may be deployed as a metabolic imaging modality by exploiting the effect on the T2* signal of increasing inspired oxygen concentrations. The technique is safe and straightforward, requiring no active patient cooperation. In this small group, it demonstrates apparent high sensitivity (62.5%) and specificity (100%) in the diagnosis and lateralization of hypometabolism associated with lesional and nonlesional temporal lobe epilepsy. Further work with a larger population and other focal epilepsy syndromes will establish OE-MRI s mainstream clinical utility, in particular, its relationship to radioligand-based metabolic imaging (PET) and MR spectroscopy in epilepsy.