Abstracts

Rationale: T2 relaxometry, quantitative assessment of T2 relaxation time in magnetic resonance (MR) data, is a sensitive tool for detecting T2 abnormalities in the adjacent temporal lobe and in extratemporal areas as well as in patients with temporal lobe epilepsy (TLE). T2 relaxometry typically uses manually drawn regions of interest (ROIs). This approach is limited by its subjectivity and its restricted scope of investigation. A recently developed approach called voxel-based relaxometry (VBR) provides an unbiased statistical analysis of the whole brain. The efficacy of VBR group analysis and single-subject VBR has been assessed previously. Our objective was to assess the clinical utility of single-subject VBR and patient-specific ROI analysis for patients with TLE, including those with normal structural MRI. Methods: Forty-five patients with TLE confirmed by history, EEG, and structural MRI and 25 control subjects were scanned at 3 T using a modified Carr-Purcell-Meiboom-Gill MR sequence. T2 maps were generated by fitting T2 parameters at each voxel where no baseline correction was implemented for ROI analysis and an optimized baseline fit3 was implemented for VBR analysis. ROIs were drawn for each patient and control subject, and measurements were made on unregistered T2 maps. VBR was performed on a single-subject ba-sis at a significance level of α = 0.05. Patients were grouped according to seizure focus (left mesial, right mesial, other), and whether structural MR imaging was normal or abnormal. Results: Up to 85% of patients in the temporal lobe groups demonstrated T2 abnormalities. VBR detected abnormalities either in equal num-bers or in more patients (up to 23% more) than ROI analysis for each group. The number of detected abnormalities per patient was higher using VBR (3.38 versus 2.04, p < 0.05). VBR also identified abnormalities that were missed by ROI analysis. The rate of VBR detection of abnormalities was higher for patients than controls (76% versus 36%). For example, the Fig shows elevated T2 in a pa-tient with right mesial TLE where the VBR maps show abnormalities that extend beyond the ROIs. One challenge of single-subject VBR is the influence of patient-specific features such as cerebrospinal fluid (CSF), which manifested as spurious regions of signifi-cant T2 increase, particularly along deep sulci. VBR was more sensitive than ROI analysis as it overcalled from 1.2-1.5 abnormalities per patient while it undercalled from 0.2-0.5 abnormalities per patient. Furthermore, additional regions of abnormalities were identi-fied that were not assessed by the ROI method. Conclusions: VBR can be performed on single subjects with TLE and it detects considerably more abnormalities than ROI analysis. VBR may be a clinically useful tool for the detection of T2 abnormalities at the seizure focus and sites remote from it.