Voxel-based relaxometry for cases of an unresolved epilepsy diagnosis

Voxel-based relaxometry (VBR) is a technique in which a voxel-level statistical comparison of quantitative MR T2 maps is performed to identify regions with significantly elevated T2 relaxation time. Our objective was to assess the performance of single-subject VBR at 3T as a diagnostic tool for patients whose diagnosis of epilepsy or seizure focus location is uncertain.

Fifty-nine patients with possible epilepsy or known epilepsy, but an unknown focus and forty-five healthy controls were studied. All subjects were scanned at 3T using a Carr-Purcell-Meiboom-Gill MR sequence. Single-subject VBR was performed at a significance level of α=0.001. Patients were classified based on whether the diagnosis of epilepsy was in question and whether there was a suspected focus. A VBR score was determined based on the presence of VBR abnormalities in any of 13 predefined regions per hemisphere.

All patients exhibited significantly more median VBR abnormalities than controls (p<0.05). VBR abnormalities were seen in 69% and 89% of patients with a normal or questionably abnormal MR scan, respectively. Nineteen of the 27 patients with a suspected focus (70%) had VBR abnormalities in the suspected focus, with additional regions of involvement being elucidated. VBR also correctly predicted the seizure focus in 50% of patients whose seizure foci were confirmed based on follow-up history or clinical investigations.

Single subject VBR can help identify potential seizure foci in patients whose seizure foci are uncertain.