Automated quantitative FLAIR analysis in hippocampal sclerosis

Abstract

Purpose: To describe and evaluate a novel MRI post-processing technique for automated quantitative hippocampal FLAIR analysis in patients with hippocampal sclerosis (HS).

Patients and methods: Based on a method for FLAIR analysis presented by Focke et al. (2009), T1 and coregistered FLAIR scans of individual subjects were processed together in SPM5 to conduct both a spatial and an intensity normalization of the FLAIR scans. In a further development described here, the resulting normalized FLAIR images were thresholded and weighted by a probabilistic hippocampal mask to determine the average FLAIR intensities of left and right hippocampus. The method was applied to the MRI data of 103 HS patients and 131 controls. Using a 95% confidence region calculated from the FLAIR intensities of controls as threshold, the performance in discriminating both groups was assessed.

Results: One hundred of 103 patients and among those all 23 patients with histologically confirmed HS fell outside the 95% confidence region, amounting to 97.1% sensitivity. All but 6 controls (=95.4%) were found within the confidence region, corresponding to the expected specificity. The method could also distinguish bilateral HS and visualize signal changes after status epilepticus.

Conclusion: Automated FLAIR analysis is a promising tool to quantify hippocampal signal alterations, to support the detection of HS, and to monitor the temporal evolution of the disease.