Double Inversion Recovery Magnetic Resonance Imaging at 3 T

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Abstract
Objective: The objective of the study was to examine the utility of double inversion recovery (DIR) magnetic resonance imaging (MRI) using a 3-T magnetic resonance imager in the preoperative evaluation of hippocampal sclerosis (HS) in patients with mesial temporal lobe epilepsy. Methods: This retrospective study had institutional review board approval, and informed consent was obtained. Twelve patients with unilateral HS and 12 age-matched healthy control subjects were included. Imaging was performed using DIR, fluid-attenuated inversion recovery (FLAIR), and T2-weighted turbo spin-echo (T2 TSE) sequences vertical to the hippocampal axis. Quantitative assessment for hippocampus of the patients and control subjects was determined. Regions of interest (ROIs) were placed on bilateral hippocampi, and signal intensity was measured. The signal-to-noise ratio (SNR) of ipsilateral hippocampus, contrast ratio of ipsilateral-to-contralateral side, contrast-to-noise ratio (CNR), and asymmetry index of bilateral hippocampi were calculated and compared among the 3 sequences. Statistical analyses were performed with 1-way analysis of variance and Student t test. Results: On DIR images, HS demonstrated extremely high signal intensity. The hippocampi ipsilateral to the seizure focus showed significantly increased signal intensity, as compared with contralateral hippocampi and healthy subjects (F = 47.876, P < 0.001). The higher SNR of ipsilateral hippocampus on DIR was significant compared with the FLAIR and T2 TSE (P < 0.01). The CNR of bilateral hippocampi on DIR was also significantly higher than that on the FLAIR and T2 TSE (P < 0.01). However, compared with the FLAIR, no significant differences of contrast ratio and asymmetry index between bilateral hippocampi were observed on DIR. Conclusions: Double inversion recovery brain imaging reveals characteristically extremely high signal intensity of hippocampus in patients with HS. Double inversion recovery images can describe HS with high SNR and CNR superior to conventional magnetic resonance sequences and can be valuable for the diagnosis of HS.

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