7T MRI Automated Software Segmentation of the Hippocampus for Epilepsy: Prospective Performance Evaluation.

Abstract

Background and purpose: 7T MRI is a promising clinical technology for epilepsy imaging. Quantification of hippocampus volume on MRI is a clinically useful biomarker in epilepsy. Applying automated hippocampus volume measurement tools to 7T MRI is needed to optimize the use of clinical ultra-high-field strength epilepsy imaging. The objective of this study is a performance evaluation of automated hippocampal volume measurement software at 7T MRI in both normal participants and those with seizure disorders.

Materials and methods: 7T MRI examinations were prospectively acquired in 50 participants. A subset of participants also underwent 3T MRI examinations, and a subset underwent 2 separate 7T acquisitions. Automated segmentation of the hippocampus was performed with 2 commonly used software packages (FreeSurfer and NeuroQuant) at 3T and 7T, with hippocampal volumes calculated for segmentations without any visually unacceptable errors as determined by radiologist review. Hippocampal volumes were also measured from manual segmentations, and the intraclass correlation coefficient (ICC) was used to compare data with automated segmentation volumes.

Results: Visually unacceptable automated hippocampus segmentation errors occurred more frequently at 7T than at 3T with NeuroQuant (11.0% versus 7.14%) and FreeSurfer (12.5% versus 0%). Computerized volume measurements at 7T correlated poorly with manual segmentation for both software programs (ICC <0.4). Hippocampal volume estimate correlation between matched 7T and 3T MRI in the same participant was fair (ICC = 0.4-0.59) to good (0.6-0.75) for software and manual segmentation. For repeated 7T MRI examinations in the same participant, hippocampus segmentation reproducibility was excellent (0.75) for automated software but poor (< 0.4) for manual segmentation.

Conclusions: Computerized volume measurement of the hippocampus at 7T correlates poorly with volumes obtained through manual segmentation and suboptimally with matched 3T examination measurements, but is highly reproducible at 7T within the same participant. Segmentation errors are more common with 7T examinations, and further development of a hippocampal segmentation method specific to 7T MRI is needed to fully realize the benefits of 7T MRI for imaging patients with epilepsy.