Automated T2 relaxometry of the hippocampus for temporal lobe epilepsy

Abstract

SummaryObjectiveHippocampal sclerosis (HS), the most common cause of refractory temporal lobe epilepsy, is associated with hippocampal volume loss and increased T2 signal. These can be identified on quantitative imaging with hippocampal volumetry and T2 relaxometry. Although hippocampal segmentation for volumetry has been automated, T2 relaxometry currently involves subjective and time‐consuming manual delineation of regions of interest. In this work, we develop and validate an automated technique for hippocampal T2 relaxometry.MethodsFifty patients with unilateral or bilateral HS and 50 healthy controls underwent T1‐weighted and dual‐echo fast recovery fast spin echo scans. Hippocampi were automatically segmented using a multi‐atlas–based segmentation algorithm (STEPS) and a template database. Voxelwise T2 maps were determined using a monoexponential fit. The hippocampal segmentations were registered to the T2 maps and eroded to reduce partial volume effect. Voxels with T2 >170 msec excluded to minimize cerebrospinal fluid (CSF) contamination. Manual determination of T2 values was performed twice in each subject. Twenty controls underwent repeat scans to assess interscan reproducibility.ResultsHippocampal T2 values were reliably determined using the automated method. There was a significant ipsilateral increase in T2 values in HS (p < 0.001), and a smaller but significant contralateral increase. The combination of hippocampal volumes and T2 values separated the groups well. There was a strong correlation between automated and manual methods for hippocampal T2 measurement (0.917 left, 0.896 right, both p < 0.001). Interscan reproducibility was superior for automated compared to manual measurements.SignificanceAutomated hippocampal segmentation can be reliably extended to the determination of hippocampal T2 values, and a combination of hippocampal volumes and T2 values can separate subjects with HS from healthy controls. There is good agreement with manual measurements, and the technique is more reproducible on repeat scans than manual measurement. This protocol can be readily introduced into a clinical workflow for the assessment of patients with focal epilepsy.

Recommendations for the use of structural magnetic resonance imaging in the care of patients with epilepsy: A consensus report from the International League Against Epilepsy Neuroimaging Task Force

“…Coronal T1-and T2-weighted MRI at the level of hippocampal body and 4-μm-thick paraffin-embedded histology sections with NeuN immunohistochemistry at a comparable level in two patients with right temporal focus. 87 Measurement of T2 relaxation times can be done by placing a manually or automatically generated region of interest within the hippocampus, 88 carefully avoiding the adjacent CSF. B, Volumetry detected subtle CA1-3 atrophy (−2.2 SD), and histology shows CA1 minimal neuronal loss.…”

Hippocampal profiling: Localized magnetic resonance imaging volumetry and T2 relaxometry for hippocampal sclerosis

“…We expanded our healthy control group with respect to Winston et al to 111 healthy controls (age mean [μ] and standard deviation [σ] = 40.0 ± 12.8, range = 17.0‐66.6 years; 52 male [M]/59 female [F]) without any history of neurologic or psychiatric disease, from previously scanned subjects. All controls were scanned on the same scanner within a 30‐month time frame in 2015‐2018.…”

“…12,13 In brief, this used a multi‐atlas–based algorithm for the segmentation (STEPS) using the 3D T1 images, which was then coregistered to the proton density (PD)/T2 scan and used as a mask to obtain qT2 values within only the hippocampus. Hippocampal volumes were corrected for total intracranial volume (TIV) as in Winston et al…”

“…For the T2 relaxometry, the transformation from the template to the T1 was concatenated with the rigid transformation from the T1 to the PD/T2 scan . Similarly, the template distance map was transformed to obtain a mapping of location and averaged within the hippocampal segmentation in the PD/T2 space (Figure E).…”

“…In recent years, both volumetry and T2 relaxometry methods have been automated, enabling routine clinical use in comparing a patient's individual values to a normative database of healthy control subjects. These methods, however, only yield a single volume and qT2 value per hippocampus and may be insensitive to subtle focal abnormalities .…”