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MRI-Based Correction for Partial-Volume Effect Improves Detectability of Intractable Epileptogenic Foci on ¹²³I-Iomazenil Brain SPECT Images

¹ Department of Nuclear Medicine and Tracer Kinetics, Osaka University Graduate School of Medicine, Suita, Japan; ² Department of Nuclear Medicine, Hyogo College of Medicine, Nishinomiya, Japan; ³ Department of Neurology, Osaka University Graduate School of Medicine, Suita, Japan; ⁴ Department of Neurosurgery, Osaka University Graduate School of Medicine, Suita, Japan; and ⁵ Department of Neurosurgery, Kinki University School of Medicine, Osaka-Sayama, Japan

Correspondence: For correspondence or reprints contact: Jun Hatazawa, MD, PhD, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, 565-0871, Japan. E-mail: hatazawa{at}tracer.med.osaka-u.ac.jp

¹²³I-Iomazenil brain SPECT has been used for the detection of epileptogenic foci, especially when surgical intervention is considered. Although epileptogenic foci exhibit a decrease in ¹²³I-iomazenil accumulation, normal cerebral cortices often exhibit similar findings because of thin cortical ribbons, gray matter atrophy, or pathologic brain structures. In the present study, we created ¹²³I-iomazenil SPECT images corrected for gray matter volume using MRI and tested whether the detectability of the epileptogenic foci improved. Methods: Seven patients (1 male patient and 6 female patients; mean age ± SD, 34 ± 17 y) with intractable epilepsy were surgically treated by resecting the cerebral cortex after surface electroencephalography. Histopathologic examination of the resected specimens and a good outcome after surgery indicated that the resected lesions were epileptogenic foci. These patients underwent ¹²³I-iomazenil SPECT and 3-dimensional T1-weighted MRI examinations before their operations. Each SPECT image was coregistered to the corresponding MR image, and its partial-volume effect (PVE) was corrected on a voxel-by-voxel basis with a smoothed gray matter distribution image. Four nuclear medicine physicians visually evaluated the ¹²³I-iomazenil SPECT images with and without the PVE correction. The SPECT count ratio of the suspected focus to the contralateral cerebral cortex was evaluated as an asymmetry index (%) based on the volume of interest. Results: The sensitivity, specificity, and accuracy of focus detection by visual assessment were higher after PVE correction (88%, 99%, and 98%, respectively) than before correction (50%, 92%, and 87%, respectively). The mean asymmetry index for the surgically resected lesions was significantly higher on the PVE-corrected SPECT images (22%) than on the PVE-uncorrected ones (16%) (P = 0.006). Conclusion: MRI-based PVE correction for ¹²³I-iomazenil brain SPECT improves the sensitivity and specificity of the detection of cortical epileptogenic foci in patients with intractable epilepsy.

Key Words: epilepsy • ¹²³I-iomazenil • SPECT • MRI • partial-volume effect

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