MRI-Based Correction for Partial-Volume Effect Improves Detectability of Intractable Epileptogenic Foci on 123I-Iomazenil Brain SPECT Images
Hiroki Kato 1,
Eku Shimosegawa 1,
Naohiko Oku 2,
Kazuo Kitagawa 3,
Haruhiko Kishima 4,
Youichi Saitoh 4,
Amami Kato 5,
Toshiki Yoshimine 4,
and
Jun Hatazawa 1*
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
5 Department of Neurosurgery, Kinki University School of Medicine, Osaka-Sayama, Japan
* To whom correspondence should be addressed. E-mail: hatazawa{at}tracer.med.osaka-u.ac.jp.
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Abstract |
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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
