Clinical Advantages of Interictal SPECT Coregistered to Magnetic Resonance Imaging in Patients with Epilepsy

Purpose The aim of this study was to investigate the clinical value of coregistration of interictal SPECT and magnetic resonance imaging (MRI) in patients with partial epilepsy. Materials and Methods Seventeen patients with partial epilepsy were examined with I-123 IMP or Tc-99m ethyl cysteinate dimer SPECT during the interictal phase. The SPECT images were automatically coregistered to axial T1 weighted MRIs. Asymmetry indexes (AIs) were calculated in both nonregistered images and coregistered images. Results SPECT images showed areas of decreased tracer uptake in 12 patients. In two patients, the relation between the tumor and the extent of decreased uptake became more accurate in the coregistered images. In five cases, the coregistered images clearly showed that the decreased uptake was located in the sulcus. The AIs were significantly reduced from 14.29 ± 7.23 to 5.86 ± 3.48 (P < 0.001) after the images were coregistered in these cases. In five cases, the coregistered images indicated that the decreased areas were in agreement with the cortical findings. No significant differences in the AIs were observed in these cases (16.50 ± 6.19 versus 17.83 ± 4.45). Thus, the coregistered images were useful not only to differentiate actual hypoperfusion from artificial hypoperfusion resulting from partial volume effects but also to improve the accuracy of AIs. Conclusion The coregistration of interictal perfusion SPECT and MRI is useful not only to provide precise functional and anatomic mapping but also to improve the accuracy of calculations of the semiquantitative analysis of regional cerebral blood flow parameters during the interictal state of epilepsy.