Use of subtraction ictal SPECT co-registered to MRI for optimizing the localization of seizure foci in children

Ictal SPECT studies are increasingly used to localize seizure foci in child ren with refractory epilepsy, but few studies have reported on ictal-interi ctal subtraction images co-registered to MRI at this age. Methods: Twenty-s even children with partial epilepsy (aged 3 mo-18 y) underwent ictal ethyl cysteinate dimer (ECD) SPECT (20 mCi/1.73 m(2)) combined with video;electro encephalography (EEG) and interictal ECD SPECT followed 2 d later by three- dimensional MRI. Ictal-interictal and interictal-ictal subtraction images w ere computed by registering and normalizing the ictal to the interictal SPE CT scans for each child. The ictal, interictal SPECT and subtraction images were registered to each child's MRI. Difference images (ictal-interictal) were then superimposed on MRI for anatomic localization of the perfusion ch anges. Intra-and interobserver reproducibility and "facility of interpretat ion" of overlay images were compared with standard analysis of the non-core gistered ictal and interictal scans. Results: Overlay images allowed the de tection of at least one hyperperfused focus in 93% of the children, compare d with 74% using ictal and interictal scans separately. Seizure onset was s uspected clinically, on EEG or on MRI in 20 children. Overlay images were c oncordant (n = 11) or larder (n = 7) than the suspected focus in 18 of 20 ( 90%), whereas these images failed to show any abnormality in I child and we re discordant with MRI in another patient. In the remaining 7, images showe d cortical localization in 6 patients. Among the 5 patients who underwent e lectrocorticography, overlay images were concordant in 3, larger in 1 and a bsent in 1, The intra- and interobserver reproducibility and facility of in terpretation were significantly higher using overlay images than standard a nalysis, even when ictal and interictal SPECT were co-registered. Conclusio n: The co-registration of ictal-interictal subtraction SPECT images to MRI seems to be a helpful technique in localizing the onset of seizure and guid ing the intracranial recording in childhood epilepsy. Moreover, this method improves sensitivity, enhances intra- and interobserver reproducibility an d makes interpretation easier.