Abstracts

Detection of interictal hypoperfusion on MRI or PET may help to identify epileptic foci and plan surgical treatment. Several methods to study cerebral blood flow (CBF), including single photon emission computed tomography, arterial spin labeling MR imaging (ASL-MRI ) and bolus ¹⁵O-H[sub]2[/sub]O positron emission tomography (¹⁵O-PET), have been developed. We studied the usefulness of pulsed ASL-MRI to detect interictal hypoperfusion in patients with temporal lobe epilepsy, by comparing ASL-MRI and ¹⁵O-PET detection of lateralized hypoperfusion in patients with temporal lobe epilepsy. Four patients with temporal lobe epileptic foci identified on ictal video-EEG monitoring were scanned on a GE Signa 3T MRI scanner using a proximal inversion with a control for off resonance effects (PICORE)- quantitative imaging of perfusion using a single subtraction, second version (QUIPSS II) ASL sequence to estimate baseline flow. (TR/TE = 2500ms/30ms, TI1/TI2 = 700ms/1400ms, FOV = 24cm, slice thickness = 7mm, matrix: 64x64, 5 axial slices). Images were corrected for subject motion. Flow values were averaged over 150 time points, in each temporal lobe. For ¹⁵O-PET, we used a GE (Waukesha, WI, USA) Advance Tomograph (FWHM = 6-7 mm), scanning 35 simultaneous slices with 4.25 mm slice separation. During scanning, in a quiet, dim room with eyes closed and ears unoccluded, a thermoplastic facemask held the subject[apos]s head in place. 10 mCi ¹⁵O-H[sub]2[/sub]O was injected, and scanning performed for two minutes, using continuous arterial blood measurements with an automatic blood counter. Quantitative CBF values were obtained in regions drawn on co-registered structural MRI. For comparison with ASL-MRI, regional CBF from hippocampal formation, amygdala, parahippocampal gyrus, and fusiform gyrus were averaged. For both ASL-MRI and ¹⁵O-PET, an asymmetry index (AI) was derived using the formula: 2 * (ipsilateral-contralateral)/ (ipsilateral+contralateral). The two procedures showed agreement for lateralization in all four patients. For ASL-MRI, temporal AI values for the four patients were: 0.45, 0.15, 0.05, 0.18; for ¹⁵O-PET: 0.18, 0.108, 0.04 and 0.104. These hypoperfusion regions were consistent with results of ictal video-EEG and structural MRI. Our study suggests that ASL-MRI using QUIPSS II saturated pulse may be a useful tool for identifying temporal lobe epileptogenic zones, providing CBF data comparable to ¹⁵O-PET. (Supported by NINDS Division of Intramural Research.)