QUANTITATIVE ESTIMATION OF I-123 IOMAZENIL RECEPTOR-BINDING IN TEMPORAL-LOBE EPILEPSIES USING 2 SPECT ACQUISITIONS - COMPARISON WITH THE REGIONAL CEREBRAL BLOOD-FLOW AND A COMPARTMENT MODEL

Aim: To compare published fractional rare constants of I-123-lomazenil (IMZ) and C-ll-Flumazenil (three-compartment/four-parameter model) wi th a I-123-lomazenil receptor index calculated from two SPECT acquisit ions and to compare the receptor index of the epileptogenic area with the contralateral side in patients with unilateral temporal lobe epile psies. Methods: 28 patients were studied. 13/28 patients had a drug-re sistant unilateral temporal lobe epilepsy with a successful focus loca lisation performed by an extensive video/EEG monitoring. 15 other pati ents with clinically suspected focal epilepsy and a normal MRI and IMZ SPECT scanning were used as controls. SPECT scanning was performed in all patients 15 and 100 min after intravenous injection of 111 MBq IM Z and 10 min after application of 740 MBq Tc-99m-HMPAO. Quantification of the regional uptake was performed using ROI-technique and the spec ific and non-specific binding of IMZ was calculated. The receptor inde x was calculated by the difference of the specific binding from 15 to 100 min p.i. divided by the time interval. Results: The receptor index showed a linear correlation with recently published fractional rate c onstants k(3) (I = 0.69 and 0.67; p = 0.15) and a moderate correlation with the k,constant (-0.53 and -0.43; p = 0,28) by the means of C-11- flumazenil PET and I-123-lomazenil SPECT studies, respectively. Howeve r, statistical significance was not reached due to the few data points available from the published reports. Furthermore, the IMZ receptor i ndex was lower in the epilep togenic area of patients with unilateral temporal lobe epilepsies compared with their contralateral side (p = 0 .02; Wilcoxon-test). The IMZ receptor index showed a weak correlation with the regional cerebral blood flow independent of the evaluated reg ion (r<0.4; p<0.05). Conclusion: The IMZ receptor index indicated to b e a simple routine approach to estimate the fractional rate constant k (3) (r = 0.67). The lower value of the receptor index within the epile ptogenic area might be due to a lower receptor density. However in fur ther studies, IMZ might be a helpful tool to find our subtle changes o f the receptor affinity due to its approximately 30-fold higher ligand -receptor affinity compared to C-l l-Flumazenil.