Comparative study of 99mTc-ECD and 99mTc-HMPAO for peri-ictal SPECT:: qualitative and quantitative analysis

Objectives-Most studies that clinically validated peri-ictal SPECT in intractable partial epilepsy had used technetium-99m-hexamethylpropylene amine oxime (Tc-99m-HMPAO or Tc-99m-exametazime) as the radiopharmaceutical. Because of some theoretical advantages, technetium-99m-ethyl cysteinate diethylester (Tc-99m-ECD or Tc-99m-bicisate) is increasingly being used instead. This study compares unstabilised Tc-99m-HMPAO and Tc-99m-ECD in the performance of peri-ictal SPECT in partial epilepsy. Methods-The injection timing and localisation rates in 49 consecutive patients with partial epilepsy who had peri-ictal injections with unstabilised Tc-99m-HMPAO were compared with 49 consecutive patients who had peri-ictal injections with Tc-99m-ECD. Quantitative cortical/subcortical and cortical/extracerebral uptake ratios were also compared. Subtraction SPECT coregistered to MRI (SISCOM) was performed in patients whose interictal SPECTS were available. Results-In the Tc-99m-ECD patients, the latency from seizure commencement to injection was shorter (median 34 v 80 seconds, p<0.0001) and there was a lower rate of postictal injections (16.3% v 57.1%, p<0.0001). The corticavl/extracerebral and cortical/subcortical uptake ratios were greater in the Tc-99m-ECD images (median 5.0 v 3.6, and 2.5 v 2.2 respectively; both p<0.005), but the relative peri-ictal increase in uptake in the cortical focus did not differ significantly (median 37.0% v 37.0%; p>0.05). Blinded review of the SISCOM images were localising in a higher proportion of the Tc-99m-ECD patients (40/45 (88.9%) v 25/37 (67.6%), p<0.05), and had a better concordance with EEG, MRI, and with the discharge diagnosis. Conclusion-Tc-99m-ECD compares favourably with unstabilised Tc-99m-HMPAO as a radiopharmaceutical for peri-ictal SPECT studies. Its use results in earlier injections and less frequent postictal injections than unstabilised Tc-99m-HMPAO, thereby enhancing the sensitivity and the specificity of peri-ictal SPECT for the localisation of intractable partial epilepsy.