Comparison of technetium-99m-HMPAO and technetium-99m-ECD cerebral SPECT images in Alzheimer's disease

SPECT has shown increasing promise as a diagnostic tool in Alzheimer's disease (AD). Recently, a new SPECT brain perfusion agent, Tc-99m-ethyl cysteinate dimer (Tc-99m-ECD) has emerged with purported advantages in image quality over the established tracer, Tc-99m-hexamethylpropyleneamine oxime (Tc-99m-HMPAO). This research aimed to compare cerebral images for Tc-99m-HMPAO and Tc-99m-ECD in discriminating patients with AD from control subjects. Methods: Twenty-four AD patients (mean age+/-s.d.=68.9+/-8.2 yr) and 13 healthy subjects (68.4+/-8.0 yr) were scanned sequentially with 20 mCi of each tracer using the CERASPECT system within 1 mo. Scanning began on average 11.5+/-2.8 min after Tc-99m-HMPAO injection and 41.8+/-10.1 min after Tc-99m-ECD. A ratio, R, was derived of count densities in ''typically affected'' brain structures (parietal and temporal association cortices) to ''unaffected'' structures (cerebellum, basal ganglia, thalamus, occipital cortex, and sensorimotor cortex). Results: Analysis of variance revealed significant interaction between diagnostic group and radiopharmaceutical (F=4.71; df=1,35; p=0.04), with Tc-99m-ECD demonstrating better separation of R values between AD patients and control subjects than Tc-99m-HMPAO. Receiver operating characteristic (ROC) analysis revealed no significant difference in the ability of the two tracers to correctly classify AD patients and control subjects. Both tracers showed high diagnostic accuracy (Tc-99m-ECD: sensitivity=100%, specificity=92%; Tc-99m-HMPAO: sensitivity=100%, specificity=85%). Conclusion: Technetium-(99)m-ECD shows greater contrast than Tc-99m-HMPAO between affected and unaffected brain structures in AD when patients are compared to age-matched control subjects. Both tracers perform equally well in correctly classifying patients and control subjects.