EFFECT OF DEADTIME LOSS ON QUANTITATIVE MEASUREMENT OF CEREBRAL BLOOD-FLOW WITH TC-99M HEXAMETHYLPROPYLENE AMINE OXIME

Deadtime count loss may cause error in quantitative measurements with a gamma camera. We evaluated the effect of deadtime loss on the measur ement of cerebral blood flow (CBF), Radionuclide angiography with tech netium-99m hexamethylpropylene amine oxime (Tc-99m-HMPAO) was performe d in 20 patients. A reference source was placed on the periphery of th e detector to monitor deadtime loss, and CBF was calculated based on t he data of radionuclide angiography with and without deadtime correcti on, In ten patients injected with 1110 MBq of the tracer, the CBF valu e without correction was 9.9%+/-1.8% higher than that with correction. This shows that deadtime loss may cause significant overestimation, T he difference between CBF values obtained with and without correction was smaller in ten patients with an injected dose of 370 MBq (3.0%+/-1 .2%). These results suggest a substantial effect of deadtime loss on C BF as measured by radionuclide angiography and Tc-99m-HMPAO.