Thallium-201 diethyldithiocarbamate: an alternative to iodine-123 N-isopropyl-p-iodoamphetamine

The study of cerebral blood flow by single photon emission computed tomography (SPECT) requires lipophilic radiopharmaceuticals. The high cost and limited availability of N-isopropyl-p-[I-123]-iodoamphetamine ( [123I]IMP) led us to search for alternatives. Following our recent development of thallium-201 diethyldithiocarbamate ( [201TI]DDC), we have compared the brain uptake of [123I]IMP and [201TI]DDC in rabbits. The brain bound 1.14 +/- 0.28% (s.e.m.) of the dose of the injected [123I]IMP and 1.46 +/- 0.28% of the [201TI]DDC. Brain activity of [201TI]DDC remained stable from 1.5 min after injection up to at least 1 hr. The [201TI]DDC uptake was more instantaneous than that of [123I]IMP. The ratios of gray to white matter distribution were about equal: 1.41 for [123I]IMP and 1.44 for [201TI]DDC. The lungs retained 8.32% of the dose of [123I]IMP and only 0.53% of the [201TI]DDC. In brain macroautoradiography [201TI]DDC yielded images of good quality with excellent demarcation of gray and white matter, persisting for at least 45 min after injection. We conclude that [123I]IMP and [201TI]DDC are equally suitable for blood flow study of the rabbit brain. The first human tomographic results obtained in two healthy volunteers demonstrate that clinical application of SPECT [201TI]DDC may be feasible.