Comparison of brain pet and sequential and simultaneous dual-isotope spect for estimation tasks in normal and parkinson subjects

Parkinson´s disease (PD) is a widespread neurodegenerative disorder characterized primarily by changes in motor function. It affects the dopamine transporter (DAT) system, and results in a reduction of DAT specific binding and volume of active dopamine transporters, in the striata. Early detection of PD, before the onset of clinical symptoms, has great potential in improving patient management. Dual-isotope SPECT allows the assessment of different brain functions under identical physiological conditions. Simultaneous dual-isotope studies have a further advantage over sequential studies as they provide perfect image registration and reduce imaging time for the same total collected counts. These advantages are limited however by cross-talk and downscatter between the two isotopes, especially in the case of ¹²³I and ^99mTc where the emission energies are very close (i.e., 159 and 140 keV). We compare DAT brain PET with sequential and simultaneous pre- and post-synaptic dual-isotope SPECT for the task of estimating striatal activity concentration and striatal size for a normal brain and for three early stages of PD. We used the Cramer-Rao lower bound, representing the theoretical best performance achievable, as our performance metric to objectively compare these modalities, and determine their performance in identifying early disease stages. Our findings show that PET and simultaneous and sequential SPECT can successfully identify the early stages of PD when estimating both pre-synaptic activity concentration and size. Post-synaptic SPECT imaging was not able to separate disease stages. PET and simultaneous SPECT perform well when estimating only activity concentration or size, but sequential SPECT has significantly degraded performance due to lower statistics.