PET measurement of cerebral acetylcholine esterase activity without blood sampling

Measurement of cerebral acetylcholine esterase (AChE) activity is of clinic al interest for the differential diagnosis of memory disorders and dementia . We developed and tested a non-invasive method for quantitation of regiona l cortical AChE activity with carbon-11-labelled N-methyl-4-piperidyl aceta te (C-11-MP4A) that does not require arterial blood sampling. AChE activity was measured in terms of the rate constant for hydrolysis of C-11-MP4A (k( 3)). The physiological model is based on the very high AChE activity in the basal ganglia, which are used as a reference structure. Non-invasive k(3) was compared with k(3) determined with a standard technique by fitting kine tic tissue and metabolite-corrected plasma data in nine subjects with and w ithout dementia. Across all regional values, a very high correlation of 0.9 2 was found, with a tendency towards moderate underestimation of k(3) by 5% -14% with the non-invasive technique as compared to the invasive technique. In addition to its advantages with respect to practicability, the new noni nvasive technique overcomes problems of the invasive technique that are rel ated to interindividual variation of delay times between cerebral and perip heral tracer arrival and measurement of very small amounts of non-hydrolyse d tracer in plasma samples.