Establishing test-retest reliability of an adapted [18F]fallypride imaging protocol in older people

[18F]fallypride is a high affinity dopamine D2/3 receptor tracer with the ability to reliably quantify D2/3 receptor sites in both striatal and corticolimbic regions. The translational potential of [18F]fallypride imaging is however limited by the lengthy scanning sessions (60-80 minutes duration over a total of 3-4 hours) required by current protocols. The aims of our study were to adapt [18F]fallypride imaging for use in clinical populations with neurological and neuropsychiatric disorders, by reducing the duration of individual scanning sessions; and to establish the reproducibility and reliability of our adapted protocol in healthy older people. Eight participants (5 male, 3 female; mean age = 75.87 ±4.39 years) were scanned twice, 4-6 weeks apart. [18F]fallypride binding potential was determined from image data collected during 3 sampling times: 0-30; 60-90; and 210-240 minutes post-injection. High reproducibility and reliability (test-retest variability <8%; intra-class correlation coefficient >0.8) were observed in all but the prefrontal regions and remained so when sampling times were reduced to 20 minutes (0-20; 70-90; 220-240 minutes). The adapted protocol is feasible for use across neuropsychiatric disorders in which dopamine has been implicated and is sufficiently sensitive to detect within-subject changes between 2.7% and 5.5% in striatal and limbic regions.