AGE-RELATED-CHANGES IN D-2 RECEPTOR-BINDING WITH IODINE-123-IODOBENZOFURAN SPECT

The purpose of this study was to evaluate the effects of age on D-2 re ceptor binding with I-123-iodobenzofuran (IBF) SPECT, Methods: Subject s were 40 healthy volunteers (age 19-83 yr), including 6 who had test/ retest studies. Scans were acquired with a triple-head SPECT camera 3 hr postinjection of IBF (300 MBq). Striatal regions (caudate and putam en) were defined by two different region-of-interest (ROI) sets consis ting of large volumes [(CLVs), 2.2 and 6.6 m] and small volumes [(SVs) , 0.6 and 1.3 ml], D-2 binding (Rv = V-3/V-2) was quantified using our previously proposed multilinear regression technique. Effects of age on D-2 binding were evaluated by fitting linear, exponential and logar ithmic models. Results: The mean Rvs were 26% lower than LV for both p utamen and caudate than the corresponding values from the SV due to th e partial-volume effect. Although the identifiability of Rv using SV d eteriorated slightly, the test/retest reproducibility of Rv measuremen ts was equally excellent for LV and SV. The mean Rvs were 11% higher f or putamen compared with those for caudate. D-2 binding declined signi ficantly with age (p < 10(-5)) for all three models. The nonlinear mod els were slightly superior to the linear model in describing the relat ionship between Rv and age. In these models, D-2 binding declined with age, equally for caudate and putamen at 7%-13% per decade; the declin e was progressively smaller with age. Conclusion: IBF SPECT permitted reliable measurements of D-2 binding in the caudate or putamen separat ely using small ROI volumes that significantly improved the quantitati on loss from the partial-volume effect. Our results agreed with previo us PET and postmortem findings of D-2 binding losses with age, However , these age effects may be nonlinear. Age-related changes in D-2 bindi ng must be taken into consideration in clinical IBF SPECT investigatio ns.