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Age-Related Changes in D₂ Receptor Binding with Iodine-123-Iodobenzofuran SPECT

Department of Nuclear Medicine, Mount Sinai Hospital; Department of Nuclear Medicine, Princess Margaret Hospital; Behavioral Neurology Program and Rotman Research Institute of Baycrest Center for Geriatric Care; University of Toronto, Toronto, Ontario, Canada

Correspondence: For correspondence or reprints contact: Masanori Ichise, MD, Room 635, Nuclear Medicine, Department of Medical Imaging, Mount Sinai Hospital, 600 University Ave., Toronto, Ontario, Canada M5G 1X5.

ABSTRACT

The purpose of this study was to evaluate the effects of age on D₂ receptor binding with ¹²³I-iodobenzofuran (IBF)SPECT. Methods: Subjects 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 putamen) were defined by two different region-of-interest (ROI)sets consisting of large volumes [(CLVs),2.2 and 6.6 m] and small volumes [(SVs),0.6 and 1.3 ml].D2 binding (Rv = V₃N₂) was quantified using our previously proposed multilinear regression technique. Effects of age on D₂ binding were evaluated by fitting linear, exponential and logarithmic models. Results; The mean Rvs were 26% lower than LV for both putamen and caudate than the corresponding values from the SV due to the partial-volume effect. Although the identifiability of Rv using SV deteriorated slightly, the test/retest reproducibility of Rv measurements was equally excellent for LV and SV. The mean Rvs were 11% higher for putamen compared with those for caudate. D₂ binding declined significantly with age (p < 10^-5) for all three models. The nonlinear models were slightly superior to the linear model in describing the relationship between Rv and age. In these models, D₂binding declined with age, equally for caudate and putamen at 7%–13% per decade; the decline was progressively smaller with age. Conclusion: IBF SPECT permitted reliable measurements of D₂ binding in the caudate or putamen separately using small ROI volumes that significantly improved the quantitation loss from the partial-volume effect. Our results agreed with previous PET and postmortem findings of D₂ binding losses with age. However, these age effects may be non linear. Age-related changes in D₂ binding must be taken into consideration in clinical IBF SPECT investigations.

Key Words: iodine-123-iodobenzofuran • dopamine D₂ receptors • aging • dopamine SPECT

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