Beta-amyloid (Abeta) imaging has great potential to aid in the diagnosis of 
Alzheimer disease and the development of therapeutics. The radiation dosimetry 
of Abeta radioligands may influence their application; therefore, we calculated 
and compared the effective doses (EDs) of 11C-PiB and a new 18F-labeled ligand, 
18F-BAY94-9172.
METHODS: Attenuation-corrected whole-body scans were performed at 0, 15, 30, 45, 
and 60 min after injection of 350+/-28 MBq (mean+/-SD) of 11C-PiB in 6 subjects 
and at 0, 20, 60, 120, and 180 min after injection of 319+/-27 MBq of 
18F-BAY94-9172 in 3 subjects. Coregistered CT was used to define volumes of 
interest (VOIs) on the PET images. The source organs were the brain, lungs, 
liver, kidneys, spleen, and vertebrae. The VOIs for the contents of the 
gallbladder, urinary bladder, lower large intestine, upper large intestine, and 
small intestine were also defined. Total activity in each organ at each time 
point was calculated by use of reference organ volumes. The resultant 
time-activity curves were fitted with constrained exponential fits, and 
cumulated activities were determined. A dynamic bladder voiding model was used. 
The OLINDA/EXM program was used to calculate the whole-body EDs from the 
acquired data.
RESULTS: For 11C-PiB, the highest absorbed doses were in the gallbladder wall 
(44.80+/-29.30 microGy/MBq), urinary bladder wall (26.30+/-8.50 microGy/MBq), 
liver (19.88+/-3.58 microGy/MBq), and kidneys (12.92+/-3.37 microGy/MBq). The ED 
was 5.29+/-0.66 microSv/MBq. For 18F-BAY94-9172, the highest doses were also in 
the gallbladder wall (132.40+/-43.40 microGy/MBq), urinary bladder wall 
(24.77+/-7.36 microGy/MBq), and liver (39.07+/-8.31 microGy/MBq). The ED was 
14.67+/-1.39 microSv/MBq.
CONCLUSION: The estimated organ doses for 11C-PiB were comparable to those 
reported in earlier research. With the doses used in published studies (300-700 
MBq), the EDs would range from 1.6 to 3.7 mSv. The ED of 18F-BAY94-9172 was 30% 
lower than that of 18F-FDG and, at the published dose of 300 MBq, would yield an 
ED of 4.4 mSv. The dosimetry of both Abeta radioligands is suitable for clinical 
and research applications.