We determined the effect of retention on the changes in regional biodistrib
ution of Tc-99m ECD in the brain. A total of 14 cases, 7 normal volunteers
and 7 patients with various diagnoses but with very minimal radiologic find
ings or none were included in the study. SPECT images were taken at 30 min,
1, 2, 3, 4 and 6 hrs after an intravenous injection. Retention rates were
calculated in various regions and were corrected according to the time deca
y of technetium. There was a tendency for the retention rate to increase up
to three hours of imaging and then a decrease was noted in most regions of
the brain. In the thalamus, increasing retention was noted. In conclusion,
Tc-99m ECD retention in the different regions of the brain varies with tim
e. These differences should always be considered when planning and interpre
ting SPECT quantitative studies.