Relationship of the sensitivity of dual-head coincidence imaging and 18F activity

Objective: To evaluate the effects of 18F activity on random coincidence rate and sensitivity in dual-head coincidence imaging. Methods: The chest model was filled with water solution added various 18F activity. The emission tomography imaging was acquired by DST-Xli dual-head SPECT and the imagings were processed with the same reconstruction procedure. Results: The more different between the true and random coincidence, the better imaging quality would be. the difference value varied from small to larger and then gradually went down in 6 consecutive imagings. At 86th min, the difference value reached maximum 8.9 MBq, the single counts rate was 3.65 x 105, the corresponding 18F activity was 17.8 MBq, and the random coincidence rate was 25%. At that time the most positive nodules were displayed with the best imaging quality. The counts rate, random coincidence rate and others had significant linear correlation. The correlation coefficient (R) between the activity X (MBq) and random coincidence rate Y(%) were 0.9974 (R2) and 0.9967 (R2) with P<0.0001, and the linear equation was Y=-1.89379 + 1.550685 X. Conclusions: Chest model suggested the best suitable 18F activity required; both higher or lower activity could not benefit for the imaging quality. When the random coincidence rate was 25%, the corresponding 18F activity could produced the best imaging sensitivity. (authors)