Evaluation of the ECAT EXACT HR+ 3-D PET scanner in H/sub 2//sup 15/O brain activation studies: dose fractionation strategies for rCBF and signal enhancing protocols

The authors evaluated the performance of the ECAT EXACT HR+ 3-D whole-body positron emission tomography (PET) scanner when employed to measure brain function using H ₂ ¹⁵O bolus activation protocols that are completed in single same-day data acquisition sessions. Using vibrotactile and auditory stimuli as independent activation tasks, the authors studied the scanner performance under different imaging conditions in five healthy volunteers. Cerebral blood flow images were acquired from each volunteer using H ₂ ¹⁵O bolus injections of activity varying from 5-20 mCi. One-session dose-fractionation strategies were analyzed for rCBF, standard activity-concentration, switched, and cold-bolus/switched protocols. Performance characteristics: The scanner dead time grew linearly with injected dose from 10% to 25%. Random events varied from 30% to 50% of the detected events. Random and scattered events were corrected adequately at all doses. Estimated noise effective-count curves plateau at about 10 mCi. One-session 12-injection bolus PET activation protocols. Using an acquisition protocol that accounts for the scanner performance and the practical aspects of imaging volunteers and neurological patients in a single same-day session, the authors assessed the correlation between the significance of activation foci and the dose/injection used. The one session protocol employs 12 bolus injections/subject. The authors present evidence suggesting that when an rCBF protocol is used, image noise is reduced significantly when the activity injected increases from 5 to 10 mCi. Increasing the dose from 10 to 15 or 20 mCi yielded further but smaller reductions. The authors´ observations also suggest that image noise will be strongly reduced if a 20-mCi dose/injection is used when data are collected using protocols that employ long acquisition times such as a switched or a cold-bolus/switched protocol.