Improved methodology for cerebral activation studies in a single subject using 15O-water and PET

The ability to detect sites of increased blood flow in activation studies using ¹⁵O-water and positron emission tomography (PET) is governed largely by signal-to-noise (S/N) in the subtracted images. The authors have investigated a number of methodological changes designed to improve S/N by boosting the signal, reducing the noise level, and accurately aligning the images. These changes include appropriate dose fractionation, 3-D data acquisition, prospective and retrospective image alignment, and a temporal modification of task performance designed to exploit the kinetics of ¹⁵O-water. A combination of these approaches leads to a two-fold increase in S/N compared with a previous activation study protocol