HEAD MOVEMENT IN NORMAL SUBJECTS DURING SIMULATED PET BRAIN IMAGING WITH AND WITHOUT HEAD RESTRAINT

Head movement during brain imaging is recognized as a source of image degradation in PET and most other forms of medical brain imaging. Howe ver, little quantitative information is available on the kind and amou nt of head movement that actually occurs during these studies. We soug ht to obtain this information by measuring head movement in normal vol unteers. Methods: Head position data were acquired for 40 min in each of 13 supine subjects with and without head restraint. These data were then used to drive a mathematically simulated head through exactly th e same set of movements. The positions of point sources embedded in th is head were computed at each location and these data summarized as mo vement at FWHM in each of the three coordinate directions. Results: He ad movement increased with the length of the sampling interval for stu dies of either type (with or without head restraint), but the amount a nd rate of increase with restraint was much smaller. In contrast, head movement during consecutive, short sampling intervals was small and d id not increase with time. Spatial gradients in head movement were det ected within each study type, and significant spatial differences in h ead movement were found between study types. Conclusions: Head movemen ts in normal, supine subjects, though small, can cause the effective r esolution of a brain imaging study to appear to vary in space and time . These effects can be reduced significantly with head restraint and m ay also be reduced by dividing the acquisition of a single image into a sequence of short images (instead of a single long image), aligning these images spatially and summing the result.