3-DIMENSIONAL IMAGING CHARACTERISTICS OF THE HEAD PENN-PET SCANNER

A volume-imaging PET scanner, without interplane septa, for brain imag ing has been designed and built to achieve high performance, specifica lly in spatial resolution and sensitivity. The scanner is unique in it s use of a single annular crystal of NaI(Tl), which allows a field of view (FOV) of 25.6 cm in both the transverse and axial directions. Dat a are reconstructed into an image matrix of 128(3) with (2 mm)3 voxels , using three-dimensional image reconstruction algorithms. Methods: Po int-source measurements are performed to determine spatial resolution over the scanner FOV, and cylindrical phantom distributions are used t o determine the sensitivity, scatter fraction and counting rate perfor mance of the system. A three-dimensional brain phantom and F-18-FDG pa tient studies are used to evaluate image quality with three-dimensiona l reconstruction algorithms. Results: The system spatial resolution is measured to be 3.5 mm in both the transverse and axial directions, in the center of the FOV. The true sensitivity, using the standard NEMA phantom (6 liter), is 660 kcps/mu Ci/ml, after subtracting a scatter f raction of 34%. Due to deadtime effects, we measure a peak true counti ng rate, after scatter and randoms subtraction, of 100 kcps at 0.7 mCi for a smaller brain-sized (1.1 liter) phantom, and 70 kcps for a head -sized (2.5 liter) phantom at the same activity. A typical F-18-FDG cl inical brain study requires only 2 mCi to achieve high statistics (100 million true events) with a scan time of 30 min. Conclusion: The HEAD PENN-PET scanner is based on a cost-effective design using NaI(Tl) an d has been shown to achieve high performance for brain studies and ped iatric whole-body studies. As a full-time three-dimensional imaging sc anner with a very large axial acceptance angle, high sensitivity is ac hieved. The system becomes counting-rate limited as the activity is in creased, but we achieve high image quality with a small injected dose. This is a significant advantage for clinical imaging, particularly fo r pediatric patients.