title: Effects of Detector Thickness on Geometric Sensitivity and Event Positioning Errors in the Rectangular PET/X Scanner.
abstract: We used simulations to investigate the relationship between sensitivity and spatial resolution as a function of crystal thickness in a rectangular PET scanner intended for quantitative assessment of breast cancers. The system had two 20 × 15-cm2and two 10 × 15-cm2flat detectors forming a box, with the larger detectors separated by 4 or 8 cm. Depth-of-interaction (DOI) resolution was modeled as a function of crystal thickness based on prior measurements. Spatial resolution was evaluated independent of image reconstruction by deriving and validating a surrogate metric from list-mode data (dFWHM). When increasing crystal thickness from 5 to 40 mm, and without using DOI information, thedFWHMfor a centered point source increased from 0.72 to 1.6 mm. Including DOI information improveddFWHMby 12% and 27% for 5- and 40-mm-thick crystals, respectively. For a point source in the corner of the FOV, use of DOI information improveddFWHMby 20% (5-mm crystal) and 44% (40-mm crystal). Sensitivity was 7.7% for 10-mm-thick crystals (8-cm object). Increasing crystal thickness on the smaller side detectors from 10 to 20 mm (keeping 10-mm crystals on the larger detectors) boosted sensitivity by 24% (relative) and degradeddFWHMby only ~3%/8% with/without DOI information. The benefits of measuring DOI must be evaluated in terms of the intended clinical task of assessing tracer uptake in small lesions. Increasing crystal thickness on the smaller side detectors provides substantial sensitivity increase with minimal accompanying loss in resolution.
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA 98195 USA.
authors.forename: Lawrence R
authors.initials: LR
authors.lastname: MacDonald
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA 98195 USA.
authors.forename: William C J
authors.initials: WC
authors.lastname: Hunter
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA 98195 USA.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Kinahan
authors.affiliation: Department of Radiology, University of Washington, Seattle, WA 98195 USA.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Miyaoka
keywords: Computer simulation; dedicated breast PET; positron emission tomography