Transmission scanning system for a gamma camera coincidence scanner

The goal of this research was to develop and evaluate a practical transmiss ion scanning system for attenuation correction on a 2-head gamma camera coi ncidence scanner. Methods: The transmission system operates in singles mode and uses point sources of Cs-137 that emit 662-keV gamma-radiation. Each p oint source is inserted between existing septa that are normally used to pr ovide an approximately 2-dimensional emission acquisition geometry. The sou rces are placed along a line parallel to the axis of rotation near the edge of 1 camera. Data are acquired with the opposing camera. The septa provide axial collimation for the sources so that the transmission system operates in a 2-dimensional offset fanbeam geometry. Camera energy and spatial reso lution were measured at 511 and 662 keV. Sensitivity was measured at 662 ke V. The effects on axial resolution of adding supplemental collimation to th e septa were shown. The system was calibrated and tested using a resolution (rod) phantom and a uniformity phantom, Torso phantom data were acquired. Patient transmission and emission scans were obtained. Postinjection transm ission data were used to correct patient emission data. Results: The camera resolution at postinjection counting rates was 11.7% full width at half ma ximum (FWHM) for 662-keV gamma-rays. Intrinsic spatial resolution was 2.7 m m (FWHM) at 662 keV, The sensitivity of the system was 280 Hz/MBq using fiv e 74-MBq sources of 137Cs in the transmission geometry, with supplemental c ollimation added to the septa to improve axial resolution. The transaxial r esolution of the system was such that the smallest rods (6-mm diameter and 12-mm spacing) were well resolved in a reconstructed resolution-phantom ima ge. The corrected patient emission scans were free of attenuation-induced a rtifacts. Conclusion: An easily implemented transmission system for a 2-hea d gamma camera coincidence scanner that can be used for postinjection trans mission scanning has been developed.