Feasibility of simultaneous emission and transmission scanning using short rod sources

The feasibility of simultaneously acquiring whole body Emission (Em) and Transmission (tx) scans using short or partially extended transmission rods was investigated. Count rate tests were performed on an ECAT HR+, where 3 rods filled with C-11 were extended fully and partially into the FOV in the presence of an emission source (cylinder phantom 0.25 mu Ci/cc). Prompt and random coincidences were acquired separately with rod windowing to allow separation of Em and Tx counts. At a total rod strength of 0.5 mCi/cm the randoms in the Em and Tx data were reduced by 90% and 65%, respectively. The Em-NEC was improved by a factor of 4 by reducing the exposed length to 4 cm. In addition, the Tx count rate was improved by 32% due to reduced dead time. Using short (or partially extended) Tx rods, randoms rates and dead-time are significantly reduced, which should allow simultaneous Em and Tx scanning using conventional strength Tx sources with-out significantly degrading the Em images from increased randoms.