Alternate Methodology For Sensitivity Testing Of A Total Body Pet Scanner

3006 Objectives: To develop methods for characterizing the sensitivity of a Total Body PET scanner. The sensitivity test measures the number of counts (coincidence detection events) per second that the scanner records for every unit of activity in the field-of-view (FOV). Current methods of testing recommended by the National Electrical Manufacture’s Association (NEMA) standards were designed for PET scanners with an axial FOV of roughly 15-25cm. With a Total Body PET scanner, the recommended NEMA sensitivity testing methods may fail to fully characterize the scanner performance due to the extended axial FOV (194cm) which is much longer than the NEMA sensitivity phantom (70cm). Methods: Three methods were utilized to measure sensitivity in a uExplorer Total Body PET scanner (United Imaging Healthcare; 8 sequential scanning units, 24.25cm each). Method 1 utilizes a 70cm line source filled with ~0.1 mCi F-18 inserted into aluminum sleeves. The line source is imaged according to NEMA standards at three different axial locations within the scanner that together cover the entire axial FOV. Method 2 utilizes a Na-22 50uCi (+10%) point source with a 0.25mm active diameter. The Na-22 source is positioned within each of the 8 units at approximately 6 cm, 12 cm and 18 cm respectively, resulting in 24 acquisition locations. A 60 second image is acquired at each location. Total counts of prompts and random coincidences are obtained from each image metadata. Method 3 also utilizes a Na-22 50uCi point source centered within the transaxial FOV at each of the 24 locations within the 194cm axial FOV. Prompts and randoms are recorded in real time from the console. All three methods for acquiring sensitivity were compared and the results were analyzed. Results: For a Total Body PET scanner such as uExplorer, sensitivity is greatest within the central units. As with conventional PET scanners (15-25cm axial FOV), the uExplorer (194 cm axial FOV) shows a tapering of sensitivity at the outer edges of scan FOV. However, unlike conventional PET scanners, there is an extended region within the center of the axial FOV where the sensitivity does not show marked change. Sensitivity results from Method 1,2 and 3 were 177 cps/kBq (17.7%), 143cps/kBq (14.3%) and 33cps/kBq (3%) respectively. Discussion: Alternative methods can be developed to optimize sensitivity testing of a scanner with an elongated axial FOV. Each of the three methods tested has benefits and limitations. Methods 2 and 3 limit the possibility of contamination and eliminate the difficulty of accurate line source filling. Methods 2 and 3 utilize a long-lived source. Method 3 measures sensitivity within each unit independent of one another. Methods 1 and 2 allow for plotting sensitivity of the entire scan range, taking into account inter unit communication. Due to challenges with source activity verification and the prompt gamma radiation from Na22, Method 1 is preferred for absolute quantification, but Methods 2 and 3 are preferred for longitudinal monitoring. Methods 2 and 3 are much simpler to acquire and allow for minimal disruption in workflow. Conclusions: All three methods for acquiring sensitivity on the uExplorer Total Body PET scanner provide results that can be used to show stability of scanner.