A phantom comparison study for measuring PEM scanner sensitivity

We compare four different methods to measure the sensitivity of a positron emission mammography (PEM) system. The first method follows the NEMA NU 2 -2007 standard, which uses a 70 cm line source with aluminum sleeves. The total system sensitivity at the center of the field of view is 1006 cps/MBq. The second method adheres to the NEMA NU 4 - 2008 standard that utilizes a ²²Na point source and steps it along the system axis. The sensitivity is 163500 cps/MBq. The third method scans a 500 mL saline bag placed within the field of view containing ¹⁸F activity. The system sensitivity measured is 3200 cps/MBq. The last method employs a flood field phantom covering the field of view and filled with ¹⁸F solution. The sensitivity is 2000 cps/MBq when only the activity within the field of view is included in the calculation. We found that the flood field phantom is the most practical to implement and best reflects the overall sensitivity, and at the same time shows the two dimensional sensitivity profile.