Comparison of two new methods to measure the sensitivity of total-body and long-axial field-of-view PET scanners

Several of the NEMA NU 2 standard measurements are not suitable for characterization of total-body or long-axial field-of-view (LAFOV) PET scanners ($\gt65 \mathrm{~cm}$ axial FOV), however there is no agreed upon standard for characterization of these recently developed PET scanners. This work outlines two suitable methods for sensitivity characterization of LAFOV PET scanners and provides a comparison to the NEMA NU 2 standard. The methods introduced here include using a point source stepped through the axial FOV and a 2-meter line source which fully characterize LAFOV PET sensitivity. We present here our evaluation of the methods’ suitability for LAFOV sensitivity assessment, the methods’ complexity and difficulty, and make a quantitative comparison between them. We discovered that the 2-meter line source sensitivity method provided a full characterization of the PET scanner sensitivity profile, and when interpolating to the central $70-\mathrm{cm}$ was within 0.4% agreement with the NEMA NU 2 method validating its accuracy. The point source method was the easiest to perform, however, it could not provide an absolute sensitivity measurement without cross-calibrating with a standard line source method. This cross-calibration procedure revealed a close (+1.2%) agreement with the 2-meter line source measurement indicating its suitability for LAFOV sensitivity assessment.