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Performance tests on lutetium oxyorthosilicate (LSO)-based PET scanners cannot be conducted strictly according to the National Electrical Manufacturers Association (NEMA) NU 2 standards because of the presence of intrinsic radioactivity within the LSO crystal scintillator material. This background radiation gives rise mainly to random coincidence events but also to a small number of true coincidences, which cannot be eliminated from measurements on such scanners and must therefore be corrected for in the data analysis. The current NU 2 standards do not take account of these backgrounds and hence can lead to erroneous results on LSO-based machines. Nevertheless, the intent of the standards can be met with appropriate modifications to the acquisition and processing procedures. In this paper, we propose certain changes to the NEMA specifications to accommodate this class of scanners. These changes affect mainly the estimation of sensitivity, scatter, randoms, and count losses. Using these modified procedures, the NU 2 performance of LSO-based systems can accurately be measured.

Unlabelled: Results of performance measurements for a lutetium oxyorthosilicate (LSO)-based PET/CT scanner using new National Electrical Manufacturers Association (NEMA) NU 2-2001 standards are reported., Methods: Performance measurements following the NU 2-2001 standards were performed on an LSO-based PET/CT scanner. In addition, issues associated with the application of the NEMA standard to LSO-based tomographs in the presence of intrinsic radiation are discussed., Results: We report on some difficulties experienced in following the suggested NEMA measurement techniques and describe alternative approaches. Measurements with the new standard (as compared with NU-1994) incorporate the effects of activity outside the scanner and facilitate measurements of the entire axial field of view. Realistic clinical conditions are also simulated in image quality measurements of a torso phantom., Conclusion: We find that, with appropriate modifications, NU 2-2001 can be successfully applied to LSO-based scanners.