Calculation of noise-equivalent image quality

It is common to characterize PET scanners by the performance measurement known as noise-equivalent count rate. Recently, measurement of this metric have been added to the suite of tests specified by the NEMA committee and has been used to aid classification of machine performance for whole-body PET. Additionally, the NEMA committee added a test for image quality. For a GE Discovery LS PET-CT system, the NEMA IQ phantom was scanned in 2D and 3D modes at several background activity concentrations following the NEMA protocol except that all scans were acquired for 4 minutes. NEMA measures of contrast and background variability were computed and used to generate a measure of contrast-to-noise. The system NECR was also computed. A comparison between NECR and (contrast-to-noise) was made. NECR correlated well with CNR, somewhat better in 2D imaging mode than in 3D. The goal of this work was evaluation of the link between NECR and IQ by computing the NEMA IQ ratio of contrast-to-noise at various NECR points.