NEC density and liver ROI S/N ratio for image quality control of whole-body FDG-PET scans: comparison with visual assessment.

PURPOSE: Patient noise equivalent count (NEC), NEC density, and liver region of interest (ROI) S/N have been proposed as physical indicators of image quality, but have not been thoroughly compared with visual assessments. In this study, those indicators were contrasted with blind visual evaluations for whole-body fluorodeoxyglucose-positron emission tomography (FDG-PET) images acquired under a variety of scanning conditions and body weights. METHODS: Images were acquired on 15 normal subjects using a SET-3000B/L PET scanner with a continuous bed motion. Body weight ranged from 50.2 to 95.7 kg, with injected activity ranging from 71 to 333 MBq (1.40 to 3.67 MBq/kg) and a scan duration from 10 to 30 min. Patient NEC (PNEC; counts/cm) was calculated as the NEC rate divided by bed speed. NEC density (counts/cm(3)) was defined as the PNEC divided by the cross-sectional area derived from transmission data. Both PNEC and NEC density were averaged from neck to abdomen. Liver S/N was obtained as the pixel mean/SD within the ROI. Blind reviews by 18 professionals were used to visually evaluate image quality. RESULTS: Average visual score correlated with liver S/N, PNEC, and NEC density, with a rank correlation coefficient of 0.81, 0.86, and 0.91, respectively (each p < 0.0003). The "acceptable" quality roughly corresponded to a liver S/N of 10, PNEC of 380 kcounts/cm, and NEC density of 550 counts/cm(3) or more. CONCLUSIONS: NEC density, representing count statistics per body volume, reflects the visual image quality assessment and may be utilized for quality control of whole-body FDG-PET images together with the liver ROI S/N ratio.

Creation and characterization of Japanese standards for myocardial perfusion SPECT: database from the Japanese Society of Nuclear Medicine Working Group.

OBJECTIVE: Standards for myocardial single-photon emission computed tomography (SPECT) adapted for a Japanese population were not available. The purpose of this study was to create standard files approved by the Japanese Society of Nuclear Medicine and to make known the characteristics of the myocardial perfusion pattern of this population. METHODS: With the collaboration of nine hospitals, a total of 326 sets of exercise-rest myocardial perfusion images were accumulated from subjects with a low likelihood of cardiac diseases. The normal database included a (99m)Tc-MIBI/tetrofosmin myocardial perfusion study with 360 degrees (n = 80) and 180 degrees (n = 56) rotations, (201)Tl study with 360 degrees (n = 115) and 180 degrees rotations (n = 54) and a dual-isotope study with 360 degrees rotation (n = 27). The projection images were transferred by digital imaging and communications in medicine (DICOM) format and reconstructed and analyzed with polar maps. RESULTS: The projection data from multiple centers were successfully transferred to a common format for SPECT reconstruction. When the average values were analyzed using a 17-segment model, myocardial counts in the septal segment differed significantly between 180 degrees and 360 degrees rotation acquisitions. Regional differences were observed between men and women in the inferior and anterior regions. A tracer difference between (99m)Tc and (201)Tl was also observed in some segments. The attenuation patterns differed significantly between subjects from the United States and those from Japan. CONCLUSIONS: Myocardial perfusion data that were specific for the Japanese population were generated. The normal database can serve a standard for nuclear cardiology work conducted in Japan.