Dedicated phantom tools using traceable 68Ge/68Ga point-like sources for dedicated-breast PET and positron emission mammography scanners.

Since the early 2000s, many types of positron emission tomography (PET) scanners dedicated to breast imaging for the diagnosis of breast cancer have been introduced. However, conventional performance evaluation methods developed for whole-body PET scanners cannot be used for such devices. In this study, we developed phantom tools for evaluating the quantitative accuracy of positron emission mammography (PEM) and dedicated-breast PET (dbPET) scanners using novel traceable point-like 68Ge/68 Ga sources. The PEM phantom consisted of an acrylic cube (100 × 100 × 40 mm) and three point-like sources. The dbPET phantom comprised an acrylic cylinder (ø100 × 100 mm) and five point-like sources. These phantoms were used for evaluating the fundamental responses of clinical PEM and dbPET scanners to point-like inputs in a medium. The results showed that reasonable recovery values were obtained based on region-of-interest analyses of the reconstructed images. The developed phantoms using traceable 68Ge/68 Ga point-like sources were useful for evaluating the physical characteristics of PEM and dbPET scanners. Thus, they offer a practical, reliable, and universal measurement scheme for evaluating various types of PET scanners using common sets of sealed sources.

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.