The aim of this study was to evaluate the imaging performance of 39-and 52-ring time-of-flight (TOF) PET/CT scanners. We also assessed the potential of reducing the scanning time using a 52-ring TOF PET/CT scanner. Methods: PET/CT scanners with 39-and 52-ring lutetium oxyorthosilicate detectors were evaluated. The axial fields of view were 16.2 and 21.6 cm, respectively. We used a National Electrical Manufacturers Association International Electrotechnical Commission body phantom filled with an 18 F solution containing background activity of 5.31 and 2.65 kBq/mL for the studies. The sphere-to-background ratio was 4:1. The PET data were acquired for 10 min in 3-dimensional list mode and then reconstructed with both ordered-subsets reconstruction maximization and ordered-subsets reconstruction maximization plus point-spread function plus time-of-flight algorithms. PET images with different acquisition times were reconstructed (from 1 to 10 min). The image quality was physically assessed using the sensitivity, noise-equivalent counting rate, coefficient of variation of background activity, and relative recovery coefficient. Results: The total system sensitivities of the 39-and 52-ring scanners were 5.6 and 9.3 kcps/MBq, respectively. Compared with the 39-ring scanner, the noise-equivalent counting rate of the 52-ring scanner was 60% higher for both the high-activity and the low-activity models. The recovery coefficient was consistent, irrespective of the number of detector rings. The coefficient of variation of the 52-ring scanner using a 3-min acquisition time was equivalent to that of the 39-ring scanner using a 4-min acquisition time. Conclusion: The image quality of the 52-ring scanner is superior to that of the 39-ring scanner. The acquisition time per bed position of the 52-ring system can be reduced by about 25% without compromising image quality. In addition, the number of bed positions required is 25% lower for the 52-ring system. Finally, the examination time required for a whole-body PET scan is considered to be reduced by about 40% if the 52-ring scanner is used. PETi s a molecular imaging technique that provides metabolic information useful for patient care and for monitoring the pharmacokinetics of drugs (1,2). High image quality is required for an accurate diagnosis (3). PET image quality is strongly dependent on scanner sensitivity (4), which in turn is associated with the length of the axial field of view (FOV) (4-6). A PET system with a longer axial FOV has a higher sensitivity because there are a large number of detectors (Fig. 1). In addition, the number of bed positions can be reduced because of the large axial range for whole-body PET. PET scanners with a longer axial range can be used to reduce the patient dose, decrease the scanning time, or reduce the image noise while maintaining other constant image characteristics. To date, however, there has been no comparison of actual PET images acquired on systems having different axial FOVs.In this study, we evaluated the PET image quality of 39-and...
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