On the Significance of Defective Block Detectors in Clinical 18F-FDG PET/CT Imaging

Abstract

Clinical positron emission tomography (PET) systems based on block detector designs suffer occasional block detector failures, which can result in patient scan cancelations. In this study, we examine the effect of defective block detectors on measurements of maximum standard uptake value (SUV(max)) and clinical image quality in 3D 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) PET/computed tomography (CT) imaging. A Data Spectrum anthropomorphic torso phantom (4.7 kBq/ml FDG concentration, defined as SUV of 1.0) was imaged in a normally functioning Siemens Biograph 16 HiRez PET/CT scanner using a whole-body imaging protocol. Spherical lesions with SUVs ranging from 10.0 to 13.5 were placed in the phantom. Defective block detectors were simulated by zeroing the appropriate lines of response in the sinograms. Eleven one-block and seventeen two-block defect configurations were simulated in the phantom sinograms. The images were reconstructed, and the measured SUV(max) was compared with the SUV(max) for the images without detector defects. Twelve clinical PET scans were evaluated before and after simulated detector defects cases ranging from a single block up to 12 blocks (bucket). The reconstructed images were independently scored for image quality and clinical diagnosis by two nuclear physicians blinded to the presence and severity of defects in the images. The mean change in phantom SUV(max) was -2% (range, -6% to +3%) in the presence of a single defective block detector and -3% (range, -11% to +7%) in the presence of two defective block detectors, respectively. For the clinical patient studies, there was no significant decline in image quality score from one to two defective block detectors. In the case of 3-4 defective block detectors, image quality became marginal, and image degradation was significant with a defective bucket (12 blocks). For one or two defective block detectors in a 3D PET camera, while waiting for the repair service, routine patient scans can proceed with the proviso that the reading physician is made aware of the detector failure.