Tumour detectability in 2-dimensional and 3-dimensional positron emission tomography using the SET-2400W: a phantom study

The purpose of this study was to investigate the detectability of small hot lesions in 2-dimensional transmission+emission (2D T/E), 2-dimensional simultaneous transmission+emission (2D simultaneous T/E) and 3-dimensional transmission+emission (3D T/E) acquisition modes in an 18F-fluorodeoxyglucose positron emission tomography (FDG PET) scan. The correlation between target detectability, target size, target to non-target uptake ratio (T/N ratio), and standardized uptake value (SUV) were studied. Small hot lesions ranging from 4.4 mm to 36.9 mm in diameter were set in a cylindrical phantom. The images of phantoms with T/N ratios of 2.0, 4.0, 6.0, 8.0, 9.6, 13.2, 17.5, 23.8 and 30.3 were obtained in 2D T/E, 2D simultaneous T/E and 3D T/E scans. Tumour uptake of 2-[18F]fluoro-2-deoxy-d-glucose (FDG) in a rabbit bearing VX-2 tumours was also studied in 2D T/E, 2D simultaneous T/E and 3D T/E scans. The target with a diameter > 10.6 mm and an actual T/N ratio from 6.0 to 30.3 could be identified on the images obtained with all the 2D T/E, 2D simultaneous T/E and 3D T/E acquisition modes. The detectability efficiency of a small hot target was found to be 77.8% in 2D T/E and 3D T/E, but 75.9% in 2D simultaneous T/E. The T/N ratio and recovery coefficient (RC) of the target from the 2D simultaneous T/E image was very similar to that from 2D T/E, and the SUV of the target from the 2D T/E image was almost the same as that from the 2D simultaneous T/E and 3D T/E images. This study indicated that 2D simultaneous T/E scanning and 3D T/E had similar abilities for detecting the tumour as did 2D T/E scanning. 2D T/E, 2D simultaneous T/E and 3D T/E scanning had the same feasibility for semi-quantitative analysis using SUV, as well as using the T/N ratios for 2D T/E and 2D simultaneous T/E. In contrast, the use of the T/N ratio in 3D T/E scanning gave an inferior result in semi-quantative analysis, although there might have been an improvement if a scatter correction had been performed.