The purpose of this study was to determine the patient radiation dose in combined whole-body positron emission tomography/computed tomography (PET/CT) examinations performed in the largest tertiary hospital in Greece. Computed tomography dose index (CTDIvol), dose length product (DLP), weight, height and administered activity of 2-[18F] fluoro-2-deoxy-D-glucose values for PET/CT examinations were recorded in a sample of 1014 randomly selected patients. The mean (±standard deviation) and median (interquartile) CTDIvol values were equal to 5.5 ± 2.4 and 4.8 (2.5) mGy, respectively. The respective DLP values were 483.3 ± 212.4 and 426 (234.6) mGy·cm. For the administered activity, mean and median were equal to 363.9 ± 68.3 and 361.6 (85.6) MBq. The mean administered activity per body weight was 4.8 ± 0.6 and the median 4.8 (0.6) MBq/kg. The results of this survey are within the range of values reported in the literature and can be used as a standard of reference until national diagnostic reference levels are established for whole-body PET/CT procedures.

The discrete shearlet transformation accurately represents the discontinuities and edges occurring in magnetic resonance imaging, providing an excellent option of a sparsifying transform. In the present paper, we examine the use of discrete shearlets over other sparsifying transforms in a low-rank plus sparse decomposition problem, denoted by L+S. The proposed algorithm is evaluated on simulated dynamic contrast enhanced (DCE) and small bowel data. For the small bowel, eight subjects were scanned; the sequence was run first on breath-holding and subsequently on free-breathing, without changing the anatomical position of the subject. The reconstruction performance of the proposed algorithm was evaluated against k-t FOCUSS. L+S decomposition, using discrete shearlets as sparsifying transforms, successfully separated the low-rank (background and periodic motion) from the sparse component (enhancement or bowel motility) for both DCE and small bowel data. Motion estimated from low-rank of DCE data is closer to ground truth deformations than motion estimated from L and S. Motility metrics derived from the S component of free-breathing data were not significantly different from the ones from breath-holding data up to four-fold undersampling, indicating that bowel (rapid/random) motility is isolated in S. Our work strongly supports the use of discrete shearlets as a sparsifying transform in a L+S decomposition for undersampled MR data.