RESUMEN
Our aim was to define a lower limit of reduced injected activity in delayed [18F]FDG total-body (TB) PET/CT in pediatric oncology patients. Methods: In this single-center prospective study, children were scanned for 20 min with TB PET/CT, 120 min after intravenous administration of a 4.07 ± 0.49 MBq/kg dose of [18F]FDG. Five randomly subsampled low-count reconstructions were generated using », â , [Formula: see text], and [Formula: see text] of the counts in the full-dose list-mode reference standard acquisition (20 min), to simulate dose reduction. For the 2 lowest-count reconstructions, smoothing was applied. Background uptake was measured with volumes of interest placed on the ascending aorta, right liver lobe, and third lumbar vertebra body (L3). Tumor lesions were segmented using a 40% isocontour volume-of-interest approach. Signal-to-noise ratio, tumor-to-background ratio, and contrast-to-noise ratio were calculated. Three physicians identified malignant lesions independently and assessed the image quality using a 5-point Likert scale. Results: In total, 113 malignant lesions were identified in 18 patients, who met the inclusion criteria. Of these lesions, 87.6% were quantifiable. Liver SUVmean did not change significantly, whereas a lower signal-to-noise ratio was observed in all low-count reconstructions compared with the reference standard (P < 0.0001) because of higher noise rates. Tumor uptake (SUVmax), tumor-to-background ratio, and total lesion count were significantly lower in the reconstructions with [Formula: see text] and [Formula: see text] of the counts of the reference standard (P < 0.001). Contrast-to-noise ratio and clinical image quality were significantly lower in all low-count reconstructions than with the reference standard. Conclusion: Dose reduction for delayed [18F]FDG TB PET/CT imaging in children is possible without loss of image quality or lesion conspicuity. However, our results indicate that to maintain comparable tumor uptake and lesion conspicuity, PET centers should not reduce the injected [18F]FDG activity below 0.5 MBq/kg when using TB PET/CT in pediatric imaging at 120 min after injection.
RESUMEN
BACKGROUND: Quadriceps fat pad edema (QFPE) is one of the causes of anterior knee pain. Real-time elastosonography (RTE) has been increasingly used in musculoskeletal disorders. PURPOSE: To evaluate the role of RTE in the diagnosis of QFPE. MATERIAL AND METHODS: A total of 23 patients with QFPE on magnetic resonance imaging (MRI) (study group) were prospectively compared with 29 patients with normal MRI findings (control group) using RTE. On MRI, the thickness of the quadriceps fat pad (QFP), and on RTE, strain ratio (SR) of QFP were measured and compared between the two groups. RESULTS: The study group contained 23 patients (12 men, 11 women; mean age = 41.6 ± 7.0 years) and the control group contained 29 patients (14 men, 15 women; mean age = 42.3 ± 6.1 years). No significant differences were found in terms of mean age and sex between the two groups (P = 0.70, P = 0.78, respectively). The median thicknesses of the QFPs were 8.10 mm and 6.75 mm in the study and control groups, respectively (P < 0.001). The median SR values of the study group and control group were found to be 63.20 and 6.24, respectively. The SR values were significantly higher in patients with QFPE (P < 0.001). CONCLUSION: RTE may be an effective imaging method for evaluating QFPE.
