Search

Given the inherent characteristics of nonlinearity and nonstationarity of iterative reconstruction algorithms in computed tomography (CT) imaging, this study aimed to perform, for the first time, a voxel-based characterization of noise properties in CT imaging with the ASiR-V and ASiR algorithms as compared with conventional filtered back projection (FBP). Multiple repeated scans of the Catphan-504 phantom were carried out. CT images were reconstructed using FBP and ASiR/ASiR-V with different blending levels of reconstruction (20%, 40%, 60%, 80%, 100%). Noise maps and their nonuniformity index (NUI) were obtained according to the approach proposed by the report of AAPM TG-233. For the homogeneous CTP486 module, ASiR-V/ASiR allowed a noise reduction of up to 63.7%/52.9% relative to FBP. While the noise reduction values of ASiR-V-/ASiR-reconstructed images ranged up to 33.8%/39.9% and 31.2%/35.5% for air and Teflon contrast objects, respectively, these values were approximately 60%/50% for other contrast objects (PMP, LDPE, polystyrene, acrylic, Delrin). Moreover, for all contrast objects but air and Teflon, ASiR-V showed a greater noise reduction potential than ASiR when the blending level was ≥40%. While noise maps of the homogenous CTP486 module showed only a slight spatial variation of noise (NUI < 5.2%) for all reconstruction algorithms, the NUI values of iterative-reconstructed images of the nonhomogeneous CTP404 module increased nonlinearly with blending level and were 19%/15% and 6.7% for pure ASiR-V/ASiR and FBP, respectively. Overall, these results confirm the potential of ASiR-V and ASiR in reducing noise as compared with conventional FBP, suggesting, however, that the use of pure ASiR-V or ASiR might be suboptimal for specific clinical applications. [ABSTRACT FROM AUTHOR]

Background: In the current clinical practice, radiometabolic therapy of Graves' disease is based on the administration of an amount of 131I-iodide defined according to two different modalities: administration of a fixed activity (up to a maximum of 555 MBq allowed by many national legislations on an outpatient basis) or an 131I-iodide activity individually defined so as to reach the certain fixed values of target thyroid-absorbed dose. The aim of this study was to prove the effectiveness of a personalized approach to cure Graves' disease based on the administration of a 131I activity defined according to the desired "optimal final thyroid mass." According to this model, one can predict the thyroid-absorbed dose following the administration of an activity as a function of the desired reduction of the baseline, pre-treatment mass of the gland. Methods: A total of 217 patients with Graves' disease were included in this study. They were randomly divided into five groups, of which four groups were divided based on fixed thyroid-absorbed dose value of 100 (Group A, n = 29), 200 (Group B, n = 25), 300 (Group C, n = 51), and 400 (Group D, n = 25), respectively, whereas patients of the final thyroid mass (mf) (Group V, n = 87) received a 131I activity calculated based on the desired "optimal" final thyroid mass according to the so-called "volume algorithm" approach. Results: At the 1-year follow-up, therapeutic success (i.e., a state of either hypothyroidism or euthyroidism) was achieved in 48% of patients in Group A (100 Gy), 64% in Group B (200 Gy), 78% in Group C (300 Gy), 96% in Group D (400 Gy), and 92% in Group V (mf). A significantly higher proportion of patients were was cured in Groups D and V (mf) than in Groups A, B, and C (P < 0.01). There was no statistical difference in cure rates between Groups D and V (mf). The median thyroid-absorbed dose was 407 Gy for Group D (400 Gy), significantly higher than 296 Gy for Group V (mf) (P < 0.001) and also significantly greater than the administered 131I activity (494 vs. 345 MBq, P < 0.001). Conclusions: This study indicates that the most effective thyroid-absorbed dose to be delivered for the radiometabolic therapy of patients with Graves' disease should not be based on a fixed dose but rather should be personalized. The new method based on thyroid mass reduction allows the optimization of 131I-iodide therapy for Graves' disease on an individual basis, achieving a high therapeutic efficacy while at the same time avoiding the administration of unjustified greater activities of 131I. [ABSTRACT FROM AUTHOR]