Advances in iterative image reconstruction enable absolute quantification of SPECT/CT studies by incorporating compensations for collimator-detector response, attenuation, and scatter. This study aimed to assess the quantitative accuracy of SPECT/CT based on different levels of 99m Tc activity (low/high) using different SUV metrics (SUV mean , SUV max , SUV 0.6 max , and SUV 0.75 max [the average values that include pixels greater than 60% and 75% of the SUV max in the volume of interest, respectively]). Methods: A Jaszczak phantom equipped with 6 fillable spheres was set up with low and high activity ratios of 1:4 and 1:10 (background-to-sphere) on background activities of 10 and 60 kBq/mL, respectively. The fixedsize volume of interest based on the diameter of each sphere was drawn on SPECT images using various metrics for SUV quantification purposes. Results: The convergence of activity concentration was dependent on the number of iterations and application of postfiltering. For the background-to-sphere ratio of 1:10 with a low background activity concentration, the SUV mean metric showed an underestimation of about 38% from the actual SUV, and SUV max exhibited an overestimation of about 24% for the largest sphere diameter. Meanwhile, bias reductions of as much as 26% and 27% for SUV 0.6 max and SUV 0.75 max , respectively, were observed. SUV max gave a more accurate reading than the others, although points that exceeded the actual value were detected. At 1:4 and 1:10 background activity of 10 kBq/mL, a low activity concentration attained a value close to the actual ratio. Use of 2 iterations and 10 subsets without postfiltering gave the most accurate values for reconstruction and the best image overall. Conclusion: SUV max is the best metric in a high-or low-contrast-ratio phantom with at least 2 iterations, 10 subsets, and no postfiltering.

Quantitative imaging gives a better understanding on the distribution of radioactivity that can be used in the estimation of absorbed dose in the specific target organ. The goal of this study was to validate the accuracy of 131I activity quantification of cumulated activity in thyroid uptake phantom using 3-dimensional (3D) SPECT/CT imaging. In this study, a series of SPECT/CT acquisition of the thyroid uptake was performed. Images of different matrix sizes and iterations number were reconstructed using ordered-subsets expectation maximization (OSEM). Quantification of the activity in the phantom was determined using a Medical Image Data Examiner (AMIDE) software based on the mean value and maximum value. The cumulated activity in the phantom was determined by calculating area under the curve (AUC) in the time-activity curve. The results showed that the mean activity for 256 voxels was underestimated between 6.18% - 13%, and overestimated between 61.56% - 64.66% for maximum value metric. The cumulated activity derived from SPECT/CT showed an error margin of 10%.

Radioiodine (131I) therapy is the mainstay of treatment for patients who had undergone total thyroidectomy for well differentiated thyroid carcinoma. Increased fluid intake has always been encouraged to minimize the risk of non-target organ exposure to I-131radiation. This study aimed to determine the minimum amount of fluids needed for patients to have the fastest time to achieve permissible level for release after high dose I-131therapy. Methodology: All the patients who were treated with high dose I-131from 18th January 2016 till 31st December 2016 in Hospital Pulau Pinang, Malaysia were recruited. The data from 126 patients on thyroxine hormone withdrawal (THW) group and 18 patients on recombinant human thyroid stimulating hormone (rhTSH) group were analysed. There is no change in patient management in terms of preparation, dose or post therapy whole-body scan. Fluid intake of patients were monitored strictly and whole-body retention of I-131are measured using ionizing chamber meter immediately after ingestion of I-131then at 1 hour, 24 hours, 48 hours, 72 hours and 96 hours. Results: The median time to achieve permissible release limit (50 μSV/hr at 1 meter) was 21.6 hours and 22.1 hours post-ingestion of I-131in the THW and rhTSH group respectively. The minimum amount of fluid needed to reach permissible release limit in the fastest time was 2,103 ml and 2,148ml for the THW and TSH respectively. Conclusion: Clinicians would be able to evidently advise their patient on the amount of fluid to consume and utilize their isolation wards faster to treat more patients.