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Introduction: In myocardial perfusion imaging, reducing the number of photons in images of obese patients reduces image quality. To solve this problem, we need to inject the tracer activity according to the patients’ weight. This study aimed to investigate the relationship between myocardial detector counts with patients’ weight, BMI, and gender. Materials and Methods: 129 patients underwent myocardial perfusion imaging in a two-day stress-first protocol, but only rest images were included in this study. Multiplication factor (MF=0.13/AVGweight0.64 ) ×body weight(kg)+1-0.13×AVGweight0.36 ) was used to determine the amount of tracer activity to patients. The total of myocardial detector counts in the raw images was calculated from the summation of 32 projections for each patient. Multiple linear regression test was used to simultaneously examine the effects of gender, BMI, and weight on photon counts. To evaluate the effect of breast attenuation, the photon counts of 22 female patients in the Breast Up position were also assessed. Results: There was no significant relationship between photon counts and patients’ weight (p=0.129), and BMI (0.406) but gender had significant effects on photon counts and myocardial detector counts were higher in males (p=0.00). There was a statistically significant difference between the images of Breast Up and non-Breast Up position, and myocardial detector counts were higher in the breast-up imaging method(p=0.00). Conclusion: Using the formula mentioned above, the image quality is similar in obese and lean patients, but myocardial detector counts are higher in males and this formula needs to be adjusted according to the patient’s gender.

Background: 90 Y and 177 Lu are two well-known radionuclides used in radionuclide therapy to treat neuroendocrine tumors. Objective: This current study aims to evaluate, compare and optimize tumor therapy with 90 Y and 177 Lu for different volumes of the tumor using the criterion of self-absorbed dose, cross-absorbed dose, absorbed dose profile, absorbed dose uniformity, and dose-volume histogram (DVH) curve using Gate Monte Carlo simulation code. Material and Methods: In our analytical study, Gate Monte Carlo simulation code has been used to model tumors and simulate particle transport. Spherical tumors were modeled from radius 0.5 to 20 mm. Tumors were uniformly designed from water (soft tissue reagent). The full energy spectrum of each radionuclide of 177 Lu and 90 Y was used in the total volume of tumors with isotropic radiation, homogeneously. Self-absorbed dose, cross-absorbed dose, absorbed dose profile, absorbed dose uniformity, and DVH curve parameters were evaluated. Results: The absorbed dose for 90 Y is higher than 177 Lu in all tumors (p-value <5%). The uniformity of the absorbed dose for 177 Lu is much greater than 90 Y. As the tumor size increases, the DVH graph improves for 90 Y. Conclusion: Based on self-absorbed dose, cross-absorbed dose, absorbed dose uniformity, and DVH diagram, 177 Lu and 90 Y are appropriate for smaller and larger tumors, respectively. Next, we can evaluate the appropriate cocktail of these radionuclides, in terms of the type of composition, for the treatment of tumors with a specific size.