Background: Single photon emission computed tomography (SPECT)-alone imaging using the Tc-99m radiopharmaceutical labeled with methylene diphosphonate or similar analogs is usually employed to diagnose metastatic bone and is typically followed by complementary magnetic resonance (MR) imaging for support in clinical decision-making. In this study, two attenuation map generation approaches from MR and SPECT non-attenuation corrected (SPECT-nonAC) images were evaluated in the context of quantitative SPECT imaging. Materials and Methods: The 2class-MR attenuation map was generated via segmenting an MR image into air and soft tissue. Likewise, SPECT-nonAC was segmented into background air and soft tissue to generate a 2class-SPECT attenuation map. The reference attenuation map was generated through manual bone segmentation from an MR image to develop a 3class-bone attenuation map. Standard uptake value (SUV) bias was calculated using the different attenuation maps on 50 vertebrae from normal patients and 16 vertebrae from metastatic patients. Results: The 2class-MR approach resulted in -16% and -8% SUV bias in normal and metastatic groups, respectively, while 2class-SPECT led to 33% and 26% SUV underestimation for the normal and metastatic patient groups, respectively. Conclusion: The 2class-SPECT approach led to a significant underestimation of SUV due to the uncertainty of body contour delineation. However, the 2class-MR approach resulted in less than -9% SUV bias in metastatic patients, demonstrating its potential to support quantitative SPECT imaging.
 

Background: Panoramic radiography is one of the common dental imaging procedures using ionizing radiation. It is necessary to control the level of exposure and use the optimized levels. So, the current work aimed to estimate the surface absorbed doses of critical organ regions, namely thyroid and parotid glands. Moreover, dose area product (DAP) values were measured and a local DRL was then established for panoramic radiography. Materials and Methods: The data from 201 patients including 141 adults and 60 children (5-10 years) were used for this cross-sectional study. Seven panoramic radiography systems were selected from 6 radiology clinics in Yazd province. For each patient, 12 thermoluminescence dosimeters (TLD GR-200) were used to obtain the surface absorbed dose in both the thyroid and parotid gland regions. The DRL values were calculated using DAP values in terms of the ICRP recommendation. Results: The mean and standard deviation (SD) of thyroid and parotid glands’ surface absorbed doses were equal to 60.6±3.7 and 290±12.4 µGy in the adult group, respectively. In the children group, these values were 40.7±2 and 189.3±11.5 µGy, respectively. Moreover, the local DRL values were obtained as 99.7 and 73.4 mGy.cm² for the adults and children groups, respectively. Conclusion: The higher surface absorbed dose values in the adult group can be related to the use of higher radiation parameters. The local DRL proposed for the adult and pediatric groups in the current study was relatively lower than those established by other reports, which seemed acceptable for panoramic radiography in Yazd, Iran.

Background: 99m-Tc Ethyl-Cysteinate-Dimer SPECT and MR imaging play a significant role in diagnosing anosmia. In this study, two-tissue class and three-tissue class attenuation maps (2C-MR and 3C-MR) obtained from MR images were compared with CT-based attenuation correction (CTAC). Afterward, the presence of hypo-perfusion in brain lobes was evaluated in SPECT images. Materials and Methods: The 2C-MRAC map was generated through segmentation of T1-W MR images into air and soft-tissue, while in the 3C-MRAC map, the cortical bone was also considered. For investigating MRAC approaches, the difference between activity concentration (ACC) values was estimated in 144 volumes of interest. Ten normal and fourteen anosmic patients were compared by calculating the average normalized count and standard uptake value ratio parameters in the brain lobes. Results: The comparison between attenuation correction strategies represented that MRAC images resulted in underestimation of the ACC values which was more substantial in the cortical area rather than in central regions (maximum 9% vs. 6% for 2C-MR and maximum 5.5% vs. 3.5% for 3C-MR). Nevertheless, there was a strong correlation between the MRAC and CTAC methods with a correlation coefficient of 0.7 for both 2C-MR and 3C-MR. The statistical analysis between normal and affected groups indicated the hypo-perfusion in the cortex of Lh_frontal, Rh and Lh_temporal lobes with p-values < 0.05. Conclusions: Using MRAC resulted in underestimation of activity concentration which was partly eliminated by considering the cortical bone in the 3C-MR attenuation map. Hypo-perfusion was perceived in Frontal and Temporal lobes in SPECT-MRAC images of the anosmic group.