Optimization of Parameters in 16-slice CT-‌‌scan Protocols for Reduction of the Absorbed Dose

Introduction In computed tomography (CT) technology, an optimal radiation dose can be achieved via changing radiation parameters such as mA, pitch factor, rotation time and tube voltage (kVp) for diagnostic images. Materials and Methods In this study, the brain, abdomen, and thorax scaning was performed using Toshiba 16-slice scannerand standard AAPM and CTDI phantoms. AAPM phantom was used for the measurement of image-related parameters and CTDI phantom was utilized for the calculation of absorbed dose to patients. Imaging parameters including mA (50-400 mA), pitch factor (1 and 1.5) and rotation time (range of 0.5, 0.75, 1, 1.5 and 2 seconds) were considered as independent variables. The brain, abdomen and chest imaging was performed multi-slice and spiral modes. Changes in image quality parameters including contrast resolution (CR) and spatial resolution (SR) in each condition were measured and determined by MATLAB software. Results After normalizing data by plotting the full width at half maximum (FWHM) of point spread function (PSF) in each condition, it was observed that image quality was not noticeably affected by each cases. Therefore, in brain scan, the lowest patient dose was in 150 mA and rotation time of 1.5 seconds. Based on results of scanning of the abdomen and chest, the lowest patient dose was obtained by 100 mA and pitch factors of 1 and 1.5. Conclusion It was found that images with acceptable quality and reliable detection ability could be obtained using smaller doses of radiation, compared to protocols commonly used by operators

Evaluation and comparison of antifungal effect of voriconazole with nystatin on candida species derived from neoplastic patients undergoing maxillofacial radiotherapy

Background: Radiotherapy is a common treatment for head-and-neck malignancies and causes complications such as oral candidiasis and the change of oral Candida species from albicans to nonalbicans. Voriconazole has acceptable antifungal effect. The aim of this study was to determine and compare the antifungal effect of nystatin with voriconazole on these species. Materials and Methods: The samples used in this in vitro study were identified by polymerase chain reaction-restriction fragment length polymorphism from patients before and 2 weeks after head-and-neck radiotherapy in Seyed Al-Shohada Hospital. The antifungal effect of nystatin and voriconazole was determined by microdilution method and measurement of the minimum inhibitory concentration (MIC) and the minimum fungicidal concentration, and the results were analyzed by Mann–Whitney analysis. Results: The results showed that all species before and after radiotherapy showed 100% sensitivity to nystatin. Prior to radiotherapy, 57.1% of albicans species isolated were in the sensitive range (MIC ≤1) and 42.9% were in the dose-dependent range (MIC = 2) to voriconazole. After radiotherapy, 58.3% of albicans species were in the sensitive range and 41.7% of these species were in the dose-dependent range to voriconazole. Conclusion: The results of the present study showed that before radiotherapy, all species were sensitive to nystatin, while a percentage of albicans and nonalbicans were resistant to voriconazole. In the 2nd week of radiotherapy similar to prior to radiotherapy, all species isolated from patients were sensitive to nystatin, while a percentage of albicans and nonalbicans were resistant to voriconazole