فهرست مطالب daryoush khorramian

There are several techniques for reducing the delivered dose from CT (Computed tomography) scanning such as the automatic exposure control (AEC). This technique modulates the tube current regarding the patient size and weight. The aim of this study was to estimate the effect of the AEC on the radiosensitive organs effective doses in women undergoing chest CT scanning.
This study was a cross-sectional, analytical and quantitative study that was performed during 3 months in the imaging section of the Firoozgar educational and therapeutic hospital (belonging to Shahid Beheshti University of Medical Sciences) in the spring of 2017. CT scan exposure parameters were gathered and registered for 54 women undergoing chest CT scan. 25 of these scans were performed using AEC system and 29 of them were performed without using AEC. CT dose indexes in the center and peripheral regions of the standard phantom were calculated using the exposure parameters. Weighted CT dose index was also calculated and effective organ doses were obtained using CT-Expo software, version 2 (Medizinische Hochschule, Hannover, Germany) for two mentioned groups. In addition, noise was measured for these two groups as an image quality parameter.
Calculated weighted CT dose indexes were 9.94 mGy and 12.46 mGy using AEC system and without using AEC, respectively. The calculated effective doses were equal to 5.4 mSv and 6.3 mSv using AEC and without using AEC, respectively. Maximum organ effective doses were 15, 14, 14 and 14 mSv for breast, esophagus, lung and thymus respectively in the non-using AEC system imaging technique.
Our measurements indicated a decrease about 15% in weighted CT dose index (from 12.46 to 9.94 mGy) using AEC system. Beside of this fact, the noise increased about 11.3% (from 4.2 to 4.74) using AEC system. So, it can be said that using of AEC was an effective way for dose reduction in women undergoing chest CT scanning, and the additional noise was in the acceptable range.

Noise and spatial resolution (SR) are the main characteristics of image quality in CT scanning affected by different radiation and technical parameters. One of the important parameters are reconstruction kernels. Different reconstruction kernels are used for noise reduction and/or edge-enhancement purposes. In this study, we investigate some reconstruction kernels about noise and SR on a commercial CT scanner.
Methods and Materials: To evaluate the noise and SR, a standard quality control phantom was used with the diameter of 16cm. Images were taken and reconstructed with 5 different kernels. Reconstructed kernels were H10, H30, H40, H50 and H70. For SR estimation we used point spread function (PSF) around narrow tungsten wire and full width at half maximum (FWHM) for each image. All measurements were performed on Siemens Emotion 6 CT scanner.
Noise of images in H10, H30, H40, H50 and H70 were 2.61±0.67, 4.33±1.20, 5.94±1.89, 8.58±3.30 and 19.59±4.53 respectively. FWHM in H10, H30, H40, H50 and H70 were 1.80±0.19, 1.44±0.11, 1.32±0.17, 1.24±0.09 and 1.04±0.17 respectively.
Discussion and In this study, the effect of implementing 5 different reconstruction kernels on noise and SR of CT images were investigated. Based on the results, the noise increased and FWHM decreased with the increment of kernels’ number from H10 to H70.