Comparing the Absorbed Doses by Skin, Thyroid, and Eyes in Ct Coronary Angiography and Conventional Angiography



Tavakoli MB¹ ; Jabbari K¹ ; Jafari S¹ ; Hashemi SM² ; Akbari M³ Show Affiliations
Source: Journal of Isfahan Medical School Published:2011

Abstract

Background: One of the diagnostic methods for cardiovascular diseases, particularly coronary artery abnormalities, is imaging. Invention of computed tomography (CT) devices with a multi-detector row in recent years has created new capabilities in the field of imaging, especially cardiovascular imaging. CT coronary angiography is a new imaging technique which can be implemented with these devices. Despite many advantages, this method imposes high absorbed dose (total ionizing dose, TID) to patients. Therefore, assessing the imposed dose rate to patients is very necessary. We assessed the doses absorbed by different organs including skin, thyroid, and eyes in CT coronary angiography and compared them with the values in conventional angiography. Methods: In this study, doses absorbed by skin, thyroid, and eyes of 67 patients were assessed. The subjects referred to Alzahra and Sina Hospitals (Isfahan, Iran) for CT coronary angiography. Doses were calculated through practical measurements of point doses using thermoluminescence dosimeter (TLD). In order for dosimetry of each of the mentioned organs, we used a pair of TLD GR-200. The average value obtained from each pair of TLD was considered as the dose of the organ. Dosimeters were calibrated using a Co-60 source. After the imaging, the dose values were separately calculated for each organ. The values were then compared with corresponding values in conventional angiography. The used CT devices were a 64-row detector CT (Lightspeed VCT, U.S.) in Alzahra Hospital and a 64-cross-sectional device (Phillips) in Sina Hospital. Findings: The mean doses absorbed by skin, thyroid, and eyes in CT coronary angiography were 8.32 ± 1.73 cGy, 2.06 ± 1.68 cGy, and 0.3 ± 0.1.6 cGy, respectively. The corresponding values in conventional angiography were 6.64 ± 9.3 cGy, 0.15 ± 0.17 cGy, and 0.03 ± 0.03 cGy. There was a significant difference between the 2 imaging methods in doses absorbed by the organs (P < 0.001). Range of doses absorbed by the skin in CT and conventional coronary angiography were 5.15-12.22 cGy and 0.07-39.00 cGy, respectively. Conclusion: Since the skin is directly irradiated, it absorbed higher doses compared to the other 2 organs in both methods. There were evident and considerable changes in skin dose range in both methods and the range of skin dose in conventional angiography was much more than CT coronary angiography. Absorbed dose of organs in CT angiography was much higher than conventional angiography. Scanning parameters can significantly alter the absorbed dose rate. Therefore, technicians should acquire adequate trainings in this regard and utilize them practically. © 2011, Isfahan University of Medical Sciences(IUMS). All rights reserved.