A Technique of Computer-Simulated Dose Reduction for Conventional Chest Computed Tomography (CT)

Abstract

Abstract: Computed Tomography is a diagnostic imaging modality giving higher patient dose in comparison with other radiological procedures. The level of CT radiation dose is of concern to radiologists, medical physicists, government regulators, and the media. This review addresses this problem with particular reference to radiation dose in chest CT. Specifically it outlines the topics of measurement units used to quantify radiation exposure, factors affecting CT scanner dose efficiency, scanner settings that determine the administered radiation dose, and radiation dose reduction in chest CT.The Objective: Aim of this study is to determine minimal tube current (mAs) required for good image quality on conventional chest CT (Computed Tomography).Patients & Methods: Prospectively, 35 consecutive patients (mean weight, 65 kg; range, 38-92 kg) older than 45 undergoing conventional chest CT with standard technique (120 kVp, 400 mAs) had four additional sections imaged at reduced tube current (200, 140, 80, 20 mAs) at two levels (tracheal carina and left atrium). CT scans were evaluated in random order by two independent observers who were blinded to technical factors used. Results: The 400 mAs scan was considered the reference standard. When compared with the reference technique (400 mAs), the first and second (200 mAs and 140 mAs) reduction levels showed no significant difference (p > .05) in subjective image quality. A significant difference (p < .001) was seen at the third and fourth (80 mAs and 20 mAs) reduction levels. A two fold reduction in tube current (400-140 mAs) and resultant radiation dose did not cause a significant change in subjective image quality or in detection of lung abnormalities with conventional chest CT. One hundred forty milliampere-seconds is the minimal tube current required to provide good image quality in patients of average weight.CT is a diagnostic imaging modality giving higher patient dose in comparison with other radiological procedures. CT scan parameters have been adjusted with the aim of working towards optimization of image quality and patient dose. Conclusions: The effective dose of our population is (1.8 mSv) compared with UK, Crawly et al and Hughes et al have the same value.Key words: Radiation dose, CT scan& Reduction dose.