Evaluation of image quality and lens's radiation dose of a low-dose cranial CT scan.

OBJECTIVE: To determine the lowest miliampere-second (mAs) of a cranial computed tomography (CT) scan that can maintain acceptable image quality on cranial CT scan which might help reducing the risk of cataract formation. MATERIAL AND METHOD: The present study was performed on the 148 patients in routine daily practice sent for diagnosis of intracranial conditions by a cranial CT scan. During the cranial CT scanning, each lens's radiation dose on patient's eyes was measured by a thermoluminescent dosimeter Clinical image quality, particularly in analysis of gray and white matter differentiation, was evaluated independently using a 5 point scale by two radiologists. RESULTS: During standard cranial CT scan protocol with 250 miliampere-second (mAs), the total dose of left and right lens's dose were about 50.93 miligray (mGy) and 51.66 mGy, respectively. When applying low dose cranial CT scan protocols by decreasing mAs to 200, 150 and 100 mAs, the total dose ofright and left lens were of 45.68 mGy and 46.04 mGy for 200 mAs, 34.65 mGy and 34.77 mGy for 150 mAs, 28.73 mGy and 29.25 mGy for 100 mAs respectively. CONCLUSION: A low dose cranial CT scan at 100 miliampere-second provides not only an acceptable clinical image quality, but also decreases the lens's radiation dose by 43%.

Effect of concentration of contrast medium on coronary CT angiography.

OBJECTIVE: To compare concentration of contrast medium for vascular opacification at ascending aorta using retrospective reconstruction of coronary CT angiography. STUDY DESIGN: Retrospective study. MATERIAL AND METHOD: Eighty-four patients undergoing coronary CT angiography with 16 multi-detector rows at Siriraj Hospital between September 2003 and July 2004 were included in this study. The patients were categorized into two groups. The first group was administrated with 350 mgl/ml contrast medium and the second group was administrated with 370 mgl/ml contrast medium. The total amount of contrast medium was about 140 ml (20 ml for timing bolus and 120 ml for CT angiography) in both groups. The CT density on peak contrast administration at ascending aorta was measured and compared between the two groups. RESULTS: The mean density at ascending aorta in 350 mgl/ml and 370 mgl/ml were 362.96 HU (SD 67.53) and 354.44 (SD 59.39), respectively. There was no statistically significant difference in mean density at the ascending aorta between the two groups. CONCLUSION: Administration of contrast medium with different concentrations of 350 or 370 mgl/ml showed no statistical difference on enhancement of the ascending aorta in coronary CT angiography (p < 0.05).