Improvement of Image Quality of Low Radiation Dose Abdominal CT by Increasing Contrast Enhancement

OBJECTIVE. The purpose of this study was to evaluate the effects of noise index and contrast material dose on radiation dose, contrast enhancement, image noise, and image quality in abdominal CT. SUBJECTS AND METHODS. Contrast-enhanced abdominal CT with tube current modulation was performed on 195 patients. The patients were prospectively randomized into three groups of equal size (protocol A, noise index of 12 HU and 521 mg I/kg; protocol B, 15 HU and 521 mg I/kg; protocol C, 15 HU and 600 mg I/kg). Scanning was initiated 5 and 45 seconds after aortic enhancement reached 100 HU. Attenuation was measured in the aorta, portal vein, and liver. Transverse CT images were qualitatively graded for diagnostic acceptability and image noise. Arterial phase volume-rendered and multiplanar reformatted (MPR) images and portal venous phase MPR CT angiograms were qualitatively graded for depiction of vessels. Contrast enhancement, objective image noise, radiation dose, and qualitative grades were analyzed and compared among the three groups. RESULTS. The contrast enhancement values of the aorta, portal vein, and liver were higher in protocol C than in protocols A and B (p < 0.05). Objective image noise was greater in protocols B and C than in protocol A (p < 0.05). The radiation dose in protocols B and C was 31-32% lower than in protocol A (p < 0.001). Depiction of vessels, diagnostic acceptability, and subjective image noise were comparable in protocols A and C. CONCLUSION. Use of higher contrast enhancement can compensate for the degradation of image quality resulting from use of a low radiation dose for CT.