AJR:179, November 2002 1101 Clinical Comparison of Standard- Dose and 50% Reduced–Dose Abdominal CT: Effect on Image Q uality OBJECTIVE. We hypothesized that radiation doses for abdominal CT could be reduced by adjusting the dose for a patient’s weight and cross-sectional abdominal dimensions, with the resultant scans still being of diagnostic quality. SUBJECTS AND METHODS. Using a multidetector CT scanner, we prospectively stud- ied 39 patients who were 65 years and older who had a known history of cancer. After performing a diagnostic contrast-enhanced CT examination, we obtained four slices each (centered at the top of the right kidney) at a standard radiation dose (240–300 mA) and at a 50% reduced dose (120– 150 mA) at a constant kilovoltage of 140. Scans were obtained during a single breath-hold, with a 2.5-mm detector configuration and a slice pitch of 6:1. Reconstructed slice thickness was 5 mm. In a blinded review, two radiologists rated the randomized CT scans for overall image quality and anatomic details of liver, spleen, adrenal glands, kidneys, pancreas, and abdominal wall, using a 5- point scale (1 = unacceptable, 2 = substandard, 3 = acceptable, 4 = above average, and 5 = superior). Patients’ weight and abdominal circumference, area, and anteroposterior and transverse diameters were correlated with image quality of scans obtained at standard-dose and 50% reduced–dose CT. Statistical analysis of the data was performed using Wilcoxon’s signed rank test. RESULT S. Overall, the image quality score was significantly higher ( p < 0.005) on the scans obtained with standard-dose CT. No statistically significant difference in image quality was noted in the 50% reduced– and standard-dose CT scans in patients who weighed less than 180 lb, or 81 kg, ( p > 0.05) and who had a transverse abdominal diameter of less than 34.5 cm ( p > 0.05), an anteroposterior diameter of less than 28 cm ( p > 0.05), a cross-sectional circumference of less than 105 cm ( p > 0.05), and a cross-sectional area of less than 800 cm 2 ( p > 0.05). Good interob- server agreement (p > 0.5) was found between the two reviewing radiologists. CONCLUSION. Abdominal CT scan quality appears to be acceptable even with a 50% reduction in radiation dose except in patients with large anthropometric measurements. A re- duction in CT radiation dose is possible if the tube current is optimized for the patient’s weight and abdominal dimensions. f all the X-ray–based diagnostic examinations, CT contributes one of the higher radiation doses to the patient population. In fact, although CT accounts for only 11% of X-ray–based ex- aminations performed in the United States, it delivers more than two thirds of the total ra- diation dose associated with medical imag- ing [1]. Hence, using the lowest acceptable dose during routine diagnostic imaging, es- pecially in the nononcologic population, is of great public health interest. Although use of low-dose radiation has been advocated for CT [2], a systematic eval- uation of reduced-dose abdominal CT in adults has not been thoroughly investigated. Therefore, we sought to study the impact on image quality of a 50% reduction in the radi- ation dose of abdominal CT. We also ana- lyzed the influence of a patient’s weight and cross-sectional abdominal dimensions— such as anteroposterior diameter, transverse diameter, and cross-sectional area and cir- cumference as independent factors—on the optimization of CT scanning parameters (tube current) for abdominal studies. Subjects and Methods In an institutional review board–approved study, we evaluated 39 patients 65 years and older who had a known history of cancer and who were referred for abdominal CT. The study population consisted of 24 women and 15 men whose ages Mannudeep K. Kalra 1 Srinivasa Prasad Sanjay Saini Michael A. Blake Jose Varghese Elkan F. Halpern James T. Rhea James H. Thrall Received March 13, 2002; accepted after revision M ay 13, 2002. 1 All authors: Department of Radiology, Massachusetts General Hospital and Harvard Medical School, White 270-E, 55 Fruit St., Boston, M A 02114. Address correspondence to S. Saini. AJR 2002;179:1101–1106 0361–803X/02/1795–1101 © American Roentgen Ray Society O Downloaded from www.ajronline.org by 52.73.204.196 on 05/17/22 from IP address 52.73.204.196. Copyright ARRS. For personal use only; all rights reserved