Mass Screening With CT Colonography: Should the Radiation Exposure Be of Concern?  David J. Brenner, Maria A. Georgsson  Gastroenterology  Volume 129, Issue 1, Pages 328-337 (July 2005) DOI: 10.1053/j.gastro.2005.05.021 Copyright © 2005 American Gastroenterological Association Terms and Conditions

Figure 1 Number of articles listed in PubMed (Medline) on CTC or virtual colonoscopy. Gastroenterology 2005 129, 328-337DOI: (10.1053/j.gastro.2005.05.021) Copyright © 2005 American Gastroenterological Association Terms and Conditions

Figure 2 Excellent radiologic contrast between a soft-tissue polyp and the air-filled lumen, with or without cathartic preparation. Two-dimensional transverse images are shown here from extremely low-dose CTC examinations.8,36 The scanner settings used here (Siemens Plus 4 Volume Zoom, Erlangen, Germany; 9 mAs; pitch, .9; collimation, 4 × 2.5 mm; 140 kV) result in doses less than one fourth of the currently typical values tabulated in Table 2. (A) A 9-mm sessile polyp imaged in a cathartically prepared colon (arrow).36 (B) CTC without cathartic preparation.8 Liquid fecal material is tagged homogeneously (arrowhead); 8-mm polyp (long arrow); 20-mm polyp identified while completely submerged in liquid fecal material (short arrow). Reproduced courtesy of Dr. Riccardo Iannaccone, University of Rome. Gastroenterology 2005 129, 328-337DOI: (10.1053/j.gastro.2005.05.021) Copyright © 2005 American Gastroenterological Association Terms and Conditions

Figure 3 Estimated radiation-related absolute cancer mortality risk/105 individuals in the United States exposed at different ages to a whole-body dose of 10 mSv. Estimates from the 1990 NAS BEIR-V report.46 Gastroenterology 2005 129, 328-337DOI: (10.1053/j.gastro.2005.05.021) Copyright © 2005 American Gastroenterological Association Terms and Conditions

Figure 4 Sources of ionizing radiation exposure (technically the collective effective dose) to an average individual in the United States. The difference in the contribution of medical x-rays between 198064 and 2000 is caused primarily by the increase in CT scans—from about 2 million per year in 1980 to about 58 million in 2000.65 Gastroenterology 2005 129, 328-337DOI: (10.1053/j.gastro.2005.05.021) Copyright © 2005 American Gastroenterological Association Terms and Conditions

Figure 5 Helical (spiral) CT scanning. Both the x-ray source and, on the other side of the patient, the x-ray detectors, rotate around the patient. If the table were not moving, a single slice of the patient would be imaged (axial CT). Because the table is moving at the same speed as the source-detector combination is rotating, the result is a helical or spiral CT scan of the patient, as depicted here. A single row of detectors is shown; modern multidetector scanners have several rows of detectors alongside each other, which allow both for thinner slice widths and shorter scan times. Gastroenterology 2005 129, 328-337DOI: (10.1053/j.gastro.2005.05.021) Copyright © 2005 American Gastroenterological Association Terms and Conditions

Figure 6 Principles of automatic tube current modulation. (A) Angular modulation in which the x-ray tube current is lowered as the x-rays are aimed in the anteroposterior directions, and increased when the x-rays are aimed in the lateral-medial directions, when there will be more x-ray attenuation. (B) Z-axis modulation in which, for example, fewer x-rays are required in the abdominal region superior to the pelvic bones compared with the pelvic region. Gastroenterology 2005 129, 328-337DOI: (10.1053/j.gastro.2005.05.021) Copyright © 2005 American Gastroenterological Association Terms and Conditions

Figure 7 Idealized computer representation of internal organs used in ImPACT calculations39 of organ doses from CTC examinations. Shaded area indicates scanning region for CTC assumed in this study. Gastroenterology 2005 129, 328-337DOI: (10.1053/j.gastro.2005.05.021) Copyright © 2005 American Gastroenterological Association Terms and Conditions