When considering an imaging examination that utilizes ionizing radiation for screening, exposure is a serious concern. Radiation dose can be decreased at CT by increasing pitch and slice collimation or by decreasing the kVp or mAs. Absorbed dose and mAs values are directly proportional. Since there is extremely high tissue contrast between insufflated gas and the colonic wall, substantial reductions in mAs can be obtained without sacrificing polyp detection. The increased noise resulting from acquisitions acquired with low mAs techniques does not appear to affect polyp detection. In 2002, a study comparing CTC to colonoscopy in 105 patients showed that the sensitivity of CTC in detecting 10 mm polyps was less than 90% using an effective mAs value of 50 . The resultant effective dose for the patient in both supine and prone imaging was 5.0 mSv for men and 7.8 mSv for women. The effective dose utilizing this technique is similar to the dose reported for a DCBE. Since that publication, several studies have shown that mAs values can be decreased even further .
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