Pregnancy is a relative contraindication to CTC. The radiation dose and absorbed dose to the fetus during the dual scan is the major issue. In these rare instances that a pregnant patient is suspected to have a colorectal cancer, there is a real risk of perforation with conventional colonoscopy and CTC
may be the safer alternative. The gestational age of the fetus is an important factor when contemplating risk. The relative risk of childhood cancers is 1.4 with an exposure of 10 mGy in utero (Kusama and Ota 2002). Radiation doses are heavily regulated and the effective dose limit to the fetus is 0.5 rem (5 mSv) (Huda and Stone 2003). The effective dose of thin-section low dose CTC is 5.0 mSv for men and 7.8 mSv for women. The effective dose to the fetus in utero, however, is less than the stated dose of 7.8 mSv (Iannaccone et al. 2003 and Macari et al. 2002).
Patients with metallic hip joint replacements will have significant artifacts in the pelvis with limited evaluation of colonic segments in this region. This is a relative contraindication depending on the clinical question asked. Intravenous iodinated contrast allergy is also a relative contraindication as any patient with a history of a mild contrast allergy can be premedicated for the exam or not receive the injection. Claustrophobia is also a relative contraindication to the study. Patients can take an oral sedative prior to the study. An incompetent ileocecal valve is another relative contra-indication for CTC as distention of the colon may be suboptimal.
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