Virtual colonoscopy

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The virtual colonoscopy (VC) is a radiological examination of the large intestine ( colon ) with usually a computed tomography (CT) and is then also called CT colonography or CT colonoscopy . Thin slices are made and two- and three-dimensional images of the inner surface of the intestine are created from them with special computer programs. With the virtual colonoscopy polyps , tumors and diverticula can be diagnosed. Virtual colonoscopy using magnetic resonance imaging (MRI), which is not discussed further in this article , is less common .

indication

The reasons (indication) for performing a virtual colonoscopy are:

  • In principle, the indications as in the diagnostic conventional colonoscopy ( colonoscopy ) except for inflammatory bowel disease
  • Search for tumors especially in the case of unclear weight loss or metastases in the case of an unknown primary tumor
  • Check-up after colon cancer therapy and / or polypectomy
  • incomplete or impracticable colonoscopy

preparation

As with a conventional colonoscopy , the colon must be emptied before the examination so that the evaluation of the images is not hindered by stool remains. There are a number of different bowel preparation protocols. The performing radiological clinic determines the bowel preparation procedure. This can consist of a multi - day low - fiber diet, a liquid diet and one or a combination of various laxatives the day before or over several days. It is important to have sufficient fluid intake, which supports colon cleansing and compensates for fluid loss during purging. Sometimes a suppository should also be administered for better rectal cleansing. Oral contrast media are often also administered, which are preparations based on iodine or barium that are taken the day before or with the special food. The contrast agent should mix with the stool that may be left behind, which can then be better differentiated from possible polyps in the intestine and thus reduce false positive results in the diagnosis. On the day of the examination, the patient is usually only allowed to drink clear drinks.

Investigation process

The entire examination takes about 10 to 20 minutes, no painkillers or sedatives are required. An intestinal relaxant , butylscopolamine or glucagon , is usually administered intravenously . At the beginning of the examination, a thin, short silicone tube ( rectal catheter ) is inserted into the patient's rectum on the CT table . Gas is usually blown into the large intestine through this with an automatic pump. As a rule, CO 2 is used, which is quickly absorbed through the intestine after the examination and thus quickly reduces the gas content in the intestinal lumen and flatulence, which is perceived as unpleasant. When the bowel is well expanded, an examination is done in the prone position. The CT table moves with the patient through the CT tube, which takes about 10 to 20 seconds. The patient then turns and an examination is carried out in the supine position. Both scans are usually carried out with a reduced radiation dose, as so-called low dose or ultra-low dose scans. If there are certain questions, the second scan is carried out with intravenous contrast and normal radiation dose.

Image editing and analysis

After the examination, the scanned sectional images are processed by computer programs. The radiologist evaluates both series of images. Possible incompletely assessable areas or suspicious changes in the prone position series are compared with the supine position series and vice versa. The usual axial , coronal and sagittal 2D images can be reconstructed from each image series . Special 3D images are also created, a kind of fly through program allows the radiologist to see the intestines as if a colonoscopy were being performed. In addition to assessing the colon, the rest of the abdomen is also assessed.

Findings

advantages

Virtual colonoscopy is more convenient for the patient and usually takes less time than conventional colonoscopy. There is no need for painkillers or sedatives. Even with extremely long and winding large intestines, the entire colon is usually examined, which can be problematic with conventional colonoscopy. The VC images are always available for a second assessment. The VC can replace conventional colonic barium contrast examinations. The VC allows additional findings outside the colon or can be combined with a planned CT of the abdomen .

disadvantage

Virtual colonoscopy by means of CT uses X-rays, although the radiation dose can be reduced considerably with appropriate ultra-low-dose protocols. Tissue samples ( biopsy ) can neither be taken nor polyps removed. If the VC is found accordingly, a colonoscopy must then be performed. With the VC, flat changes in the intestinal mucosa, inflammatory changes and angiodysplasias cannot be diagnosed. Not least because of this, the conventional colonoscopy is still regarded as the gold standard for assessing the large intestine.

See also

Web links

Individual evidence

  1. ↑ Virtual Colonoscopy - Mayo Clinic . "Virtual colonoscopy is typically faster than traditional colonoscopy. A scan of your colon takes about 10 minutes. Expect the entire virtual colonoscopy procedure to take 20 to 30 minutes."
  2. ↑ Menardo G: Sensitivity of diagnostic examinations for colorectal polyps . In: Tech Coloproctol . 8 Suppl 2, December 2004, pp. 273-5. doi : 10.1007 / s10151-004-0175-0 . PMID 15666105 .
  3. ↑ Yee J, Kumar NN, Godara S, et al. : Extracolonic abnormalities discovered incidentally at CT colonography in a male population . In: Radiology . 236, No. 2, August 2005, pp. 519-26. doi : 10.1148 / radiol.2362040166 . PMID 16040909 .