Virtual colonoscopy (VC, also called CT colonography or CT pneumocolon) is the use of
CT scanning or
magnetic resonance imaging
Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio wave ...
(MRI) to produce two- and
three-dimensional
Three-dimensional space (also: 3D space, 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called ''parameters'') are required to determine the position of an element (i.e., point). This is the informal ...
images of the
colon (large intestine), from the lowest part, the
rectum
The rectum is the final straight portion of the large intestine in humans and some other mammals, and the Gastrointestinal tract, gut in others. The adult human rectum is about long, and begins at the rectosigmoid junction (the end of the s ...
, to the lower end of the
small intestine
The small intestine or small bowel is an organ in the gastrointestinal tract where most of the absorption of nutrients from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the p ...
, and to display the images on an electronic
display device
A display device is an output device for presentation of information in visual or tactile form (the latter used for example in tactile electronic displays for blind people). When the input information that is supplied has an electrical signal the ...
.
The procedure is used to screen for colon cancer and
polyps
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are roughly cylindrical in shape and elongated at the axis of the vase-shaped body. In solitary polyps, the aboral (opposite to oral) end i ...
, and may detect
diverticulosis
Diverticulosis is the condition of having multiple pouches (diverticulum, diverticula) in the colon (anatomy), colon that are not inflamed. These are outpockets of the colonic mucosa and submucosa through weaknesses of muscle layers in the col ...
. A virtual colonoscopy can provide 3D reconstructed endoluminal views of the bowel. VC provides a secondary benefit of revealing diseases or abnormalities outside the colon.
Procedure
While preparations for VC vary, the patient will usually be asked to take
laxative
Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation.
Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lubri ...
s or other oral agents at home the day before the procedure to clear
stool from the colon. A
suppository
A suppository is a dosage form used to deliver medications by insertion into a body orifice where it dissolves or melts to exert local or systemic effects. There are three types of suppositories, each to insert into a different sections: rectal su ...
is also used to cleanse the rectum of any remaining fecal matter. The patient may also be given a solution designed to coat any residual faeces which may not have been cleared by the laxative, called 'faecal tagging'. This allows the physician (usually a
consultant radiologist), viewing the 3D images to effectively subtract the left-over faeces, which may otherwise give false positive results.
VC takes place in the
radiology
Radiology ( ) is the medical discipline that uses medical imaging to diagnose diseases and guide their treatment, within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiat ...
department of a
hospital
A hospital is a health care institution providing patient treatment with specialized health science and auxiliary healthcare staff and medical equipment. The best-known type of hospital is the general hospital, which typically has an emerge ...
or medical center. The examination takes about 10 minutes and does not require
sedatives
A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are CNS depressants and interact with brain activity causing its deceleration. Various kinds of sedatives can be distinguished, but th ...
.
During the procedure:
* The patient is placed in a
supine position
The supine position ( or ) means lying horizontally with the face and torso facing up, as opposed to the prone position, which is face down. When used in surgical procedures, it grants access to the peritoneal, thoracic and pericardial regions; ...
on the examination table
* The patient may be given a dosage of
Butylscopolamine
Hyoscine butylbromide, also known as scopolamine butylbromide and sold under the brandname Buscopan among others, is an anticholinergic medication used to treat crampy abdominal pain, esophageal spasms, renal colic, and bladder spasms. It is a ...
intravenously to minimize muscle activity in the area.
* A thin tube is inserted into the rectum, so that air can be pumped through the tube in order to inflate the colon for better viewing.
* The table moves through the scanner to produce a series of two-dimensional cross-sections along the length of the colon. A
computer program
A computer program is a sequence or set of instructions in a programming language for a computer to execute. Computer programs are one component of software, which also includes documentation and other intangible components.
A computer program ...
puts these images together to create a three-dimensional picture that can be viewed on the
video screen.
* The patient is asked to hold his/her breath during the scan to avoid distortion on the images.
* The scan is then repeated with the patient lying in a
prone position
Prone position () is a body position in which the person lies flat with the chest down and the back up. In anatomical terms of location, the dorsal side is up, and the ventral side is down. The supine position is the 180° contrast.
Etymolog ...
.
After the examination, the images produced by the scanner must be processed into a 3D image, +/- a fly through (a cine program which allows the user move through the bowel as if performing a normal colonoscopy). A radiologist evaluates the results to identify any abnormalities.
The patient may resume normal activity after the procedure, but if abnormalities are found and the patient needs conventional
colonoscopy
Colonoscopy () or coloscopy () is the endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It can provide a visual diagnosis (''e. ...
, it may be performed the same day.
Advantages
VC may be more comfortable for some individuals, as it does not require the use of a colonoscope. As a result, no sedation is needed, and the patient can return to his/her usual activities or go home after the procedure without the aid of another person. The lack of sedation also lowers the risk of the procedure since some people may have adverse reactions to sedative medications used during conventional colonoscopy. VC provides clearer, more detailed images than a conventional x-ray using a
barium enema
A lower gastrointestinal series is a medical procedure used to examine and diagnose problems with the human colon of the large intestine. Radiographs (X-ray pictures) are taken while barium sulfate, a radiocontrast agent, fills the colon via an ...
, sometimes called a lower gastrointestinal (GI) series. Further, about 1 in 10 patients will not have a complete right colon (cecum) evaluation completed with conventional colonoscopy.
It also takes less time than either a conventional colonoscopy or a lower GI series.
VC provides a secondary benefit of revealing diseases or abnormalities outside the colon.
One study of asymptomatic adults undergoing routine VC found that approximately one unsuspected extracolonic cancer was detected per 300 screenings in addition to about one invasive colorectal cancer per 500 screenings, for an overall rate of approximately one unsuspected cancer of any type detected per 200 screenings. Invasive colorectal cancer was the most common malignancy detected, followed by
renal cell carcinoma
Renal cell carcinoma (RCC) is a kidney cancer that originates in the lining of the proximal convoluted tubule, a part of the very small tubes in the kidney that transport primary urine. RCC is the most common type of kidney cancer in adults, resp ...
.
Disadvantages
During virtual colonoscopy, it is not possible to take tissue samples (
biopsy
A biopsy is a medical test commonly performed by a surgeon, interventional radiologist, or an interventional cardiologist. The process involves extraction of sample cells or tissues for examination to determine the presence or extent of a diseas ...
) or remove polyps, so a conventional
colonoscopy
Colonoscopy () or coloscopy () is the endoscopic examination of the large bowel and the distal part of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. It can provide a visual diagnosis (''e. ...
must be performed if abnormalities are found. Also, VC does not show as much detail as a conventional colonoscopy, so polyps smaller than between 2 and 10 millimeters in diameter may not show up on the images. Furthermore virtual colonoscopy performed with CT exposes the patient to
ionizing radiation
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
, on the order of a milli
gray
Grey (more common in British English) or gray (more common in American English) is an intermediate color between black and white. It is a neutral or achromatic color, meaning literally that it is "without color", because it can be composed o ...
. Some research has demonstrated that ultra-low dose VC can be just as effective in demonstrating bowel disease due to the great difference in x-ray absorption between air and the tissue comprising the inner wall of the colon.
Optical colonoscopy is taken as the "
gold standard
A gold standard is a monetary system in which the standard economic unit of account is based on a fixed quantity of gold. The gold standard was the basis for the international monetary system from the 1870s to the early 1920s, and from the la ...
" for colorectal cancer screening by the vast majority of the medical and research communities. However, some radiologists recommend VC as a preferred approach to colorectal screening. Virtual colonoscopy is favored by some professionals because it permits complete visualization of the entire colon, hence providing more opportunity to identify precancerous polyps and cancer, and to then do prompt diagnostic biopsies or therapeutic removal of these lesions.
Alternatives
MRI colonography (MRC) allows similar visualizing without radiation exposure. It can detect larger adenomas and neoplasia with high specificity, but less sensitivity than conventional colonoscopy.
Notes
References
* Adapted from public domai
Virtual Colonoscopy National Digestive Diseases Information Clearinghouse.
External links
RadiologyInfo- The radiology information resource for patients
American College of Gastroenterology(ACG)
International Foundation for Functional Gastrointestinal Disorders(IFFGD)
Virtual colonoscopy information and articles from Viatronix
{{DEFAULTSORT:Virtual Colonoscopy
Digestive system imaging
X-ray computed tomography
Articles containing video clips
Large intestine
Cancer screening