Virtual colonoscopy
Encyclopedia
Virtual colonoscopy is a medical imaging
procedure which uses x-ray
s and computer
s to produce two- and three-dimensional
images of the colon
(large intestine) from the lowest part, the rectum
, all the way to the lower end of the small intestine
and display them on a screen. The procedure is used to diagnose
colon and bowel disease, including polyps
, diverticulosis
and cancer
. VC is performed via computed tomography
(CT), sometimes called a CAT scan, or with magnetic resonance imaging (MRI).
Not to be confused with a similar procedure called a CT Pneumocolon, a virtual colonoscopy can provide 3D reconstructed endoluminal views of the bowel.
s or other oral agents at home the day before the procedure to clear stool
from the colon. A suppository
is also used to cleanse the rectum of any remaining fecal matter. The patient may also given a solution designed to coat any residual faeces which may not have been cleared by the laxative. This is called 'faecal tagging'. This allows the user (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
department of a hospital
or medical center. The examination takes about 10 minutes and does not require sedatives.
During the procedure:
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
, it may be performed the same day.
, 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.
) or remove polyps during VC, so a conventional colonoscopy 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, however some research has demonstrated that ultra-low dose VC can be just as effective in demonstrating colon and 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" for colorectal cancer screening by the vast majority of the medical and research communities. Some radiologists recommend VC as a preferred approach to colorectal screening. However, optical colonoscopy is considered the gold standard by some professionals because it permits complete visualization of the entire colon, hence providing the opportunity to identify precancerous polyps and cancer, and then to do diagnostic biopsies or therapeutic removal of these lesions, as soon as possible.
Medical imaging
Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
procedure which uses x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s and computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
s to produce two- and three-dimensional
3D computer graphics
3D computer graphics are graphics that use a three-dimensional representation of geometric data that is stored in the computer for the purposes of performing calculations and rendering 2D images...
images of the colon
Colon (anatomy)
The colon is the last part of the digestive system in most vertebrates; it extracts water and salt from solid wastes before they are eliminated from the body, and is the site in which flora-aided fermentation of unabsorbed material occurs. Unlike the small intestine, the colon does not play a...
(large intestine) from the lowest part, the rectum
Rectum
The rectum is the final straight portion of the large intestine in some mammals, and the gut in others, terminating in the anus. The human rectum is about 12 cm long...
, all the way to the lower end of the small intestine
Small intestine
The small intestine is the part of the gastrointestinal tract following the stomach and followed by the large intestine, and is where much of the digestion and absorption of food takes place. In invertebrates such as worms, the terms "gastrointestinal tract" and "large intestine" are often used to...
and display them on a screen. The procedure is used to diagnose
Diagnosis
Diagnosis is the identification of the nature and cause of anything. Diagnosis is used in many different disciplines with variations in the use of logics, analytics, and experience to determine the cause and effect relationships...
colon and bowel disease, including polyps
Polyp (medicine)
A polyp is an abnormal growth of tissue projecting from a mucous membrane. If it is attached to the surface by a narrow elongated stalk, it is said to be pedunculated. If no stalk is present, it is said to be sessile. Polyps are commonly found in the colon, stomach, nose, sinus, urinary bladder...
, diverticulosis
Diverticulosis
Diverticulosis also known as "diverticular disease" is the condition of having diverticula in the colon, which are outpocketings of the colonic mucosa and submucosa through weaknesses of muscle layers in the colon wall. These are more common in the sigmoid colon, which is a common place for...
and cancer
Cancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
. VC is performed via computed tomography
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
(CT), sometimes called a CAT scan, or with magnetic resonance imaging (MRI).
Not to be confused with a similar procedure called a CT Pneumocolon, a virtual colonoscopy can provide 3D reconstructed endoluminal views of the bowel.
Procedure
While preparations for VC vary, the patient will usually be asked to take laxativeLaxative
Laxatives are foods, compounds, or drugs taken to induce bowel movements or to loosen the stool, most often taken to treat constipation. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and/or bowel examinations, and may be supplemented by enemas under...
s or other oral agents at home the day before the procedure to clear stool
Feces
Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...
from the colon. A suppository
Suppository
A suppository is a drug delivery system that is inserted into the rectum , vagina or urethra , where it dissolves.They are used to deliver both systemically-acting and locally-acting medications....
is also used to cleanse the rectum of any remaining fecal matter. The patient may also given a solution designed to coat any residual faeces which may not have been cleared by the laxative. This is called 'faecal tagging'. This allows the user (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
Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...
department of a hospital
Hospital
A hospital is a health care institution providing patient treatment by specialized staff and equipment. Hospitals often, but not always, provide for inpatient care or longer-term patient stays....
or medical center. The examination takes about 10 minutes and does not require sedatives.
During the procedure:
- The patient is placed in a supine positionSupine positionThe supine position is a position of the body: lying down with the face up, as opposed to the prone position, which is face down, sometimes with the hands behind the head or neck. When used in surgical procedures, it allows access to the peritoneal, thoracic and pericardial regions; as well as the...
on the examination table - The patient may be given a dosage of Butylscopolamine 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 programComputer programA computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
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 positionProne positionThe term means to lie on bed or ground in a position with chest downwards and back upwards.-Etymology :The word "prone," meaning "naturally inclined to something, apt, liable," has been recorded in English since 1382; the meaning "lying face-down" was first recorded in 1578, but is also referred to...
.
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
Colonoscopy 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 may provide a visual diagnosis and grants the opportunity for biopsy or removal of suspected...
, it may be performed the same day.
Advantages
VC is more comfortable than conventional colonoscopy for some people because it does not use 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 enemaBarium enema
A lower gastrointestinal series, also called a barium enema, is a medical procedure used to examine and diagnose problems with the human colon . X-ray pictures are taken while barium sulfate fills the colon via the rectum.-Procedure:...
, 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.
Disadvantages
According to an article on niddk.nih.gov, the main disadvantage to VC is that a radiologist cannot take tissue samples (biopsyBiopsy
A biopsy is a medical test involving sampling of cells or tissues for examination. It is the medical removal of tissue from a living subject to determine the presence or extent of a disease. The tissue is generally examined under a microscope by a pathologist, and can also be analyzed chemically...
) or remove polyps during VC, so a conventional colonoscopy 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, however some research has demonstrated that ultra-low dose VC can be just as effective in demonstrating colon and 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" for colorectal cancer screening by the vast majority of the medical and research communities. Some radiologists recommend VC as a preferred approach to colorectal screening. However, optical colonoscopy is considered the gold standard by some professionals because it permits complete visualization of the entire colon, hence providing the opportunity to identify precancerous polyps and cancer, and then to do diagnostic biopsies or therapeutic removal of these lesions, as soon as possible.
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
- Fly-Over, A New Visualization for Colonoscopy
- Virtual Camera Path Planning for Colonoscopy
Source
- Adapted from public domain Virtual Colonoscopy. National Digestive Diseases Information Clearinghouse.