Editing Virtual colonoscopy

{{Short description|Medical imaging of the colon}}
{{Infobox interventions |
  Name        = Virtual colonoscopy |
  Image       = CT colonography of a rectal mass.jpg |
  Caption     = CT colonography of a rectal mass. Left image is a [[volume rendering]] and right image is a thin slice. It also shows the rectal tube used for insufflation of gas to distend the colon.|
  ICD10       = |
  ICD9        = |
  MedlinePlus = 007253 |
  MeshID      = D023881 |
  OtherCodes  = |
}}
'''Virtual colonoscopy''' ('''VC''', also called '''CT colonography''' or '''CT pneumocolon''') is the use of [[CT scan]]ning or [[magnetic resonance imaging]] (MRI)  to produce two- and [[3D computer graphics|three-dimensional]] images of the [[colon (anatomy)|colon]] (large intestine), from the lowest part, the [[rectum]], to the lower end of the [[small intestine]], and to display the images on an electronic [[display device]].<ref name="Heiken">{{cite journal | last=Heiken | first=JP |author2=Peterson CM |author3=Menias CO  | title=Virtual colonoscopy for colorectal cancer screening: current status: Wednesday 5 October 2005, 14:00–16:00 | journal=Cancer Imaging | volume=5 | issue=Spec No A | pages=S133–S139 | publisher=International Cancer Imaging Society | date=November 2005 | pmid=16361129 | doi=10.1102/1470-7330.2005.0108 | pmc=1665314 }}</ref><ref name="pmid16106357">{{cite journal |author=Bielen DJ |title=Clinical validation of high-resolution fast spin-echo MR colonography after colon distention with air |journal=J Magn Reson Imaging |volume=22 |issue=3 |pages=400–5 |date=September 2005 |pmid=16106357 |doi=10.1002/jmri.20397 |name-list-style=vanc|author2=Bosmans HT |author3=De Wever LL |display-authors=3 |last4=Maes |first4=Frederik |last5=Tejpar |first5=Sabine |last6=Vanbeckevoort |first6=Dirk |last7=Marchal |first7=Guy J.F.|s2cid=22167728 |doi-access= }}</ref> The procedure is used to screen for colon cancer and [[polyp (medicine)|polyps]], and may detect [[diverticulosis]].  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==
[[File:Vc3.theora.ogv|thumb|right|This video shows a virtual colonoscopy of the rectosigmoid colon performed in a retrograde fashion. There is a 10-mm colonoscopically-proven polyp in the sigmoid colon seen at the top of the frame at the midpoint of the movie. The movie concludes at the tip of the rectal tube which was used to insufflate the colon.]]
While preparations for VC vary, the patient will usually be asked to take [[laxative]]s or other oral agents at home the day before the procedure to clear [[feces|stool]] from the colon. A [[suppository]] 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 [[Radiologist|consultant radiologist]]), viewing the 3D images to effectively subtract the left-over faeces, which may otherwise give false positive results.{{cn|date=January 2022}}

VC takes place in the [[radiology]] department of a [[hospital]] or medical center. The examination takes about 10 minutes and does not require [[sedatives]].{{cn|date=January 2022}}

During the procedure:{{cn|date=January 2022}}
* The patient is placed in a [[supine position]] 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 program]] puts these images together to create a three-dimensional picture that can be viewed on the [[Electronic visual display|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]].

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.<ref>[http://digestive.niddk.nih.gov/ddiseases/pubs/virtualcolonoscopy/ "Virtual Colonoscopy"] {{Webarchive|url=https://web.archive.org/web/20141009020407/http://digestive.niddk.nih.gov/ddiseases/pubs/virtualcolonoscopy/ |date=2014-10-09 }} - National Digestive Diseases Information Clearinghouse - NIH</ref>

==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]], 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.<ref name="pmid15666105">{{cite journal |author=Menardo G |title=Sensitivity of diagnostic examinations for colorectal polyps |journal=Tech Coloproctol |volume=8 |pages=s273–5 |date=December 2004 |issue=Suppl 2 |pmid=15666105 |doi=10.1007/s10151-004-0175-0|s2cid=12918901 }}</ref> It also takes less time than either a conventional colonoscopy or a lower GI series.<ref>[http://www.mayoclinic.com/health/virtual-colonoscopy/CO00025 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."</ref>

VC provides a secondary benefit of revealing diseases or abnormalities outside the colon.<ref name="pmid16040909">{{cite journal |author=Yee J |title=Extracolonic abnormalities discovered incidentally at CT colonography in a male population |journal=Radiology |volume=236 |issue=2 |pages=519–26 |date=August 2005 |pmid=16040909 |doi=10.1148/radiol.2362040166 |url=http://radiology.rsnajnls.org/cgi/pmidlookup?view=long&pmid=16040909 |access-date=2008-12-22 |name-list-style=vanc|author2=Kumar NN |author3=Godara S |display-authors=3 |last4=Casamina |first4=J. A. |last5=Hom |first5=R. |last6=Galdino |first6=G. |last7=Dell |first7=P. |last8=Liu |first8=D.|url-access=subscription }}</ref> 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]].<ref>{{cite journal|last=Pickhardt|first=Perry J.|date=April 2010|title=Colorectal and Extracolonic Cancers Detected at Screening CT Colonography in 10,286 Asymptomatic Adults|url=https://pubs.rsna.org/doi/pdf/10.1148/radiol.09090939|journal=Radiology|volume=255-1|issue=1 |pages=83–88|doi=10.1148/radiol.09090939 |pmid=20308446 |url-access=subscription}}</ref>

==Disadvantages==
During virtual colonoscopy, it is not possible to take tissue samples ([[biopsy]]) or remove polyps, so a conventional [[colonoscopy]] must be performed if abnormalities are found.<ref>{{cite web |url=https://www.niddk.nih.gov/health-information/diagnostic-tests/virtual-colonoscopy |title=Virtual Colonoscopy |website= National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), US|access-date= 11 December 2018}}</ref> 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.<ref>[http://www.eurekalert.org/pub_releases/2006-10/wfub-cc102406.php Findings presented at the American College of Gastroenterology] annual scientific meeting in Las Vegas, Nev. An abstract of the study was printed in the September 2006 issue of The American Journal of Gastroenterology.</ref> Furthermore virtual colonoscopy performed with CT exposes the patient to [[ionizing radiation]], on the order of a milli[[Gray (unit)|gray]].<ref>{{cite journal|title = Does the amount of tagged stool and fluid significantly affect the radiation exposure in low-dose CT colonography performed with an automatic exposure control?|date = Feb 2011|doi = 10.1007/s00330-010-1922-4|pmid = 20700594|volume=21 |pages=345–52| last1=Lim | first1=Hyun Kyong | last2=Lee | first2=Kyoung Ho | last3=Kim | first3=So Yeon | last4=Kim | first4=Kil Joong | last5=Kim | first5=Bohyoung | last6=Lee | first6=Hyunna | last7=Park | first7=Seong Ho | last8=Yanof | first8=Jeffrey H. | last9=Hwang | first9=Seung-sik | last10=Kim | first10=Young Hoon | journal=European Radiology | issue=2 | s2cid=20987597 }}</ref> 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 (test)|gold standard]]" 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.{{cn|date=January 2022}}

==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.<ref>{{cite journal|title = Magnetic resonance colonography for the detection of colorectal neoplasia in asymptomatic adults.|date = Apr 2013|journal = Gastroenterology|doi = 10.1053/j.gastro.2012.12.041|pmid = 23415805|volume=144 |pages=743–750.e2| last1=Graser | first1=Anno | last2=Melzer | first2=Anja | last3=Lindner | first3=Evelyn | last4=Nagel | first4=Dorothea | last5=Herrmann | first5=Karin | last6=Stieber | first6=Petra | last7=Schirra | first7=Jörg | last8=Mansmann | first8=Ulrich | last9=Reiser | first9=Maximilian F. | last10=Göke | first10=Burkhard | last11=Kolligs | first11=Frank T. | issue=4 | doi-access=free }}</ref>

==Notes==
{{Reflist|2}}

==References==
* Adapted from public domain [http://digestive.niddk.nih.gov/ddiseases/pubs/virtualcolonoscopy/index.htm Virtual Colonoscopy] {{Webarchive|url=https://web.archive.org/web/20110514210907/http://digestive.niddk.nih.gov/ddiseases/pubs/virtualcolonoscopy/index.htm |date=2011-05-14 }}. National Digestive Diseases Information Clearinghouse.

==External links==
* [http://radiologyinfo.org/en/info.cfm?PG=ct_colo RadiologyInfo] - The radiology information resource for patients
* [https://web.archive.org/web/20050211084119/http://www.acg.gi.org/ American College of Gastroenterology] (ACG)
* [http://www.iffgd.org International Foundation for Functional Gastrointestinal Disorders] (IFFGD)
* [http://www.viatronix.com/virtual-colonoscopy/ Virtual colonoscopy information and articles from Viatronix]

{{Digestive system procedures}}
{{Medical imaging}}

{{DEFAULTSORT:Virtual Colonoscopy}}
[[Category:Cancer screening]]
[[Category:Diagnostic medical imaging]]
[[Category:Digestive system imaging]]
[[Category:Large intestine]]
[[Category:X-ray computed tomography]]
[[Category:Articles containing video clips]]