An optical fiber (or optical fibre) is a flexible, transparent fiber made of high quality extruded glass (silica) or plastic, slightly thicker than a human hair. It can function as a waveguide, or “light pipe”, to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of optical fibers is known as fiber optics. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communication. Fibers are used instead of metal wires because signals travel along them with less loss and are also immune to electromagnetic interference. Fibers are also used for illumination, and are wrapped in bundles so that they may be used to carry images, thus allowing viewing in confined spaces. Specially designed fibers are used for a variety of other applications, including sensors and fiber lasers.
Optical fibers typically include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light is kept in the core by total internal reflection. This causes the fiber to act as a waveguide. Fibers that support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those that only support a single mode are called single-mode fibers (SMF). Multi-mode fibers generally have a wider core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. Single-mode fibers are used for most communication links longer than 1,000 meters (3,300 ft).
Gastrointestinal cancer refers to malignant conditions of the gastrointestinal tract (GI tract) and accessory organs of digestion, including the esophagus, stomach, biliary system, pancreas, small intestine, large intestine, rectum and anus. The symptoms relate to the organ affected and can include obstruction (leading to difficulty swallowing or defecating), abnormal bleeding or other associated problems. The diagnosis often requires endoscopy, followed by biopsy of suspicious tissue. The treatment depends on the location of the tumor, as well as the type of cancer cell and whether it has invaded other tissues or spread elsewhere. These factors also determine the prognosis.
Overall, the GI tract and the accessory organs of digestion (pancreas, liver, gall bladder) are responsible for more cancers and more deaths from cancer than any other system in the body. There is significant geographic variation in the rates of different gastrointestinal cancers.
Colorectal cancer, also known as colon cancer, rectal cancer, or bowel cancer, is a cancer from uncontrolled cell growth in the colon or rectum (parts of the large intestine), or in the appendix. Genetic analysis shows that essentially colon and rectal tumours are genetically the same cancer. Symptoms of colorectal cancer typically include rectal bleeding and anemia which are sometimes associated with weight loss and changes in bowel habits.
Most colorectal cancer occurs due to lifestyle and increasing age with only a minority of cases associated with underlying genetic disorders. It typically starts in the lining of the bowel and if left untreated, can grow into the muscle layers underneath, and then through the bowel wall. Screening is effective at decreasing the chance of dying from colorectal cancer and is recommended starting at the age of 50 and continuing until a person is 75 years old. Localized bowel cancer is usually diagnosed through sigmoidoscopy or colonoscopy.
Virtual colonoscopy (VC, also called CT Colonography or CT Pneumocolon) is a medical imaging procedure which uses x-rays and computers 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). A virtual colonoscopy can provide 3D reconstructed endoluminal views of the bowel.
While preparations for VC vary, the patient will usually be asked to take laxatives 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 be 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.
Capsule endoscopy is a way to record images of the digestive tract for use in medicine. The capsule is the size and shape of a pill and contains a tiny camera. After a patient swallows the capsule, it takes pictures of the inside of the gastrointestinal tract. The primary use of capsule endoscopy is to examine areas of the small intestine that cannot be seen by other types of endoscopy such as colonoscopy or esophagogastroduodenoscopy (EGD). The technique was invented in Israel. It was approved by the U.S. Food and Drug Administration in 2001.
Capsule endoscopy is used to examine parts of the gastrointestinal tract that cannot be seen with other types of endoscopy. Upper endoscopy, also called EGD, uses a camera attached to a long flexible tube to view the esophagus, the stomach and the beginning of the first part of the small intestine called the duodenum. A colonoscope, inserted through the rectum, can view the colon and the distal portion of the small intestine, the terminal ileum. These two types of endoscopy cannot visualize the majority of the middle portion of the gastrointestinal tract, the small intestine. Capsule endoscopy is useful when disease is suspected in the small intestine, and can sometimes diagnose sources of occult bleeding [blood visible microscopically only] or causes of abdominal pain such as Crohn's disease, or peptic ulcers. Capsule endoscopy can be used to diagnose problems in the small intestine, but unlike EGD or colonoscopy it cannot treat pathology that may be discovered. Capsule endoscopy can use bluetooth to transfer the captured images. A transmitted radio-frequency signal can be used to accurately estimate the location of the capsule and to track it in real time inside the body and gastrointestinal tract.