Capsule mechanics

Published : Nov 08, 2002 00:00 IST

WHAT does the capsule used in capsule endoscopy contain? It is the size of a vitamin pill, 26 millimetres long and 11mm wide. It weighs 3.7 gm and has a field view of 140 degrees. With a magnification power of 1:8, the capsule can detect objects smaller than 0.1 mm. This means that even a fur-like micro villa pattern in the small intestine can be detected using the capsule. The capsule has an optical dome, four light-emitting diodes, a complementary metal oxide semi-conductor (CMOS) video imaging chip, a lens, two silver oxide batteries, an antenna and a radio frequency transmitter. The capsule transmits radio signals as satellites do. As it emits no radiation the capsule is safe and can be used even during pregnancy. The batteries can power the capsule for eight and a half hours, the times it takes to pass through the small intestine. After that the capsule ceases to work. Being non-digestible and non-hazardous it passes out through the bowel. There are no side-effects.

How does the capsule work? Eight leads are attached to the chest and abdomen of the patient. These leads are connected to a computerised video recording device or a compact disc (CD) recorder, on a belt-pouch strapped to the patient's waist. The batteries on the belt-pouch power the CD recorder. The capsule is stored in a magnetic shell. Once it is removed from the shell, the light-emitting diodes start blinking, give out white light and then becomes active. From then on, the capsule is powered for eight and a half hours. Once the capsule is swallowed, the images are picked up through the optical dome by the lens and are transmitted at the rate of two frames a second. The transmission, by the antenna, is picked up by the leads fixed on the body. And the data are stored in the CD recorder in the belt-pouch. The images can be stored in a static mode or in the form of clippings (of 100 frames at a time) in Windows. All the images are recorded and given to patients in the form of colour printouts and also in CDs.

What are the contraindications? While there is generally no restriction on the use of capsule endoscopy, after swallowing the capsule one should not go near a magnetic resonance imaging (MRI) machine as it could interfere with the progression of the capsule. It is best that people with a cardiac pace-maker avoid this procedure as it is not yet known if the pace-maker will interfere with the capsule. Capsule endoscopy is also not recommended for those with a very tight stricture in the intestine as this would not admit a 26 mm object to pass through the constriction and the capsule may get stuck at that point. In such a situation, the capsule may have to be removed surgically. But if the stricture has not been discovered earlier, this procedure helps it to be identified.

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