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Video Capsule Endoscopy
Capsule endoscopy was originally developed as a means to image the tortuous path of the small bowel without the discomfort and risk of introducing a large diameter cable into that area. Development took advantage of advances in electronic miniaturization techniques, medical radio-telemetry and small, low power and noise image sensors to provide a swallowable capsule capable of transmitting video images. In July 2003, Given Imaging’s PillCam SB™ capsule endoscopy system for detection of abnormalities of the small bowel received FDA clearance for marketing in the United States. In November, a second system, the PillCam ESO™ was approved for marketing by the FDA for visualization of the esophageal mucosa.
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| Figure 1 |
Both capsules feature a small size (26 mm length x 11 mm diameter), low weight (0.12 oz), and internal battery. Capsules contain the LED source, video camera(s) for image acquisition, and an UHF transmitter for sending images to a portable recorder carried in a belt worn by the patient. The color video imager is designed with a short focal length lens and wide depth of field to exhibit a focal region from the pill surface to a depth of a few centimeters. After swallowing the capsule with a glass of water, images are obtained as the capsule is pushed by peristalsis through the gastrointestinal system. The SB model has one camera port with a 120 degree field of view, while the ESO model has two such camera ports, one at each end of the capsule. (For a descriptive video clip of the Pill Cam ESO™, please visit the Given Imaging website by clicking here. Please note: The video clip is 8.7 MB and make take awhile to download.) The SB captures two image frames per second with up over 50,000 images collected during its 8 hour flight through the body. The patient can go about their normal daily routine during image acquisition. The ESO captures 14 image frames per second (7 per camera) with up over 2,600 images collected during flight through the esophagus. An array of eight sensors is placed on the patient to allow triangulation of the capsule location so that the capsule trajectory can be displayed on the image monitor during image review. This allows correlation of discovered pathology with location. Specifications indicate that lesion as small as 0.1 mm can be detected, while localization of the trajectory can be done within 3 cm.
After the prescribed imaging, the belt is removed and images downloaded to a review workstation. Download time can run from 1.5 to 2 hours or trimmed by a factor of 2 with a booster capture board. Current system requirements for review software are 128 MB RAM, 640x480 video, 24 bit color, and Windows system. Images can be displayed at a rates up to 25 frames per second and integrated with the localization track. Both forward and retrograde ESO images can be simultaneously reviewed. Processing software (Figure 2, courtesy of Given Imaging Ltd.) allows for auto-detection of red areas for presence of blood as well as zoom, automatic brightness control, and calculation of capsule transit time for motility studies. Image data can be exported, from a proprietary format, as JPEG images or AVI movies.
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Figure 2 |
Because the capsule is propelled by peristalsis, the clinician is unable to direct additional imaging, biopsy or treatment of suspected areas. Researchers at the University of Colorado are working with vortex ring thrusters as a means to propel and maneuver the capsules. Such capsules create propulsion by emitting tiny puffs of air into the air-filled intestine. The resulting ring vortex moves the capsule forward in a direction opposite to that of the air emission, similar to the fluid propulsion of squid and jellyfish when they squirt pulses of water from their mouths. A model capsule, the size of a penny, has been built and researchers hope to have a capsule ready for clinical testing in a few years.
Capsule endoscopy is contraindicated for patients swallowing disorders, with know or suspected gastrointestinal obstruction, strictures or fistulas as well as patients with cardiac pacemakers or other implanted electromedical devices. A special pediatric kit with smaller belt and adapted sensor array geometry has been introduced. Insurance reimbursement is generally available for GI bleed as an indication. Other indications have mixed reimbursement approvals.
References
1. Given Imaging. http://www.givenimaging.com.
2. Gorder PF. Vortex Drive. In New Scientist (Issue 2470) [electronic journal]. London, England, 2004. Available at www.newscientist.com; INTERNET.
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