How do doctors take pictures and video inside the human body using an endoscope?

Using strands made of 100,000 hair like glass fibers drawn into a bundle, medical scientists can see around corners and even take pictures in the darkest reaches of the human body.

The technology is called fiber optic endoscopy, and with it doctors can photograph the inner surfaces of the esophagus, stomach, intestines, lungs, arteries, and sometimes the heart, kidneys, and pancreas.

An individual optical fiber is about one tenth the diameter of a human hair and has a peculiar ability to carry light from one place to another without losing much of it on the way.

The fiber has two parts: an inner core and an outer cladding. The core and cladding are made of two different grades of clear glass. The core glass has a higher refractive index, which is to say it is denser and bends light rays more, than the glass of the cladding, in the same way that water has a higher refractive index than air, which is why a spoon stuck into a glass of water looks bent.

The effect of the fiber core’s greater density is to keep light inside the fiber: light projected into the core strikes the cladding around it, but instead of leaking away, its rays are bent at such an angle that they bounce back to the fiber’s core. Thus light can be sent along a clear, flexible fiber without losing strength, no matter how many twists and turns it takes.

To get an image of an internal organ, a doctor sends an endoscope into the body, either through one of its natural openings or through one made especially for the purpose.

An endoscope is a flexible tube containing two separate bundles of fibers, each serving a different purpose. One carries light into the opening, to illuminate the area being examined; the other picks up light reflected off the tissues and carries it back to the physician’s eye or to the camera.

The second bundle has a wide angle lens, less than 1/8 inch in diameter, with a field of view of 60 to 100 degrees, attached to the remote end and an eyepiece, photographic lens, or viewing screen on the doctor’s end. Each fiber in the receiving bundle acts like a single tile in a mosaic, to form 1/100,000 of the image. Also inside the tube are pathways alongside the glass strands through which a doctor can insert instruments or fluids.

Using fiber optic “image bundles,” surgeons can watch and photograph many of the body’s internal processes in their natural colors, to check for problems and locate tissues more accurately for surgical repairs. The filth is slightly more sensitive than ordinary color film; this allows for fast shutter speeds, so that moving organs don’t blur the image.

Optical fiber is made by fitting a foot long glass rod about 1/2 inch in diameter inside a glass tube of a lower refractive index and heating the two until they bond. Then, in a “drawing tower,” the softened glass cylinder is stretched like taffy into a wispy fiber nearly 1 million feet long; the machines that do the stretching can turn out 1,000 miles of fiber in an hour. A hundred thousand or more fibers are bundled together to make a strand V8 inch in diameter, capable of carrying an image.

Fiber optic technology is actually used more for examining patients than for photographing them. Its special advantage as a diagnostic tool is that the body is not disturbed as much as it is by other methods of information gathering.

In exploratory surgery, the body is traumatized by being cut open, and the patient is exposed to the danger of infection; X ray photography fires potentially harmful ionizing radiation at the body, which carries long term cancer risks. Optical fibers make many examinations less painful, and less risky.