American Medical Association Family Medical Guide - American Medical Association [87]
Brain hemorrhage
This three-dimensional angiogram shows a brain after a type of stroke caused by a hemorrhage, or bleeding inside the brain. The white areas are major arteries. The large yellow area in the center is the hemorrhage.
Brain during a migraine
This single photon emission computed tomography (SPECT) scan of a brain was taken during a migraine headache. Areas of high brain activity are yellow or red. Areas of low activity are gray or blue. Migraines usually affect one side of the brain. The grayish area at the lower left is an area of reduced blood flow (and low brain activity) from the migraine.
X-Rays
X-rays are high-energy electromagnetic waves that have a shorter wavelength than visible light or radio waves. When a beam of X-rays is passed through the body, some parts of the body absorb more radiation than other parts, producing a darker, shadowy image on the X-ray film, or radiograph. X-ray images can also be viewed on a fluorescent screen, or monitor. Dense structures (such as bone) allow few X-rays to pass through, so these structures appear lighter, or white, on the film. Fat and other soft tissues absorb less radiation, and so they look somewhat gray. Hollow structures (such as the lungs) allow even more radiation to pass through, making them appear darker, or black, on film.
Structures that are hollow (such as the intestines and blood vessels) can show up more clearly on X-rays if they are filled with a contrast medium (dye) such as barium sulfate, which blocks the X-rays. For example, for an X-ray examination of the upper digestive tract, a person fasts for several hours and then drinks a barium sulfate liquid. As the barium moves through the digestive tract, it highlights the outlines of the esophagus, stomach, and upper intestine on the X-ray film. For an
X-ray examination of the lower intestine, barium is introduced into the intestine through the rectum (called a barium enema). Iodine is used as a contrast medium to examine the thyroid gland, blood vessels, and urinary tract.
THE PROCEDURE
Before an X-ray examination, you may be asked to remove some of your clothing to help produce a better X-ray image. The part of your body to be examined will be positioned between the X-ray machine and the film, usually touching or very close to the machine. The technician will position you or immobilize the body part to obtain the best possible view. Several images may be taken from various angles. The X-rays themselves cause no discomfort because you cannot feel X-rays pass through your body.
The parts of your body not being examined may be shielded from the X-rays in some way (such as with a lead apron) to protect them from exposure to radiation. Your exposure to the radiation lasts only a fraction of a second. Because of a small risk of tissue damage from exposure to radiation, X-rays are performed only when necessary, and never during pregnancy.
Skull
This X-ray shows the dense bone of a healthy human skull, which encloses and protects the brain. Because X-rays provide little information about the brain itself, they are used primarily to diagnose and evaluate skull fractures.
Mammogram
Mammography uses low doses of X-rays to produce images of the soft tissues of the breast to detect abnormal growths such as tumors. This mammogram shows a cancerous tumor (bright white spot) in its early stages.
Broken arm
This X-ray shows severe fractures of both bones in the lower arm—the radius and the ulna.
Pacemaker in chest cavity
In this X-ray of the chest, the hollow lungs are the two large dark areas, and the heart is barely visible between the lungs. A pacemaker, which is implanted just beneath the skin, is attached to the heart with wires to regulate