American Medical Association Family Medical Guide - American Medical Association [92]
Radionuclide scanning can also be used with a computer to help form images with techniques such as single photon emission computed tomography (SPECT). In SPECT, cross-sectional images of the body (usually the brain) are created using a gamma camera that rotates around the person. PET (positron emission tomography) scans combine nuclear scanning with chemical analysis to show blood flow and chemical processes in action. In SPECT/PET, chemicals such as the sugar glucose (the brain’s energy source) and key neurotransmitters (brain cell messengers) are made slightly radioactive and injected into the person. As they work in the brain, the chemicals emit photons (particles of light) that can be picked up like X-rays. SPECT and PET are often used to study the working brain.
THE PROCEDURE
Because the radioactive chemicals used during nuclear imaging can affect a fetus, tell your doctor before the procedure if you are (or could be) pregnant. After the radioactive tracer is swallowed or injected, you may need to wait for it to travel through your bloodstream and collect in the target organ before you are examined by the gamma camera. Because this may take several hours, you may be allowed to leave the facility and return later to take the scan. While you are having the scan, you lie or sit on the examination table, and the gamma camera is moved close to the area being examined. You must stay very still during the scan, but you may be asked to change positions; the technician will reposition you and the camera if necessary. The amount of time the procedure takes varies from about 1 to 5 hours. In some cases, a second or third scan is required. Radionuclide scanning is painless (except for the injection of the tracer). The tracer quickly breaks down into harmless substances and is eliminated from the body.
Thyroid gland
This is a gamma scan (front view) of the two lobes of a healthy thyroid gland (located at the base of the neck). The radioactive tracer has highlighted areas of activity in the gland. Areas of high activity are green or red; areas of low activity are blue.
Lower legs and feet
This image is a gamma scan of the bones in the lower legs and feet. Bone shows up on the image in blue or yellow.
Bone cancer
This gamma scan shows a side view of the head, neck, and upper chest of a person who has cancer that has spread to the vertebrae in the neck (white area). Cancerous bone appears as bright “hot spots” on the image because the radionuclide tracer concentrates in cancerous bone more strongly than it does in normal bone.
Endoscopy
An endoscope is a thin (usually flexible) viewing tube that enables a doctor to examine the inside of the body directly. Endoscopes have a light source, flexible bundles of glass or plastic fibers (called fiberoptic bundles) that transmit light, an eyepiece at one end, and lenses or a video computer chip at the other. Endoscopes also have a suction channel and a channel or tube through which instruments can be passed and manipulated.
Calcium deposits in knee
A thin, rigid type of endoscope (called an arthroscope) is used to see directly inside a joint. This arthroscopic image shows calcium deposits inside a knee joint.
Uterus
This image is the inside of a uterus as seen through a special endoscope called a hysteroscope. The hysteroscope is guided into the uterus through the vagina and cervix.
Endoscopes are used to view the upper airways and lungs (bronchoscope); the esophagus, stomach, and first part of the small intestine (gastroscope); the abdominal cavity (laparoscope); the entire large intestine (colonoscope); the lower part of the large intestine and rectum (sigmoidoscope); the bladder (cystoscope); the cervix and uterus (hysteroscope); and the joints, particularly the knee (arthroscope).