Radioactive or nuclear scans are tests in which the patient is given a weak radioactive substance called a radioactive tracer by injection into the bloodstream. The material is taken up by the body. A machine, which looks like an x-ray machine, moves over the area being tested and produces a series of pictures.
How can the doctor tell if cancer is present?
Deposits of cancer may show up as areas of either increased radioactivity or decreased radioactivity, depending upon the organ being studied, the type of radioactive substance used, and the kind of scan being done.
What kinds of substances are used in nuclear scans?
The kind of tracer used depends upon the part of the body which is being studied. Certain substances accumulate in certain body organs. An element like cobalt 60 allows doctors to track its progress as it makes its way through the digestive system by the radioactive trace elements it leaves behind. Radioactive iodine can be used for looking at the thyroid gland. Gallium is capable of showing rapidly dividing cells. New substances are constantly being tested and reviewed.
Where are radioactive scans done?
These tests must be done in special laboratories by doctors and technicians who are trained in handling radiotracers. Other conditions can, at times, look similar to cancer on the scans, so it takes a skilled practitioner to interpret them. Nuclear scans have been commonly used for detecting tumors since the early 1950s, and initially the tests were an offshoot of radiology. Now many hospitals have departments of nuclear medicine and it is a rapidly growing field in its own right. There is an American Board of Nuclear Medicine which certifies physicians in this field.
Who performs radioactive scans?
A skilled physician who has had special training after completing medical school including several years of intensive postgraduate training to qualify as an expert in diagnosis with extensive technical knowledge of the machinery used, the chemistry of radioactive compounds, and nuclear physics and radiation safety is responsible for nuclear scans. The American Board of Nuclear Medicine certifies doctors in this field. A nuclear medicine technologist assists the doctor, positions you, and operates the equipment during the examination. The technician has had special training and experience in nuclear medicine technology.
Are nuclear scans different from x-rays?
Yes, they are. X-rays involve passing radiation through your body from an external source (an x-ray tube) and recording the image on a film (radiograph) which the radiologist can examine. In a scan, the radioactive substance is introduced into your body, usually through an injection in your vein. The machine translates the substance into spots of light that expose the film, which is developed and called a scan. By observing how and where the radioactive compounds travel in your body, the doctor can detect changes in your body's processes.
What kinds of machines are used?
There are two main types. A "scanner" moves back and forth in straight lines, and as it moves it records images of the radiation given out. The other machine, called a "camera," records the radiation without the machine moving. It is larger than the scanner. The areas where the radioactivity is concentrated are seen as dots on the film. Places where there is high activity have more dots than those where there is low activity.
Is there any discomfort or danger to radioactive scans?
The scans involve little discomfort. The danger involved depends upon the part of the body. Some of the radiation given offby the tracer substance can be absorbed. However, the radioactive substance is weak, so the risks associated with nuclear scans are similar to those associated with diagnostic x-rays.
When are radioactive scans done?
It depends upon the kind of cancer suspected and the stage of the disease. Scans can be used to detect the primary source of cancer. They can also be used to estimate the progress of the treatment. Scans are also part of what is known as a metastatic workup that is, checking the body for distant cancer. A metastatic workup is usually used before treatment is begun if there is a diagnosis of cancer or if a very high suspicion of cancer is present. Metastatic workups are part of the "clinical staging system" which determines the person's state of cancer at the time it is diagnosed.
What kinds of scans are done for a metastatic workup?
Again it depends upon the kind of cancer and knowledge of where that cancer is likely to spread. A metastatic workup can include bone scans, liver scans, and brain scans along with a battery of other tests.
How are bone scans done?
The liquid which has been "tagged" with the mildly radioactive substance is injected into a vein and carried by the bloodstream to the bones. Cancerous areas in the bone will usually pick up more ofthe radioactive material than normal bone, so these show up as "hot spots" on the films taken of the area. Most of the liquid injected into the body for the bone scan disappears within a few hours. The liquid is excreted from the body within 48 hours after the test is done.
Are bone scans difficult to interpret?
Yes, because injured bone, arthritis, infection, and certain other abnormal conditions may show up as hot spots on the bone scans.
Do bone scans show different things than routine x-rays?
Yes, bone scans can detect cancerous areas in some cases earlier than x-rays. They are more sensitive. Bone scans are also better than x-rays in following the disease; they can show progress or regression. Routine x-rays have some drawbacks. Approximately 50 percent of the bone tissues must be destroyed by cancer in a given area before it will show up on an x-ray. On the other hand, x-rays also have some advantages: they are quick, easily obtained, involve no discomfort and little risk, and are relatively accurate.
Do brain scans also show hot spots?
The picture that appears as a result of a scan depends on the person's individual situation, because each kind of lesion in each particular organ creates its own variation in the isotope's pattern. In a brain scan the picture is of the blood pools carrying the isotope around. The isotope accumulates within a lesion to form a hot spot. Regions that are only lightly represented on the scan of a normal brain usually show up much more darkly when they contain a lesion.
What are liver scans?
A substance is injected in a vein and circulates through the entire bloodstream. Because of the size of the particle injected, it is trapped by the normal cells in the liver and spleen (the major organs in the body which will trap particles of that particular size) accumulating enough of it to give an image. If there is a lesion, it is seen as a "cold spot" because the abnormal liver cells aren't performing their normal trapping function. Liver scans are used to evaluate liver size, shape, and position and to detect the presence of lesions in the liver. Liver scans are usually routinely recommended before major tumor operations in many sites.
When is a thyroid scan done?
A thyroid scan is done ifa tumor is suspected after the doctor has examined the thyroid area with his hands. A small amount of radioactive material is swallowed or injected. A cold spot (showing decreased concentration of the radioisotope) makes the physician suspicious of cancer, although a great percentage of cold spots can also prove to be benign. A hot spot of great activity is usually a sign of a benign growth. A thyroid scan is used to determine the size, position, and function of the thyroid gland and to detect metastases of thyroid cancer. Sometimes two thyroid scan readings are taken usually at 2 and 24 hours after administration of the radioactive material.
Would having a radioactive scan be a problem for a pregnant woman?
The radioactive material can be carried to your baby through your circulation system. The amount of radiation is small, but you and the doctor should discuss the problem and the alternatives together. Be sure you tell the doctor if you are pregnant or think you are pregnant.
What is a gallium scan?
A gallium scan is used to determine if the cancer has spread to more than one area of the body because it is capable of showing rapidly dividing cells. One of the main uses of this test is in detecting lymph node involvement in lymphoma or other tumor masses.
Are lasers being used to diagnose cancer?
Yes. The carbon dioxide (C02 ) laser is being used to diagnose cancer of the vocal cord and colon, among others.