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Nuclear Medicine



Nuclear Medicine

What is Nuclear Medicine?
Taking a Picture

Most of us have had a routine x-ray, like a chest x-ray at sometime in the past. During this type of test, a beam of radiation in the form of x-rays comes out of a machine and passes through your body. Your body blocks the x-rays and casts a "shadow" on the special film behind you - much like your hand blocks the light and creates a shadow on the wall. Some tissues, such as bones, block the path of X-rays more than others giving your doctor a picture inside your body.

The diagnostic tests done in the nuclear medicine department are different. Sometimes referred to as "nuke med" or "nukes," these tests have one major thing in common: low dose radioactive materials are taken into your body either by injection, swallowed as pills, or inhaled as a gas. The radiation then leaves your body as gamma rays which are detected by a specialized Geiger counter called a scintillation or gamma camera. This camera then creates an image for your doctor such as a picture of your liver or thyroid gland. Over 10 million nuclear medicine imaging studies are performed in the United States each year with over 100 different nuclear medicine imaging procedures available today. Some of the more common nuclear medicine exams include diagnosis and treatment of thyroid problems, cardiac stress tests to analyze heart function, bone scans for orthopedic injuries, lung scans for blood clots, and liver and gall bladder procedures to diagnose abnormal function or blockages.

Nuclear Medicine Physician

The Nuclear Medicine Physician is a usually a hospital based specialist. After obtaining his medical (MD) degree, these physicians undergo additional training making them eligible for examination by the American Board of Nuclear Medicine or the American Board of Radiology. This training includes special instruction in the safe handling, storage and administration of radiopharmaceuticals (radionuclides). The nuclear medicine physician reviews the request from your doctor and then "approves" the nuclear medicine study as medically necessary and appropriate. He instructs the technologists in how to modify the image for your special needs and decides if the scan is technically adequate. After the computer processes your test data, the nuclear medicine physician interprets the study and sends a report to your referring physician.

Nuclear Medicine Technologist

The Nuclear Medicine Technologist assists the nuclear medicine physician and is specially trained to operate the complicated gamma cameras and computers used for diagnosis in nuclear medicine. Typically, technologists have had two or more years of training in nuclear medicine and are certified by the Nuclear Medicine Technology Certification Board (NMTCB) or the American Registry of Radiologic Technologists (ARRT-NM). The nuclear medicine technologist performs the patient examination under the supervision of the nuclear medicine physician.

How Are These Tests Performed?

Most nuclear medicine exams begin when the technologist gives you an injection. The injection in your arm is just like a blood test, although usually a smaller needle is used so it hurts less. This injection contains a radioactive material - called an isotope, radiopharmaceutical, or tracer. This tracer is attached to a specific chemical that concentrates in a particular part of the body. This interaction, which involves the absorption and incorporation of these substances into living tissue, is referred to as the uptake of the isotope.

For example, the thyroid gland in the neck selectively attracts iodine. If iodine molecules are tagged with a radioactive tracer, they will accumulate in the thyroid gland making it "light up" when scanned. This thyroid scan allows your doctor to check the thyroid gland for swelling or tumors.

Examples of a few of the common radioactive tracers used to accomplish imaging include the following:

  • Technetium MDP for bone scans
  • Technetium MAA, Xenon or Technetium DTPA for lung scans
  • technetium or iodine for thyroid uptakes and scans
  • Cardiolite, thallium or myoview for cardiac imaging.
After the injection, you will be asked to wait between 15 minutes to four hours, occasionally longer, before scanning can begin - depending on the type of test. The scans or "pictures" usually take between 15 minutes to a little over an hour. The scintillation camera used in performing the test does not emit radiation or get hot. It simply detects gamma rays that come from the radioactive tracer in the patient's body to form an image. The camera detectors are placed as close to the patient as possible in order to obtain high quality images. However, the detectors will not apply any painful pressure to the patient. The scanning process does not hurt - you simply lie still on a table for several minutes for each picture.

Isn't Radioactivity Dangerous?

No, the amount of radiation in a nuclear medicine procedure is similar to that received during a routine x-ray. Used in proper amounts, radioactive materials have been shown to be extremely safe in adults and may even be used in children. The overall safety record of Nuclear Medicine is unmatched by any other medical field. These tests will not make you "glow it the dark" and you need not fear about being around other people afterwards. Nuclear medicine procedures are painless and do not require anesthesia.

Taking a Picture

Gamma cameras may have one, two or even three separate heads to detect and measure radioactivity. Imaging can be done in one of two ways: planar or Single photon emission computerized tomography (SPECT).

Planar imaging, the older method produces a picture in two dimensions. To simplify this description, think of a Halloween skeleton. It shows all of the basic bones (ribs, legs, skull, etc.), but if you move to the side, you don't get a sense of depth.

SPECT imaging, however, is a type of scanning that allows greater detail. SPECT also may be called ECT (emission computerized tomography) or tomographic scanning. In SPECT, the gamma camera acquires the imaging data (radioactivity). Sophisticated computers process the data to allow the doctor to see a specific area in not just one plane, but several. This tomography enables the viewer to see the volume of the area and allows the image to be finely examined in multiple planes.

For example, a loaf of bread may be cut in slices from one end to the other (front to back or even side to side). SPECT imaging allows the area of the body also to be "cut" in these ways. In a body organ or structure, images taken from end to end (head to toe) are called transverse, axial or transaxial images. The cuts from side to side (or left to right) are sagittal images. Slicing that occurs top to bottom (from the front of the body to the back) is known as the coronal image.

Being able to create pictures or images in multiple dimensions lets the nuclear physician define not only whether there is an abnormal area but also its location in all three dimensions. This type of imaging can be done alone or in addition to the basic planar study. Not all gamma cameras can produce SPECT images but all do have the ability to produce planar images.

Nuclear Medicine Can Also Be Used As Treatment

Nuclear medicine also may be used in therapeutic ways. Two common uses are to treat patients with hyperthyroidism (Graves' disease) or cancer. As in diagnostic studies, radioactive iodine is used but in larger amounts or doses.

How do I prepare for a Nuclear Medicine Scan?

Unless you are told otherwise, you don't need to do anything special before your nuclear medicine test. Tests of the stomach, gall bladder and heart stress test do require you to skip breakfast. Otherwise, you may eat normally and take any medication you normally take. When your appointment is made, you will be told how much time to allow for your procedure, and about any other preparation or restrictions, which may apply.

After the Examination

After your scan is completed you are able to immediately return to your normal daily routine - there are no effects of the small amounts of radioactive materials, so you will feel perfectly normal. It is reasonable to drink lots of fluid and void frequently for 24 hours after the scan, as many of the tracers are cleared from the body via the urinary tract. Likewise the amounts are so small that there are no restrictions on your being around other people.

How long will it take to get my results?

After the nuclear medicine doctor dictates the final report, it is transcribed, reviewed, signed, and sent to your family doctor. The nuclear staff will do everything it can to have a written report in your doctor's hand within three to five days. Emergency scans or unexpected results are usually called in immediately. Some hospitals have acquired a new recording technology, which allows your doctor to dial a telephone number and listen to your report immediately after it has been dictated even before it is sent for typing.

 

Radiology vs Nuclear Medicine

Radiology
  • In Radiology, radiation is outside of the patient. An image is formed when a patient stands between a x-ray tube and x-ray film.
  • Each picture taken requires exposure to a small dose of radiation. So, taking extra pictures means more patient radiation
  • Some newer methods in radiology such as ultrasound and magnetic resonance do not rely on x-radiation to produce their images. CT scan does.

Nuclear Medicine
  • In Nuclear Medicine, the radiation is inside the patient, usually having been given by injecting a small amount of radioactive material intravenously.
  • Images (pictures) of where the radiotracer is in the body -- and how long it stays there -- are made using a special camera, called a nuclear medicine gamma camera.
  • Images are made using a special camera, which detects radiation, but does not itself produce radiation. Taking extra pictures does not mean more patient radiation.

 

Copyright:

Kenneth Humphreys, R.T.
Office Manager T R Imaging, P.C.
Sewickley, PA 15143

Web page: http://speed.city-net.com/~trimage
Email: trimage@city-net.com


Text & Images Courtesy of Three Rivers Endoscopy Center
© Dr. Robert Fusco, Three Rivers Endoscopy Center, All Rights Reserved





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