General Nuclear Medicine

What is General Nuclear Medicine

Nuclear medicine is a subspecialty within the field of radiology that uses very small amounts of radioactive material to diagnose or treat disease and other abnormalities within the body.

Nuclear medicine imaging procedures are noninvasive and usually painless medical tests that help physicians diagnose medical conditions. These imaging scans use radioactive materials called a radiopharmaceutical or radiotracer.

Depending on the type of nuclear medicine exam you are undergoing, the radiotracer is injected into a vein, swallowed by mouth or inhaled as a gas and eventually collects in the area of your body being examined, where it gives off energy in the form of gamma rays. This energy is detected by a device called a gamma camera, a (positron emission tomography) PET scanner and/or probe. These devices work together with a computer to measure the amount of radiotracer absorbed by your body and to produce special pictures offering details on both the structure and function of organs and other internal body parts.

In some centers, nuclear medicine images can be superimposed with computed tomography (CT) or magnetic resonance imaging (MRI) to produce special views, a practice known as image fusion or co-registration. These views allow the information from two different studies to be correlated and interpreted on one image, leading to more precise information and accurate diagnoses.

Nuclear medicine also offers therapeutic procedures such as radioactive iodine (I-131) therapy that uses radioactive material to treat medical conditions affecting the thyroid gland.

What are some common uses of the procedure?

Physicians use nuclear imaging to visualize the structure and function of an organ, tissue, bone or system of the body.

Nuclear medicine imaging scans are performed to:

• analyze kidney function
• visualize heart blood flow and function (such as a myocardial perfusion scan)
• scan lungs for respiratory and blood flow problems
• identify blockage in the gallbladder
• evaluate bones for fracture, infection, arthritis and tumors
• determine the presence or spread of cancer
• identify bleeding into the bowel
• locate the presence of infection
• measure thyroid function to detect an overactive or underactive thyroid
• investigate abnormalities in the brain

Nuclear medicine therapies include:

• Radioactive iodine (I-131) therapy used to treat hyperthyroidism, Graves’ disease, a goiter, thyroid nodules, and thyroid cancer

How should I prepare?

You may be asked to wear a gown during the exam or you may be allowed to wear your own clothing.

Women should always inform their physician or technologist if there is any possibility that they are pregnant or if they are breastfeeding their baby. See the Safety page for more information about pregnancy and breastfeeding related to nuclear medicine imaging.

You should inform your physician of any medications you are taking as well as vitamins and herbal supplements and if you have any allergies. Also inform your doctor about recent illnesses or other medical conditions.

Jewelry and other accessories should be left at home if possible, or removed prior to the exam because they may interfere with the procedure.

You will receive specific instructions based on the type of scan you are undergoing.

See the Radioactive iodine (I-131) therapy page for instructions on how to prepare for the procedure.

What does the equipment look like?

Most nuclear medicine procedures use a gamma camera, a specialized camera encased in metal that is capable of detecting radiation and taking pictures from different angles. It may be suspended over the examination table from a tall, moveable post or it may be part of a metal arm that hangs over the table. The camera could also be located within a large, doughnut-shaped scanner similar in appearance to a computed tomography (CT) scanner. In some imaging centers, the gamma camera is located beneath the exam table and out of view.

A positron emission tomography (PET) scanner is a large machine with a round, doughnut shaped hole in the middle, similar to a CT unit. Within this machine are multiple rings of detectors that record the emission of energy from the radiotracer in your body.

A nearby computer aids in creating the images from the data obtained by the camera or scanner.

A probe is a small hand-held device resembling a microphone that can detect and measure the amount of the radiotracer in a small area of your body.

There is no equipment used during radioactive iodine therapy.

How does the procedure work?

With ordinary x-ray examinations, an image is made by passing x-rays through your body from an outside source. In contrast, nuclear medicine procedures use a radioactive material called a radiotracer, which is injected into your bloodstream, swallowed by mouth or inhaled as a gas. This radioactive material accumulates in the organ or area of your body being examined, where it gives off a small amount of energy in the form of gamma rays. A gamma camera, PET scanner, or probe detect this energy and with the help of a computer create pictures offering details on both the structure and function of organs and other parts of your body.

Unlike other imaging techniques, PET does not produce clear structural images but rather a rendering that reflects the level of chemical activity in your body. Areas of greater intensity, called hot spots, indicate where large amounts of the radiotracer have accumulated and where there is a high level of chemical activity. Less intense areas, or cold spots, indicate a smaller concentration of radiotracer and less chemical activity.

In radioactive iodine (I-131) therapy, radioactive iodine (I-131) is swallowed and absorbed into the thyroid gland where it destroys the organ's cells.

How is it performed?

Nuclear medicine imaging is usually performed on an outpatient basis, but is often performed on hospitalized patients as well.

You will be positioned on an examination table. If necessary, a nurse or technologist will insert an intravenous (IV) line into a vein in your hand or arm.

Depending on the type of nuclear medicine exam you are undergoing, the dose of radiotracer is then injected intravenously, swallowed by mouth or inhaled as a gas.

It can take several seconds to several days for the radiotracer to travel through your body and accumulate in the organ or area being studied. As a result, imaging may be done immediately, a few hours later, or even several days after you have received the radioactive material.

When it is time for the imaging to begin, the gamma camera will take a series of images. The camera may rotate around you or it may stay in one position and you will be asked to change positions in between images. While the camera is taking pictures, you will need to remain still for brief periods of time.

If a probe is used, this small hand-held device will be passed over the area of the body being studied to measure levels of radioactivity. Other nuclear medicine tests measure radioactivity levels in blood, urine or breath.

The length of time for nuclear medicine procedures varies greatly, depending on the type of exam. Actual scanning time for nuclear imaging exams can take from 20 minutes to several hours and may be conducted over several days.

When the examination is completed, you may be asked to wait until the technologist checks the images in case additional images are needed.

If you had an intravenous line inserted for the procedure, it will be removed.

During radioactive iodine (I-131) therapy, which is most often an outpatient procedure, the radioactive iodine is swallowed in a single dose, in capsule or liquid form.

What will I experience during and after the procedure?

Most nuclear medicine procedures are painless.

If the radiotracer is given intravenously, you will feel a slight pin prick when the needle is inserted into your vein for the intravenous line. When the radioactive material is injected into your arm, you may feel a cold sensation moving up your arm, but there are generally no other side effects.

When swallowed, the radiotracer has little or no taste. When inhaled, you should feel no differently than when breathing room air or holding your breath.

With some procedures, a catheter may be placed into your bladder, which may cause temporary discomfort.

It is important that you remain still while the images are being recorded. Though nuclear imaging itself causes no pain, there may be some discomfort from having to remain still or to stay in one particular position during imaging.

Unless your physician tells you otherwise, you may resume your normal activities after your nuclear medicine scan.

Through the natural process of radioactive decay, the small amount of radiotracer in your body will lose its radioactivity over time. In many cases, the radioactivity will dissipate over the first 24 hours following the test and pass out of your body through your urine or stool. You may be instructed to take special precautions after urinating, to flush the toilet twice and to wash your hands thoroughly. You should also drink plenty of water to help flush the radioactive material out of your body.

Following radioactive iodine therapy, a patient may experience some mild pain in the region of the thyroid gland. You should ask your physician to recommend an over-the-counter pain reliever to treat this pain, should it occur.

Who interprets the results and how do I get them?

A radiologist who has specialized training in nuclear medicine will interpret the images and forward a report to your referring physician.

What are the benefits vs. risks?

Benefits

• The information provided by nuclear medicine examinations is unique and often unattainable using other imaging procedures.
• For many diseases, nuclear medicine scans yield the most useful information needed to make a diagnosis or to determine appropriate treatment, if any.
• Nuclear medicine is much less traumatic than exploratory surgery.

Risks

• Because the doses of radiotracer administered are small, diagnostic nuclear medicine procedures result in minimal radiation exposure. Thus, the radiation risk is very low compared with the potential benefits.
• Nuclear medicine has been used for more than five decades, and there are no known long-term adverse effects from such low-dose exposure.
• Allergic reactions to radiopharmaceuticals may occur but are extremely rare.
• Injection of the radiotracer may cause slight pain and redness which should rapidly resolve.
• Women should always inform their physician or radiology technologist if there is any possibility that they are pregnant or if they are breastfeeding their baby. See the Safety page for more information about pregnancy, breastfeeding and nuclear medicine exams.

What are the limitations of General Nuclear Medicine?

Nuclear medicine procedures can be time-consuming. It can take hours to days for the radiotracer to accumulate in the part of the body under study and imaging may take up to several hours to perform, though new equipment is available that can substantially shorten the procedure time.

The resolution of structures of the body with nuclear medicine may not be as clear as with other imaging techniques, such as CT or MRI. However, the information gained from nuclear medicine is unequaled in other imaging techniques.