Nuclear scans use radioactive substances to see structures and functions inside your body. They use a special camera that detects radioactivity.

Before the test, you receive a small amount of radioactive material. You may get it as an injection. Sometimes you swallow it or inhale it. Then you lie still on a table while the camera makes images. Most scans take 20 to 45 minutes.

Nuclear scans can help doctors diagnose many conditions, including cancers, injuries, and infections. They can also show how organs like your heart and lungs are working.

Nuclear medicine is a medical specialty that uses radioactive tracers (radiopharmaceuticals) to assess bodily functions and to diagnose and treat disease. Specially designed cameras allow doctors to track the path of these radioactive tracers. Single Photon Emission Computed Tomography or SPECT and Positron Emission Tomography or PET scans are the two most common imaging modalities in nuclear medicine.

Nuclear medicine uses radioactive material inside the body to see how organs or tissue are functioning (for diagnosis) or to target and destroy damaged or diseased organs or tissue (for treatment).

Nuclear medicine vs common imaging procedures using x-rays: how they work

Although we all are exposed to ionizing radiation every day from the natural environment, added exposures like those from nuclear medicine procedures can slightly increase the risk of developing cancer later in life.

Talk to your healthcare provider to decide on the best procedure for your health needs and discuss any concerns you have.

What You Should Know

Your healthcare provider may recommend a nuclear medicine procedure to diagnose or treat a health problem.

When It’s Used for Diagnosis

Nuclear medicine can show how the organs or tissues are functioning. For most diagnostic procedures, a tracer, which contains the radioactive material, is injected, swallowed, or inhaled. Then the healthcare provider or radiologist (a healthcare professional with special training to use radiation in healthcare) uses a radiation detector to see how much of the tracer is absorbed or how it reacts in the organ or tissue. This will give the provider information about how well it is functioning.

Common uses of nuclear medicine for diagnosis include:

• Scans of the heart, lung, kidneys, gallbladder, and thyroid

In a type of nuclear medicine called positron emission tomography (PET), the tracer is used to show the natural activity of cells, providing more detailed information on how organs are working and if there is damage to the cells. PET scans are often combined with computed tomography (CT) scans or magnetic resonance imaging (MRI) which provide three-dimensional images of the organ.

Common uses of PET scans include:

• Diagnosing heart disease, Alzheimer’s disease, and brain disorders
• Getting detailed information about cancerous tumors to decide the best treatment option

When it’s used for treatment

When used in treatment, the tracer targets a harmful organ or tissue and radioactivity damages or stops the growth of its cells.

Two common uses of nuclear medicine for treatment include radioactive iodine therapy and brachytherapy (a form of radiation treatment where a sealed radiation source is placed inside or next to the area requiring treatment).

What To Expect

Before the procedure

• You will receive a tracer either through an injection, inhalation (breathing it in), or through a pill or substance to swallow.
• You may need to wait a certain amount of time for the tracer to travel through your body to the tissue or organ being diagnosed or treated.

During the procedure

• You may be asked to lie down on a table or to walk on a treadmill.
• A camera that detects radiation will be placed over your body to collect information on how the tracer is acting in an organ or tissue.

After the procedure

• The radiologist and your healthcare provider use this information to see how an organ or tissue is functioning.
• The radioactive material from the tracer will pass out of your body in a few hours to a few days, depending on the type of tracer and test you receive.

When You Go Home

Right after your procedure, your body is very slightly radioactive (giving off radiation) but this wears off with time and is not directly harmful to others. Your healthcare provider may give you special instructions to help reduce any small amounts of radiation you give off from exposing others such as washing your hands frequently. Drinking a lot of water may help the radioactive material leave your body quicker.

• Before you leave, ask your healthcare provider if there are steps you should take to protect others or if you have any concerns or questions about information you were given.
• Talk to your healthcare provider if you are currently breastfeeding.

The ionizing radiation dose for these procedures is typically higher than the dose received from a common x-ray procedure. There are always some possible risks from exposure to ionizing radiation in healthcare, but these procedures should be used when the health benefits outweigh these risks.

Benefits and Risks of Nuclear Medicine

Benefits

• Provides information on how organs, tissues, and cells are working. (Other common imaging procedures only show the structures.)
• Can be used also in targeted treatments to kill or damage harmful or cancerous cells, reduce the size of tumors, or reduce pain.

Risks

• Radiation doses are usually higher than in common imaging like x-rays. This means these procedures are slightly more likely to increase the possibility you may get cancer later in life.
• Some nuclear medicine procedures are longer and use more radiation than others. These could cause skin reddening and hair loss.
• You may give off small amounts of radiation right after your procedure and need to take steps to protect others from exposure.

Radioactive tracers are made up of carrier molecules that are bonded tightly to a radioactive atom. These carrier molecules vary greatly depending on the purpose of the scan. Some tracers employ molecules that interact with a specific protein or sugar in the body and can even employ the patient’s own cells. For example, in cases where doctors need to know the exact source of intestinal bleeding, they may radiolabel (add radioactive atoms) to a sample of red blood cells taken from the patient. They then reinject the blood and use a SPECT scan to follow the path of the blood in the patient. Any accumulation of radioactivity in the intestines informs doctors of where the problem lies.

For most diagnostic studies in nuclear medicine, the radioactive tracer is administered to a patient by intravenous injection. However a radioactive tracer may also be administered by inhalation, by oral ingestion, or by direct injection into an organ. The mode of tracer administration will depend on the disease process that is to be studied.

Approved tracers are called radiopharmaceuticals since they must meet FDA’s exacting standards for safety and appropriate performance for the approved clinical use. The nuclear medicine physician will select the tracer that will provide the most specific and reliable information for a patient’s particular problem. The tracer that is used determines whether the patient receives a SPECT or PET scan.

SPECT scans are primarily used to diagnose and track the progression of heart disease, such as blocked coronary arteries. There are also radiotracers to detect disorders in bone, gall bladder disease and intestinal bleeding. SPECT agents have recently become available for aiding in the diagnosis of Parkinson's disease in the brain, and distinguishing this malady from other anatomically-related movement disorders and dementias.

The major purpose of PET scans is to detect cancer and monitor its progression, response to treatment, and to detect metastases. Glucose utilization depends on the intensity of cellular and tissue activity so it is greatly increased in rapidly dividing cancer cells. In fact, the degree of aggressiveness for most cancers is roughly paralleled by their rate of glucose utilization. In the last 15 years, slightly modified radiolabeled glucose molecules (F-18 labeled deoxyglucose or FDG) have been shown to be the best available tracer for detecting cancer and its metastatic spread in the body.

A combination instrument that produces both PET and CT scans of the same body regions in one examination (PET/CT scanner) has become the primary imaging tool for the staging of most cancers worldwide.

Recently, a PET probe was approved by the FDA to aid in the accurate diagnosis of Alzheimer's disease, which previously could be diagnosed with accuracy only after a patient's death. In the absence of this PET imaging test, Alzheimer's disease can be difficult to distinguish from vascular dementia or other forms of dementia that affect older people.

SPECT imaging instruments provide three-dimensional (tomographic) images of the distribution of radioactive tracer molecules that have been introduced into the patient’s body. The 3D images are computer generated from a large number of projection images of the body recorded at different angles. SPECT imagers have gamma camera detectors that can detect the gamma ray emissions from the tracers that have been injected into the patient. Gamma rays are a form of light that moves at a different wavelength than visible light. The cameras are mounted on a rotating gantry that allows the detectors to be moved in a tight circle around a patient who is lying motionless on a pallet.

PET scans also use radiopharmaceuticals to create three-dimensional images. The main difference between SPECT and PET scans is the type of radiotracers used. While SPECT scans measure gamma rays, the decay of the radiotracers used with PET scans produce small particles called positrons. A positron is a particle with roughly the same mass as an electron but oppositely charged. These react with electrons in the body and when these two particles combine they annihilate each other. This annihilation produces a small amount of energy in the form of two photons that shoot off in opposite directions. The detectors in the PET scanner measure these photons and use this information to create images of internal organs.

What is Single Photon Emission Computed Tomography (SPECT)?

SPECT imaging instruments provide three-dimensional (tomographic) images of the distribution of radioactive tracer molecules that have been introduced into the patient’s body. The 3D images are computer generated from a large number of projection images of the body recorded at different angles. SPECT imagers have gamma camera detectors that can detect the gamma rayemissions from the tracers that have been injected into the patient. Gamma rays are a form of light that moves at a different wavelength than visible light. The cameras are mounted on a rotating gantry that allows the detectors to be moved in a tight circle around a patient who is lying motionless on a pallet.

What is Positron Emission Tomography (PET)?

PET scans also use radiopharmaceuticals to create three-dimensional images. The main difference between SPECT and PET scans is the type of radiotracers used. While SPECT scans measure gamma rays, the decay of the radiotracers used with PET scans produce small particles called positrons. A positron is a particle with roughly the same mass as an electron but oppositely charged. These react with electrons in the body and when these two particles combine they annihilate each other. This annihilation produces a small amount of energy in the form of two photons that shoot off in opposite directions. The detectors in the PET scanner measure these photons and use this information to create images of internal organs.

A procedure that produces pictures (scans) of structures inside the body, including areas where there are cancer cells. Scintigraphy is used to diagnose, stage, and monitor disease. A small amount of a radioactive chemical (radionuclide) is injected into a vein or swallowed. Different radionuclides travel through the blood to different organs. A machine with a special camera moves over the person lying on a table and detects the type of radiation given off by the radionuclides. A computer forms an image of the areas where the radionuclide builds up. These areas may contain cancer cells. Also called radionuclide scanning.

The production of an image obtained by cameras that detect the radioactive emissions of an injected radionuclide as it has distributed differentially throughout tissues in the body. The image obtained from a moving detector is called a scan, while the image obtained from a stationary camera device is called a scintiphotograph.

Graphic tracing over a time period of radioactivity measured externally over the kidneys following intravenous injection of a radionuclide which is taken up and excreted by the kidneys.

The measurement of visualization by radiation of any organ after a radionuclide has been injected into its blood supply. It is used to diagnose heart, liver, lung, and other diseases and to measure the function of those organs, except renography, for which radioisotope renography is available.

The total radiation dose conferred to patients by the majority of radiopharmaceuticals used in diagnostic nuclear medicine studies is no more than what is conferred during routine chest x-rays or CT exams. There are legitimate concerns about possible cancer induction even by low levels of radiation exposure from cumulative medical imaging examinations, but this risk is accepted to be quite small in contrast to the expected benefit derived from a medically needed diagnostic imaging study.

Like radiologists, nuclear medicine physicians are strongly committed to keeping radiation exposure to patients as low as possible, giving the least amount of radiotracer needed to provide a diagnostically useful examination.

Research in nuclear medicine involves developing new radio tracers as well as technologies that will help physicians produce clearer pictures.

Developing new tracers

A bacterial infection is a common complication of implanting a medical device into the body. With more patients receiving device implants than ever before, infections from implants are a growing problem. Currently, these types of infections are diagnosed based on physical exam results and microbial cultures. However, such techniques are only useful for detecting late stage infections, which usually have already become difficult to treat. Conversely, medical devices may be needlessly removed when doctors mistake inflammation that is a normal consequence of surgery with inflammation due to an infection. NIBIB is currently supporting research to develop a new family of PET imaging contrast agents that are taken up specifically by bacterial cells, but not human cells. Such imaging agents would allow doctors to visualize early-stage bacterial infections so they can be easily treated, thereby reducing the number of implanted devices that are unnecessarily removed. They also have the potential to be used for diagnosing infections not associated with medical devices, for example, those affecting the heart or lungs.

Creating new technology

A SPECT tracer is currently available for accurate diagnosis of Parkinson's disease. However, the small region in the brain that must be imaged requires a dedicated brain SPECT imager with special gamma cameras to provide high resolution, which adds to the cost of the procedure. NIBIB is supporting research to create an inexpensive adapter for the conventional SPECT imagers that most hospitals already have. The adapter would allow standard clinical SPECT cameras to provide the same high resolution that currently only dedicated SPECT brain imaging systems can produce. These improvements would make Parkinson’s diagnosis less costly and more widely available.

Most nuclear medicine procedures involve using small amounts of radioactive materials to detect or treat diseases.

About Radiation Used in Nuclear Medicine

Nuclear medicine procedures help detect and treat diseases by using a small amount of radioactive material, called a radiopharmaceutical. Some radiopharmaceuticals are used with imaging equipment to detect diseases. Radiopharmaceuticals can also be placed inside the body near a cancerous tumor to shrink or destroy it.

A positron emission tomography (PET) scan is an example of a nuclear medicine procedure used to diagnose disease. A PET scan uses a radioactive substance that is inserted into the bloodstream and travels to a specific organ. Doctors use a special camera to watch how the tracer moves. The camera sends information to a computer, which takes pictures as the tracer moves thorough the organ. Doctors use the images to detect problems with the organ.

Radiopharmaceuticals are also used to treat disease by shrinking tumors and killing cancerous cells. During a brachytherapy procedure doctors surgically place small radioactive “seeds” near or inside a cancerous tumor. The radiation from the seeds helps destroy the nearby cancer cells.

Different radioactive elements are absorbed differently by different organs. For example, iodine is absorbed by the thyroid gland, so iodine-131 is used to diagnose and treat thyroid cancer. The doctors choose the best radiopharmaceutical for the part of the body they need to diagnose or treat.

What You Can Do

• Inform your doctor about past treatments. Let the doctor know about other nuclear medicine tests or treatments.
• Tell your doctor if you are pregnant. Let the doctor know if you are pregnant, might be pregnant, or are breastfeeding.
• Discuss the risks. It’s important to talk to your doctor about the risks associated with using nuclear medicine with the doctor or the technician before the procedure.
• Follow all instructions given by the doctor. After certain procedures, patients may need to take extra precautions for a few days as the radiopharmaceutical is eliminated from their bodies. Be sure to talk with your doctor about post-treatment guidelines.