PET scan – Indications, Procedures, Results

Last updated: February 8, 2026 Medically reviewed by: RxHarun Orthopedic Specialist Doctor Reading time: 4 min read

Positron emission tomography; Tumor imaging – PET; PET/CT

A positron emission tomography scan is a type of imaging test. It uses a radioactive substance called a tracer to look for disease in the body.

A positron emission tomography (PET) scan shows how organs and tissues are working.

This is different than MRI and CT scans. These tests show the structure of, and blood flow to and from organs.
Machines that combine the PET and CT images, called a PET/CT, are commonly used.

How the Test is Performed

A PET scan uses a small amount of radioactive tracer. The tracer is given through a vein (IV). The needle is most often inserted on the inside of your elbow. The tracer travels through your blood and collects in organs and tissues. This helps the radiologist see certain areas more clearly.

You will need to wait as the tracer is absorbed by your body. This takes about 1 hour.

Then, you will lie on a narrow table that slides into a large tunnel-shaped scanner. The PET detects signals from the tracer. A computer changes the signals into 3D pictures. The images are displayed on a monitor for your health care provider to read.

You must lie still during the test. Too much movement can blur images and cause errors.

How long the test takes depends on what part of the body is being scanned.

How to Prepare for the Test

You may be asked not to eat anything for 4 to 6 hours before the scan. You will be able to drink water but not other beverages including coffee. If you have diabetes, your provider will tell you not to take your diabetes medicine before the test. These medicines will interfere with the results.

Tell your provider if:

You are afraid of close spaces (have claustrophobia). You may be given a medicine to help you feel sleepy and less anxious.
You are pregnant or think you might be pregnant.
You have any allergies to injected dye (contrast).

Always tell your provider about the medicines you are taking. Let your provider know about the medicines you bought without a prescription. Sometimes, medicines may interfere with the test results.

How the Test will Feel

You may feel a sharp sting when the needle with the tracer is placed into your vein.

A PET scan causes no pain. The table may be hard or cold, but you can request a blanket or pillow.

An intercom in the room allows you to speak to someone at any time.

There is no recovery time, unless you were given a medicine to relax.

Why the Test is Performed

A PET scan can reveal the size, shape, position, and some function of organs.

The most common use for a PET scan is for cancer, when it may be done:

To see how far cancer has spread. This helps to select the best treatment approach.
To check how well your cancer is responding, either during treatment or after treatment is completed.

This test can also be used to:

Check brain function
Identify the source of epilepsy in the brain
Show areas in which there is poor blood flow to the heart
Determine if a mass in your lung is cancerous or harmless

Normal Results

A normal result means there were no problems seen in the size, shape, or position of an organ. There are no areas in which the tracer has abnormally collected.

What Abnormal Results Mean

Abnormal results depend on the part of the body being studied. Abnormal results may be due to:

Change in the size, shape, or position of an organ
Cancer
Infection
Problem with organ function

Risks

The amount of radiation used in a PET scan is about the same amount as used in most CT scans. These scans use short-lived tracers, so the radiation is gone from your body in about 2 to 10 hours. Having many x-rays, CT or PET scans over time may increase your risk for cancer. However, the risk from any one scan is small. You and your doctor should weigh this risk against the benefits of getting a correct diagnosis for a medical problem.

Tell your provider before having this test if you are pregnant or breastfeeding. Infants and babies developing in the womb are more sensitive to radiation because their organs are still growing.

Rarely, people may have an allergic reaction to the tracer material. Some people have pain, redness, or swelling at the injection site.

Considerations

It is possible to have false results on a PET scan. Blood sugar or insulin levels may affect the test results in people with diabetes.

Most PET scans are now performed along with a CT scan. This combination scan is called a PET/CT. This helps find the exact location of the tumor.

Frequently Asked Questions

Is this article a replacement for a doctor?

No. It is educational content only. Patients should consult a qualified clinician for diagnosis and treatment.

When should I seek urgent care?

Seek urgent care for severe symptoms, rapidly worsening condition, breathing difficulty, severe pain, neurological changes, or any emergency warning sign.

References

Add references, clinical guidelines, textbooks, journal articles, or trusted medical sources here. You can edit this area later with a custom field named _rx_references.

Written by Dr. Harun Ar Rashid, MD - Arthritis, Bones, Joints Pain, Trauma, and Internal Medicine Specialist

Dr. Md. Harun Ar Rashid, MPH, MD, PhD, is a highly respected medical specialist celebrated for his exceptional clinical expertise and unwavering commitment to patient care. With advanced qualifications including MPH, MD, and PhD, he integrates cutting-edge research with a compassionate approach to medicine, ensuring that every patient receives personalized and effective treatment. His extensive training and hands-on experience enable him to diagnose complex conditions accurately and develop innovative treatment strategies tailored to individual needs. In addition to his clinical practice, Dr. Harun Ar Rashid is dedicated to medical education and research, writing and inventory creative thinking, innovative idea, critical care managementing make in his community to outreach, often participating in initiatives that promote health awareness and advance medical knowledge. His career is a testament to the high standards represented by his credentials, and he continues to contribute significantly to his field, driving improvements in both patient outcomes and healthcare practices. Born and educated in Bangladesh, Dr. Rashid earned his BPT from the University of Dhaka before pursuing postgraduate training internationally. He completed his MD in Internal Medicine at King’s College London, where he developed a special interest in inflammatory arthritis and metabolic bone disease. He then undertook a PhD in Orthopedic Science at the University of Oxford, conducting pioneering research on cytokine signaling pathways in rheumatoid arthritis. Following his doctoral studies, Dr. Rashid returned to clinical work with a fellowship in interventional pain management at the Rx University School of Medicine, refining his skills in image-guided joint injections and minimally invasive pain-relief techniques.