Short Answer

A PET scan, or Positron Emission Tomography scan, is a medical imaging technique that uses radioactive tracers to show how organs and tissues inside the body are functioning. It helps doctors study blood flow, oxygen use, and chemical activity. The tracer releases positrons, which interact with electrons to produce signals that a scanner detects and converts into images.

PET scans are widely used to detect cancer, examine heart diseases, study brain disorders, and monitor how well treatments are working. Because it shows activity inside the body, not just structure, a PET scan provides more detailed information than many other imaging methods.

Detailed Explanation :

PET scan

A PET scan, short for Positron Emission Tomography, is an advanced medical imaging technique used to study the function and activity of organs and tissues in the human body. Unlike X-rays or CT scans, which mainly show structure, a PET scan reveals how different parts of the body are working at a molecular and cellular level. This makes it extremely useful in diagnosing diseases, planning treatments, and monitoring the progress of therapies.

A PET scan uses a small amount of a radioactive substance called a tracer or radioactive isotope. The tracer emits positrons (positively charged particles) as it decays. When these positrons meet electrons in the body, they produce gamma rays. A special scanner detects these gamma rays and uses them to create detailed images that show the activity inside the organs.

How a PET scan works

A PET scan follows a few important steps:

1. Injection of radioactive tracer

A small amount of a radioactive tracer is injected into the patient’s bloodstream. The tracer is usually a form of glucose, such as Fluorine-18, because active tissues use more glucose.

2. Movement of tracer inside the body

Once inside the body, the tracer travels through the bloodstream and is absorbed by organs and tissues depending on their activity level. Tissues with higher activity absorb more tracer.

3. Emission of positrons

The radioactive tracer emits positrons, which interact with electrons in the surrounding tissues.

4. Production of gamma rays

When a positron meets an electron, they annihilate each other, producing two gamma rays that travel in opposite directions.

5. Detection by PET scanner

The PET scanner detects these gamma rays and records the locations where they were produced.

6. Formation of images

A computer processes the signals and creates colour-coded images showing areas of high or low activity.

Why PET scans are useful

PET scans allow doctors to understand how the body is working internally. They show the function of organs rather than just their appearance. For this reason, PET scans are extremely valuable in medical diagnosis and research.

Some key uses include:

• detecting cancer at early stages
• studying brain disorders like Alzheimer’s disease
• checking blood flow to the heart
• finding infections
• analysing how the body’s metabolism works

Applications of PET scans

1. Cancer detection and treatment

Cancer cells grow quickly and use more glucose than normal cells. PET scans highlight these high-activity areas, helping doctors:

• detect cancer early
• determine if cancer has spread
• check whether treatment like chemotherapy is working
• plan surgery or radiation therapy

PET scans are especially important for cancers of the lung, breast, colon, and lymph nodes.

2. Brain imaging

PET scans are one of the best tools for studying the brain. They help diagnose and monitor:

• Alzheimer’s disease
• Parkinson’s disease
• epilepsy
• brain tumours
• stroke
• memory and behavioural disorders

Because the brain uses glucose as its main energy source, PET scans clearly show which parts of the brain are active or damaged.

3. Heart disease diagnosis

Doctors use PET scans to study how blood flows to the heart. The scan helps identify:

• damaged heart tissue
• reduced blood supply
• coronary artery disease
• effects of heart attack

This information helps plan treatment such as bypass surgery or stent placement.

4. Research and drug development

PET scans are used in medical research to study how drugs move through the body. Scientists also use PET to understand:

• how the brain processes emotions
• how diseases progress
• how new medicines affect the body

Advantages of PET scans

PET scans have several important advantages:

• show organ function, not just structure
• detect diseases at very early stages
• help monitor treatment progress
• provide accurate and detailed images
• useful for whole-body scanning

Limitations of PET scans

Despite their benefits, PET scans also have limitations:

• use radioactive materials (small amount but still controlled)
• expensive compared to other scans
• require specialised equipment and trained experts
• cannot show very fine structural details
• may not be suitable for pregnant women

Often, PET scans are combined with CT or MRI scans for more complete information.

PET-CT and PET-MRI

Modern hospitals use combined machines such as:

• PET-CT scan
• PET-MRI scan

These devices give both functional and structural images in one test. This improves accuracy and reduces the time needed for diagnosis.

Safety of PET scans

PET scans are generally safe because:

• the amount of radioactive tracer used is very small
• the tracer decays quickly and leaves the body through urine
• the radiation dose is similar to other imaging tests

Doctors still avoid PET scans for pregnant women or cases where radiation must be limited.

Conclusion

A PET scan is a powerful medical imaging technique that uses radioactive tracers to study how organs and tissues function. It provides detailed information about metabolism, blood flow, and cellular activity, making it extremely useful in diagnosing cancer, brain disorders, and heart diseases. With its ability to detect early changes in the body, a PET scan plays a vital role in modern medicine, treatment planning, and research.