A PET scan is an advanced medical imaging test that helps doctors observe how tissues and organs are functioning inside the body. Unlike many imaging tests that mainly show the structure of organs, PET imaging can reveal changes in metabolic activity.
This makes PET particularly valuable in areas such as cancer diagnosis and treatment monitoring. Today, PET is commonly combined with CT imaging as a PET/CT scan, providing both functional and anatomical information in a single examination.
If your doctor has recommended a PET scan, understanding how it works and how to prepare can make the experience easier.
What Is a PET Scan?
PET stands for Positron Emission Tomography.
The examination uses a small amount of a radioactive substance called a radiotracer. One of the most commonly used tracers is fluorodeoxyglucose (FDG), a substance related to glucose.
Cells in the body use glucose for energy. Some tissues and abnormal cells can have higher metabolic activity and therefore take up more of the tracer.
A PET scanner detects signals from the tracer and creates images showing its distribution throughout the body.
This gives doctors information about how tissues are functioning, rather than only what they look like.
What Is a PET/CT Scan?
Modern PET imaging is frequently combined with Computed Tomography (CT).
The two technologies provide different types of information.
PET shows metabolic or functional activity within tissues, while CT provides detailed information about anatomical structures.
Combining them allows doctors to correlate an area of increased or decreased metabolic activity with its precise anatomical location.
This is why PET/CT has become an important imaging technique in oncology and several other areas of medicine.
What Is a PET Scan Used For?
PET imaging has several clinical applications, but it is particularly associated with cancer evaluation.
A doctor may recommend PET/CT for purposes including:
- Detecting or evaluating certain cancers
- Determining the extent of disease
- Assessing whether cancer has spread
- Planning certain treatments
- Evaluating response to treatment
- Checking for possible recurrence
- Selected neurological investigations
- Selected cardiac investigations
Whether PET is appropriate depends on the particular disease and clinical situation.
Not every cancer or medical condition requires a PET scan.
Why Is PET Used for Cancer?
Cancer cells can behave differently from normal cells, and many types of cancer have increased glucose metabolism.
FDG PET imaging can identify areas where tracer uptake is higher than expected.
This information can help doctors evaluate disease activity and may complement findings from CT, MRI, biopsy and other investigations.
PET/CT can also be useful when assessing how certain cancers respond to treatment. Changes in metabolic activity can sometimes provide clinically useful information even when structural changes are less obvious.
However, increased FDG uptake does not automatically mean cancer. Infection, inflammation and some normal tissues can also show increased tracer uptake.
PET findings therefore need to be interpreted by qualified specialists alongside other clinical information.
How Should You Prepare for a PET Scan?
Preparation is important because factors such as food intake, physical activity and blood glucose can influence the distribution of FDG.
Your diagnostic centre will provide instructions based on your examination.
Typical PET scan preparation may include:
- Fasting for several hours before the scan
- Drinking plain water as instructed
- Avoiding strenuous exercise before the examination
- Taking regular medication only as advised
- Keeping warm and relaxed before tracer administration
You should tell the imaging team if you have diabetes, are pregnant or think you may be pregnant, or are breastfeeding.
Patients with diabetes may require specific scheduling and preparation instructions because blood glucose levels can affect FDG PET imaging.
Always follow the instructions provided specifically for your appointment.
What Happens During a PET/CT Scan?
A PET/CT examination involves several stages.
1. Initial preparation
When you arrive, the imaging team may review your medical history and check whether you’ve followed the required preparation.
For FDG PET examinations, your blood glucose level may also be checked.
2. Radiotracer injection
A small amount of radiotracer is administered, usually through a vein.
3. Uptake period
After receiving the tracer, you’ll normally rest quietly while it distributes through the body.
The uptake period commonly takes around an hour, although the exact timing depends on the examination protocol.
Talking, walking or other unnecessary muscle activity may sometimes be restricted during this period.
4. Image acquisition
You’ll lie on the scanner table, which moves through the PET/CT scanner.
It is important to remain still while images are being acquired.
The imaging portion is generally shorter than the total appointment because much of the time is spent preparing and allowing the tracer to distribute.
Is a PET Scan Painful?
The scanning procedure itself is generally painless.
You may feel brief discomfort from the needle used to administer the tracer.
During imaging, you’ll need to lie relatively still on the scanner table. Some people may find remaining in one position uncomfortable, but the examination itself does not normally cause pain.
If you experience significant anxiety or discomfort, tell the imaging team.
Does a PET Scan Use Radiation?
Yes.
PET imaging involves a radioactive tracer, and the CT component of a PET/CT examination uses X-rays.
The amount of radiation depends on the examination protocol and the CT technique being used.
Doctors recommend PET/CT when the expected diagnostic benefit justifies the exposure.
Patients should inform the imaging team if they are pregnant, may be pregnant or are breastfeeding so that appropriate medical advice can be provided.
The International Atomic Energy Agency provides further information about radiation protection in nuclear medicine.
PET Scan vs CT Scan: What’s the Difference?
PET and CT provide different kinds of information.
A CT scan primarily shows anatomy. It can reveal the size, shape and location of structures or abnormalities.
A PET scan primarily provides functional information, showing patterns of metabolic activity.
PET/CT combines these two datasets so that metabolic findings can be accurately located within the body’s anatomy.
Depending on the condition, doctors may use CT, PET/CT, MRI or a combination of imaging methods.
PET Scan vs MRI
MRI uses magnetic fields and radiofrequency signals to create detailed anatomical images and does not use ionising radiation.
PET uses a radioactive tracer to evaluate physiological or metabolic processes.
Because the two examinations answer different clinical questions, one isn’t simply a replacement for the other.
Your doctor selects the appropriate imaging method according to the condition being investigated.
What Do PET Scan Results Show?
PET images show how the radiotracer has accumulated throughout the body.
Areas with relatively increased tracer uptake may appear more prominent on the images. These areas are sometimes informally called “hot spots.”
However, tracer uptake must be interpreted carefully.
Normal organs can naturally show significant FDG uptake, and inflammation or infection can sometimes produce increased activity.
A nuclear medicine physician or appropriately qualified imaging specialist interprets the scan in combination with the CT findings, medical history and other investigations.
The resulting report is then provided to the referring doctor.
What Should You Do After a PET Scan?
Most patients can generally return to normal activities after the examination unless they have received different instructions.
Because the tracer gradually leaves the body, you may be advised to drink plenty of water following the scan.
There may also be temporary precautions regarding close contact with pregnant women or young children depending on the radiotracer and examination protocol.
Follow the instructions provided by the nuclear medicine team after your scan.
PET/CT Scan at Elite Scan Centre, Thrissur
PET/CT provides doctors with a combination of anatomical and metabolic information that can be valuable in the evaluation and management of several medical conditions.
At Elite Scan Centre, Thrissur, PET/CT imaging is available as part of advanced diagnostic imaging services.
Patients referred for PET/CT receive preparation instructions according to the examination requested so that the scan can be performed under appropriate conditions.
If your doctor has recommended a PET/CT scan, contact Elite Scan Centre before your appointment to confirm availability, preparation requirements, previous reports to bring and any special instructions relating to medications or diabetes.
Frequently Asked Questions
How long does a PET scan take?
The scan itself may take considerably less time than the overall appointment. Preparation and tracer uptake typically mean patients should expect to spend a few hours at the imaging centre, depending on the examination protocol.
Can I eat before a PET scan?
For many FDG PET examinations, fasting is required for several hours beforehand. Follow the specific preparation instructions given by your diagnostic centre.
Can diabetic patients undergo a PET scan?
Yes, but special preparation may be necessary because blood glucose levels can affect FDG distribution. Inform the imaging centre about diabetes when scheduling the examination.
Does a PET scan confirm cancer?
PET can provide important information about metabolic activity, but abnormal tracer uptake does not by itself confirm cancer. Findings need to be interpreted alongside clinical information and other investigations.
Is PET/CT the same as a PET scan?
PET/CT combines PET functional imaging with CT anatomical imaging. Most modern clinical PET examinations are performed using integrated PET/CT systems.
Do I need to bring previous reports?
Previous CT, MRI, PET scans, biopsy reports and relevant medical records can be useful for comparison and interpretation. Ask the imaging centre which documents you should bring.
