What Is a PET-CT Scan?

PET-CT imaging is a modern procedure that combines two imaging technologies into one: Positron Emission Tomography (PET) and Computed Tomography (CT). PET shows activity and metabolism in tissues, while CT provides detailed images of the body's internal structures. The combination of these two types of information is used to help a physician look not only at the location of abnormal areas but also at their activity level.

PET-CT is widely used in cancer evaluation and management, especially for some cancers, to determine if the cancer has metastasized (spread), to plan cancer treatment, and to look for signs of response to cancer treatment. Also, it is used in specific heart and neurological diseases as appropriate in individual cases.

What Is a PET-CT Scan?

A PET-CT scan is a PET scan performed under the same conditions as those of a computed tomography (CT) scan, which also uses a computed tomography scanner. A tiny dose of radioactive material, called a radiotracer, is administered before the scan, typically intravenously. Many PET scans use a glucose analogue labeled with fluorine-18, known as FDG (fluorodeoxyglucose). Areas that are undergoing metabolic activities different from those of normal tissues appear differently on PET images. 

However, the uptake rate does not only have to do with cancer, as it occurs in some normal tissues or inflammatory diseases as well. The CT gives information about the size, shape, and location of organs and other structures. PET-CT information is used together to relate metabolic activity with anatomical information.

Why Is PET-CT Done?

A PET-CT is recommended for several reasons, primarily to examine cancer. It aids in the diagnosis or evaluation of types of cancer, and is helpful in determining if a cancer has spread to other areas of the body and in providing information that could be beneficial in planning treatment. PET-CT is used after, or during treatment, to see how the disease is responding and, in rare cases, to detect signs of recurrence. Whether PET-CT has a primary or secondary role is dependent on the kind of disease, the clinical question asked, prior tests performed, and the therapy planned.

How Does PET-CT Work?

PET and CT scans both give different information. The PET scan examines biological or metabolic activity. A radiotracer enters the bloodstream and is taken up by tissues. The PET scanner records the signals emitted by the radiotracer and generates images of where the tracer is located in the body. A CT scan produces detailed cross-sectional images of the structures in the body using X-rays. The images are fused back together, and the doctor compares the region of the increased or decreased uptake with the corresponding anatomical region. This gives data that can be more beneficial than that obtained from either kind of imaging alone.

PET-CT Scan Procedure

Typically, the PET-CT procedure starts with preparation before injection of the radiotracer. The patient should not consume food for a few hours before the PET-CT and is instructed to drink plenty of water before the scan as appropriate for the type of PET-CT and radiotracer. An IV line is typically inserted into a vein, and the radiotracer is injected by a health care professional. The patient then lies still so that the tracer passes through the body, concentrating in the tissues that are being examined. This is a typical time of waiting of 30-60 minutes.

The patient then rests on a table that is used to conduct the scan. The table runs in the PET-CT scanner, and the images are taken. During the scan, it is very important not to be in movement, to avoid the image being affected. The scanning time is usually approximately 30 minutes, although this can be longer for some imaging procedures, and it can depend on the examination.

How Should You Prepare for a PET-CT Scan?

Depending on the type of PET-CT, one may need to prepare for the CT. Patients are usually advised to not eat for a certain time before an FDG PET-CT exam and will be able to drink water during the procedure. Blood glucose might be especially critical for FDG PET-CT as fluctuations in blood glucose or insulin levels may impact the distribution of the tracer and assessment results of the examination.

If they have been diagnosed with diabetes, have been prescribed any medication, have had any recent illness, may have had any type of allergy, or have been pregnant or breast feeding should be conveyed to the medical team before examination. Specific preparations are explained by the imaging centre according to the procedure of the examination.

What Are the Benefits of PET-CT?

One very important advantage of PET-CT is that the functional information that is provided by PET can be overlaid onto the anatomical information provided by CT. This can aid in identifying abnormal metabolic rate locations and, indeed, their position in the body. PET-CT can be used to evaluate the disease, stage the cancer, plan treatment, and assess response to treatment in cancer care. One added advantage is that PET and CT exams can be performed at the same time, and the two types of data can be correlated without having to book a separate appointment for the two scans.

Is PET-CT Only Used for Cancer?

No, PET-CT is used in oncology but has other uses in medicine. Depending on the radiotracer and clinical need, PET imaging can be used to assess some heart diseases and neurological disorders. As a case in point, PET can be used to evaluate metabolism and function in the brain or heart, depending on the radiotracer and clinical indication. The type of radiotracer and imaging procedure depend on the condition that is being studied.

Is PET-CT Safe?

PET-CT involves exposure to radiation because it uses a radioactive tracer and CT X-rays. The radiotracer used for PET is given in a small amount and loses its radioactivity over time. The route of elimination depends on the radiotracer. As with other medical imaging procedures, doctors consider the expected clinical benefit before recommending the examination. Patients should inform the medical team if they are pregnant or breastfeeding because special precautions may be required.

What Does a PET-CT Report Show?

A PET-CT report describes findings seen on the PET and CT images. Depending on the examination, the report may discuss areas of increased or decreased tracer uptake, anatomical abnormalities, and other relevant findings. The report is interpreted by a suitably trained specialist and should be considered together with the patient's symptoms, medical history, previous investigations, and other clinical information.

Importantly, an area of increased tracer uptake does not automatically mean cancer. Some infections, inflammation, and normal tissues can also show increased uptake. Therefore, PET-CT findings may need to be correlated with other tests or clinical information.

What Happens After a PET-CT Scan?

After the scan, most patients can return to their normal activities unless their healthcare provider gives different instructions. Drinking adequate water may help the body eliminate the radiotracer through urine. The radiotracer loses radioactivity naturally over time, and the healthcare team may provide specific instructions depending on the radiotracer and examination.

Limitations of PET-CT

PET-CT is a valuable diagnostic tool, but it does not provide all the information needed in every medical situation. PET images generally have lower anatomical resolution than CT or MRI, although PET provides functional information that these imaging techniques may not provide in the same way. In addition, blood glucose levels can affect some PET examinations, and very small or less metabolically active abnormalities may not always be clearly detected. For this reason, doctors may recommend other imaging tests, laboratory tests, or a biopsy depending on the suspected condition.

PET-CT at Molecular Diagnostics and Therapy

At Molecular Diagnostics and Therapy, advanced diagnostic imaging services include Digital PET-CT, which can provide both functional and anatomical information in a single examination. The appropriate PET-CT protocol and radiotracer depend on the patient's medical condition and the clinical question. Our diagnostic team follows the required preparation and imaging protocols to support doctors in evaluating disease and planning further management.

Conclusion

PET-CT is a powerful study which integrates the functional information provided by the PET with the detailed anatomical images obtained with the CT. PET-CT is widely used in cancer evaluation for disease assessment, staging, treatment planning, and assessment of treatment response where clinically appropriate 

The PET-CT process includes giving the patient the radiotracer, then a waiting time and imaging. However, good preparation is necessary, particularly when taking an examination with FDG, and patients must follow the instructions of their healthcare team. Although very useful, PET-CT is not a definitive single test to diagnose all conditions. Doctors use the information from PET scans and other tests along with symptoms, medical history, and, if needed, tissue diagnosis to determine the patient's disease.