PET-CT
PET-CT (Positron Emission Tomography – Computed Tomography) is an advanced nuclear medicine method that brings together metabolic-activity imaging and anatomical imaging within a single system. In the field of oncology, it is recognised as one of the principal tools evaluated in the processes of cancer imaging, staging and treatment monitoring.
What Is PET-CT ?
PET-CT consists of the combination of two separate imaging technologies. The PET (Positron Emission Tomography) component makes the cellular metabolic activity in the body visible through radiopharmaceutical agents. The CT (Computed Tomography) component, in turn, provides anatomical structure information in the same session. This combination allows the imaging not only of morphological changes but also of metabolic differences at the tissue level.
The most widely used radiopharmaceutical in oncology is FDG (18F-fluorodeoxyglucose). This radioactively labelled glucose derivative is taken up intensively by tissues with high metabolic activity. The PET component maps this uptake, while the CT component determines its anatomical location.
In addition to cancer imaging, PET-CT is a method that can also be used in some neurological and cardiac assessments. In which clinical situation and for which purpose it is used is determined individually for each patient.
How Is a PET-CT Scan Performed ?
A PET-CT scan is a painless and non-invasive process consisting of several steps, from the preparation stage to the acquisition of the images.
- Radiopharmaceutical administration. FDG or the other agent to be used is administered intravenously. This step takes a short time.
- Waiting period. Generally 45 to 60 minutes are allowed for the agent to distribute to the tissues. During this time the patient is advised to remain still and calm; physical activity may affect FDG distribution.
- Image acquisition. The patient lies still on the device; PET and CT images are obtained simultaneously. The imaging duration is generally completed within 20 to 30 minutes.
- Reporting. The images obtained are evaluated by the nuclear medicine specialist and interpreted together with the clinical team.
The total process, including the waiting period, is generally completed within 1.5 to 2 hours. The great majority of patients can continue their daily activities after the scan.
Who Is PET-CT Not Suitable For ?
Although PET-CT is an imaging method that can be used in many clinical situations, its application is an option that needs to be evaluated separately in certain patient groups.
Pregnant and Breastfeeding Individuals
Since radiation exposure is involved in the PET-CT application, its use during pregnancy is not recommended as a rule. In clinical situations deemed essential, the potential risk and benefit are evaluated by the relevant specialist. In breastfeeding individuals, breastfeeding may need to be paused for a certain period after the agent is administered; obtaining individual instructions from the clinician on this matter is recommended.
High Blood Sugar and Diabetes
FDG is a glucose-based molecule. When the blood sugar level is high, the tissue distribution and uptake of the agent may be adversely affected; this may make image interpretation more difficult. Individuals with diabetes are advised to discuss blood sugar management with their clinician before the scan.
Impaired Kidney Function
Some agents used in PET-CT are excreted by the kidneys. In individuals with impaired kidney function, the necessity and safety of the application must be evaluated separately; alternative imaging methods may come into consideration.
Individuals Who Have Difficulty Remaining Still
During a PET-CT scan it is necessary to remain still for a certain period. Severe pain, anxiety in enclosed spaces or certain neurological conditions that restrict movement may make this process difficult. In such situations, the clinician evaluates the appropriate approach, including the option of sedation.
Children
In children, PET-CT is applied only in situations the clinician deems necessary and with dose adjustment specific to the child. Minimising radiation exposure is a priority assessment criterion in paediatric cases.
After Intense Physical Activity
Heavy physical activity performed before the scan increases glucose consumption in the muscle tissues, affecting FDG distribution and potentially making image interpretation more difficult. For this reason, avoiding intense exercise within the 24 hours before the scan is recommended.
This information provides a general framework. Whether or not PET-CT can be applied is determined only through individual clinical assessment. The final decision rests with the clinician.
What to Do Before PET-CT ?
Preparation before the scan directly affects image quality and the correct distribution of the agent. The generally recommended preparation steps are as follows.
- Fasting period. Generally, not eating for at least 6 hours before the scan is requested. Drinking water is permitted; sugary drinks and foods should be avoided.
- Blood sugar control. Blood sugar being within the normal range is important for FDG to distribute in the desired manner. The preparation process may differ for individuals with diabetes.
- Avoiding exercise. Heavy physical activity within the 24 hours before the scan is not recommended.
- Metal accessories. Metal jewellery and accessories should be removed before entering the PET-CT device.
- Current medications. Information about the medications being used should be shared in advance with the team conducting the scan.
- Pregnancy and breastfeeding status. This information must be reported at the appointment stage.
Individual preparation instructions may differ according to the radiopharmaceutical applied and the patient’s clinical condition. Precise instructions are conveyed by the clinician.
How Long Does PET-CT Take ?
The PET-CT process consists of several stages; the total duration may vary according to the type of disease and the protocol applied.
- Agent administration. A few minutes
- Waiting period. Generally 45 to 60 minutes
- Image acquisition time. 20 to 30 minutes
- Total process. Approximately 1.5 to 2 hours
In some cases, additional imaging or a delayed-phase scan may be required; in this case the total duration may be extended. The reporting time varies according to the institution and the scan workload.
What to Do After PET-CT ?
After the scan is completed, drinking plenty of water is recommended to support the excretion of the radiopharmaceutical from the body.
- Contact with infants and pregnant individuals. Avoiding close contact with infants and pregnant individuals for a few hours after the scan is recommended.
- Breastfeeding. Breastfeeding individuals should pause breastfeeding for the period recommended by their clinician.
- Mild side effects. Some individuals may experience temporary headache or nausea after the scan. If these symptoms persist, getting in touch with the clinician is recommended.
- Normal activity. Most patients can continue their daily activities after the scan. Individual instructions are conveyed by the clinician.
In Which Situations Is PET-CT Required ?
The main clinical situations in which PET-CT may come into consideration as an assessment tool can be summarised as follows; however, whether it is applied in each case is determined through individual clinical assessment.
- Evaluating the extent of the disease following a cancer diagnosis (staging)
- Monitoring the response to chemotherapy, radiotherapy or other systemic treatments
- Investigating whether disease activity has re-emerged after treatment is completed (suspicion of recurrence)
- Contributing to the determination of the target tumour volume in radiotherapy planning
- Examining brain metabolism in some neurological diseases (such as Alzheimer’s and epilepsy)
- Evaluating certain cardiac conditions
PET-CT is a method recommended only as a result of individual clinical assessment. It is not applicable in every disease and at every stage; the decision rests with the clinician.
Differences Between PET-CT, MR and CT
These three methods are not alternatives to one another, but complementary tools intended to answer different clinical questions.
- CT. Images anatomical structure quickly and over a wide area. It is frequently preferred in the evaluation of bone and lung. It involves radiation.
- MR. Does not involve radiation. Its soft-tissue differentiation is high; it stands out in the evaluation of the brain, spinal cord, pelvis and musculoskeletal system. It may be evaluated as a safer option in pregnant individuals.
- PET-CT. In addition to the anatomical image, it visualises tissue metabolism. It may allow the evaluation of foci with increased metabolic activity even when a change in size or shape has not yet become apparent. It involves radiation.
Which method is used is determined by the clinician according to the type of disease and the clinical question.
Related to PET-CT — Ga-68 PSMA Imaging
Ga-68 PSMA is a nuclear medicine imaging method that uses a radiopharmaceutical different from traditional FDG-based PET-CT and that may come into consideration particularly in clinical assessments related to prostate cancer. Both methods run on the same PET-CT infrastructure; the difference in the agent used is determined according to the clinical objective.
Frequently Asked Questions About PET-CT
Does PET-CT give a definitive result for a cancer diagnosis? PET-CT is a tool that images an increase in metabolic activity; however, it does not on its own serve to establish a definitive cancer diagnosis. The imaging findings are interpreted together with clinical assessment and, where necessary, pathological examination. The final diagnostic decision is based on an integrated evaluation of this data.
Is a PET-CT scan a painful procedure? No. Pain is not felt during the PET-CT application. While the intravenous administration of the agent involves a momentary needle sensation, the imaging stage is entirely painless. Patients must remain still throughout the procedure.
How long does it take for the radiation to leave the body? Radiopharmaceuticals with a short half-life, such as FDG, are generally excreted from the body within 6 to 12 hours. For this reason, special isolation is not required in most patients; however, avoiding close contact with infants and pregnant individuals is recommended for the first few hours.
Is PET-CT safe for children? In paediatric cases, PET-CT is applied only in situations the clinician deems necessary and with dose adjustment specific to the child. Minimising radiation exposure is a priority assessment criterion in paediatric cases.
Can PET-CT be performed during pregnancy? As a rule, it is not a recommended method. However, in cases of clinical urgency it may be decided upon under a doctor’s supervision, taking the risk-benefit balance into account. This situation requires individual clinical assessment.
When are PET-CT results evaluated? After the images are reported by the nuclear medicine specialist, they are evaluated together with the clinical team. The reporting time varies according to the institution and the scan workload. Reflecting the results in the treatment plan is part of the multidisciplinary assessment process.
Would You Like Information About Your PET-CT Results ?
For the interpretation of your PET-CT imaging, its place in your oncology process or an assessment regarding the next steps, you can reach the clinic of Dr. Hasan Morcalı. You can use the phone and WhatsApp line at +90 531 559 25 68, or visit the website for an online appointment.
The information on this page is for general information purposes and does not constitute a diagnosis or treatment recommendation. Consulting a physician for an assessment of your health condition is recommended.
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