Chest PET Scan: When to Go for It

A chest PET scan is an advanced imaging test that delivers information regarding both the structure and metabolic activity of tissues, generally done as an integrated PET-CT scan. It can be helpful for doctors' further evaluation/staging of selected abnormalities already identified on CT or other imaging,  if a person has a current case of lung cancer, or if any cancer has spread to the lymph nodes or other parts of their body.

PET-CT is not usually the first imaging test for an undiagnosed lung abnormality. Chest computed tomography (CT) is often used to assess the extent of pulmonary disease and lung nodules, and PET-CT may be helpful if further information is desirable regarding the metabolic activity or extent of disease. In Molecular Diagnostics and Therapy, PET-CT imaging can be employed to assist with the assessment and staging of a selected range of cancers and other disorders as needed in a clinical setting.

What Is a Chest PET-CT Scan?

A chest PET-CT is a combination of two imaging technologies, Positron Emission Tomography (PET) and Computed Tomography (CT) scan. A small amount of radioactive tracer is injected into a vein, and PET is used to gather information from metabolic activity. 

Fluorodeoxyglucose (FDG) is a substance related to the sugar glucose that is used most often in PET scans for cancer. The CT basically gives doctors a lot of fine detail on the anatomy; they can see where the increased and decreased tracer uptake is in the structure. When combined, PET and CT can give complementary information that may assist a doctor in assessing a suspected and/or known cancer.

When Is a Chest PET Scan Recommended?

When considering previous test results and medical history, several reasons for a chest PET scan may merit consideration.

Evaluation of a Suspicious Lung Nodule

A lung nodule can be found during a chest X-ray or CT scan. Many pulmonary nodules are benign, while some are cancerous. FDG-PET-CT could be considered in the further evaluation of some indeterminate nodules, especially those sized and clinically appropriate to be evaluated with PET-CT in the first place. Decisions are made by the size and characteristics of the nodules, age, and other risk factors of a patient.

Staging of Confirmed Lung Cancer

A PET-CT scan for lung cancer can be useful after a diagnosis and makes use of one of the most important features of the scan: staging. Staging is important to see if the cancer (tumor) is contained in the lung or has migrated to the nearby lymph nodes or other parts of the body. PET–CT can be used to give metabolic information as well as anatomical information, and can help direct treatment planning.

Checking for Spread of Cancer

PET-CT can be used to help determine if there are areas of high metabolism away from the main lung mass. Depending on the clinical situation, this can include lymph nodes and distant sites. Findings from PET, however, are not specific for cancer. There is also a possibility of increased FDG uptake due to infection/inflammation; therefore, the following studies may need to be used with CT findings to interpret the findings on PET-CT.

Evaluating Response to Treatment

In some cases, a PET-CT can be performed in individuals to find out whether a known cancer has responded to treatment or not. It can give information on changes in metabolic activity, which may be added to changes observed by anatomical imaging.

Checking for Recurrence

PET-CT can be ordered in other patients with cancer who have previously received treatment when clinical or imaging history suggests that the disease has returned. It is programmed by the kind of cancer as well as the outcomes of other examinations and previous treatment.

Is PET-CT the Same as a Chest CT?

No. Chest CT provides detailed anatomical images, while PET-CT combines CT with PET to provide information about metabolic activity. PET-CT also involves radiation from both the radiotracer and CT component. Chest computed tomography (CT) provides detailed anatomical images of the lungs, airways, blood vessels, and other tissues in the chest. It is a crucial imaging exam for identifying lung nodules and numerous other lung diseases.

These anatomical images and information on tissue metabolism are combined in a PET CT. This may be of value when doctors want to look at the metabolic activity of a lesion or lesions and the extent of disease in the body if they already know or are aware of having cancer. The two examinations thus perform different functions and cannot substitute for each other.

Chest PET-CT Procedure

This information helps patients understand what they can expect from the chest PET-CT procedure.

1. Preparation

Patients are typically instructed to fast a few hours before an FDG PET-CT and can usually have water. Preparation may differ for different tracers and exam procedures. A blood sugar level can be tested prior to an FDG examination as well. Patients should inform the medical team if the patient has diabetes, medications previously been administered, has recently suffered illness, has allergies or pregnancy/breastfeeding.

2. Tracer Injection

A small amount of radioactive tracer is injected into a vein, usually through an IV line.

3. Uptake Period

The patient usually rests quietly for about 30–60 minutes while the tracer circulates and is taken up by tissues. During this time, reducing activity and talking may be a part of the examination procedure.

4. Scanning

The patient is placed on a scanner table inside a PET/CT scanner that is used to move the patient through the scanner. The patient needs to remain still during imaging. 

The PET and CT parts of the examination are done together. The scanning portion commonly takes about 30 minutes; the total appointment is longer because of preparation and the tracer uptake period.

What Does a PET-CT Show in Lung Cancer?

A PET-CT can provide information about metabolic activity in a lung lesion and other areas of the body. In lung cancer evaluation, it may help doctors assess:

• The primary lung lesion
• Nearby lymph nodes
• Possible spread to other parts of the body
• Metabolic activity before treatment
• Changes after treatment

Remember that PET-CT can be a useful part of the staging and treatment plan but should not supplant tissue diagnosis if a biopsy is needed. When tissue confirmation is required, biopsy or another appropriate tissue-sampling method may be used to confirm the diagnosis.

Does Increased PET Uptake Always Mean Cancer?

No, increased uptake on a PET scan does not automatically mean that a lesion is cancerous. FDG can accumulate in areas of inflammation or infection as well as in many cancers. Conversely, some cancers may show relatively low FDG uptake. Therefore, PET-CT findings must be interpreted in the context of the patient's symptoms, CT findings, medical history, and other investigations.

PET-CT Test Details

The exact PET-CT scan test details depend on the tracer and the reason for the examination. For a commonly performed FDG PET-CT:

• Fasting may be required for several hours.
• Blood glucose may be checked.
• A small amount of radioactive tracer is injected through an IV.
• A resting period of about 30–60 minutes may follow.
• The patient needs to remain still during imaging.
• The actual scanning portion is commonly around 30 minutes.
• Drinking water after the examination may help the tracer leave the body through urine.

The diagnostic centre provides specific preparation and aftercare instructions.

Is a Chest PET-CT Safe?

PET-CT involves exposure to radiation from both the radioactive tracer and CT component. The amount is controlled according to the examination protocol, and the test is generally performed when the expected clinical benefit justifies the exposure. Patients should tell their healthcare team if they are pregnant, may be pregnant, or are breastfeeding before the examination.

Conclusion

A chest PET scan can give useful information about the metabolism of the tissues, in addition to the anatomical information obtained from a CT scan. PET-CT can help evaluate suspicious lung masses and assess the extent of disease, as part of the overall staging process for diagnosed lung cancer, to help identify areas that may represent regional or distant spread to another part of the body, or to help evaluate suspected recurrence; distinguishing recurrence from a new primary tumour may require correlation with other imaging and sometimes tissue sampling.

A lung cancer PET scan is typically performed in addition to other tests and procedures to help with the diagnosis and staging of the cancer. A biopsy or other tissue-sampling method may be needed to confirm cancer when tissue diagnosis is required. MolecularDiagnostics and Therapy has PET-CT that is used for appropriate clinical indications, and the protocol is chosen based on the need for the exam.