It is the most modern non-invasive diagnostic imaging method in Nuclear Medicine, which combines positron emission tomography (PET) with computed tomography (CT) in one machine, the PET/CT scanner, providing a hybrid imaging of the human body. It is an extremely sensitive imaging technique used primarily in oncology, but also in cardiology, neurology, and in infectious and inflammatory diseases.

The combination of these two techniques provides high-quality images combining the anatomical information provided by the computed tomographer (CT) with information about the metabolic activity of the studied tissues and organs at cellular and subcellular levels from the positron tomographer (PET).

Positron emission tomography - PET requires the use of molecules that are labeled with radioactive nuclides (radiotracers or radiopharmaceuticals). The quantities of radiopharmaceutical administered are extremely small (10-6 -10-9 g) and essentially cause no pharmacological side effects.

The in vivo recognition of metabolic changes using radiopharmaceuticals that mimic endogenous molecules provides the ability to detect potential pathological conditions at an earlier stage, since the biochemical alterations that PET imaging shows typically manifest before the anatomical alterations shown by conventional imaging methods (CT, MRI).

Almost all diseases alter the biological processes of the body. Positron emission tomography - PET is able to discover these changes in their early stages, often before symptoms appear.

Although the number of molecular tracers that can be radiolabeled with positron-emitting radionuclides is extremely large and clinical research applications number in the thousands, clinical practice has been mainly limited to the use of a glucose analog labeled with 18F (radioactive Fluorine), called 18F-fluorodeoxyglucose (18F-fluorodeoxyglucose) or abbreviated as 18F-FDG.

18F (radioactive Fluorine) has a short half-life (110 minutes) with less radiation exposure time to the patient compared to other commonly used radionuclides in Nuclear Medicine, such as 99mTechnetium (6 hours) and 201Thallium (72 hours).

18F-FDG PET is able to evaluate a fundamental change that is common to all malignant neoplasms and involves cellular glucose metabolism. Increased glucose uptake is one of the key changes associated with the high glycolytic rate of cancer cells. This characteristic formed the basis for FDG-PET imaging and clinical study in diagnosis, staging, restaging, prediction of treatment response, and indication of overall prognosis of neoplastic processes.

The PET scanner detects the radioactive decay of 18F-FDG and forms images of the glucose metabolic pathway in the tissues and organs of the human body. Cancer cells, due to their high glycolytic rate (increased uptake of 18F-FDG), appear as "bright" areas in the PET examination, resulting in in vivo (live) mapping of malignancy and semi-quantitative analysis of high glucose uptake (e.g., standardized uptake value, SUV) throughout the body.

Metabolic changes in neoplastic cells generally occur before tumor size increases, making FDG/PET an important diagnostic and therapeutic tool for monitoring response in oncology. Effective treatment plans can be initiated earlier with information about early developing cancers.

• The appropriate timing of the PET/CT study for maximum accuracy is crucial. To avoid false-positive results, the best time to conduct a PET/CT study is eight weeks after the completion of the last chemotherapy cycle, but definitely not less than three weeks.

• The minimum interval between PET imaging and ongoing chemotherapy should be approximately ten days and as close as possible to the next chemotherapy cycle.

This is usually determined by your referring physician, often in consultation with the physician performing the examination.

The desired timeframe is 12 weeks after the completion of radiation therapy (RT) to minimize the risk of false-positive findings, as morphological and metabolic changes due to RT are time-dependent, and RT-induced changes can be misinterpreted as recurring disease and vice versa.

The appropriate timing for the examination should be:

• One week after biopsy.
• Six weeks after surgery.
• This often depends on the body site and the type of surgical procedure.

The radiation received by the patient during the examination is the sum of radiation from the low-dose computed tomography (CT) plus the radiation from positron emission tomography (PET). This total radiation dose to the patient is approximately equivalent to what one receives from a full-body CT scan. However, newer imaging units with faster crystals, such as the cutting-edge Discovery IQ Gen 2 PET/CT by GE available at our center, featuring the PET Light Burst detector, represents a high-performance diagnostic system capable of producing exceptional quality images using reduced radioactive FDG dose without loss of diagnostic performance compared to older technology PET/CT systems, resulting in lower radiation exposure for the patient.

Yes, you can. The intravenously administered radiopharmaceutical (FDG) does not cause allergic reactions.

COVID-19 vaccination impacts the medical evaluation of cancer patients undergoing diagnostic imaging, particularly positron emission tomography with 18F-fluorodeoxyglucose (FDG) and computed tomography (PET/CT). Post-vaccination inflammatory changes may cause false-positive imaging findings.

• It has been noted that after vaccination in the deltoid muscle, ipsilateral regional lymphadenopathy may appear, primarily affecting axillary, but also supraclavicular or cervical lymph nodes.
• FDG-avid lymphadenopathy may be observed for 4 to 6 weeks or longer after the most recent vaccination dose. Therefore, PET/CT examination questionnaires should be revised to include details about vaccination dates, injection sites, and the type of vaccine administered.
• If possible, COVID-19 vaccination should be administered in the contralateral arm for patients with a history of breast cancer and head and neck cancer. These recommendations can help oncologists determine appropriate examination timing and advise breast cancer patients to get vaccinated on their healthy side to avoid unnecessary biopsies.