What is a PET Scan?
A Positron Emission Tomography (PET) scan is an advanced imaging technique that visualizes the metabolic activity of tissues by detecting differences in glucose metabolism, providing functional information that complements the anatomical details from other imaging modalities. 1
Basic Principles and Mechanism
- PET scanning uses radioactive tracers, most commonly 2-[18F]fluoro-2-deoxy-D-glucose (FDG), which is a glucose analog that competes with glucose at the level of transmembrane transporters 1
- After injection, FDG is taken up by cells with high metabolic activity (particularly cancer cells), phosphorylated by hexokinase, and trapped within the cells, allowing for visualization of areas with increased glucose metabolism 1
- The technique is based on Warburg's discovery that cancer cells demonstrate increased glycolytic activity under both aerobic and anaerobic conditions 1
- Neoplastic cells show higher FDG uptake due to increased expression of glucose transporters (particularly GLUT1) and enhanced activity of glycolytic enzymes 1
PET/CT Integration
- Modern PET scanning is typically performed using combined PET/CT devices that were first commercially introduced in 2001 1
- PET/CT scanners combine a multidetector helical CT scanner (for anatomical information) with a PET ring (for metabolic information) in the same gantry, allowing precise coregistration of both images 1
- This integration overcomes the limitations of PET-only scanning, which provides little information on exact anatomic localization of lesions 1
- PET/CT fusion provides both anatomical and functional imaging in a single examination, significantly improving diagnostic accuracy 2
Clinical Applications
According to the FDA label, FDG-PET is indicated for:
- Assessment of abnormal glucose metabolism to assist in evaluation of malignancy in patients with known or suspected abnormalities found by other testing modalities 3
- Evaluation of coronary artery disease and left ventricular dysfunction 3
- Identification of regions of abnormal glucose metabolism associated with epileptic seizures 3
In oncology, PET/CT is valuable for:
- Diagnosis of indeterminate lesions, with significantly higher accuracy than CT alone in differentiating benign from malignant lesions 1
- Staging of cancers, particularly for lymph node assessment and detection of distant metastases 1
- Detection of recurrent disease and monitoring response to therapy 1
- Identification of primary tumors in cases of occult cancer, with detection rates of 25-57% of primary sites 1
Performance Characteristics
- In lung cancer diagnosis, PET demonstrates high sensitivity (96%, range 83-100%), specificity (79%, range 52-100%), and accuracy (91%, range 86-100%) 1
- For occult primary tumors, a meta-analysis showed PET/CT detected primary tumors in 37% of cases, with pooled sensitivity and specificity both at 84% 1
- PET/CT has become the standard imaging approach for many cancers, providing both metabolic and anatomic information in a single examination 2
Limitations and Pitfalls
- False-negative results can occur in:
- False-positive results can occur in:
- PET/CT is not recommended for routine screening but may be warranted in specific clinical scenarios 1
Technical Considerations
- PET/CT scanning involves both a low-dose CT component for attenuation correction and anatomic localization, and a higher-dose diagnostic CT when full diagnostic quality is needed 1
- Radiation exposure comes from both the CT component and the injected radiotracer 1
- Advances include improved spatial resolution, development of new radiopharmaceutical probes, and applications in molecular biology 1