When doctors want to see deeper into your body, PET-CT is a popular choice. It is a super powerful imaging tool that is widely used in diagnosis, staging, and monitoring of various diseases, particularly in oncology, cardiology, and neurology. It’s especially useful in detecting cancer, guiding treatment plans, and understanding conditions affecting the heart or brain. But how does it actually work — and why does it matter so much? Let’s figure it out.
What is PET-CT exactly? The answer is quite straightforward. It is just PET plus CT! This means before we get into PET-CT, we have to learn about both PET and CT.
Taking advantage of radioisotope signals, PET is an imaging method that enables the measurement of the change in metabolic activities and other physiological activities in vivo (Fowler & Volkow, 2022). All the radioisotopes are positron emitters that will emit positrons to keep them stable. Gamma rays will be produced and detected by sensors, which will be mapped. After millions of records, a clear map that provides information about the quantity and location of the positrons in the body will be produced (Basu et al., 2011).
When interpreting the PET scanning image, the hot spots and the cold spots are what we need to focus on. Hot spots are the regions with bright colors (white, yellow, orange, and red). In these regions, the uptake rate of the radiotracer is higher, which indicates a higher rate of metabolic activity. Therefore, these regions will represent cancer, inflammation, or active regions of our body. Cold spots, on the contrary, represent dead tissue and reduced function that lower metabolism in that region (TerPogossian et al., 1980).
Computed tomography (CT) is what we are more familiar with. It is a frequently used and widely available non-invasive imaging modality and has been applied in measuring the size of body tissues like bones, muscles, and brains. X-rays will be emitted from different directions, pass through the body, and be received by the detector, forming images of projections of the body in different directions. Through computer calculation based on the X-ray attenuation characteristics of the tissues within the voxel, sizes of targeted tissues will be measured (Mazonakis & Damilakis, 2016).
With the basic knowledge of both PET and CT, it is easy to understand that PET-CT is just a combination of the two technologies. It can trace both the change in metabolism of the tissue and the size of it. On the other hand, the combination of these two technologies is quite revolutionary. One of the biggest limitations of a PET scan is its lack of spatial resolution and a clear anatomical reference frame. This defect hinders PET from accurately presenting the anatomic structure of lesion tissues, which negatively affects diagnosing diseases such as cancers and Alzheimer’s disease. Fortunately, CT addresses this problem. When combined, PET shows functional activity and CT shows structure, helping distinguish between normal and pathological signals. This fusion is especially important in cancer diagnosis, where identifying the exact location and stage of a tumor is critical for accurate treatment planning (Basu et al., 2011). With different kinds of radiotracers, PET-CT can be used in different aspects of imaging, including glucose metabolism, tumor proliferation, myocardial perfusion imaging, skeletal imaging, and brain imaging (Anand et al., 2009).
With a lot of advantages, PET-CT is pervasively used around the world. Besides improving the accuracy of diagnosis, PET-CT also contributes to the early detection of certain cancers and the early detection of cancer recurrence, impacting patient management by assisting in defining potential candidates for curative surgery, planning the appropriate surgical or radiotherapy approach, and referring patients with unresectable disease to other therapeutic options (Israel & Kuten, 2007).
It is clear that PET-CT is a life-saving tool for humans. However, there are still limitations we need to overcome. One of the major limitations of PET-CT as a cancer screening tool is its radiation exposure, which poses a potential health risk, especially when used routinely in healthy people. A standard PET-CT scan involves both a radioactive tracer and a CT scan. It is a combined radiation dose that can be significantly higher than most diagnostic imaging tests. This raises concerns about the long-term effects of repeated exposure, particularly in asymptomatic populations. Additionally, high cost and questionable cost-effectiveness further limit its practicality. PET-CT scans are expensive. When they detect abnormalities, they often lead to further testing and interventions, but many of them are unnecessary due to false positives or clinically insignificant findings. Moreover, PET-CT has limited sensitivity for certain cancers, especially those that are slow-growing or have low glucose metabolism, such as early-stage prostate cancer or some lung adenocarcinomas. These cancers may not show up clearly on PET scans, which could give patients a false sense of security and delay diagnosis. Overall, while PET-CT has diagnostic value in high-risk or symptomatic individuals, its limitations make it a controversial and potentially problematic tool for routine cancer screening in the general population (Schöder & Gönen, 2007).
Despite its remarkable capabilities, PET-CT is not without challenges. While it has revolutionized the way we diagnose and monitor diseases, especially cancer, it is not yet ideal for general screening. The combined radiation dose, high cost, and limited sensitivity for certain low-activity cancers mean that routine use in healthy individuals may do more harm than good. False positives can lead to anxiety, unnecessary procedures, and added burden on healthcare systems. Still, in the hands of experienced clinicians and when used appropriately—particularly in high-risk or symptomatic patients—PET-CT remains an invaluable tool that can save lives by guiding targeted treatment decisions. As research continues and technology advances, there’s hope that PET-CT will become safer, more affordable, and even more precise. Until then, its greatest value lies in thoughtful, case-by-case application rather than widespread use for screening the general population. After all, smarter imaging leads to smarter care.
References
Featured image from Metastatic Trail Talk https://metastatictrialtalk.org/from-the-experts/pet-ct-scans/
Anand, S., Singh, H., & Dash, A. (2009). Clinical Applications of PET and PET-CT. Medical Journal Armed Forces India, 65(4), 353–358. https://doi.org/10.1016/s0377-1237(09)80099-3
Basu, S., Kwee, T. C., Surti, S., Akin, E. A., Yoo, D., & Alavi, A. (2011). Fundamentals of PET and PET/CT imaging. Annals of the New York Academy of Sciences, 1228(1), 1–18. https://doi.org/10.1111/j.1749-6632.2011.06077.x
Fowler, J. S., & Volkow, N. D. (2022). Molecular Imaging: Positron Emission Tomography. Neuroscience in the 21st Century, 3297–3321. https://doi.org/10.1007/978-3-030-88832-9_149
Israel, O., & Kuten, A. (2007). Early Detection of Cancer Recurrence: 18F-FDG PET/CT Can Make a Difference in Diagnosis and Patient Care. Journal of Nuclear Medicine, 48(1 suppl), 28S35S. https://jnm.snmjournals.org/content/48/1_suppl/28S.short
Mazonakis, M., & Damilakis, J. (2016). Computed tomography: What and how does it measure? European Journal of Radiology, 85(8), 1499–1504. https://doi.org/10.1016/j.ejrad.2016.03.002
Schöder, H., & Gönen, M. (2007). Screening for Cancer with PET and PET/CT: Potential and Limitations. Journal of Nuclear Medicine, 48(1 suppl), 4S18S. https://jnm.snmjournals.org/content/48/1_suppl/4S.short
TerPogossian, M. M., Raichle, M. E., & Sobel, B. E. (1980). PositronEmission Tomography. Scientific American, 243(4), 170–181. JSTOR. https://doi.org/10.2307/24966439
