01/15/2026
Cancer screening tools like MRI, CT, and PET scans each serve different purposes, and understanding when and why they’re used matters just as much as the scan itself. These technologies don’t “find cancer” in the same way—each looks at a different aspect of structure or function, and each comes with its own trade-offs.
MRI (Magnetic Resonance Imaging) uses magnetic fields and radio waves to create highly detailed images of soft tissue. It does not use ionizing radiation, which makes it especially useful for repeated imaging, brain and spinal cord evaluation, breast imaging, pelvic organs, and assessing soft tissue changes. MRI is best when the question is about anatomy, tissue characteristics, or subtle structural differences. The downsides are cost, time, and that it’s not ideal for every organ or for detecting very small, metabolically active lesions.
CT (Computed Tomography) scans use X-rays to create cross-sectional images and are excellent for quickly visualizing anatomy, especially in the chest, abdomen, and pelvis. CT is often used for initial evaluation, staging, or to monitor known disease. The trade-off is radiation exposure. While modern CT scanners use lower doses than in the past, cumulative exposure matters—particularly for patients undergoing repeated scans over time.
PET (Positron Emission Tomography) looks at metabolic activity, not structure. By using a radioactive glucose tracer, PET scans highlight areas of increased glucose uptake, which can correlate with cancer activity, inflammation, or infection. PET is most useful for staging, detecting recurrence, or evaluating how active a tumor is—not as a general screening tool in healthy people. Because PET involves radiation (often combined with CT), it should be used thoughtfully and with a clear clinical question.
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