Diagnosis basics · 5 min read
PET, CT, and MRI scans in cancer
Cancer imaging tests create pictures or functional information that help doctors find, stage, monitor, or plan treatment.
Written by OncosAI Editorial Team · Editorial review 2026-07-04
Key takeaways
- Different scans answer different questions.
- CT shows anatomy; MRI is often strong for soft tissue detail; PET can show metabolic activity.
- A scan result is interpreted with symptoms, pathology, labs, and prior imaging.
- Ask what question the scan is meant to answer.
The simple version
Scans are tools. A CT, MRI, PET, ultrasound, x-ray, or other imaging test may be chosen based on the cancer type and clinical question.
Imaging can help detect cancer, estimate stage, guide biopsy or radiation planning, monitor response, or check for recurrence.
How common scan types differ
- CT uses x-rays to show detailed body structures.
- MRI uses magnets and radio waves and can show soft tissues in detail.
- PET uses a tracer to show areas with certain kinds of activity.
- PET/CT combines functional and anatomic information.
Questions to ask
- What question is this scan trying to answer?
- Do I need contrast, and are there kidney or allergy concerns?
- How should we compare this scan with prior imaging?
- Could inflammation or treatment effects affect the result?
- When will we review the findings?
Sources
- NCI Cancer Imaging Basics — NCI overview of imaging tools used in cancer research and care.
- Mayo Clinic: PET scan — Explains PET scans and cancer-related uses.
This guide is educational and does not replace advice from your oncology care team.