CT vs MRI vs PET-CT: The Modality Choice Cheatsheet
Share
Patients facing a choice between CT, MRI, and PET-CT often don't know what their physician is actually deciding between. This concise cheatsheet summarizes what each modality does best, the trade-offs, and which to request for common clinical questions.
The One-Sentence Summary
- CT: best for bone, lung, rapid trauma evaluation, vascular structures
- MRI: best for brain, spine, joints, soft tissue characterization
- PET-CT: best for cancer metabolism, staging, treatment response
Each excels in different applications. Asking "should I have CT or MRI" misses the better question: "What clinical information is needed, and which modality answers that question?"
CT: Best for Bone, Lung, Quick Trauma
CT strengths:
- Bone fractures, dense bone pathology
- Lung parenchyma (nodules, masses, consolidation)
- Vascular evaluation with IV contrast (CTA)
- Acute abdominal pain workup
- Trauma evaluation (rapid, comprehensive)
- Pulmonary embolism diagnosis
- Cardiac calcification (CAC score)
CT limitations:
- Soft tissue detail less than MRI
- Ionizing radiation (5–15 mSv typical)
- Iodine contrast risks (allergy, nephropathy)
- Cannot show metabolism
CT cost (US cash): $400–1,500. China: ¥800–2,500.
MRI: Best for Brain, Spine, Joints, Soft Tissue
MRI strengths:
- Brain structural pathology
- Spinal cord and disc disease
- Joint cartilage, ligaments, meniscus, labrum
- Soft tissue masses with high contrast resolution
- Cardiac function and tissue characterization
- Prostate, breast, pelvic detail
- No radiation
MRI limitations:
- Patients with implanted metal (pacemakers — some types incompatible)
- Claustrophobia
- Long scan times (15–60 minutes)
- Higher cost than CT
- Gadolinium contrast risks in renal failure
MRI cost (US cash): $400–4,500 depending on body part and field strength. China: ¥600–4,500.
PET-CT: Best for Cancer Staging and Metabolism
PET-CT strengths:
- Cancer staging (especially FDG-avid: lymphoma, lung, head-neck)
- Treatment response monitoring
- Cancer recurrence detection
- Active inflammation localization (sarcoidosis, vasculitis)
- Infection localization (fever of unknown origin)
- Specific cancers with specialized tracers (PSMA for prostate, DOTATATE for NET)
PET-CT limitations:
- Higher cost than CT or MRI
- Higher radiation dose (8–15 mSv)
- Cannot show sub-resolution lesions
- Not useful for many cancers (prostate, RCC, mucinous — need specialized tracers)
- Schedule typically slower than CT or MRI
PET-CT cost (US cash): $3,500–7,500. China: ¥6,500–15,000.
Radiation Comparison
| Modality | Typical effective dose (mSv) |
|---|---|
| MRI | 0 (no radiation) |
| Ultrasound | 0 |
| Chest X-ray | 0.05–0.1 |
| Mammogram | 0.4 |
| LDCT chest | 1.0–1.5 |
| Chest CT (diagnostic) | 5–10 |
| Abdomen-pelvis CT (with contrast) | 8–14 |
| Coronary CTA | 5–15 |
| FDG PET-CT (whole-body) | 8–15 |
| Bone scan (Tc-99m) | 4–6 |
For patients sensitive to cumulative radiation (children, multiple repeat scans), MRI substitutes for CT when feasible.
Cost and Time Comparison
Typical scan time on the table:
| Scan | Time on table |
|---|---|
| Chest X-ray | 1 minute |
| Brain CT | 5 minutes |
| Abdomen-pelvis CT with contrast | 10 minutes |
| Brain MRI | 20–30 minutes |
| Knee MRI | 30 minutes |
| Multi-region MRI | 45–60 minutes |
| FDG PET-CT (whole-body) | 30 minutes (after 60-min uptake wait) |
Total clinic time is longer than scan time, especially for PET-CT (90–120 minutes total).
For choosing the right modality for your specific clinical question, our team can help.
Which to Ask Your Doctor For
Quick reference for common scenarios:
| Scenario | Best modality |
|---|---|
| Suspected stroke | Brain MRI (or non-contrast CT in acute setting) |
| Knee pain after injury | Knee MRI |
| Chest pain, suspected MI | ECG + troponin + sometimes coronary CTA |
| Back pain with leg symptoms | Lumbar spine MRI |
| Unexplained weight loss + suspected cancer | Whole-body FDG PET-CT |
| Prostate cancer staging | Multiparametric MRI + PSMA PET |
| Lung nodule on chest X-ray | Chest CT (diagnostic) |
| Lymphoma diagnosis confirmed | Whole-body FDG PET-CT |
| Headache without red flags | Brain MRI (or CT in some cases) |
| Pelvic pain in woman | Pelvic ultrasound or MRI |
| Pulmonary embolism suspected | Chest CT angiography (CTPA) |
| Stroke follow-up | Brain MRI |
For most clinical questions, your physician's order is appropriate. If you have questions about why a particular modality was chosen, asking is reasonable.
Need Help Booking?
SinoCareLink can pre-book CT, MRI, or PET-CT at a top Chinese hospital, matched to your specific clinical question, with English-language reports and airport pickup. Contact us for a free consultation.