CT vs MRI vs PET-CT: The Modality Choice Cheatsheet

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.