MRI Scan Explained: Physics, Process, and Clinical Applications

How MRI Works (Physics)

1. Strong magnetic field (1.5–3 T): Aligns hydrogen protons (in water/fat) parallel/anti-parallel.
2. RF pulse (Larmor frequency): Tips net magnetization into transverse plane.
3. Relaxation: Protons return to equilibrium (T1 recovery, T2 decay), emitting RF signal.
4. Signal detection: Receiver coils capture emitted signal.
5. Spatial encoding: Gradient coils create position-dependent frequencies/phases.
6. Fourier reconstruction: Computer transforms signals into grayscale images.

Key Advantages

• No ionizing radiation
• Superior soft-tissue contrast
• Multiplanar imaging (axial, sagittal, coronal, oblique)
• Functional/physiological info (fMRI, DTI, perfusion, spectroscopy)

Common Clinical Indications

• Neurologic: Stroke, MS, tumor, epilepsy, dementia
• Musculoskeletal: Ligament/meniscus tears, marrow edema, occult fracture
• Cardiac: Structure, function, viability, congenital
• Abdominal/pelvic: Liver, pancreas, adnexal, prostate, rectal cancer staging
• Vascular: MRA (aneurysm, dissection, stenosis)

Contraindications & Safety

• Ferromagnetic implants (some pacemakers, cochlear, aneurysm clips—check MRI-conditional labeling)
• Pregnancy (first trimester caution; gadolinium contraindicated)
• Claustrophobia (open MRI, sedation options)
• Renal impairment (gadolinium NSF risk)