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MRI Explained: Magnetic Resonance Imaging Principles and Uses

What Is MRI?

Magnetic Resonance Imaging (MRI) is a non-invasive medical imaging technique that uses strong magnetic fields and radiofrequency pulses to generate detailed anatomical and functional images of the body.

Physics in Brief

  1. Patient placed in a strong static magnetic field (B₀: 1.5T or 3T clinical).
  2. Hydrogen protons (¹H) align with B₀.
  3. RF pulse at Larmor frequency tips protons into transverse plane.
  4. Protons relax (T1 longitudinal, T2 transverse), emitting signal.
  5. Receiver coils detect signal; Fourier transform reconstructs image.
  6. Contrast weighted by sequence parameters (T1-w, T2-w, FLAIR, DWI, GRE, etc.).

Key Advantages

  • No ionizing radiation.
  • Superior soft tissue contrast (brain, spine, joints, pelvis, heart).
  • Multiplanar imaging (axial, sagittal, coronal, oblique).
  • Functional/physiological info: fMRI, perfusion, spectroscopy, angiography (MRA).

Common Clinical Indications

  • Neurologic: stroke, MS, tumor, epilepsy, dementia.
  • Musculoskeletal: ligament/meniscus tears, labral tears, osteonecrosis.
  • Oncologic: staging, treatment response.
  • Cardiac: structure, function, viability, congenital.
  • Abdominal/pelvic: liver, pancreas, prostate, uterine, rectal.

Safety & Contraindications

  • Absolute: Ferromagnetic implants (some aneurysm clips, cochlear implants, metal fragments in eyes), non-MRI-conditional pacemakers/ICDs.
  • Relative: Claustrophobia, obesity (bore size), pregnancy (1st trimester caution), renal impairment (gadolinium risk – NSF).
  • Screening questionnaire mandatory.

Patient Experience

30–60 min; loud knocking (ear protection); IV contrast if ordered; communicate via intercom.

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