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MRI
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Cardiac MRI

Cardiac MRI (CMR) is the reference standard for quantifying biventricular volumes, mass, and function and for non-invasive myocardial tissue characterization. Cine imaging, late gadolinium enhancement, and parametric mapping allow differentiation of ischemic and non-ischemic cardiomyopathies, detection of edema and fibrosis, and assessment of viability and infiltration. It is central to diagnosis in myocarditis, cardiomyopathy, congenital heart disease, and cardiac masses. Stress perfusion CMR provides accurate ischemia assessment without ionizing radiation.

Indications

  • Characterization of cardiomyopathy (dilated, hypertrophic, restrictive, arrhythmogenic, non-compaction)
  • Suspected acute or chronic myocarditis using Lake Louise criteria
  • Myocardial viability assessment before revascularization
  • Detection and quantification of myocardial ischemia via vasodilator stress perfusion
  • Assessment of congenital heart disease anatomy, shunts, and postoperative anatomy
  • Evaluation and characterization of cardiac and pericardial masses/thrombus
  • Infiltrative disease including cardiac amyloidosis, sarcoidosis, and iron overload (T2*)
  • Accurate quantification of ventricular volumes/EF and valvular regurgitant fraction

Contraindications & Cautions

  • Non-MRI-conditional pacemakers/ICDs and other incompatible devices (many modern devices are now conditional)
  • Severe renal impairment (eGFR <30) limits gadolinium; use macrocyclic agents cautiously
  • Gadolinium hypersensitivity
  • Vasodilator stress contraindications: severe reactive airways disease/bronchospasm (adenosine/regadenoson), high-grade AV block, severe hypotension, recent caffeine intake
  • Pregnancy: avoid gadolinium and stress agents unless essential
  • Inability to breath-hold or significant arrhythmia degrades gated imaging

Patient Preparation

  • Screen for devices and implants; verify device MRI conditionality and program appropriately
  • Check renal function and obtain contrast consent
  • For stress CMR, withhold caffeine 12-24 hours and hold rate-limiting/vasodilator drugs per protocol
  • Fasting typically 4 hours before a stress study
  • Apply MRI-compatible ECG electrodes for gating; coach breath-holding
  • Establish reliable IV access (often two cannulae for stress: contrast and stress agent)
  • Position supine with a torso phased-array coil and monitor hemodynamics during stress

Technique & Parameters

  • 1.5T or 3T with ECG gating and cardiac phased-array coil
  • Balanced SSFP cine in short-axis stack and 2-, 3-, and 4-chamber long-axis views for function
  • T2-weighted/STIR or T2 mapping for myocardial edema; T1 and ECV mapping for diffuse fibrosis/infiltration
  • First-pass vasodilator stress perfusion (adenosine/regadenoson) with gadolinium bolus, then rest perfusion
  • Late gadolinium enhancement 10-15 minutes post 0.1-0.2 mmol/kg gadolinium with inversion-recovery to null myocardium
  • Phase-contrast flow imaging for shunt (Qp/Qs) and valvular regurgitation quantification
  • T2* sequence for iron quantification when overload is suspected

Systematic Review

  • Assess LV and RV size, wall thickness, regional wall motion, and global systolic function/EF
  • Review the short-axis stack systematically per AHA 17-segment model
  • Evaluate T2/edema imaging for regional or global signal elevation
  • Analyze stress vs rest perfusion for inducible subendocardial defects and artifact (dark rim)
  • Characterize LGE pattern and distribution (subendocardial/transmural vs mid-wall/epicardial)
  • Assess valves, atria, pericardium, and great vessels
  • Review parametric maps (native T1, T2, ECV, T2*) against normal ranges
  • Inspect extracardiac structures on the field of view

Key Findings & Significance

  • Subendocardial or transmural LGE in a coronary territory indicates prior myocardial infarction and predicts viability by transmural extent
  • Mid-wall or epicardial LGE indicates non-ischemic cardiomyopathy or myocarditis
  • Regional edema with epicardial LGE plus impaired function supports acute myocarditis (Lake Louise)
  • Reversible perfusion defect on stress with normal LGE indicates inducible ischemia
  • Diffuse subendocardial LGE with abnormal gadolinium kinetics and elevated ECV suggests amyloidosis
  • Asymmetric septal hypertrophy with patchy mid-wall LGE at RV insertion points suggests HCM
  • Low myocardial T2* (<20 ms) indicates iron overload

Differential Considerations

  • LGE pattern: ischemic (subendocardial/transmural) vs non-ischemic (mid-wall/epicardial/RV insertion)
  • Dilated ventricles: idiopathic DCM, ischemic, myocarditis-related, tachycardia-induced
  • Hypertrophy: HCM, hypertensive heart disease, amyloid, Fabry (low native T1), athlete's heart
  • Elevated native T1/ECV: amyloid, diffuse fibrosis, edema, inflammation
  • Low native T1: Fabry disease, iron overload, lipomatous change
  • Cardiac mass: thrombus (nonenhancing), myxoma, fibroma, lipoma, metastasis, angiosarcoma

Pearls & Pitfalls

  • Inversion time must be set to null normal myocardium; incorrect TI mimics or hides LGE
  • Dark-rim (Gibbs) artifact can mimic a perfusion defect; true ischemia is subendocardial, persists, and matches wall motion
  • Thrombus is best shown on early/long-TI LGE as a nonenhancing filling defect
  • Correlate edema, LGE, and mapping together; single-sequence interpretation is unreliable
  • Arrhythmia and poor breath-holding degrade cine and mapping; use real-time or single-shot techniques
  • RV assessment (ARVC) requires careful cine and fat/aneurysm evaluation, not LGE alone
  • Always report incidental extracardiac and vascular findings

Structured Report

  • State indication, technique (including stress agent and gadolinium dose), and image quality
  • Report biventricular volumes, mass, EF, and regional wall motion with reference ranges
  • Describe edema, perfusion, and LGE pattern with segmental localization
  • Report parametric mapping values (native T1, T2, ECV, T2*) against normal thresholds
  • Quantify flow/shunt and valvular regurgitant fractions where measured
  • Impression: integrate findings into a specific diagnosis (e.g., ischemic vs non-ischemic) and prognostic implications
  • Recommend correlation or intervention (e.g., viability favoring revascularization)

References

  • SCMR Guidelines for Cardiovascular Magnetic Resonance acquisition and reporting
  • Ferreira et al., 2018 Lake Louise Criteria for myocarditis
  • AHA 17-segment myocardial model (Cerqueira et al.)
  • ACR Appropriateness Criteria: known or suspected cardiomyopathy / chest pain
  • RadioGraphics reviews on LGE patterns and myocardial tissue characterization

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.