What are the key findings evaluated on cardiac magnetic resonance imaging (MRI)?

Key Findings Evaluated on Cardiac MRI

Cardiac MRI comprehensively evaluates cardiac structure, function, tissue characterization, blood flow, and myocardial viability through multiple specialized sequences that provide information unattainable by other imaging modalities.

Core Assessment Categories

1. Ventricular Function and Morphology

Cine imaging (balanced steady-state free precession) provides the reference standard for:

• Biventricular volumes (end-diastolic and end-systolic volumes) 1, 2
• Ejection fraction with high reproducibility 1, 3
• Ventricular mass quantification 4, 1
• Regional wall motion abnormalities 1
• Ventricular mass index (RV mass/LV mass ratio, with >0.6 being abnormal) 4

CMR excels at visualizing areas limited by echocardiography including the LV apex, LV lateral wall, LV basal septum, and right ventricle 1. It accurately assesses RV morphology and function, including RV hypokinesis, interventricular septal bowing, and RV dysfunction parameters 4.

2. Myocardial Tissue Characterization

Late Gadolinium Enhancement (LGE) identifies:

• Myocardial scar and fibrosis with distinct patterns differentiating ischemic from non-ischemic cardiomyopathy 1, 5
• Pattern recognition: linear mid-myocardial, patchy mid-myocardial, subepicardial, RV insertion point, or diffuse subendocardial patterns 1
• Prognostic information: LGE extent predicts malignant arrhythmia risk and heart failure regardless of etiology 1
• RV insertion point enhancement indicating fibrosis from RV stress in pulmonary hypertension 4

Parametric Mapping Techniques provide quantitative tissue characterization:

• T1 mapping (native and post-contrast):

  • Detects diffuse fibrosis, infiltration, and edema 1
  • Prolonged values at RV insertion points indicate pulmonary hypertension 4
  • Useful in renal dysfunction when contrast is contraindicated 1

• T2 mapping:

  • Identifies myocardial edema in inflammatory processes 1, 2
  • More sensitive and reproducible than conventional T2-weighted imaging 1

• T2 mapping*:

  • Quantifies iron overload 1

• Extracellular Volume (ECV):

  • Quantifies diffuse fibrosis using native and post-contrast T1 mapping with hematocrit 1
  • Increased in multiple disorders 1

3. Myocardial Inflammation Assessment

Updated Lake Louise Criteria (2018) require 2, 5:

• One T2-based marker (T2 mapping or T2-weighted imaging showing edema) PLUS
• One T1-based marker (abnormal T1, ECV, or LGE indicating injury)

Early Gadolinium Enhancement (EGE) evaluates capillary hyperemia in acute inflammatory processes 1.

4. Blood Flow and Hemodynamics

Phase-Contrast Imaging quantifies:

• Valve regurgitation and stenosis with accurate quantification 1, 2
• Shunt flow (Qp/Qs ratio calculation) 2, 6
• Pressure gradients across stenotic regions 6
• Average blood flow velocity in main pulmonary artery correlating with mean PAP 4
• Tricuspid regurgitation severity for estimating MPA pressure 4

4D Flow Imaging detects hemodynamic alterations:

• Wall shear stress changes 4
• Abnormal vortex blood flow patterns 4
• Early-onset systolic retrograde flow 4

5. Myocardial Perfusion and Viability

Stress Perfusion Imaging (pharmacological or physiological):

• Detects myocardial ischemia through perfusion defects 1, 3
• Combined with wall motion abnormalities during stress 3
• Enables simultaneous viability analysis with LGE 7

First-pass perfusion evaluates ischemia with dynamic imaging 1.

6. Valvular Assessment

• Qualitative evaluation in cine imaging 1
• Quantitative assessment using 2D or 4D phase-contrast sequences 1
• Regurgitant volumes and fractions with superior reproducibility compared to echocardiography 8

7. Pericardial Disease

• Pericardial thickening and effusion 4, 1
• Real-time cine imaging to exclude constrictive pericarditis 1

8. Myocardial Strain and Mechanics

Strain imaging techniques (feature tracking, tagging, tissue phase mapping):

• Regional function quantification detecting early dysfunction 1, 2
• Longitudinal, radial, and circumferential strain 2
• Independent outcome prediction though not yet replacing conventional volumes/EF 2

9. Congenital Heart Disease Evaluation

• Cardiovascular shunts location, magnitude, and direction 2
• Complex anatomy including Fontan circuitry, vascular rings, and anomalous vessels 6
• Systemic-to-pulmonary collateral flow predicting outcomes 6
• 3D rendering for presurgical planning 6

10. Diastolic Function

• E/A ratio assessment using phase-contrast CMR 2
• Myocardial velocities measured directly 2
• Ventricular filling dynamics 2

Common Pitfalls to Avoid

• Incomplete tissue characterization: Always combine multiple sequences rather than relying on single parameters 5
• Timing sensitivity: Inflammatory changes are optimally detected within weeks of presentation 5
• Contraindications: Screen for non-MRI-conditional devices, severe gadolinium allergy, and severe renal insufficiency (eGFR <30) 2, 6
• Calcification detection: CMR poorly visualizes calcification; consider CT for bioprosthetic valve assessment 6
• Small defects: CMR may miss small atrial/ventricular septal defects better seen on echocardiography 6

Prognostic Value

CMR parameters provide independent prognostic information:

• RV ejection fraction, RV end-diastolic volume, and RV-PA coupling predict pulmonary hypertension outcomes 4
• LGE extent predicts arrhythmia and heart failure risk 1
• Absence of LGE with edema suggests better recovery in myocarditis 5
• MPA pulsatility <40% diagnoses mild pulmonary hypertension with 95% sensitivity and 94% specificity 4