Cardiac MRI for Aortic Measurements and Disease Assessment

Measurement Capabilities and Technique

Cardiac MRI provides highly accurate and reproducible measurements of the aorta at all levels, from the aortic root through the descending thoracic and abdominal aorta, and is considered superior to echocardiography for this purpose, according to the American Heart Association 1, 2
The inner-wall to inner-wall technique is used at end-diastole to measure the aorta at multiple standardized locations, including the aortic root, sinotubular junction, and proximal tubular ascending aorta, as recommended by the American College of Cardiology 2
Double-oblique imaging planes are required to ensure measurements are perpendicular to the vessel axis, which is critical for accuracy, as stated by the European Society of Cardiology 2
ECG-gated acquisition is essential to minimize cardiac motion artifacts, particularly in the ascending aorta and root, according to the American Heart Association 3

CMR measurements are systematically 5-12% larger than echocardiography measurements because of differences in measurement conventions, as noted by the American College of Cardiology 1, 2

Cardiac MRI provides critical hemodynamic data, including pressure gradients across stenotic segments, flow quantification, and collateral flow assessment, as reported by the Journal of the American College of Radiology 4
CMR can assess aortic valve function, including regurgitant fraction, and myocardial contractility and strain, according to the American Heart Association 1, 5
Wall shear stress and hemodynamic parameters can be evaluated with 4D flow sequences, as described by the American College of Cardiology 4, 5

CMR is the recommended surveillance modality for patients with genetic aortopathies, such as Marfan syndrome, and is essential for accurate aortic measurements, as emphasized by the American Heart Association 1
CMR should be used for serial monitoring in patients with bicuspid aortic valve when echocardiography cannot adequately visualize the aortic root or ascending aorta, as recommended by the American College of Cardiology 5

Consistency in measurement technique is essential for surveillance, and CMR and CT use inner-to-inner edge measurements, as stated by the European Society of Cardiology 2
Measurements must be obtained in double-oblique planes perpendicular to the vessel, as recommended by the American College of Cardiology 2

Do not rely on axial images alone for aortic measurements, as this can underestimate true maximum diameters when asymmetry exists, as warned by the European Heart Journal 6
Avoid non-gated acquisitions in the ascending aorta, as cardiac motion creates significant artifacts, according to the American Heart Association 3

The American Heart Association recommends transthoracic echocardiography (TTE) as the initial imaging test for diagnosing ascending aorta ectasia, but CT angiography (CTA) or MRI should be obtained for comprehensive evaluation of the entire thoracic aorta, as TTE has critical blind spots in the distal ascending aorta and arch 7, 8
TTE is the Class I recommended initial imaging modality for evaluating suspected ascending aortic dilation, providing excellent visualization of the aortic root and proximal ascending aorta 7, 8
The European Society of Cardiology recommends ordering TTE with specific instructions to measure the aortic root using parasternal long-axis view and the aortic arch using suprasternal view, with measurements taken at end-diastole using the leading edge-to-leading edge convention 9

The American College of Cardiology recommends CT or MRI for definitive evaluation of the entire thoracic aorta, using inner-to-inner edge convention at end-diastole with double-oblique technique 7, 8
ECG-gated CTA is the gold standard for assessment of all thoracic aortic segments, minimizing motion artifact and allowing precise measurement of aortic root and ascending aortic dimensions 7, 8
The American College of Radiology recommends ECG-gated balanced steady-state free precession (bSSFP) MRA or contrast-enhanced MRA for excellent agreement with CTA for thoracic aortic measurements 10

The European Heart Journal notes that TTE uses leading edge-to-leading edge (L-L) convention, measuring from the outer anterior wall to the inner posterior wall, while CTA and MRI use inner edge-to-inner edge (I-I) convention, measuring the internal lumen diameter 9
Despite L-L convention theoretically providing measurements 2-4 mm larger, TTE actually underestimates aortic size compared to CTA/MRI in clinical practice due to oblique imaging planes and limited acoustic windows 10

The American Heart Association recommends follow-up imaging in 6 to 12 months to determine the rate of aortic enlargement; if stable, surveillance imaging every 6 to 24 months (depending on aortic diameter) is reasonable 7, 8
The European Society of Cardiology recommends using the same imaging modality with the same measurement method over time for accurate serial monitoring to avoid erroneous findings of arterial growth 9