Non-gadolinium-enhanced 3-dimensional magnetic resonance angiography for the evaluation of thoracic aortic disease: a preliminary experience

Abstract

We compared image quality and diagnostic accuracy of a noncontrast 3-dimensional magnetic resonance angiography (NC-MRA) technique (balanced steady-state free-precession sequence) to contrast-enhanced MRA (CE-MRA) for evaluation of thoracic aortic disease.The CE-MRA provides 3-dimensional high-resolution images of the thoracic aorta that are important in the evaluation of patients with aortic disease. However, recent concerns with the potential nephrotoxic effects of gadolinium contrast medium limit the application of CE-MRA for patients who have significant renal insufficiency.Twenty-one patients (mean age, 51 yr; 18 men) who underwent NC-MRA and CE-MRA for evaluation of thoracic aortic disease were retrospectively identified. Data sets were reviewed by 2 readers who were blinded to the patients' information. The thoracic aorta was divided into 5 segments. Image quality and reader confidence for diagnosis of aortic pathology were rated on 5-point scales. The Wilcoxon matched-pairs signed rank test and the Student t test were used for comparisons.The NC-MRA identified all pathologic findings with 100% diagnostic accuracy and similar reader confidence, when compared with CE-MRA. Although overall image quality was not significantly different, superior image quality was observed at the aortic root (4.4 +/- 0.8 vs 3.2 +/- 0.9, P <0.0005) and ascending aorta (4.1 +/- 1 vs 3.7 +/- 0.9, P=0.05) respectively.In conclusion, NC-MRA is a useful alternative for evaluation and follow-up of thoracic aortic disease, especially for patients with poor intravenous access or contraindications to gadolinium use.

Keywords: Aneurysm, dissecting/diagnosis; aorta, thoracic/pathology; aortic aneurysm, thoracic/diagnosis; aortic diseases/diagnosis/radiography; artifacts; contrast media/toxici-ty; gadolinium/diagnostic use/toxicity; magnetic resonance angiography; retrospective studies.

Fig. 1 This diagram of the thoracic aorta demonstrates the segments used for the evaluation of image quality and the levels used for the measurement of aortic dimensions, including the sinus of Valsalva (A), sinotubular junction (B), mid-ascending aorta (C), mid-aortic arch (D), mid-descending aorta (E), and diaphragm level (F).

Fig. 2 Multiplanar reformation of A) noncontrast magnetic resonance angiography (NC-MRA) and B) contrast-enhanced MRA in a patient with aneurysm of the aortic root. Image quality, particularly distinct visualization of the aortic walls, was better with NC-MRA for the aortic root and ascending aorta levels (black arrows). Magnetic-field inhomogeneities from lung parenchyma surrounding the left subclavian artery caused signal artifact in that region and consequently reduced image quality at that level (white arrow) on the NC-MRA image (top).

Fig. 3 Comparison of image-quality scores between noncontrast and contrast-enhanced magnetic resonance angiography.

Fig. 4 Noncontrast magnetic resonance angiography A) before and B) after localized shimming of the ascending aorta and arch in a patient with prior coronary artery bypass grafting. Before local shimming, artifact from sternal wires obscures the ascending aorta (arrowheads), and consequently the bypass graft origin (arrow). Local shimming also improves visualization of the great-vessel origins (curved arrows).

Fig. 5 A) Multiplanar reformation of noncontrast magnetic resonance angiography at the level of the aortic sinuses shows good visualization of the right (white arrow) and left (black arrow) coronary arteries from their respective sinuses. B) Corresponding multiplanar reformation of contrast-enhanced magnetic resonance angiography at the same level shows partial visualization of the left coronary artery (black arrow) and non-visualization of the right coronary artery (white arrow).

Fig. 6 Comparison of aortic dimension measurements between noncontrast and contrast-enhanced magnetic resonance angiography. AA = ascending aorta; Arch = aortic arch; CE-MRA = contrast-enhanced magnetic resonance angiography; DA = descending aorta; Diaphragm = at level of diaphragm; LCC = left common carotid artery; LSA = left subclavian artery; NC-MRA = noncontrast magnetic resonance angiography; RBC = right brachioce-phalic artery; Sinus = sinus of Valsalva; STJ = sinotubular junction

Fig. 7 Multiplanar reformation of A) noncontrast and B) contrast-enhanced magnetic resonance angiography in a patient with type B aortic dissection. Locations of true (T) and false (F) lumina, as well as the proximal entry site (arrow), are seen with both techniques. Of note, a susceptibility artifact due to metallic sternal wires obscures the ascending aorta in the noncontrast image.