Image quality and diagnostic accuracy of unenhanced SSFP MR angiography compared with conventional contrast-enhanced MR angiography for the assessment of thoracic aortic diseases

Abstract

Objectives: The purpose of this study was to determine the image quality and diagnostic accuracy of three-dimensional (3D) unenhanced steady state free precession (SSFP) magnetic resonance angiography (MRA) for the evaluation of thoracic aortic diseases.

Methods: Fifty consecutive patients with known or suspected thoracic aortic disease underwent free-breathing ECG-gated unenhanced SSFP MRA with non-selective radiofrequency excitation and contrast-enhanced (CE) MRA of the thorax at 1.5 T. Two readers independently evaluated the two datasets for image quality in the aortic root, ascending aorta, aortic arch, descending aorta, and origins of supra-aortic arteries, and for abnormal findings. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were determined for both datasets. Sensitivity, specificity, and diagnostic accuracy of unenhanced SSFP MRA for the diagnosis of aortic abnormalities were determined.

Results: Abnormal aortic findings, including aneurysm (n = 47), coarctation (n = 14), dissection (n = 12), aortic graft (n = 6), intramural hematoma (n = 11), mural thrombus in the aortic arch (n = 1), and penetrating aortic ulcer (n = 9), were confidently detected on both datasets. Sensitivity, specificity, and diagnostic accuracy of SSFP MRA for the detection of aortic disease were 100% with CE-MRA serving as a reference standard. Image quality of the aortic root was significantly higher on SSFP MRA (P < 0.001) with no significant difference for other aortic segments (P > 0.05). SNR and CNR values were higher for all segments on SSFP MRA (P < 0.01).

Conclusion: Our results suggest that free-breathing navigator-gated 3D SSFP MRA with non-selective radiofrequency excitation is a promising technique that provides high image quality and diagnostic accuracy for the assessment of thoracic aortic disease without the need for intravenous contrast material.

Fig. 1

Depiction of the navigator gating, FOV, and data acquisition of 3D SSFP MRA of thoracic aorta without intravenous contrast material. A column of tissue (a, arrowhead) at the intersection of two slices over the diaphragm (a, arrow) generates a spin-echo that is utilized to track the diaphragm (lung-liver interface). Coronal scout image of the whole chest (b) illustrates the imaging volume, which is typically a large FOV for this technique (b, yellow box), the navigator echo (b, dotted blue bars), and the right-to-left phase-encoding direction (b, yellow arrow). The end-expiratory position of the diaphragm is tracked by the narrow 4-mm adaptive gating window, which is highlighted on the narrow central bar (c). Data falling outside this narrow window were rejected (c, central narrow bar). The absolute distance scale of the diaphragm is shown on the y-axis (c). The 3D navigator gated motion adaptive sequence utilizes the reference position of the diaphragm (174 in this case) to place the gating window to track the end-expiratory position of the diaphragm. Liver and pulmonary parenchyma are indicated by white and gray bars, respectively (c)

Fig. 2

A 34-year-old male patient with aortic coarctation. Oblique sagittal view of unenhanced 3D SSFP MRA (a) and CE-MRA (b) demonstrate the significant focal stenosis of the distal transverse arch consistent with aortic coarctation (a and b, arrow). Three-dimensional volume rendered image also shows the coarctation (c, arrow)

Fig. 3

A 51-year-old male patient, status post-surgical repair of type I dissection with residual intimal flap in the arch and descending aorta. Sagittal oblique image from non-contrast 3D SSFP MRA (a) and corresponding sagittal oblique image from CE-MRA (b) demonstrate the ascending aortic surgical graft (a and b, small thin arrow), anterior true lumen (a and b, small arrow), posterior false lumen (a and b, arrowhead), aneurysmal dilatation of the distal transverse arch, and the residual low signal intimal flap (a and b, large arrow). Mural thrombus in the false lumen of the aortic arch (a and b, large thin arrow) is better appreciated on non-contrast SSFP MRA

Fig. 4

A 44-year-old female patient with a history of type I aortic dissection and status post-ascending aortic graft. Oblique sagittal views of non-contrast SSFP MRA (a) and conventional CE-MRA (b) demonstrate the ascending aortic graft (a and b, arrowhead), aneurysmal native aortic arch (a and b, large arrow), a small residual dissection flap in the distal aortic arch (a and b, thin arrow), and kinking at the junction of the aortic arch and descending aorta (a and b, small arrow)

Fig. 5

A 64-year-old male patient with aortic root aneurysm. Coronal image from unenhanced SSFP MRA (a) demonstrates aneurysm of the aortic root (a, large arrow) and thickening of the aortic valve (a, arrowhead) without evidence of motion artifact. Excellent correlation with cardiac gated coronal CT angiography (b) for the aortic root aneurysm (b, large arrow) and aortic valve thickening (b, arrowhead). Left main coronary artery is also clearly visualized with both techniques because of cardiac gating (a and b, small arrow). Step artifacts are noted in CTA but not in SSFP MRA

Fig. 6

a Graph showing significant correlation between unenhanced SSFP MRA and conventional CE-MRA for quantitative measures of the largest diameter of the aortic aneurysm and the smallest diameter of the coarctation (r = 0.99, P < 0.001). b Bland–Altman plot for evaluation of the differences between measurements of the aortic diameter in diseased segments on unenhanced SSFP MRA and CE-MRA. All differences fall within two standard deviations of the mean difference (0.16 mm) with no more than 1 mm absolute difference between measurements