Retrograde embolism from the descending aorta: visualization by multidirectional 3D velocity mapping in cryptogenic stroke.

BACKGROUND AND PURPOSE: The purpose of this study was to determine the role of plaques >or=4 mm and thrombi (complex plaques) in the descending aorta (DAo) as an embolic high-risk source for stroke. METHODS: In 63 acute stroke patients scheduled for TEE, territory and embolic pattern of brain ischemia were prospectively assessed. Multidirectional 3D MRI velocity mapping of the aorta was performed to correlate the extent of retrograde diastolic blood flow with the distance of complex DAo plaques from the left subclavian artery (LSA). Embolic risk from the DAo was present for (1) retrograde flow connecting complex DAo plaques with the LSA, (2) embolic pattern of brain ischemia in a territory supplied by the left vertebral artery, and (3) stroke that could not be explained by other means. RESULTS: 33 of 63 patients had complex DAo plaques (distance to LSA 28.1+/-29.9 mm). Mean retrograde flow in these subjects was 26.2+/-12.3 mm. In 20 of 63 patients (31.7%) retrograde flow connected complex DAo plaques with the LSA. In 4 of these 20 patients (20%) with an embolic stroke in the territory of the brain stem, cerebellum or posterior cerebral artery, etiology could not be explained by other means. CONCLUSIONS: Substantial diastolic retrograde flow originating from complex plaques in the descending aorta was detected by multidirectional 3D MRI velocity mapping and constitutes a stroke mechanism that was previously not demonstrable.

Optimized 3D bright blood MRI of aortic plaque at 3 T.

PURPOSE: To evaluate the feasibility of an optimized bright blood MRI protocol at 3 T in combination with contrast agent administration for the detection and characterization of aortic high-risk plaques for the improved workup of acute stroke patients. MATERIALS AND METHODS: ECG synchronized T1-weighted 3D gradient echo MRI was performed in 45 acute stroke patients. Data were acquired with high near isotropic spatial resolution (approximately 1 mm(3)) covering the entire thoracic aorta. To compensate for breathing and vessel motion artifacts, images were collected using respiratory navigator gating in combination with short diastolic data acquisition windows adjusted on a patient-by-patient basis. In patients with aortic plaques > or =3 mm in thickness, gadolinium contrast agent was administered and both pre- and post-contrast T1-weighted 3D measurements with identical vessel coverage were performed. RESULTS: Bright blood 3D MRI detected 33 high-risk plaques with an average maximum plaque thickness of 4.2+/-1.0 mm in 23 of 45 acute stroke patients. The availability of pre- and post-contrast images acquired within the same session enhanced the identification of calcified plaque components in 77% of all analyzed plaques: post-contrast MRI clearly improved the delineation of hypointense plaque cores in 23 of 30 cases and assisted in the classification of core shape and of core fraction. CONCLUSION: 3D bright blood MRI at 3 T was feasible for the detection of aortic high-risk sources and may help to improve the detection of causes of cerebral embolism in acute stroke patients.

Plaques in the descending aorta: a new risk factor for stroke? Visualization of potential embolization pathways by 4D MRI.

The combination of morphologic and hemodynamic information can help in assessing the risk of embolic stroke associated with thrombi and plaques in the descending aorta. For two acute stroke patients, the determination of individual embolic pathways using flow-sensitive four-dimensional (4D) MRI are reported. 3D visualization of local flow patterns, i.e., retrograde flow channels originating at the site of the atheroma, in conjunction with exact plaque localization, suggested potential embolization of high-risk plaques in the descending aorta although they are located downstream from the supraaortic arteries. Our findings indicate that taking plaques of the descending aorta into consideration may help improve the spectrum of pathologies considered as high-risk sources for brain ischemia.