The aim of this study was to determine the value of flow-sensitive four-dimensional MRI for the assessment of pulse wave velocity as a measure of vessel compliance in the thoracic aorta. Findings in 12 young healthy volunteers were compared with those in 25 stroke patients with aortic atherosclerosis and an age-matched normal control group (n 5 9). Results from pulse wave velocity calculations incorporated velocity data from the entire aorta and were compared to those of standard methods based on flow waveforms at only two specific anatomic landmarks. Global aortic pulse wave velocity was higher in patients with atherosclerosis (7.03 6 0.24 m/ sec) compared to age-matched controls (6.40 6 0.32 m/sec). Both were significantly (P < 0.001) increased compared to younger volunteers (4.39 6 0.32 m/sec). Global aortic pulse wave velocity in young volunteers was in good agreement with previously reported MRI studies and catheter measurements. Estimation of measurement inaccuracies and error propagation analysis demonstrated only minor uncertainties in measured flow waveforms and moderate relative errors below 16% for aortic compliance in all 46 subjects. These results demonstrate the feasibility of pulse wave velocity calculation based on fourdimensional MRI data by exploiting its full volumetric coverage, which may also be an advantage over standard two-dimensional techniques in the often-distorted route of the aorta in patients with atherosclerosis. Magn Reson Med 63:1575-1582, 2010. V C 2010 Wiley-Liss, Inc. Key words: pulse wave velocity; compliance; phase contrast; atherosclerosis; aorta Increased pulse wave velocity (PWV) as a measure of aortic stiffness is an important marker for both agerelated changes in aortic compliance and the presence of atherosclerosis (1,2) and is an independent predictor of cardiovascular mortality and stroke (3,4). Reliable measurement of PWV is of particular interest for monitoring the progression or regression of vessel compliance during therapy (5,6).Pressure catheter measurements can be considered the gold standard for the assessment of the development of aortic pressure wave, but their use is limited due to the invasiveness of the procedure (7). To provide a noninvasive estimate of PWV, phase contrast (PC) MRI has been applied in a number of in vivo studies determining blood flow based on flow waveform measurements in single two-dimensional (2D) planes transecting the aorta (8-10). For PWV estimation, typically transit-time methods are employed estimating temporal differences of specific features of blood flow waveforms, e.g., time from foot to foot or peak to peak, between two locations of the vessel with known distance (11-24). However, the precision of this method highly depends on the exact calculation of flow difference and distance between only two measuring points (16,25,26).Methodological improvements include a more continuous evaluation along a vessel center line and cross-correlation (XCor) analysis for the estimation of waveform delays, which improved the accuracy of PWV...

Minor stroke and TIA are associated with a 10% risk of new lesions on MRI and half of these new lesions are asymptomatic. This risk is lower than seen in more severely affected patients with stroke. Patients with multiple lesions at baseline are at an increased risk for new ischemic lesions.

and much work needs to be done to identify the causes of regional variability. Finally, it needs to be emphasized that "fistula first" does not mean "fistula only." Patients with poor likelihood of maturation of a fistula, or a short life expectancy, may be better candidates for a graft.Complex Plaques in the Proximal Descending Aorta: An Underestimated Embolic Source of Stroke Harloff A, Simon J, Brendecke S, et al. Stroke 2010;41:1145-50. Conclusion: Retrograde flow from complex descending aorta plaques is a potential source of emboli to all brain territories.Summary: Complex aortic plaques are defined as Ն4 mm in thickness, or those associated with ulceration or that have mobile thrombi. Such plaques are considered a significant source of stroke. When such plaques are located in the ascending aorta or the aortic arch, embolization can be through antegrade flow from the aorta into a major cerebral vessel. However, the incidence of complex plaques is highest in the proximal descending aorta. Plaques in this location have only previously been considered a source of stroke in the setting of severe aortic valve insufficiency resulting in retrograde flow in the aorta during diastole. However, it now appears that diastolic retrograde flow in the descending thoracic aorta may be common in patients with atherosclerosis and therefore serve as a potentially overlooked mechanism of stroke (Svedlund S, et al, Cerebrovasc Dis 2009;27:22-8).The authors hypothesize that retrograde flow in the proximal descending thoracic aorta has the potential to reach all the supra-aortic arteries and, thus, may be a previously underappreciated source of stroke in the setting of a complex descending aorta plaque. They studied 94 consecutive acute stroke patients who had aortic plaques Ն3 mm in thickness as determined by transesophageal echocardiography. All subjects underwent magnetic resonance imaging (MRI) to localize complex plaques and to measure timeresolved 3-dimensional (3D) blood flow within the aorta. The 3D visualization was then used to determine if diastolic retrograde flow connected plaque location with origins of the left subclavian, left common carotid, or innominate artery. If retrograde flow associated with a complex descending thoracic aortic plaque reached a supra-aortic vessel that supplied the territory of an MRI-determined acute embolic retinal or cerebral infarction, the distal thoracic aortic plaque was considered a possible embolic source for the stroke.Decreasing heart rate was correlated with increasing flow reversal to the aortic arch (P Ͻ .02). Retrograde flow associated with complex proximal descending aortic plaques reached the left subclavian artery in 58.5% of cases, the left common carotid artery in 24.5%, and the brachiocephalic artery in 13.8%. Stroke etiology was determined in 57 of the 94 patients in the study and was not determined in the remaining 37 patients, so-called cryptogenic stroke. Potential embolization from a descending thoracic aortic plaque was identified in 19 of 57 patients (33.3%) wi...

Background and Purpose-To investigate the incidence of retrograde flow from complex plaques (Ն4-mm-thick, ulcerated, or superimposed thrombi) of the descending aorta (DAo) and its potential role in embolic stroke. Methods-Ninety-four consecutive acute stroke patients with aortic plaques Ն3-mm-thick in transesophageal echocardiography were prospectively included. MRI was performed to localize complex plaques and to measure time-resolved 3-dimensional blood flow within the aorta. Three-dimensional visualization was used to evaluate if diastolic retrograde flow connected plaque location with the outlet of the left subclavian artery, left common carotid artery, or brachiocephalic trunk. Complex DAo plaques were considered an embolic source if retrograde flow reached a supra-aortic vessel that supplied the territory of visible acute and embolic retinal or cerebral infarction. Results-Only decreasing heart rate was correlated (PϽ0.02) with increasing flow reversal to the aortic arch. Retrograde flow from complex DAo plaques reached the left subclavian artery in 55 (58.5%), the left common carotid artery in 23 (24.5%), and the brachiocephalic trunk in 13 patients (13.8%). Based on routine diagnostics and MRI of the ascending aorta/aortic arch, stroke etiology was determined in 57 and cryptogenic in 37 patients. Potential embolization from DAo plaques was then identified in 19 of 57 patients (33.3%) with determined and in 9 of 37 patients (24.3%) with cryptogenic stroke. Conclusions-Retrograde flow from complex DAo plaques was frequent in both determined and cryptogenic stroke and could explain embolism to all brain territories. These findings suggest that complex DAo plaques should be considered a new source of stroke. (Stroke. 2010;41:1145-1150.)Key Words: acute stroke Ⅲ aorta Ⅲ atherosclerosis Ⅲ magnetic resonance Ⅲ pathogenesis C omplex aortic plaques defined as Ն4-mm-thick, ulcerated or containing mobile thrombi are considered a major source of stroke. 1 Although their incidence is highest in the proximal descending aorta (DAo), such plaques are only considered an embolic source of stroke in the unlikely coincidence of severe aortic valve insufficiency causing retrograde flow and embolization in case of plaque rupture. 1,2 However, there is growing evidence that diastolic retrograde flow in the DAo may be a frequent phenomenon in the presence of atherosclerosis and thus an overlooked mechanism of retrograde embolization in stroke patients. Oscillating thrombus mobility 3 and Doppler flow curves in the DAo in transesophageal echocardiography (TEE) indirectly proved the existence of flow reversal. 4 In contrast to TEE, flowsensitive 4-dimensional MRI permits the precise analysis of individual 3-dimensional flow patterns at the site of complex DAo plaques. [5][6][7] Moreover, it allows for a more reliable detection and characterization of aortic plaques compared to TEE. 8,9 In this context, retrograde embolization from complex DAo plaques was recently described as a proof-ofprinciple and constituted the only proba...

Purpose: To compare 3D magnetic resonance imaging (3D MRI) with transesophageal echocardiography (TEE) for the detection of complex aortic plaques (!4 mm thick, ulcerated, or containing mobile thrombi). Materials and Methods:In all, 99 consecutive patients with acute cryptogenic stroke and !3 mm thick aortic plaques in TEE were prospectively included. 3D MRI comprised T1-weighted bright blood MRI with complete aortic coverage (spatial resolution 1 mm 3 ). Wall thickness and occurrence of complex plaques in ascending aorta (AAo), aortic arch (AA), and descending aorta (DAo) and image quality for each segment was rated for MRI and TEE.Results: MRI detected more complex plaques than TEE (MRI vs. TEE): AAo 13 vs. 7; AA 37 vs. 11; differences were smaller in the DAo: 101 vs. 70. Image quality was higher for MRI in AAo and AA (P < 0.001) and superior for TEE in DAo (P < 0.001). MRI revealed additional complex plaques in the proximal aorta in 19 of 58 patients (32.8%) categorized as cryptogenic after complete routine diagnostics including TEE. Conclusion:Due to improved visualization of the aorta 3D MRI allows to detect more complex plaques than TEE. This renders 3D MRI particularly valuable for patients with cryptogenic stroke and for trials evaluating optimal treatment in aortic atherosclerosis.