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Background: Hemodynamic alterations of extracranial veins are considered an etiologic factor in multiple sclerosis (MS). However, ultrasound and MRI studies could not confirm a pathophysiological link. Because of technical challenges using standard diagnostics, information about the involvement of superficial intracranial veins in proximity to the affected brain in MS is scarce.Purpose: To comprehensively investigate the hemodynamics of intracranial veins and of the venous outflow tract in MS patients and controls.Study Type: Prospective.Population: Twenty-eight patients with relapsing-remitting MS (EDSS1.9 ± 1.1; range 0-3) and 41 healthy controls.Field Strength/sequence: 3T/2D phase-contrast and time-resolved 4D flow MRI, extra- and transcranial sonography.Assessment: Hemodynamics within the superficial and deep intracranial venous system and outflow tract including the internal, basal, and great cerebral vein, straight, superior sagittal, and transverse sinuses, internal jugular and vertebral veins. Sonography adhered to the chronic cerebrospinal venous insufficiency (CCSVI) criteria.Statistical Tests: Multivariate repeated measure analysis of variance, Student's two-sample t-test, chi-square, Fisher's exact test; separate analysis of the entire cohort and 32 age- and sex-matched participants.Results: Multi- and univariate main effects of the factor group (MS patient vs. control) and its interactions with the factor vessel position (lower flow within dorsal superior sagittal sinus in MS, 3 ± 1 ml/s vs. 3.8 ± 1 ml/s; P < 0.05) in the uncontrolled cohort were attributable to age-related differences. Age- and sex-matched pairs showed a different velocity gradient in a single segment within the deep cerebral veins (great cerebral vein, vena cerebri magna [VCM] 7.6 ± 1.7 cm/s; straight sinus [StS] 10.5 ± 2.2 cm/s vs. volunteers: VCM 9.2 ± 2.3 cm/s; StS 10.2 ± 2.3 cm/s; P = 0.01), reaching comparable velocities instantaneously downstream. Sonography was not statistically different between groups.Data Conclusion: Consistent with previous studies focusing on extracranial hemodynamics, our comprehensive analysis of intracerebral venous blood flow did not reveal relevant differences between MS patients and controls. Level of Evidence 1. Technical Efficacy Stage 3. J. Magn. Reson. Imaging 2020;51:205-217. [ABSTRACT FROM AUTHOR]

Purpose Despite numerous publications describing the ability of prospective motion correction to improve image quality in magnetic resonance imaging of the brain, a reliable approach to assess this improvement is still missing. A method that accurately reproduces motion artifacts correctable with prospective motion correction is developed, and enables the quantification of the improvements achieved. Methods A software interface was developed to simulate rigid body motion by changing the scanning coordinate system relative to the object. Thus, tracking data recorded during a patient scan can be used to reproduce the prevented motion artifacts on a volunteer or a phantom. The influence of physiological motion on image quality was investigated by filtering these data. Finally, the method was used to reproduce and quantify the motion artifacts prevented in a patient scan. Results The accuracy of the method was tested in phantom experiments and in vivo. The calculated quality factor, as well as a visual inspection of the reproduced artifacts shows a good correspondence to the original. Conclusion Precise reproduction of motion artifacts assists qualification of prospective motion correction strategies. The presented method provides an important tool to investigate the effects of rigid body motion on a wide range of sequences, and to quantify the improvement in image quality through prospective motion correction. Magn Reson Med 71:182-190, 2014. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the effect of field strength on flowsensitive 4D magnetic resonance imaging (MRI) of the thoracic aorta. A volunteer study at 1.5 T and 3 T was conducted to compare phase-contrast MR angiography (MRA) and 3D flow visualization quality as well as quantification of aortic hemodynamics. Materials and Methods: Ten healthy volunteers were examined by flow-sensitive 4D MRI at both 1.5 T and 3 T MRI with identical imaging parameters (TE/TR = 6/5.1 msec, spatial/temporal resolution ≈2 mm/40.8 msec). Analysis included assessment of image quality of derived aortic 3D phase contrast (PC) angiography and 3D flow visualization (semiquantitative grading on a 0-2 scale, two blinded observers) and quantification of blood flow velocities, net flow per cardiac cycle, wall shear stress (WSS), and velocity noise. Results: Quality of 3D blood flow visualization (average grading = 1.8 ± 0.4 at 3 T vs. 1.1 ± 0.7 at 1.5 T) and the depiction of aortic lumen geometry by 3D PC-MRA (1.7 ± 0.5 vs. 1.2 ± 0.6) were significantly (P < 0.01) improved at 3 T while velocity noise was significantly higher (P < 0.01) at 1.5 T. Velocity quantification resulted in minimally altered (0.05 m/s, 3 mL/cycle and 0.01 N/m2) but not statistically different (P = 0.40, P = 0.39, and P = 0.82) systolic peak velocities, net flow, and WSS for 1.5 T compared to 3 T. Conclusion: Flow-sensitive 4D MRI at 3 T provided improved image quality without additional artifacts related to higher fields. Imaging at 1.5 T MRI, which is more widely available, was also feasible and provided information on aortic 3D hemodynamics of moderate quality with identical performance regarding quantitative analysis [ABSTRACT FROM AUTHOR]

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 mm3). 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. J. Magn. Reson. Imaging 2012;36:604-611. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose: To measure aortic pulse wave velocity (PWV) using flow-sensitive four-dimensional (4D) MRI and to evaluate test-retest reliability, inter- and intra-observer variability in volunteers and correlation with characteristics in patients with aortic atherosclerosis. Materials and Methods: Flow-sensitive 4D MRI was performed in 12 volunteers (24 ± 3 years) and 86 acute stroke patients (68 ± 9 years) with aortic atherosclerosis. Retrospectively positioned 28 ± 4 analysis planes along the entire aorta (inter-slice-distance = 10 mm) and frame wise lumen segmentation yielded flow-time-curves for each plane. Global aortic PWV was calculated from time-shifts and distances between the upslope portions of all available flow-time curves. Results: Inter- and intra-observer variability of PWV measurements in volunteers (7% and 8%) was low while test-retest reliability (22%) was moderate. PWV in patients was significantly higher compared with volunteers (5.8 ± 2.9 versus 3.8 ± 0.8 m/s; P = 0.02). Among 17 patient characteristics considered, statistical analysis revealed significant ( P < 0.05) but low correlation of PWV with age ( r = 0.25), aortic valve insufficiency ( r = 0.29), and pulse pressure ( r = 0.28). Multivariate modeling indicated that aortic valve insufficiency and elevated pulse pressure were significantly associated with higher PWV (adjusted R2 = 0.13). Conclusion: Flow-sensitive 4D MRI allows for estimating aortic PWV with low observer dependence and moderate test-retest reliability. PWV in patients correlated with age, aortic valve insufficiency, and pulse pressure. J. Magn. Reson. Imaging 2012;. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Our purpose was to correlate atherogenic low wall shear stress (WSS) and high oscillatory shear index (OSI) with the localization of aortic plaques. Flow-sensitive four-dimensional MRI was used to acquire three-dimensional blood flow in the aorta of 62 patients with proven aortic atherosclerosis and 31 healthy volunteers. Multiplanar data analysis of WSS magnitude and OSI in 12 wall segments was performed in analysis planes distributed along the aorta. Disturbed WSS and OSI were defined as areas exposed to low WSS magnitude and high OSI beyond individual 15% thresholds. Planewise analysis revealed a good correlation ( r = 0.85) of individual low WSS magnitude but not of high OSI with plaque distribution. Although plaques occurred only rarely in the ascending aorta, the incidence of low WSS magnitude and high OSI was similar to findings in other aortic segments where plaques occurred more frequently. Case-by-case comparisons of plaque location and critical wall parameters revealed a shift of atherogenic WSS magnitude (78% of all cases) and OSI (91%) to wall segments adjacent to the atheroma. Our results indicate that the predictive value of WSS for plaque existence depends on the aortic segment and that locations of critical wall parameters move to neighboring segments of regions affected by atherosclerosis. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

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 = 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 ± 0.24 m/sec) compared to age-matched controls (6.40 ± 0.32 m/sec). Both were significantly ( P < 0.001) increased compared to younger volunteers (4.39 ± 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 four-dimensional 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, 2010. © 2010 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Purpose To assess the distribution and regional differences of flow and vessel wall parameters such as wall shear stress (WSS) and oscillatory shear index (OSI) in the entire thoracic aorta. Materials and Methods Thirty-one healthy volunteers (mean age = 23.7 ± 3.3 years) were examined by flow-sensitive four-dimensional (4D)-MRI at 3T. For eight retrospectively positioned 2D analysis planes distributed along the thoracic aorta, flow parameters and vectorial WSS and OSI were assessed in 12 segments along the vascular circumference. Results Mean absolute time-averaged WSS ranged between 0.25 ± 0.04 N/m2 and 0.33 ± 0.07 N/m2 and incorporated a substantial circumferential component (-0.05 ± 0.04 to 0.07 ± 0.02 N/m2). For each analysis plane, a segment with lowest absolute WSS and highest OSI was identified which differed significantly from mean values within the plane ( P < 0.05). The distribution of atherogenic low WSS and high OSI closely resembled typical locations of atherosclerotic lesions at the inner aortic curvature and supraaortic branches. Conclusion The normal distribution of vectorial WSS and OSI in the entire thoracic aorta derived from flow-sensitive 4D-MRI data provides a reference constituting an important perquisite for the examination of patients with aortic disease. Marked regional differences in absolute WSS and OSI may help explaining why atherosclerotic lesions predominantly develop and progress at specific locations in the aorta. J. Magn. Reson. Imaging 2009;30:77-84. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Purpose To qualitatively and quantitatively evaluate the image quality in accelerated time-resolved 3D contrast-enhanced MR angiography (tr-CE-MRA) at 3T. Materials and Methods In all, 113 MRA were performed in 107 patients on a 3T MR system after written informed consent and approval by the ethics committee. Twenty consecutive thoracic ( n = 87) or craniocervical ( n = 26) 3D data volumes were acquired. The timeframes with maximum arterial and venous contrast were determined and a total of 663 arterial and venous segments were analyzed by two blinded observers. Diagnostic image quality was graded by applying a 0 (low) to 3 (excellent) scale. Additionally, local signal-to-noise (SNR) and contrast-to-noise ratios (relative CNR) were evaluated. Results Tr-CE-MRA was successfully performed in all patients. Good to excellent image quality (2.42 ± 0.31) was observed in all individuals with preserved discrimination of arteries (2.43 ± 0.48) and veins (2.20 ± 0.56). Minor image degradation due to artifacts (2.62 ± 0.25) and constantly high vascular signal and contrast were detected. There was a significant superiority of coronal orientation during thoracic MRA ( P < 0.05). In 18 cases tr-CE-MRA provided additional information on vascular pathologies. Conclusion Large field of view tr-CE-MRA enables constantly high-quality thoracic and craniocervical angiographies. In addition, the dynamics of tr-CE-MRA can offer additional information on vascular pathologies. J. Magn. Reson. Imaging 2008;28:1116-1124. © 2008 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

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. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Purpose To evaluate an improved image acquisition and data-processing strategy for assessing aortic vascular geometry and 3D blood flow at 3T. Materials and Methods In a study with five normal volunteers and seven patients with known aortic pathology, prospectively ECG-gated cine three-dimensional (3D) MR velocity mapping with improved navigator gating, real-time adaptive k-space ordering and dynamic adjustment of the navigator acceptance criteria was performed. In addition to morphological information and three-directional blood flow velocities, phase-contrast (PC)-MRA images were derived from the same data set, which permitted 3D isosurface rendering of vascular boundaries in combination with visualization of blood-flow patterns. Results Analysis of navigator performance and image quality revealed improved scan efficiencies of 63.6% ± 10.5% and temporal resolution (<50 msec) compared to previous implementations. Semiquantitative evaluation of image quality by three independent observers demonstrated excellent general image appearance with moderate blurring and minor ghosting artifacts. Results from volunteer and patient examinations illustrate the potential of the improved image acquisition and data-processing strategy for identifying normal and pathological blood-flow characteristics. Conclusion Navigator-gated time-resolved 3D MR velocity mapping at 3T in combination with advanced data processing is a powerful tool for performing detailed assessments of global and local blood-flow characteristics in the aorta to describe or exclude vascular alterations. J. Magn. Reson. Imaging 2007. © 2007 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]