Pegah Entezari

Bicuspid Aortic Cusp Fusion Morphology Alters Aortic Three-Dimensional Outflow Patterns, Wall Shear Stress, and Expression of Aortopathy

Background— Aortic 3-dimensional blood flow was analyzed to investigate altered ascending aorta (AAo) hemodynamics in bicuspid aortic valve (BAV) patients and its association with differences in cusp fusion patterns (right-left, RL versus right-noncoronary, RN) and expression of aortopathy. Methods and Results— Four-dimensional flow MRI measured in vivo 3-dimensional blood flow in the aorta of 75 subjects: BAV patients with aortic dilatation stratified by leaflet fusion pattern (n=15 RL-BAV, mid AAo diameter=39.9±4.4 mm; n=15 RN-BAV, 39.6±7.2 mm); aorta size controls with tricuspid aortic valves (n=30, 41.0±4.4 mm); healthy volunteers (n=15, 24.9±3.0 mm). Aortopathy type (0–3), systolic flow angle, flow displacement, and regional wall shear stress were determined for all subjects. Eccentric outflow jet patterns in BAV patients resulted in elevated regional wall shear stress (P<0.0125) at the right-anterior walls for RL-BAV and right-posterior walls for RN-BAV in comparison with aorta size controls. Dilatation of the aortic root only (type 1) or involving the entire AAo and arch (type 3) was found in the majority of RN-BAV patients (87%) but was mostly absent for RL-BAV patients (87% type 2). Differences in aortopathy type between RL-BAV and RN-BAV patients were associated with altered flow displacement in the proximal and mid AAo for type 1 (42%–81% decrease versus type 2) and distal AAo for type 3 (33%–39% increase versus type 2). Conclusions— The presence and type of BAV fusion was associated with changes in regional wall shear stress distribution, systolic flow eccentricity, and expression of BAV aortopathy. Hemodynamic markers suggest a physiological mechanism by which the valve morphology phenotype can influence phenotypes of BAV aortopathy.

k-t GRAPPA accelerated four-dimensional flow MRI in the aorta: effect on scan time, image quality, and quantification of flow and wall shear stress.

The purpose of this study was to evaluate the utility of k‐t parallel imaging for accelerating aortic four‐dimensional (4D)‐flow MRI. The aim was to systematically investigate the impact of different acceleration factors and number of coil elements on acquisition time, image quality and quantification of hemodynamic parameters.

Four-dimensional flow assessment of pulmonary artery flow and wall shear stress in adult pulmonary arterial hypertension: results from two institutions.

To compare pulmonary artery flow using Cartesian and radially sampled four‐dimensional flow‐sensitive (4D flow) MRI at two institutions.

Improved semiautomated 4D flow MRI analysis in the aorta in patients with congenital aortic valve anomalies versus tricuspid aortic valves

Objective The aim of this study was to systematically investigate a newly developed semiautomated workflow for the analysis of aortic 4-dimensional flow MRI and its ability to detect hemodynamic differences in patients with congenitally altered aortic valve (bicuspid or quadricuspid valves) compared with tricuspid aortic valves. Methods Four-dimensional flow MRI data were acquired in 20 patients with aortic dilatation (9 tricuspid aortic valves, 11 congenitally altered aortic valves). A semiautomated workflow was evaluated regarding interobserver variability, accuracy of net flow, regurgitant fraction and peak systolic velocity, and the ability to detect differences between cohorts. Results were compared with manual segmentation of vessel contours. Results Despite the significantly reduced analysis time, a good interobserver agreement was found for net flow and peak systolic velocity, and a moderate agreement was found for regurgitation. Significant differences in peak velocities in the descending aorta (P = 0.014) could be detected. Conclusions Four-dimensional flow MRI-based semiautomated analysis of aortic hemodynamics can be performed with good reproducibility and accuracy.

Evaluation of aortic stenosis severity using 4D flow jet shear layer detection for the measurement of valve effective orifice area.

AIMS The objective of this study was to evaluate the potential of 4D flow MRI to assess valve effective orifice area (EOA) in patients with aortic stenosis as determined by the jet shear layer detection (JSLD) method. METHODS AND RESULTS An in-vitro stenosis phantom was used for validation and in-vivo imaging was performed in 10 healthy controls and 40 patients with aortic stenosis. EOA was calculated by the JSLD method using standard 2D phase contrast MRI (PC-MRI) and 4D flow MRI measurements (EOAJSLD-2D and EOAJSLD-4D, respectively). As a reference standard, the continuity equation was used to calculate EOA (EOACE) with the 2D PC-MRI velocity field and compared to the EOAJSLD measurements. The in-vitro results exhibited excellent agreement between flow theory (EOA=0.78cm(2)) and experimental measurement (EOAJSLD-4D=0.78±0.01cm(2)) for peak velocities ranging from 0.9 to 3.7m/s. In-vivo results showed good correlation and agreement between EOAJSLD-2D and EOACE (r=0.91, p<0.001; bias: -0.01±0.38cm(2); agreement limits: 0.75 to -0.77cm(2)), and between EOAJSLD-4D and EOACE (r=0.95, p<0.001; bias: -0.09±0.26cm(2); limits: 0.43 to -0.62cm(2)). CONCLUSION This study demonstrates the feasibility of measuring EOAJSLD using 4D flow MRI. The technique allows for optimization of the EOA measurement position by visualizing the 3D vena contracta, and avoids potential sources of EOACE measurement variability.

From unicuspid to quadricuspid: influence of aortic valve morphology on aortic three-dimensional hemodynamics.

To assess the impact of aortic valve morphology on aortic hemodynamics between normal tricuspid and congenitally anomalous aortic valves ranging from unicuspid to quadricuspid morphology.

Analysis of the thoracic aorta using a semi-automated post processing tool

OBJECTIVE To evaluates a semi-automated method for Thoracic Aortic Aneurysm (TAA) measurement using ECG-gated Dual Source CT Angiogram (DSCTA). METHODS This retrospective HIPAA compliant study was approved by our IRB. Transaxial maximum diameters of outer wall to outer wall were studied in fifty patients at seven anatomic locations of the thoracic aorta: annulus, sinus, sinotubular junction (STJ), mid ascending aorta (MAA) at the level of right pulmonary artery, proximal aortic arch (PROX) immediately proximal to innominate artery, distal aortic arch (DIST) immediately distal to left subclavian artery, and descending aorta (DESC) at the level of diaphragm. Measurements were performed using a manual method and semi-automated software. All readers repeated their measurements. Inter-method, intra-observer and inter-observer agreements were evaluated according to intraclass correlation coefficient (ICC) and Bland-Altman plot. The number of cases with manual contouring or center line adjustment for the semi-automated method and also the post-processing time for each method were recorded. RESULTS The mean difference between semi-automated and manual methods was less than 1.3mm at all seven points. Strong inter-method, inter-observer and intra-observer agreement was recorded at all levels (ICC ≥ 0.9). The maximum rate of manual adjustment of center line and contour was at the level of annulus. The average time for manual post-processing of the aorta was 19 ± 0.3 min, while it took 8.26 ± 2.1 min to do the measurements with the semi-automated tool (Vitrea version 6.0.0.1 software). The center line was edited manually at all levels, with most corrections at the level of annulus (60%), while the contour was adjusted at all levels with highest and lowest number of corrections at the levels of annulus and DESC (75% and 0.07% of the cases), respectively. CONCLUSION Compared to the commonly used manual method, semi-automated measurement of vessel dimensions is feasible in the thoracic aorta with the advantage of reduced post-processing time.

From unicuspid to quadricuspid: the impact of aortic valve morphology on 3D hemodynamics

Background The purpose of this study was to assess the impact of aortic valve morphology on aortic 3D blood flow dynamics and wall shear stress (WSS) in normal and a wide range of congenitally altered aortic valves ranging from unicuspid to quadricuspid morphology. Methods In-vivo aortic 3D hemodynamics were evaluated by MRI in 17 patients with unicuspid (n=3), bicuspid (n=9, 3 true bicuspid, 3 right-left (RL) coronary leaflet fusion, and 3 right-non (RN) coronary leaflet fusion), trileaflet (n=3), and quadricuspid aortic valves (n=2). Valve morphology and dynamics were assessed using 2D CINE MRI. Aortic blood flow was measured using ECG and respiration synchronized 4D flow MRI with full volumetric coverage of the aorta. Data analysis included co-registered visualization of aortic valve morphology with systolic 3D blood flow and grading of valve-specific aortic out-flow patterns. The influence of valve geometry on aortic hemodynamics was quantified by calculation of valve flow angle and segmental distribution of ascending aorta WSS. Results All congenitally altered valves showed marked flow derangement, elevated velocity jets along the aortic wall and distinct flow impingement locations. While all RLBAV valves were associated with flow jets directed towards the right anterior aortic wall, RN-fusion and unicuspid valves showed jet patterns towards the right-posterior wall. Quantitative analysis revealed higher flow angles for unicuspid, true BAV, RN-BAV, RL-BAV, and quadricuspid

4D flow jet shear layer detection method for the measurement of effective orifice area and assessment of aortic stenosis severity

Background Aortic stenosis (AS) is the most common cause of valve replacement and its severity is mainly assessed by transthoracic Doppler echocardiography (TTE) to quantify valve effective orifice area (EOA) as determined by the continuity equation. In a previous study we demonstrated that EOA can be directly determined with 2D flow MRI downstream of the AS using the jet shear layer detection (JSLD) method and the acoustical source term (AST) concept. However, both TTE and 2D flow MRI rely on the measurement of local and single-directional velocities and thus incomplete assessment of the complex post-valve flow dynamics in a significant proportion of patients. 3D CINE phase contrast MRI with 3-directional velocity encoding (4D flow MRI) may improve EOA estimation by the JSLD method coupled with full volumetric coverage of ascending aortic 3D blood flow. The objective of this study was to validate 4D flow MRI based EOA estimation using an in-vitro stenosis phantom and to apply the technique for the in-vivo measurement of the valve EOA compared to the reference standard 2D flow MRI. Methods

Impact of beta-blockade premedication on image quality of ECG-gated thoracic aorta CT angiography

Background Thoracic aortic aneurysm is one of the most common aorta pathologies worldwide, which is commonly evaluated by computed tomography angiography (CTA). One of the routine methods to improve the image quality of CTA is heart rate reduction prior to study by beta-blockade administration. Purpose To assess the effect of beta-blockade on image quality of the ascending aorta in electrocardiography (ECG)-gated dual-source CTA (DSCTA) images. Material and Methods In this retrospective study, ECG-gated thoracic aorta CTA images of 40 patients without beta-blocker administration were compared with ECG-gated images of 40 patients with beta-blockade. Images of the aorta were analyzed objectively and subjectively at three levels: sinus of Valsalva (sinus), sinotubular junction (STJ), and mid ascending aorta (MAA). Quantitative sharpness index (SI) and signal-to-noise ratio (SNR) were calculated and two radiologists evaluated the image quality using a 3-point scale. Results Mean heart rate in beta-blocker and non-beta-blocker groups was 61.7 beats per minute (bpm) (range, 58.1–63.9 bpm) and 72.9 bpm (range, 69.3–84.1 bpm), respectively (P <0.05). Aorta wall SI, SNR, and subjective grading were comparable between the two groups at all three levels (P >0.05). Conclusion Beta-blocker premedication may not be necessary for imaging of ascending aorta with ECG-gated DSCTA.