Emilie Bollache

L'aorte conduit le sang oxygéné aux organes et amortit l'onde pulsatile cardiaque. Au cours du vieillissement, elle est exposée à des altérations hémodynamiques et à une rigidité augmentée, elle-même associée à la mortalité.L'objectif de ma thèse est de proposer, à partir de l'IRM et des simulations, des indices non-invasifs de l'hémodynamique aortique locale, qui soient simples, rapides et complémentaires aux indices IRM de géométrie et de fonction aortiques établis.Un premier volet est consacré au développement et la personnalisation d'un modèle 1D de l'aorte descendante, validé qualitativement et quantitativement avec des données IRM sur 7 sujets, afin d'extraire des paramètres de pression, vitesse et surface.Un second volet, dédié aux données IRM, est centré sur :la comparaison de 7 méthodes d'évaluation de la pulsatilité aortique et leur validation avec la référence sur 70 sujets sains la quantification du flux réverse aortique et l'étude de sa variation avec l'âge, ainsi que l'identification de ses déterminants sur 96 sujets sains l'estimation automatique d'indices hémodynamiques de la sténose valvulaire aortique (SVA) et leur comparaison à l'échocardiographie Doppler sur 53 patients avec une SVA et 21 contrôles.Ainsi, le modèle aortique pourrait aider à identifier les déterminants des altérations aortiques et à consolider les observations in vivo. Par ailleurs, les outils mis au point pour l'analyse reproductible des données d'IRM fournissent des indices caractéristiques du vieillissement, qui pourraient être étudiés vis-à-vis des organes cibles (coeur, cerveau, rein, etc.) dans les pathologies cardiovasculaires (hypertension artérielle, drépanocytose).

Background: Heart involvement is frequent although often clinically silent in systemic sclerosis (SSc) patients. Early identification of cardiac involvement can be improved by noninvasive methods such as MRI, in addition to transthoracic echocardiography (TTE).Purpose: To assess the ability of phase‐contrast (PC)‐MRI to detect subclinical left (LV) and right (RV) ventricular diastolic dysfunction in SSc patients.Study Type: Prospective.Population: Thirty‐five consecutive SSc patients (49 ± 14 years) and 35 sex‐ and age‐matched healthy controls (48.6 ± 13.5 years) who underwent TTE and MRI in the same week.Field Strength/Sequence: 5 T/PC‐MRI using a breath‐hold velocity‐encoded gradient echo sequence.Assessment: LV TTE (E/E′) and LV and RV PC‐MRI indices of diastolic function (LV early and late transmitral [E_M, Ef_M, A_M, Af_M] and RV transtricuspid [E_T, Ef_T, A_T, Af_T] peak filling flow velocities and flow rates, as well as LV [] and RV [] peak longitudinal myocardial velocities during diastole) were measured.Statistical Tests: Two‐tailed t‐test, Wilcoxon test, or Fischer test for comparison of variables between SSc and healthy control groups; sensitivity, specificity, receiver‐operating‐characteristic (ROC) area under the curve (AUC) to assess discriminative ability of variables. A P‐value E/E′ and MRI E_M/ and E_T/ were significantly higher in SSc patients than in controls (8.27 ± 1.25 vs. 6.70 ± 1.66; 9.43 ± 2.7 vs. 6.51 ± 1.50; 6.51 [4.70–10.40] vs. 4.13 [3.22–5.75], respectively) and separated SSc patients and healthy controls with good sensitivity (68%, 71%, and 80%), specificity (85%, 94%, and 62%), and AUC (0.787, 0.807, and 0.765). LV Ef_M was significantly higher in SSc patients than in controls (347.1 ± 113.7 vs. 284.7 ± 94.6) as RVAf_T (277 [231–355] vs. 220 [154–253] mL/sec) with impaired relaxation pattern (Ef_T/Af_T, 0.95 [0.87–1.21] vs. 1.12 [0.93–1.47]).Data Conclusion: MRI was able to detect LV and RV diastolic dysfunction in SSc patients with good accuracy in the absence of LV systolic dysfunction at echocardiography. Use of MRI can allow to better assess the early impact of myocardial fibrosis related to SSc.Level of Evidence: 1Technical Efficacy Stage: 2

This study shows the feasibility in a clinical setting of 2-minute aortic four-dimensional flow MRI in 68 healthy volunteers and patients from two centers, providing reproducible velocity and wall ... Purpose To investigate the two-center feasibility of highly k-space and time (k-t)–accelerated 2-minute aortic four-dimensional (4D) flow MRI and to evaluate its performance for the quantification ...

Children with bicuspid aortic valve (BAV) are at risk for serious complications including aortic valve stenosis and aortic rupture. Most studies investigating biomarkers predictive of BAV complications are focused on adults.

Background: Left ventricular (LV) remodeling and aortic stiffness have independent predictive value for all causes and cardiovascular mortality. Because elastic properties of the arterial wall vary along the aortic pathway, we hypothesized that local and regional aortic stiffness could differently impact on LV remodeling. Methods and results: Regional aortic stiffness was determined from carotid–femoral pulse wave velocity (cfPWV) measured by aplanation tonometry. Aortic arch pulse wave velocity was measured by phase contrast cardiovascular magnetic resonance (CMR). Local stiffness was calculated in the ascending aorta pulse wave velocity (aaPWV) and descending aorta pulse wave velocity using central pulse pressure measurement, cine CMR acquisition, and surface change estimation. CMR LV remodeling was expressed as LV mass to end-diastolic volume ratio. We evaluated 146 study participants (41 ± 15 years) free of overt cardiovascular disease. In stepwise multivariate regression analysis, cfPWV and aaPWV were significantly and independently correlated to mass to end-diastolic volume ratio (partial R² = 0.07 and R² = 0.10, respectively, all P < 0.005) after adjustment for age, sex, BMI, brachial mean blood pressure, and central pulse pressure. Descending aorta pulse wave velocity was correlated with mass to end-diastolic volume ratio to a lower extent (R² = 0.04, P = 0.0115) and aortic arch pulse wave velocity was not independently associated with mass to end-diastolic volume ratio. CfPWV and aaPWV were both independently associated with mass to end-diastolic volume ratio, explaining 5 and 8% of mass to end-diastolic volume ratio variance, respectively. Conclusion: In study participants free of overt cardiovascular disease, stiffness of the ascending aorta representing the local proximal aortic function face to the LV and of the downstream aortic pathway assessed by cfPWV reflecting more advanced alterations of material properties involving the entire aorta, are independent determinants of LV remodeling after adjustment to age, BMI, mean blood pressure, and sex.

Purpose: To apply flow distribution analysis in the entire aorta across a wide age range from pediatric to adult subjects.Material and Methods: In all, 98 healthy subjects (age 9–78 years, 41 women) underwent 4D flow MRI at 1.5T and 3T for the assessment of 3D blood flow in the thoracic aorta. Subjects were categorized into age groups: group 1 (n = 9, 5 women): 9–15 years; group 2 (n = 13, 8 women): 16–20 years; group 3 (n = 27, 14 women): 21–39 years; group 4 (n = 40, 11 women): 40–59 years; group 5 (n = 9, 3 women): >60 years. Data analysis included the 3D segmentation of the aorta, aortic valve peak velocity, mid‐ascending aortic diameter, and calculation of flow velocity distribution descriptors (mean, median, standard deviation, incidence of velocities >1 m/s, skewness, and kurtosis of aortic velocity magnitude). Ascending aortic diameter was normalized by body surface area.Results: Age was significantly associated with normalized aortic diameter (R = 0.73, P < 0.001), skewness (R = 0.76, P < 0.001), and kurtosis (R = 0.74, P < 0.001), all adjusted by heart rate. Aortic peak velocity and velocity distribution descriptors, adjusted by heart rate, were significantly different between age groups (P < 0.001, analysis of covariance). Skewness and kurtosis significantly increased (P < 0.001) during adulthood (>40 years) as compared with childhood (P ≤ 0.05) for peak velocity, incidence, mean, median, standard deviation, and skewness, all adjusted by heart rate.Conclusion: Aortic hemodynamics significantly change with age and gender, indicating the importance of age‐ and gender‐matched control cohorts for the assessment of the impact of cardiovascular disease on aortic blood flow.Level of Evidence: 3Technical Efficacy: Stage 5J. Magn. Reson. Imaging 2018;47:487–498.

We aimed (1) determine if systemic right ventricle filling parameters influence systemic right ventricle stroke volume in adult patients with D-transposition of the great arteries (D-TGA) palliated by atrial switch, using cardiac magnetic resonance imaging and echocardiography, and (2) to study relationship of these diastolic parameters with exercise performance and BNP, in patients with preserved systolic systemic right ventricle function. Single-center, cross-sectional, prospective study. In patients with D-TGA palliated by atrial switch, diastolic dysfunction of the systemic right ventricle may precede systolic dysfunction. Forty-five patients with D-TGA and atrial switch and 45 age and sex-matched healthy subjects underwent cardiac magnetic resonance imaging and echocardiography. Filling flow-rates measured by phase-contrast cardiac magnetic resonance imaging were analyzed using customized software to estimate diastolic parameters and compared with exercise performance. In D-TGA, early filling of systemic right ventricle was impaired with a lower peak filling rate normalized by filling volume (Ef/FV measured by cardiac magnetic resonance imaging) and a higher early filling peak velocity normalized by early peak myocardial velocity (E_US/Ea measured by echocardiography) compared with controls (P ≤ .04). Stroke volume of systemic right ventricle showed a direct and significant association with pulmonary venous pathway size (respectively r = 0.50, P < .01). Systemic right atrial area and systemic right ventricle mass/volume index measured by cardiac magnetic resonance imaging, as well as Ef/FV were significantly correlated with exercise performances and BNP (P < .01). All correlations were independent of age, gender, body mass index and blood pressure. Systemic right ventricle pre-load and stroke volume depend mainly on intraatrial pathway function. Moreover, systemic right ventricle remodeling and right atrial dysfunction impair systemic right ventricle filling, leading to BNP increase and exercise limitation. Cardiac magnetic resonance imaging should assess systemic right ventricle filling abnormalities in D-TGA patients.

Purpose: To assess the performance of highly accelerated free‐breathing aortic four‐dimensional (4D) flow MRI acquired in under 2 minutes compared to conventional respiratory gated 4D flow.Methods: Eight k‐t accelerated nongated 4D flow MRI (parallel MRI with extended and averaged generalized autocalibrating partially parallel acquisition kernels [PEAK GRAPPA], R = 5, TRes = 67.2 ms) using four k_y‐k_z Cartesian sampling patterns (linear, center‐out, out‐center‐out, random) and two spatial resolutions (SRes1 = 3.5 × 2.3 × 2.6 mm³, SRes2 = 4.5 × 2.3 × 2.6 mm³) were compared in vitro (aortic coarctation flow phantom) and in 10 healthy volunteers, to conventional 4D flow (16 mm‐navigator acceptance window; R = 2; TRes = 39.2 ms; SRes = 3.2 × 2.3 × 2.4 mm³). The best k‐t accelerated approach was further assessed in 10 patients with aortic disease.Results: The k‐t accelerated in vitro aortic peak flow (Qmax), net flow (Qnet), and peak velocity (Vmax) were lower than conventional 4D flow indices by ≤4.7%, ≤ 11%, and ≤22%, respectively. In vivo k‐t accelerated acquisitions were significantly shorter but showed a trend to lower image quality compared to conventional 4D flow. Hemodynamic indices for linear and out‐center‐out k‐space samplings were in agreement with conventional 4D flow (Qmax ≤ 13%, Qnet ≤ 13%, Vmax ≤ 17%, P > 0.05).Conclusion: Aortic 4D flow MRI in under 2 minutes is feasible with moderate underestimation of flow indices. Differences in k‐space sampling patterns suggest an opportunity to mitigate image artifacts by an optimal trade‐off between scan time, acceleration, and k‐space sampling. Magn Reson Med 79:195–207, 2018. © 2018 International Society for Magnetic Resonance in Medicine.