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  1. Bernard, Olivier ; Clarysse, Patrick ; Duchateau, Nicolas ; Ohayon, Jacques ; Viallon, Magalie (Ed.)
    Porcine hearts (N = 14) underwent ex vivo diffusion tensor imaging (DTI) at 3T. DTI analysis showed regional differences in helix angle (HA) range. The HA range in the posterior free wall was significantly greater than that of the anterior free wall (p = 0.02), the lateral free wall (p < 0.001) and the septum (p = 0.008). The best-fit transmural HA function also varied by region, with eight regions best described by an arctan function, seven by an arcsine function, and a single region by a linear function. Tractography analysis was performed, and the length that the tracts spanned within the epicardial, midwall, and endocardial segments was measured. A high number of tracts span the epicardial and mid-wall thirds, with fewer tracts spanning the mid-wall and endocardial thirds. Connectivity analysis of the number of tracts connecting different ventricular regions showed a high prevalence of oblique tracts that may be critical for long-range connectivity. 
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    Free, publicly-accessible full text available June 16, 2024
  2. Bernard, Olivier ; Clarysse, Patrick ; Duchateau, Nicolas ; Ohayon, Jacques ; Viallon, Magalie (Ed.)
    Porcine hearts (N = 14) underwent ex vivo diffusion tensor imaging (DTI) at 3T. DTI analysis showed regional differences in helix angle (HA) range. The HA range in the posterior free wall was significantly greater than that of the anterior free wall (p = 0.02), the lateral free wall (p < 0.001) and the septum (p = 0.008). The best-fit transmural HA function also varied by region, with eight regions best described by an arctan function, seven by an arcsine function, and a single region by a linear function. Tractography analysis was performed, and the length that the tracts spanned within the epicardial, midwall, and endocardial segments was measured. A high number of tracts span the epicardial and mid-wall thirds, with fewer tracts spanning the mid-wall and endocardial thirds. Connectivity analysis of the number of tracts connecting different ventricular regions showed a high prevalence of oblique tracts that may be critical for long-range connectivity. 
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    Free, publicly-accessible full text available June 16, 2024
  3. Bernard, O. ; Clarysse, P. ; Duchateau, N. ; Ohayon, J. ; Viallon, M (Ed.)
    Increased passive myocardial stiffness is implicated in the pathophysiology of many cardiac diseases, and its in vivo estimation can improve management of heart disease. MRI-driven computational constitutive modeling has been used extensively to evaluate passive myocardial stiffness. This approach requires subject-specific data that is best acquired with different MRI sequences: conventional cine (e.g. bSSFP), tagged MRI (or DENSE), and cardiac diffusion tensor imaging. However, due to the lack of comprehensive datasets and the challenge of incorporating multi-phase and single-phase disparate MRI data, no studies have combined in vivo cine bSSFP, tagged MRI, and cardiac diffusion tensor imaging to estimate passive myocardial stiffness. The objective of this work was to develop a personalized in silico left ventricular model to evaluate passive myocardial stiffness by integrating subject-specific geometric data derived from cine bSSFP, regional kinematics extracted from tagged MRI, and myocardial microstructure measured using in vivo cardiac diffusion tensor imaging. To demonstrate the feasibility of using a complete subject-specific imaging dataset for passive myocardial stiffness estimation, we calibrated a bulk stiffness parameter of a transversely isotropic exponential constitutive relation to match the local kinematic field extracted from tagged MRI. This work establishes a pipeline for developing subject-specific biomechanical ventricular models to probe passive myocardial mechanical behavior, using comprehensive cardiac imaging data from multiple in vivo MRI sequences. 
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    Free, publicly-accessible full text available June 16, 2024
  4. Abstract Purpose

    Parallel imaging and compressed sensing reconstructions of large MRI datasets often have a prohibitive computational cost that bottlenecks clinical deployment, especially for three‐dimensional (3D) non‐Cartesian acquisitions. One common approach is to reduce the number of coil channels actively used during reconstruction as in coil compression. While effective for Cartesian imaging, coil compression inherently loses signal energy, producing shading artifacts that compromise image quality for 3D non‐Cartesian imaging. We propose coil sketching, a general and versatile method for computationally‐efficient iterative MR image reconstruction.

    Theory and Methods

    We based our method on randomized sketching algorithms, a type of large‐scale optimization algorithms well established in the fields of machine learning and big data analysis. We adapt the sketching theory to the MRI reconstruction problem via a structured sketching matrix that, similar to coil compression, considers high‐energy virtual coils obtained from principal component analysis. But, unlike coil compression, it also considers random linear combinations of the remaining low‐energy coils, effectively leveraging information from all coils.

    Results

    First, we performed ablation experiments to validate the sketching matrix design on both Cartesian and non‐Cartesian datasets. The resulting design yielded both improved computatioanal efficiency and preserved signal‐to‐noise ratio (SNR) as measured by the inverse g‐factor. Then, we verified the efficacy of our approach on high‐dimensional non‐Cartesian 3D cones datasets, where coil sketching yielded up to three‐fold faster reconstructions with equivalent image quality.

    Conclusion

    Coil sketching is a general and versatile reconstruction framework for computationally fast and memory‐efficient reconstruction.

     
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  5. Abstract

    Right ventricular (RV) failure remains a significant clinical burden particularly during the perioperative period surrounding major cardiac surgeries, such as implantation of left ventricular assist devices (LVADs), bypass procedures or valvular surgeries. Device solutions designed to support the function of the RV do not keep up with the pace of development of left‐sided solutions, leaving the RV vulnerable to acute failure in the challenging hemodynamic environments of the perioperative setting. This work describes the design of a biomimetic, soft, conformable sleeve that can be prophylactically implanted on the pulmonary artery to support RV ventricular function during major cardiac surgeries, through afterload reduction and augmentation of flow. Leveraging electrohydraulic principles, a technology is proposed that is non‐blood contacting and obviates the necessity for drivelines by virtue of being electrically powered. In addition, the integration of an adjacent is demonstrate, continuous pressure sensing module to support physiologically adaptive control schemes based on a real‐time biological signal. In vitro experiments conducted in a pulsatile flow‐loop replicating physiological flow and pressure conditions show a reduction of mean pulmonary arterial pressure of 8 mmHg (25% reduction), a reduction in peak systolic arterial pressure of up to 10 mmHg (20% reduction), and a concomitant 19% increase in diastolic pulmonary flow. Computational simulations further predict substantial augmentation of cardiac output as a result of reduced RV ventricular stress and RV dilatation.

     
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  6. Background

    Clinical management of boys with Duchenne muscular dystrophy (DMD) relies on in‐depth understanding of cardiac involvement, but right ventricular (RV) structural and functional remodeling remains understudied.

    Purpose

    To evaluate several analysis methods and identify the most reliable one to measure RV pre‐ and postcontrast T1 (RV‐T1) and to characterize myocardial remodeling in the RV of boys with DMD.

    Study Type

    Prospective.

    Population

    Boys with DMD (N = 27) and age‐/sex‐matched healthy controls (N = 17) from two sites.

    Field Strength/Sequence

    3.0 T using balanced steady state free precession, motion‐corrected phase sensitive inversion recovery and modified Look‐Locker inversion recovery sequences.

    Assessment

    Biventricular mass (Mi), end‐diastolic volume (EDVi) and ejection fraction (EF) assessment, tricuspid annular excursion (TAE), late gadolinium enhancement (LGE), pre‐ and postcontrast myocardial T1 maps. The RV‐T1 reliability was assessed by three observers in four different RV regions of interest (ROI) using intraclass correlation (ICC).

    Statistical Tests

    The Wilcoxon rank sum test was used to compare RV‐T1 differences between DMD boys with negative LGE(−) or positive LGE(+) and healthy controls. Additionally, correlation of precontrast RV‐T1 with functional measures was performed. AP‐value <0.05 was considered statistically significant.

    Results

    A 1‐pixel thick RV circumferential ROI proved most reliable (ICC > 0.91) for assessing RV‐T1. Precontrast RV‐T1 was significantly higher in boys with DMD compared to controls. Both LGE(−) and LGE(+) boys had significantly elevated precontrast RV‐T1 compared to controls (1543 [1489–1597] msec and 1550 [1402–1699] msec vs. 1436 [1399–1473] msec, respectively). Compared to healthy controls, boys with DMD had preserved RVEF (51.8 [9.9]% vs. 54.2 [7.2]%,P = 0.31) and significantly reduced RVMi (29.8 [9.7] g vs. 48.0 [15.7] g), RVEDVi (69.8 [29.7] mL/m2vs. 89.1 [21.9] mL/m2), and TAE (22.0 [3.2] cm vs. 26.0 [4.7] cm). Significant correlations were found between precontrast RV‐T1 and RVEF (β = −0.48%/msec) and between LV‐T1 and LVEF (β = −0.51%/msec).

    Data Conclusion

    Precontrast RV‐T1 is elevated in boys with DMD compared to healthy controls and is negatively correlated with RVEF.

    Level of Evidence

    1

    Technical Efficacy

    Stage 2

     
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