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PURPOSE: To develop a three-dimensional (two dimensions + time) convolutional neural network trained with displacement encoding with stimulated echoes (DENSE) data for displacement and strain analysis of cine MRI. MATERIALS AND METHODS: In this retrospective multicenter study, a deep learning model (StrainNet) was developed to predict intramyocardial displacement from contour motion. Patients with various heart diseases and healthy controls underwent cardiac MRI examinations with DENSE between August 2008 and January 2022. Network training inputs were a time series of myocardial contours from DENSE magnitude images, and ground truth data were DENSE displacement measurements. Model performance was evaluated using pixelwise end-point error (EPE). For testing, StrainNet was applied to contour motion from cine MRI. Global and segmental circumferential strain (E(cc)) derived from commercial feature tracking (FT), StrainNet, and DENSE (reference) were compared using intraclass correlation coefficients (ICCs), Pearson correlations, Bland-Altman analyses, paired t tests, and linear mixed-effects models. RESULTS: The study included 161 patients (110 men; mean age, 61 years ± 14 [SD]), 99 healthy adults (44 men; mean age, 35 years ± 15), and 45 healthy children and adolescents (21 males; mean age, 12 years ± 3). StrainNet showed good agreement with DENSE for intramyocardial displacement, with an average EPE of 0.75 mm ± 0.35. The ICCs between StrainNet and DENSE and FT and DENSE were 0.87 and 0.72, respectively, for global E(cc) and 0.75 and 0.48, respectively, for segmental E(cc). Bland-Altman analysis showed that StrainNet had better agreement than FT with DENSE for global and segmental E(cc). CONCLUSION: StrainNet outperformed FT for global and segmental E(cc) analysis of cine MRI. Keywords: Image Postprocessing, MR Imaging, Cardiac, Heart, Pediatrics, Technical Aspects, Technology Assessment, Strain, Deep Learning, DENSE Supplemental material is available for this article. © RSNA, 2023

Left ventricle myocardium has a complex micro-architecture, which was revealed to consist of myocyte bundles arranged in a series of laminar sheetlets. Recent imaging studies demonstrated that these sheetlets re-orientated and likely slided over each other during the deformations between systole and diastole, and that sheetlet dynamics were altered during cardiomyopathy. However, the biomechanical effect of sheetlet sliding is not well-understood, which is the focus here. We conducted finite element simulations of the left ventricle (LV) coupled with a windkessel lumped parameter model to study sheetlet sliding, based on cardiac MRI of a healthy human subject, and modifications to account for hypertrophic and dilated geometric changes during cardiomyopathy remodeling. We modeled sheetlet sliding as a reduced shear stiffness in the sheet-normal direction and observed that (1) the diastolic sheetlet orientations must depart from alignment with the LV wall plane in order for sheetlet sliding to have an effect on cardiac function, that (2) sheetlet sliding modestly aided cardiac function of the healthy and dilated hearts, in terms of ejection fraction, stroke volume, and systolic pressure generation, but its effects were amplified during hypertrophic cardiomyopathy and diminished during dilated cardiomyopathy due to both sheetlet angle configuration and geometry, and that (3) where sheetlet sliding aided cardiac function, it increased tissue stresses, particularly in the myofibre direction. We speculate that sheetlet sliding is a tissue architectural adaptation to allow easier deformations of the LV walls so that LV wall stiffness will not hinder function, and to provide a balance between function and tissue stresses. A limitation here is that sheetlet sliding is modeled as a simple reduction in shear stiffness, without consideration of micro-scale sheetlet mechanics and dynamics.

International audience; Cardiac diffusion tensor imaging (DTI) is an emerging technique for the in vivo characterisation of myocardial microstructure, and there is a growing need for its validation and standardisation. We sought to establish the accuracy, precision, repeatability and reproducibility of state-of-the-art pulse sequences for cardiac DTI among 10 centres internationally. Phantoms comprising 0%-20% polyvinylpyrrolidone (PVP) were scanned with DTI using a product pulsed gradient spin echo (PGSE; N = 10 sites) sequence, and a custom motion-compensated spin echo (SE; N = 5) or stimulated echo acquisition mode (STEAM; N = 5) sequence suitable for cardiac DTI in vivo. A second identical scan was performed 1-9 days later, and the data were analysed centrally. The average mean diffusivities (MDs) in 0% PVP were (1.124, 1.130, 1.113) x 10-3 mm2 /s for PGSE, SE and STEAM, respectively, and accurate to within 1.5% of reference data from the literature. The coefficients of variation in MDs across sites were 2.6%, 3.1% and 2.1% for PGSE, SE and STEAM, respectively, and were similar to previous studies using only PGSE. Reproducibility in MD was excellent, with mean differences in PGSE, SE and STEAM of (0.3 ± 2.3, 0.24 ± 0.95, 0.52 ± 0.58) x 10-5 mm2 /s (mean ± 1.96 SD). We show that custom sequences for cardiac DTI provide accurate, precise, repeatable and reproducible measurements. Further work in anisotropic and/or deforming phantoms is warranted.

Background Cardiovascular magnetic resonance (CMR) cine displacement encoding with stimulated echoes (DENSE) measures heart motion by encoding myocardial displacement into the signal phase, facilitating high accuracy and reproducibility of global and segmental myocardial strain and providing benefits in clinical performance. While conventional methods for strain analysis of DENSE images are faster than those for myocardial tagging, they still require manual user assistance. The present study developed and evaluated deep learning methods for fully-automatic DENSE strain analysis. Methods Convolutional neural networks (CNNs) were developed and trained to (a) identify the left-ventricular (LV) epicardial and endocardial borders, (b) identify the anterior right-ventricular (RV)-LV insertion point, and (c) perform phase unwrapping. Subsequent conventional automatic steps were employed to compute strain. The networks were trained using 12,415 short-axis DENSE images from 45 healthy subjects and 19 heart disease patients and were tested using 10,510 images from 25 healthy subjects and 19 patients. Each individual CNN was evaluated, and the end-to-end fully-automatic deep learning pipeline was compared to conventional user-assisted DENSE analysis using linear correlation and Bland Altman analysis of circumferential strain. Results LV myocardial segmentation U-Nets achieved a DICE similarity coefficient of 0.87 ± 0.04, a Hausdorff distance of 2.7 ± 1.0 pixels, and a mean surface distance of 0.41 ± 0.29 pixels in comparison with manual LV myocardial segmentation by an expert. The anterior RV-LV insertion point was detected within 1.38 ± 0.9 pixels compared to manually annotated data. The phase-unwrapping U-Net had similar or lower mean squared error vs. ground-truth data compared to the conventional path-following method for images with typical signal-to-noise ratio (SNR) or low SNR (p Conclusions Deep learning enables fully-automatic global and segmental circumferential strain analysis of DENSE CMR providing excellent agreement with conventional user-assisted methods. Deep learning-based automatic strain analysis may facilitate greater clinical use of DENSE for the quantification of global and segmental strain in patients with cardiac disease.

In vivo cardiac diffusion tensor imaging (cDTI) characterizes myocardial microstructure. Despite its potential clinical impact, considerable technical challenges exist due to the inherent low signal-to-noise ratio.To reduce scan time toward one breath-hold by reconstructing diffusion tensors for in vivo cDTI with a fitting-free deep learning approach.Retrospective.A total of 197 healthy controls, 547 cardiac patients.A 3 T, diffusion-weighted stimulated echo acquisition mode single-shot echo-planar imaging sequence.A U-Net was trained to reconstruct the diffusion tensor elements of the reference results from reduced datasets that could be acquired in 5, 3 or 1 breath-hold(s) (BH) per slice. Fractional anisotropy (FA), mean diffusivity (MD), helix angle (HA), and sheetlet angle (E2A) were calculated and compared to the same measures when using a conventional linear-least-square (LLS) tensor fit with the same reduced datasets. A conventional LLS tensor fit with all available data (12 ± 2.0 [mean ± sd] breath-holds) was used as the reference baseline.Wilcoxon signed rank/rank sum and Kruskal-Wallis tests. Statistical significance threshold was set at P = 0.05. Intersubject measures are quoted as median [interquartile range].For global mean or median results, both the LLS and U-Net methods with reduced datasets present a bias for some of the results. For both LLS and U-Net, there is a small but significant difference from the reference results except for LLS: MD 5BH (P = 0.38) and MD 3BH (P = 0.09). When considering direct pixel-wise errors the U-Net model outperformed significantly the LLS tensor fit for reduced datasets that can be acquired in three or just one breath-hold for all parameters.Diffusion tensor prediction with a trained U-Net is a promising approach to minimize the number of breath-holds needed in clinical cDTI studies.4 TECHNICAL EFFICACY: Stage 1.

Highlights •DT-CMR is a unique technique for noninvasive assessment of myocardial microstructure. •DT-CMR has identified novel cardiomyocyte and sheetlet abnormalities in cardiac disease in vivo. •DT-CMR has the potential to aid clinical diagnosis and risk stratification through microscopic phenotyping.

Purpose In this work we develop and validate a fully automated postprocessing framework for in vivo diffusion tensor cardiac magnetic resonance (DT‐CMR) data powered by deep learning. Methods A U‐Net based convolutional neural network was developed and trained to segment the heart in short‐axis DT‐CMR images. This was used as the basis to automate and enhance several stages of the DT‐CMR tensor calculation workflow, including image registration and removal of data corrupted with artifacts, and to segment the left ventricle. Previously collected and analyzed scans (348 healthy scans and 144 cardiomyopathy patient scans) were used to train and validate the U‐Net. All data were acquired at 3 T with a STEAM‐EPI sequence. The DT‐CMR postprocessing and U‐Net training/testing were performed with MATLAB and Python TensorFlow, respectively. Results The U‐Net achieved a median Dice coefficient of 0.93 [0.92, 0.94] for the segmentation of the left‐ventricular myocardial region. The image registration of diffusion images improved with the U‐Net segmentation (P < .0001), and the identification of corrupted images achieved an F1 score of 0.70 when compared with an experienced user. Finally, the resulting tensor measures showed good agreement between an experienced user and the fully automated method. Conclusion The trained U‐Net successfully automated the DT‐CMR postprocessing, supporting real‐time results and reducing human workload. The automatic segmentation of the heart improved image registration, resulting in improvements of the calculated DT parameters.

Aims:\ud There is an important need for better biomarkers to predict left ventricular (LV) remodelling in dilated cardiomyopathy (DCM). We undertook a comprehensive assessment of cardiac structure and myocardial composition to determine predictors of remodelling.\ud \ud Methods and results:\ud Prospective study of patients with recent‐onset DCM with cardiovascular magnetic resonance (CMR) assessment of ventricular structure and function, extracellular volume (T1 mapping), myocardial strain, myocardial scar (late gadolinium enhancement) and contractile reserve (dobutamine stress). Regression analyses were used to evaluate predictors of change in LV ejection fraction (LVEF) over 12 months. We evaluated 56 participants (34 DCM patients, median LVEF 43%; 22 controls). Absolute LV contractile reserve predicted change in LVEF (1% increase associated with 0.4% increase in LVEF at 12 months, P = 0.02). Baseline myocardial strain (P = 0.39 global longitudinal strain), interstitial myocardial fibrosis (P = 0.41), replacement myocardial fibrosis (P = 0.25), and right ventricular contractile reserve (P = 0.17) were not associated with LV reverse remodelling. There was a poor correlation between contractile reserve and either LV extracellular volume fraction (r = −0.22, P = 0.23) or baseline LVEF (r = 0.07, P = 0.62). Men were more likely to experience adverse LV remodelling (P = 0.01) but age (P = 0.88) and disease‐modifying heart failure medication (beta‐blocker, P = 0.28; angiotensin‐converting enzyme inhibitor, P = 0.92) did not predict follow‐up LVEF.\ud \ud Conclusions:\ud Substantial recovery of LV function occurs within 12 months in most patients with recent‐onset DCM. Women had the greatest improvement in LVEF. A low LV contractile reserve measured by dobutamine stress CMR appears to identify patients whose LVEF is less likely to recover.

BackgroundCardiac motion results in image artefacts and quantification errors in many cardiovascular magnetic resonance (CMR) techniques, including microstructural assessment using diffusion tensor cardiovascular magnetic resonance (DT-CMR). Here we develop a CMR compatible isolated perfused porcine heart model that allows comparison of data obtained in beating and arrested states.Methods10 porcine hearts (8/10 for protocol optimisation) were harvested using a donor heart retrieval protocol and transported to the remote CMR facility. Langendorff perfusion in a 3D printed chamber and perfusion circuit re-established contraction. Hearts were imaged using cine, parametric mapping and STEAM DT-CMR at cardiac phases with the minimum and maximum wall thickness. High potassium and lithium perfusates were then used to arrest the heart in a slack and contracted state respectively. Imaging was repeated in both arrested states. After imaging, tissue was removed for subsequent histology in a location matched to the DT-CMR data using fiducial markers.ResultsRegular sustained contraction was successfully established in 6/10 hearts, including the final 5 hearts. Imaging was performed in 4 hearts and one underwent the full protocol including co-localised histology. Image quality was good and there was good agreement between DT-CMR data in equivalent beating and arrested states. Despite the use of autologous blood and dextran within the perfusate, T2, DT-CMR measures and an increase in mass was consistent with development of myocardial edema resulting in failure to achieve a true diastolic-like state. A contiguous stack of 313 5μm histological sections at and a 100μm thick section showing cell morphology on 3D fluorescent confocal microscopy co-localised to DT-CMR data were obtained.ConclusionsA CMR compatible isolated perfused beating heart setup for large animal hearts allows direct comparisons of beating and arrested heart data with subsequent co-localised histology without the need for onsite pre-clinical facilities.

Background While multiple cardiovascular magnetic resonance (CMR) methods provide excellent reproducibility of global circumferential and global longitudinal strain, achieving highly reproducible segmental strain is more challenging. Previous single-center studies have demonstrated excellent reproducibility of displacement encoding with stimulated echoes (DENSE) segmental circumferential strain. The present study evaluated the reproducibility of DENSE for measurement of whole-slice or global circumferential (Ecc), longitudinal (Ell) and radial (Err) strain, torsion, and segmental Ecc at multiple centers. Methods Six centers participated and a total of 81 subjects were studied, including 60 healthy subjects and 21 patients with various types of heart disease. CMR utilized 3 T scanners, and cine DENSE images were acquired in three short-axis planes and in the four-chamber long-axis view. During one imaging session, each subject underwent two separate DENSE scans to assess inter-scan reproducibility. Each subject was taken out of the scanner and repositioned between the scans. Intra-user, inter-user-same-site, inter-user-different-site, and inter-user-Human-Deep-Learning (DL) comparisons assessed the reproducibility of different users analyzing the same data. Inter-scan comparisons assessed the reproducibility of DENSE from scan to scan. The reproducibility of whole-slice or global Ecc, Ell and Err, torsion, and segmental Ecc were quantified using Bland–Altman analysis, the coefficient of variation (CV), and the intraclass correlation coefficient (ICC). CV was considered excellent for CV ≤ 10%, good for 10% 40. ICC values were considered excellent for ICC > 0.74, good for ICC 0.6 Results Based on CV and ICC, segmental Ecc provided excellent intra-user, inter-user-same-site, inter-user-different-site, inter-user-Human-DL reproducibility and good–excellent inter-scan reproducibility. Whole-slice Ecc and global Ell provided excellent intra-user, inter-user-same-site, inter-user-different-site, inter-user-Human-DL and inter-scan reproducibility. The reproducibility of torsion was good–excellent for all comparisons. For whole-slice Err, CV was in the fair-good range, and ICC was in the good–excellent range. Conclusions Multicenter data show that 3 T CMR DENSE provides highly reproducible whole-slice and segmental Ecc, global Ell, and torsion measurements in healthy subjects and heart disease patients.

The 3D microarchitecture of the cardiac muscle underlies the mechanical and electrical properties of the heart. Cardiomyocytes are arranged helically through the depth of the wall, and their shortening leads to macroscopic torsion, twist, and shortening during cardiac contraction. Furthermore, cardiomyocytes are organized in sheetlets separated by shear layers, which reorientate, slip, and shear during macroscopic left ventricle (LV) wall thickening. Cardiac diffusion provides a means for noninvasive interrogation of the 3D microarchitecture of the myocardium. The fundamental principle of MR diffusion is that an MRI signal is attenuated by the self-diffusion of water in the presence of large diffusion-encoding gradients. Since water molecules are constrained by the boundaries in biological tissue (cell membranes, collagen layers, etc.), depicting their diffusion behavior elucidates the shape of the myocardial microarchitecture they are embedded in. Cardiac diffusion therefore provides a noninvasive means to understand not only the dynamic changes in cardiac microstructure of healthy myocardium during cardiac contraction but also the pathophysiological changes in the presence of disease. This unique and innovative technology offers tremendous potential to enable improved clinical diagnosis through novel microstructural and functional assessment. in vivo cardiac diffusion methods are immediately translatable to patients, opening new avenues for diagnostic investigation and treatment evaluation in a range of clinically important cardiac pathologies. This review article describes the 3D microstructure of the LV, explains in vivo and ex vivo cardiac MR diffusion acquisition and postprocessing techniques, as well as clinical applications to date. Level of Evidence: 1 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2019. J. Magn. Reson. Imaging 2020;52:348-368.

A mathematical model has been developed to assist with the development of a hollow fibre bioreactor (HFB) for hepatotoxicity testing of xenobiotics; specifically, to inform the HFB operating set-up, interpret data from HFB outputs and aid in optimizing HFB design to mimic certain hepatic physiological conditions. Additionally, the mathematical model has been used to identify the key HFB and compound parameters that will affect xenobiotic clearance. The analysis of this model has produced novel results that allow the operating set-up to be calculated, and predictions of compound clearance to be generated. The mathematical model predicts the inlet oxygen concentration and volumetric flow rate that gives a physiological oxygen gradient in the HFB to mimic a liver sinusoid. It has also been used to predict the concentration gradients and clearance of a test drug and paradigm hepatotoxin, paracetamol (APAP). The effect of altering the HFB dimensions and fibre properties on APAP clearance under the condition of a physiological oxygen gradient is analysed. These theoretical predictions can be used to design the most appropriate experimental set up and data analysis to quantitatively compare the functionality of cell types that are cultured within the HFB to those in other systems.

Objective Develop an accelerated cine displacement encoding with stimulated echoes (DENSE) cardiovascular magnetic resonance (CMR) sequence to enable clinically feasible myocardial strain evaluation in patients with dilated cardiomyopathy (DCM). Materials and methods A spiral cine DENSE sequence was modified by limiting the field of view in two dimensions using in-plane slice-selective pulses in the stimulated echo. This reduced breath hold duration from 20RR to 14RR intervals. Following phantom and pilot studies, the feasibility of the sequence to assess peak radial, circumferential, and longitudinal strain was tested in control subjects (n = 18) and then applied in DCM patients (n = 29). Results DENSE acquisition was possible in all participants. Elements of the data were not analysable in 1 control (6%) and 4 DCM r(14%) subjects due to off-resonance or susceptibility artefacts and low signal-to-noise ratio. Peak radial, circumferential, short-axis contour strain and longitudinal strain was reduced in DCM patients (p 0.80), except peak radial strain. Discussion We demonstrate the feasibility of CMR strain assessment in healthy controls and DCM patients using an accelerated cine DENSE technique. This may facilitate integration of strain assessment into routine CMR studies. Electronic supplementary material The online version of this article (10.1007/s10334-019-00735-5) contains supplementary material, which is available to authorized users.

Background Diffusion Tensor Cardiovascular Magnetic Resonance (DT-CMR) can quantify metrics of tissue integrity (mean diffusivity [MD] and fractional anisotropy [FA]) and changes in laminar microstructures (sheetlets), which reorientate from more wall-parallel in diastole (DIA) towards wall-perpendicular in systole (SYS) as the myocardium thickens, quantified by E2 angle [E2A]. Microstructural changes after STEMI may provide new insights into adverse LV remodelling and risk stratification. Methods In vivo DT-CMR was performed 3–5 days after PPCI for first presentation STEMI (N=19, mean age 57±9, 79% male). DT-CMR was acquired in 2 short-axes (SYS & DIA) using a STEAM-EPI sequence. 12 segment analysis of MD, FA, E2A and E2A mobility (ΔE2A = E2ASYS − E2ADIA) was performed. Infarct (INF) segments were defined as >25% LGE, adjacent (ADJ, located contiguous to INF) and remote (REM, all other segments). Wilcoxon signed rank tests were used with threshold P Results See Table. MD in both SYS and DIA was significantly higher in INF and ADJ regions compared to REM. FA in both SYS and DIA was lower in the INF and ADJ compared to REM. E2ADIA was higher in INF, indicating a more wall-perpendicular orientation of sheetlets, compared to ADJ and REM zones. E2ASYS in INF was significantly reduced, indicating a more wall-parallel orientation of sheetlets, compared to ADJ and REM regions, resulting in significantly reduced sheetlet mobility (ΔE2A). Conclusions Microstructural changes can be detected after acute STEMI by in vivo DT-CMR. Zonal changes in MD and FA may suggest loss of barriers to water diffusion and altered cardiomyocyte organisation, respectively. We provide the first report of reduced sheetlet mobility after acute STEMI in INF. Ongoing work is evaluating the mechanisms and prognostic importance of altered sheetlet mobility after STEMI. Funding Acknowledgement Type of funding source: Foundation. Main funding source(s): British Heart Foundation Clinical Research Training Fellowship

Background Cardiac amyloidosis (CA) is a disease of interstitial myocardial infiltration, usually by light chains or transthyretin. We used diffusion tensor cardiovascular magnetic resonance (DT-CMR) to noninvasively assess the effects of amyloid infiltration on the cardiac microstructure. Methods DT-CMR was performed at diastole and systole in 20 CA, 11 hypertrophic cardiomyopathy, and 10 control subjects with calculation of mean diffusivity, fractional anisotropy, and sheetlet orientation (secondary eigenvector angle). Results Mean diffusivity was elevated and fractional anisotropy reduced in CA compared with both controls and hypertrophic cardiomyopathy ( P r =0.68, P =0.004), and fractional anisotropy was inversely correlated with circumferential strain ( r =−0.65, P =0.02). In CA, diastolic secondary eigenvector angle was elevated, and secondary eigenvector angle mobility was reduced compared with controls (both P Conclusions DT-CMR can characterize the microstructural effects of amyloid infiltration and is a contrast-free method to identify the location and extent of the expanded disorganized myocardium. The diffusion biomarkers mean diffusivity and fractional anisotropy effectively discriminate CA from hypertrophic cardiomyopathy. DT-CMR demonstrated that failure of sheetlet relaxation in diastole correlated with extracellular volume in transthyretin, but not light chain amyloidosis. This indicates that different mechanisms may be responsible for impaired contractility in CA, with an amyloid burden effect in transthyretin, but an idiosyncratic effect in light chain amyloidosis. Consequently, DT-CMR offers a contrast-free tool to identify novel pathophysiology, improve diagnostics, and monitor disease through noninvasive microstructural assessment.

Background Stimulated-echo (STEAM) and, more recently, motion-compensated spin-echo (M2-SE) techniques have been used for in-vivo diffusion tensor cardiovascular magnetic resonance (DT-CMR) assessment of cardiac microstructure. The two techniques differ in the length scales of diffusion interrogated, their signal-to-noise ratio efficiency and sensitivity to both motion and strain. Previous comparisons of the techniques have used high performance gradients at 1.5 T in a single cardiac phase. However, recent work using STEAM has demonstrated novel findings of microscopic dysfunction in cardiomyopathy patients, when DT-CMR was performed at multiple cardiac phases. We compare STEAM and M2-SE using a clinical 3 T scanner in three potentially clinically interesting cardiac phases. Methods Breath hold mid-ventricular short-axis DT-CMR was performed in 15 subjects using M2-SE and STEAM at end-systole, systolic sweet-spot and diastasis. Success was defined by ≥50% of the myocardium demonstrating normal helix angles. From successful acquisitions DT-CMR results relating to tensor orientation, size and shape were compared between sequences and cardiac phases using non-parametric statistics. Strain information was obtained using cine spiral displacement encoding with stimulated echoes for comparison with DT-CMR results. Results Acquisitions were successful in 98% of STEAM and 76% of M2-SE cases and visual helix angle (HA) map scores were higher for STEAM at the sweet-spot and diastasis. There were significant differences between sequences (p

PURPOSE Diffusion tensor cardiovascular MR (DT-CMR) using stimulated echo acquisition mode (STEAM) with echo-planar-imaging (EPI) readouts is a low signal-to-noise-ratio (SNR) technique and therefore typically has a low spatial resolution. Spiral trajectories are more efficient than EPI, and could increase the SNR. The purpose of this study was to compare the performance of a novel STEAM spiral DT-CMR sequence with an equivalent established EPI technique. METHODS A STEAM DT-CMR sequence was implemented with a spiral readout and a reduced field of view. An in vivo comparison of DT-CMR parameters and data quality between EPI and spiral was performed in 11 healthy volunteers imaged in peak systole and diastasis at 3 T. The SNR was compared in a phantom and in vivo. RESULTS There was a greater than 49% increase in the SNR in vivo and in the phantom measurements (in vivo septum, systole: SNREPI = 8.0 ± 2.2, SNRspiral = 12.0 ± 2.7; diastasis: SNREPI = 8.1 ± 1.6, SNRspiral = 12.0 ± 3.7). There were no significant differences in helix angle gradient (HAG) (systole: HAGEPI = -0.79 ± 0.07 °/%; HAGspiral = -0.74 ± 0.16 °/%; P = 0.11; diastasis: HAGEPI = -0.63 ± 0.05 °/%; HAGspiral = -0.56 ± 0.14 °/%; P = 0.20), mean diffusivity (MD) in systole (MDEPI = 0.99 ± 0.06 × 10-3 mm2 /s, MDspiral = 1.00 ± 0.09 × 10-3 mm2 /s, P = 0.23) and secondary eigenvector angulation (E2A) (systole: E2AEPI = 61 ± 10 °; E2Aspiral = 63 ± 10 °; P = 0.77; diastasis: E2AEPI = 18 ± 11 °; E2Aspiral = 15 ± 8 °; P = 0.20) between the sequences. There was a small difference (≈ 20%) in fractional anisotropy (FA) (systole: FAEPI = 0.49 ± 0.03, FAspiral = 0.41 ± 0.04; P

BACKGROUND Cardiomyocytes are organized in microstructures termed sheetlets that reorientate during left ventricular thickening. Diffusion tensor cardiac magnetic resonance (DT-CMR) may enable noninvasive interrogation of in vivo cardiac microstructural dynamics. Dilated cardiomyopathy (DCM) is a condition of abnormal myocardium with unknown sheetlet function. OBJECTIVES This study sought to validate in vivo DT-CMR measures of cardiac microstructure against histology, characterize microstructural dynamics during left ventricular wall thickening, and apply the technique in hypertrophic cardiomyopathy (HCM) and DCM. METHODS In vivo DT-CMR was acquired throughout the cardiac cycle in healthy swine, followed by in situ and ex vivo DT-CMR, then validated against histology. In vivo DT-CMR was performed in 19 control subjects, 19 DCM, and 13 HCM patients. RESULTS In swine, a DT-CMR index of sheetlet reorientation (E2A) changed substantially (E2A mobility ~46°). E2A changes correlated with wall thickness changes (in vivo r2 = 0.75; in situ r2 = 0.89), were consistently observed under all experimental conditions, and accorded closely with histological analyses in both relaxed and contracted states. The potential contribution of cyclical strain effects to in vivo E2A was ~17%. In healthy human control subjects, E2A increased from diastole (18°) to systole (65°; p < 0.001; E2A mobility = 45°). HCM patients showed significantly greater E2A in diastole than control subjects did (48 ; p < 0.001) with impaired E2A mobility (23°; p < 0.001). In DCM, E2A was similar to control subjects in diastole, but systolic values were markedly lower (40° ; p < 0.001) with impaired E2A mobility (20°; p < 0.001). CONCLUSIONS Myocardial microstructure dynamics can be characterized by in vivo DT-CMR. Sheetlet function was abnormal in DCM with altered systolic conformation and reduced mobility, contrasting with HCM, which showed reduced mobility with altered diastolic conformation. These novel insights significantly improve understanding of contractile dysfunction at a level of noninvasive interrogation not previously available in humans. (J Am Coll Cardiol 2017;69:661–76) Published by Elsevier on behalf of the American College of Cardiology Foundation.

Objectives Diffusion tensor cardiovascular magnetic resonance (DT-CMR) interrogates myocardial microstructure. Two frequently used in vivo DT-CMR techniques are motion-compensated spin echo (M2-SE) and stimulated echo acquisition mode (STEAM). Whilst M2-SE is strain-insensitive and signal to noise ratio efficient, STEAM has a longer diffusion time and motion compensation is unnecessary. Here we compare STEAM and M2-SE DT-CMR in patients. Materials and methods Biphasic DT-CMR using STEAM and M2-SE, late gadolinium imaging and pre/post gadolinium T1-mapping were performed in a mid-ventricular short-axis slice, in ten hypertrophic cardiomyopathy (HCM) patients at 3 T. Results Adequate quality data were obtained from all STEAM, but only 7/10 (systole) and 4/10 (diastole) M2-SE acquisitions. Compared with STEAM, M2-SE yielded higher systolic mean diffusivity (MD) (p = 0.02) and lower fractional anisotropy (FA) (p = 0.02, systole). Compared with segments with neither hypertrophy nor late gadolinium, segments with both had lower systolic FA using M2-SE (p = 0.02) and trend toward higher MD (p = 0.1). The negative correlation between FA and extracellular volume fraction was stronger with STEAM than M2-SE (r2 = 0.29, p r2 = 0.10, p = 0.003 M2-SE). Discussion In HCM, only STEAM reliably assesses biphasic myocardial microstructure. Higher MD and lower FA from M2-SE reflect the shorter diffusion times. Further work will relate DT-CMR parameters and microstructural changes in disease.

Genotoxicity testing methods in vitro provide a means to predict the DNA damaging effects of chemicals on human cells. This is hindered in the case of hydrophobic test compounds, however, which will partition to in vitro components such as plastic-ware and medium proteins, in preference to the aqueous phase of the exposure medium. This affects the freely available test chemical concentration, and as this freely dissolved aqueous concentration is that bioavailable to cells, it is important to define and maintain this exposure. Passive dosing promises to have an advantage over traditional ‘solvent spiking’ exposure methods and involves the establishment and maintenance of known chemical concentrations in the in vitro medium, and therefore aqueous phase. Passive dosing was applied in a novel format to expose the MCL-5 human lymphoblastoid cell line to the pro-carcinogen, benzo[a]pyrene (B[a]P) and was compared to solvent (dimethyl sulphoxide) spiked B[a]P exposures over 48 h. Passive dosing induced greater changes, at lower concentrations, to micronucleus frequency, p21 mRNA expression, cell cycle abnormalities, and cell and nuclear morphology. This was attributed to a maintained, definable, free chemical concentration using passive dosing and the presence or absence of solvent, and highlights the influence of exposure choice on genotoxic outcomes.

5 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:319-320.

Dermal bioavailability is currently estimated through skin penetration studies using ex vivo models, which lack any measure of capillary bed function, and thus do not fully reproduce physiological conditions. We propose a novel strategy to mimic skin vascularization using newly fabricated hollow fibers made from a biocompatible membrane material, polystyrene, which is hydrophobic if left untreated, or hydrophilic when its surface polarity is modified through plasma-treatment. Caffeine has been well studied in skin penetration assays and was used here to determine the permeation properties of the hollow fibers in a novel jacketed glass bioreactor. For hydrophobic fibers, approximately 87.2% of the caffeine dose did not penetrate the porous surface; 0.2% of the dose was collected after 24 h (permeated through the pores), and therefore 12.6% of the initial dose was suspected to block the membrane. For hydrophilic fibers, both the percentage of the initial dose that permeated and that of blocking caffeine increased to 1.2% and 35.2% respectively. It was concluded that caffeine permeated the hollow fibers at similar times of clearance to those observed in vivo, and therefore shows that this new model could provide a surrogate for capillary-based clearance in in vitro skin absorption studies.

Highlights • Mechanistic evaluation of SHE CTA, specific to B(a)P. • Applicability of the Syrian hamster as a relevant model of carcinogenesis. • Molecular analysis of immortal lines derived from benzo(a)pyrene-induced MT clones. • Morphological transformation (MT) does not guarantee senescence bypass. • Secondary events to MT are necessary for cellular immortalisation., The implementation of the Syrian hamster embryo cell transformation assay (SHE CTA) into test batteries and its relevance in predicting carcinogenicity has been long debated. Despite prevalidation studies to ensure reproducibility and minimise the subjective nature of the assay’s endpoint, an underlying mechanistic and molecular basis supporting morphological transformation (MT) as an indicator of carcinogenesis is still missing. We found that only 20% of benzo(a)pyrene-induced MT clones immortalised suggesting that, alone, the MT phenotype is insufficient for senescence bypass. From a total of 12 B(a)P- immortalised MT lines, inactivating p53 mutations were identified in 30% of clones, and the majority of these were consistent with the potent carcinogen’s mode of action. Expression of p16 was commonly silenced or markedly reduced with extensive promoter methylation observed in 45% of MT clones, while Bmi1 was strongly upregulated in 25% of clones. In instances where secondary events to MT appeared necessary for senescence bypass, as evidenced by a transient cellular crisis, clonal growth correlated with monoallelic deletion of the CDKN2A/B locus. The findings further implicate the importance of p16 and p53 pathways in regulating senescence while providing a molecular evaluation of SHE CTA −derived variant MT clones induced by benzo(a)pyrene.

There is growing interest in cardiac diffusion tensor imaging (cDTI), but, unlike other diffusion MRI applications, there has been little investigation of the effects of noise on the parameters typically derived. One method of mitigating noise floor effects when there are multiple image averages, as in cDTI, is to average the complex rather than the magnitude data, but the phase contains contributions from bulk motion, which must be removed first. The effects of noise on the mean diffusivity (MD), fractional anisotropy (FA), helical angle (HA) and absolute secondary eigenvector angle (E2A) were simulated with various diffusion weightings (b values). The effect of averaging complex versus magnitude images was investigated. In vivo cDTI was performed in 10 healthy subjects with b = 500, 1000, 1500 and 2000 s/mm(2). A technique for removing the motion-induced component of the image phase present in vivo was implemented by subtracting a low-resolution copy of the phase from the original images before averaging the complex images. MD, FA, E2A and the transmural gradient in HA were compared for un-averaged, magnitude- and complex-averaged reconstructions. Simulations demonstrated an over-estimation of FA and MD at low b values and an under-estimation at high b values. The transition is relatively signal-to-noise ratio (SNR) independent and occurs at a higher b value for FA (b = 1000-1250 s/mm(2)) than MD (b ≈ 250 s/mm(2)). E2A is under-estimated at low and high b values with a transition at b ≈ 1000 s/mm(2), whereas the bias in HA is comparatively small. The under-estimation of FA and MD at high b values is caused by noise floor effects, which can be mitigated by averaging the complex data. Understanding the parameters of interest and the effects of noise informs the selection of the optimal b values. When complex data are available, they should be used to maximise the benefit from the acquisition of multiple averages. The combination of complex data is also a valuable step towards segmented acquisitions.

Imaging the heart is central to cardiac phenotyping, but in clinical practice, this has been restricted to macroscopic interrogation. Diffusion tensor cardiovascular magnetic resonance (DT-CMR) is a novel, noninvasive technique that is beginning to unlock details of this microstructure in humans in vivo. DT-CMR demonstrates the helical cardiomyocyte arrangement that drives rotation and torsion. Sheetlets (functional units of cardiomyocytes, separated by shear layers) have been shown to reorientate between diastole and systole, revealing how microstructural function facilitates cardiac thickening. Measures of tissue diffusion can also be made: fractional anisotropy (a measure of myocyte organization) and mean diffusivity (a measure of myocyte packing). Abnormal myocyte orientation and sheetlet function has been demonstrated in congenital heart disease, cardiomyopathy, and after myocardial infarction. It is too early to predict the clinical importance of DT-CMR, but such unique in vivo information will likely prove valuable in early diagnosis and risk prediction of cardiac dysfunction and arrhythmias.

Purpose Diffusion tensor cardiovascular magnetic resonance (DT-CMR) has a limited spatial resolution. The purpose of this study was to demonstrate high-resolution DT-CMR using a segmented variable density spiral sequence with correction for motion, off-resonance, and T2*-related blurring. Methods A single-shot stimulated echo acquisition mode (STEAM) echo-planar-imaging (EPI) DT-CMR sequence at 2.8 × 2.8 × 8 mm3 and 1.8 × 1.8 × 8 mm3 was compared to a single-shot spiral at 2.8 × 2.8 × 8 mm3 and an interleaved spiral sequence at 1.8 × 1.8 × 8 mm3 resolution in 10 healthy volunteers at peak systole and diastasis. Motion-induced phase was corrected using the densely sampled central k-space data of the spirals. STEAM field maps and T2* measures were obtained using a pair of stimulated echoes each with a double spiral readout, the first used to correct the motion-induced phase of the second. Results The high-resolution spiral sequence produced similar DT-CMR results and quality measures to the standard-resolution sequence in both cardiac phases. Residual differences in fractional anisotropy and helix angle gradient between the resolutions could be attributed to spatial resolution and/or signal-to-noise ratio. Data quality increased after both motion-induced phase correction and off-resonance correction, and sharpness increased after T2* correction. The high-resolution EPI sequence failed to provide sufficient data quality for DT-CMR reconstruction. Conclusion In this study, an in vivo DT-CMR acquisition at 1.8 × 1.8 mm2 in-plane resolution was demonstrated using a segmented spiral STEAM sequence. Motion-induced phase and off-resonance corrections are essential for high-resolution spiral DT-CMR. Segmented variable density spiral STEAM was found to be the optimal method for acquiring high-resolution DT-CMR data.

Introduction Diffusion Tensor Cardiovascular Magnetic Resonance (DT-CMR) assesses myocardial microstructure in vivo, providing information on myocyte and sheetlet organisation. Dilated cardiomyopathy (DCM) patients exhibit impaired sheetlet mobility. Approximately 1/3 DCM patients recover (R-DCM), exhibiting improved left ventricular (LV) size and ejection fraction (EF). However, there has been no study of microstructural recovery in R-DCM. Methods DT-CMR was performed in 12 DCM, 12 R-DCM, and 12 control subjects. R-DCM patients had normal indexed LV size and EF. A STEAM-EPI sequence with b=150 and b=600 at 3 T was used. LV cardiomyocyte orientation (helix angle, HA), sheetlet orientation (secondary eigenvector angulation, E2A), EF and peak radial strain were calculated. The Mann-Whitney test was used for statistical analysis. Results Groups were age and sex matched. In R-DCM, median [IQR] EF at baseline was 27[13]% and current EF was 64[7]%. The EF was 33[16]% in DCM, and 66[4]% in controls. Median [IQR] diastolic E2A in R-DCM was 25[9]°, similar to DCM (19[11]°, p=0.11) and controls (20[14]° p=0.24). However, systolic E2A in R-DCM was 59[14]°, significantly greater than DCM (35[17]° (p Conclusion Despite normal LV size and EF, R-DCM patients have persistent microstructural abnormalities. Sheetlet mobility may offer a role in disease monitoring and assessment of recovery.

Purpose To develop histology‐informed simulations of diffusion tensor cardiovascular magnetic resonance (DT‐CMR) for typical in‐vivo pulse sequences and determine their sensitivity to changes in extra‐cellular space (ECS) and other microstructural parameters. Methods We synthesised the DT‐CMR signal from Monte Carlo random walk simulations. The virtual tissue was based on porcine histology. The cells were thickened and then shrunk to modify ECS. We also created idealised geometries using cuboids in regular arrangement, matching the extra‐cellular volume fraction (ECV) of 16–40%. The simulated voxel size was 2.8 × 2.8 × 8.0 mm3 for pulse sequences covering short and long diffusion times: Stejskal–Tanner pulsed‐gradient spin echo, second‐order motion‐compensated spin echo, and stimulated echo acquisition mode (STEAM), with clinically available gradient strengths. Results The primary diffusion tensor eigenvalue increases linearly with ECV at a similar rate for all simulated geometries. Mean diffusivity (MD) varies linearly, too, but is higher for the substrates with more uniformly distributed ECS. Fractional anisotropy (FA) for the histology‐based geometry is higher than the idealised geometry with low sensitivity to ECV, except for the long mixing time of the STEAM sequence. Varying the intra‐cellular diffusivity (D IC) results in large changes of MD and FA. Varying extra‐cellular diffusivity or using stronger gradients has minor effects on FA. Uncertainties of the primary eigenvector orientation are reduced using STEAM. Conclusions We found that the distribution of ECS has a measurable impact on DT‐CMR parameters. The observed sensitivity of MD and FA to ECV and D IC has potentially interesting applications for interpreting in‐vivo DT‐CMR parameters.

Author(s): Ferreira, Pedro F; Nielles-Vallespin, Sonia; Scott, Andrew D; de Silva, Ranil; Kilner, Philip J; Ennis, Daniel B; Auger, Daniel A; Suever, Jonathan D; Zhong, Xiaodong; Spottiswoode, Bruce S; Pennell, Dudley J; Arai, Andrew E; Firmin, David N | Abstract: PurposeTo evaluate the importance of strain-correcting stimulated echo acquisition mode echo-planar imaging cardiac diffusion tensor imaging.MethodsHealthy pigs (n = 11) were successfully scanned with a 3D cine displacement-encoded imaging with stimulated echoes and a monopolar-stimulated echo-planar imaging diffusion tensor imaging sequence at 3 T during diastasis, peak systole, and strain sweet spots in a midventricular short-axis slice. The same diffusion tensor imaging sequence was repeated ex vivo after arresting the hearts in either a relaxed (KCl-induced) or contracted (BaCl2 -induced) state. The displacement-encoded imaging with stimulated echoes data were used to strain-correct the in vivo cardiac diffusion tensor imaging in diastole and systole. The orientation of the primary (helix angles) and secondary (E2A) diffusion eigenvectors was compared with and without strain correction and to the strain-free ex vivo data.ResultsStrain correction reduces systolic E2A significantly when compared without strain correction and ex vivo (median absolute E2A = 34.3° versus E2A = 57.1° (P = 0.01), E2A = 60.5° (P = 0.006), respectively). The systolic distribution of E2A without strain correction is closer to the contracted ex vivo distribution than with strain correction, root mean square deviation of 0.027 versus 0.038.ConclusionsThe current strain-correction model amplifies the contribution of microscopic strain to diffusion resulting in an overcorrection of E2A. Results show that a new model that considers cellular rearrangement is required. Magn Reson Med 79:2205-2215, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Understanding the structure of the heart at the microscopic scale of cardiomyocytes and their aggregates provides new insights into the mechanisms of heart disease and enables the investigation of effective therapeutics. Diffusion Tensor Cardiac Magnetic Resonance (DT-CMR) is a unique non-invasive technique that can resolve the microscopic structure, organisation, and integrity of the myocardium without the need for exogenous contrast agents. However, this technique suffers from relatively low signal-to-noise ratio (SNR) and frequent signal loss due to respiratory and cardiac motion. Current DT-CMR techniques rely on acquiring and averaging multiple signal acquisitions to improve the SNR. Moreover, in order to mitigate the influence of respiratory movement, patients are required to perform many breath holds which results in prolonged acquisition durations (e.g., \(\sim \)30 min using the existing technology). In this study, we propose a novel cascaded Convolutional Neural Networks (CNN) based compressive sensing (CS) technique and explore its applicability to improve DT-CMR acquisitions. Our simulation based studies have achieved high reconstruction fidelity and good agreement between DT-CMR parameters obtained with the proposed reconstruction and fully sampled ground truth. When compared to other state-of-the-art methods, our proposed deep cascaded CNN method and its stochastic variation demonstrated significant improvements. To the best of our knowledge, this is the first study using deep CNN based CS for the DT-CMR reconstruction. In addition, with relatively straightforward modifications to the acquisition scheme, our method can easily be translated into a method for online, at-the-scanner reconstruction enabling the deployment of accelerated DT-CMR in various clinical applications.

Risk assessment methodologies in toxicology have remained largely unchanged for decades. The default approach uses high dose animal studies, together with human exposure estimates, and conservative assessment (uncertainty) factors or linear extrapolations to determine whether a specific chemical exposure is 'safe' or 'unsafe'. Although some incremental changes have appeared over the years, results from all new approaches are still judged against this process of extrapolating high-dose effects in animals to low-dose exposures in humans. The US National Research Council blueprint for change, entitled Toxicity Testing in the 21st Century: A Vision and Strategy called for a transformation of toxicity testing from a system based on high-dose studies in laboratory animals to one founded primarily on in vitro methods that evaluate changes in normal cellular signalling pathways using human-relevant cells or tissues. More recently, this concept of pathways-based approaches to risk assessment has been expanded by the description of 'Adverse Outcome Pathways' (AOPs). The question, however, has been how to translate this AOP/TT21C vision into the practical tools that will be useful to those expected to make safety decisions. We have sought to provide a practical example of how the TT21C vision can be implemented to facilitate a safety assessment for a commercial chemical without the use of animal testing. To this end, the key elements of the TT21C vision have been broken down to a set of actions that can be brought together to achieve such a safety assessment. Such components of a pathways-based risk assessment have been widely discussed, however to-date, no worked examples of the entire risk assessment process exist. In order to begin to test the process, we have taken the approach of examining a prototype toxicity pathway (DNA damage responses mediated by the p53 network) and constructing a strategy for the development of a pathway based risk assessment for a specific chemical in a case study mode. This contribution represents a 'work-in-progress' and is meant to both highlight concepts that are well-developed and identify aspects of the overall process which require additional development. To guide our understanding of what a pathways-based risk assessment could look like in practice, we chose to work on a case study chemical (quercetin) with a defined human exposure and to bring a multidisciplinary team of chemists, biologists, modellers and risk assessors to work together towards a safety assessment. Our goal was to see if the in vitro dose response for quercetin could be sufficiently understood to construct a TT21C risk assessment without recourse to rodent carcinogenicity study data. The data presented include high throughput pathway biomarkers (p-H2AX, p-ATM, p-ATR, p-Chk2, p53, p-p53, MDM2 and Wip1) and markers of cell-cycle, apoptosis and micronuclei formation, plus gene transcription in HT1080 cells. Eighteen point dose response curves were generated using flow cytometry and imaging to determine the concentrations that resulted in significant perturbation. NOELs and BMDs were compared to the output from biokinetic modelling and the potential for in vitro to in vivo extrapolation explored. A first tier risk assessment was performed comparing the total quercetin concentration in the in vitro systems with the predicted total quercetin concentration in plasma and tissues. The shortcomings of this approach and recommendations for improvement are described. This paper therefore describes the current progress in an ongoing research effort aimed at providing a pathways-based, proof-of-concept in vitro-only safety assessment for a consumer use product.

The Syrian hamster embryo (SHE) cell transformation assay (pH 6.7) has a reported sensitivity of 87% and specificity of 83%, and an overall concordance of 85% with in vivo rodent bioassay data. To date, the SHE assay is the only in vitro assay that exhibits multistage carcinogenicity. The assay uses morphological transformation, the first stage towards neoplasm, as an endpoint to predict the carcinogenic potential of a test agent. However, scoring of morphologically transformed SHE cells is subjective. We treated SHE cells grown on low-E reflective slides with 2,6-diaminotoluene, N-nitroso-N-ethylnitroguanidine, N-nitroso-N-methylurea, N-nitroso-N-ethylurea, EDTA, dimethyl sulphoxide (DMSO; vehicle control), methyl methanesulfonate, benzo[e]pyrene, mitomycin C, ethyl methanesulfonate, ampicillin or five different concentrations of benzo[a]pyrene. Macroscopically visible SHE colonies were located on the slides and interrogated using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy acquiring five spectra per colony. The acquired IR data were analysed using Fisher's linear discriminant analysis (LDA) followed by principal component analysis (PCA)-LDA cluster vectors to extract major and minor discriminating wavenumbers for each treatment class. Each test agent vs. DMSO and treatment-induced transformed cells vs. corresponding non-transformed were classified by a unique combination of major and minor discriminating wavenumbers. Alterations associated with Amide I, Amide II, lipids and nucleic acids appear to be important in segregation of classes. Our findings suggest that a biophysical approach of ATR-FTIR spectroscopy with multivariate analysis could facilitate a more objective interrogation of SHE cells towards scoring for transformation and ultimately employing the assay for risk assessment of test agents.