Assessment of Myocardial Microstructure in a Murine Model of Obesity-Related Cardiac Dysfunction by Diffusion Tensor Magnetic Resonance Imaging at 7T

Figures

• 

  FIGURE 1. Study protocol and physiological measures. (A) Study protocol. (B) Body weight development during the study period. (C) Relative body weight change from baseline to final assessment. (D) Systolic blood pressure (SBP) at 14 weeks of dietary intervention. (E) Weight of perirenal and epididymal fat depots after 15 weeks of dietary intervention. Echo, echocardiography; SBP, systolic blood pressure. Mean ± SD; n = 10–11 per group; two-way repeated measures ANOVA (B), unpaired Student’s t-test (C,E, right panel), or Mann-Whitney U test (E, left panel).

• 

  FIGURE 2. Cardiovascular tissue analyses. (A) Heart weight normalized to tibia length. (B) Wet-to-dry lung weight ratio. (C) Representative cardiac cross sections stained with hematoxylin/eosin (scale bars = 100 μm and 50 μm, respectively). Semiquantitative histological scores for (D) cellular damage and (E) cardiomyocyte hypertrophy. (F) Representative cardiac cross sections stained with Picrosirius Red for the detection of collagen fibers (scale bars = 1 mm and 100 μm, respectively). (G) Quantification of myocardial collagen content in the whole LV and the different myocardial segments. (H) Gene expression analysis of ANP, Col1a1, and Col3a1 in myocardial tissue. ANP, atrial natriuretic peptide; Col1a1, collagen type I alpha 1 chain; Col3a1, collagen type III alpha 1 chain. Mean ± SD; n = 5–6 (A,G,H) and 10–11 (B,D,E) per group; unpaired Student’s t-test or Mann-Whitney U test (no significant differences were found).

• 

  FIGURE 3. Analysis of myocardial longitudinal deformation. (A) Representative B-Mode image in the parasternal long axis view used for speckle-tracking analysis (scale bar = 2 mm; vector arrows along the endocardial border). (B) The myocardium was divided into six segments, and longitudinal strain was assessed as their average (global longitudinal strain) or separately for basal, mid-cavity and apical segments (segmental longitudinal strain). (C) Representative longitudinal strain (orange dotted line) and -strain rate (blue solid line) curves along the endocardial border during three consecutive cardiac cycles. LS indicates longitudinal peak systolic strain. Peak strain rate was assessed during diastole (SRdia) and systole (SRsys), respectively. The interval between two R waves was defined as one cardiac cycle (corresponding ECG tracing is displayed on top). (D) Analysis of endocardial longitudinal strain. (E) Analysis of endocardial longitudinal SRsys. (F) Analysis of epicardial longitudinal strain. (G) Analysis of epicardial longitudinal SRsys. (H) Analysis of longitudinal SRdia. Mean ± SD or median and quartiles with 95% confidence interval; n = 10–11 per group; unpaired Student’s t-test…

• 

  FIGURE 4. Analysis of myocardial diffusion metrics. (A) Illustration of DT-MRI segmentation. All DT-MRI parameters were assessed for both the global myocardium or separately for the subendocardial and subepicardial layer as well for the entire LV and its different segments (base/mid-cavity/apex). (B) Representative MD maps. Analysis of MD in the global myocardium (C), the subendocardium (D), and subepicardium (E) of the LV. Median and quartiles with 95% confidence interval; unpaired Student’s t-test; n = 5 per group.

• 

  FIGURE 5. Eigenvalues of the diffusion tensor and FA. (A) Representative maps of the first eigenvalue of the diffusion tensor (lambda 1). (B) Analysis of lambda 1 (largest eigenvalue). (C) Representative maps of the second eigenvalue of the diffusion tensor (lambda 2). (D) Analysis of lambda 2. (E) Representative maps of the third (smallest) eigenvalue of the diffusion tensor (lambda 3). (F) Analysis of lambda 3. (G) Representative FA maps. (H) Analysis of FA. Median and quartiles with 95% confidence interval; n = 5 per group; unpaired Student’s t-test or Mann-Whitney U test.

• 

  FIGURE 6. Schematic diagram of helix angle and sheetlet angle. (A) Transmural region of interest of the LV with exemplary visualization of subendocardial, mesocardial and subepicardial layers (fiber bundle excerpts are based on tractography in respective myocardial layers). In order to determine established DT-MRI metrics such as helix and sheetlet angle, a local coordinate system with circumferential, longitudinal, and radial axes is established for every voxel. (B) The primary eigenvector of the diffusion tensor (E1) was projected into the local tangential plane (given by local circumferential and longitudinal axes). The angle between E1 projection and the circumferential axis provides the so-called helix angle. As depicted in panel (A), myofibers in the LV are arranged in two counter-directional helices with progressively changing pitch (positive in the subendocardium over neutral in the mesocardium to negative in the subepicardium). (C) The local cross-myocyte plane (given by local cross-myocyte orientation and radial axis) was determined perpendicular to the local primary eigenvector orientation (myofiber bundle orientation). A projection of the secondary eigenvector (E2) was placed…

• 

  FIGURE 7. Assessment of left-ventricular microstructure by DT-MRI. (A) Number of reconstructed fiber tracts according to minimal fiber tract length as termination criterion (0.1 and 1 mm, respectively). (B) Representative reconstruction of cardiac fiber tracts with color-coded helix angle in an animal of the HFD group. Left: transverse section of the heart with a view in the direction of the apex. Right: longitudinal section of the heart in anterior-posterior direction with magnified regions of interest at basal, mid-cavity and apical level of the interventricular septum. (C) Transmural helix angle profiles in the LV and different myocardial segments. (D) Helix angles values in the different myocardial layers and segments. (E) Ratio of fiber tracts with a positive helix angle to fiber tracts with a negative helix angle in the different myocardial segments. (F) Visualization of the diffusion tensor in the cardiac short axis at mid-cavity level using superquadric glyphs. Color-coding corresponds to absolute sheetlet angle values (|E2A|). (G) Analysis of |E2A| in the different myocardial layers and segments. Mean ± SD (C,E) or median and quartiles with 95% confidence interval (D,G); n = 5 per…