Regional variations in ex-vivo diffusion tensor anisotropy are associated with cardiomyocyte remodeling in rats after left ventricular pressure overload

Figures

• 

  Fig. 1. Diffusion weighted images and registration. a Representative b = 0 image (i.e. no diffusion weighting). Signal-to-noise (SNR) was roughly 33 ± 1 across all animals. b Diffusion weighted image of the same slice as in (a). SNR was roughly 24 ± 1 across all animals. c Rendered diffusion tensors from a single short axis slice superimposed on the corresponding finite element mesh

• 

  Fig. 2. Transmural gradients of diffusion tensor (DT) parameters in equatorial LV free wall. Of note is the slight increase in helix angle at all points across the wall in transverse aortic constriction (TAC) vs SHAM. Transmural differences in planar anisotropy and sheet angle dispersion are apparent in this region between TAC and SHAM

• 

  Fig. 3. Regional variation in helix angle. The right column is the mean of all SHAM rats, the middle column is mean of the TAC group, and the left column is the calculated t-score between TAC and SHAM groups. The rows represent the longitudinal location of each slice, and the radial position of each plot represents transmural location. In the t-score plot, red indicates TAC > SHAM, green indicates TAC < SHAM, with bright colors indicating a t-score that would give rise to an uncorrected p-value < 0.05. Note the increase in helix angle in the equatorial region of the LV free wall, and lowered helix angles in the anterior wall

• 

  Fig. 4. Regional variation in planar anisotropy (CP). The right column is the mean of all SHAM rats, the middle column is mean of TAC group, and the left column is the calculated t-score between TAC and SHAM groups. The rows represent the longitudinal location of each slice, and the radial position of each plot represents transmural location. In the t-score plot, red indicates TAC > SHAM, with bright red indicating a t-score that would give rise to an uncorrected p-value < 0.05. Planar anisotropy was generally lower in sub-endocardial regions in TAC hearts compared to SHAM, but slightly higher in the sub-epicardium

• 

  Fig. 5. Orthogonal views of a representative confocal image volume. The extracellular space is clearly visible with the wheat germ agglutinin (WGA) stain (red), including some t-tubule patterns (arrowhead). Cell ends are also visible, making measurement of myocyte length possible, as shown for example by the arrow. Out-of-plane dimension can also readily be measured in orthogonal views. Scale bar: 50 μm

• 

  Fig. 6. Summary of myocyte measurements from histological sections. Data are presented as mean ± SD of measurements in each region for SHAM (n = 4) and TAC (n = 4) groups. a As expected, helix angles from histological sections correlated strongly (R2 = 0.71, p < 0.001) with those from DTI. Grayscale color of markers indicates transmural location (black: ENDO, white: EPI). b A transmural gradient in myocyte fractional anisotropy (MFA) was observed, with lower values in the ENDO than EPI, especially in SHAM myocytes. c Myocyte cross sectional area (CSA) also exhibited a transmural gradient in SHAM hearts, with larger values in the ENDO. In TAC hearts, CSA was elevated, and the transmural gradient was diminished

• 

  Fig. 7. Correlations between select DTI-derived parameters (ordinate) and measurements from histological sections (abscissa). Grayscale color of markers indicates transmural location (black: ENDO, white: EPI). a Fractional anisotropy from DTI exhibited a strong correlation with helix angle (R2 = 0.48, p < 0.001). b Mean diffusivity correlated with myocyte width:height ratio (R2 = 0.25, p < 0.01), and c Planar anisotropy correlated negatively with MFA (R2 = 0.24, p < 0.01)