Diffusion biomarkers in chronic myocardial infarction

Abstract

Cardiac diffusion tensor magnetic resonance imaging (cDTI) allows estimating the aggregate cardiomyocyte architecture in healthy subjects and its remodeling as a result of cardiac disease. In this study, cDTI was used to quantify microstructural changes occurring in swine (N=7) six to ten weeks after myocardial infarction. Each heart was extracted and imaged ex vivo with 1mm isotropic spatial resolution. Microstructural changes were quantified in the border zone and infarct region by comparing diffusion tensor invariants - fractional anisotropy (FA), mode, and mean diffusivity (MD) - radial diffusivity, and diffusion tensor eigenvalues with the corresponding values in the remote myocardium. MD and radial diffusivity increased in the infarct and border regions with respect to the remote myocardium (p<0.01). In contrast, FA and mode decreased in the infarct and border regions (p<0.01). Diffusion tensor eigenvalues also increased in the infarct and border regions, with a larger increase in the secondary and tertiary eigenvalues.

Keywords: Cardiac Diffusion Tensor Imaging; Cardiac Microstructure; Myocardial Infarction; Radial Diffusivity.

Fig. 5.

Grouped box plots overlaid on top of corresponding Mean diffusivity (MD) and Radial diffusivity (Rd) data points (cross and circular markers) in the infarct (left, purple), border (center, yellow), and remote (right, blue) myocardial regions for each subject. Cross markers represent data points 1.5 IQR above Q3 or below Q1.

Fig. 1.

T1-weighted, T2-weighted, b = 0 s/mm², and b = 1000 s/mm² images for representative short-axis slices in an infarcted subject (subject number 3 in the current study).

Fig. 2.

T1-weighted, Fractional Anisotropy (FA), Mean Diffusivity (MD), primary (e₁), secondary (e₂), and tertiary (e₃) eigenvalue maps for representative short-axis slices. Infarct and border regions are visible from diffusion tensor invariants, eigenvalues, and Rd maps. Images are shown for subject 3 in the current study.

Fig. 3.

Rain-cloud plots [1] overlaid to the corresponding box plots for FA, MD, Mode, eigenvalues e₁, e₂, and e₃, radial diffusivity (Rd), normalized T1- and T2-weighted signal intensities in the infarct, border, and remote myocardial regions.

Fig.4.

Bar plots illustrating percent differences in median FA, MD, Mode, e₁, e₂, e₃, Rd, T1-weighted, and T2-weighted normalized signal intensities in the border and infarct regions with respect to the remote myocardium. The dotted line indicates the median percentage change when data from all subjects are considered together. The percent differences reported directly on the plots are computed between remote-border and remote-infarct overall medians.