MR diffusion tensor imaging study of postinfarct myocardium structural remodeling in a porcine model

Abstract

This study aimed to investigate postinfarct left ventricular (LV) fiber structural alterations by ex vivo diffusion tensor imaging (DTI) in a porcine heart model. In vivo cardiac MR imaging was first performed to measure ventricular function in six adult pigs with septal infarction near apex induced by the LAD ligation 13 weeks earlier. Hearts were then excised from the infarct pigs (n ‫؍‬ 6) and six intact controls (n ‫؍‬ 6) and fixed in formalin. High-resolution DTI was employed to examine changes in fractional anisotropy (FA), apparent diffusion coefficient (ADC), and transmural helix angle distribution in the infarct, adjacent and remote regions as compared to the sham regions in the controls. FA values were found to decrease in the infarct and differ between the adjacent and remote regions. ADC increase in the infarct region was substantial, while changes in the adjacent and remote regions were insignificant. Structurally, the doublehelix myocardial structure shifted toward more left-handed around the infarcted myocardium. Accordingly, the histological analysis revealed clear fiber structural degradation in the adjacent region. These findings confirmed the subtle alterations in the myocardial fiber quality and structure not only in the in- Key words: myocardium infarction; borderzone; diffusion tensor imaging; fiber architecture Both structural and functional assessments are important in our understanding of myocardial contraction and relaxation in normal and pathologic states (1,2). It has been long known that left ventricular (LV) myocardial microstructure or fiber structure plays a critical role in determining mechanical properties, such as ventricular torsion, strain, and stress (3,4). Owing to the recent advances in cardiac MR and ultrasound imaging, there is an increasing interest in investigating LV by directly associating the LV myocardial fiber geometry to the complex spatial-temporal sequence of electrical activation and mechanical contraction/relaxation in beating hearts (1,2,5). LV is known to electrically activate first at the exits of Purkinje system, close to apical endocardium. The electrical activation then propagates from apex to base via depolarization and repolarization in both septum and free wall (1,6). This is accompanied by successive mechanical shortenings and intracavitary blood flow along the parallel apex-to-base direction, although highly transient and localized myocardial deformations exist.In infarcted myocardium, remodeling involves both structural and functional changes. Such changes have been found to occur in both infarcted myocardium and adjacent and remote myocardium (7-11). The effects of myocardial infarction (MI) on LV function have been investigated in numerous studies. In recent years, cardiac MR (CMR) imaging has become the accepted reference standard to assess LV function since CMR methods are both accurate and highly reproducible (12). These CMR techniques can be used to detect, localize, and quantify both MI and LV functions. Patten et al. (13) found that hearts...

Sequential Changes of Myocardial Microstructure in Patients Postmyocardial Infarction by Diffusion-Tensor Cardiac MR

“…19 In our study, we found MD progressively increased from remote to infarct myocardium, suggesting that MD might be a sensitive marker for myocardial edema and could detect the subtle increase of edema in the remote region. Our finding is not consistent with an ex vivo DT-CMR study on a porcine model by Wu et al 23 in which no significant difference in MD was found when compared with the control group in the adjacent and remote regions. The discrepancy may be related to the dehydration procedure performed in formalin fixation, which may reduce the myocardial water content and consequently MD.…”

Polarization birefringence measurements for characterizing the myocardium, including healthy, infarcted, and stem-cell-regenerated tissues

“…However, neither of these techniques provides information on the organizational structure of the tissue, but rather on the elastic and conductive properties, respectively. Diffusion tensor magnetic resonance imaging provides information regarding fiber organization and orientation, 23 but currently is limited to ex vivo tissues and suffers from lower spatial resolution than optical methods. Thus, polarized-lightbased birefringence measurements, if successful, may enable previously unavailable assessment of myocardial organization.…”

Characterization of Post-infarct Scars in a Porcine Model – A Combined Experimental and Theoretical Study

“…Efforts have been made to characterize the post-infarct scars using imaging techniques like MRI and PET. For instance, using diffusion-weighted MRI methods, it was demonstrated in ex-vivo formalin-fixed porcine hearts that the regions of increased apparent diffusion coefficient (ADC) correlated very well with dense scars [5]. Similar findings were seen in patients with prior myocardial infarct.…”