on March 19, 2009
Published online before print March 19, 2009, doi: 10.1161/CIRCIMAGING.108.815050
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Original Article |
Diffusion Spectrum MRI Tractography Reveals the Presence of a Complex Network of Residual Myofibers in Infarcted Myocardium.
1 Massachusetts General Hospital, Harvard Medical School, Boston;
2 Massachusetts General Hospital, Harvard Medical School, Boston, MA;
3 Massachusetts Institute of Technology, Cambridge, MA;
4 Leducq Foundation Network, Harvard Medical School, Boston, MA;
5 Beth Israel Deacones Medical Center, Harvard Medical School, Boston, MA
6 E-mail: sosnovik{at}nmr.mgh.harvard.edu
Background—Changes in myocardial microstructure are important components of the tissue response to infarction but are difficult to resolve with current imaging techniques. A novel technique, diffusion spectrum MRI tractography (DSI-tractography), was thus used to image myofiber architecture in normal and infarcted myocardium. Unlike diffusion tensor imaging, DSI-tractography resolves multiple myofiber populations per voxel, thus generating accurate 3D tractograms, which we present in the myocardium for the first time.
Methods and Results—DSI-tractography was performed at 4.7 Tesla in excised rat hearts 3 weeks following left coronary artery ligation (n=4), and in 4 age-matched controls. Fiber architecture in the control hearts varied smoothly from endocardium to epicardium, producing a symmetric array of crossing helical structures in which orthogonal myofibers were separated by fibers with intermediate helix angles. Fiber architecture in the infarcted hearts was severely perturbed. The infarct boundary in all cases was highly irregular and punctuated repeatedly by residual myofibers extending from within the infarct to the border zones. In all infarcts longitudinal myofibers extending towards the basal-anterior wall and transversely oriented myofibers extending towards the septum lay in direct contact with each other, forming nodes of orthogonal myofiber intersection or contact.
Conclusions—DSI-tractography resolves 3D myofiber architecture and reveals a complex network of orthogonal myofibers within infarcted myocardium. Mesh-like networks of orthogonal myofibers in infarcted myocardium may resist mechanical remodeling, but likely also increase the risk for lethal re-entrant arrhythmias. DSI-tractography thus provides a new and important readout of tissue injury following myocardial infarction.
Key Words: magnetic resonance imaging • myocardial infarction • myocardium • diffusion • fiber architecture
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Circ Cardiovasc Imaging 2009 2: 169-170.
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