title: Magnetic susceptibility anisotropy of myocardium imaged by cardiovascular magnetic resonance reflects the anisotropy of myocardial filament α-helix polypeptide bonds.
abstract: BACKGROUND
  A key component of evaluating myocardial tissue function is the assessment of myofiber organization and structure. Studies suggest that striated muscle fibers are magnetically anisotropic, which, if measurable in the heart, may provide a tool to assess myocardial microstructure and function.
  
  
  METHODS
  To determine whether this weak anisotropy is observable and spatially quantifiable with cardiovascular magnetic resonance (CMR), both gradient-echo and diffusion-weighted data were collected from intact mouse heart specimens at 9.4 Tesla. Susceptibility anisotropy was experimentally calculated using a voxelwise analysis of myocardial tissue susceptibility as a function of myofiber angle. A myocardial tissue simulation was developed to evaluate the role of the known diamagnetic anisotropy of the peptide bond in the observed susceptibility contrast.
  
  
  RESULTS
  The CMR data revealed that myocardial tissue fibers that were parallel and perpendicular to the magnetic field direction appeared relatively paramagnetic and diamagnetic, respectively. A linear relationship was found between the magnetic susceptibility of the myocardial tissue and the squared sine of the myofiber angle with respect to the field direction. The multi-filament model simulation yielded susceptibility anisotropy values that reflected those found in the experimental data, and were consistent that this anisotropy decreased as the echo time increased.
  
  
  CONCLUSIONS
  Though other sources of susceptibility anisotropy in myocardium may exist, the arrangement of peptide bonds in the myofilaments is a significant, and likely the most dominant source of susceptibility anisotropy. This anisotropy can be further exploited to probe the integrity and organization of myofibers in both healthy and diseased heart tissue.
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Box 3302, Durham, NC, 27710, USA. russell.dibb@duke.edu.|Biomedical Engineering, Duke University Medical Center, Campus Box 90281, Durham, NC, 27708, USA. russell.dibb@duke.edu.
authors.forename: Russell
authors.initials: R
authors.lastname: Dibb
authors.affiliation: Center for In Vivo Microscopy, Duke University Medical Center, Box 3302, Durham, NC, 27710, USA. yi.qi@duke.edu.
authors.forename: Yi
authors.initials: Y
authors.lastname: Qi
authors.affiliation: Brain Imaging & Analysis Center, Duke University Medical Center, Box 3918, Durham, NC, 27710, USA. chunlei.liu@duke.edu.|Radiology, Duke University Medical Center, Box 3808, Durham, NC, 27710, USA. chunlei.liu@duke.edu.
authors.forename: Chunlei
authors.initials: C
authors.lastname: Liu
mesh_terms: D000818:Animals; D016880:Anisotropy; D003198:Computer Simulation; D038524:Diffusion Magnetic Resonance Imaging; D007090:Image Interpretation, Computer-Assisted; D016014:Linear Models; D008297:Male; D008810:Mice, Inbred C57BL; D008955:Models, Cardiovascular; D009124:Muscle Proteins / Q000737:chemistry*; D009206:Myocardium / Q000737:chemistry* / Q000166:cytology; D009210:Myofibrils / Q000737:chemistry*; D011237:Predictive Value of Tests; D017433:Protein Structure, Secondary
chemical_list: D009124:Muscle Proteins