Fiber architecture in remodeled myocardium revealed with a quantitative diffusion CMR tractography framework and histological validation.
BACKGROUND
The study of myofiber reorganization in the remote zone after myocardial infarction has been performed in 2D. Microstructural reorganization in remodeled hearts, however, can only be fully appreciated by considering myofibers as continuous 3D entities. The aim of this study was therefore to develop a technique for quantitative 3D diffusion CMR tractography of the heart, and to apply this method to quantify fiber architecture in the remote zone of remodeled hearts.


METHODS
Diffusion Tensor CMR of normal human, sheep, and rat hearts, as well as infarcted sheep hearts was performed ex vivo. Fiber tracts were generated with a fourth-order Runge-Kutta integration technique and classified statistically by the median, mean, maximum, or minimum helix angle (HA) along the tract. An index of tract coherence was derived from the relationship between these HA statistics. Histological validation was performed using phase-contrast microscopy.


RESULTS
In normal hearts, the subendocardial and subepicardial myofibers had a positive and negative HA, respectively, forming a symmetric distribution around the midmyocardium. However, in the remote zone of the infarcted hearts, a significant positive shift in HA was observed. The ratio between negative and positive HA variance was reduced from 0.96 ± 0.16 in normal hearts to 0.22 ± 0.08 in the remote zone of the remodeled hearts (p < 0.05). This was confirmed histologically by the reduction of HA in the subepicardium from -52.03° ± 2.94° in normal hearts to -37.48° ± 4.05° in the remote zone of the remodeled hearts (p < 0.05).


CONCLUSIONS
A significant reorganization of the 3D fiber continuum is observed in the remote zone of remodeled hearts. The positive (rightward) shift in HA in the remote zone is greatest in the subepicardium, but involves all layers of the myocardium. Tractography-based quantification, performed here for the first time in remodeled hearts, may provide a framework for assessing regional changes in the left ventricle following infarction.
Athinoula A, Martinos Center For Biomedical Imaging, Boston, MA, USA.
Choukri
C
Mekkaoui
Shuning
S
Huang
Howard H
HH
Chen
Guangping
G
Dai
Timothy G
TG
Reese
William J
WJ
Kostis
Aravinda
A
Thiagalingam
Pal
P
Maurovich-Horvat
Jeremy N
JN
Ruskin
Udo
U
Hoffmann
Marcel P
MP
Jackowski
David E
DE
Sosnovik
D000818:Animals; D056324:Diffusion Tensor Imaging; D004195:Disease Models, Animal; D006352:Heart Ventricles / Q000473:pathology* / Q000503:physiopathology; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D021621:Imaging, Three-Dimensional; D015233:Models, Statistical; D009203:Myocardial Infarction / Q000175:diagnosis* / Q000473:pathology / Q000503:physiopathology; D009206:Myocardium / Q000473:pathology*; D009210:Myofibrils / Q000473:pathology*; D011237:Predictive Value of Tests; D051381:Rats; D015203:Reproducibility of Results; D012756:Sheep; D020257:Ventricular Remodeling