Myocardial Scar Delineation Using Diffusion Tensor Magnetic Resonance Tractography

Abstract

BackgroundLate gadolinium enhancement (LGE) is the current standard for myocardial scar delineation. In this study, we introduce the tractographic propagation angle (PA), a metric of myofiber curvature (degrees/unit distance) derived from diffusion tensor imaging (DTI), and compare its use to LGE and invasive scar assessment by endocardial voltage mapping.Methods and Results DTI was performed on 7 healthy human volunteers, 5 patients with myocardial infarction, 6 normal mice, and 7 mice with myocardial infarction. LGE to delineate the infarct and border zones was performed with a 2‐dimensional inversion recovery gradient‐echo sequence. Ex vivo DTI was performed on 5 normal human and 5 normal sheep hearts. Endocardial electroanatomic mapping and subsequent ex vivo DTI was performed on 5 infarcted sheep hearts. PA in the normal human hearts varied smoothly and was generally <4. The mean PA in the infarct zone was significantly elevated (10.34±1.02 versus 4.05±0.45, P<0.05). Regions with a PA ≤4 consistently had a bipolar voltage ≥1.5 mV, whereas those with PA values between 4 and 10 had voltages between 0.5 and 1.5 mV. A PA threshold >4 was the most accurate DTI‐derived measure of infarct size and demonstrated the greatest correlation with LGE (r=0.95).ConclusionsWe found a strong correlation between infarct size by PA and LGE in both mice and humans. There was also an inverse relationship between PA values and endocardial voltage. The use of PA may enable myocardial scar delineation and characterization of arrhythmogenic substrate without the need for exogenous contrast agents.

Novel insights into in‐vivo diffusion tensor cardiovascular magnetic resonance using computational modelling and a histology‐based virtual microstructure

“…Due to constraints with stacking blocks, cardiomyocytes are assumed to be parallel within each building block and hence any three‐dimensional nature of the sheetlets may be lost. Recent work has found cardiomyocyte curvature to be 2 ∘ /mm . Since DTI is rotationally invariant, resultant changes around should be small.…”

“…Recent work has found cardiomyocyte curvature to be 2 ∘ /mm. 55 Since DTI is rotationally invariant, resultant changes around ⃗ E 1 should be small. The effect of intra-voxel fiber dispersion and myocyte branching is assumed to be minimal, but if implemented may lead to a decrease in anisotropy.…”

Diffusion tensor imaging and arterial tissue: establishing the influence of arterial tissue microstructure on fractional anisotropy, mean diffusivity and tractography

“…Fibre tractography has also been shown to be sensitive to the time-dependent orientation of collagen fibres in biodegradable tissue engineered constructs seeded with human-derived vascular cells 20 . Similarly, the orientation of cardiomyocytes 21,22 has been illustrated by tractography, as well as the differentiation between healthy and diseased cardiac architecture [23][24][25] . Together, these studies allude to the ability of DTI metrics to be selectively sensitive to specific microstructural components, but this has yet to be conclusively determined in arterial tissue.…”

Longitudinal assessment of tissue properties and cardiac diffusion metrics of the ex vivo porcine heart at 7 T: Impact of continuous tissue fixation using formalin

“…In addition, our results highlight the importance of proper method selection and reproducible tissue handling, preparation and storage. In recent years, metrics of microstructure been shown to be precise and specific markers for remodeling in cardiac pathologies 3–5,19 . The preservation of anisotropy and overall microstructure following even long periods of immersion in formalin may enable future studies assessing ventricular remodeling of cardiac microstructure in various cardiac pathologies in more detail.…”

“…Cardiac diffusion tensor imaging (cDTI) has become an emerging application in the characterization of cardiac tissue and its functional and structural integrity. It has since been applied in a variety of cardiovascular pathologies, such as hypertrophic 1–3 and dilative cardiomyopathy 3,4 as well as myocardial infarction 5 . In recent years the number of in vivo studies in humans 6–8 and animals 3,9 has increased.…”