A Computational Framework for the Statistical Analysis of Cardiac Diffusion Tensors: Application to a Small Database of Canine Hearts

Abstract

Abstract-We propose a unified computational framework to build a statistical atlas of the cardiac fiber architecture from diffusion tensor magnetic resonance images (DT-MRIs). We apply this framework to a small database of nine ex vivo canine hearts. An average cardiac fiber architecture and a measure of its variability are computed based on most recent advances in diffusion tensor statistics. This statistical analysis confirms the already established good stability of the fiber orientations and a higher variability of the laminar sheet orientations within a given species. The statistical comparison between the canine atlas and a standard human cardiac DT-MRI shows a better stability of the fiber orientations than their laminar sheet orientations between the two species. The proposed computational framework can be applied to larger databases of cardiac DT-MRIs from various species to better establish intra-and inter-species statistics on the anatomical structure of cardiac fibers. This information will be useful to guide the adjustment of average fiber models onto specific patients from in vivo anatomical imaging modalities.

Statistical Atlas of Human Cardiac Fibers: Comparison with Abnormal Hearts

“…All hearts are registered to an initial reference image, which is updated toward the morphological average of all hearts [7]. Once the transformations of all hearts toward the average cardiac shape are computed, the diffusion tensors are warped [15] to the morphological atlas. The processing of abnormal hearts is performed within the same framework [12].…”

Variability of the Human Cardiac Laminar Structure

“…Warping of Diffusion Tensors -Fourthly, and last, the resulting deformation fields computed from the registration process are used to warp all tensor fields to the morphological atlas. The diffusion tensors are reoriented using the Finite Strain strategy since it preserves the geometric features [22].…”

“…The fibrous nature of the heart has been known for centuries, tracing back to as early as 1694 [28], but has been limited to tedious histological studies [20]. The cardiac fiber structure can now be imaged with diffusion tensor magnetic resonance imaging (DT-MRI) [2,15], however the variability of the fiber structure in humans is still not well known (due to the very limited number and the value of post-mortem healthy human hearts) and is largely speculated from studies on other species (dogs [12,13,11,26,22,21,9], goats [8], and rats [3]). Recently, Lombaert et al [17,18] constructed a statistical atlas of the human cardiac fiber architecture and assessed its variability.…”

Statistical Analysis of the Human Cardiac Fiber Architecture from DT-MRI

“…The availability of a full 3D atlas of the cardiac architecture opens the door to not only the construction of more accurate extrapolation models for in vivo acquisitions, but also to a better understanding of various cardiac mechanical functions, cardiac electrophysiology patterns, and remodeling processes. So far only ex vivo canine DT-MRI studies [9,13] have been considered, and in humans, only cases using a single ex vivo heart has been studied [15] and visualized in 3D [16]. Histological and DT-MRI studies all lead to similar findings.…”

“…The fibers, locally organised as laminar sheets, appear to be consistently structured as two counter wound spirals where the fibers smoothly change orientation from the endocardium to the epicardium. Their orientation seems to be more stable than the laminar sheet orientation [9,13]. The availability of human hearts is extremely difficult (they are rather transplanted than used for research), and thanks to a unique post-mortem human dataset [6,14], we have built a statistical atlas from ex vivo DT-MRI and extended previous studies [9,13] to humans.…”