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Table 1 Glossary of terms used

From: In vivo cardiovascular magnetic resonance diffusion tensor imaging shows evidence of abnormal myocardial laminar orientations and mobility in hypertrophic cardiomyopathy

Myocyte:

Used here for a heart muscle cell, capable of contracting lengthwise, along its principal axis. We have not used `fiber', which we do not consider appropriate in relation to myocardial structure.

Cross-myocyte:

Directions perpendicular to the principal axis of local myocytes.

Sheetlets:

Laminar arrays of myocytes, as visualized in cross-myocyte histological sections of mammalian myocardium. We use `sheetlets' rather than `sheets' because each is typically only a few myocytes thick and is of limited individual extent before either branching or merging with adjoining sheetlets. Sheetlets are generally orientated oblique to the local wall tangent plane, and can occur in sub-populations with opposing orientations that give herringbone-like appearances in some cross-myocyte sections.

Shear layers:

Collagen lined fissures or interstices between adjacent sheetlets which may be important in relation to the extents and preferential directions of aqueous diffusion through myocardium over the course of a heart cycle. The fissures are thought to allow adjacent sheetlets to slide relative to one another as they collectively swivel, increasing their obliquity (transmural angle) relative to the local wall tangent plane during contraction.

Laminar:

An inclusive adjective referring to myocardial `sheetlet and shear layer' structure.

E1:

The principal eigenvector of aqueous diffusion. Previous studies have shown its direction to be aligned with local myocytes.

E2 and E3:

Represent the greater and the least eigenvectors, respectively, of cross-myocyte diffusion in a voxel. They are orthogonal to E1 and to each other. Although E2 and E3 may represent the sheetlet and sheet-normal directions perpendicular to myocytes, it should be remembered that DTI can only measure the mean of all diffusions in any single voxel and that a voxel of 3×3×8 mm3 may include two or more sub-populations of sheetlets with different orientations.

Helix angle or E1 angle (E1A):

Angle of obliquity of E1 in the local wall tangent plane relative to the local circumferential direction.

Transmural angle or E2 angle (E2A):

Angle of through-wall obliquity of E2 in the local cross-myocyte plane relative to the line of intersection of this plane with the local wall tangent plane (see Figure1).

Isotropic diffusion:

Diffusion that takes place with equal a freedom in all directions, i.e. spherically, on average, from any given starting point.

Anisotropic diffusion:

Diffusion that is constrained by anisotropic structures so that it proceeds preferentially along certain directions or planes.