Results: 5

1.
Figure 4

Figure 4. Tractography of fiber tracts (color-coded by HA) passing through a region-of-interest in the lateral LV wall.. From: Diffusion MRI Tractography of the Developing Human Fetal Heart.

(A) At 10 weeks few tracts are present. (B) By 14 weeks tract density has increased and the crossing-helical pattern of the subendocardial and subepicardial fibers can be seen. (C) At 19 weeks the fiber tracts resemble the pattern seen after birth (D) and in adults. (PN = P6 neonatal). (E) Tractography of the entire heart at 19 weeks.

Choukri Mekkaoui, et al. PLoS One. 2013;8(8):e72795.
2.
Figure 5

Figure 5. Histological sections of the lateral LV wall.. From: Diffusion MRI Tractography of the Developing Human Fetal Heart.

The sections were cut tangential to the epicardial surface. (A–C) At 10 weeks the myocardium is isotropic with no clear structural pattern. (D–F) At 14 weeks structural anisotropy begins to evolve and distinct patterns of fiber orientation can be seen at different transmural depths. (G–I) By 19 weeks clear differences in fiber orientation can be resolved in all layers of the myocardium, and the alignment of the myofibers resembles that seen in the adult heart. However, no sign of a dense sheet structure is seen.

Choukri Mekkaoui, et al. PLoS One. 2013;8(8):e72795.
3.
Figure 3

Figure 3. Fractional anisotropy (FA) in the developing heart.. From: Diffusion MRI Tractography of the Developing Human Fetal Heart.

(A) FA maps of the left ventricle in its short axis are shown of a 10-week, 14-week, 19-week, P6 and adult heart. The arrowhead points to the interventricular septum. (B) Histograms of FA values in each voxel of the entire left ventricle of these hearts. The histograms at 10 and 14 weeks are virtually identical, and a shift towards higher FA values is seen only at 19 weeks. The P6 histogram contains FA values that overlap with both those seen in adult and fetal hearts. This reflects the relative structural immaturity and plasticity of the neonatal heart.

Choukri Mekkaoui, et al. PLoS One. 2013;8(8):e72795.
4.
Figure 2

Figure 2. Transition from tissue isotropy to anisotropy in the developing human fetal heart.. From: Diffusion MRI Tractography of the Developing Human Fetal Heart.

(A, B) At 10 weeks the diffusion glyphs are disordered and spherical. (B = magnified view of white box shown in panel A). (C) At 14 weeks the orientation of the glyphs resembles that seen in the adult heart but they remain highly spherical. (D) At 19 weeks of gestation the glyphs are highly ordered and are now somewhat elliptical in shape. (E) At P6 (day 6 post-natal) the orientation and elliptical shape of the glyphs is very similar to that seen in adult hearts. (F) Fractional anisotropy (FA) at 10, 14 and 19 weeks of gestation remains very low. While the coherence and orientation of the myofibers has evolved by 19 weeks, their sheet structure has not. *p<0.01.

Choukri Mekkaoui, et al. PLoS One. 2013;8(8):e72795.
5.
Figure 1

Figure 1. Fiber architecture in the adult human heart.. From: Diffusion MRI Tractography of the Developing Human Fetal Heart.

(A) Fiber tracts in the lateral LV wall. The tracts are color-coded by their inclination or helix angle (HA). Tracts in the subendocardium have a positive (right-handed) HA, tracts in the subepicardium have a negative (left-handed) HA, and those in the midmyocardium are circumferential. (B) The diffusion tensor in each voxel in the LV is represented by an ellipsoidal glyph. The color and orientation of the glyph is determined by its HA (inclination angle of primary eigenvector). The shape of the glyph is determined by the relative magnitudes of the diffusion eigenvalues. In isotropic tissues the eigenvalues are similar and the diffusion glyphs are thus spherical. In anisotropic tissues the primary eigenvalue is significantly larger, producing high FA values and elliptical glyphs. (B, C) The diffusion glyphs in the adult LV have a highly ordered arrangement, show a consistent gradient in their transmural orientation and are highly elliptical. (White box in panel B = magnified area shown in panel C).

Choukri Mekkaoui, et al. PLoS One. 2013;8(8):e72795.

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