Figure 1: Schematic of basic principles underlying DSI-tractography. Panel A: Schematic of a voxel with

Transcription

1 Figure 1 Figure 1: Schematic of basic principles underlying DSI-tractography. Panel A: Schematic of a voxel with 2 fiber populations. Water diffuses primarily in the direction of fiber orientation (arrows). Panel B: Each point in q-space represents signal intensity in the voxel during application of a particular diffusionencoding vector. Signal intensity is lowest when the diffusion gradient is strongest and is applied in the direction of fiber orientation. Panel C: Fourier transformation of q-space produces a probability density map of fiber orientation in that voxel, which is converted into an orientation density function (ODF). Integration of the local maxima in the ODFs of each voxel into multivoxel streamlines produces the 3D tractograms. David E. Sosnovik Page 1 3/18/08

2 Figure 2 Figure 2: Helix angle encoding of myofiber architecture. The left ventricle is being viewed from its lateral wall in the schematic shown in panel A. Fibers tilting towards the antero-apex have a positive or right-handed helix angle (thumb points to apex), while those tilting towards the antero-base have a negative or left handed helix angle. (Panels B-F) Fibers in the subendocardium have positive helix angles, transition smoothly to a zero helix angle (circumferential) in the midmyocardium, and then transition smoothly to negative helix angles in the subepicardum. (B, C) Tomographic image of myofibers (with helix angle encoding) in (B) the short axis of left ventricle and (C) viewed from the lateral wall. (D-F) Only those fibers intersecting a spherical region of interest (ROI) are shown. The ROI has been placed in the subendocardium (D), midmyocardium (E) and subepicardium (F), showing the transmural evolution of myofiber helix angle. David E. Sosnovik Page 2 3/18/08

3 Figure 3 Figure 3. Fiber architecture (coded by helix angle) in a normal rat heart viewed (Panels A-E) from the LV apex and (Panels F-J) from the lateral wall. Fibers in both the subendocardium (A, B) and subepicardium (D, E) form a half-turn of a spiral. However, in the lateral wall, the fibers in the subendocardium (F, G) are tilted towards the antero-apex while the fibers in the subepicardium (I, J) are tilted towards the anterobase. Fibers in the midmyocardium (C, H) are circumferential and have a length approximately equal to the circumference of the ventricle. David E. Sosnovik Page 3 3/18/08

4 Figure 4: Figure 4: Myofiber architecture in a normal rat heart. A projection DSI-tractogram, looking down onto the anterior and anterolateral walls of the left ventricle, is shown in panel A. The visualized fibers have helix angles consistent with subepicardial (green-yellow) and midmyocardial (blue) myofibers and are arranged in an orderly and dense network of myofiber sheets. A high degree of correlation is seen between the DSI-tractogram and its corresponding histological section (demarcated by the black lines), shown in Panel B. David E. Sosnovik Page 4 3/18/08

5 Figure 5: Figure 5: Myofiber architecture is severely perturbed in infarcted myocardium. A projection image looking down onto the anterior wall of the left ventricle (same orientation as Figure 4) is shown in Panel A. The infarct boundary does not resemble a smooth wavefront, but rather is highly irregular and characterized by frequent strands of myofibers penetrating the infarct from its basal and septal border zones. The anterolateral apex, however, is virtually devoid of penetrating myofibers. A tomographic DSI reconstruction through the infarct is shown in Panel B. In both panels A and B, longitudinally oriented subendocardial fibers (pink) can be visualized penetrating the infarct from its basal border zone and forming an intersecting mesh with transversely oriented subepicardial fibers (green) penetrating the infarct from its septal border zone. David E. Sosnovik Page 5 3/18/08

6 Figure 6: Figure 6: DSI-tractography and corresponding histological sections in a rat hart with a large antero-apical myocardial infarction. Panel B is a magnified view of Panel A. The infarct is characterized by the presence of numerous strands of penetrating myofibers, which form a prominent intersecting mesh in the more basal and septal portions of the infarct. The longitudinally oriented fibers (pink) arising in the basal border zone are of subendocardial origin, while the transversely oriented myofibers penetrating the infarct from the septum (blue) are of midmyocardial origin. The presence of penetrating transverse myofibers David E. Sosnovik Page 6 3/18/08

7 arising in the septum is confirmed in the Mason s trichrome (myofibers stain brown, collagen stains blue) section, shown in Panel C. Longitudinally oriented myofibers arising in the basal border zone of the infarct are shown in the H and E section in Panel D. Despite the histological sections being only 5 um thick and confined to one transmural plane, a high degree of correlation is seen between the DSItractograms and the corresponding histological sections. David E. Sosnovik Page 7 3/18/08