Figure 1a:

Tractography of the entire human heart in vivo. (a) Dual-gated STE sequence. Three 90° excitation pulses (RF) are applied over two successive heartbeats. The excitation (RF-1), refocusing (RF-3), and diffusion dephase and rephase occur at the same time in the R-R intervals, thereby exploiting the periodicity of heart motion to rewind motion-related dephasing. Additionally, the long diffusion time (including mixing time), allows a sufficient b value to be produced on clinical imagers without the need for an excessively long echo time (TE). (b) Tractograms of the heart in a healthy male subject in his mid-30s, acquired with STE. Twelve contiguous short-axis sections were acquired with no SMS excitation during multiple breath holds. Tractograms of the whole heart were generated and color-coded by using myofiber helix angle (HA). A magnified view of fiber tracts intersecting a region of interest in the LV lateral wall exhibits the progression in HA from endocardium to epicardium. ECG = electrocardiogram, EPI = echo-planar imaging, Gd = diffusion-encoding gradient.