Figure 3.
Idealized cartoon depicting the evolution of the longitudinal magnetization of water in different compartments with the goal of venular signal isolation. Preserved, inverted and nulled spins are denoted by upright arrows, downright arrows and solid circles, respectively. The consecutive FT-VSI and NSI pulses invert spins in arteries/large arterioles (red) and large venules/veins (blue) flowing above the VCUTOFF and preserve the spins in capillaries as well as small arterioles and veins (black) moving below the VCUTOFF. The inverted arterial (red) and venous (blue) blood are nulled at TI and the downstream arterial blood will flow into capillaries. Meanwhile, the spins with preserved magnetization (in black) will flow out from the capillary bed into the venules during the inversion time (TI). The final FT-VSS label/control modules separate out the venular signal before data acquisition. FT-VSS or FT-VSI: Fourier-Transform based velocity-selective saturation or inversion. NSI: Non-selective inversion.