Figure 4.

Vortex area for varying CTTH, MTT and ΔSO2-levels. A parametric plot of the gradient echo and spin echo relaxation rate curves forms a vessel vortex curve and is characterized by the vortex direction, long axis, slope value and the vortex area (a). The vortex area decreases as the ΔSO2 increases (b) and can thus indicate the oxygenation status of the tissue. However, the vortex area is modified by the MTT and CTTH in the vessel system. The combined effects of CTTH and ΔSO2 on vortex area are shown for low MTT (c), intermediate MTT (d) and high MTT (e). Coloured lines in (c–e) correspond to the coloured lines in (b). Low CTTH and low MTT produces higher vortex area values than high CTTH and long MTT, and must be accounted for to obtain an accurate estimation of the SO2-level. No data for upper values of CTTH in (c) and (d), as maximum CTTH is dependent on MTT.