Figure 1

Function of the relaxation R1. The signal intensity of the central k-space lines, which determines the overall image contrast, was calculated for a rapid gradient echo sequence (TR = 2 ms, flip angle = 15°) with magnetization preparation and linear phase-encoding order as a function of R1. The red line is for the case where the temporal separation (TI) between saturation pulse and the central k-space line equals 130 ms, corresponding to a total of 128 phase encoding steps. The blue curve corresponds to a low-resolution image with 45 phase-encoding steps. The signal intensity initially shows a linear dependence on R1, which starts to show a convex shape for higher R1 values. This deviation from the linear dependence is referred to as signal saturation. The initial linear dependence of SI on R1 was extrapolated to larger R1 values, and represents the ideal case for a quantitative perfusion analysis, where signal intensity in blood is linearly proportional to contrast concentration. For the shorter TI, the linear regime extends to higher R1 values, than with a longer TI. A short TI setting is therefore preferable to avoid signal saturation (e.g. in the blood pool).