T-2 ACCURACY ON A WHOLE-BODY IMAGER

MR oximetry requires a T-2, measurement that is accurate within 5% in vivo. Simple methods are susceptible to signal loss and tend to undere stimate T-2. Current methods utilize RF pulses or RF cycling patterns that prevent signal loss at each data acquisition, However, using thes e methods with imperfect pulses, T-2 tends to be overestimated due to temporary storage of the magnetization along the longitudinal axis whe re it decays more slowly with a time constant T-1 > T-2 To reduce the T-1 dependence while preventing signal loss, we utilize simple 90(x)18 0(y)90(x) composite pulses and good RF cycling patterns, These trains are critical for T-2 accuracy over typical ranges of RF and static fie ld inhomogeneities and refocusing intervals, T-1 signal decay during e ach 90(x)180(y)90(x) pulse must be accounted for to yield accuracy wit hin 5% when the pulsewidth is 10% or more of the refocusing interval, A simple correction scheme compensates for this T-1-related error effe ctively.