Simultaneous T2* and diffusion measurements with 3He.

It has recently been demonstrated that magnetic resonance (MR) imaging of human lungs and airways is possible with hyperpolarized gases such as 3He. Because the influence of the apparent transversal relaxation (T2* decay) and diffusion in 3He imaging have not been quantified, an imaging pulse sequence was developed to measure these two parameters simultaneously. The imaging pulse sequence generates two series of multiply recalled gradient echo images with both different echo-spacings and diffusion-sensitizing gradients. From differences in exponential signal decay between the two series, T2* and diffusion coefficients, D, of both hyperpolarized and unpolarized 3He samples could be measured on a standard clinical imager using a home-built Helmholtz coil. In a hyperpolarized sample of pure 3He values of D = (1.8 +/- 0.2) x 10(-4) m2/s and T2* = 36 +/- 13 ms were measured, while D = (0.3 +/- 0.1) x 10(-4) m2/s and T2* = 136 +/- 66 ms were found in a Boltzmann-polarized 3He/O2 mixture.