SIMULTANEOUS T-2-ASTERISK AND DIFFUSION MEASUREMENTS WITH HE-3

It has recently been demonstrated that magnetic resonance (MR) imaging of human lungs and airways is possible with hyperpolarized gases such as He-3. Because the influence of the apparent transversal relaxation (T-2 decay) and diffusion in He-3 imaging have not been quantified, an imaging pulse sequence was developed to measure these two parameter s simultaneously, The imaging pulse sequence generates two series of m ultiply recalled gradient echo images with both different echo-spacing s and diffusion-sensitizing gradients. From differences in exponential signal decay between the two series, T-2 and diffusion coefficients, D, of both hyperpolarized and unpolarized 3He samples could be measur ed 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) . 10(-4 ) m(2)/s and T-2 = 36 +/- 13 ms were measured, while D = (0.3 +/- 0.1 ) . 10(-4) m(2)/s and T-2 = 136 +/- 66 ms were found in a Boltzmann-p olarized He-3/O-2 mixture.