Multiple regression method for pulmonary apparent diffusion coefficient measurement by hyperpolarized ³He MRI

Purpose: To develop and validate a new multiple regression technique for the separation of flip angle effect in pulmonary apparent diffusion coefficient (ADC) measurement. Materials and Methods: Hyperpolarized ³He MRI (HP ³He MRI) ADC measurements were performed on phantom, pig, and human models. The diffusion-sensitization sequence is modified from a standard gradient echo (GRE) sequence with a nonlinear progression in the bipolar gradient amplitude with each image. In the self-diffusion phantom experiment, four images were acquired with base gradient factor b₀ = 0.15 second/cm²; in the pig and human experiment, six images were acquired with base gradient factor b₀ = 1.4 second/cm². Results: The self-diffusion coefficient measured in the phantom experiment was 1.98 ± 0.16 cm²/second. The measured uncertainty curve was consistent with the theoretically predicted curve. The measured in vivo ADC values (three coronal slices in the supine direction) were 0.20/0.16/0.13 cm²/second and 0.20/0.18/0.16 cm²/second for pig and human experiments, respectively. Conclusion: With the introduction of a nonlinear progression in the diffusion-sensitization gradients, the multiple regression technique is capable of separating the flip angle effect in ADC measurement. In addition, this technique can perform a rigorous measurement uncertainty analysis and provide the optimal scan parameters that yield best noise performance.