MR imaging of anisotropic and restricted diffusion by simultaneous use of spin and stimulated echoes

A new magnetic resonance imaging technique for evaluating anisotropic and restricted diffusion effects in a single experiment is described. The method is based on a pulse sequence that simultaneously excites a spin echo (SE) and a stimulated echo (STE) and contains two pairs of diffusion-sensitive gradient pulses. The diffusion attenuation of the SE and STE can be controlled independently by separate adjustment of the parameters associated with each pair of the diffusion-sensitive gradient pulses. This method can be more time efficient than acquiring separate SE and STE images for the same study. Furthermore, the pulse sequence minimizes the effect of motion and instrumental and physiological variations that occur between separate image acquisitions which can give rise to artifactual results when difference imaging is employed. In addition to applications to anisotropic and restricted diffusion, this technique can be used for: (1) simultaneous acquisition of T2-weighted and diffusion-weighted images during cerebral ischemia studies; (2) calculation of diffusion coefficients from a pair of diffusion-weighted images; (3) separating fast and slow diffusion components in a single imaging experiment; and (4) two-dimensional velocity-encoded imaging.