Self-diffusion NMR imaging using stimulated echoes

Abstract NMR imaging of molecular self-diffusion is demonstrated for the first time using stimulated-echo (STE) NMR signals. Stimulated-echo acquisition-mode (STEAM) imaging has been described in a preceding paper. It is based on a 90°-t1-90°-t2-90°-t3 rf excitation sequence and relies on the detection of the STE signal appearing at t3 = t1. By incorporating a pair of pulsed magnetic field gradients into the first and third intervals of the STEAM sequence, the effect of molecular self-diffusion on NMR images may be qualitatively demonstrated. A variation of the strength of the gradient pulses and/or the diffusion time, i.e., the length of the second interval, yields a series of diffusion weighted images which allows the calculation of a synthetical image solely displaying the self-diffusion coefficient. Experimental results on 1H NMR images of phantoms are presented which clearly demonstrate the potential of diffusion imaging as a new tool in medical diagnosis as well as for nonmedical applications.