Introduction

Diffusion-weighted imaging is an MR imaging technique in which contrast within the image is based on microscopic motion of water. It was first described in 1965 by two physical chemists, Stejskal and Tanner. Diffusion-weighted images are obtained by adding a series of two sequential gradient pulses to a 90-180-degree spin-echo sequence. The first gradient pulse is applied between the 90 and the 180-degree pulse. Motion after this pulse causes molecules to acquire phase shifts of their transverse magnetization. Both the 180-degree and the second gradient pulse rephase stationary spins. Phase shifts acquired in mobile molecules lead to failure of such molecules to rephase completely, resulting in substantial signal loss. 

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Dr P.Rakesh

SMVMCH Pondicherry