Echo‐planar imaging of diffusion and perfusion

Use of the Stejskal-Tanner sequence for performing diffusion images in the human brain tends to be complicated by the presence of artifacts caused by voluntary or involuntary, sometimes pulsatile, motion. We describe the implementation of the technique of echo-planar diffusion imaging, which avoids these artifacts and allows reproducible quantitative values of the diffusion coefficient to be measured in vivo. The effects of perfusion are easily visible in a phantom containing a gel. The results for human brain show a significant "perfusion fraction" in grey matter, consistent with an extracellular, possibly microvascular, volume of about 10%.