Referenceless interleaved echo-planar imaging

Interleaved echo-planar imaging (EPI) is an ultrafast imaging technique imp ortant for applications that require high time resolution or short total ac quisition times. Unfortunately, EPI is prone to significant ghosting artifa cts, resulting primarily from system time delays that cause data matrix mis registration. In this work, it is shown mathematically and experimentally t hat system time delays are orientation dependent, resulting from anisotropi c physical gradient delays. This analysis characterizes the behavior of tim e delays in oblique coordinates, and a new ghosting artifact caused by anis otropic delays is described. "Compensation blips" are proposed for time del ay correction. These blips are shown to remove the effects of anisotropic g radient delays, eliminating the need for repeated reference scans and postp rocessing corrections. Examples of phantom and in vivo images are shown. Ma gn Reson Med 41:87-94, 1999. (C) 1999 Wiley-Liss, Inc.