First principles of fast spin echo.

Fast spin echo (FSE), a variant of the rapid acquisition with refocused echoes pulse sequence, is now being widely considered as an alternative to conventional spin echo for proton density and T2-weighted imaging. Although the medical experience with this sequence is relatively limited, relevant aspects of the technique have been well understood in the context of spectroscopic applications for many years. This article attempts to portray the subject in an appropriate historical context. Such a viewpoint promotes a deeper understanding of the artifacts, determinants of contrast, and future evolution of FSE. Hopefully, this may not only be of benefit in the design of optimal clinical imaging protocols for current state of the art but may also be of use in fashioning the criteria by which new developments in this field may be judged.