Adiabatic RARE imaging

The practical implementation of ultra-fast spin-echo, or RARE imaging with adiabatic RF pulses and surface coil transmission at 7 T is described. Despite the large RF inhomogeneities, the adiabatic character of the 180degrees BIR-4 refocusing pulses ensures optimal sensitivity and minimal image artifacts. An internal 'phase-cycle' is used to remove spurious unwanted coherences. The short T-2 relaxation times in rat brain at 7 T demand a centric, rather than a linear coverage of k-space in order to avoid excessive signal loss. T2 relaxation during k-space coverage also leads to image blurring, which can be counteracted by interleaved k-space sampling. The coverage of k-space in four acquisitions provides high-quality anatomical images comparable to conventional spin-echo images. A two-scan RARE implementation provides sufficient spatial and temporal resolution for most applications. Quantitative mapping of T, relaxation and cerebral blood flow changes during forepaw stimulation in the rat are demonstrated. Copyright (C) 2003 John Wiley Sons, Ltd.