Compensation of slice profile mismatch in combined spin- and gradient-echo echo-planar imaging pulse sequences

摘要

Combined acquisition of gradient-echo and spin-echo signals in MRI time series reveals additional information for perfusion-weighted imaging and functional MRI because of differences in the sensitivity of gradient-echo and spin-echo measurements to the properties of the underlying vascular architecture. The acquisition of multiple echo trains within one time frame facilitates the simultaneous estimation of the transversal relaxation parameters R 2 and R 2*. However, the simultaneous estimation of these parameters tends to be incorrect in the presence of slice profile mismatches between signal excitation and subsequent refocusing pulses. It is shown here that improvements in pulse design reduced R 2 and R 2* estimation errors. Further improvements were achieved by augmented parameter estimation through the introduction of an additional parameter δ to correct for discordances in slice profiles to facilitate more quantitative measurements. Moreover, the analysis of time-resolved acquisitions revealed that the temporal stability of R 2 estimates could be increased with improved pulse design, counteracting low contrast-to-noise ratios in spin-echo-based perfusion and functional MRI. Magn Reson Med, 2012.