Applications of stimulated echo correction to multicomponent T2 analysis

We propose a multicomponent fitting algorithm for multiecho T2 data which allows for correction of T2 distributions in the presence of stimulated echoes. Tracking the population of spins in many coherence pathways via the iterated method of the Extended Phase Graph algorithm allows for accurate quantification of echo magnitudes. The resulting decay curves allow for correction of errors due to nonideal refocusing pulses as a result of inhomogeneities in the B1 transmit field. Non-Negative Least Squares fitting is used to quantify the magnitude of T2 components at various T2 values. This method, allowing calculation of the T2 distribution with simultaneous extraction of the refocusing pulse flip angle, requires no change to image acquisition procedures and no extra data input. Validation by means of both simulations and in vivo data shows excellent interscan reproducibility while vastly improving the accuracy of extracted T2 parameters in voxels where poor B1 homogeneity leads to refocusing pulse flip angles significantly less than 180 degrees. Most notably, myelin water fraction values in these regions are found to have increased consistency and accuracy. Magn Reson Med, 2011. (c) 2011 Wiley Periodicals, Inc.