Applications of stimulated echo correction to multicomponentT2 analysis

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We propose a multicomponent fitting algorithm for multiechoT2 data which allows for correction ofT2 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 theB1 transmit field. Non-Negative Least Squares fitting is used to quantify the magnitude ofT2 components at variousT2 values. This method, allowing calculation of theT2 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 extractedT2 parameters in voxels where poorB1 homogeneity leads to refocusing pulse flip angles significantly less than 180°. Most notably, myelin water fraction values in these regions are found to have increased consistency and accuracy.

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