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°. Most notably, myelin water fraction values in these regions are found to have increased consistency and accuracy.