Modified Look-Locker T1 evaluation using Bloch simulations: Human and phantom validation

Modified Look-Locker imaging is frequently used for T1 mapping of the myocardium. However, the specific effect of various MRI parameters (e.g., encoding scheme, modifications of flip angle, heart rate, T2, and inversion times) on the accuracy of T1 measurement has not been studied through Bloch simulations. In this work, modified Look-Locker imaging was characterized through a numerical solution for Bloch equations. MRI sequence parameters that may affect T1 accuracy were systematically varied in the simulation. For validation, phantoms were constructed with various T2 and T1 times and compared with Bloch equation simulations. Human volunteers were also evaluated with various pulse sequences parameters to assess the validity of the numerical simulations. There was close agreement between simulated T1 times and T1 times measured in phantoms and volunteers. Lower T2 times (i.e., <30 ms) resulted in errors greater than 5% for T1 determination. Increasing maximum inversion time value improved T1 accuracy particularly for precontrast myocardial T1. Balanced steady-state free precession k space centric encoding improved accuracy for short T1 times (post gadolinium), but linear encoding provided improved accuracy for precontrast T1 values. Lower flip angles are preferred if the signal-to-noise ratio is sufficiently high. Bloch simulations for modified Look-Locker imaging provide an accurate method to comprehensively quantify the effect of pulse sequence parameters on T1 accuracy. As an alternative to otherwise lengthy phantom studies or human studies, such simulations may be useful to optimize the modified Look-Locker imaging sequence and compare differences in T1-derived measurements from different scanners or institutions. Magn Reson Med, 2013. (C) 2012 Wiley Periodicals, Inc.