Real-time quantification of T*2 changes using multiecho planar imaging and numerical methods

Conventional approaches to quantify whole brain T-2* maps use nonlinear regression with intensive computational requirements that therefore likely limit quantitative T-2* mapping for real-time applications. To overcome these limitations an alternative method, NumART(2)* (NUMerical Algorithm for Real-time T-2* mapping) that directly calculates T-2* by a linear combination of images obtained at three or more different echo times was developed. NumART(2)*, linear least-squares, and nonlinear regression techniques were applied to multiecho planar images of the human brain and to simulated data. Although NumART(2)* may overestimate T-2*, it yields comparable values to regression techniques in cortical and subcortical areas, with only moderate deviations for echo spacings between 18 and 40 ms. NumART(2)*, like linear regression, requires 2% of the computational time needed for nonlinear regression and compares favorably with linear regression due to its higher precision. The use of NumART(2)* for continuous on-line T-2* mapping in real time fMRI studies is shown. (C) 2002 Wiley-Liss, Inc.