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. © 2002 Wiley-Liss, Inc.