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. Magn Reson Med 48:877–882, 2002. © 2002 Wiley‐Liss, Inc.