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.