Real‐time quantification of T changes using multiecho planar imaging and numerical methods

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Abstract
Conventional approaches to quantify whole brain T maps use nonlinear regression with intensive computational requirements that therefore likely limit quantitative T mapping for real‐time applications. To overcome these limitations an alternative method, NumART (NUMerical Algorithm for Real‐time T mapping) that directly calculates T by a linear combination of images obtained at three or more different echo times was developed. NumART, linear least‐squares, and nonlinear regression techniques were applied to multiecho planar images of the human brain and to simulated data. Although NumART may overestimate T, 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, 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 for continuous on‐line T mapping in real time fMRI studies is shown. Magn Reson Med 48:877–882, 2002.