A Single-Scan T2* Mapping Method Based on Two Gradient-Echo Images with Compensation for Macroscopic Field Inhomogeneity

T-2*-weighted imaging (T-2*WI) and quantitative T-2* mapping with conventional gradient-echo acquisition are often hindered by severe signal loss induced by macroscopic field inhomogeneity. Various z-shimming approaches have been developed for T-2*WI/T-2* mapping in which the effects of macroscopic field inhomogeneity are suppressed while the sensitivity of T-2*-related signal intensity to alterations in the microscopic susceptibility is maintained. However, this is often done at the cost of significantly increased imaging time. In this work, a fast T-2* mapping method with compensation for macroscopic field inhomogeneity was developed. A proton density-weighted image and a composite T-2*-weighted image, both of which were essentially free from macroscopic field inhomogeneity-induced signal loss, were used for the T-2* calculation. The composite T-2*-weighted image was reconstructed from a number of gradient-echo images acquired with successively incremented z-shimming compensation. Because acquisition of the two images and z-shimming compensation were realized in a single scan, the total acquisition time for obtaining a T-2* map with the proposed method is the same as the time taken for a conventional multiecho gradient-echo imaging sequence without compensation. The performance and efficiency of the proposed method were demonstrated and evaluated at 4.7 T. Magn Reson Med 60:1388-1395, 2008. (C) 2008 Wiley-Liss, Inc.