An estimation and correction scheme for system imperfections in multiple-echo magnetic resonance imaging.

Multiecho sequences are widely used in MRI because they are an efficient means of acquiring data and they can be used to quantitatively estimate T2. However, the uniformity of each image and the accuracy of each T2 estimate may be corrupted by several instrumental factors such as rf pulse imperfections and static field inhomogeneities. We propose a scheme based on our prior knowledge of the effects of such factors and using the Levenberg-Marquardt method of nonlinear estimation that produces accurate estimates of T2 even in the presence of substantial system imperfections and improves the image quality of later echo images in a multiecho sequence. A further extension of this scheme permits mapping the distribution of the static magnetic field from a single multiecho imaging study of a uniform object. Simulations have been performed to test the efficacy of this scheme and the results are substantiated with experiments performed on a whole-body imager operating at 6.35 MHz.