Nmr, mri, and spectroscopic mri in inhomogeneous fields

Abstract

A method for locally creating effectively homogeneous or 'clean' magnetic field gradients (of high uniformity) for imaging (with NMR, MRI, or spectroscopic MRI) both in in-situ and ex-situ systems with high degrees of inhomogeneous field strength. The method of imaging comprises: a) providing a functional approximation of an inhomogeneous static magnetic field strength B({right arrow over (r)}) at a spatial position {right arrow over (r)}; b) providing a temporal functional approximation of {right arrow over (G)}(t) with i basis functions and j variables for each basis function, resulting in vvariables; c) providing a measured value Ω, which is an temporally accumulated dephasing due to the inhomogeneities of B({right arrow over (r)}); and d) minimizing a difference in the local dephasing angle φ({right arrow over (r)},t)=γ∫√{square root over (|{right arrow over (B)}({right arrow over (r)},t')|+({right arrow over (r)}·{right arrow over (G)}G(t′)+∥{right arrow over (B)}({right arrow over (r)})∥Δω({right arrow over (r)},t′)/γ))}dt′−Ω by varying the vvariables to form a set of minimized vvariables. The method requires calibration of the static fields prior to minimization, but may thereafter be implemented without such calibration, may be used in open or closed systems, and potentially portable systems.