NMR Fresnel transform imaging technique using a quadratic nonlinear field gradient

A new NMR imaging technique using a quadratic nonlinear field gradient is described. The center position of the nonlinear field gradient where the field intensity is minimum is moved spatially at a fixed amount in each imaging pulse sequence to produce nonlinear phase encoding as a function of position. A NMR image is reconstructed from the collected data by the computer data processing. The principle of this technique and many experimental results using a low field imaging system operating at 0.0192 T are presented. Theoretical and experimental comparison of the S/N of the image in this technique with that of the conventional Fourier imaging technique are made and the results show that both techniques have almost the same S/N. Moreover, the theoretical and experimental results show that this technique has a feasibility of a spatially localized imaging without using a conventional localization technique such as the use of the selective excitation in the presence of a linear field gradient.