Localized volume selection technique using an additional radial gradient coil.

Abstract

A volume selection technique for the localized NMR imaging using an additional radial gradient is proposed. This volume selection gradient is the fourth gradient in addition to the usual 3-dimensional imaging gradients, i.e., x-, y-, and z-directional gradients, and is of the radial form. The principle of the proposed method is the use of the radial gradient in conjunction with the selective RF pulse thereby selecting a small cylindrical volume which can be used for the 3-dimensional volume imaging with fewer encoding steps than those of the conventional full 3-dimensional volume imaging. The present technique combined with the fast steady state free precession gradient echo imaging sequence allows us to reduce the total scan time to several minutes for the 3-dimensional volume imaging with the spatial resolution of 1 x 1 x 1 mm or to spend the same scan time for the 3-dimensional imaging with improved spatial resolution. The basic principle of the radial gradient coil consisting of a main circular loop coil and an offset compensating Helmholtz coil is discussed and the construction details are presented. Some experimental results of the proposed volume selection imaging technique as well as computer simulation results are also given.