4684891 Rapid magnetic resonance imaging using multiple phase encoded spin echoes in each of plural measurement cycles

Abstract

Slice selective 90° and plural subsequent 180° NMR RF pulses are utilized to elicit a train of NMR spin echoes from a given slice or "planar volume" of the object under test in each of plural measurement cycles. Spatial information is encoded within the spin echo by imposing a G x gradient during each spin echo readout. Phase encoding in a second G y dimension is achieved by using (1) a cycle-dependent βG y gradient at least once during each NMR measurement cycle and (2) further δG y magnetic gradient pulses in association with some or all of the individual spin echo responses within each measurement cycle. The two different types of G y gradient pulses are dimensioned and timed so as to result in the desired number of phase encoded spin echo signals which subsequently can be arranged in a linearly increasing progression of phase encoding so as to be usable in a two-dimensional Fourier transformation process to produce an NMR image. Because the spin echo data are taken at different times of echo occurrences within a given measurement cycle, T2 artifact may be present in such an image. However T2 correction may be provided by calculating T2 and scaling all of the time domain spin echo data to a single common equivalent time of echo occurrence before performing the final two-dimensional Fourier transformation process which results in a final T2-corrected NMR image.