Rapid local rectangular views and magnifications: reduced phase encoding of orthogonally excited spin echoes

A method is described for rapid, artifact-free imaging and magnification of small regions within a larger sample. This combines a rectangular window, reconstructed from a reduced number of phase-encoding steps, and confinement of spin echoes to a similar rectangular strip by orthogonal pi/2 and pi excitations. Phase encoding is along the width of the strip (along Y). Off-center strips are excited by offsetting the Y slice-selecting gradient, and the reconstruction window is kept coincident with excitation by similarly offsetting the Y phase-encoding gradient. The excited strip is centered in the reconstruction window by setting the radiofrequency transmitter on resonance. The method is shown to be useful for long narrow structures such as the spine where the acquisition time is reduced by over a factor of 5 determined by the image aspect ratio.