Phase rotated spoiling for spatial and spectral saturation techniques

Abstract

Magnets (12) create a temporally constant magnetic field through an examination region (14). Radio frequency coils (26, 34) and a transmitter (24) transmit radio frequency saturation pulses (52) and the resonance excitation and manipulation pulses of a magnetic resonance imaging sequence (72) into the examination region. Gradient amplifiers (20) and gradient coils (22, 32) create magnetic field gradients across the examination region for spatially focusing the saturation, for spoiling (62, 66, 70) residual transverse magnetization and for frequency and phase encoding in the magnetic resonance imaging sequence. A sequence controller (40) includes a saturation pulse controller (44) for generating the saturation pulse (52) and slice select gradients (58) and a steady state sequence controller (48) for generating the imaging sequence (72). The saturation is spectrally focused by limiting the frequency of the saturation pulse to selected frequencies. The saturation is spatially focused by applying the slice or other spatially limiting gradient pulses concurrently with the radio frequency saturation pulse. A phase shift controller (76) increments the phase of the RF saturation pulse by a preselected phase increment, e.g., 105.degree.. Preferably, the phase shift increment increases linearly in each cyclic repetition, i.e., increases 105.degree. in the first repetition, 210.degree. in the next repetition, 315.degree. in the next repetition, etc. A reconstruction processor (80) reconstructs resonance signals generated during the imaging sequences into an image representation for storage in a memory (82) and display on a video monitor (86).