Richard Scott Hinks

Stabilized fast spin echo NMR pulse sequence with improved slice selection

A fast spin echo NMR pulse sequence is modified to stabilize the magnitude of early NMR echo signals produced during each shot. Stabilization is accomplished by modifying the amplitude of the nutation angle produced in the spins by the corresponding RF refocusing pulses. This stabilization is relaxed for the first RF refocusing pulse so that its maximum RF power can be reduced relative to that of the other RF refocusing pulses and the bandwidth thereof increased to improve the slice select profile.

Measurement and calibration of eddy currents for magnetic resonance imagers

A sample (80) is disposed in an examination region (10) through which a strong, uniform magnetic field is generated. A gradient pulse (24, 82) is created across the magnetic field. After the gradient field has been turned off, a rapid succession of radio frequency pulses (52, 84) are applied. Each radio frequency pulse is followed by a free induction decay signal (54, 86). For each free induction decay signal, the evolution of phase vs. time is determined (60) because the slope of the changing phase vs. changing time curve is proportional to resonance frequency (66) and the resonance frequency is proportional to magnetic field strength (68). For each free induction decay signal, the magnetic field strength and the time since the determination of the gradient field pulse are determined and stored (70). From the plurality of free induction decay signals, a decaying curve (28) representing eddy current induced gradient field strength vs. time is produced.