Magnetic field gradient waveform correction of motion-sensitized SPRITE by pre-equalization.

Abstract

Eddy currents caused by pulsed field gradients in magnetic resonance measurements of high-speed flow cause the magnetic field gradient amplitude waveform experienced by the sample to be different from the waveform demanded of the magnetic field gradient amplifiers. By measuring and using the system impulse response, pre-equalization magnetic field gradient waveform correction can be used to counteract the resulting errors in measured signal phase at the cost of minimal additional experimental time. The effectiveness of the pre-equalization method of magnetic field gradient waveform correction is tested with a motion-sensitized (pulsed field gradient) version of the SPRITE imaging pulse sequence which requires extreme gradient slew rates in excess of 1000 T/m/s in a 6.7-cm-bore set of gradient windings. Pre-equalized, motion-sensitized SPRITE is used to create velocity maps of high-speed (c. 4 m/s) water flow through a pipe constriction.