Calibration of timing delays using alternating/repeating waveforms and epi

Abstract

A magnetic resonance imaging system includes a gradient hardware subsystem ( ), a radio frequency transmission hardware subsystem ( ), and a data sampling and digitization hardware subsystem ( ) A sequence control processor ( ) applies control signals or pulses to the hardware subsystems to cause the implementation of a selected EPI imaging sequence. Due to inductive loads, analog filters, and other circuit constructions within the hardware subsystems, each of the hardware subsystems has a different inherent delay between receipt of a control signal and actually achieving the controlled function such as applying a gradient or RF pulse or sampling data. Due to these different inherent delays, the imaging sequence occurs with timing variations from the intended sequence. Echo planar imaging sequences are very sensitive to phase errors caused by these relative delays, which phase errors manifest themselves in the form of Nyquist ghosts. A calibration processor ( ) analyzes resultant EPI images for Nyquist ghosts and adjusts a relative delay in the control signals from the signal processor until ghosting is minimized.