MR GRADIENT RESPONSE MODELING TO ENSURE EXCITATION COHERENCE

Gradient system response has a significant effect on the shape and dis persion of complex k-space trajectories, as used in echo-planar magnet ic resonance imaging and designed excitation. The authors have develop ed a method that characterizes the gradient response directly by placi ng k-space ''landmarks'' in the raw data. The method produces a clear delineation of the k-space trajectory. while providing information abo ut related factors such as magnetic field homogeneity and temporal coh erence of the radio-frequency (RF) and gradient waveforms. By using pa rameters derived from data collected under varying conditions, gradien t response is modeled as a linear system consisting of a response dela y function with a frequency-dependent slope. The results allow correct ions that can be applied to the RF waveform or to the k-space trajecto ry. Application of this correction to designed excitation with the sin usoidal k-space trajectory is demonstrated and discussed.