Inductive Measurement of Gradient System Transfer Function of an MRI Scanner for Artifacts Correction

Gradient imperfections remain a challenge in MRI, which could introduce artifacts in imaging protocols. A simple gadget for characterization of gradient system is proposed by real-time measurement of the magnetic field. It is composed of a small senor coil and a sample resistor, and digital integration of the induced voltage is used to recover the pulsed gradient. Thus, this inductive method is independent of static magnetic field inhomogeneities. Transfer function can then be obtained by assuming the tested gradient chain as a linear and time-invariant system. Triangular inputs are utilized to probe the gradient system and responses are measured by placing the coil along each investigated gradient direction. Error caused by electronic parameters is below 0.2% with a matched sample resistor. For validation, experiments were performed on a 50 mT head MRI scanner and image artifacts in both Cartesian and non-Cartesian imaging protocols were corrected by the obtained transfer function. The proposed device can also be extended to record cross-responses or different spatial orders by additional sensor coils, rendering the method suitable for being used in the process of gradient system design and optimization.