Modelling a change in potential in an electromagnetic coil for small changes in head pose inside MR scanner.

Abstract

Purpose: A linear model is used for characterising the relationship between head pose and the induced voltages in a set of five coils in an initial set of imaging experiments, and subsequently using this relationship to calculate changes in head pose inside MR scanner from the measured voltages. Methods: To monitor position, we used an MR-compatible EEG amplifier system (Brain Products GmbH) to measure the voltage induced in the five coils by three gradient pulses successively applied along the right-left (RL), anterior-posterior (AP) and foot-head (FH) directions. Each pulse had ramp up and down periods of 5 ms at a rate of 2 Tm−1 s −1 inducing voltages of a few mV in the coils. The position (z) and orientation (ϕ, ψ) of the phantom was also measured by using SPM to co-register Fast Field Echo (FFE) images. The resulting model used to identify the phantom position from the voltage measurements and the results compared to parameters identified using the SPM registration. Results: The small differences in the position parameters estimated from the measured voltages in the coils and from the image corregistration by SPM8 indicate that the measurements of gradient-induced voltages in coils can provide accurate estimates of movement parameters. Conclusions: Initial results reveals potential utility of modelling a change in induced voltage in an inductive coil for monitoring small changes in head pose inside MR scanner.