Motion detection and estimation using impedances of an 8-channel parallel transmit head coil at 7T

Abstract

Magnetic Resonance Imaging (MRI) is a medical imaging technique to form images of the anatomy or structures of the human body using strong magnetic fields. Because of motion of the scanned patient, these images may be distorted causing so called motion artifacts in the image. There are several techniques available to correct for motion. The MR system contains directional couplers (DICOs), those were originally added to the hardware for safety measurements by monitoring the forward and reflected data of the radiofrequency (RF) signal for the eight channels on the head coil. The aim of this research is to see if the forward and reflected data can be used to detect motion. Subsequently is examined whether motion parameters of the subjects head and the RF data are linearly related. The accuracy and reproducibility of the estimated motion is examined within and over subject. To obtain a motion correction matrix (MCM), motion parameter data from FSL/FEAT (a library of analysis tools for MRI data) was linearly related to the impedance of the 8-channel head coil by left array division of the two matrices. The quality of the fit of the estimated motion is very high. The estimated motion within the same subject, but with use of another MCM, show the same pattern, but with a shift. The method does not work when used over subjects. Additional research, concerning the data processing technique, is required to optimize the method to have it implemented as a real-time motion correction technique.