Measurement and Correction of Microscopic Head Motion during Magnetic Resonance Imaging of the Brain

Abstract

Magnetic resonance imaging (MRI) is a widely used method for non-invasive study of the structure and function of the human brain. Increasing magnetic field strengths enable higher resolution imaging; however, long scan times and high motion sensitivity mean that image quality is often limited by the involuntary motion of the subject. Prospective motion correction is a technique that addresses this problem by tracking head motion and continuously updating the imaging pulse sequence, locking the imaging volume position and orientation relative to the moving brain. The accuracy and precision of current MR-compatible tracking systems and navigator methods allows the quantification and correction of large-scale motion, but not the correction of very small involuntary movements in six degrees of freedom. In this work, we present an MR-compatible tracking system comprising a single camera and a single 15 mm marker that provides tracking precision in the order of 10 m and 0.01 degrees. We show preliminary results, which indicate that when used for prospective motion correction, the system enables improvement in image quality at both 3 T and 7 T, even in experienced and cooperative subjects trained to remain motionless during imaging. We also report direct observation and quantification of the mechanical ballistocardiogram (BCG) during simultaneous MR imaging. This is particularly apparent in the head-feet direction, with a peak-to-peak displacement of 140 m.

Prospective motion correction improves the sensitivity of fMRI pattern decoding

“…Layered gratings and the design of the marker allow all three translational and three rotational degrees of freedom to be measured. The precision of the translational and rotational measurements were previously reported to be 0.1 mm and 0.1°, respectively (Maclaren et al, 2012). This information is logged to the PMC system and transferred to the scanner host computer.…”

“…The PMC system employed here utilizes an in‐bore optical camera (Kineticor, HI) to track the motion of a passive Moiré phase marker at a frame rate of 80 Hz (Maclaren et al, 2012; Weinhandl, Armstrong, Kusik, Barrows, & Connor, 2010). Layered gratings and the design of the marker allow all three translational and three rotational degrees of freedom to be measured.…”

“…PMC requires an acquisition of the movement parameters of the participant's head concurrently with the acquisition of the imaging volume (Callaghan et al, 2015; Maclaren et al, 2012). The motion parameters are used to update the position of the acquisition box within the participant's head just before each radiofrequency (RF) pulse.…”

Functional Magnetic Resonance Imaging of the Domestic Dog: Research, Methodology, and Conceptual Issues

“…Some of these issues were partially addressed by Jia, Pustovyy, et al (2014) and Kyathanahally et al (2015) by employing a single external infrared camera to record dogs’ head motion with high temporal resolution (order of milliseconds) and spatial precision (order of micrometers) and then correcting for those effects post hoc . However, in an ideal scenario, we suggest employing prospective motion correction by either employing an external camera (Todd, Josephs, Callaghan, Lutti, & Weiskopf, 2015; Maclaren et al, 2012) or using imagebased tracking (as in 3D PACE; Thesen, Heid, Mueller, & Schad, 2000). …”

Motion correction in MRI of the brain

“…According to Maclaren et al (2010) the accuracy of the tracking system should be five to ten times higher than the resolution of the data being acquired. The best implementations using external tracking systems such as described in (Andrews-Shigaki et al 2011, Maclaren et al 2012) have a latency of about 20–30 ms. Thus, for a resolution of 1.0 mm, velocities of about 3.0–10.0 mm s −1 would be acceptable.…”