Correction: 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.

In-vivo magnetic resonance imaging (MRI) of laminae in the human cortex

“…A promising motion correction technique providing the necessary precision in the range of a 1/10th voxel size (i.e., approximately 50 μm) and speed (approximate sampling rate 100 Hz) is prospective motion correction based on optical tracking (see Fig. 2; Callaghan et al, 2015;Maclaren et al, 2012;Schulz et al, 2012). However, sophisticated hardware, like MR compatible video cameras, are necessary.…”

Correction of B 0-induced geometric distortion variations in prospective motion correction for 7T MRI

“…PMC was performed with a tracking system consisting of a single camera mounted inside the scanner bore and a tracking marker with a multilayer structure, which generates moiré patterns for accurate orientation measurement [30]. Communication with the tracking system was implemented directly on the real-time control unit of the scanner as previously described by Zaitsev et al [6].…”

Towards high-quality simultaneous EEG-fMRI at 7 T: Detection and reduction of EEG artifacts due to head motion

“…The main artifact contributions were associated with the MRI gradients and the cardiac cycle, but while these contributions are approximately periodic, and thus more suited to temporal segmentation for averaging and subtraction, spontaneous motion does not follow regular patterns, and can thus highly benefit from an external monitoring system. Several approaches for head motion detection have been proposed, including the use of highly sensitive optical systems (Maclaren et al, 2012), piezoelectric sensors (Bonmassar et al, 2002), and conductive wire loops (Masterton et al, 2007). We opted for loop-based sensors since they share similar mechanisms of artifact generation with EEG loops, and can be directly incorporated in linear regression models for EEG signal correction (as shown in the Motion artifact generation section).…”