Optical tracking with two markers for robust prospective motion correction for brain imaging

Abstract

Object Prospective motion correction (PMC) during brain imaging using camera-based tracking of a skin-attached marker may suffer from problems including loss of marker visibility due to the coil and false correction due to non-rigid-body facial motion, such as frowning or squinting. A modified PMC system is introduced to mitigate these problems and increase the robustness of motion correction. Materials and Methods The method relies on simultaneously tracking two markers, each providing six degrees of freedom, that are placed on the forehead. This allows us to track head motion when one marker is obscured, and detect skin movements to prevent false corrections. Experiments were performed to compare the performance of the two-marker motion correction technique to the previous single-marker approach. Results Experiments validate the theory developed for adaptive marker tracking and skin movement detection, and demonstrate improved image quality during obstruction of the line-of-sight of one marker, when subjects squint, or when subjects squint and move simultaneously. Conclusion The proposed methods eliminate two common failure modes of PMC and substantially improve the robustness of PMC and can be applied to other optical tracking systems capable of tracking multiple markers. The methods presented can be adapted to the use of more than two markers.

Motion correction for diffusion weighted SMS imaging

“…However, instabilities due to incorrect motion correction have also been reported [12], [13]. The combination of external tracking data with image-based navigator information can help overcome this problem.…”

“…Integrating optical and image based motion correction effectively removed errors related to slippage of the optical marker, which is one of the challenges for external motion tracking [12], [13]. Furthermore, motion-induced inconsistencies in coil sensitivity profiles resulted in small but noticeable errors in SMS reconstruction of phantom data.…”

“…Motion correction with external optical tracking can improve DWI data quality [8]–[11]. However, affixation of tracking markers can be challenging and marker “slippage” during the scan will compromise the quality of motion correction or even introduce artifacts [12], [13]. …”

Prospective motion correction for 3D pseudo-continuous arterial spin labeling using an external optical tracking system

“…The large gaps between coil rungs in the 8-channel head coil used in this study helps to maintain the line-of-sight that is required for optical tracking to work. However, even for coils with large gaps between coil rungs, a standard optical marker can be obstructed or partly leave the camera field-of-view [28]. Reasons for this include changes in initial marker placement and/or patient positioning, patient drifting during scan, or patient head being large such that the marker is very close to the camera.…”

Motion correction in MRI of the brain

“…With optical tracking the range of trackable motion can be limited by line-of-sight requirements. A redundant multi-camera or multi-marker approach can increase the possible range of motion (Singh et al 2015). …”