Self-encoded marker for optical prospective head motion correction in MRI

The tracking and compensation of patient motion during a magnetic resonance imaging (MRI) acquisition is an unsolved problem. For brain MRI, a promising approach recently suggested is to track the patient using an in-bore camera and a checkerboard marker attached to the patient’s forehead. However, the possible tracking range of the head pose is limited by the fact that the locally attached marker must be entirely visible inside the camera’s narrow field of view (FOV). To overcome this shortcoming, we developed a novel self-encoded marker where each feature on the pattern is augmented with a 2-D barcode. Hence, the marker can be tracked even if it is not completely visible in the camera image. Furthermore, it offers considerable advantages over the checkerboard marker in terms of processing speed, since it makes the correspondence search of feature points and marker-model coordinates, which are required for the pose estimation, redundant. The motion correction with the novel self-encoded marker recovered a rotation of 18° around the principal axis of the cylindrical phantom in-between two scans. After rigid registration of the resulting volumes, we measured a maximal error of 0.39 mm and 0.15° in translation and rotation, respectively. In in vivo experiments, the motion compensated images in scans with large motion during data acquisition indicate a correlation of 0.982 compared to a corresponding motion-free reference.

Improved pose estimation using a novel self-encoded marker for optical prospective motion correction in neuro-MRI. In vivo experiments show enhanced image quality using the pose estimates of self-encoded marker compared to checkerboard marker for motion correction.Figure optionsDownload high-quality image (103 K)Download as PowerPoint slideHighlights
► We introduce a novel marker design for optical prospective motion correction in MRI.
► Embedded codes on this marker allow an independent identification of features.
► Without the need of all features visible to the camera the tracking range is extended.
► The novel marker shows an improved accuracy compared to a checkerboard marker.
► These improvements result in enhanced image quality in performed in vivo experiments.