1. A motion tracking system for tracking and compensating for motion of a patient during a medical imaging scan, the motion tracking system comprising: an optical marker configured to be attached to the patient, wherein the optical marker comprises a plurality of optically visible landmarks, the plurality of optically visible landmarks defining a plurality of reference points; a plurality of optical detectors, wherein each of the plurality of optical detectors is positioned to view the optical marker along a different line of sight; one or more computer readable storage devices configured to store a plurality of computer executable instructions; and one or more hardware computer processors in communication with the one or more computer readable storage devices and configured to execute the plurality of computer executable instructions in order cause the motion tracking system to: receive a digital image from each of the plurality of optical detectors, wherein each digital image represents a view along a different line of sight; determine, for each digital image, whether the digital image includes a view of the optical marker; determine, for each digital image that includes a view of the optical marker, positions of the plurality of reference points in the digital image; calculate a plurality of baseline attributes related to the plurality of reference points, the plurality of baseline attributes calculated based on the determined positions of the plurality of reference points; and estimate iteratively a three-dimensional pose of the patient, until a measure of error is within a threshold amount, the measure of error calculated based on the plurality of baseline attributes as compared to a plurality of comparison attributes, the plurality of comparison attributes calculated by assuming the object is in an estimated pose.