1. A motion compensation system for tracking and compensating for subject motion during a medical imaging scan, the motion compensation system comprising: an optical target configured to be fixed to a subject; at least two cameras positioned so as to view the optical target from different directions with each of the at least two cameras being configured to record two dimensional images of the optical target defining a target point, wherein the at least two cameras are attached to a head coil configured to be used in conjunction with a medical imaging scanner; 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 to cause the system to determine a position of the subject, wherein the determining the position of the subject comprises: identifying the target point and displacement of the target point based on optical images collected by the at least two cameras; utilizing an iteration procedure, wherein the iteration procedure comprises testing an approximate first-order solution against the identified target point to determine residual errors and dividing the determined residual errors by local derivatives with respect to rotation and translation to determine an iterative correction; repeating the iteration procedure until the residual errors are within predetermined levels of accuracy; and utilizing the repeated iteration procedure to determine the position of the subject at rates of at least 100 times per second.