A markerless motion tracking (MT) system developed for use in PET brain imaging has been tested in the limited field of view (FOV) of the MR head coil from the Siemens Biograph mMR. The system is a 3D surface scanner that uses structured light (SL) to create point cloud reconstructions of the facial surface. The point clouds are continuously realigned to a reference scan to obtain pose estimates. The system has been tested on a mannequin head performing controlled rotational and translational axial movements within the head coil outside the range of the magnetic field. The RMS of the residual error of the rotation was 0.11° and the RMS difference in the translation with the control system was 0.17 mm, within the trackable range of movement.