Multiple target marker tracking for real-time, accurate, and robust rigid body motion tracking of the head for brain PET

Although motion correction in medical imaging is well established and has attracted much interest and research funding, a gap still exists in that there is a lack of reliable, low-cost hardware to enable such techniques to be widely adopted in healthcare. For PET, motion during scanning causes image blur which degrades image quality and quantifiability. In most marker based motion tracking systems used for brain imaging, a single tracking tool is fixed to the subject, however it is crucially important to ensure that the tool is rigidly fixed to the subject´s head otherwise the tool may slip and the tracking data becomes unreliable. A tracking system has been developed using open source code and a single low cost digital camera that tracks multiple, small (≤10 mm²) target markers printed onto adhesive paper which are attached to the subject´s forehead. The system can track the 6 degree of freedom motion of the head to sub mm precision and in real-time while being robust against facial deformations that may move the target markers non-rigidly. In this study a standard, consumer grade, visible light webcam was used with a resolution of 1600×1200, operated at 30 Hz, and achieved simultaneous tracking of multiple markers with 0.2 mm and 0.3° mean error. Calibration to PET space was performed using simultaneous tracking of a ¹⁸F point source doped marker with mean positional error of 0.7 mm.