K. Scheidhauer, A. Ehlerding, J. Saeckl, A. Rieger, K. Herrmann, A. Schnelzer, M. E. Martignoni, T. Wendler Feasibility evaluation of freehand SPECT for intraoperative 3D lymphatic mapping Proceedings of the International Sentinel Node Society Meeting, Yokohama, Japan, 2010 (bib)
	AIM: Development and evaluation of system for intraoperative visualization of SPECT/CT data for the case of SLNB in head and neck cancer. MATERIALS & METHODS: SPECT/CT images are automatically registered with the coordinates of a positioning system by using known geometry marker fixed to the anatomy/phantom to be imaged. The registration succeeds automatically based on segmented CT data and known Hounsfield units and geometry of marker. Marker is designed to be detectable and tracked in real-time by the positioning system allowing thus to know relative position of SPECT/CT data t o patient in real time. Further tracked instrument by positioning system was added to control angle of visualization of SPECT/CT data (VR mode). For more intuitive visualization in a different mode (AR mode), an optical camera is attached to the positioning system and calibrated in order to visualize SPECT/CT data correctly rendered and overlaid on video image in real-time. Calibration of camera succeeds using OpenCV? camera calibration methods and Tsai algorithm for hand-eye -calibration. In a first phantom experiment SPECT/CT images of a phantom with 5 radioactive spheres of different sizes (250, 2x125, 62.5 and 31.5mul, constant concentration 0.5MBq/ml) were used as input for the system. Registration error o f marker and on overlay were quantified. RESULTS: The combined video/SPECT/CT enables intuitive localization of radioactive spheres and visualization of imaging data from almost any direction providing a fully 3D sensation. Registration error was in mean 0.5mm and error of overlay was at most 6mm with an average of 4mm. CONCLUSIONS: The visualization of SPECT/CT images overlaid on the video of the patient (AR mode) and/or from arbitrary perspectives (VR mode) is possible with the proposed system. The use of such visualization may help evaluating in the OR the optimal path to get to the sentinel nodes and exploit optimally the 3D hybri d nature of SPECT/CT in particular in head and neck SLNB. ACKNOWLEDGEMENTS: This research was partly funded by the DFG’s SFB-824, TUM's GSISH and SurgicEye? GmbH?.
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