J. Traub, K. Herrmann, T. Lasser, N. Navab, S. I. Ziegler, A. K. Buck, T. Wendler Freehand SPECT/Ultrasound Fusion for Hybrid Image-guided Resection Proceedings of RSNA 2009, Chicago, USA, December 2009 (bib)
	PURPOSE Integrate the intraoperative technology of freehand SPECT with ultrasound for fused functional and anatomical (hybrid) image-guidance in the OR and thus extend the success of preoperative hybrid imaging into the surgical field. METHOD AND MATERIALS A freehand SPECT (fhSPECT) system based on an infrared optical positioning system (NDI Vicra, Waterloo, Canada) and a gamma probe (IMI NodeSeeker?, Los Angeles, California, USA) is extended by an ultrasound (US) probe (7.5L40 Siemens, Erlangen, Germany). The positioning system allows the localization of both probes in the same coordinate system (0.2mm mean error inside 50x50x50cm3 volume) and thus allows fusion of 3D functional images of fhSPECT generated with the gamma probe and the 2D anatomical images of US. For visualization the 2D US plane is augmented with the information of the fhSPECT by calculating the oblique US plane through the fhSPECT and overlaying it semitransparently over the live US stream. In a first phantom experiment 3 radioactive and 3 non-radioactive spheres are implanted in a phantom. After 3D fhSPECT imaging (6min acquisition, 5x5x5mm3 voxels, 15x15x5cm3 reconstruction volume, 20 iteration MLEM), the phantom is scanned with the US probe. RESULTS The fused visualization allows an intuitive determination of radioactive and non radioactive spheres in the US plane. No artifacts occurred. The deviation of the centroids of the spheres seen in fhSPECT and US was below 5mm. CONCLUSION This preliminary experience shows that a fused fhSPECT/US system is feasible. Such systems can bring major advantages towards hybrid image-guidance in the OR. CLINICAL RELEVANCE/APPLICATION The increased sensitivity of preoperative hybrid systems allows locating focal malignancy precisely. Combining fhSPECT and US is a consequent and promising way of bringing these successes into the OR.
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