T. Wendler, A. Hartl, J. Traub, S. I. Ziegler, N. Navab Intraoperative nuclear imaging using navigated gamma-probes for tumor localization Proceedings of Annual Meeting of Society of Nuclear Medicine (SNM 2007), Washington D.C., USA, June 2007 (bib)
	Objectives Intraoperative gamma imaging using so called imaging probes has been restricted mainly to 2D, easily accessible areas and low-energy gamma radiation. By spatially localizing a single handheld detector and synchronizing its readings to its position and orientation we are able to do 2D reconstructions of simple radioactivity distributions, introducing a new approach for intraoperative gamma imaging without the said constrains. Methods: We designed a system that synchronizes the readings of a high-energy gamma-probe with its position and orientation as provided by an optical spatial localization device. As a first approach, we filled 2 and 3 wells of a 96-well culture plate with 0.1-0.5 MBq of an aqueous solution of F-18 and scanned during 2-3 minutes, sampling every 0.1 seconds. Using the acquired positions and orientations of the probe, the positions of each well, and ad-hoc developed models of the detection process we generated a system matrix as it is done in SPECT and calculated the source distribution using standard reconstruction techniques. Results: In all experiments the system was able to detect the wells with radioactivity (voxel and well size 1x1x1 cm3). The qualitative results correlate with the average quadratic error of the real and calculated gamma readings showing that increasing the number of points (long scans, more information) and distance to the source (far scans, less variance) yield better results. The error arises only from blurring effects and not from false positives. Conclusions: The introduced system showed that 2D reconstruction is possible from tracked gamma-probe readings. Using single detectors allows easier handling and more flexibility than with an imaging probe. Moreover, it facilitates the use of probes designed for detecting high-energy radiation. The introduce approach is not restricted to 2D and is also extendable for laparoscopic and low-energy probes. Thus, these preliminary results introduce a promising new alternative toward intraoperative 3D functional imaging. Research Support: The gamma-probe was kindly provided by Dr. Farhad Daghighian from IntraMedical? Imaging LLC (Los Angeles, California).
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