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@INPROCEEDINGS{wendler2007snmgamma,
  author = {Thomas Wendler and Alexander Hartl and Joerg Traub and Sibylle Ziegler
	and Nassir Navab},
  title = {Intraoperative nuclear imaging using navigated gamma-probes for tumor
	localization},
  booktitle = {Proceedings of SNM 2007},
  year = {2007},
  address = {Washington D.C., USA},
  month = {Jun.},
  organization = {Society of Nuclear Medicine},
  abstract = {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).}
}

