J. Gardiazabal, B. Frisch, P. Matthies, J. Vogel, S. I. Ziegler, N. Navab, T. Lasser List-Mode Reconstruction for Continuous Freehand SPECT Acquisitions IEEE Nuclear Science Symposium and Medical Imaging Conference, San Diego, USA, November 2015 (bib)
	Nuclear imaging with low-energy gamma-emitting tracers for diagnostic purposes, such as for pathologies of the thyroid, is usually performed with whole-body scintigraphy and SPECT systems. Interventional radioguidance, such as for targeted biopsy, mostly relies on single-channel gamma probes and multi-channel 2D gamma cameras. 3-dimensional SPECT acquisitions with tracked handheld detectors have been introduced but are limited by the dependence on the operator. We introduce a system for flexible, reproducible and patient-specific diagnostic or interventional gamma imaging. It consists in a mini gamma camera mounted on a robotic arm that provides precise tracking information. Data is continuously acquired and stored in a list mode format while the robot moves the gamma camera around the volume of interest. It is reconstructed by a list-mode expectation-maximisation (LM-EM) algorithm. We present results acquired on a custom 3D thyroid phantom containing hot and cold nodules that confirm the feasibility of this approach. We further simulate different uptake values by statistically thinning out the acquired data, showing that even low uptakes of 0.3 MBq can be reliably reconstructed within a few minutes.
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