Chair for Computer Aided Medical Procedures & Augmented Reality
Lehrstuhl für Informatikanwendungen in der Medizin & Augmented Reality

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J. Gardiazabal, P. Matthies, J. Vogel, B. Frisch, N. Navab, S. I. Ziegler, T. Lasser
Flexible Mini Gamma Camera Reconstructions of Extended Sources using Step and Shoot and List Mode
Medical Physics 43(12):6418-6428, 2016. (bib)

Hand- and robot-guided mini gamma cameras have been introduced for the acquisition of SPECT images. Less cumbersome than whole-body scanners, they allow for a fast acquisition of the radioactivity distribution, for example to differentiate cancerous from hormonally hyperactive lesions inside the thyroid. This work compares acquisition protocols and reconstruction algorithms in an attempt to identify the most suitable approach for fast acquisition and efficient image reconstruction, suitable for localization of extended sources, such as lesions inside the thyroid. Methods: Our setup consists of a mini gamma camera with precise tracking information provided by a robotic arm, which also provides reproducible positioning for our experiments. ased on a realistic phantom of the thyroid including hot and cold nodules as well as background radioactivity, we compare ``step and shoot' (SAS) and continuous data (CD) acquisition protocols in combination with two different statistical reconstruction methods: Maximum-Likelihood Expectation-Maximization (ML-EM) for time-integrated count values and List-Mode Expectation-Maximization (LM-EM) for individually detected gamma rays. In addition, we simulate lower uptake values by statistically sub-sampling the experimental data in order to study the behavior of our approach without changing other aspects of the acquired data. Results: All compared methods yield suitable results, resolving the hot nodules and the cold nodule from the background. However, the CD acquisition is twice as fast as the SAS acquisition, while yielding better coverage of the thyroid phantom, resulting in qualitatively more accurate reconstructions of the isthmus between the lobes. For CD acquisitions, the LM-EM reconstruction method is preferable, as it yields comparable image quality to ML-EM at significantly higher speeds, on average by an order of magnitude. Conclusions: This work identifies CD acquisition protocols combined with LM-EM reconstruction as a prime candidate for the wider introduction of SPECT imaging with flexible mini gamma cameras in the clinical practice.
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