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

D. I. Shakir, N. Navab, S. I. Ziegler
Acquisition Model for Iterative Reconstruction of Navigated Beta-Probe Surface Images
Proceedings of the IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS-MIC), Knoxville, TN, USA, November 2010 (bib)

Intraoperative beta surface imaging with navigated beta-probes in conjunction with positron-emitting radiotracers like FDG has been shown to be biologically feasible and may enable control of tumor resection borders. However, the imaging quality can still be improved by considering detection physics with ad hoc acquisition models. In this study we evaluate such a model that accounts for some of the probe parameters. Simulations of tumor with peritumoral tissue were obtained in three Petri dishes with bladder cancer cells and human foreskin fibroblasts. Bioluminescence images (showing tumor only) were taken. Following FDG incubation, each setup was scanned in 1mm steps with a navigated beta-probe, acquiring 3sec of data per step. Activity distribution images on the discretized surface of interest (SOI) were obtained using two methods: 1. Projection obtains the value of each suxel (surface voxel) by averaging all probe readings that fall spatially in there (detector assumed as a single point), 2. Reconstruction represents each reading as a linear combination of suxels (of unknown value) within the probe field of view, with weights calculated according to the model; the resulting linear system is inverted using a maximum-likelihood expectation-maximization method. The SOI was registered to the bioluminescence images to calculate the normalized cross-correlation (NCC). In addition, the tumor spots were segmented out of the bioluminescence images as a mask for calculating the average tumor-to-background ratio (T/B). Reconstruction outperformed projection with 8.35±0.47:1 vs. 4.13±0.20:1 T/B. Reconstruction yielded a slightly lower NCC (84.14%±3.18%) to bioluminescence compared to projection (87.17%±2.44%). However, bioluminescence images tell only where cell colonies are, and not the radiotracer uptake, which is the ground truth. These results suggest that the imaging quality can be further enhanced by improving the acquisition model.
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