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Maximum a posteriori event positioning in high-resolution PET CZT detectors

¹ Stanford University, Stanford, California

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Objectives: Cadmium-Zinc-Telluride (CZT) may be useful for PET, but its photo-fraction is low and multiple interactions in the detectors are frequent. However, a CZT detector can localize the 3D coordinates of individual photon interactions with high spatial and energy resolution. A challenge is to correctly estimate the first interaction, which best defines the correct line of response. Previously, we had proposed a maximum-likelihood (ML) approach. In this work, we investigate a maximum a posteriori (MAP) positioning method.

Methods: Monte-Carlo integration is used to compute the likelihood of each possible sequence of interaction. An accurate physical model is used to compute the a priori probability of each sequence and obtain a posteriori probabilities. This model uses the exponential photon linear attenuation law and the Klein Nishina formula. A parameter β defines the relative weights of the likelihood and the prior model (β=0 for ML). For fast computation, we are investigating using graphics processing units to parallelize the algorithm.

Results: We generated data using Monte-Carlo for two simulated CZT-based PET systems. The high-specs (HS) system has 1x1x1 mm³ spatial and 3% fwhm energy resolution. The low-specs (LS) system has 1x1x5 mm³ spatial and 12% energy resolution. The method was evaluated on both systems with β varying. The performance is measured as the success rate in recovering either the full sequence of interactions or just the first interaction.

Conclusions: For the HS system, MAP performs worse than ML as β increases. This indicates that low-noise data should be trusted more than the prior model. For the LS system and β=2, MAP outperforms ML by 7% for recovering the correct interaction sequence and 8% for the first interaction. An accurate prior model makes the position estimate more robust to noise in the data.

Research Support: NIH R01CA119056, R33EB003283, R01CA120474

This Article Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Pratx, G. Articles by Levin, C. PubMed Articles by Pratx, G. Articles by Levin, C.