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Budapest, Hungary

Lorincz E.,Budapest University of Technology and Economics | Erdei G.,Budapest University of Technology and Economics | Peczeli I.,Budapest University of Technology and Economics | Steinbach C.,Budapest University of Technology and Economics | And 2 more authors.
IEEE Transactions on Nuclear Science | Year: 2010

A new Zemax model has been developed, which reliably predicts the light output of scintillator crystal pins for Positron Emission Tomography. Different configurations, including pin shape, surface finish and reflector types are investigated. The simulations use the actual measured wavelength-dependent parameters of the scintillator crystal, of the reflector and of the PMT's components. Good agreement is demonstrated between simulated and measured light output figures for 33 different pin configurations. The highest light output was found by both simulation and experiment for the pins with polished superficies (either polished or diffuse γ-side) with a non-coupled high reflectivity specular reflector around the superficies and an optically coupled high reflectivity diffuse reflector on the γ-side. We also present the measured light output homogeneity of a scintillator array fabricated according to one of the best pin configurations. © 2010 IEEE. Source

Steinbach C.O.,Budapest University of Technology and Economics | Erdei G.,Budapest University of Technology and Economics | Ujhelyi F.,Budapest University of Technology and Economics | Major P.,Mediso Ltd. | Lorincz E.,Budapest University of Technology and Economics
IEEE Transactions on Nuclear Science | Year: 2012

Controlled deflection of light cones from excited crystal pins has been realized in a positron emission tomography (PET) block detector that allows the enhancement of spatial resolution. The new light sharing module consists of special double prism units optically coupled to a continuous light guide. Slope angle in the prism units can be optimized for each pin in the array. We present well correlating results of light distribution measurements and simulations of single crystal pins with double prisms with different slope angles. First test results of spatial resolution improvement with optimized pixels of a block detector are also presented. © 2012 IEEE. Source

Szirmay-Kalos L.,Budapest University of Technology and Economics | Toth B.,Budapest University of Technology and Economics | Jakab G.,Mediso Ltd.
2014 IEEE Nuclear Science Symposium and Medical Imaging Conference, NSS/MIC 2014 | Year: 2014

Positron Emission Tomography reconstruction is ill posed. The result obtained with the iterative ML-EM algorithm is often noisy, which can be controlled by regularization. Common regularization methods penalize high frequency features or the total variation, thus they compromise even valid solutions that have such properties. Bregman iteration offers a better choice enforcing regularization only where needed by the noisy data. Bregman iteration requires a nested optimization, which poses problems when the algorithm is implemented on the GPU where storage space is limited and data transfer is slow. Another problem is that the strength of the regularization is set by a single global parameter, which results in overregularization for voxels measured by fewer LORs. To handle these problems, we propose a modified scheme that merges the two optimization steps into one, eliminating the overhead of Bregman iteration. The algorithm is demonstrated for a 2D test scenario and also in fully 3D reconstruction. The benefits over TV regularization are particularly high if the data has higher variation and point like features. The proposed algorithm is built into the TeraTomo™ system. © 2014 IEEE. Source

Szlavecz A.,Budapest University of Technology and Economics | Bukki T.,Mediso Ltd. | Steinbach C.,Budapest University of Technology and Economics | Benyo B.,Budapest University of Technology and Economics
Biomedical Signal Processing and Control | Year: 2011

Abstract: In this paper we present the development of a modelling convention and a modelling environment, called PetDetSim, able to describe different PET detector block geometries. Using the developed simulation environment, the PET detector block designer can easily define different detector block configurations and test their optical behaviour regarding the characteristic features that determine the imaging quality of the device. In addition to the common optical behaviour of the detector block the developed modelling environment is also able to model gamma photon penetration. The PetDetSim environment is designed to use on a computer cluster and in a grid computing environment in order to reduce the computation time of the simulation. The validation of PetDetSim has been successfully done in the case of basic detector models, i.e. consisting of a single crystal needle. © 2010 Published by Elsevier Ltd. All rights reserved. Source

Szirmay-Kalos L.,Budapest University of Technology and Economics | Magdics M.,Budapest University of Technology and Economics | Toth B.,Budapest University of Technology and Economics | Bukki T.,Mediso Ltd.
IEEE Transactions on Medical Imaging | Year: 2013

Iterative positron emission tomography (PET) reconstruction computes projections between the voxel space and the lines of response (LOR) space, which are mathematically equivalent to the evaluation of multi-dimensional integrals. The dimension of the integration domain can be very high if scattering needs to be compensated. Monte Carlo (MC) quadrature is a straightforward method to approximate high-dimensional integrals. As the numbers of voxels and LORs can be in the order of hundred millions and the projection also depends on the measured object, the quadratures cannot be precomputed, but Monte Carlo simulation should take place on-the-fly during the iterative reconstruction process. This paper presents modifications of the maximum likelihood, expectation maximization (ML-EM) iteration scheme to reduce the reconstruction error due to the on-the-fly MC approximations of forward and back projections. If the MC sample locations are the same in every iteration step of the ML-EM scheme, then the approximation error will lead to a modified reconstruction result. However, when random estimates are statistically independent in different iteration steps, then the iteration may either diverge or fluctuate around the solution. Our goal is to increase the accuracy and the stability of the iterative solution while keeping the number of random samples and therefore the reconstruction time low. We first analyze the error behavior of ML-EM iteration with on-the-fly MC projections, then propose two solutions: averaging iteration and Metropolis iteration. Averaging iteration averages forward projection estimates during the iteration sequence. Metropolis iteration rejects those forward projection estimates that would compromise the reconstruction and also guarantees the unbiasedness of the tracer density estimate. We demonstrate that these techniques allow a significant reduction of the required number of samples and thus the reconstruction time. The proposed methods are built into the Teratomo system. © 1982-2012 IEEE. Source

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