Improved Image Reconstruction In Small Animal PET Using a Priori Estimates of Single-Pixel Events (original) (raw)
Related papers
2006
We are developing cadmium zinc telluride detectors with three-dimensional photon positioning capabilities for highresolution PET imaging. These detectors exhibit high spatial resolution (1 mm), energy resolution (2.5% full width at half maximum for 511 keV photons), and the ability to resolve individual Compton interactions within the detector. Using these measurements, non-coincident single photons can be reconstructed by estimating the incoming direction of the photon using the kinematics of Compton scatter within the detector. In this paper, we investigated image reconstruction methods for combining two different types of measurements: conventional coincidence photon events and non-coincident single photon events. We introduce a new image reconstruction method that uses a Bayesian projector function. Using Monte Carlo simulated data generated by GATE (Geant4), we showed that this new approach has the potential to improve contrast and resolution with comparable signal-to-noise ratio.
IEEE Transactions on Nuclear Science, 2015
Scanner sensitivity is often critical in high-resolution Positron Emission Tomography (PET) dedicated to molecular imaging. In neighboring pixelated detectors with individual readout, sensitivity decreases because of multiple coincidences produced by Compton scattering. Correct analysis of those coincidences would enable a substantial sensitivity increase. However, including scattering byproducts in the image often lead to image quality degradation because of inaccurate Line-of-Response (LOR) assessment. In such scanners, to support high count rates, multiple coincidences are usually discarded when image degradation is not acceptable, or blindly accepted for a low computational burden. This paper presents a new, real-time capable method that includes Inter-Crystal Scatter (ICS) triple coincidences in the image without significant quality degradation. The method computes the LOR using a neural network fed by preprocessed raw data. As a proof of principle, this paper analyzes the simplest ICS scenario, triple coincidences where one photoelectric 511-keV event coincides with two more whose energy sum is also 511 keV. The paper visits the algorithm structure, presents Monte Carlo assessment with the LabPET model, and displays images reconstructed from real data. With an energy window of 360-660 keV and a singles energy threshold of 125 keV, the inclusion of triple coincidences yielded a sensitivity increase of 54%, a resolution degradation similar to that of other sensitivity-increasing methods, and only a slight contrast degradation for real LabPET data, with potential for numerous further improvements.
Simulation of triple coincidences in PET
Physics in medicine and biology, 2015
Although current PET scanners are designed and optimized to detect double coincidence events, there is a significant amount of triple coincidences in any PET acquisition. Triple coincidences may arise from causes such as: inter-detector scatter (IDS), random triple interactions (RT), or the detection of prompt gamma rays in coincidence with annihilation photons when non-pure positron-emitting radionuclides are used (β(+)γ events). Depending on the data acquisition settings of the PET scanner, these triple events are discarded or processed as a set of double coincidences if the energy of the three detected events is within the scanner's energy window. This latter option introduces noise in the data, as at most, only one of the possible lines-of-response defined by triple interactions corresponds to the line along which the decay occurred. Several novel works have pointed out the possibility of using triple events to increase the sensitivity of PET scanners or to expand PET imagin...
Statistical LOR estimation for a high-resolution dMiCE PET detector
Physics in Medicine and Biology, 2009
We develop a statistical line of response (LOR) estimator of the threedimensional interaction positions of a pair of annihilation photons in a PET detector module with depth of interaction capability. The three-dimensional points of interaction of a coincidence pair of photons within the detector module are estimated by calculation of an expectation of the points of interaction conditioned on the signals measured by the photosensors. This conditional expectation is computed from estimates of the probability density function of the light collection process and a model of the kinetics of photon interactions in the detector module. Our algorithm is capable of handling coincidences where each annihilation photon interacts any number of times within the detector module before being completely absorbed or escaping. In the case of multiple interactions, our algorithm estimates the position of the first interaction for each of the coincidence photons. This LOR estimation algorithm is developed for a high-resolution PET detector capable of providing depth-of-interaction information. Depth of interaction is measured by tailoring the light shared between two adjacent detector elements. These light-sharing crystal pairs are referred to as dMiCE and are being developed in our lab. Each detector element in the prototype system has a 2 × 2 mm 2 cross section and is directly coupled to a micro-pixel avalanche photodiode (MAPD). In this set-up, the distribution of the ratio of light shared between two adjacent detector elements can be expressed as a function of the depth of interaction. Monte Carlo experiments are performed using our LOR estimation algorithm and compared with Anger logic. We show that our LOR estimation algorithm provides a significant improvement over Anger logic under a variety of parameters. 0031-9155/09/206369+14$30.00 © 2009 Institute of Physics and Engineering in Medicine Printed in the UK 6369 6370 K M Champley et al 100 mm d e t e c t o r B d e t e c t o r A 200 mm 2 0 0 m m point source MAPDs Figure 1. Left: simulated PET system utilized for initial testing of the DOI reconstruction algorithm. Right: diagram showing the dMiCE light-sharing crystal pair with a triangular-shaded light reflector. Individual crystals are of size 2 × 2 × 20 mm 3 .
2003 IEEE Nuclear Science Symposium. Conference Record (IEEE Cat. No.03CH37515), 2003
We present a preliminary study on the design of a small animal positron emission tomograph with octagonal geometry. The main goal is to evaluate the impact of critical design parameters on the quality of the reconstructed images. Monte Carlo simulations take into account the depth of interaction in individual crystals. The activity sources are simulated as parametric distributions within the field of view and images are reconstructed with iterative algorithms based on the estimation of maximum likelihood and Bayesian regularization. The probability system matrix used by these algorithms is also calculated based on statistical models and Monte Carlo simulation. 2D and 3D techniques have been employed.
2007 IEEE Nuclear Science Symposium Conference Record, 2007
Present Positron Emission Tomography (PET) detectors suffer from degradation of the spatial resolution due to the lack of depth-of-interaction (DOI) information leading to uncertainty in deducing the Lines of Response (LOR) between coincident events. The Centre for Medical Radiation Physics at the University of Wollongong has developed a novel detector module which will provide depth of interaction information while retaining the sensitivity of current scanners. This will result in superior imaging together with the ability to locate smaller lesions. This work focuses on preliminary investigations of the suitability of replacing the bulky scintillator crystals and photomultiplier tubes of traditional PET detector modules with compact 3 × 3 × 3 mm 3 LYSO scintillator crystals individually coupled to Si photdetectors.