Dynamic 18F-fluorodeoxyglucose positron emission tomography (PET) studies can successfully be use... more Dynamic 18F-fluorodeoxyglucose positron emission tomography (PET) studies can successfully be used for diagnosis, therapy planning and monitoring in oncology. Using similarity mapping, we assessed the accuracy of anatomical localization of lesions and the detectability of metastases. 17 patients with co- lorectal cancer and 3 patients with plasmocytoma were included in the study. All dynamic 18F-FDG PET data sets were iteratively
Background: Dynamic positron emission tomography studies produce a large amount of image data, fr... more Background: Dynamic positron emission tomography studies produce a large amount of image data, from which clinically useful parametric information can be extracted using tracer kinetic methods. Data reduction methods can facilitate the initial interpretation and visual analysis of these large image sequences and at the same time can preserve important information and allow for basic feature characterization.
Dynamic Positron Emission Tomography (PET) offers differential diagnostic information and has inc... more Dynamic Positron Emission Tomography (PET) offers differential diagnostic information and has increasingly been used for diagnosis, therapy management and evaluation. We have applied Principal Component Analysis (PCA) on dynamic PET studies. Its general objectives are data reduction and interpretation. PCA in PET images reduces the dimensionality of dynamic data sets and can be used to identify the structures with different kinetic patterns prior to other types of analysis (e.g. ROI analysis).
GATE (Geant4 Application for Tomographic Emission) simulation toolkit has become a well validated... more GATE (Geant4 Application for Tomographic Emission) simulation toolkit has become a well validated toolkit for the simulation of SPECT and PET systems. A very important feature of GATE is that it allows modelling of time-dependent phenomena. In addition, complex voxelized object such as realistic anthropomorphic or small animal phantoms can be used as emission sources. In this work two small field of view scanners have been evaluated experimentally, modelled in GATE and mice studies have been simulated using MOBY mouse phantom. Two scanners have been simulated: The first one is a mouse sized gamma camera (field of view is 5xlOcm) that is based on two Hamamatsu H8500 PSPMTs, a Nat pixelized scintillator and a tungsten collimator with hexagonal parallel holes. The system has been modelled in GATE and good agreement has been found between simulation and experimental results. MOBY mouse has been introduced as a voxelized source and planar and tomography simulations were carried out. The second small animal PET scanner has four heads which are equipped with a H8500 PSPMTs and a pixelated LYSO scintillator. System's geometry has been modelled in GATE. The results of both systems simulation and comparison between simulation and experimental data are presented. In addition, mouse bone scans were simulated both for SPECT and PET and tomographic image are derived. The presented methodology is aimed to provide all necessary tools in order to perform optimized simulations of small animal emission tomography scans..
Worldwide, people living in rural and remote areas struggle to access timely, quality medical car... more Worldwide, people living in rural and remote areas struggle to access timely, quality medical care. Residents of these areas often have substandard access to specialty healthcare, primarily because specialist physicians are more likely to be located in areas of concentrated ...
The purpose of this study is to evaluate the average performance of algebraic and statistical ite... more The purpose of this study is to evaluate the average performance of algebraic and statistical iterative reconstruction methods, using phantom data from a prototype small-animal PET system. The algorithms that are being compared are the simultaneous versions of ART (SART) and MART (SMART), EM-ML, ISRA and WLS. The evaluation study was based on reconstructed image quality, as it is derived
IEEE Symposium Conference Record Nuclear Science 2004., 2004
We present an efficient methodology for the calculation of the transition matrix for 3D-OSEM iter... more We present an efficient methodology for the calculation of the transition matrix for 3D-OSEM iterative image reconstruction, including a model of the gamma-event detection in crystal with photoelectric and Compton scatter interaction. The method is adapted for high resolution PET cameras composed of pixelated scintillator crystal arrays and with axial symmetry. 2D-OSEM algorithm, in combination with rebinning methods such as SSRB and FORE, can also be performed using a subset of this transition matrix.
3rd International Conference on Imaging Technologies in Biomedical Sciences, 2006
An efficient iterative image reconstruction methodology is presented, adapted to high-resolution ... more An efficient iterative image reconstruction methodology is presented, adapted to high-resolution flat-head 3D positron emission tomography cameras. It is based on the ordered subsets expectation maximization algorithm and applies to systems with axial symmetry. The associated system matrix is calculated off-line, including a model of the g-event detection in the crystal, taking into account photoelectric effect and Compton scattering interactions. The nonzero elements of the sparse system matrix are stored in disc in an efficient way that allows the fast sequential access to the matrix elements during the reconstruction. A detailed calculation is performed for the voxels corresponding to central plane within the field of view (FOV) of the camera and the remaining values of the system matrix are obtained via translations based on the symmetries of the system along the axial dimension. GATE-based simulations have been used for the validation of the results. r
Respiratory motion is a major source of reduced quality in positron emission tomography (PET). In... more Respiratory motion is a major source of reduced quality in positron emission tomography (PET). In order to minimize its effects, the use of respiratory synchronized acquisitions, leading to gated frames, has been suggested. Such frames, however, are of low signal-to-noise ratio (SNR) as they contain reduced statistics. Super-resolution (SR) techniques make use of the motion in a sequence of images in order to improve their quality. They aim at enhancing a low-resolution image belonging to a sequence of images representing different views of the same scene. In this work, a maximum a posteriori (MAP) super-resolution algorithm has been implemented and applied to respiratory gated PET images for motion compensation. An edge preserving Huber regularization term was used to ensure convergence. Motion fields were recovered using a B-spline based elastic registration algorithm. The performance of the SR algorithm was evaluated through the use of both simulated and clinical datasets by assessing image SNR, as well as the contrast, position and extent of the different lesions. Results were compared to summing the registered synchronized frames on both simulated and clinical datasets. The super-resolution image had higher SNR (by a factor of over 4 on average) and lesion contrast (by a factor of 2) than the single respiratory synchronized frame using the same reconstruction matrix size. In comparison to the motion corrected or the motion free images a similar SNR was obtained, while improvements of up to 20% in the recovered lesion size and contrast were measured. Finally, the recovered lesion locations on the SR images were systematically closer to the true simulated lesion positions. These observations concerning the SNR, lesion contrast and size were confirmed on two clinical datasets included in the study. In conclusion, the use of SR techniques applied to respiratory motion synchronized images lead to motion compensation combined with improved image SNR and contrast, without any increase in the overall acquisition times.
An experimental structured light projection system which includes a miniaturized projector is des... more An experimental structured light projection system which includes a miniaturized projector is described. The system has been designed to be integrated in a fluorescence molecular tomography (FMT) prototype in order to reconstruct the surface of mice and phantom studies. A high-accuracy phase map is retrieved with phase-shifted sinusoidal fringes. Phase error due to the nonlinear gamma function of the pico-projector is calibrated and compensated. Robust phase unwrapping is performed with an additional Gray-code projection sequence. An automatic phase-to-height non-linear calibration scheme has been applied using objects located in the extremes of the field of view. The accuracy of the proposed method has been tested with a realistic mouse model and ray-tracing software.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
In this work the performance of novel small animal positron/single-photon emission (PET/SPECT) sc... more In this work the performance of novel small animal positron/single-photon emission (PET/SPECT) scanner is estimated via Monte Carlo simulation, considering a YAP/LSO phoswich detector. To overcome the differences between PET and SPECT and in order to simplify the design, the system implements most signal processing digitally with programmable devices. The estimated performance of the described setup, expressed in terms of spatial image resolution and sensitivity, is 1.4 mm/0.6% for PET and 2.5 mm/0.025% for SPECT, figures that are comparable with state of the art dedicated scanners. r
A fully 3D iterative image reconstruction algorithm has been developed for high-resolution PET ca... more A fully 3D iterative image reconstruction algorithm has been developed for high-resolution PET cameras composed of pixelated scintillator crystal arrays and rotating planar detectors, based on the ordered subsets approach. The associated system matrix is precalculated with Monte Carlo methods that incorporate physical effects not included in analytical models, such as positron range effects and interaction of the incident gammas with the scintillator material. Custom Monte Carlo methodologies have been developed and optimized for modelling of system matrices for fast iterative image reconstruction adapted to specific scanner geometries, without redundant calculations. According to the methodology proposed here, only one-eighth of the voxels within two central transaxial slices need to be modelled in detail. The rest of the system matrix elements can be obtained with the aid of axial symmetries and redundancies, as well as in-plane symmetries within transaxial slices. Sparse matrix techniques for the non-zero system matrix elements are employed, allowing for fast execution of the image reconstruction process. This 3D image reconstruction scheme has been compared in terms of image quality to a 2D fast implementation of the OSEM algorithm combined with Fourier rebinning approaches. This work confirms the superiority of fully 3D OSEM in terms of spatial resolution, contrast recovery and noise reduction as compared to conventional 2D approaches based on rebinning schemes. At the same time it demonstrates that fully 3D methodologies can be efficiently applied to the image reconstruction problem for high-resolution rotational PET cameras by applying accurate pre-calculated system models and taking advantage of the system's symmetries.
Dynamic 18F-fluorodeoxyglucose positron emission tomography (PET) studies can successfully be use... more Dynamic 18F-fluorodeoxyglucose positron emission tomography (PET) studies can successfully be used for diagnosis, therapy planning and monitoring in oncology. Using similarity mapping, we assessed the accuracy of anatomical localization of lesions and the detectability of metastases. 17 patients with co- lorectal cancer and 3 patients with plasmocytoma were included in the study. All dynamic 18F-FDG PET data sets were iteratively
Background: Dynamic positron emission tomography studies produce a large amount of image data, fr... more Background: Dynamic positron emission tomography studies produce a large amount of image data, from which clinically useful parametric information can be extracted using tracer kinetic methods. Data reduction methods can facilitate the initial interpretation and visual analysis of these large image sequences and at the same time can preserve important information and allow for basic feature characterization.
Dynamic Positron Emission Tomography (PET) offers differential diagnostic information and has inc... more Dynamic Positron Emission Tomography (PET) offers differential diagnostic information and has increasingly been used for diagnosis, therapy management and evaluation. We have applied Principal Component Analysis (PCA) on dynamic PET studies. Its general objectives are data reduction and interpretation. PCA in PET images reduces the dimensionality of dynamic data sets and can be used to identify the structures with different kinetic patterns prior to other types of analysis (e.g. ROI analysis).
GATE (Geant4 Application for Tomographic Emission) simulation toolkit has become a well validated... more GATE (Geant4 Application for Tomographic Emission) simulation toolkit has become a well validated toolkit for the simulation of SPECT and PET systems. A very important feature of GATE is that it allows modelling of time-dependent phenomena. In addition, complex voxelized object such as realistic anthropomorphic or small animal phantoms can be used as emission sources. In this work two small field of view scanners have been evaluated experimentally, modelled in GATE and mice studies have been simulated using MOBY mouse phantom. Two scanners have been simulated: The first one is a mouse sized gamma camera (field of view is 5xlOcm) that is based on two Hamamatsu H8500 PSPMTs, a Nat pixelized scintillator and a tungsten collimator with hexagonal parallel holes. The system has been modelled in GATE and good agreement has been found between simulation and experimental results. MOBY mouse has been introduced as a voxelized source and planar and tomography simulations were carried out. The second small animal PET scanner has four heads which are equipped with a H8500 PSPMTs and a pixelated LYSO scintillator. System's geometry has been modelled in GATE. The results of both systems simulation and comparison between simulation and experimental data are presented. In addition, mouse bone scans were simulated both for SPECT and PET and tomographic image are derived. The presented methodology is aimed to provide all necessary tools in order to perform optimized simulations of small animal emission tomography scans..
Worldwide, people living in rural and remote areas struggle to access timely, quality medical car... more Worldwide, people living in rural and remote areas struggle to access timely, quality medical care. Residents of these areas often have substandard access to specialty healthcare, primarily because specialist physicians are more likely to be located in areas of concentrated ...
The purpose of this study is to evaluate the average performance of algebraic and statistical ite... more The purpose of this study is to evaluate the average performance of algebraic and statistical iterative reconstruction methods, using phantom data from a prototype small-animal PET system. The algorithms that are being compared are the simultaneous versions of ART (SART) and MART (SMART), EM-ML, ISRA and WLS. The evaluation study was based on reconstructed image quality, as it is derived
IEEE Symposium Conference Record Nuclear Science 2004., 2004
We present an efficient methodology for the calculation of the transition matrix for 3D-OSEM iter... more We present an efficient methodology for the calculation of the transition matrix for 3D-OSEM iterative image reconstruction, including a model of the gamma-event detection in crystal with photoelectric and Compton scatter interaction. The method is adapted for high resolution PET cameras composed of pixelated scintillator crystal arrays and with axial symmetry. 2D-OSEM algorithm, in combination with rebinning methods such as SSRB and FORE, can also be performed using a subset of this transition matrix.
3rd International Conference on Imaging Technologies in Biomedical Sciences, 2006
An efficient iterative image reconstruction methodology is presented, adapted to high-resolution ... more An efficient iterative image reconstruction methodology is presented, adapted to high-resolution flat-head 3D positron emission tomography cameras. It is based on the ordered subsets expectation maximization algorithm and applies to systems with axial symmetry. The associated system matrix is calculated off-line, including a model of the g-event detection in the crystal, taking into account photoelectric effect and Compton scattering interactions. The nonzero elements of the sparse system matrix are stored in disc in an efficient way that allows the fast sequential access to the matrix elements during the reconstruction. A detailed calculation is performed for the voxels corresponding to central plane within the field of view (FOV) of the camera and the remaining values of the system matrix are obtained via translations based on the symmetries of the system along the axial dimension. GATE-based simulations have been used for the validation of the results. r
Respiratory motion is a major source of reduced quality in positron emission tomography (PET). In... more Respiratory motion is a major source of reduced quality in positron emission tomography (PET). In order to minimize its effects, the use of respiratory synchronized acquisitions, leading to gated frames, has been suggested. Such frames, however, are of low signal-to-noise ratio (SNR) as they contain reduced statistics. Super-resolution (SR) techniques make use of the motion in a sequence of images in order to improve their quality. They aim at enhancing a low-resolution image belonging to a sequence of images representing different views of the same scene. In this work, a maximum a posteriori (MAP) super-resolution algorithm has been implemented and applied to respiratory gated PET images for motion compensation. An edge preserving Huber regularization term was used to ensure convergence. Motion fields were recovered using a B-spline based elastic registration algorithm. The performance of the SR algorithm was evaluated through the use of both simulated and clinical datasets by assessing image SNR, as well as the contrast, position and extent of the different lesions. Results were compared to summing the registered synchronized frames on both simulated and clinical datasets. The super-resolution image had higher SNR (by a factor of over 4 on average) and lesion contrast (by a factor of 2) than the single respiratory synchronized frame using the same reconstruction matrix size. In comparison to the motion corrected or the motion free images a similar SNR was obtained, while improvements of up to 20% in the recovered lesion size and contrast were measured. Finally, the recovered lesion locations on the SR images were systematically closer to the true simulated lesion positions. These observations concerning the SNR, lesion contrast and size were confirmed on two clinical datasets included in the study. In conclusion, the use of SR techniques applied to respiratory motion synchronized images lead to motion compensation combined with improved image SNR and contrast, without any increase in the overall acquisition times.
An experimental structured light projection system which includes a miniaturized projector is des... more An experimental structured light projection system which includes a miniaturized projector is described. The system has been designed to be integrated in a fluorescence molecular tomography (FMT) prototype in order to reconstruct the surface of mice and phantom studies. A high-accuracy phase map is retrieved with phase-shifted sinusoidal fringes. Phase error due to the nonlinear gamma function of the pico-projector is calibrated and compensated. Robust phase unwrapping is performed with an additional Gray-code projection sequence. An automatic phase-to-height non-linear calibration scheme has been applied using objects located in the extremes of the field of view. The accuracy of the proposed method has been tested with a realistic mouse model and ray-tracing software.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
In this work the performance of novel small animal positron/single-photon emission (PET/SPECT) sc... more In this work the performance of novel small animal positron/single-photon emission (PET/SPECT) scanner is estimated via Monte Carlo simulation, considering a YAP/LSO phoswich detector. To overcome the differences between PET and SPECT and in order to simplify the design, the system implements most signal processing digitally with programmable devices. The estimated performance of the described setup, expressed in terms of spatial image resolution and sensitivity, is 1.4 mm/0.6% for PET and 2.5 mm/0.025% for SPECT, figures that are comparable with state of the art dedicated scanners. r
A fully 3D iterative image reconstruction algorithm has been developed for high-resolution PET ca... more A fully 3D iterative image reconstruction algorithm has been developed for high-resolution PET cameras composed of pixelated scintillator crystal arrays and rotating planar detectors, based on the ordered subsets approach. The associated system matrix is precalculated with Monte Carlo methods that incorporate physical effects not included in analytical models, such as positron range effects and interaction of the incident gammas with the scintillator material. Custom Monte Carlo methodologies have been developed and optimized for modelling of system matrices for fast iterative image reconstruction adapted to specific scanner geometries, without redundant calculations. According to the methodology proposed here, only one-eighth of the voxels within two central transaxial slices need to be modelled in detail. The rest of the system matrix elements can be obtained with the aid of axial symmetries and redundancies, as well as in-plane symmetries within transaxial slices. Sparse matrix techniques for the non-zero system matrix elements are employed, allowing for fast execution of the image reconstruction process. This 3D image reconstruction scheme has been compared in terms of image quality to a 2D fast implementation of the OSEM algorithm combined with Fourier rebinning approaches. This work confirms the superiority of fully 3D OSEM in terms of spatial resolution, contrast recovery and noise reduction as compared to conventional 2D approaches based on rebinning schemes. At the same time it demonstrates that fully 3D methodologies can be efficiently applied to the image reconstruction problem for high-resolution rotational PET cameras by applying accurate pre-calculated system models and taking advantage of the system's symmetries.
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Papers by G. Kontaxakis