George Kontaxakis

George Kontaxakis
Universidad Politécnica de Madrid | UPM · Departmento de Ingeniería Electrónica

PhD

About

83
Publications
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959
Citations

Publications

Publications (83)
Conference Paper
We have proposed a method for the estimation of the optimal iteration for the Maximum Likelihood Expectation Maximization (MLEM) algorithm used in Positron Emission Tomography (PET) image reconstruction. For the calculation of the transition matrix and the generation of the projection data a PET scanner was simulated using Monte-Carlo techniques. O...
Conference Paper
Full-text available
An efficient, two-dimensional, analytic, Spline Reconstruction Technique (SRT) has been presented earlier in the literature. This technique involves the Hilbert transform of the sinogram which is approximated in terms of natural cubic splines. The aim of this study is to evaluate the SRT algorithm using Monte-Carlo simulated sinograms and real PET...
Article
Full-text available
In the present work, the authors compare geometrical and Monte Carlo projectors in detail. The geometrical projectors considered were the conventional geometrical Siddon ray-tracer (S-RT) and the orthogonal distance-based ray-tracer (OD-RT), based on computing the orthogonal distance from the center of image voxel to the line-of-response. A compari...
Article
We have studied the properties of the pixel updating coefficients in the 2D ordered subsets expectation maximization (OSEM) algorithm for iterative image reconstruction in positron emission tomography, in order to address the problem of image quality degradation-a known property of the technique after a number of iterations. The behavior of the upd...
Article
Full-text available
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 analyt...
Conference Paper
Full-text available
We address here the problem of the noise deterioration of the quality of the reconstructed images when employing the maximum likelihood expectation maximization (MLEM) algorithm for iterative image reconstruction in positron emission tomography (PET). It is observed that despite the fact the cost function (log-likelihood) is monotonically increasin...
Conference Paper
Full-text available
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. P...
Article
The user evaluation of the Albira small animal positron emission tomography scanner is presented. The system has a $backslash$varnothing80 mm x 40 mm field of view. In the center of the field of view, it has 2.49% sensitivity, with 33% solid angle coverage, and 0.88% sensitivity for a mouse phantom. The maximum of noise equivalent counts is 14.6 kc...
Article
An empirical stopping criterion for the 2D-maximum-likelihood expectation-maximization (MLEM) iterative image reconstruction algorithm in positron emission tomography (PET) has been proposed. We have applied the MLEM algorithm on Monte Carlo generated noise-free projection data and studied the properties of the pixel updating coefficients (PUC) in...
Conference Paper
In this paper, we are going to introduce a multimodal portable medical device for both medical imaging tele-collaboration and monitoring of vital parameters. The introduced portable unit offers diversity of medical devices and is in position to acquire ultrasound images, ECG 12 leads, and blood pressure and be able to measure oxygen level in the bl...
Conference Paper
Full-text available
Respiratory synchronized acquisitions lead to noisy images. Super-resolution techniques deal with the enhancement of several slightly different low-resolution images into a single high-resolution image. A maximum a-posteriori (MAP) super-resolution algorithm has been implemented and applied to respiratory gated PET images for motion compensation. T...
Conference Paper
Full-text available
A fully 3D statistical image reconstruction algorithm has been developed for a high-resolution coplanar PET/CT scanner based on rotating planar PET detectors. The system matrix has been modeled with custom Monte Carlo techniques optimized for the specific scanner architecture. The system model includes positron range, non-colinearity of gamma rays...
Conference Paper
Full-text available
We have studied certain properties of the OSEM algorithm for iterative image reconstruction in PET. This work is within the framework of our principal objective that is the development and evaluation of a stopping criterion for this iterative algorithm. To investigate the problem of the deterioration of the image quality after several iterations, t...
Article
Full-text available
Positron emission tomography (PET) requires accurate timing of scintillation events to properly discriminate between coincident and noncoincident pairs. The traditional solution to timing is based on custom application specific integrated circuits (ASIC) designs, whose cost may not be justified in the design of experimental small animal PET scanner...
Conference Paper
A preliminary user evaluation of the Albira small animal PET scanner is presented. The system has Oslash 80 times 40 mm2 field of view. In the center of the field of view it has 0.8% sensitivity with 33% solid angle coverage. Maximum of noise equivalent counts is 25 kcps for 8.9 MBq for a mouse phantom. The scanner employs an innovative crystal des...
Article
Full-text available
Respiratory motion in emission tomography leads to reduced image quality. Developed correction methodology has been concentrating on the use of respiratory synchronized acquisitions leading to gated frames. Such frames, however, are of low signal-to-noise ratio as a result of containing reduced statistics. In this work, we describe the implementati...
Conference Paper
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 recon...
Article
Full-text available
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 informat...
Conference Paper
Full-text available
Respiratory motion causes image degradation and artifacts in positron emission tomography (PET) images and constitutes an important source or error for the interpretation and proper quantization of thoracic and abdominal studies. Current work towards the correction of respiratory motion effects is mostly based on the acquisition of respiratory sync...
Article
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 γ-event de...
Article
A realistic dynamic positron-emission tomography (PET) thoracic study was generated, using the 4D NURBS-based (non-uniform rational B-splines) cardiac-torso (NCAT) phantom and a sophisticated model of the PET imaging process, simulating two solitary pulmonary nodules. Three data reduction and blind source separation methods were applied to the simu...
Article
A pilot network of positron emission tomography centers across Europe has been setup employing telemedicine services. The primary aim is to bring all PET centers in Europe (and beyond) closer, by integrating advanced medical imaging technology and health telematics networks applications into a single, easy to operate health telematics platform, whi...
Article
The majority of present position emission tomography (PET) animal systems are based on the coupling of high-density scintillators and light detectors. A disadvantage of these detector configurations is the compromise between image resolution, sensitivity and energy resolution. In addition, current combined imaging devices are based on simply placin...
Conference Paper
Full-text available
Room temperature semiconductor detectors, such as CdZnTe (CZT), are promising candidates for the design and development of a true integrated multimodality imaging system. However, hitherto no detailed analysis of the real potential of such a CZT-based canner has been carried out. In this work we report the modifications and developments implemented...
Conference Paper
Full-text available
Positron emission tomography (PET) requires accurate timing of events in order to properly discriminate between coincident and non-coincident events. The traditional solution to timing is based on custom ASIC designs, whose cost may not be justified in the design of an experimental small animal PET scanner. The new generation of PET scanners introd...
Conference Paper
Full-text available
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...
Conference Paper
Full-text available
A fast statistical iterative image reconstruction algorithm has been developed for high resolution PET scanners based on rotating plane detectors. The proposed technique consists of a multi-grid version of the 3D ordered subsets expectation-maximization (3D-OSEM) algorithm. The associated system matrix is precalculated for the fine grid resolution...
Conference Paper
Full-text available
Respiratory motion in emission tomography leads to reduced image quality. Proposed correction methodology has been concentrating on the use of respiratory synchronised acquisitions leading to gated frames. Such frames however are of low signal to noise ratio as a result of containing reduced statistics. Therefore a method accounting for respiratory...
Article
We are developing a small animal PET scanner consisting of two block detectors, each made of 216 BGO crystals of dimensions 3.75 mm×3.75 mm×20 mm, cylindrically arranged and coupled to a position-sensitive photomultiplier tube (R2486 PSPMT). Our design was based on a very detailed Monte Carlo, that simulates the function of a PET scanner from the s...
Article
This paper explores the advantages and disadvantages of a medical network based on point-to-point communication and a medical network based on Jabber instant messaging protocol. Instant messaging might be, for many people, a convenient way of chatting over the Internet. We will attempt to illustrate how an instant messaging protocol could serve in...
Article
Full-text available
This work describes a new digital front-end for a high-resolution low-cost animal PET scanner which is currently under development. The advances in flexibility and size of modern FPGAs together with the release of new tools enable the integration of most of the front-end electronics in a single FPGA. The implemented system includes a small 32-bit R...
Article
Full-text available
The availability of synthetic realistic data eases design optimization, algorithm evaluation and verification of any digital system where a significant amount of digital signal processing is performed. The evolution of positron emission tomography cameras towards continuous sampling of individual position-sensitive photomultiplier anodes with proce...
Chapter
Positron emission tomography (PET) is a powerful, proven diagnostic molecular imaging modality that displays the biological basis of function in the organs and systems of the human body unobtainable through any other means. PET allows the quantitative evaluation of the distribution of several pharmaceuticals in a target area in vivo. It is a unique...
Chapter
Positron emission tomography (PET) is a powerful diagnostic imaging modality that depicts the biological basis of function in the organs and systems in a living body, in a unique manner that cannot be obtained by other methods. This article reviews in brief the physical principles of the technique, presents a short historical review from its first...
Article
Full-text available
The analysis of dynamic positron emission tomography (PET) studies provides clinically useful parametric information, but often requires complex and time-consuming compartmental or non-compartmental techniques. Independent component analysis (ICA), a statistical method used for feature extraction and signal separation, is applied to dynamic PET stu...
Article
TENPET (Trans European Network for Positron Emission Tomography) aims to evaluate the provision of integrated teleconsultation and intelligent computer supported cooperative work services for clinical positron emission tomography (PET) in Europe at its current stage, as it is a multi-centre project financially supported by the European Commission (...
Conference Paper
Full-text available
Respiratory motion in emission tomography leads to reduced image quality. Proposed correction methodology has been concentrating on the use of respiratory synchronised acquisitions leading to gated frames. Such frames however are of low signal to noise ratio as a result of containing reduced statistics. Therefore a method accounting for respiratory...
Article
Full-text available
This paper describes a feasibility study on an Internet-based compliance system to provide personalized care for patients suffering from chronic diseases. Relevant medical trials from three different European countries provided preliminary evidence of the feasibility of the system and its efficacy in helping patients to manage their diseases at hom...
Article
Full-text available
A preliminary study is presented on the potential role of similarity mapping (SM) in the evaluation of oncological dynamic 18F-fluorodeoxyglucose positron emission tomography studies, mainly in lesion localisation and detectability. Similarity maps were calculated using previously described (correlation coefficient (COR) and normalised correlation...
Conference Paper
Full-text available
Dynamic positron emission tomography studies produce a large amount of image data, from which clinically useful parametric information can be extracted with the use of tracer kinetic methods. In order to facilitate the initial interpretation and visual analysis of these large image sequences, data reduction methods can be applied which at the same...
Conference Paper
Full-text available
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 simu...
Article
Performance evaluation of principal component analysis (PCA) of dynamic F-18-FDG-PET studies of patients with recurrent colorectal cancer. Principal component images (PCI) of 17 iteratively reconstructed data sets were visually and quantitatively evaluated. The F-18-FDG compartment model parameters were estimated using polynomial regression. All st...
Conference Paper
Full-text available
C-MONITOR proporciona servicios avanzados de telemedicina a los pacientes y a los profesionales sanitarios para en tiempo real a la información médica y a los datos almacenados en el registro electrónico del paciente favorece una gestión rentable de los recursos de servicios sanitarios. Los médicos trabajan de una manera eficiente en cualquier tiem...
Article
The development, implementation and validation of simple, flexible and efficient iterative image reconstruction (IIR) methods for their take-up in routine clinical positron emission tomography (PET) static or dynamic studies. The ordered subsets (OS) technique applied for the acceleration of the maximum likelihood expectation maximization (MLEM) II...
Article
The iterative image reconstruction (IIR) is a promising approach to achieve a betterimage quality in PET. However, limitations exist with respect to the required computation time and the influence of reconstruction parameters on quantitative PET data. We implemented different reconstruction algorithms in a PC based reconstruction program and evalua...
Article
Full-text available
eight tumors. CONCLUSION: Inhomogeneous drug distribution and drug dilution in the target area are likely to be the major limiting parameters for therapy response. Percutaneous ethanol injection is used for curative or palliative treatment of hepatocellular carcinomas. Percutaneous ethanol injection is considered a reliable alternative to surgical...
Conference Paper
Full-text available
A transportable telemedicine workstation has been designed, developed and evaluated for use in isolated areas such as islands, rural areas and crisis situation areas. The EU-TeleInViVo is a custom-made device integrating in one solid case: a portable PC with telecommunication capabilities and a light, portable 3D ultrasound station. The system deve...
Conference Paper
Full-text available
Presents the design of a small animal PET prototype based on block detectors in which EGO scintillators are coupled to position sensitive photomultiplier tubes (PSPMT). The scanner will consist of 4 such blocks, each made of 288 crystals. By varying the distance one can allow for different size of the field of view. The full set of projections will...
Article
The aim of the study was the evaluation of the detectability of treated liver metastases using one FDG-PET measurement. The study includes 42 patients (80 lesions) from different primary tumours. Standardized Uptake Values (SUV) as well as the tumour to liver Ratio (T/L) were used for evaluation. A T/L > 1.0 was considered to be pathological. Clini...
Article
To evaluate the carbon 11 ethanol kinetics with positron emission tomography after intratumoral injection of the tracer and assess its redistribution and dilution in patients who have hepatocellular carcinomas and who were scheduled for treatment with percutaneous ethanol injection. The study included eight patients with hepatocellular carcinomas....
Article
Full-text available
The EM (Expectation-Maximization) algorithm is becoming more and more popular as a solution to the image reconstruction problem in Positron Emission Tomography (PET). However, as an iterative method, it shows high computational cost in terms of the time required to complete the reconstruction procedure and the computer memory needed (main memory an...
Article
Full-text available
INTRODUCTION The goal in all medical imaging modalities is to get an image of the internal organs of the body, either structural and anatomical (Computerized Tomography, CT, or Magnetic Resonance Imaging, MRI) or functional (Positron Emission Tomography, PET, or Single Photon Emission Tomography, SPET), in a non-invasive way. The main principle of...
Article
Positron emission tomography in the last decade was shown to be an efficient imaging tool in decreasing the number of biopsies, detecting axillary metastases and eliminating uncessecary ALNDs, assessing the efficacy of hormono- and chemotherapy, detecting recurrencies of metastatic diseases and reducing the overall costs of the breast cancer patien...
Conference Paper
Full-text available
The main objective of this work is the development and evaluation of iterative image reconstruction (IIR) methods for multitracer dynamic positron emission tomography (mdPET) studies. The ordered subsets (OS) technique applied for the acceleration of the maximum likelihood expectation maximization (ML-EM) IIR algorithm, is here extended to include...
Article
Maximum likelihood estimation image reconstruction algorithms for emission tomography received much attention during the last decade because of their potential to produce high quality images. A detailed study of the convergence properties of the expectation–maximization (EM) algorithm for PETimage reconstruction is presented. The main problems asso...
Conference Paper
We have recently presented a new stopping criterion for the EM-MLE algorithm for PET, based on the properties of the multiplicative correction factors Δx applied to the image vector after each iteration. The criterion is based on the relationship between the image quality descriptors and the statistical properties of the updating coefficients and w...