G. Opposits | University of Debrecen (original) (raw)
Papers by G. Opposits
Defect and Diffusion Forum, 2001
Defect and Diffusion Forum, 2003
ABSTRACT There are strong experimental evidences that considerable stress develops in mutual diff... more ABSTRACT There are strong experimental evidences that considerable stress develops in mutual diffusion. The non-local character of the stress equilibrium also leads to strong dependence on the sample geometry. Stress effects are expected to be stronger in cylindrical and spherical samples having closed geometry than in the usually studied planar geometry. We will give an overview of the interrelation of stress and diffusion, and introduce equations of the theoretical model describing material transport, stress development and convective matter transport. These differential equations can be integrated only numerically. Simulation results and experimental findings will be presented for planar and cylindrically bent diffusion couples.
2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 2012
ABSTRACT The aims of this study were (I) to describe statistically the fluctuation of the goodnes... more ABSTRACT The aims of this study were (I) to describe statistically the fluctuation of the goodness of automated CT-MRI registration method (2) to evaluate a numerical parameter, scaled to [0,1] interval (lambda), for characterizing the population level accuracy of any automated CT-MRI registration algorithm on voxel similarity basis. The population level distribution of crosscorrelation values between the reference T1-weighted images and the automatically registered images were investigated in five patient groups (brain metastatis, cavernoma, cranial nerve schwannoma, meningioma, trigeminal neuralgia). The evaluated distributions appeared as the mixture of two Gaussians and a peak at the 1.0 value. The evaluated distributions appeared as the mixture of two Gaussians and a peak at the 1.0 value, therefore we classified the result of automated registration into three accuracy types (AT), AT1: cross-correlation equals to 1.0, AT2: when the automatically registered image slightly differs from the reference one, cross-correlation ≈1.0, and AT3: when the crosscorrelation is about 0.4. Pauto was introduced as the ratio of well fitted automated registration relative to number of all the registrations, Cupper and Clower are the mean of AT2 and A T3 distributions. The A=Pauto *Cupper/Clower product was used as the measure of the goodness of automated image registration procedure at population level. The evaluated lambda parameter will be used to control the impacts of software modifications and to optimize the functional parameters of the evaluated preprocessing steps.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
In vivo imaging of small laboratory animals is a valuable tool in the development of new drugs. F... more In vivo imaging of small laboratory animals is a valuable tool in the development of new drugs. For this purpose, miniPET, an easy to scale modular small animal PET camera has been developed at our institutes. The system has four modules, which makes it possible to rotate the whole detector system around the axis of the field of view. Data collection and image reconstruction are performed using a data acquisition (DAQ) module with Ethernet communication facility and a computer cluster of commercial PCs. Performance tests were carried out to determine system parameters, such as energy resolution, sensitivity and noise equivalent count rate. A modified GEANT4based GATE Monte Carlo software package was used to simulate PET data analogous to those of the performance measurements. GATE was run on a Linux cluster of 10 processors (64 bit, Xeon with 3.0 GHz) and controlled by a SUN grid engine. The application of this special computer cluster reduced the time necessary for the simulations by an order of magnitude. The simulated energy spectra, maximum rate of true coincidences and sensitivity of the camera were in good agreement with the measured parameters. r
IEEE Transactions on Electron Devices, 2003
We have made recombination and generation lifetime measurements on silicon p-epitaxial layers on ... more We have made recombination and generation lifetime measurements on silicon p-epitaxial layers on p + and on p-substrates. The recombination lifetimes are dominated by surface/interface recombination for layers only a few microns thick. By coupling measurements of p/p with those of p/p + samples, it is possible to extract the epi-layer lifetime. For p/p + samples, recombination lifetimes are poorly suited to characterize epi-layers. Generation lifetime measurements are eminently suitable for epi-layer characterization, since carrier generation occurs in the space-charge region confined to the epitaxial layer, and when coupled with corona charge/Kelvin probe, allow contact-less measurements.
European Journal of Nuclear Medicine and Molecular Imaging, 2011
Epilepsy Research, 2013
The neuronal mechanisms of enduring seizure propensity and seizure precipitation in juvenile myoc... more The neuronal mechanisms of enduring seizure propensity and seizure precipitation in juvenile myoclonic epilepsy (JME) are not known. We investigated these issues, within the framework of the "network concept" of epilepsy. Design1: 19, unmedicated JME patients were compared with nineteen, age-, and sex-matched normal control persons (NC). A total of 120s, artifact-free, paroxysm-free, eyes-closed, resting state EEG background activity was analyzed for each person. Design2: interictal and immediate preictal periods of the JME patients were compared in order to explore interictal-preictal network differences. For both comparison designs, statistically significant differences of EEG functional connectivity (EEGfC), nodal and global graph parameters were evaluated. Design1: maximum abnormalities were: increased delta, theta, alpha1 EEGfC and decreased alpha2 and beta EEGfC in the JME group as compared to the NC group, mainly among cortical areas that are involved in sensory-motor integration. Nodal degree and efficiency of three, medial, basal frontal nodes were greater in JME than in NC, in the alpha1 band. Design2: preictal delta EEGfC showed further increase in the above-mentioned areas, as compared to the interictal state. Increased EEGfC indicates a hypercoupled state among the specified cortical areas. This interictal abnormality further increases in the preictal state. Nodal graph statistics indicates abnormal neuronal dynamics in the cortical area that is the ictal onset zone in JME. Interictal and preictal neuronal dysfunction has been described in terms of network dynamics and topography in JME patients. Forthcoming investigations of seizure precipitation and therapeutic drug effects are encouraged on this basis.
Epilepsy Research, 2012
Introduction: Benign rolandic epilepsy of childhood (BERS) is an epilepsy syndrome with presumabl... more Introduction: Benign rolandic epilepsy of childhood (BERS) is an epilepsy syndrome with presumably genetic-developmental etiology. The pathological basis of this syndrome is completely unknown. We postulated that a developmental abnormality presumably results in abnormal EEG background activity findings. Patients and methods: 20 children with typical BERS and an age-and sex-matched group of healthy control children underwent EEG recording and analysis. 60 × 2 s epochs of waking EEG background activity (without epileptiform potentials and artifacts) were analyzed in the 1-25 Hz frequency range, in very narrow bands (VNB, 1 Hz bandwidth). LORETA (Low Resolution Electromagnetic Tomography) localized multiple distributed sources of EEG background activity in the Talairach space. LORETA activity (current source density) was computed for 2394 voxels and 25 VNBs. Normalized LORETA data were processed to voxel-wise comparison between the BERS and control groups. Bonferroni-corrected p < 0.05 Student's t-values were accepted as statistically significant. Results: Increased LORETA activity was found in the BERS group (as compared to the controls) in the left and right temporal lobes (fusiform gyri, posterior parts of the superior, middle and inferior temporal gyri) and in the angular gyri in the parietal lobes, in the 4-6 Hz VNBs, mainly at 5 Hz. No. of Pages 6 2 M. Besenyei et al.
Defect and Diffusion Forum, 2003
ABSTRACT The stress distribution and marker movements are simulated for concentration dependent i... more ABSTRACT The stress distribution and marker movements are simulated for concentration dependent intrinsic diffusion coefficients for the case of stable and unstable Kirkendall marker planes., It is usually assumed is that the marker is fixed to a single atomic plane and indicates the movement of this plane. First we consider this idealized situation than the effect of the marker size is studied. At the beginning of the diffusion process the size of the markers are larger than the size of the diffusion zone. Stress gradients around the marker particles are identified as another source of marker shift. The effect of this additional marker movement on the selection and stability of the Kirkendall marker plane will be discussed.
2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), 2009
A full ring small animal PET camera (MiniPET-II) has been built in our institute as part of an R+... more A full ring small animal PET camera (MiniPET-II) has been built in our institute as part of an R+D project. In this work we determined the performance parameters of the MiniPET-II scanner. The measurements and data evaluation for this purpose were based on the National Electrical Manufacturers Association (NEMA) NU-4 standards. The spatial resolution varies between 1.4 to 2.1 mm from central to 25 mm radial distances. The system sensitivity was 1.14%. The counting rate capability, expressed in noise equivalent counting rate (NEC), was shown to peak of over 55.1 kcps at 38.9 MBq using a mouse phantom. The scatter fraction with the same acquisition was 12.3%. Evaluations of image quality and quantization accuracy were also performed using the NEMA NU-4 required image-quality phantom and animal studies. The study proved that the MiniPET-II scanner has a good imaging capability and ability to perform real animal studies.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2013
ABSTRACT Abstract This paper presents results of the performance of a small animal PET system (Mi... more ABSTRACT Abstract This paper presents results of the performance of a small animal PET system (MiniPET-II) installed at our Institute. MiniPET-II is a full ring camera that includes 12 detector modules in a single ring comprised of 1.27×1.27×12 mm3 LYSO scintillator crystals. The axial field of view and the inner ring diameter are 48 mm and 211 mm, respectively. The goal of this study was to determine the NEMA-NU4 performance parameters of the scanner. In addition, we also investigated how the calculated parameters depend on the coincidence time window (τ=2, 3 and 4 ns) and the low threshold settings of the energy window (Elt=250, 350 and 450 keV). Independent measurements supported optimization of the effective system radius and the coincidence time window of the system. We found that the optimal coincidence time window and low threshold energy window are 3 ns and 350 keV, respectively. The spatial resolution was close to 1.2 mm in the center of the FOV with an increase of 17% at the radial edge. The maximum value of the absolute sensitivity was 1.37% for a point source. Count rate tests resulted in peak values for the noise equivalent count rate (NEC) curve and scatter fraction of 14.2 kcps (at 36 MBq) and 27.7%, respectively, using the rat phantom. Numerical values of the same parameters obtained for the mouse phantom were 55.1 kcps (at 38.8 MBq) and 12.3%, respectively. The recovery coefficients of the image quality phantom ranged from 0.1 to 0.87. Altering the τ and Elt resulted in substantial changes in the NEC peak and the sensitivity while the effect on the image quality was negligible. The spatial resolution proved to be, as expected, independent of the τ and Elt. The calculated optimal effective system radius (resulting in the best image quality) was 109 mm. Although the NEC peak parameters do not compare favorably with those of other small animal scanners, it can be concluded that under normal counting situations the MiniPET-II imaging capability assures remarkably good image quality, sensitivity and spatial resolution. Keywords Small-animal PET scanner; Image quality; Coincidence time window; NEMA; Preclinical imaging
2011 IEEE Nuclear Science Symposium Conference Record, 2011
The examination of small animals using high resolution in-vivo imaging methods is a crucial tool ... more The examination of small animals using high resolution in-vivo imaging methods is a crucial tool in pharmaceutical research projects. These type of studies frequently require the measurement of very low activity lesions in a background region or high activity body parts for instance in case of dynamic investigations. To suffice these demands, two independent qualities of the PET scanner need to be appropriate, the low count detectability and the count rate performance. In our study we investigated the detectability of the low level activity area using our LYSO based small animal PET camera.
PLoS ONE, 2014
Functional Magnetic Resonance Imaging (fMRI) based brain connectivity analysis maps the functiona... more Functional Magnetic Resonance Imaging (fMRI) based brain connectivity analysis maps the functional networks of the brain by estimating the degree of synchronous neuronal activity between brain regions. Recent studies have demonstrated that ''resting-state'' fMRI-based brain connectivity conclusions may be erroneous when motion artifacts have a differential effect on fMRI BOLD signals for between group comparisons. A potential explanation could be that in-scanner displacement, due to rotational components, is not spatially constant in the whole brain. However, this localized nature of motion artifacts is poorly understood and is rarely considered in brain connectivity studies. In this study, we initially demonstrate the local correspondence between head displacement and the changes in the resting-state fMRI BOLD signal. Than, we investigate how connectivity strength is affected by the population-level variation in the spatial pattern of regional displacement. We introduce Regional Displacement Interaction (RDI), a new covariate parameter set for second-level connectivity analysis and demonstrate its effectiveness in reducing motion related confounds in comparisons of groups with different voxel-vise displacement pattern and preprocessed using various nuisance regression methods. The effect of using RDI as second-level covariate is than demonstrated in autism-related group comparisons. The relationship between the proposed method and some of the prevailing subject-level nuisance regression techniques is evaluated. Our results show that, depending on experimental design, treating in-scanner head motion as a global confound may not be appropriate. The degree of displacement is highly variable among various brain regions, both within and between subjects. These regional differences bias correlation-based measures of brain connectivity. The inclusion of the proposed second-level covariate into the analysis successfully reduces artifactual motion-related group differences and preserves real neuronal differences, as demonstrated by the autism-related comparisons.
British Poultry Science, 2013
1. Computed tomography was used for the in vivo determination of yolk ratio in 7000 domestic hen ... more 1. Computed tomography was used for the in vivo determination of yolk ratio in 7000 domestic hen eggs, originated from two markedly different genotypes, in order to examine the effect of egg yolk ratio, gender and genotype on the development of hatched chicks. 2. Eggs with extremely low, average and extremely high yolk ratio were chosen for further investigation (n = 350 in each group in both genotypes). After incubating the selected eggs, hatched birds were reared and slaughtered at 11 weeks of age. 3. The yolk ratio of eggs significantly affected the body composition of the chickens at hatching and during rearing to 8-9 weeks of age. 4. Chickens of a genotype selected partly for weight gain had significantly higher live weight from hatching to the end of the rearing period and had better slaughter characteristics than those of the dual purpose TETRA-H genotype. 5. At hatching, only the dry matter content of the body was affected by the gender of the birds. The effect of gender on the live weight and body composition of chickens was evident from the 5th week of age to the time of slaughter. 6. It was concluded that eggs with a low yolk ratio were most beneficial for broiler production, because chickens hatched from these eggs had the highest slaughter weight and muscle index and the lowest fat index for their body mass.
Defect and Diffusion Forum, 2001
Defect and Diffusion Forum, 2003
ABSTRACT There are strong experimental evidences that considerable stress develops in mutual diff... more ABSTRACT There are strong experimental evidences that considerable stress develops in mutual diffusion. The non-local character of the stress equilibrium also leads to strong dependence on the sample geometry. Stress effects are expected to be stronger in cylindrical and spherical samples having closed geometry than in the usually studied planar geometry. We will give an overview of the interrelation of stress and diffusion, and introduce equations of the theoretical model describing material transport, stress development and convective matter transport. These differential equations can be integrated only numerically. Simulation results and experimental findings will be presented for planar and cylindrically bent diffusion couples.
2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS/MIC), 2012
ABSTRACT The aims of this study were (I) to describe statistically the fluctuation of the goodnes... more ABSTRACT The aims of this study were (I) to describe statistically the fluctuation of the goodness of automated CT-MRI registration method (2) to evaluate a numerical parameter, scaled to [0,1] interval (lambda), for characterizing the population level accuracy of any automated CT-MRI registration algorithm on voxel similarity basis. The population level distribution of crosscorrelation values between the reference T1-weighted images and the automatically registered images were investigated in five patient groups (brain metastatis, cavernoma, cranial nerve schwannoma, meningioma, trigeminal neuralgia). The evaluated distributions appeared as the mixture of two Gaussians and a peak at the 1.0 value. The evaluated distributions appeared as the mixture of two Gaussians and a peak at the 1.0 value, therefore we classified the result of automated registration into three accuracy types (AT), AT1: cross-correlation equals to 1.0, AT2: when the automatically registered image slightly differs from the reference one, cross-correlation ≈1.0, and AT3: when the crosscorrelation is about 0.4. Pauto was introduced as the ratio of well fitted automated registration relative to number of all the registrations, Cupper and Clower are the mean of AT2 and A T3 distributions. The A=Pauto *Cupper/Clower product was used as the measure of the goodness of automated image registration procedure at population level. The evaluated lambda parameter will be used to control the impacts of software modifications and to optimize the functional parameters of the evaluated preprocessing steps.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2007
In vivo imaging of small laboratory animals is a valuable tool in the development of new drugs. F... more In vivo imaging of small laboratory animals is a valuable tool in the development of new drugs. For this purpose, miniPET, an easy to scale modular small animal PET camera has been developed at our institutes. The system has four modules, which makes it possible to rotate the whole detector system around the axis of the field of view. Data collection and image reconstruction are performed using a data acquisition (DAQ) module with Ethernet communication facility and a computer cluster of commercial PCs. Performance tests were carried out to determine system parameters, such as energy resolution, sensitivity and noise equivalent count rate. A modified GEANT4based GATE Monte Carlo software package was used to simulate PET data analogous to those of the performance measurements. GATE was run on a Linux cluster of 10 processors (64 bit, Xeon with 3.0 GHz) and controlled by a SUN grid engine. The application of this special computer cluster reduced the time necessary for the simulations by an order of magnitude. The simulated energy spectra, maximum rate of true coincidences and sensitivity of the camera were in good agreement with the measured parameters. r
IEEE Transactions on Electron Devices, 2003
We have made recombination and generation lifetime measurements on silicon p-epitaxial layers on ... more We have made recombination and generation lifetime measurements on silicon p-epitaxial layers on p + and on p-substrates. The recombination lifetimes are dominated by surface/interface recombination for layers only a few microns thick. By coupling measurements of p/p with those of p/p + samples, it is possible to extract the epi-layer lifetime. For p/p + samples, recombination lifetimes are poorly suited to characterize epi-layers. Generation lifetime measurements are eminently suitable for epi-layer characterization, since carrier generation occurs in the space-charge region confined to the epitaxial layer, and when coupled with corona charge/Kelvin probe, allow contact-less measurements.
European Journal of Nuclear Medicine and Molecular Imaging, 2011
Epilepsy Research, 2013
The neuronal mechanisms of enduring seizure propensity and seizure precipitation in juvenile myoc... more The neuronal mechanisms of enduring seizure propensity and seizure precipitation in juvenile myoclonic epilepsy (JME) are not known. We investigated these issues, within the framework of the "network concept" of epilepsy. Design1: 19, unmedicated JME patients were compared with nineteen, age-, and sex-matched normal control persons (NC). A total of 120s, artifact-free, paroxysm-free, eyes-closed, resting state EEG background activity was analyzed for each person. Design2: interictal and immediate preictal periods of the JME patients were compared in order to explore interictal-preictal network differences. For both comparison designs, statistically significant differences of EEG functional connectivity (EEGfC), nodal and global graph parameters were evaluated. Design1: maximum abnormalities were: increased delta, theta, alpha1 EEGfC and decreased alpha2 and beta EEGfC in the JME group as compared to the NC group, mainly among cortical areas that are involved in sensory-motor integration. Nodal degree and efficiency of three, medial, basal frontal nodes were greater in JME than in NC, in the alpha1 band. Design2: preictal delta EEGfC showed further increase in the above-mentioned areas, as compared to the interictal state. Increased EEGfC indicates a hypercoupled state among the specified cortical areas. This interictal abnormality further increases in the preictal state. Nodal graph statistics indicates abnormal neuronal dynamics in the cortical area that is the ictal onset zone in JME. Interictal and preictal neuronal dysfunction has been described in terms of network dynamics and topography in JME patients. Forthcoming investigations of seizure precipitation and therapeutic drug effects are encouraged on this basis.
Epilepsy Research, 2012
Introduction: Benign rolandic epilepsy of childhood (BERS) is an epilepsy syndrome with presumabl... more Introduction: Benign rolandic epilepsy of childhood (BERS) is an epilepsy syndrome with presumably genetic-developmental etiology. The pathological basis of this syndrome is completely unknown. We postulated that a developmental abnormality presumably results in abnormal EEG background activity findings. Patients and methods: 20 children with typical BERS and an age-and sex-matched group of healthy control children underwent EEG recording and analysis. 60 × 2 s epochs of waking EEG background activity (without epileptiform potentials and artifacts) were analyzed in the 1-25 Hz frequency range, in very narrow bands (VNB, 1 Hz bandwidth). LORETA (Low Resolution Electromagnetic Tomography) localized multiple distributed sources of EEG background activity in the Talairach space. LORETA activity (current source density) was computed for 2394 voxels and 25 VNBs. Normalized LORETA data were processed to voxel-wise comparison between the BERS and control groups. Bonferroni-corrected p < 0.05 Student's t-values were accepted as statistically significant. Results: Increased LORETA activity was found in the BERS group (as compared to the controls) in the left and right temporal lobes (fusiform gyri, posterior parts of the superior, middle and inferior temporal gyri) and in the angular gyri in the parietal lobes, in the 4-6 Hz VNBs, mainly at 5 Hz. No. of Pages 6 2 M. Besenyei et al.
Defect and Diffusion Forum, 2003
ABSTRACT The stress distribution and marker movements are simulated for concentration dependent i... more ABSTRACT The stress distribution and marker movements are simulated for concentration dependent intrinsic diffusion coefficients for the case of stable and unstable Kirkendall marker planes., It is usually assumed is that the marker is fixed to a single atomic plane and indicates the movement of this plane. First we consider this idealized situation than the effect of the marker size is studied. At the beginning of the diffusion process the size of the markers are larger than the size of the diffusion zone. Stress gradients around the marker particles are identified as another source of marker shift. The effect of this additional marker movement on the selection and stability of the Kirkendall marker plane will be discussed.
2009 IEEE Nuclear Science Symposium Conference Record (NSS/MIC), 2009
A full ring small animal PET camera (MiniPET-II) has been built in our institute as part of an R+... more A full ring small animal PET camera (MiniPET-II) has been built in our institute as part of an R+D project. In this work we determined the performance parameters of the MiniPET-II scanner. The measurements and data evaluation for this purpose were based on the National Electrical Manufacturers Association (NEMA) NU-4 standards. The spatial resolution varies between 1.4 to 2.1 mm from central to 25 mm radial distances. The system sensitivity was 1.14%. The counting rate capability, expressed in noise equivalent counting rate (NEC), was shown to peak of over 55.1 kcps at 38.9 MBq using a mouse phantom. The scatter fraction with the same acquisition was 12.3%. Evaluations of image quality and quantization accuracy were also performed using the NEMA NU-4 required image-quality phantom and animal studies. The study proved that the MiniPET-II scanner has a good imaging capability and ability to perform real animal studies.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2013
ABSTRACT Abstract This paper presents results of the performance of a small animal PET system (Mi... more ABSTRACT Abstract This paper presents results of the performance of a small animal PET system (MiniPET-II) installed at our Institute. MiniPET-II is a full ring camera that includes 12 detector modules in a single ring comprised of 1.27×1.27×12 mm3 LYSO scintillator crystals. The axial field of view and the inner ring diameter are 48 mm and 211 mm, respectively. The goal of this study was to determine the NEMA-NU4 performance parameters of the scanner. In addition, we also investigated how the calculated parameters depend on the coincidence time window (τ=2, 3 and 4 ns) and the low threshold settings of the energy window (Elt=250, 350 and 450 keV). Independent measurements supported optimization of the effective system radius and the coincidence time window of the system. We found that the optimal coincidence time window and low threshold energy window are 3 ns and 350 keV, respectively. The spatial resolution was close to 1.2 mm in the center of the FOV with an increase of 17% at the radial edge. The maximum value of the absolute sensitivity was 1.37% for a point source. Count rate tests resulted in peak values for the noise equivalent count rate (NEC) curve and scatter fraction of 14.2 kcps (at 36 MBq) and 27.7%, respectively, using the rat phantom. Numerical values of the same parameters obtained for the mouse phantom were 55.1 kcps (at 38.8 MBq) and 12.3%, respectively. The recovery coefficients of the image quality phantom ranged from 0.1 to 0.87. Altering the τ and Elt resulted in substantial changes in the NEC peak and the sensitivity while the effect on the image quality was negligible. The spatial resolution proved to be, as expected, independent of the τ and Elt. The calculated optimal effective system radius (resulting in the best image quality) was 109 mm. Although the NEC peak parameters do not compare favorably with those of other small animal scanners, it can be concluded that under normal counting situations the MiniPET-II imaging capability assures remarkably good image quality, sensitivity and spatial resolution. Keywords Small-animal PET scanner; Image quality; Coincidence time window; NEMA; Preclinical imaging
2011 IEEE Nuclear Science Symposium Conference Record, 2011
The examination of small animals using high resolution in-vivo imaging methods is a crucial tool ... more The examination of small animals using high resolution in-vivo imaging methods is a crucial tool in pharmaceutical research projects. These type of studies frequently require the measurement of very low activity lesions in a background region or high activity body parts for instance in case of dynamic investigations. To suffice these demands, two independent qualities of the PET scanner need to be appropriate, the low count detectability and the count rate performance. In our study we investigated the detectability of the low level activity area using our LYSO based small animal PET camera.
PLoS ONE, 2014
Functional Magnetic Resonance Imaging (fMRI) based brain connectivity analysis maps the functiona... more Functional Magnetic Resonance Imaging (fMRI) based brain connectivity analysis maps the functional networks of the brain by estimating the degree of synchronous neuronal activity between brain regions. Recent studies have demonstrated that ''resting-state'' fMRI-based brain connectivity conclusions may be erroneous when motion artifacts have a differential effect on fMRI BOLD signals for between group comparisons. A potential explanation could be that in-scanner displacement, due to rotational components, is not spatially constant in the whole brain. However, this localized nature of motion artifacts is poorly understood and is rarely considered in brain connectivity studies. In this study, we initially demonstrate the local correspondence between head displacement and the changes in the resting-state fMRI BOLD signal. Than, we investigate how connectivity strength is affected by the population-level variation in the spatial pattern of regional displacement. We introduce Regional Displacement Interaction (RDI), a new covariate parameter set for second-level connectivity analysis and demonstrate its effectiveness in reducing motion related confounds in comparisons of groups with different voxel-vise displacement pattern and preprocessed using various nuisance regression methods. The effect of using RDI as second-level covariate is than demonstrated in autism-related group comparisons. The relationship between the proposed method and some of the prevailing subject-level nuisance regression techniques is evaluated. Our results show that, depending on experimental design, treating in-scanner head motion as a global confound may not be appropriate. The degree of displacement is highly variable among various brain regions, both within and between subjects. These regional differences bias correlation-based measures of brain connectivity. The inclusion of the proposed second-level covariate into the analysis successfully reduces artifactual motion-related group differences and preserves real neuronal differences, as demonstrated by the autism-related comparisons.
British Poultry Science, 2013
1. Computed tomography was used for the in vivo determination of yolk ratio in 7000 domestic hen ... more 1. Computed tomography was used for the in vivo determination of yolk ratio in 7000 domestic hen eggs, originated from two markedly different genotypes, in order to examine the effect of egg yolk ratio, gender and genotype on the development of hatched chicks. 2. Eggs with extremely low, average and extremely high yolk ratio were chosen for further investigation (n = 350 in each group in both genotypes). After incubating the selected eggs, hatched birds were reared and slaughtered at 11 weeks of age. 3. The yolk ratio of eggs significantly affected the body composition of the chickens at hatching and during rearing to 8-9 weeks of age. 4. Chickens of a genotype selected partly for weight gain had significantly higher live weight from hatching to the end of the rearing period and had better slaughter characteristics than those of the dual purpose TETRA-H genotype. 5. At hatching, only the dry matter content of the body was affected by the gender of the birds. The effect of gender on the live weight and body composition of chickens was evident from the 5th week of age to the time of slaughter. 6. It was concluded that eggs with a low yolk ratio were most beneficial for broiler production, because chickens hatched from these eggs had the highest slaughter weight and muscle index and the lowest fat index for their body mass.