P. Liaparinos

• University of West Attica

Medical imaging instrumentation is mostly based on the use of luminescent materials coupled to optical sensors. These materials are employed in the form of granular screens, structured crystals, single transparent crystals, ceramics, etc. Storage phosphors are also incorporated in particular X-ray imaging systems. The physical properties of these m...

The present manuscript introduces an investigation of the structural and functional changes in the optic nerve in patients undergoing glaucoma treatment by comparing optical coherence tomography (OCT) measurements and RETeval system parameters. For such a purpose, 140 eyes were examined at the Ophthalmology Clinic of the “Elpis” General Hospital of...

Background: Mammographic digital imaging is based on X-ray sensors with solid image quality characteristics. These primarily include (a) a response curve that yields high contrast and image latitude, (b) a frequency response given by the Modulation Transfer Function (MTF), which enables small detail imaging and (c) the Normalize Noise Power Spectru...

The structural properties of phosphor materials, such as their grain size distribution (GSD), affect their overall optical emission performance. In the widely used gadolinium oxysulfide (Gd2O2S) host material, the type of activator is one significant parameter that also changes the GSD of the powder phosphor. For this reason, in this study, differe...

This manuscript attempts to present a proof of concept from a physics perspective of a hybrid detective system based on the utilization of contrast agents with the purpose of indicating breast tissue abnormalities. In the present concept, the photon-counting module of the detector is set up to the K-characteristic radiation emitted by the contrast...

In digital phosphor-based imaging modalities, one important intermediate stage is the optical coupling between the phosphor material and the optical sensor. The performance of the optical compatibility is affected by surface-roughness issues, for which further research should be paid. This paper investigates the surface-roughness influence between...

In this paper, the LIGHTAWE Monte Carlo simulation tool is introduced and presented. LIGHTAWE has been developed to provide case studies of light spread in powder materials for both research and educational purposes. The algorithms of LIGHTAWE are based on Mie scattering theory and Henyey–Greenstein distribution. LIGHTAWE simulates the light ray in...

In this paper, the LIGHTAWE Monte Carlo simulation tool is introduced and presented. LIGHTAWE has been developed to provide case studies of light spread in powder materials for both research and educational purposes. The algorithms of LIGHTAWE are based on Mie scattering theory and Henyey–Greenstein distribution. LIGHTAWE simulates the light ray in...

In indirect medical imaging systems, the optical transfer properties of powder phosphor materials are affected by the intrinsic mechanisms of light extinction. Light extinction (absorption and scattering) can be described either through theoretical models or with Monte Carlo simulation techniques. The purpose of the present paper is to compare both...

The light emission performance of powder phosphors, employed in a variety of imaging applications, is affected by their structural (i.e., the particle size and packing) and optical properties (i.e., the wavelength of the light rays and the refractive index of the grains). In the chemical synthesis and the corresponding construction development of p...

The scope of the present work was to evaluate the role of the complex refractive index in optical diffusion studies for imaging purposes. In particular, phosphor materials and their corresponding optical transmission characteristics play significant role in x-ray detectors, cathode ray tubes, microscopy techniques, white LED applications and have a...

The present paper summarizes the examination of packing density effect within a phosphor layer by using Mie scattering theory and Monte Carlo simulation techniques. Light propagation in the phosphor layer was modeled by considering the following cases: (i) phosphors of different layer thickness, 100 μm (thin layer) and 200 μm (thick layer), respect...

Image quality for medical purposes is related to the useful diagnostic information that can be extracted from an image. The performance of indirect X-ray detectors, which in turn affects the quality of the medical image, can be significantly influenced by the characteristics of the phosphor, employed to convert incident radiation into emitted light...

X-ray phosphor-based detectors have enormously improved the quality of medical imaging examinations through the optimization of optical diffusion. In recent years, with the development of science and technology in the field of materials, improved powder phosphors require structural and optical properties that contribute to better optical signal pro...

Granular phosphors are commonly used in several applications in biomedical imaging and instrumentation. The structural and optical properties of phosphor materials affect the optical signal transferred out and play a critical role in the quality of the final signal or image. In recent years, following developments in materials science and technolog...

Phosphor materials are widely used in X-ray medical imaging detector applications, coupled with suitable photoreceptors. Upon the most demanding imaging modality is X-ray mammography, since the best defense against breast cancer is its early detection. A material suitable as a mammographic detector should efficiently absorb X-ray photons and transf...

Luminescent materials are used as X-ray detectors of medical imaging systems. Out of a large variety of materials, Terbium (Tb)-activated phosphors and needle-like columnar structured CsI:Tl phosphors are currently the most widely used ones. Parameters commonly used to assess the imaging performance of luminescent materials are: the Quantum Detecti...

Nanocrystallic europium-activated lutetium oxide (Lu2O3:Eu) is a strong candidate for use in digital medical imaging applications, due to its spectroscopic and structural properties. The aim of the present study was to investigate the imaging and efficiency properties of a 33.3 mg/cm2 Lu2O3:Eu scintillating screen coupled to a high resolution RadEy...

Single crystal scintilators are used in various radiation detectors applications. The efficiency of the crystal can be determined by the Detector Optical Gain (DOG) defined as the ratio of the emitted optical photon flux over the incident radiation photons flux. A parameter affecting DOG is the intrinsic conversion efficiency (nC) giving the percen...

The purpose of the present study was to experimentally evaluate the imaging characteristics of the Lu2O3:Eu nanophosphor thin screen coupled to a high resolution CMOS sensor under radiographic conditions. Parameters such as the Modulation Transfer Function (MTF), the Normalized Noise Power Spectrum (NNPS) and the Detective Quantum Efficiency (DQE)...

Luminescent materials are employed as radiation to light converters in detectors of medical imaging systems, often referred to as phosphor screens. Several processes affect the light transfer properties of phosphors. Amongst the most important is the interaction of light. Light attenuation (absorption and scattering) can be described either through...

The purpose of this study was to perform the influence of the strain (lattice and radius) effects on the optical parameters of nanocrystals for use in medical imaging instrumentation technology. The present manuscript involved (a) quantum dots (QD) based nanophosphors with particle size 3-5 nm in diameter, (b) dielectric constants (core) of nanopho...

Single crystal scintilators are used in various radiation detectors applications. The efficiency of the crystal can be determined by the Detector Optical Gain (DOG) defined as the ratio of the emitted optical photon flux over the incident radiation photons flux. A parameter affecting DOG is the intrinsic conversion efficiency (nC) giving the percen...

The aim of the present study was to investigate the luminescence efficiency (XLE) of gadolinium aluminum perovskite (GdAlO3:Ce) powder scintillator. This powder phosphor, also known as GAP:Ce scintillator, is a non-hygroscopic material, emitting blue light with short decay time. For the purposes of this study, five scintillating screens with coatin...

Digital detectors based on complementary metal-oxide-semiconductors (CMOS) active pixel sensor (APS) technology have been introduced recently in many scientific applications. This work is focused on the X-ray performance evaluation of a novel CMOS APS detector in low energy medical imaging applications using monochromatic synchrotron radiation (i.e...

Purpose Phosphor materials provide challenges to both fundamental research and breakthrough development of technologies in research areas. In recent years, with the development of science and technology in the field of materials, a number of physical or chemical synthesis methods have been developed and successfully used for the preparation of subm...

The quality of medical images can be characterized by the signal transfer properties of the x-ray converter. Various studies have previously investigated the influence of the detector configuration on the optimization of medical imaging systems. However, novel technologies related to new luminescent materials seem to be promising for further improv...

Powder phosphors scintillators are used in indirect digital radiography as x-ray to light converters coupled to electronic optical sensors (photodiodes, CCDs, CMOS). Recently, nanophosphors have been reported to have enhanced luminescence efficiency. The purpose of the present study was to evaluate Lu2O3:Eu nanophosphor as a candidate for digital m...

PurposeThe purpose of this study was to provide an analysis of imaging performance in digital mammography, using indirect detector instrumentation, by combining the Linear Cascaded Systems (LCS) theory and the Signal Detection Theory (SDT). Observer performance was assessed, by examining frequently employed detectors, consisting of phosphor-based X...

Recent technologies, such as nanotechnology, provide new opportunities for next generation scintillation devices and instruments. New nanophosphor-based materials seem to be promising for further improvements in optical diffusion studies. In medical imaging, detector technology has found widespread use, offering improved signal capabilities. Howeve...

Purpose In x‐ray mammography, some of the components that play significant role to early diagnosis are the x‐ray source, the breast composition as well as the composition of the x‐ray converter. Various studies have previously investigated separately the influence of breast characteristics and detector configuration on the optimization of mammograp...

The aim of the present study was to investigate the imaging transfer characteristics and the luminescence efficiency (XLE) of Gd₂O₂S:Eu powder scintillator for use in X-ray mammography detectors. Gd₂O₂S:Eu emits in the red part of the visible spectrum, having very good spectral compatibility with optical...

A theoretical model based on Linear Cascaded Systems (LCS) theory was developed in order to study the noise properties of a commercially available high resolution CMOS sensor (RadEye CMOS). The parameters studied were the Normalized Noise Power Spectrum (NNPS) and the Noise Transfer Function (NTF). The modeling was applied to digital mammography co...

Scintillator materials are widely used in X-ray imaging detector applications, coupled with photoreceptors like radiographic film, a-Si, charge coupled devises (CCD), complementary metal-oxide-semiconductor (CMOS) and GaAs). The light emission properties of the scintillator can be assessed by X-ray absolute efficiency which is defined as the ratio...

The performance of various x-ray converters, employed in medical imaging systems, has been widely examined by several methodologies (experimental, analytical, and Monte Carlo techniques). The x-ray converters most frequently employed in energy integrating digital radiology detectors are the Gd2O2S:Tb granular phosphor, the CsI:TI structured phospho...

Scintillator materials are widely used in X-ray medical imaging detector applications, coupled with available photoreceptors like radiographic film or photoreceptors suitable for digital imaging like a-Si, charge-coupled devises (CCD), complementary metal-oxide-semiconductors (CMOS) and GaAs). In addition, scintillators can be utilized in non-medic...

In the present study scintillating screens prepared from Y₃Al₅O₁₂:Ce (YAG:Ce) powder phosphor were evaluated for use in digital mammography. YAG:Ce has never previously been used in X-ray medical imaging, however since it emits green light (i.e peak at 550 nm), it is expected to match well the spectral sensitivities...

Purpose To evaluate Gd2O2S:Eu powder phosphor as a radiographic image receptor and to compare it to phosphors often used in radiography. Gd2O2S:Eu is nonhygroscopic, emitting red light with decay time close to that of Gd2O2S:Tb. Methods The light intensity emitted per unit of x‐ray exposure rate (absolute luminescence efficiency) was measured for...

The aim of the present work is to study the performance of scintillators currently used in PET and animal PET systems, under conditions met in radiation therapy and PET/CT imaging. The results of this study will be useful in applications where both CT and PET photons as well as megavoltage cone beam CT (MV CBCT) photons could be detected using a co...

Computer models and simulations of X-ray imaging systems are becoming a very precious tool during the development and evaluation of new X-ray imaging techniques. To provide, however, a faithful simulation of a system, all components must be accurately modelled and tested, followed by verification through experimental measurements. This paper presen...

In medical mammographic imaging systems, one type of detector configuration, often referred to as indirect detectors, is based on a scintillator layer (phosphor screen) that converts the x-ray radiation into optical signal. The indirect detector performance may be optimized either by improving the structural parameters of the screen or by employing...

The aim of this study was to estimate the influence of K-characteristic radiation on the performance of x-ray scintillating screens containing two heavy elements by Monte Carlo methods. K-characteristic radiation is produced within materials of at least one heavy (high atomic number) element. This radiation may result either in spatial resolution d...

The imaging performance of phosphor screens, used as x-ray detectors in diagnostic medical imaging systems, is affected by their both noise and resolution properties. Amplification and blurring processes are due to a sequence of conversion stages within the screen which contribute to fluctuations in the number and spatial distribution of the optica...

This paper investigates the light emission efficiency of Lu₂SiO₅:Ce (LSO) powder scintillator under conditions employed in projection X-ray imaging. Although single-crystal LSO has been thoroughly studied in medical imaging energies, the efficiency of powder LSO has not been previously investigated experimentally under X-ray m...

The aim of the present study was to examine the Gd2O2S:Eu powder scintillator under general X-ray Radiographic imaging conditions. For this purpose five scintillator screens with coating thicknesses 33.1, 46.4, 63.1, 78.3 and 139.8 mg/cm2 were prepared in our laboratory by sedimentation of Gd2O2S:Eu powder. Light emission efficiency and optical emi...

Phosphor materials are employed in intensifying screens of both digital and conventional X-ray imaging detectors. High packing density powder screens have been developed (e.g. screens in ceramic form) exhibiting high-resolution and light emission properties, and thus contributing to improved image transfer characteristics and higher radiation to li...

Lu2SiO5: Ce (LSO) scintillator is a relatively new luminescent material which has been successfully applied in positron emission tomography systems. Since it has been recently commercially available in powder form, it could be of value to investigate its performance for use in x-ray projection imaging as both physical and scintillating properties i...

The luminescence properties of Lu0.7Y0.3AlO3:Ce (LuYAP:Ce) and (Lu0.9,Y0.1)2SiO5:Ce (LYSO:Ce) crystals were studied for use in medical X-ray imaging. LuYAP:Ce and LYSO:Ce are single-crystal scintillators of high density, non-hygroscopic, high light yield and short decay time. The two cerium doped crystals have dimensions of 2×2×8 mm3 with all surfa...

The aim of the present study was to evaluate the imaging performance of Lu2SiO5:Ce (LSO:Ce) powder scintillator for use in X-ray detectors used in mammography. LSO:Ce scintillator is a high efficiency, fast emitting material, which in single-crystal form is used in positron emission tomography detectors. A scintillating screen, with a coating thick...

The aim of the present study was to examine the light emission efficiency of Lu2SiO5:Ce (LSO) powder scintillator under X-ray mammographic imaging conditions. Powder LSO scintillator has never been used in X-ray imaging. For the purposes of the present study, a 25 mg/cm2 thick scintillating screen was prepared in our laboratory, by sedimentation of...

The recently developed Geant4 Application for Tomographic Emission (GATE) toolkit is a Monte Carlo simulation platform developed for PET and SPECT simulations and is freely distributed by the OpenGATE collaboration. GATE provides the ability of modelling time-dependent phenomena, such as geometry element movements and source decay kinetics, allowin...

The intrinsic phosphor properties are of significant importance for the performance of phosphor screens used in medical imaging systems. In previous analytical-theoretical and Monte Carlo studies on granular phosphor materials, values of optical properties, and light interaction cross sections were found by fitting to experimental data. These value...

The aim of the present study was to examine the light emission efficiency of Lu2SiO5:Ce (LSO) powder scintillator under X-ray mammographic imaging conditions. LSO is an efficient and extremely fast scintillator, employed in positron tomography, which however has never been used in X-ray imaging. For the purposes of the present study a 25 mg/cm2 thi...

This work investigates the effect of the energy-weighting technique on the signal to noise ratio (SNR) response of X-ray imaging detectors. So far in the literature all scintillation-detector characteristics (detection efficiency, conversion efficiency, light-attenuation effects, etc) that degrade image quality have been ignored. A theoretical eval...

The purpose of this study was to investigate the radiation detection efficiency of the recently introduced RbGd2Br7:Ce (RGB) scintillator material by a custom developed Monte Carlo simulation code. Considering its fast principal decay constant (45 ns) and its high light yield (56 000 photons/MeV), RbGd2Br7:Ce appears to be a quite promising scintil...

The aim of this study was to evaluate the effect of K-characteristic radiation on the performance of scintillator crystals incorporated in nuclear medicine detectors (LSO, BGO, GSO). K-characteristic radiation is produced within materials of at least one high atomic number element (e.g. Lu, Gd, Bi). This radiation may either be reabsorbed or it may...

The aim of this study was to examine the angular distribution of the light emitted from radiation-excited scintillators in medical imaging detectors. This distribution diverges from Lambert's cosine law and affects the light emission efficiency of scintillators, hence it also affects the dose burden to the patient. In the present study, the angular...

The aim of this study was to examine the angular distribution of the light emitted from radiation excited scintillators in medical imaging detectors. This distribution diverges from Lambert’s cosine law and affects the light emission efficiency of scintillators. Hence it also affects the dose burden to the patient. In the present study the angular...

The aim of this study was to predict quantum detection efficiency (QDE) and modulation transfer function (MTF) of granular phosphor screens, used in detectors of medical imaging systems, using Monte Carlo methods. The transfer of energy through the screen was modeled as a series of energy converting stages, assuming that the screen was divided into...

Monte Carlo techniques were applied to evaluate the performance of YAP scintillator for use in medical imaging applications. The energy range considered was from 50 to 800 keV and the thickness range from 5 to 30 mm. The absorption efficiency of YAP decreases rapidly in the energy range from 50 up to 200 keV. For higher energies up to 800 keV, slow...

The aim of this study was to evaluate the performance of GdAlO3:Ce powder scintillator screens for use in medical imaging applications. This powder phosphor, also known as GAP:Ce scintillator, is a non-hygroscopic material, emitting blue light with short decay time and it has never been used in medical imaging. Various scintillator screens with coa...

The purpose of this study was to examine the effect of K x-ray radiation on the performance of scintillator crystals applied in nuclear medicine detectors. The K x-ray photons are intrinsically produced within the scintillating material, when a photoelectric effect takes place and may either be reabsorbed or may escape the scintillator. In both cas...