Lutetium Oxyorthosilicate Research Articles

Modelization of extended axial field-of-view PET scanners to analyze the performance improvement

Positron Emission Tomography (PET) offers non-invasive insights into physiological processes. However, in clinical practice conventional PET scanners face limitations in comprehensive imaging due to their restricted axial field of view (FOV).This study explores the benefits and challenges of extending PET scanner AFOV using Monte Carlo simulation with GATE 9.1. The Biograph Vision Quadra scanner is a novel system based on the Digital Biograph Vision 600 scanner. Both devices use silicon photomultipliers and 3.2 x 3.2 × 20 mm Lutetium Oxyorthosilicate crystals (LSO). However, the 32 detector rings of the Quadra scanner enable a four-fold expansion in the Axial Field Of View (FOV) compared to Vision. As a result, higher sensitivity, and an enhancement of noise equivalent count rate and image quality are achieved. The purpose of this study is to analyze the effect of increasing the number of detector rings and the axial FOV on the scanner performance. To accomplish this, four different geometries are modeled using GATE (GEANT4 Application for Tomographic Emission). Based on the Biograph Vision 600 model, the length and the number of detector rings are gradually extended to reach the length of the Quadra scanner. Thus, four geometries with 8 (25.6 cm), 16 (51.2 cm), 24 (76.8 cm) and 32 (102.4 cm) detector rings are simulated, keeping the crystal configuration and the dimensions in the transaxial plane. The study evaluates sensitivity, Noise Equivalent Count Rate (NECR), and image quality parameters. Results indicate a significant increase in sensitivity and NECR with FOV extension, underscoring enhanced performance. However, artifact occurrence, particularly concentric circular patterns and background homogeneity changes, accentuates with extended AFOV. Normalization algorithms, particularly component-based normalization, mitigate these artifacts. This study contributes to the understanding of the advantages and limitations of extending PET scanner AFOV, offering insights into the effectiveness of component-based normalization for improving PET image quality.

Evaluation of new scintillation crystals with MCDM methods for brain PET

Brain Positron Emission Tomography (PET) imaging has been increasingly important in recent decades for improved detection and staging of brain cancer and other brain illnesses. Many elements, including the choice of radiation detecting medium, contribute to the overall image quality used to characterize a PET system's performance. In our previous study, novel transparent optical scintillator crystals for brain PET system were simulated. Therefore, there is a need to evaluate these materials using advanced computational techniques. Hence, in this study, we evaluated and compared them using two Multi-Criteria Decision-Making (MCDM) techniques, namely Preference Ranking Organization Method for Enrichment Evaluations (PROMETHEE) and Visekriterijumska Optimizacija I Kompromisno Resenje (VIKOR). The crystals used in this study were strontium hafnate (SHO), gadolinium aluminum gallium garget (GAGG), gadolinium yttrium gallium aluminum garget (GYGAG), gadolinium lutetium gallium aluminum garget (GLuGAG), and lastly lutetium oxyorthosilicate (LSO) for comparison. Density, effective atomic number, energy resolution, light output, and decay time were selected as important criteria. Importance weights of each criteria were then assigned by considering the high resolution and high sensitivity detectors. With both MCDM methods, the results showed that SHO outranked the other scintillator materials followed by LSO and GLuGAG. GYGAG, and GAGG is revealed as the least favorable crystals, in agreement with the previous simulation studies. This study can be extended by including more scintillators as they become available in the future.

A strategy for low thermal conductivity of lutetium oxyorthosilicate ceramics fabricated via texture engineering

AbstractSubmicrometer lutetium‐gadolinium oxyorthosilicate ((Lu0.95Gd0.05)2SiO5, LGSO) powder with a magnetic susceptibility of 4.19 10−6 (5.4 times that of lutetium oxyorthosilicate) was synthesized via a sol‐gel method. Slip casting with a 6 T assisted magnetic field and pressureless sintering at 1600°C for 16 h in the air effectively produced the textured LGSO ceramics with an orientation factor f of 0.96. The grains of textured LGSO ceramics grow with the preferred orientation along the b‐axis. The thermal conductivity of the textured LGSO ceramics reaches only 2.05 W·m−1·K−1 at 300 K, which is 34.5% lower than that of untextured LGSO ceramics. Textured LGSO ceramics provide increased fracture toughness. This work presents a microstructural design method for RE2SiO5 ceramics to regulate thermal and mechanical properties through texture engineering, as well as advice for the selection or optimization of RE2SiO5 ceramics as a Thermal Barrier Coatings (TBCs) material.

Terahertz permittivity parameters of monoclinic single crystal lutetium oxyorthosilicate

The anisotropic permittivity parameters of monoclinic single crystal lutetium oxyorthosilicate, Lu2SiO5 (LSO), have been determined in the terahertz spectral range. Using terahertz generalized spectroscopic ellipsometry (THz-GSE), we obtained the THz permittivities along the a, b, and c⋆ crystal directions, which correspond to the εa, εb, and εc⋆ on-diagonal tensor elements. The associated off diagonal tensor element εac⋆ was also determined experimentally, which is required to describe LSO's optical response in the monoclinic a–c crystallographic plane. From the four tensor elements obtained in the model fit, we calculate the direction of the principal dielectric axes in the a–c plane. We find good agreement when comparing THz-GSE permittivities to the static permittivity tensors from previous infrared and density functional theory studies.

A-Si EPID Modeling in GATE for Monte Carlo Investigation on the Optical Properties of Gd<sub>2</sub>O<sub>2</sub>S:Tb and Lu<sub>2</sub>SiO<sub>5</sub>:Ce Scintillators

A detailed a-Si Electronic Portal Imaging Device (EPID) was implemented in GATE (Geant4 application for tomographic emission) toolkit for Monte Carlo simulations, employing the standard electromagnetic processes and optical photon processes. The composition of the scintillating material is varied using the conventional terbium-doped gadolinium oxysulfide phosphor (Gd2O2S:Tb) and cerium-doped lutetium oxyorthosilicate (Lu2SiO5:Ce) which is widely used in Positron Emission Tomography (PET) detectors due to its supremacy in aiding the detection of low-energy photons. It was found that the number of optical photons produced is higher when using the Lu2SiO5:Ce scintillator resulting in a slightly better signal-to-noise ratio (SNR). The scattering within the EPID components was also investigated where the majority of the detected secondary particles were created in the scintillator. The results also show that the copper plate layer of the EPID contributes to additional Compton electrons and bremsstrahlung and annihilation photons to the measurements in the scintillator and photodiode layer. The glass substrate, graphite plates, electronic components, and aluminum bottom cover are also found to contribute a huge fraction of backscattered particles to the measurements at the photodiode layer.

Background energy spectra of lutetium-based inorganic scintillators for radiation detection

In this work the predictions of the background spectra of ten scintillating crystals with lutetium for 1 cm3 cubes are presented. These spectra were obtained by performing Monte Carlo simulations of the 176Lu decay, and the radiation interaction mechanisms in the crystal materials, using PENELOPE and GATE, and by using an analytic model based on the 176Lu decay radiation emission and absorption probabilities. To properly simulate these materials, the mass density and elemental composition were investigated from various references, from which other important properties were derived, such as the expected count rate due to their intrinsic radiation and the intrinsic quantum efficiency for a continuous range of crystal thickness and photon energies, presented as two-dimensional maps. Additionally, other physical properties important for radiation detection of the lutetium-based scintillators are also compared to those of lutetium oxyorthosilicate, the most prevailing material in current detector technology for various imaging applications.

Luminescence from oxygen vacancies in Lu2SiO5 crystal and ceramics at room temperature

Photoluminescence (PL) of Lu2SiO5 crystal and ceramics with a high concentration of oxygen vacancies (0.1-0.5 at.%) is studied. Oxygen vacancies were created using two ways. The first method is a growth of crystal from the non-stoichiometric Lu2Si0.98O4.96 melt and the second one is a doping of Lu2SiO5 matrix with divalent Ca2+ ions at the concentration of 1 at.%. For the first time we observe a fairly bright room-temperature ultraviolet PL of both crystal grown from the Lu2Si0.98O4.96 melt with the composition Lu2Si0.996O4.992 and Lu2SiO5 ceramics doped with Ca2+ ions. A band at 290 nm in the PL spectrum of the crystal and a band at 283 nm in the PL spectrum of the calcium-doped ceramics are observed. The spectral and kinetic properties of these bands are close to each other. This fact indicates similar origins of these bands. The results of the work show that the studied ultraviolet luminescence is related to oxygen vacancies in lutetium oxyorthosilicate

Charge Transfer and Charge Trapping Processes in Ca- or Al-Co-doped Lu2SiO5 and Lu2Si2O7 Scintillators Activated by Pr3+ or Ce3+ Ions.

Lutetium oxyorthosilicate Lu2SiO5 (LSO) and pyrosilicate Lu2Si2O7 (LPS) activated by Ce3+ or Pr3+ are known to be effective and fast scintillation materials for the detection of X-rays and γ-rays. Their performances can be further improved by co-doping with aliovalent ions. Herein, we investigate the Ce3+(Pr3+) → Ce4+(Pr4+) conversion and the formation of lattice defects stimulated by co-doping with Ca2+ and Al3+ in LSO and LPS powders prepared by the solid-state reaction process. The materials were studied by electron paramagnetic resonance (EPR), radioluminescence spectroscopy, and thermally stimulated luminescence (TSL), and scintillation decays were measured. EPR measurements of both LSO:Ce and LPS:Ce showed effective Ce3+ → Ce4+ conversions stimulated by Ca2+ co-doping, while the effect of Al3+ co-doping was less effective. In Pr-doped LSO and LPS, a similar Pr3+ → Pr4+ conversion was not detected by EPR, suggesting that the charge compensation of Al3+ and Ca2+ ions is realized via other impurities and/or lattice defects. X-ray irradiation of LPS creates hole centers attributed to a hole trapped in an oxygen ion in the neighborhood of Al3+ and Ca2+. These hole centers contribute to an intense TSL glow peak at 450-470 K. In contrast to LPS, only weak TSL peaks are detected in LSO and no hole centers are visible via EPR. The scintillation decay curves of both LSO and LPS show a bi-exponential decay with fast and slow component decay times of 10-13 ns and 30-36 ns, respectively. The decay time of the fast component shows a small (6-8%) decrease due to co-doping.

Evaluation of a modular all-in-one high-resolution PET detector and readout electronics setup

Objective. The all-in-one solution and modularity of the C13500 series TOF-PET detector modules (Hamamatsu Photonics K.K., Hamamatsu, Japan) make them a highly attractive candidate for the development of positron emission tomography (PET) systems. However, the commercially available portfolio targets clinical whole-body PET systems with a scintillation crystal cross area of 3.1 × 3.1 mm2. To extend the modules for high resolution (preclinical or organ specific) systems, the support for smaller scintillation crystals is required. Approach. In this work, a PET detector was developed based on the TOF-PET modules using a light sharing approach, 16 × 16 lutetium oxyorthosilicate (LSO) scintillation crystals with a size of 1.51 × 1.51 × 10.00 mm3 readout with 8 × 8 photosensor channels of size 3.0 × 3.0 mm2. In addition to hardware and software development, the optimized parameter settings for the adapted configuration were evaluated. Main Results. A factor of two in amplification of the analog signal compared to the minimum gain setting was necessary for an accurate crystal identification (peak-to-valley ratio 14.9 ± 5.9). A further increase to a factor of three was not determined as optimum as the time over threshold duration, thus pile-up probability, increased from 1032.1 ± 109.5 to 1789.5 ± 218.5 ns (photopeak position). With this amplification a full width at half maximum (FWHM) energy resolution of 14.1 ± 2.0% and a high linearity of the energy detection was obtained. A FWHM coincidence resolving time (CRT) of 313 ps was achieved by using a low timing threshold, increasing the bandwidth of the front-end circuit and using a narrow ± 1σ energy window. To approximately double the sensitivity and reduce the power consumption, the timing parameters were adjusted resulting in a FWHM CRT of 354 ps (±2σ). Significance. Based on the results obtained with the proof-of-concept detector setup, we confirm the modularity and flexibility of the all-in-one TOF-PET detector modules for the future development of application-specific high-resolution PET systems.

Evaluation of cost-effective system designs for long axial field-of-view PET scanners

Objective. Current commercial positron emission tomography (PET) scanners have excellent performance and diagnostic image quality primarily due to improvements in scanner sensitivity and time-of-flight (TOF) resolution. Recent years have seen the development of total-body PET scanners with longer axial field-of-view (AFOV) that increase sensitivity for single organ imaging, and also image more of the patient in a single bed position thereby enabling multi-organ dynamic imaging. While studies have shown significant capabilities of these systems, cost will be a major factor in their widespread adoption in the clinic. Here we evaluate alternative designs that achieve many advantages of long AFOV PET while utilizing cost-effective detector hardware. Approach. We utilize Monte Carlo simulations and clinically relevant lesion detectability metric to study the impact of scintillator type lutetium oxyorthosilicate or bismuth germanate (LSO or BGO), scintillator thickness (10–20 mm), and TOF resolution on resultant image quality in a 72 cm long scanner. Detector TOF resolution was varied based on current scanner performance, as well as expected future performance from detector designs that currently hold most promise for scaling into a scanner. Main results. Results indicate that BGO is competitive with LSO (both 20 mm thick) if we assume that it uses TOF (e.g. Cerenkov timing with 450 ps fwhm and Lorentzian distribution) and the LSO scanner has TOF resolution similar to the latest PMT-based scanners (∼500–650 ps). Alternatively, a system using 10 mm thick LSO with 150 ps TOF resolution can also provide similar performance. Both these alternative systems can provide cost savings (25%–33%) relative to a scanner using 20 mm LSO with ∼50% of effective sensitivity, but still 500%–700% higher than a conventional AFOV scanner. Significance. Our results have relevance to the development of long AFOV PET, where reduced cost of these alternative designs can provide wider accessibility for use in situations requiring imaging of multiple organs simultaneously.

Performance evaluation of SimPET-L and SimPET-XL: MRI-compatible small-animal PET systems with rat-body imaging capability

BackgroundSimPET-L and SimPET-XL have recently been introduced with increased transaxial fields of view (FOV) compared with their predecessors (SimPET™ and SimPET-X), enabling whole-body positron emission tomography (PET) imaging of rats. We conducted performance evaluations of SimPET-L and SimPET-XL and rat-body imaging with SimPET-XL to demonstrate the benefits of increased axial and transaxial FOVs.ProceduresThe detector blocks in SimPET-L and SimPET-XL consist of two 4 × 4 silicon photomultiplier arrays coupled with 20 × 9 array lutetium oxyorthosilicate crystals. SimPET-L and SimPET-XL have an inner diameter (bore size) of 7.6 cm, and they are composed of 40 and 80 detector blocks yielding axial lengths of 5.5 and 11 cm, respectively. Each system was evaluated according to the National Electrical Manufacturers Association NU4-2008 protocol. Rat imaging studies, such as 18F-NaF and 18F-FDG PET, were performed using SimPET-XL.ResultsThe radial resolutions at the axial center measured using the filtered back projection, 3D ordered-subset expectation maximization (OSEM), and 3D OSEM with point spread functions correction were 1.7, 0.82, and 0.82 mm FWHM in SimPET-L and 1.7, 0.91, and 0.91 mm FWHM in SimPET-XL, respectively. The peak sensitivities of SimPET-L and SimPET-XL were 6.30% and 10.4% for an energy window of 100–900 keV and 4.44% and 7.25% for a window of 250–750 keV, respectively. The peak noise equivalent count rate with an energy window of 250–750 keV was 249 kcps at 44.9 MBq for SimPET-L and 349 kcps at 31.3 MBq for SimPET-XL. In SimPET-L, the uniformity was 4.43%, and the spill-over ratios in air- and water-filled chambers were 5.54% and 4.10%, respectively. In SimPET-XL, the uniformity was 3.89%, and the spill-over ratio in the air- and water-filled chambers were 3.56% and 3.60%. Moreover, SimPET-XL provided high-quality images of rats.ConclusionSimPET-L and SimPET-XL show adequate performance compared with other SimPET systems. In addition, their large transaxial and long axial FOVs provide imaging capability for rats with high image quality.

Potential of Depth-of-Interaction-Based Detection Time Correction in Cherenkov Emitter Crystals for TOF-PET.

Cherenkov light can improve the timing resolution of Positron Emission Tomography (PET) radiation detectors, thanks to its prompt emission. Coincidence time resolutions (CTR) of ~30 ps were recently reported when using 3.2 mm-thick Cherenkov emitters. However, sufficient detection efficiency requires thicker crystals, causing the timing resolution to be degraded by the optical propagation inside the crystal. We report on depth-of-interaction (DOI) correction to mitigate the time-jitter due to the photon time spread in Cherenkov-based radiation detectors. We simulated the Cherenkov and scintillation light generation and propagation in 3 × 3 mm2 lead fluoride, lutetium oxyorthosilicate, bismuth germanate, thallium chloride, and thallium bromide. Crystal thicknesses varied from 9 to 18 mm with a 3-mm step. A DOI-based time correction showed a 2-to-2.5-fold reduction of the photon time spread across all materials and thicknesses. Results showed that highly refractive crystals, though producing more Cherenkov photons, were limited by an experimentally obtained high-cutoff wavelength and refractive index, restricting the propagation and extraction of Cherenkov photons mainly emitted at shorter wavelengths. Correcting the detection time using DOI information shows a high potential to mitigate the photon time spread. These simulations highlight the complexity of Cherenkov-based detectors and the competing factors in improving timing resolution.

A novel method for investigating optically stimulated luminescence in scintillators

Optically stimulated luminescence (OSL) is a known property in many scintillators, and investigating the branching ratio of thermalized carriers to this photon-emission mechanism could aid both scintillator development and OSL-based dosimetry. We present a novel method for determining the branching ratio of thermalized carriers to OSL in scintillators while monitoring the energy deposition from 511 keV gamma photons on an event-by-event basis. We demonstrate the method using a cerium-doped lutetium oxyorthosilicate (LYSO:Ce) crystal, and validate that the observed signal indeed originates from OSL photons by estimating the lifetime of the OSL traps, which is consistent with values found in the literature. We report a branching ratio of thermalized carriers to the OSL traps in LYSO:Ce of (1.0±0.2)% upon excitation with 511 keV gamma photons, using a one-trap-one-recombination-center model.

Multipanel Limited Angle PET System With 50 ps FWHM Coincidence Time Resolution: A Simulation Study

In this simulation study, we evaluate the performance of a limited angular coverage PET system consisting of two/four fast-timing 50 ps FWHM CTR flat-panel detectors made of 5–20 mm long pixelated lutetium oxyorthosilicate crystals. We studied image quality and count rates following the National Electrical Manufacturers Association standard, spatial resolution by imaging a Derenzo phantom and a hot rod, and investigated the sensitivity of different scanner designs. We demonstrated the possible use of such a scanner by imaging a human head and a torso of the extended cardiac-torso (XCAT) digital phantom. All the designs were compared to the reference scanner, based on Siemens Biograph Vision PET/CT scanner geometry. We show that good coincidence timing resolution (CTR) can compensate for lower detection efficiency or smaller angular coverage. Good image quality can be obtained with a simple limited-angle PET system without distortions or artefacts. Substantial degradation of the spatial resolution with increased crystal length is observed in the two-panel design due to the parallax error, but not in the four-panel design. The four-panel design simulated with a CTR of 50 ps FWHM is comparable to that of the current state-of-the-art clinical PET/CT scanner. Similar fast-timing limited-angle planar detectors could enable much less expensive total-body or single organ (dynamically selectable) imaging devices.

Investigation on the effects of Ce3+:Lu2SiO5 nanocrystalline phosphors in reducing environment

Lutetium oxyorthosilicate doped with cerium (Ce3+:Lu2SiO5) is a high resolution and highly responsive detector used in medical imaging frequently in the form of single crystals. Fabrication of ceramic polycrystalline lutetium oxyorthosilicate (LSO) doped with cerium is an upcoming alternative that requires high temperatures and a non-oxidising atmosphere for sintering. However, the stability of the nano phosphor itself under the sintering conditions is inconsistent and has stumped many investigators. This paper presents a systematic study of the formation of lutetium oxyorthosilicate from its respective constituents (lutetia and silica) and of the behavior of LSO under sintering conditions. The study shows a breakdown of the compound in highly reducing atmospheres to form lutetium oxide, as confirmed by x-ray diffraction studies. The decomposition of hot pressed Ce:LSO in a reducing environment studied by scanning electron micrography, Raman spectroscopy, shows the correlation of its structure and defects with its radioluminescence.

Physical performance of adaptive axial FOV PET scanners with a sparse detector block rings or a checkerboard configuration

Objective. Using Monte-Carlo simulations, we evaluated the physical performance of a hypothetical state-of-the-art clinical PET scanner with adaptive axial field-of-view (AFOV) based on the validated GATE model of the Siemens Biograph VisionTM PET/CT scanner. Approach. Vision consists of 16 compact PET rings, each consisting of 152 mini-blocks of 5 × 5 Lutetium Oxyorthosilicate crystals (3.2 × 3.2 × 20 mm3). The Vision 25.6 cm AFOV was extended by adopting (i) a sparse mini-block ring (SBR) configuration of 49.6 cm AFOV, with all mini-block rings interleaved with 16 mm axial gaps, or (ii) a sparse mini-block checkerboard (SCB) configuration of 51.2 cm AFOV, with all mini-blocks interleaved with gaps of 16 mm (transaxial) × 16 mm (axial) width in checkerboard pattern. For sparse configurations, a ‘limited’ continuous bed motion (limited-CBM) acquisition was employed to extend AFOVs by 2.9 cm. Spatial resolution, sensitivity, image quality (IQ), NECR and scatter fraction were assessed per NEMA NU2-2012. Main Results. All IQ phantom spheres were distinguishable with all configurations. SBR and SCB percent contrast recovery (% CR) and background variability (% BV) were similar (p-value > 0.05). Compared to Vision, SBR and SCB %CRs were similar (p-values > 0.05). However, SBR and SCB %BVs were deteriorated by 30% and 26% respectively (p-values < 0.05). SBR, SCB and Vision exhibited system sensitivities of 16.6, 16.8, and 15.8 kcps MBq−1, NECRs of 311 kcps @35 kBq cc−1, 266 kcps @25.8 kBq cc−1, and 260 kcps @27.8 kBq cc−1, and scatter fractions of 31.2%, 32.4%, and 32.6%, respectively. SBR and SCB exhibited a smoother sensitivity reduction and noise enhancement rate from AFOV center to its edges. SBR and SCB attained comparable spatial resolution in all directions (p-value > 0.05), yet, up to 1.5 mm worse than Vision (p-values < 0.05). Significance. The proposed sparse configurations may offer a clinically adoptable solution for cost-effective adaptive AFOV PET with either highly-sensitive or long-AFOV acquisitions.

Fabrication of textured cerium‐doped lutetium oxyorthosilicate ceramics by slip casting in a strong magnetic field

Abstract Cerium‐doped lutetium oxyorthosilicate (Lu2SiO5:Ce, LSO:Ce) slurry with 35 vol.% solid content and viscosity of 70 mPa s (at a shear rate of 4 s–1) was prepared via a 24‐h ball milling for the powder calcined at 1200°C and adding ammonium polyacrylate of 0.2 wt.%. Textured LSO:Ce ceramics were fabricated via slip casting in a vertical magnetic field and subsequently pressureless sintering of 1650°C and hot isostatic pressing. The maximum Lotgering factor f and relative density of the textured ceramics were 0.48% and 98.8%, respectively. Effects of grain size, dispersant, viscosity of slurry, and magnetic flux density on the grain orientation of LSO:Ce ceramics were systematically investigated. Based on the spatial state of grains, we proposed the rotation rule that LSO:Ce grains with or without space constraints in the slurry align along a and c‐axis under the induction of a strong magnetic field.

Elaboration and luminescence of cerium-doped lutetium silicate glass-ceramics via in-situ growth from containerless processed lutetium silicate glass

Amorphous cerium-doped lutetium silicate scintillator was fabricated through aerodynamic levitation method. The lutetium silicate glass scintillator transformed into glass-ceramics after annealing at 950 °C in air. The crystalline phase of the glass-ceramics was composed with lutetium oxyorthosilicate (Lu2SiO5:Ce, LSO:Ce) and lutetium pyrosilicate (Lu2Si2O7:Ce, LPS:Ce). The crystalline parts of the glass-ceramics, i.e., the micro-sized polycrystalline LPS/LSO particles, consist of nano-sized LPS and LSO grains. The in-line transmittance of the LPS/LSO:Ce glass and glass-ceramics are 86% at 600 nm. The luminescence characteristics of the highly transparent LPS/LSO:Ce glass and glass-ceramics were investigated through Photoluminescence (PL), Photoluminescence Excitation (PLE) and Cathodoluminescence (CL). It suggests that combination of containerless processing and in-situ growth of lutetium silicate from glass matrix is a promising route to fabricate highly transparent lutetium silicate scintillators.

Investigation of phase evolution and Gd occupation in (Lu1-xGdx)2SiO5 lattice by Rietveld refinement and DFT simulation

Cerium-doped lutetium oxyorthosilicate (LSO:Ce, Lu2SiO5:Ce) is considered to be a typical scintillator with comprehensive good scintillation properties. The doping of Gd3+ elements with different concentrations strongly influences the structure and luminescence performance of LSO. The full concentration range of LGSO ((Lu1-xGdx)2SiO5) powders were prepared using a sol-gel method. The influences of the doping Gd3+ ion concentration on the phase evolution and lattice parameters of LGSO were investigated via X-ray diffraction (XRD), Rietveld refinement and density functional theory (DFT) simulations. It was found that the monoclinic crystal structure of LGSO gradually transitioned from C2/c to P21/c under elevated temperatures and phase transition temperature varied from 975 to 1400 ​°C as Gd replaced Lu. The lattice constants (a, b, and c) of LGSO lattice increased with the addition of Gd. The Rietveld refinement results indicate that doping Gd3+ in LGSO was prone to occupy the RE1 site rather than the RE2 site and Gd dopants was easily to form GdRE1-GdRE1 defect complex. The formation energy results of Gd3+ replacing different Lu3+ sites calculated by using the first-principles pseudopotential approach further proved this occupation mode. The intensity of photoluminescence of Ce:(Lu1-xGdx)2SiO5 attained the peak value when the content of Gd doping reached 0.05.

Feasibility of cerium-doped LSO particles as a scintillator for x-ray induced optogenetics

Objective. Non-invasive light delivery into the brain is needed for in vivo optogenetics to avoid physical damage. An innovative strategy could employ x-ray activation of radioluminescent particles (RLPs) to emit localized light. However, modulation of neuronal or synaptic function by x-ray induced radioluminescence from RLPs has not yet been demonstrated. Approach. Molecular and electrophysiological approaches were used to determine if x-ray dependent radioluminescence emitted from RLPs can activate light sensitive proteins. RLPs composed of cerium doped lutetium oxyorthosilicate (LSO:Ce), an inorganic scintillator that emits blue light, were used as they are biocompatible with neuronal function and synaptic transmission. Main results. We show that 30 min of x-ray exposure at a rate of 0.042 Gy s−1 caused no change in the strength of basal glutamatergic transmission during extracellular field recordings in mouse hippocampal slices. Additionally, long-term potentiation, a robust measure of synaptic integrity, was induced after x-ray exposure and expressed at a magnitude not different from control conditions (absence of x-rays). We found that x-ray stimulation of RLPs elevated cAMP levels in HEK293T cells expressing OptoXR, a chimeric opsin receptor that combines the extracellular light-sensitive domain of rhodopsin with an intracellular second messenger signaling cascade. This demonstrates that x-ray radioluminescence from LSO:Ce particles can activate OptoXR. Next, we tested whether x-ray activation of the RLPs can enhance synaptic activity in whole-cell recordings from hippocampal neurons expressing channelrhodopsin-2, both in cell culture and acute hippocampal slices. Importantly, x-ray radioluminescence caused an increase in the frequency of spontaneous excitatory postsynaptic currents in both systems, indicating activation of channelrhodopsin-2 and excitation of neurons. Significance. Together, our results show that x-ray activation of LSO:Ce particles can heighten cellular and synaptic function. The combination of LSO:Ce inorganic scintillators and x-rays is therefore a viable method for optogenetics as an alternative to more invasive light delivery methods.