X-ray-Sensitive Doped CaF2-Based MRI Contrast Agents for Local Radiation Dose Measurement.

Ionizing radiation has become widely used in medicine, with application in diagnostic techniques, such as computed tomography (CT) and radiation therapy (RT), where X-rays are used to diagnose and treat tumors. The X-rays used in CT and, in particular, in RT can have harmful side effects; hence, an accurate determination of the delivered radiation dose is of utmost importance to minimize any damage to healthy tissues. For this, medical specialists mostly rely on theoretical predictions of the delivered dose or external measurements of the dose. To extend the practical use of ionizing radiation-based medical techniques, such as magnetic resonance imaging (MRI)-guided RT, a more precise measurement of the internal radiation dose internally is required. In this work, a novel approach is presented to measure dose in liquids for potential future in vivo applications. The strategy relies on MRI contrast agents (CAs) that provide a dose-sensitive signal. The demonstrated materials are (citrate-capped) CaF2 nanoparticles (NPs) doped with Eu3+ or Fe2+/Fe3+ ions. Free electrons generated by ionizing radiation allow the reduction of Eu3+, which produces a very small contrast in MRI, to Eu2+, which induces a strong contrast. Oxidative species generated by high-energy X-rays can be measured indirectly using Fe2+ because it oxidizes to Fe3+, increasing the contrast in MRI. Notably, in the results, a strong increase in the proton relaxation rates is observed for the Eu3+-doped NPs at 40 kV. At 6 MV, a significant increase in proton relaxation rates is observed using CaF2 NPs doped with Fe2+/Fe3+ after irradiation. The presented concept shows great promise for use in the clinic to measure in vivo local ionizing radiation dose, as these CAs can be intravenously injected in a saline solution.

The effect of annealing on optical transmittance and structure of ZLANI fluorozirconate glass thin films.

We report the effect of thermal annealing on structure, composition, optical transmittance and thickness of a novel fluorozirconate glass (ZLANI) containing Zr, La, Al, Na and In fluorides. In this work, pulsed laser deposition was used to grow thin films of ZLANI, and thermal annealing at different temperatures was performed on the films. Annealing did not change the composition, but a clear structural evolution of the ZLANI glass was observed by transmission electron microscopy (TEM), showing that we can control microstructure independent of composition. An increase in transmittance after the film was subject to a 100 °C thermal anneal was ascribed to the removal of defects and structural relaxation in the amorphous state. Following an anneal of 200 °C, the transmittance decreases due to heterogeneous formation of crystalline nuclei and changes in the local bonding. After the final annealing at 300 °C, a wider-scale crystallization occurred, with some major crystal phases formed as Zr2F8(H2O)6 and ZrO2, which alters the shape of the transmittance curve. The crystalline content of the crystal phases that form in the annealed films was quantified using hollow cone dark field TEM imaging. The 100 °C or 200 °C annealing decreases the film thickness by inducing structural relaxation and densification of the amorphous films, while the thickness increase of the 300 °C annealed film resulted from the formed large crystals. These results provide insights for the design of multilayer nanocomposites with a ZLANI glass matrix, which have potential applications as up-/down-conversion luminescent materials and X-ray storage phosphors.

Characterization of Luminescent Materials with 151Eu Mössbauer Spectroscopy.

The application of Mössbauer spectroscopy to luminescent materials is described. Many solids doped with europium are luminescent, i.e., when irradiated with light they emit light of a longer wavelength. These materials therefore have practical applications in tuning the light output of devices like light emitting diodes. The optical properties are very different for the two possible valence states Eu 2 + and Eu 3 + , the former producing ultraviolet/visible light that shifts from violet to red depending on the host and the latter red light, so it is important to have a knowledge of their behavior in a sample environment. Photoluminescence spectra cannot give a quantitative analysis of Eu 2 + and Eu 3 + ions. Mössbauer spectroscopy, however, is more powerful and gives a separate spectrum for each oxidation state enabling the relative amount present to be estimated. The oxidation state can be identified from its isomer shift which is between - 12 and - 15 mm/s for Eu 2 + compared to around 0 mm/s for Eu 3 + . Furthermore, within each oxidation state, there are changes depending on the ligands attached to the europium: the shift is more positive for increased covalency of the bonding ligand X, or Eu concentration, and decreases for increasing Eu⁻X bond length.

Topotactic Fluorine Insertion into the Channels of FeSb2O4-Related Materials.

This paper discusses the fluorination characteristics of phases related to FeSb2O4, by reporting the results of a detailed study of Mg0.50Fe0.50Sb2O4 and Co0.50Fe0.50Sb2O4. Reaction with fluorine gas at low temperatures (typically 230 °C) results in topotactic insertion of fluorine into the channels, which are an inherent feature of the structure. Neutron powder diffraction and solid state NMR studies show that the interstitial fluoride ions are bonded to antimony within the channel walls to form Sb-F-Sb bridges. To date, these reactions have been observed only when Fe2+ ions are present within the chains of edge-linked octahedra (FeO6 in FeSb2O4) that form the structural channels. Oxidation of Fe2+ to Fe3+ is primarily responsible for balancing the increased negative charge associated with the presence of the fluoride ions within the channels. For the two phases studied, the creation of Fe3+ ions within the chains of octahedra modify the magnetic exchange interactions to change the ground-state magnetic symmetry to C-type magnetic order in contrast to the A-type order observed for the unfluorinated oxide parents.

Oxygen Insertion Reactions within the One-Dimensional Channels of Phases Related to FeSb2O4.

The structure of the mineral schafarzikite, FeSb2O4, has one-dimensional channels with walls comprising Sb3+ cations; the channels are separated by edge-linked FeO6 octahedra that form infinite chains parallel to the channels. Although this structure provides interest with respect to the magnetic and electrical properties associated with the chains and the possibility of chemistry that could occur within the channels, materials in this structural class have received very little attention. Here we show, for the first time, that heating selected phases in oxygen-rich atmospheres can result in relatively large oxygen uptakes (up to ∼2% by mass) at low temperatures (ca. 350 °C) while retaining the parent structure. Using a variety of structural and spectroscopic techniques, it is shown that oxygen is inserted into the channels to provide a structure with the potential to show high one-dimensional oxide ion conductivity. This is the first report of oxygen-excess phases derived from this structure. The oxygen insertion is accompanied not only by oxidation of Fe2+ to Fe3+ within the octahedral chains but also Sb3+ to Sb5+ in the channel walls. The formation of a defect cluster comprising one 5-coordinate Sb5+ ion (which is very rare in an oxide environment), two interstitial O2- ions, and two 4-coordinate Sb3+ ions is suggested and is consistent with all experimental observations. To the best of our knowledge, this is the first example of an oxidation process where the local energetics of the product dictate that simultaneous oxidation of two different cations must occur. This reaction, together with a wide range of cation substitutions that are possible on the transition metal sites, presents opportunities to explore the schafarzikite structure more extensively for a range of catalytic and electrocatalytic applications.

The magnetic and crystal structures of Sr1-δFeO2-xFx, a new oxyfluoride.

A new quasi-two-dimensional oxyfluoride, Sr1-δFeO2-xFx, has been successfully synthesized by combining topotactic fluoridation and CaH2 reduction. The introduction of F through this synthesis provides a new route to introducing charge carriers into the square layered lattice through the formation of Fe(1+) ions. While the average crystal symmetry and magnetic structure remain the same as in the parent compound, the addition of F results in an enhanced buckling of the Fe(O/F)2 square plaquettes that is most likely topologically driven.

Opportunities for Fluorochlorozirconate and Other Glass-Ceramic Detectors in Medical Imaging Devices.

This article gives an overview of fluorochlorozirconate glass-ceramic scintillators and storage phosphor materials: how they are synthesized, what their properties are, and how they can be used in medical imaging. Such materials can enhance imaging in x-ray radiography, especially mammography and dental imaging, computed tomography, and positron emission tomography. Although focusing on fluorochlorozirconate materials, the reader will find the discussion is relevant to other luminescent glass and glass-ceramic systems.

The reaction mechanism of FeSb(2) as anode for sodium-ion batteries.

The electrochemical reaction of FeSb2 with Na is reported for the first time. The first discharge (sodiation) potential profile of FeSb2 is characterized by a gentle slope centered at 0.25 V. During charge (Na removal) and the subsequent discharge, the main reaction takes place near 0.7 V and 0.4 V, respectively. The reversible storage capacity amounts to 360 mA h g(-1), which is smaller than the theoretical value of 537 mA h g(-1). The reaction, studied by ex situ and in situ X-ray diffraction, is found to proceed by the consumption of crystalline FeSb2 to form an amorphous phase. Upon further sodiation, the formation of nanocrystalline Na3Sb domains is evidenced. During desodiation, Na3Sb domains convert into an amorphous phase. The chemical environment of Fe, probed by (57)Fe Mössbauer spectroscopy, undergoes significant changes during the reaction. During sodiation, the well-resolved doublet of FeSb2 with an isomer shift around 0.45 mm s(-1) and a quadrupole splitting of 1.26 mm s(-1) is gradually converted into a doublet line centered at about 0.15 mm s(-1) along with a singlet line around 0 mm s(-1). The former signal results from the formation of a Fe-rich FexSb alloy with an estimated composition of 'Fe4Sb' while the latter signal corresponds to superparamagnetic Fe due to the formation of nanosized pure Fe domains. Interestingly the signal of 'Fe4Sb' remains unaltered during desodiation. This mechanism is substantially different than that observed during the reaction with Li. The irreversible formation of a Fe-rich 'Fe4Sb' alloy and the absence of full desodiation of Sb domains explain the lower than theoretical practical storage capacity.

Optical diagnostic and therapy applications of femtosecond laser radiation using lens-axicon focusing.

Diagnostic modalities by means of optical and/or near infrared femtosecond radiation through biological media can in principle be adapted to therapeutic applications. Of specific interest are soft tissue diagnostics and subsequent therapy through hard tissue such as bone. Femto-second laser pulses are delivered to hydroxyapatite representing bone, and photo-acoustic spectroscopy is presented in order to identify the location of optical anomalies in an otherwise homogeneous medium. Imaging through bone is being considered for diagnostic, and potentially therapeutic, applications related to brain tumors. The use of mesomeric optics such as lens-axicon combinations is of interest to achieve the favorable distribution of focused radiation. Direct therapy by increasing local temperature to induce hyperthermia is one mode of brain tumor therapy. This can be enhanced by seeding the tumor with nanoparticles. Opto-acoustic imaging using femtosecond laser radiation is a further opportunity for diagnosis.

Nanocrystallization in Fluorochlorozirconate Glass-Ceramics.

Heat treating fluorochlorozirconate (FCZ) glasses nucleates nanocrystals in the glass matrix, resulting in a nanocomposite glass-ceramic that has optical properties suitable for use as a medical imaging plate. Understanding the way in which the nanocrystal nucleation proceeds is critical to controlling the optical behavior. The nucleation and growth of nanocrystals in FCZ glass-ceramics was investigated with in situ transmission electron microscopy heating experiments. The experiments showed the nucleation and growth of previously unreported BaF2 nanocrystals in addition to the expected BaCl2 nanocrystals. Chemical analysis of the BaF2 nanocrystals shows an association with the optically active dopant previously thought only to interact with BaCl2 nanocrystals. The association of the dopant with BaF2 crystals suggests that it plays a role in the photoluminescent (PL) properties of FCZ glass-ceramics.

Intervertebral and intravertebral ratios in Doberman pinscher dogs with cervical spondylomyelopathy.

No screening method is currently available to differentiate dogs with and without cervical spondylomyelopathy. Intravertebral and intervertebral ratios are used in horses and can predict cervical vertebral malformation. Intervertebral ratios could be a useful screening method for canine cervical spondylomyelopathy. Our purpose was to compare cervical intervertebral and intravertebral ratios in normal vs. affected Doberman pinschers. Forty dogs were studied, 27 affected and 13 normal. Cervical radiographs were obtained in all dogs. The minimum intra- and intervertebral sagittal diameter ratios were established for each cervical vertebrae and disc space from C(2) to C(7) . Comparisons were made between groups and specific vertebral body and disc levels. The effect of gender, age, and method of measurement (analog or digital radiographs) was also studied. There was no difference in either the intervertebral or intravertebral ratio between normal vs. affected dogs. The ratios decreased progressively along the cervical spine, being smallest at C(6) -C(7) and C(7) , respectively. Age, gender, and method of measurement had a significant influence on both inter- and intravertebral ratios, with smaller ratios seen as dogs aged and in male dogs. Based on our results, inter- or intravertebral ratios have no value to distinguish between clinically normal Doberman pinschers and Doberman pinschers with cervical spondylomyelopathy.

Kinematic motion patterns of the cranial and caudal canine cervical spine.

OBJECTIVE: To define the kinematic motion patterns of the canine cervical spine, with a particular emphasis on identifying differences between the cranial (C(2)-C(4)) and caudal (C(5)-C(7)) segments, and to determine the significance of coupled motions (CM) in the canine cervical spine. STUDY DESIGN: Cadaveric biomechanical study. SAMPLE POPULATION: Cervical spines of 8 Foxhounds. METHODS: Spinal specimens were considered free of pathology based on radiographic, computed tomography, and magnetic resonance imaging examinations. All musculature was removed without damaging ligaments or joint capsules. Spines were mounted in a customized pure-moment spine testing jig, and data were collected using an optoelectronic motion capture system. Range of motion, neutral zone and CM in flexion/extension, left/right lateral bending and left/right axial rotation were established. Data were analyzed using mixed-effects maximum likelihood regression models. RESULTS: Total flexion/extension did not change across the 4 levels. There was no difference between flexion and extension, and no CM was identified. Lateral bending was not different across levels, but tended to be greater in the cranial spine. Axial rotation was ∼2.6 times greater in the caudal segments. Lateral bending and axial rotation were coupled. CONCLUSIONS: Kinematics of the cranial and caudal cervical spine differed markedly with greater mobility in the caudal cervical spine.

XANES studies on Eu-doped fluorozirconate based glass ceramics.

The influence of adding InF3 as a reducing agent on the oxidation state of Eu in fluorochloro- (FCZ) and fluorobromozirconate (FBZ) glass ceramics was investigated using x-ray absorption near edge (XANES) and photoluminescence (PL) spectroscopy. For both materials, it was found that InF3 decreases the Eu2+-to-Eu3+ ratio significantly. PL spectroscopy proved that an annealing step leads to the formation of Eu-doped BaCl2 and BaBr2 nanocrystals in the FCZ and FBZ glasses, respectively. In the case of FCZ glass ceramics the hexagonal phase of BaCl2 could be detected in indium-free and InF3-doped ceramics, but only for InF3 containing FCZ glass ceramics a phase transition of the nanoparticles from hexagonal to orthorhombic structure is observed. For the FBZ glass ceramics, the hexagonal phase of BaBr2 can be formed with and without indium doping, but only in the indium-free case a phase transition to orthorhombic BaBr2 could be found.

Zr and Ba edge phenomena in the scintillation intensity of fluorozirconate-based glass-ceramic X-ray detectors.

The energy-dependent scintillation intensity of Eu-doped fluorozirconate glass-ceramic X-ray detectors has been investigated in the energy range from 10 to 40 keV. The experiments were performed at the Advanced Photon Source, Argonne National Laboratory, USA. The glass ceramics are based on Eu-doped fluorozirconate glasses, which were additionally doped with chlorine to initiate the nucleation of BaCl(2) nanocrystals therein. The X-ray excited scintillation is mainly due to the 5d-4f transition of Eu(2+) embedded in the BaCl(2) nanocrystals; Eu(2+) in the glass does not luminesce. Upon appropriate annealing the nanocrystals grow and undergo a phase transition from a hexagonal to an orthorhombic phase of BaCl(2). The scintillation intensity is investigated as a function of the X-ray energy, particle size and structure of the embedded nanocrystals. The scintillation intensity versus X-ray energy dependence shows that the intensity is inversely proportional to the photoelectric absorption of the material, i.e. the more photoelectric absorption the less scintillation. At 18 and 37.4 keV a significant decrease in the scintillation intensity can be observed; this energy corresponds to the K-edge of Zr and Ba, respectively. The glass matrix as well as the structure and size of the embedded nanocrystals have an influence on the scintillation properties of the glass ceramics.