Diagnostic Performance in Low- and High-Contrast Tasks of an Image-Based Denoising Algorithm Applied to Radiation Dose-Reduced Multiphase Abdominal CT Examinations.

BACKGROUND. Anatomic redundancy between phases can be used to achieve denoising of multiphase CT examinations. A limitation of iterative reconstruction (IR) techniques is that they generally require use of CT projection data. A frequency-split multi-band-filtration algorithm applies denoising to the multiphase CT images themselves. This method does not require knowledge of the acquisition process or integration into the reconstruction system of the scanner, and it can be implemented as a supplement to commercially available IR algorithms. OBJECTIVE. The purpose of the present study is to compare radiologists' performance for low-contrast and high-contrast diagnostic tasks (i.e., tasks for which differences in CT attenuation between the imaging target and its anatomic background are subtle or large, respectively) evaluated on multiphase abdominal CT between routine-dose images and radiation dose-reduced images processed by a frequency-split multiband-filtration denoising algorithm. METHODS. This retrospective single-center study included 47 patients who underwent multiphase contrast-enhanced CT for known or suspected liver metastases (a low-contrast task) and 45 patients who underwent multiphase contrast-enhanced CT for pancreatic cancer staging (a high-contrast task). Radiation dose-reduced images corresponding to dose reduction of 50% or more were created using a validated noise insertion technique and then underwent denoising using the frequency-split multi-band-filtration algorithm. Images were independently evaluated in multiple sessions by different groups of abdominal radiologists for each task (three readers in the low-contrast arm and four readers in the high-contrast arm). The noninferiority of denoised radiation dose-reduced images to routine-dose images was assessed using the jackknife alternative free-response ROC (JAFROC) figure-of-merit (FOM; limit of noninferiority, -0.10) for liver metastases detection and using the Cohen kappa statistic and reader confidence scores (100-point scale) for pancreatic cancer vascular invasion. RESULTS. For liver metastases detection, the JAFROC FOM for denoised radiation dose-reduced images was 0.644 (95% CI, 0.510-0.778), and that for routine-dose images was 0.668 (95% CI, 0.543-0.792; estimated difference, -0.024 [95% CI, -0.084 to 0.037]). Intraobserver agreement for pancreatic cancer vascular invasion was substantial to near perfect when the two image sets were compared (κ = 0.53-1.00); the 95% CIs of all differences in confidence scores between image sets contained zero. CONCLUSION. Multiphase contrast-enhanced abdominal CT images with a radiation dose reduction of 50% or greater that undergo denoising by a frequency-split multiband-filtration algorithm yield performance similar to that of routine-dose images for detection of liver metastases and vascular staging of pancreatic cancer. CLINICAL IMPACT. The image-based denoising algorithm facilitates radiation dose reduction of multiphase examinations for both low- and high-contrast diagnostic tasks without requiring manufacturer-specific hardware or software.

Predicting Risk of Surgery in Patients With Small Bowel Crohn's Disease Strictures Using Computed Tomography and Magnetic Resonance Enterography.

BACKGROUND: We aimed to determine if patient symptoms and computed tomography enterography (CTE) and magnetic resonance enterography (MRE) imaging findings can be used to predict near-term risk of surgery in patients with small bowel Crohn's disease (CD). METHODS: CD patients with small bowel strictures undergoing serial CTE or MRE were retrospectively identified. Strictures were defined by luminal narrowing, bowel wall thickening, and unequivocal proximal small bowel dilation. Harvey-Bradshaw index (HBI) was recorded. Stricture observations and measurements were performed on baseline CTE or MRE and compared to with prior and subsequent scans. Patients were divided into those who underwent surgery within 2 years and those who did not. LASSO (least absolute shrinkage and selection operator) regression models were trained and validated using 5-fold cross-validation. RESULTS: Eighty-five patients (43.7 ± 15.3 years of age at baseline scan, majority male [57.6%]) had 137 small bowel strictures. Surgery was performed in 26 patients within 2 years from baseline CTE or MRE. In univariate analysis of patients with prior exams, development of stricture on the baseline exam was associated with near-term surgery (P = .006). A mathematical model using baseline features predicting surgery within 2 years included an HBI of 5 to 7 (odds ratio [OR], 1.7 × 105; P = .057), an HBI of 8 to 16 (OR, 3.1 × 105; P = .054), anastomotic stricture (OR, 0.002; P = .091), bowel wall thickness (OR, 4.7; P = .064), penetrating behavior (OR, 3.1 × 103; P = .096), and newly developed stricture (OR: 7.2 × 107; P = .062). This model demonstrated sensitivity of 67% and specificity of 73% (area under the curve, 0.62). CONCLUSIONS: CTE or MRE imaging findings in combination with HBI can potentially predict which patients will require surgery within 2 years.

Computed tomography and magnetic resonance enterography imaging measurements and observations, in combination with patient symptoms, can potentially predict which patients will require surgery within 2 years with modest degree of accuracy.

Impact of dual-energy 50-keV virtual monoenergetic images on radiologist confidence in detection of key imaging findings of small hepatocellular carcinomas using multiphase liver CT.

BACKGROUND: Dual-energy virtual monoenergetic images can increase iodine signal, potentially increasing the conspicuity of hepatic masses. PURPOSE: To determine if dual-energy 50-keV virtual monoenergetic images improve visualization of key imaging findings or diagnostic confidence for small (≤2 cm) hepatocellular carcinomas (HCC) at multiphase, contrast-enhanced liver computed tomography (CT). MATERIAL AND METHODS: Patients with chronic liver disease underwent multiphase dual-energy CT imaging for HCC, with late arterial and delayed phase dual-energy 50-keV images reconstructed. Two non-reader subspecialized gastrointestinal (GI) radiologists established the reference standard, determining the location and diagnosis of all hepatic lesions using predetermined criteria. Three GI radiologists interpreted mixed kV CT images without or with dual-energy 50-keV images. Radiologists identified potential HCCs and rated their confidence (0-100 scales) in imaging findings of arterial enhancement, enhancing capsule, tumor washout, and LI-RADS 5 (2018) category. RESULTS: In total, 45 patients (14 women; mean age = 59.5 ± 10.9 years) with chronic liver disease were included. Of them, 19 patients had 25 HCCs ≤2 cm (mean size = 1.5 ± 0.4 cm). There were 17 LI-RADS 3 and 4 lesions and 19 benign lesions. Reader confidence in imaging findings of arterial enhancement, enhancing capsule, and non-peripheral washout significantly increased with dual-energy images (P ≤ 0.022). Overall confidence in HCC diagnosis increased significantly with dual-energy 50-keV images (52.4 vs. 68.8; P = 0.001). Dual-energy images demonstrated a slight but significant decrease in overall image quality. CONCLUSION: Radiologist confidence in key imaging features of small HCCs and confidence in imaging diagnosis increases with use of dual-energy 50-keV images at multiphase, contrast-enhanced liver CT.

A Pilot Study to Estimate the Impact of High Matrix Image Reconstruction on Chest Computed Tomography.

OBJECTIVES: The objectives of the study were to estimate the impact of high matrix image reconstruction on chest computed tomography (CT) compared to standard image reconstruction. MATERIAL AND METHODS: This retrospective study included patients with interstitial or parenchymal lung disease, airway disease, and pulmonary nodules who underwent chest CT. Chest CT images were reconstructed using high matrix (1024 × 1024) or standard matrix (512 × 512), with all other parameters matched. Two radiologists, blinded to reconstruction technique, independently examined each lung, viewing image sets side by side and rating the conspicuity of imaging findings using a 5-point relative conspicuity scale. The presence of pulmonary nodules and confidence in classification of internal attenuation was also graded. Overall image quality and subjective noise/artifacts were assessed. RESULTS: Thirty-four patients with 68 lungs were evaluated. Relative conspicuity scores were significantly higher using high matrix image reconstruction for all imaging findings indicative of idiopathic lung fibrosis (peripheral airway visualization, interlobular septal thickening, intralobular reticular opacity, and end-stage fibrotic change; P ≤ 0.001) along with emphysema, mosaic attenuation, and fourth order bronchi for both readers (P ≤ 0.001). High matrix reconstruction did not improve confidence in the presence or classification of internal nodule attenuation for either reader. Overall image quality was increased but not subjective noise/artifacts with high matrix image reconstruction for both readers (P < 0.001). CONCLUSION: High matrix image reconstruction significantly improves the conspicuity of imaging findings reflecting interstitial lung disease and may be useful for diagnosis or treatment response assessment.

Alternaria alternata uses two siderophore systems for iron acquisition.

Iron is one of the most abundant elements on earth and essential for life. However, Fe3+ ions are rather insoluble and microorganisms such as fungi may use siderophores as strong chelators for uptake. In addition, free cytoplasmic iron is rather toxic and intracellular siderophores are used to control the toxicity. Siderophores are also important for iron storage. We studied two siderophore systems in the plant necrotrophic fungus Alternaria alternata and show that the non-ribosomal peptide synthase, Nps2, is required for the biosynthesis of intracellular ferricrocin, whereas Nps6 is needed for the formation of extracellular coprogen and coprogen B. Whereas nps2 was dispensable for growth on iron-depleted medium, nps6 was essential under those conditions. nps2 deletion caused an increase in spore formation and reduced pathogenicity on tomato. Our results suggest that A. alternata employs an external and an internal siderophore system to adapt to low iron conditions.

Dose Reduction for Sinus and Temporal Bone Imaging Using Photon-Counting Detector CT With an Additional Tin Filter.

OBJECTIVE: The aim of this study was to quantitatively demonstrate radiation dose reduction for sinus and temporal bone examinations using high-resolution photon-counting detector (PCD) computed tomography (CT) with an additional tin (Sn) filter. MATERIALS AND METHODS: A multienergy CT phantom, an anthropomorphic head phantom, and a cadaver head were scanned on a research PCD-CT scanner using ultra-high-resolution mode at 100-kV tube potential with an additional tin filter (Sn-100 kV) and volume CT dose index of 10 mGy. They were also scanned on a commercial CT scanner with an energy-integrating detector (EID) following standard clinical protocols. Thirty patients referred to clinically indicated sinus examinations, and two patients referred to temporal bone examinations were scanned on the PCD-CT system after their clinical scans on an EID-CT. For the sinus cohort, PCD-CT scans were performed using Sn-100 kV at 4 dose levels at 10 mGy (n = 9), 8 mGy (n = 7), 7 mGy (n = 7), and 6 mGy (n = 7), and the clinical EID-CT was performed at 120 kV and 13.7 mGy (mean CT volume dose index). For the temporal bone scans, PCD-CT was performed using Sn-100 kV (10.1 mGy), and EID-CT was performed at 120 kV and routine clinical dose (52.6 and 66 mGy). For both PCD-CT and EID-CT, sinus images were reconstructed using H70 kernel at 0.75-mm slice thickness, and temporal bone images were reconstructed using a U70 kernel at 0.6-mm slice thickness. In addition, iterative reconstruction with a dedicated sharp kernel (V80) was used to obtain high-resolution PCD-CT images from a sinus patient scan to demonstrate improved anatomic delineation. Improvements in spatial resolution from the dedicated sharp kernel was quantified using modulation transfer function measured with a wire phantom. A neuroradiologist assessed the H70 sinus images for visualization of critical anatomical structures in low-dose PCD-CT images and routine-dose EID-CT images using a 5-point Likert scale (structural detection obscured and poor diagnostic confidence, score = 1; improved anatomic delineation and diagnostic confidence, score = 5). Image contrast and noise were measured in representative regions of interest and compared between PCD-CT and EID-CT, and the noise difference between the 2 acquisitions was used to estimate the dose reduction in the sinus and temporal bone patient cohorts. RESULTS: The multienergy phantom experiment showed a noise reduction of 26% in the Sn-100 kV PCD-CT image, corresponding to a total dose reduction of 56% compared with EID-CT (clinical dose) without compromising image contrast. The PCD-CT images from the head phantom and the cadaver scans demonstrated a dose reduction of 67% and 83%, for sinus and temporal bone examinations, respectively, compared with EID-CT. In the sinus cohort, PCD-CT demonstrated a mean dose reduction of 67%. The 10- and 8-mGy sinus patient images from PCD-CT were significantly superior to clinical EID-CT for visualization of critical sinus structures (median score = 5 ± 0.82 and P = 0.01 for lesser palatine foramina, median score = 4 ± 0.68 and P = 0.039 for nasomaxillary sutures, and median score = 4 ± 0.96 and P = 0.01 for anterior ethmoid artery canal). The 6- and 7-mGy sinus patient images did not show any significant difference between PCD-CT and EID-CT. In addition, V80 (sharp kernel, 10% modulation transfer function = 18.6 cm) PCD-CT images from a sinus patient scan increased the conspicuity of nasomaxillary sutures compared with the clinical EID-CT images. The temporal bone patient images demonstrated a dose reduction of up to 85% compared with clinical EID-CT images, whereas visualization of inner ear structures such as the incudomalleolar joint were similar between EID-CT and PCD-CT. CONCLUSIONS: Phantom and cadaver studies demonstrated dose reduction using Sn-100 kV PCD-CT compared with current clinical EID-CT while maintaining the desired image contrast. Dose reduction was further validated in sinus and temporal bone patient studies. The ultra-high resolution capability from PCD-CT allowed improved anatomical delineation for sinus imaging compared with current clinical standard.

The protein corona suppresses the cytotoxic and pro-inflammatory response in lung epithelial cells and macrophages upon exposure to nanosilica.

Engineered amorphous silica nanoparticles (nanosilica) are one of the most abundant nanomaterials and are widely used in industry. Furthermore, novel nanosilica materials are promising theranostic tools for biomedicine. However, hazardous effects of nanosilica especially after inhalation into the lung have been documented. Therefore, the safe development of nanosilica materials urgently requires predictive assays to monitor toxicity. Here, we further investigate the impact of the protein corona on the biological activity of two different types of nanosilica (colloidal and pyrogenic) in lung cells. As previously described, adsorption of serum proteins to the nanosilica surface suppresses cytotoxicity in macrophages and lung epithelial cells. As the increase of pro-inflammatory mediators is a hallmark of inflammation in the lung upon nanosilica exposure, we studied the potential coupling of the cytotoxic and pro-inflammatory response in A549 human lung epithelial cells and RAW264.7 mouse macrophages. Indeed, cytotoxicity precedes the onset of pro-inflammatory gene expression and cytokine release as exemplified for IL-8 in A549 cells and TNF-alpha in RAW264.7 macrophages after exposure to 0-100 µg/mL nanosilica in medium without serum. Formation of a protein corona not only inhibited cellular toxicity, but also the pro-inflammatory response. Of note, uptake of nanosilica into cells was negligible in the absence, but enhanced in the presence of a protein corona. Hence, the prevailing explanation that the protein corona simply interferes with cellular uptake thus preventing adverse effects needs to be revisited. In conclusion, for the reliable prediction of adverse effects of nanosilica in the lung, in vitro assays should be performed in media not complemented with complete serum. However, in case of different exposure routes, e.g., injection into the blood stream as intended for biomedicine, the protein corona prevents acute toxic actions of nanosilica.

Rheumatoid Arthritis vs Osteoarthritis: Comparison of Demographics and Trends of Joint Replacement Data from the Nationwide Inpatient Sample.

Current literature regarding complications following total joint arthroplasty have primarily focused on patients with osteoarthritis (OA), with less emphasis on the trends and in-hospital outcomes of rheumatoid arthritis (RA) patients undergoing these procedures. The purpose of this study is to analyze the outcomes and trends of RA patients undergoing total knee arthroplasty (TKA) or total hip arthroplasty (THA) compared to OA patients. Data from the Nationwide Inpatient Sample from 2006 to 2011 was extracted using the International Classification of Diseases, Ninth Revision codes for patients that received a TKA or THA. Outcome measures included cardiovascular complications, cerebrovascular complications, pulmonary complications, wound dehiscence, and infection. Inpatient and hospital demographics including primary diagnosis, age, gender, primary payer, hospital teaching status, Charlson Comorbidity Index score, hospital bed size, location, and median household income were analyzed. Logistic regression analysis of OA vs RA patients with patient outcomes revealed that osteoarthritic THA candidates had lower risk for cardiovascular complications, pulmonary complications, wound dehiscence, infections, and systemic complications, compared to rheumatoid patients. There was a significantly elevated risk of cerebrovascular complication in osteoarthritic THA compared to RA THA. OA patients undergoing TKA had significantly higher risk for cardiovascular and cerebrovascular complications. There were significant decreases in mechanical wounds, infection, and systemic complications in the OA TKA patients. RA patients are at higher risk for postoperative infection, wound dehiscence, and systemic complications after TKA and THA compared to OA patients. These findings highlight the importance of preoperative medical clearance and management to optimize RA patients and improve the postoperative outcomes.

Establishment of CRISPR/Cas9 in Alternaria alternata.

The filamentous fungus Alternaria alternata is a potent producer of many secondary metabolites, some of which like alternariol or alternariol-methyl ether are toxic and/or cancerogenic. Many Alternaria species do not only cause post-harvest losses of food and feed, but are aggressive plant pathogens. Despite the great economic importance and the large number of research groups working with the fungus, the molecular toolbox is rather underdeveloped. Gene deletions often result in heterokaryotic strains and therefore, gene-function analyses are rather tedious. In addition, A. alternata lacks a sexual cycle and classical genetic approaches cannot be combined with molecular biological methods. Here, we show that CRISPR/Cas9 can be efficiently used for gene inactivation. Two genes of the melanin biosynthesis pathway, pksA and brm2, were chosen as targets. Several white mutants were obtained after several rounds of strain purification through protoplast regeneration or spore inoculation. Mutation of the genes was due to deletions from 1bp to 1.5kbp. The CRISPR/Cas9 system was also used to inactivate the orotidine-5-phosphate decarboxylase gene pyrG to create a uracil-auxotrophic strain. The strain was counter-selected with fluor-orotic acid and could be re-transformed with pyrG from Aspergillus fumigatus and pyr-4 from Neurospora crassa. In order to test the functioning of GFP, the fluorescent protein was fused to a nuclear localization signal derived from the StuA transcription factor of Aspergillus nidulans. After transformation bright nuclei were visible.

A Meta-Analysis Comparing All-Polyethylene Tibial Component to Metal-Backed Tibial Component in Total Knee Arthroplasty: Assessing Survivorship and Functional Outcomes.

BACKGROUND: This meta-analysis compares the clinical performance of all-polyethylene tibial (APT) to the metal-backed tibial (MBT) components. METHODS: We included comparative studies in primary total knee arthroplasty involving APT and MBT implant components. The primary outcomes were function, durability, and reports of adverse events. RESULTS: Twenty-eight articles with 95 847 knees were available for synthesis. The meta-analysis showed an association of APT with lower revision rates (incidence rate ratio, 0.709; P = .002) and adverse events (incidence rate ratio, 0.785; P = .204). Moderator analyses were performed to determine the effect of posterior cruciate ligament status on outcome, and no statistically significant effect was found for revision risk or adverse events incidence. CONCLUSION: All-polyethylene tibial components seem to be an equal option, with less financial burden than the MBT.

Perioperative Treatment of Patients with Rheumatoid Arthritis.

Rheumatoid arthritis is an autoimmune disease mediated by a widespread, chronic, and systematic inflammatory process that causes joint deterioration, which leads to pain, disability, and poor quality of life. The increased use of disease-modifying antirheumatic drugs has been shown to markedly slow disease progression, which has translated into a decrease in the need for orthopaedic intervention in this population. However, in a substantial percentage of patients with the disease, optimal pharmacologic treatment fails and surgical intervention is required. A thorough understanding of medical considerations in these patients and improved knowledge of the medical complications caused by the disease process and the pharmacologic therapy used to treat it may lead to improved preoperative planning and medical clearance, which may ultimately improve the overall postoperative outcome.

Characterization of multifunctional ß-NaEuF4/NaGdF4 core-shell nanoparticles with narrow size distribution.

The properties of ß-NaEuF4/NaGdF4 core-shell nanocrystals have been thoroughly investigated. Nanoparticles with narrow size distribution and an overall diameter of ∼22 nm have been produced with either small ß-NaEuF4 cores (∼3 nm diameter) or large ß-NaEuF4 cores (∼18 nm diameter). The structural properties and core-shell formation are investigated by X-ray diffraction, transmission electron microscopy and electron paramagnetic resonance, respectively. Optical luminescence measurements and X-ray photoelectron spectroscopy are employed to gain information about the optical emission bands and valence states of the rare earth constituents. Magnetic characterization is performed by SQUID and X-ray magnetic circular dichroism measurements at the rare earth M(4,5) edges. The characterization of the core-shell nanoparticles by means of these complementary techniques demonstrates that partial intermixing of core and shell materials takes place, and a significant fraction of europium is present in the divalent state which has significant influence on the magnetic properties. Hence, we obtained a combination of red emitting Eu(3+) ions and paramagnetic Gd(3+) ions, which may be highly valuable for potential future applications.

Perioperative Treatment of Patients with Rheumatoid Arthritis.

Rheumatoid arthritis is an autoimmune disease mediated by a widespread chronic systematic inflammatory process that causes joint deterioration, which leads to pain, disability, and poor quality of life. The increased use of disease-modifying antirheumatic drugs has been shown to markedly slow disease progression, which has translated into a decrease in the need for orthopaedic intervention in this population. However, a substantial percentage of patients with the disease fail optimal pharmacologic treatment and still require surgical intervention. A thorough understanding of medical considerations in these patients and improved knowledge of the medical complications caused by the disease process and the pharmacologic therapy used to treat it may lead to improved preoperative planning and medical clearance, which may ultimately improve the overall postoperative outcome.

Bee pollen and honey for the alleviation of hot flushes and other menopausal symptoms in breast cancer patients.

Hot flushes, night sweats, pain during sexual intercourse, hair loss, forgetfulness, depression and sleeping disturbances are common problems among breast cancer patients undergoing antihormonal treatment. The aim of this study was to investigate whether bee pollen can alleviate menopausal symptoms in patients receiving tamoxifen and aromatase inhibitors/inactivators. We compared a pollen-honey mixture with pure honey (placebo) in a prospective, randomized crossover trial in breast cancer patients receiving antihormonal treatment. The menopausal complaints were assessed using the Menopause Rating Scale (MRS). A total of 46 patients were recruited; 68.3% (28/41) of the patients reported an improvement in their symptoms while taking honey, compared with 70.9% (22/31) who reported an improvement with pollen (the difference was non-significant). The results were confirmed by significant improvements in the postmenopausal complaints in the two groups in a pre-post analysis in the MRS and its 3 subscales. This study provided evidence that honey and bee pollen may improve the menopausal symptoms of breast cancer patients on antihormonal treatment. Of note, honey, which was intended to be used as a placebo, produced similar effects as pollen and they both exceeded the extent of a placebo effect in this setting (~25%).

Renal and Gastrointestinal Considerations in Joint Replacement Surgery.

Renal and gastrointestinal diseases affect a significant portion of the general population. The process of decision making regarding surgical clearance and pre-operative management of the various complexities and medical conditions associated with these diseases hence becomes crucial. To optimize postoperative outcomes, the considerations for the care of this patient population revolve around effective management of hemostasis and electrolyte status. This subset of conditions is uniquely important with regard to the negative impact of improper administration of medications and perioperative care on patients' prognoses. A thorough understanding and knowledge of standards of care and treatment guidelines for patients with renal dysfunction and gastrointestinal disease assures comprehensive preoperative planning and surgical clearance. This may ultimately lead to improvement of surgical outcomes and potential decrease in postoperative morbidity and mortality.

Ultrafine sanding paper: a simple tool for creating small particles.

A top-down approach, i.e., creating small particles by mechanical force starting from bulk materials, probably presents the most logical approach to particle size reduction and, therefore, top-down techniques are among the first to achieve small particles. A new solvent-free, amazingly simple approach is reported, suitable to achieve nanoparticles and sub-micro particles.

Intrinsic focusing of the particle size distribution in colloids containing nanocrystals of two different crystal phases.

We have studied the Ostwald ripening of colloids containing nanocrystals of two different crystal phases of the same material. Ostwald ripening in such polymorphic systems is shown to result in an intrinsic focusing of the particle size distribution of the thermodynamically preferred phase while the particles of the less stable phase completely dissolve. Experimentally, a colloidal system of this kind was realized by mixing small NaEuF4 nanocrystals of the cubic α-phase with particles of the hexagonal ß-phase having the same mean size and size distribution. The temporal evolution of the particle sizes of both phases can be understood and numerically simulated within the framework of LSW theory. The simulations show that small differences in the bulk solubility or the surface energy of the two phases are sufficient to explain the experimentally observed narrowing of the particle size distribution.

Photoluminescence study of nanocrystalline Y2O3:Ho3+ phosphor.

The Y2O3:Ho(3+) powder phosphors have been prepared by using low temperature combustion method. Powder X-ray diffraction, scanning electron microscope and transmission electron microscopy techniques were used to characterize the as-prepared phosphor. The UV-Vis-NIR absorption, excitation and emission studies have been performed and the phenomenological Judd-Ofelt intensity parameters which are critically important in calculating the radiative properties and stimulated emission crosssection have been calculated by using Judd-Ofelt theory. Based on the calculated values of the inter electronic parameter, covalency and bonding parameter the bonding between the Ho(3+) ions and surrounding oxygen atoms have been found to be covalent in nature. The color purity has also been verified by using the chromaticity diagram. The analysis shows that the Y2O3:Ho(3+) phosphor may be used for producing the green light emitting diodes and display applications.

Effect of the crystal structure of small precursor particles on the growth of ß-NaREF4 (RE = Sm, Eu, Gd, Tb) nanocrystals.

The origin of the narrow particle size distributions obtained in the oleic acid-based synthesis of hexagonal phase ß-NaREF(4) nanocrystals (RE = Sm, Eu, Gd, Tb) has been investigated. Compared to the standard synthesis, the growth conditions were simplified by using small purified particles of either α-NaREF(4) (cubic phase) or ß-NaREF(4) (hexagonal phase) as single-source precursors, thereby avoiding the complications arising from the simultaneous presence of molecular educts and intermediately formed small particles. The study shows that α-phase as well as ß-phase particles grow by Ostwald-ripening but narrow particle size distributions of the ß-NaREF(4) product particles are only obtained when α-phase precursor particles are employed. Since the small particles are also formed as intermediate products in the standard synthesis of ß-NaSmF(4), ß-NaEuF(4), ß-NaGdF(4) and ß-NaTbF(4) particles, their crystal phase is an important parameter to obtain a narrow size distribution in these systems.

An electron paramagnetic resonance spectroscopic investigation on the growth mechanism of NaYF4:Gd nanocrystals.

Doped nanocrystals of NaYF(4) and NaGdF(4) are currently studied as upconversion luminescence markers and magnetic resonance imaging contrast agents. An EPR investigation on the growth mechanism of NaYF(4):Gd and NaGdF(4) nanocrystals showed that these nanomaterials grow in the standard oleic acid-based reaction medium by a dissolution/recrystallization mechanism and not by the aggregation or oriented attachment of smaller particles.