Adjusting the Low Energy Threshold for Large Bodies in PET

The performance of a PET scanner on three different phantom sizes was studied as a function of low energy threshold (LET). Phantom cross sections ranged from 20 cm diameter circular to 28 cm x 43 cm oval and LET\u27\u27s ranged from 350 keV to 475 keV, in 25 keV increments. System sensitivity, scatter fraction, and NEC were measured over a wide range of radioactivity levels. Increasing the low energy threshold lowered both sensitivity and scatter fraction. The statistical quality of the raw data was maximized for the 425 keV setting for all three phantoms. System stability and uniformity of response was also studied for 375 keV to 450 keV thresholds, and indicated acceptable performance for this system through 425 keV

Image Quality vs. NEC in 2D and 3D PET

To investigate the relationship between NEC and image quality to 2D and 3D PET, while simultaneously optimizing 3D low energy threshold (LET), we have performed a series of phantom measurements. The phantom consisted of 46 1 cm fillable hollow spheres on a random grid inside a water-filled oval cylinder, 21 cm tall, 36 cm wide, and 40 cm long. The phantom was imaged on a Discovery ST PET/CT system (GE Healthcare, Milwaukee, WI) in a series of 3 min scans as it decayed from an activity of 7.2 mCi. The scans included LET settings of 375,400, and 425 keV in 3D, and 375 keV in 2D. Image signal-to-noise (SNR) was calculated and compared wash NEC. While both NEC and image quality in 3D improved for LETs above the default of 375 keV, we found that there were significant differences between NEC and image quality for 2D and 3D. Most importantly, 3D image-quality was strongly dependent on the reconstruction algorithm and its associated parameters. In conclusion, a direct measure of image quality as necessary for comparing 2D vs. 3D performance

Explorando o efeito das experiências de avaliação de professores na satisfação profissional de professores americanos

Teacher satisfaction is a key affective reaction to working conditions and an important predictor of teacher attrition. Teacher evaluation as a tool for measuring teacher quality has been one source of teacher stress in recent years in the United States. There is a growing body of evidence on how to evaluate teachers in ways which support their growth and development as practitioners. For this study, we inquired: What is the relationship between supportive teacher evaluation experiences and U.S. teachers’ overall job satisfaction? To answer this question, we employed a multilevel regression analysis to multiply-imputed data on U.S. lower-secondary teachers’ experiences from the 2013 Teaching and Learning International Survey (TALIS). We found a small, positive relationship between the perceptions of supportive teacher evaluation experiences and U.S. secondary teachers’ satisfaction after controlling for other important teacher and school characteristics and working conditions. Further, teachers who felt their evaluation led to positive changes in their practice had higher satisfaction. Teachers whose primary evaluator was a fellow teacher as opposed to the principal also had higher satisfaction on average. We discuss the implications of these findings for school leaders as well as future teacher evaluation policy.La satisfacción del maestro es una reacción afectiva clave a las condiciones de trabajo y un importante predictor del desgaste del docente. La evaluación de los maestros como una herramienta para medir la calidad de los docentes ha sido una de las causas del estrés docente en los últimos años en los Estados Unidos. Existe un cuerpo creciente de evidencia sobre cómo evaluar a los maestros de maneras que apoyen su crecimiento y desarrollo como profesionales. Para este estudio, preguntamos: ¿Cuál es la relación entre las experiencias de evaluación docente y la satisfacción laboral general de los docentes de EE. UU.? Para responder a esta pregunta, empleamos un análisis de regresión multinivel para datos de imputación múltiple en las experiencias de docentes de secundaria de EE. UU. De la Encuesta Internacional de Enseñanza y Aprendizaje 2013 (TALIS). Encontramos una relación pequeña y positiva entre las percepciones de las experiencias de evaluación docente de apoyo y la satisfacción de los docentes de secundaria de los EE. UU. Después de controlar otras características importantes del docente y la escuela y las condiciones de trabajo. Además, los maestros que sintieron que su evaluación llevó a cambios positivos en su práctica tuvieron una mayor satisfacción. Los docentes cuyo evaluador principal fue un compañero profesor en comparación con el director también tuvieron una mayor satisfacción en promedio. Discutimos las implicaciones de estos hallazgos para los líderes escolares, así como la política futura de evaluación docente.A satisfação do professor é uma reação afetiva fundamental às condições de trabalho e um importante preditor do desgaste do professor. A avaliação dos professores como uma ferramenta para medir a qualidade dos professores tem sido uma das causas do estresse do professor nos últimos anos nos Estados Unidos. Há um crescente corpo de evidências sobre como avaliar os professores de forma a apoiar seu crescimento e desenvolvimento como profissionais. Para este estudo, perguntamos: Qual é a relação entre as experiências de avaliação do apoio ao professor e a satisfação geral do trabalho dos professores de EE. UU? Para responder a essa questão, utilizamos uma análise de regressão multinível para dados de múltiplas imputações nas experiências de professores do ensino médio em EE. UU Do Inquérito Internacional de Ensino e Aprendizagem 2013 (TALIS). Encontramos uma relação pequena e positiva entre as percepções das experiências de avaliação do apoio ao professor e a satisfação dos professores do ensino médio nos EUA. UU Depois de controlar outras características importantes do professor e da escola e condições de trabalho. Além disso, os professores que sentiram que sua avaliação levou a mudanças positivas em sua prática tiveram maior satisfação. Os professores cujo principal avaliador era um colega professor em comparação com o diretor também tiveram uma satisfação maior em média. Discutimos as implicações dessas descobertas para os líderes das escolas, bem como a futura política de avaliação de professores

Recombination in bdelloid rotifer genomes: asexuality, transfer and stress

Bdelloid rotifers constitute a class of microscopic animals living in freshwater habitats worldwide. Several strange features of bdelloids have drawn attention: their ability to tolerate desiccation and other stresses, a lack of reported males across the clade despite centuries of study, and unusually high numbers of horizontally acquired, non-metazoan genes. Genome sequencing is transforming our understanding of their lifestyle and its consequences, while in turn providing wider insights about recombination and genome organisation in animals. Many questions remain, not least how to reconcile apparent genomic signatures of sex with the continued absence of reported males, why bdelloids have so many horizontally acquired genes, and how their remarkable ability to survive stress interacts with recombination and other genomic processes

Investigating the Optimum Lower Energy Threshold of a New Research PET/CT Scanner

An investigation of the optimum 3D lower energy threshold (LET) setting of the Discovery-RX, a new LYSO based GE research PET/CT scanner is conducted. Sensitivity and noise equivalent count rate (NECR) performance of the scanner in 3D mode were evaluated at multiple LET settings: 400, 425, 450, 460, 470 and 480 KeV. The performance evaluations were conducted according to the NEMA NU2-2001 standard. In addition, the NECR was also evaluated for the same LET settings using the Data Spectrum whole body phantom in order to more accurately simulate a true clinical setting. For the sensitivity measurements, the line source was filled with 9.25 MBq of F-18. For the NECR measurements, the NEMA and the Data Spectrum phantoms were fitted with a line source having an initial activity of 1400 MBq of F-18. As expected, the sensitivity decreases with increasing LET. The sensitivity at 400 and 450 keV was 13.2% higher and 18.9% lower than the sensitivity at the scanners default LET of 425 keV. Also as expected, the scatter fraction (SF) decreased with increasing LET for both NECR phantoms. The NECR curve corresponding to the 450 keV had the highest values over the clinical range of activity concentration usually used. Initial performance evaluation suggests that a LET of 450 keV is the best setting for the phantoms tested. Further clinical tests are needed to validate this observation

First-in-Human Phase I Study to Evaluate the Brain-Penetrant PI3K/mTOR Inhibitor GDC-0084 in Patients with Progressive or Recurrent High-Grade Glioma.

PurposeGDC-0084 is an oral, brain-penetrant small-molecule inhibitor of PI3K and mTOR. A first-in-human, phase I study was conducted in patients with recurrent high-grade glioma.Patients and methodsGDC-0084 was administered orally, once daily, to evaluate safety, pharmacokinetics (PK), and activity. Fluorodeoxyglucose-PET (FDG-PET) was performed to measure metabolic responses.ResultsForty-seven heavily pretreated patients enrolled in eight cohorts (2-65 mg). Dose-limiting toxicities included 1 case of grade 2 bradycardia and grade 3 myocardial ischemia (15 mg), grade 3 stomatitis (45 mg), and 2 cases of grade 3 mucosal inflammation (65 mg); the MTD was 45 mg/day. GDC-0084 demonstrated linear and dose-proportional PK, with a half-life (∼19 hours) supportive of once-daily dosing. At 45 mg/day, steady-state concentrations exceeded preclinical target concentrations producing antitumor activity in xenograft models. FDG-PET in 7 of 27 patients (26%) showed metabolic partial response. At doses ≥45 mg/day, a trend toward decreased median standardized uptake value in normal brain was observed, suggesting central nervous system penetration of drug. In two resection specimens, GDC-0084 was detected at similar levels in tumor and brain tissue, with a brain tissue/tumor-to-plasma ratio of >1 and >0.5 for total and free drug, respectively. Best overall response was stable disease in 19 patients (40%) and progressive disease in 26 patients (55%); 2 patients (4%) were nonevaluable.ConclusionsGDC-0084 demonstrated classic PI3K/mTOR-inhibitor related toxicities. FDG-PET and concentration data from brain tumor tissue suggest that GDC-0084 crossed the blood-brain barrier

Optimizing Sequential Dual Tracer P.E.T. Studies using a Combined 2D/3D Imaging Protocol

We have investigated a combined 2D/3D protocol for minimizing contamination in dual tracer P.E.T. studies in which the tracers are administered on a timescale that is short compared to the half-lives. We have performed a series of phantom studies on an Advance and a Discovery ST (GE Healthcare Technologies), using a torso phantom with cardiac insert (Data Spectrum Corporation) to simulate a combined FDG and NH3 scan protocol for a patient with ischemia. The phantom was imaged in a series of alternating 2D/3D acquisitions as it decayed over 6 half-lives. By comparing 2D and 3D images, we have verified that 3D images are of comparable accuracy to 2D images, even with realistic out-of-field activity challenging the 3D scans. Based on scan and image statistical quality, we have recommended optimal doses for maximizing the image quality of both scans

Synthesis and Characterization of Pyridine-Armed Reinforced Macrocycles and Their Transition Metal Complexes as Potential Oxidation Catalysts

Oxidation catalysts stable in aqueous solution under both harsh pH\u27s and at high temperature would be environmentally friendly alternatives to current technologies. Transition metal complexes of tetraazamacrocycles reinforced with additional ethylene bridges have produced such oxidation catalysts. A controlling aspect of the usefulness of any metal catalyst is its set of oxidation and reduction potentials. Reversible redox processes that bracket a potential window within which useful oxidation of substrate molecules can occur are desirable. Though quite robust, and exhibiting reversible electrochemistry, some reinforced macrocycle complexes are not useful catalysts because their redox potentials are not in a desired potential range. An established method of modifying the electrochemical properties of a transition metal complex is to modify the ligand, which subsequently modifies the properties of its complexed metal ion. We wished to determine if the addition of pyridine pendant arms to the known reinforced macrocycle ligands would result in beneficial shifts in the redox potentials of their transition metal complexes. The resulting ligands must allow at least one open coordination site on the bound metal ion for oxidant and/or substrate binding. We have synthesized and characterized both cross-bridged and side-bridged cyclen and cyclam tetraazamacrocycles with pyridine pendant arms. Cobalt, nickel, copper, and zinc complexes were made. The synthesis and characterization of the ligands and the synthesis and characterization of their complexes will be presented