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"Estudo comparativo da cefalometria do perfil tegumentar com base na análise facial de Arnett relacionada à horizontal verdadeira com a realizada a partir do plano de Frankfurt horizontal"; A comparative study of the cephalometric of the soft tissue profile based on Arnett´s facial analysis in relation to the true horizontal as this has been put into practice starting from the Frakfurt horizontal plane.

Sousa, Cláudia Maria Romano de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/03/2007 PT
Relevância na Pesquisa
25.98%
Nesta pesquisa foi comparada a diferença das medidas obtidas utilizando-se a análise cefalométrica do perfil tegumentar tendo como base a análise facial de Arnett relacionada à Horizontal Verdadeira com a análise cefalométrica do perfil tegumentar feita a partir do Plano de Frankfurt. Utilizamos 140 radiografias cefalométricas requisitadas como parte de documentação ortodôntica, obtidas de pacientes com idade variando de 06 a 49 anos, sendo 64 do sexo masculino e 76 do sexo feminino, pertencentes ao arquivo do IOM - (Instituto de Odontologia Multidisciplinar) ? RJ. As radiografias cefalométricas em norma lateral foram obtidas pelo mesmo operador, obedecendo ao protocolo adotado pelo IOM. Todos os pacientes foram orientados a assumir a Posição Natural da Cabeça, tendo como referência um espelho posicionado a frente e a Linha Vertical Verdadeira foi obtida por meio da utilização de um fio metálico unido à um prumo de chumbo, posicionado próximo à margem anterior do chassi porta-filme, de forma que apareça à frente do perfil tegumentar do paciente. A partir das medidas lineares obtidas nas Análises Cefalométricas dos Tecidos Moles, foram realizadas análises estatísticas visando dois objetivos: comparar as medidas de A à I obtidas nos traçados (um utilizando como referência uma perpendicular ao Plano Horizontal de Frankfurt e o outro à Linha Vertical Verdadeira) e analisar os resultados comparativamente. Após a análise estatística (Kolmogorov-Smirnov...

Douramento com laser de vidro cristal

Pires, Mariana Raquel de Sousa
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
POR
Relevância na Pesquisa
16.01%
Os processos térmicos de decoração a ouro das garrafas Rome de vidro cristal produzidas na fábrica Atlantis® levam ao aparecimento de defeitos resultantes das elevadas temperaturas de cura das tintas de ouro, próximas da temperatura de amolecimento do vidro. De forma a minimizar os defeitos provenientes da cura tradicional num forno, no presente trabalho as amostras de vidro cristal com uma camada de tinta de ouro foram tratadas com um laser de Nd:YAG ( =1064 nm). As amostras foram pintadas com tinta de ouro para pincel e uma tinta de ouro para decalque, ambas utilizadas na decoração das garrafas Rome na fábrica Atlantis®. As tintas de ouro foram caracterizadas através de análise termogravimétrica (ATG) e espetroscopia de dispersão de energia (EDS) de forma a identificar os constituintes das tintas e os processos de decomposição. O douramento com laser foi efetuado utilizando os modos de varrimento com feixe em linha (com o auxílio de uma mesa móvel) e com feixe em serpentina (com o auxílio de uma cabeça galvanométrica). O varrimento em linha demonstrou ser o mais vantajoso para a tinta de ouro a pincel, obtendo-se uma película brilhante e uniforme, contudo sem boa adesão ao substrato. De forma a solucionar a falta de adesão após douramento a laser efetuaram-se tratamentos térmicos num forno a temperaturas inferiores às utilizadas na fábrica para decoração das garrafas Rome: 380...

Chiral discrimination in a monolayer of a triple-chain phosphatidylcholine.

Bringezu, F; Brezesinski, G; Nuhn, P; Möhwald, H
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1996 EN
Relevância na Pesquisa
15.72%
Monolayers of an enantiomeric and a racemic triple-chain phosphatidylcholine (PC) at the air/water interface are studied by film balance measurements and x-ray diffraction. Although the area per three tails exceeds that per head, we observe tail ordering dependent on headgroup chirality and chain tilt. This indicates lateral headgroup interactions. The influence of the chiral carbon is suppressed at higher lateral pressures, and a centered-rectangular unit cell with tails tilted into the nearest neighbor (NN) direction is observed for both the enantiomer and the racemate. The distortion of the lattice changes at medium pressures from NN to NNN (next-nearest neighbor direction) with decreasing temperature. The phase behavior of the racemate at 15 degrees C is compared with that of a triple-chain PC with a branched chain of reduced length. Whereas the PC with the longer branched chain exhibits only a NN tilted phase at all pressures, the PC with the shorter branched chain has a rich polymorphism (NNN-NN-upright hexagonal packing) under increased lateral pressure.

3D dosimetry by optical-CT scanning

Oldham, Mark
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2006 EN
Relevância na Pesquisa
15.72%
The need for an accurate, practical, low-cost 3D dosimetry system is becoming ever more critical as modern dose delivery techniques increase in complexity and sophistication. A recent report from the Radiological Physics Center (RPC) (1), revealed that 38% of institutions failed the head-and-neck IMRT phantom credentialing test at the first attempt. This was despite generous passing criteria (within 7% dose-difference or 4mm distance-to-agreement) evaluated at a half-dozen points and a single axial plane. The question that arises from this disturbing finding is – what percentage of institutions would have failed if a comprehensive 3D measurement had been feasible, rather than measurements restricted to the central film-plane and TLD points? This question can only be adequately answered by a comprehensive 3D-dosimetry system, which presents a compelling argument for its development as a clinically viable low cost dosimetry solution. Optical-CT dosimetry is perhaps the closest system to providing such a comprehensive solution. In this article, we review the origins and recent developments of optical-CT dosimetry systems. The principle focus is on first generation systems known to have highest accuracy but longer scan times.

Investigation of the feasibility of relative 3D dosimetry in the Radiologic Physics Center Head and Neck IMRT phantom using Presage/optical-CT

Sakhalkar, Harshad; Sterling, David; Adamovics, John; Ibbott, Geoffrey; Oldham, Mark
Fonte: American Association of Physicists in Medicine Publicador: American Association of Physicists in Medicine
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
25.81%
This study presents the application of the Presage∕optical-CT 3D dosimetry system for relative dosimetry in the Radiologic Physics Center (RPC) Head and Neck (H&N) IMRT phantom. Performance of the system was evaluated by comparison with the “gold-standard” RPC credentialing test. A modified Presage cylindrical insert was created that extended the capability of the RPC H&N phantom to 3D dosimetry. The RPC phantom was taken through the entire treatment planning procedure with both the standard RPC insert and the modified Presage insert. An IMRT plan was created to match the desired dose constraints of the credentialing test. This plan was delivered twice to the RPC phantom: first containing the standard insert, and then again containing the Presage insert. After irradiation, the standard insert was sent for routine credentialing analysis; including point dose measurements (TLD) and planar Gafchromic® EBT film measurement. The 3D dose distribution from Presage was read out at Duke using the OCTOPUS™ 5X optical-CT scanner. The Presage distribution was compared with gold-standard EBT measurement (determined by the RPC) and the calculated Eclipse distribution. The agreement between the normalized EBT, Presage, and Eclipse distributions...

Dosimetrie und Qualitätssicherung bei fluenzmodulierten Bestrahlungstechniken (IMRT) in der Strahlentherapie; Dosimetry and Quality Assurance for Intensity Modulated Radiotherapy (IMRT)

Bakai, Annemarie
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
26.02%
Fluenzmodulierte Bestrahlungstechniken (IMRT) in der Strahlentherapie haben sich trotz ihres hohen Potentials bisher vielerorts noch nicht als Standardverfahren etablieren können. Dies hängt wesentlich mit den hohen Anforderungen der IMRT an die Qualitätssicherung zusammen. Im Rahmen der vorliegenden Arbeit erfolgte die kritische Auseinandersetzung mit dem physikalischen Qualitätsmanagement bei statischen (Step & Shoot) IMRT-Techniken. Schwerpunkte der Untersuchungen waren die Entwicklung eines Verfahrens für die effiziente klinische IMRT-Dosimetrie basierend auf Messungen mit einem Ionisationskammer-Array (PTW LA48) sowie die Prüfung verschiedener Plausibilitätstests – etwa zur Abschätzung der bei einer Bestrahlung benötigten Monitorwerte. Daneben wurden Konzepte für die reproduzierbar korrekte Patientenpositionierung bei Prostata-Bestrahlungen sowie für die Berücksichtigung von Lagerungs-Restunsicherheiten während der IMRT-Bestrahlungsplanung erarbeitet. Für die IMRT-Bestrahlungsplanung steht in Tübingen ein hauseigenes System zur Verfügung, in welches ein schneller Monte-Carlo-Code (XVMC) für Routine-Präzisionsdosisberechnungen integriert ist. Die Genauigkeit dieses Codes – insbesondere die Validität des darin enthaltenen Beschleunigerkopfmodells – wurde kritisch geprüft. Die Arbeit präsentiert Beispiele klinischer Dosimetrievergleiche...

Structure, wettability, and barrier properties of self-assembled monolayers on metallic surfaces

Srivastava, Piyush
Fonte: Universidade Rice Publicador: Universidade Rice
ENG
Relevância na Pesquisa
15.72%
Self-assembled monolayers (SAMs) offer a convenient approach for fabricating molecularly tailored interfaces with well-defined compositions, structures, and thicknesses. SAMs have been suggested for use as corrosion barriers, antifouling coatings, and as components of molecular electronics and lithography. Still, researchers lack the molecular description of the interfacial properties, structural features, and barrier properties of SAMs that would be useful for optimizing and tailoring the behavior of SAMs. This dissertation makes connections between the molecular level structural features of SAMs and macroscopic properties such as wettability and barrier properties using molecular dynamics (MD) simulations and experimental techniques. MD simulations were performed to explain the unexpected experimental observation that the wetting properties of some liquids on SAMs prepared using alkanethiols (CnSH) depend on whether the chain length (n) is odd or even. The difference in near-surface structure of the liquid (and not that of reorganization events by the monolayer) appears responsible for the high sensitivity of hexadecane and the general insensitivity of water to the structural differences expressed by odd- and even-chained monolayer surfaces. MD simulations were also performed to investigate the influences of molecular structure on the ability of n-alkanethiolate SAMs on gold and copper to act as barrier films against through-film oxygen transport as relevant to the uses of these films in corrosion inhibition. The barrier resistances offered by these films towards oxygen transport...

Morphometry of the spinal canal at cervical region in asymptomatic military young men

Malzac, Augustin; Barros Filho, Tarcísio Eloy Pessoa de
Fonte: Acta Ortopédica Brasileira Publicador: Acta Ortopédica Brasileira
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
15.82%
Spinal canal measurements obtainned from radiographic imaging studies are an integral part of diagnostic evaluation of cervical spine stenosis. Before abnormal spinal morphometry can be determined, it is first necessary to establish normal values for the specific patient population being evaluated. Cervical spinal canal stenosis increase risk of quadriplegia after "minor trauma" in the head or neck, mainly in athletes who participate in contact or collision sports. Prospective and random selection of 500 plain film of the lateral cervical spine in young militaries population in age group 18-20 years old. Those were performed a hundred set of film were for each geographic region, including Manaus, Recife, São Paulo, Porto Alegre and Campo Grande. The first part of this study established normal values for cervical morphometry. The second part determined the most accurate screenning method for detecting cervical spinal stenosis. Normal spinal canal mean value for C3 was 18,27mm, C4 17,98mm, C5 18,33mm and 18,76mm in C6. The TORG ratio was evaluated as a method to detect significant cervical spinal stenosis and was shown to have sensitivity and high positive predictive value. It was observed TORG's ratio of 0,80 or less in 14,4% of the X-rays.; A medição do diâmetro sagital do canal vertebral é parte integrante da avaliação diagnóstica de estenose da coluna cervical. Antes de identificar a morfometria anormal é necessário estabelecer valores normais para uma população específica. A estenose do canal cervical pode se converter em fator agravante na vigência de um "trauma menor" na cabeça ou no pescoço...

Relationship between maxillary and mandibular base lengths and dental crowding in patients with complete Class II malocclusions

JANSON, Guilherme; GOIZUETA, Oscar Edwin Francisco Murillo; GARIB, Daniela G.; JANSON, Marcos
Fonte: E H ANGLE EDUCATION RESEARCH FOUNDATION, INC Publicador: E H ANGLE EDUCATION RESEARCH FOUNDATION, INC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.72%
Objective: To verify the relationship between maxillary and mandibular effective lengths and dental crowding in patients with Class II malocclusions. Materials and Methods: The sample comprised 80 orthodontic patients with complete Class II malocclusions in the permanent dentition (47 male, 33 female) who were divided into two groups according to the amount of mandibular tooth-arch size discrepancy. The maxillary and mandibular effective lengths (Co-A and Co-Gn) and tooth-arch size discrepancies were measured on the initial cephalograms and dental casts, respectively. Intergroup comparisons of apical base lengths were performed with independent t-tests. Correlation between base length and dental crowding was examined by means of Pearson's correlation coefficient (P < .05). Results: Patients with Class II malocclusion and moderate to severe crowding had significantly smaller maxillary and mandibular effective lengths than subjects with the same malocclusion and slight mandibular crowding. A weak inverse correlation was also found between maxillary and mandibular effective lengths and the severity of dental crowding. Conclusion: Decreased maxillary and mandibular effective lengths constitute an important factor associated with dental crowding in patients with complete Class II malocclusion. (Angle Orthod. 2011;81:217-221.)

Monte Carlo Simulation of Siemens ONCOR Linear Accelerator with BEAMnrc and DOSXYZnrc Code

Jabbari, Keyvan; Anvar, Hossein Saberi; Tavakoli, Mohammad Bagher; Amouheidari, Alireza
Fonte: Medknow Publications & Media Pvt Ltd Publicador: Medknow Publications & Media Pvt Ltd
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
26.01%
The Monte Carlo method is the most accurate method for simulation of radiation therapy equipment. The linear accelerators (linac) are currently the most widely used machines in radiation therapy centers. In this work, a Monte Carlo modeling of the Siemens ONCOR linear accelerator in 6 MV and 18 MV beams was performed. The results of simulation were validated by measurements in water by ionization chamber and extended dose range (EDR2) film in solid water. The linac's X-ray particular are so sensitive to the properties of primary electron beam. Square field size of 10 cm × 10 cm produced by the jaws was compared with ionization chamber and film measurements. Head simulation was performed with BEAMnrc and dose calculation with DOSXYZnrc for film measurements and 3ddose file produced by DOSXYZnrc analyzed used homemade MATLAB program. At 6 MV, the agreement between dose calculated by Monte Carlo modeling and direct measurement was obtained to the least restrictive of 1%, even in the build-up region. At 18 MV, the agreement was obtained 1%, except for in the build-up region. In the build-up region, the difference was 1% at 6 MV and 2% at 18 MV. The mean difference between measurements and Monte Carlo simulation is very small in both of ONCOR X-ray energy. The results are highly accurate and can be used for many applications such as patient dose calculation in treatment planning and in studies that model this linac with small field size like intensity-modulated radiation therapy technique.

Neonatal skin temperature distribution using infra-red colour thermography.

Clark, R P; Stothers, J K
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1980 EN
Relevância na Pesquisa
15.72%
1. Infra-red Colour Thermography was used to visualize skin temperatures over seven neonates nursed in a modified temperature controlled incubator. 2. Temperature distributions were recorded on cine film which was analysed to evaluate mean skin temperatures; these were subsequently compared with values obtained from multiple, weighted measurements from a thermocouple thermometer. In all cases, there was agreement to within +/- 0 . 6 degrees C. 3. Thermograms in thermo-neutral conditions (approximately 32 degrees C) showed a temperature distribution with the warmest skin overlying the central hot 'core' and temperatures falling towards the extremities. Temperature patterns in a cooler environment (approximately 28 degrees C) showed features due to the conductive or thermogenic nature of the structures underlying the skin. 4. Multiple skin temperature recordings made at two environmental temperatures were obtained from a further twelve infants. 5. Linear regression of skin temperature against rectal--environmental difference, performed for each of the measured sites, showed that the upper arm and, to a lesser extent, the upper thigh temperatures represented the mean value most closely. The upper abdomen and head were both warmer and less responsive to environmental change than the mean skin temperature. These findings were supported by the thermographic observations.

Dosimetric analysis of beam-matching procedure of two similar linear accelerators

Bhangle, Janhavi R.; Narayanan, V. K. Sathiya; Kumar, Namitha K.; Vaitheeswaran, R.
Fonte: Medknow Publications Pvt Ltd Publicador: Medknow Publications Pvt Ltd
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
15.82%
Linear accelerators from the same vendor in a radiation therapy center are usually beam-matched following Vendor's acceptance criteria. This protocol is limited to check the difference at particular points on the ionization curve for depth dose or beam profiles. This article describes different tests done after commissioning to evaluate the level of agreement between matched beams of two ONCOR Impression plus linear accelerators from Siemens. Total scatter factors, collimator scatter factors, wedge transmission factors were measured in water for 6-MV photon. All these factors for ONCOR2 were within ±1% of those values for ONCOR1. Along with these point dose measurements we have essentially used γ-index to compare the planar dose distribution from two beam-matched accelerators. For this study a set of ready packed EDR2 films was exposed on both accelerators. The set consisted of films for percentage depth dose, beam profiles, a pyramid shape, multileaf collimator's positional and dose delivery accuracy, and a film to compare head scatter at tray level. To include treatment planning system calculations, a film kept in axial plane was exposed to 3DCRT and IMRT plans with actual gantry angles and monitor units. These films were analyzed for γ in OmniPro IMRT software using different combinations of Δdose and - Δdistances. All these films have shown good agreement for - Δdistance of 3 mm and Δdose of 3 %.

Morphometry of the spinal canal at cervical region in asymptomatic military young men

Malzac,Augustin; Barros Filho,Tarcísio Eloy Pessoa de
Fonte: Sociedade Brasileira de Ortopedia e Traumatologia Publicador: Sociedade Brasileira de Ortopedia e Traumatologia
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2002 EN
Relevância na Pesquisa
15.82%
Spinal canal measurements obtainned from radiographic imaging studies are an integral part of diagnostic evaluation of cervical spine stenosis. Before abnormal spinal morphometry can be determined, it is first necessary to establish normal values for the specific patient population being evaluated. Cervical spinal canal stenosis increase risk of quadriplegia after "minor trauma" in the head or neck, mainly in athletes who participate in contact or collision sports. Prospective and random selection of 500 plain film of the lateral cervical spine in young militaries population in age group 18-20 years old. Those were performed a hundred set of film were for each geographic region, including Manaus, Recife, São Paulo, Porto Alegre and Campo Grande. The first part of this study established normal values for cervical morphometry. The second part determined the most accurate screenning method for detecting cervical spinal stenosis. Normal spinal canal mean value for C3 was 18,27mm, C4 17,98mm, C5 18,33mm and 18,76mm in C6. The TORG ratio was evaluated as a method to detect significant cervical spinal stenosis and was shown to have sensitivity and high positive predictive value. It was observed TORG's ratio of 0,80 or less in 14,4% of the X-rays.

Development of a 3-Dimensional Dosimetry System for Leksell Gamma Knife-Perfexion

Yoon, KyoungJun; Kwak, JungWon; Lee, DoHeui; Cho, ByungChul; Lee, SangWook; Ahn, SeungDo
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/03/2015
Relevância na Pesquisa
15.92%
The purpose of our study is to develop a new, 3-dimensional dosimetry system to verify the accuracy of dose deliveries in Leksell Gamma Knife-Perfexion TM (LGKP) (Elekta, Norcross, GA, USA). The instrument consists of a moving head phantom, an embedded thin active layer and a CCD camera system and was designed to be mounted to LGKP. As an active material concentrically located in the hemispheric head phantom, we choose Gafchromic EBT3 films and Gd2O2S;Tb phosphor sheets for dosimetric measurements. Also, to compensate the lack of backscatter, we located a 1 cm thick PMMA plate downstream of the active layer. The PMMA plate was transparent for scintillation lights to reach the CCD with 1200x1200 pixels by a 5.2 um pitch. Using this system, three hundred images by a 0.2 mm slice gap were acquired under each of three collimator setups, i.e. 4 mm, 8 mm, and 16 mm, respectively. The 2D projected images taken by CCD camera were compared with the dose distributions measured by EBT3 films in the same conditions. All 2D distributions were normalized by the maximum values derived by fitting peaks for each collimator setup. The FWHM differences of 2D profiles between of CCD images and of film doses were measured to be less than 0.3 mm. The scanning task for whole peak regions took less than three minutes with the new instrument. It could be utilized as a QA tool for the Gamma Knife radiosurgery system instead of film dosimetry...

Universality classes and crossover scaling of Barkhausen noise in thin films

Laurson, Lasse; Durin, Gianfranco; Zapperi, Stefano
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/06/2013
Relevância na Pesquisa
15.81%
We study the dynamics of head-to-head domain walls separating in-plane domains in a disordered ferromagnetic thin film. The competition between the domain wall surface tension and dipolar interactions induces a crossover between a rough domain wall phase at short length-scales and a large-scale phase where the walls display a zigzag morphology. The two phases are characterized by different critical exponents for Barkhausen avalanche dynamics that are in quantitative agreement with experimental measurements on MnAs thin films.; Comment: 5 pages, 5 figures

Basal hydraulic system of a West Antarctic ice stream: constraints from borehole observations

Engelhardt, Hermann; Kamb, Barclay
Fonte: International Glaciological Society Publicador: International Glaciological Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em //1997
Relevância na Pesquisa
15.72%
Pressure and tracer measurements in boreholes drilled to the bottom of Ice Stream B, West Antarctica, are used to obtain information about the basal water conduit system in which high water pressures are developed. These high pressures presumably make possible the rapid movement of the ice stream. Pressure in the system is indicated by the borehole water level once connection to the conduit system is made. On initial connection, here also called "breakthrough" to the basal water system, the water level drops in a few minutes to an initial depth in the range 96- 117 m below the surface. These water levels are near but mostly somewhat deeper than the flotation level of about 100m depth (water level at which basal water pressure and ice overburden pressure are equal), which is calculated from depth-density profiles and is measured in one borehole. The conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed; the thickness of the gap δ has to be about 2 mm to account for the water-level drop on breakthrough, and about 4 mm to fit the results of a salt-tracer experiment indicating downstream transport at a speed of 7.5 mm s^-1. The above gap-conduit model is, however, ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole...

Strong motion earthquake accelerograms, digitized and plotted data, Volume I - uncorrected accelerograms; Part A - Accelerograms IA1 through IA20

Earthquake Engineering Research Laboratory,
Fonte: California Institute of Technology Publicador: California Institute of Technology
Tipo: Report or Paper; PeerReviewed Formato: application/pdf
Publicado em 01/01/1969
Relevância na Pesquisa
26.07%
Preface to the Series The object of the present series is to make available accurate digitized data prepared in a uniform way for all recorded strong-motion earthquakes. This first report is the initial step in a continuing data processing program which will ultimately include all past recorded earthquakes as well as current data as it is collected. In addition to digitized ground acceleration records, certain basic calculated information such as integrated velocity and displacement curves, response spectra, and Fourier spectra, will also be issued in a standard form. The existence of this standardized data will allow all investigators to begin with the same basic numerical data, and should thus reduce the scatter of numerical results, the meaning of which has sometimes been difficult to assess. In addition to an improvement in the consistency of numerical results, several other advantages will be derived from the standardized data. (1) A number of earthquake records will be available which have not hitherto been analyzed in any form; (2) Vertical component data will be available for all earthquakes, digitized on a simultaneous time basis with the two horizontal components; (3)A small overall improvement in data accuracy will result from the inclusion of corrections for baseline distortion on the original record...

CONE BEAM COMPUTED TOMOGRAPHY (CBCT) DOSIMETRY: MEASUREMENTS AND MONTE CARLO SIMULATIONS

Kim, Sangroh
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Dissertação Formato: 3120074 bytes; application/pdf
Publicado em //2010 EN_US
Relevância na Pesquisa
26.06%

Cone beam computed tomography (CBCT) is a 3D x-ray imaging technique in which the x-ray beam is transmitted to an object with wide beam geometry producing a 2D image per projection. Due to its faster image acquisition time, wide coverage length per scan, and fewer motion artifacts, the CBCT system is rapidly replacing the conventional CT system and becoming popular in diagnostic and therapeutic radiology. However, there are few studies performed in CBCT dosimetry because of the absence of a standard dosimetric protocol for CBCT. Computed tomography dose index (CTDI), a standardized metric in conventional CT dosimetry, or direct organ dose measurements have been limitedly used in the CBCT dosimetry.

This dissertation investigated the CBCT dosimetry from the CTDI method to the organ, effective dose, risk estimations with physical measurements and Monte Carlo (MC) simulations.

An On-Board Imager (OBI, Varian Medical Systems, Palo Alto, CA) was used to perform old and new CBCT scan protocols. The new CBCT protocols introduced both partial and full angle scan modes while the old CBCT protocols only used the full angle mode. A metal-oxide-semiconductor-field-effect transistor (MOSFET) and an ion chamber were employed to measure the cone beam CTDI (CTDICB) in CT phantoms and organ dose in a 5-year-old pediatric anthropomorphic phantom. Radiochromic film was also employed to measure the axial dose profiles. A point dose method was used in the CTDI estimation.

The BEAMnrc/EGSnrc MC system was used to simulate the CBCT scans; the MC model of the OBI x-ray tube was built into the system and validated by measurements characterizing the cone beam quality in the aspects of the x-ray spectrum...

Toward Accurate Small Animal Dosimetry and Irradiator Quality Assurance

Rodrigues, Anna Elisabeth
Fonte: Universidade Duke Publicador: Universidade Duke
Tipo: Tese de Doutorado
Publicado em //2012
Relevância na Pesquisa
16.05%

Purpose: To demonstrate specific methods of small animal dosimetry and quality assurance through (1) machine-specific quality assurance and (2) target-specific quality assurance (QA) protocols for different types of biological irradiators: (a) a large-field orthovoltage irradiator, (b) a small-field orthovoltage irradiator, and (c) a 137Cs irradiator. Additionally, (3) a dosimetric characterization of a novel nano-scale phosphor detector for small animal dosimetry is performed.

Materials and Methods: (1) Machine-specific QA: (a) Large-field irradiator: Dose measurements were performed with an ion chamber and include: beam profile measurements at 50 cm SSD, linearity of output, in-air output for various irradiation settings, and light and radiation field coincidence measurement. A kVp meter was used to measure kVp and HVL for different irradiation settings. (b) Small-field irradiator: Dose measurements were completed using an ion chamber and MOSFET dosimeters. For the diagnostic mode measurements, the ion chamber was placed on the irradiation table and various diagnostic protocols were measured including table attenuation. MOSFETs were used to measure the backscatter factors (BSF) for various collimator sizes under therapy mode.

(2) Target-specific QA: (a) Large-field irradiator: A tissue-equivalent mouse phantom (2 cm diameter...

Isomeric and concentration effects of C4-cosurfactants on four-component microemulsions investigated by neutron spin-echo and small-angle scattering

Zambrano, Elvis; Kotlarchyk, Michael; Langner, Andreas; Faraone, Antonio
Fonte: Institute of Physics and IOP Publishing Limited Publicador: Institute of Physics and IOP Publishing Limited
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
15.72%
Neutron spin-echo spectroscopy and small-angle scattering measurements were performed to determine how the isomeric structure and concentration of C4-cosurfactants (i.e. butyl alcohols) influence structure and dynamics in four-component water-in-oil microemulsions. The system investigated was AOT/butanol/water/n-octane at room temperature (AOT denotes sodium di-2-ethyl hexylsulfosuccinate), deuterated to achieve contrast of the surfactant/cosurfactant film. At a fixed volume fraction of 0.06 and a fixed molar ratio of [water]/[AOT] = 20, we studied the effects of increasing the molar ratio of [butanol]/[AOT] from 0 to 30. Data from samples containing the cosurfactant n-butyl alcohol were compared with samples prepared with tert-butyl alcohol and, in a few cases, sec-butyl alcohol. Data were analysed using a core–shell model for polydisperse spherical droplets, allowing for the presence of shape fluctuations. It was found that all structural isomers of the cosurfactant led to a similar decrease in droplet size with increasing alcohol content. In all cases, droplet size and shape fluctuations were observed to increase with alcohol content; however, the effect was most pronounced for size fluctuations (i.e. polydispersity) in the presence of tert-butanol. The data indicates that tert-butanol has a higher degree of penetration into the water core...