Geometric distortion in clinical MRI systems - Part I: evaluation using a 3D phantom

Recently, a 3D phantom that can provide a comprehensive and accurate measurement of the geometric distortion in MRI has been developed. Using this phantom, a full assessment of the geometric distortion in a number of clinical MRI systems (GE and Siemens) has been carried out and detailed results are presented in this paper. As expected, the main source of geometric distortion in modern superconducting MRI systems arises from the gradient field nonlinearity. Significantly large distortions with maximum absolute geometric errors ranged between 10 and 25 mm within a volume of 240 x 240 x 240 mm(3) were observed when imaging with the new generation of gradient systems that employs shorter coils. By comparison, the geometric distortion was much less in the older-generation gradient systems. With the vendor's correction method, the geometric distortion measured was significantly reduced but only within the plane in which these 2D correction methods were applied. Distortion along the axis normal to the plane was, as expected, virtually unchanged. Two-dimensional correction methods are a convenient approach and in principle they are the only methods that can be applied to correct geometric distortion in a single slice or in multiple noncontiguous slices. However, these methods only provide an incomplete solution to the problem and their value can be significantly reduced if the distortion along the normal of the correction plane is not small. (C) 2004 Elsevier Inc. All rights reserved.

Improving environmental performance in the tourism accommodation sector

While environmental legislation in Australia regulates tourism development, it is less effective in operational areas because of the dependency of tourism on environmental resources that are not managed by operators, and the small but incremental nature of operational impacts. The absence of functional environmental standards for tourism means that little guidance exists: a problem compounded by variability in the diversity of operation types and receiving environments, as well as the accessibility of information by a non-technical audience. While legislation and economic considerations may provide impetus to adopt environmental practices, it is proposed that an environmental philosophy is necessary for tourism businesses to seek out and maintain alternative sustainable modes of operation. Review of the environmental audit process used by a Queensland resort suggests commitment to continual improvement in environmental performance is attributable to individual and corporate ethics. While the case is an ecotourism operation, the literature indicates that these factors have relevance to tourism generally. Although client satisfaction and return on investment objectives are constraints, environmental auditing can provide impetus for practical expression of environmental objectives. Facilitation of ethically-motivated voluntary action may be more effective in achieving tourism's environmental objectives than codifying standards in static legislation.

An inverse methodology for high-frequency RF coil design for MRI with de-emphasized B-1 fields

An inverse methodology for the design of biologically loaded radio-frequency (RF) coils for magnetic resonance imaging applications is described. Free space time-harmonic electromagnetic Green's functions and de-emphasized B-1 target fields are used to calculate the current density on the coil cylinder. In theory, with the B-1 field de-emphasized in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the central overemphasis effect caused by field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T (170 MHz) is calculated using an inverse methodology with de-emphasized B-1. target fields. An in-house finite-difference time-domain routine is employed to evaluate B-1 field and signal intensity inside a homogenous cylindrical phantom and then a complete human head model. A comparison with a conventional RF birdcage coil is carried out and demonstrates that this method can help in decreasing the normal bright region caused by field/tissue interactions in head images at 170 MHz and higher field strengths.

Mechanisms of axon guidance in the developing nervous system

The human brain assembles an incredible network of over a billion neurons. Understanding how these connections form during development in order for the brain to function properly is a fundamental question in biology. Much of this wiring takes place during embryonic development. Neurons are generated in the ventricular zone, migrate out, and begin to differentiate. However, neurons are often born in locations some distance from the target cells with which they will ultimately form connections. To form connections, neurons project long axons tipped with a specialized sensing device called a growth cone. The growing axons interact directly with molecules within the environment through which they grow. In order to find their targets, axonal growth cones use guidance molecules that can either attract or repel them. Understanding what these guidance cues are, where they are expressed, and how the growth cone is able to transduce their signal in a directionally specific manner is essential to understanding how the functional brain is constructed. In this chapter, we review what is known about the mechanisms involved in axonal guidance. We discuss how the growth cone is able to sense and respond to its environment and how it is guided by pioneering cells and axons. As examples, we discuss current models for the development of the spinal cord, the cerebral cortex, and the visual and olfactory systems. (c) 2005, Elsevier Inc.

Implantation of a scaffold following bulbectomy induces laminar organization of regenerating olfactory axons

Primary olfactory axons expressing different odorant receptors are interspersed within the olfactory nerve. However, upon reaching the outer nerve fiber layer of the olfactory bulb they defasciculate, sort out, and refasciculate prior to targeting glomeruli in fixed topographic positions. While odorant receptors are crucial for the final targeting of axons to glomeruli, it is unclear what directs the formation of the nerve fiber and glomerular layers of the olfactory bulb. While the olfactory bulb itself may provide instructive cues for the development of these layers, it is also possible that the incoming axons may simply require the presence of a physical scaffold to establish the outer laminar cytoarchitecture. In order to begin to understand the underlying role of the olfactory bulb in development of the outer layers of the olfactory bulb, we physically ablated the olfactory bulbs in OMP-IRES-LacZ and P2-IRES-tau-LacZ neonatal mice and replaced them with artificial biological scaffolds molded into the shape of an olfactory bulb. Regenerating axons projected around the edge of the cranial cavity at the periphery of the artificial scaffold and were able to form an olfactory nerve fiber layer and, to some extent, a glomerular layer. Our results reveal that olfactory axons are able to form rudimentary cytoarchitectonic layers if they are provided with an appropriately shaped biological scaffold. Thus, the olfactory bulb does not appear to provide any tropic substance that either attracts regenerating olfactory axons into the cranial cavity or induces these axons to form a plexus around its outer surface. (c) 2006 Elsevier B.V. All rights reserved.

Comparative studies of hyperhomodesmotic reactions for the calculation of standard heats of formation of fullerenes

How can the accuracy of the calculated standard heats of formation Delta H-f(0) of fullerenes be improved? How reliable are the values of Delta H-f(0) calculated from hyperhomodesmotic reactions? This work is the first to address these questions. By comparing the results obtained from three hyperhomodesmotic reactions containing only fullerenes, it is illustrated that both the resonance contribution and the strain energy contribution should be considered in the construction of hyperhomodesmotic reactions. An attempt to construct such hyperhomodesmotic reactions for fullerenes has been carried out, and several new insights are indicated.

Cryosections of pre-irradiated adult rat spinal cord tissue support axonal regeneration in vitro

Neonatal X-irradiation of central nervous system (CNS) tissue markedly reduces the glial population in the irradiated area. Previous in vivo studies have demonstrated regenerative success of adult dorsal root ganglion (DRG) neurons into the neonatally-irradiated spinal cord. The present study was undertaken to determine whether these results could be replicated in an in vitro environment. The lumbosacral spinal cord of anaesthetised Wistar rat pups, aged between 1 and 5 days, was subjected to a single dose (40 Gray) of X-irradiation. A sham-irradiated group acted as controls. Rats were allowed to reach adulthood before being killed. Their lumbosacral spinal cords were dissected out and processed for sectioning in a cryostat. Cryosections (10 mum-thick) of the spinal cord tissue were picked up on sterile glass coverslips and used as substrates for culturing dissociated adult DRG neurons. After an appropriate incubation period, cultures were fixed in 2% paraformaldehyde and immunolabelled to visualise both the spinal cord substrate using anti-glial fibrillary acidic protein (GFAP) and the growing DRG neurons using anti-growth associated protein (GAP-43). Successful growth of DRG neurites was observed on irradiated, but not on non-irradiated, sections of spinal cord. Thus, neonatal X-irradiation of spinal cord tissue appears to alter its environment such that it can later support, rather than inhibit, axonal regeneration. It is suggested that this alteration may be due, at least in part, to depletion in the number of and/or a change in the characteristics of the glial cells. (C) 2000 ISDN. Published by Elsevier Science Ltd. All rights reserved.

Distance measurement using the change in junction voltage across a laser diode due to the self-mixing effect

Conventional detection scheme for self-mixing sensors uses an integrated photodiode within the laser package to monitor the self mixing signal. This arrangement can be simplified by directly obtaining the self-mixing signals across the laser diode itself and omitting the photodiode. This work reports on a Vertical-Cavity Surface-Emitting Laser (VCSEL) based selfmixing sensor using the laser junction voltage to obtain the selfmixing signal. We show that the same information can be obtained with only minor changes to the extraction circuitry leading to potential cost saving with reductions in component costs and complexity and significant increase in bandwidth favoring high speed modulation. Experiments using both photo current and voltage detection were carried out and the results obtained show good agreement with the theory.

CONSIDERAÇÕES ACERCA DA AUSÊNCIA PATERNA NA ADOLESCÊNCIA

O presente estudo teve por objetivos: a) Caracterizar uma amostra de adolescentes participantes de projetos sociais de uma Instituição de uma cidade do litoral paulista; b) Investigar aspectos da estrutura e dinâmica de adolescentes oriundos de famílias monoparentais, convencionais e de outras configurações familiares e, c) Compreender as relações estabelecidas com as figuras parentais por esses adolescentes pertencentes à essas diferentes organizações familiares.Para isso foi realizado inicialmente uma caracterização do perfil desses adolescentes e, posteriormente estudado seis casos de adolescentes de 12 a 18 anos participantes de Projetos Sociais do Terceiro Setor(Ong) pertencentes a diferentes formas de organizações familiares. Esses adolescentes freqüentavam a Instituição, local onde foram coletados os dados. Foram utilizados como instrumentos a entrevista semi-estruturada e o Teste de Apercepção Temática. De modo geral, os resultados mostraram que os adolescentes de famílias convencionais, ou seja, que possuem o pai e mãe no seio familiar conseguiram introjetar a imago paterna de forma mais integrada e, transitam pela adolescência de maneira mais estável. O esforço frente à elaboração dos lutos é vivenciado condizendo com a dita Síndrome da Adolescência Normal . Já os jovens pertencentes a famílias em que o pai não se faz presente no seio familiar, as defesas e as angustias apresentam-se condizentes aos estágios mais primitivos do desenvolvimento. Conclui-se que são necessários mais estudos frente a esta demanda para que o trabalho preventivo possa criar condições de um bom desenvolvimento psíquico para que este jovem passe pela adolescência e, chegue à vida adulta de maneira integrada.

CONSIDERAÇÕES ACERCA DA AUSÊNCIA PATERNA NA ADOLESCÊNCIA

O presente estudo teve por objetivos: a) Caracterizar uma amostra de adolescentes participantes de projetos sociais de uma Instituição de uma cidade do litoral paulista; b) Investigar aspectos da estrutura e dinâmica de adolescentes oriundos de famílias monoparentais, convencionais e de outras configurações familiares e, c) Compreender as relações estabelecidas com as figuras parentais por esses adolescentes pertencentes à essas diferentes organizações familiares.Para isso foi realizado inicialmente uma caracterização do perfil desses adolescentes e, posteriormente estudado seis casos de adolescentes de 12 a 18 anos participantes de Projetos Sociais do Terceiro Setor(Ong) pertencentes a diferentes formas de organizações familiares. Esses adolescentes freqüentavam a Instituição, local onde foram coletados os dados. Foram utilizados como instrumentos a entrevista semi-estruturada e o Teste de Apercepção Temática. De modo geral, os resultados mostraram que os adolescentes de famílias convencionais, ou seja, que possuem o pai e mãe no seio familiar conseguiram introjetar a imago paterna de forma mais integrada e, transitam pela adolescência de maneira mais estável. O esforço frente à elaboração dos lutos é vivenciado condizendo com a dita Síndrome da Adolescência Normal . Já os jovens pertencentes a famílias em que o pai não se faz presente no seio familiar, as defesas e as angustias apresentam-se condizentes aos estágios mais primitivos do desenvolvimento. Conclui-se que são necessários mais estudos frente a esta demanda para que o trabalho preventivo possa criar condições de um bom desenvolvimento psíquico para que este jovem passe pela adolescência e, chegue à vida adulta de maneira integrada.

O LÚDICO VIA FÁBULAS EM ATENDIMENTO PSICOTERAPÊUTICO: UM ESTUDO DE CASO CLÍNICO DE MOBBING

Esta pesquisa verifica a validade da utilização de fábulas em processo psicoterapêutico de paciente de Mobbing acometida de depressão e síndrome de pânico. Desenvolve-se por meio de estudo de caso avaliativo-interventivo evolutivo prolongado, com um total de 116 sessões semanais. Inicialmente realiza o diagnóstico clínico elaborado a partir do desenho da figura humana, extraído do teste projetivo House Tree and Person, de entrevista inicial semi-dirigida, e de coleta de relatos verbais e observações feitas durante os primeiros atendimentos. As sessões são realizadas com utilização ocasional de fábulas, associada ou não a técnicas de relaxamento de Schultz e Jacobson, com interpretação de sonhos e recomendação de filmes. O objetivo é verificar se as fábulas contribuem de forma positiva para o paciente compreender com mais facilidade as interpretações do psicoterapeuta, se diminui sua resistência ao falar dos seus conteúdos e se amplia à consciência simbólica. O primeiro momento interventivo tem a duração de aproximadamente 16 meses, o segundo, de 04 meses, quando é solicitado o segundo desenho e o terceiro processa-se em 09 meses, quando é solicitado o último desenho. No primeiro momento é proporcionado à paciente um ambiente facilitador com sustentação emocional (Holding), buscando resgatar sua ilusão, numa visão winnicottiana. Revela-se uma situação de Mobbing acompanhada de depressão manifesta e síndrome do pânico; com alto nível de exigência pessoal e profissional; grande passividade nos relacionamentos e na dinâmica do casal. Ao final desse momento, já consegue começar a desviar sua auto-agressividade para o meio externo de maneira mais positiva e socialmente aceita. No segundo momento predomina o encontro e aceitação de seu verdadeiro jeito de ser; enxerga o quanto estava se deixando prejudicar; mostra-se mais confiante, comunica-se e enfrenta melhor suas dificuldades afetivas. No terceiro momento demonstra estar segura e feliz. Cuida de sua aparência e sente prazer em ser notada socialmente. Demonstra ter aprendido a se defender em situações de confronto, com maior autonomia e verbaliza estar muito feliz com as mudanças, sorri com freqüência. A análise evolutiva dos desenhos confirmam esta boa evolução. A utilização de fábulas foi muito bem aceita pela paciente, que conseguiu por meio da leitura simbólica contida nas mesmas, aproximar-se de sua problemática e aprender a lidar com ela de forma mais saudável. Os resultados também indicam que a utilização de relaxamento associado à leitura das fábulas contribuiu para sua assimilação mais abrangente e profunda. O estudo ilustra a evolução do caso por meio de 24 vinhetas, devidamente analisadas em relação aos momentos descritos.(AU)

CORRELAÇÕES ENTRE PERCEPÇÃO DA PASSAGEM DO TEMPO, ATENÇÃO DIFUSA E ANSIEDADE

O presente estudo teve como objetivo avaliar aspectos psicofisiológicos da ansiedade em particular a atenção e a percepção da passagem do tempo. Foi aplicada a escala psicométrica de ansiedade do IDATE em 180 alunos do curso de Educação Física da Universidade de São Paulo em sala de aula. Foram selecionados 15 voluntários mais ansiosos e 15 menos ansiosos foi considerado o IDATE traço por apresentar características mais constantes da ansiedade. O experimento 1 foi a tarefa de Tempo Espontâneo onde os participantes deviam bater o dedo no botão A do joystick da forma mais regular e precisa possível por um minuto. Já no experimento 2 os participantes foram orientados a responder o mais rápido possível ao surgimento do estimulo (ponto branco 0,4 grau) com uma luminância de 80 cd/m contra um fundo cinza pressionando o botão A do joystick com qualquer dedo da mão dominante (TRS). Os estímulos eram apresentados randomicamente por 82 posições diferentes na tela do computador. Após tratamento dos dados e analise estatística, o estudo de caráter geral e exploratório apresentado aqui mostra tendências, mas não correlações significativas entre as medidas. Alguns dados, no entanto, chamam a atenção e devem ser considerados no planejamento de experimentos futuros.

A longitudinal study of vergence adaptation in incipient presbyopia

Background: To investigate vergence adaptation during the incipient phase of presbyopia, when the amplitude of accommodation approaches the level where the first reading addition is required. The study aimed to assess the ability of the vergence system to counteract changes in the component contributions to the overall vergence response with the decline in the amplitude of accommodation in presbyopia, although previous reports on the nature of changes in accommodative, tonic and proximal vergence are equivocal. Methods: Using a 'flashed' Maddox rod technique, an assessment of vergence adaptation to 6 Δ base-out and 6Δ base-in prism was made for 28 subjects (aged 35-45 years at the commencement of the study). The measurements were taken four times over a 2-year period. Results: Using a repeated measures analysis of variance, the results show that with the decline in amplitude of accommodation, there is a statistically significant reduction in the magnitude of vergence adaptation to both base-out (p < 0.05) and base-in prism (p < 0.01). Conclusions: This study shows that with ageing, there is a decrease in the ability of the slow vergence mechanism to overcome a change in fusional vergence demand and would suggest that either the fast component of fusional vergence must cope with any change in fusional vergence demand or that the sum of the accommodative, tonic and proximal vergence responses are virtually stable with age. © 2003 The College of Optometrists.

The tribology of linear tape recording systems

This thesis is devoted to the tribology at the head~to~tape interface of linear tape recording systems, OnStream ADRTM system being used as an experimental platform, Combining experimental characterisation with computer modelling, a comprehensive picture of the mechanisms involved in a tape recording system is drawn. The work is designed to isolate the mechanisms responsible for the physical spacing between head and tape with the aim of minimising spacing losses and errors and optimising signal output. Standard heads-used in ADR current products-and prototype heads- DLC and SPL coated and dummy heads built from a AI203-TiC and alternative single-phase ceramics intended to constitute the head tape-bearing surface-are tested in controlled environment for up to 500 hours (exceptionally 1000 hours), Evidences of wear on the standard head are mainly observable as a preferential wear of the TiC phase of the AI203-TiC ceramic, The TiC grains are believed to delaminate due to a fatigue wear mechanism, a hypothesis further confirmed via modelling, locating the maximum von Mises equivalent stress at a depth equivalent to the TiC recession (20 to 30 nm). Debris of TiC delaminated residues is moreover found trapped within the pole-tip recession, assumed therefore to provide three~body abrasive particles, thus increasing the pole-tip recession. Iron rich stain is found over the cycled standard head surface (preferentially over the pole-tip and to a lesser extent over the TiC grains) at any environment condition except high temperature/humidity, where mainly organic stain was apparent, Temperature (locally or globally) affects staining rate and aspect; stain transfer is generally promoted at high temperature. Humidity affects transfer rate and quantity; low humidity produces, thinner stains at higher rate. Stain generally targets preferentially head materials with high electrical conductivity, i.e. Permalloy and TiC. Stains are found to decrease the friction at the head-to-tape interface, delay the TiC recession hollow-out and act as a protective soft coating reducing the pole-tip recession. This is obviously at the expense of an additional spacing at the head-to-tape interface of the order of 20 nm. Two kinds of wear resistant coating are tested: diamond like carbon (DLC) and superprotective layer (SPL), 10 nm and 20 to 40 nm thick, respectively. DLC coating disappears within 100 hours due possibly to abrasive and fatigue wear. SPL coatings are generally more resistant, particularly at high temperature and low humidity, possibly in relation with stain transfer. 20 nm coatings are found to rely on the substrate wear behaviour whereas 40 nm coatings are found to rely on the adhesive strength at the coating/substrate interface. These observations seem to locate the wear-driving forces 40 nm below the surface, hence indicate that for coatings in the 10 nm thickness range-· i,e. compatible with high-density recording-the substrate resistance must be taken into account. Single-phase ceramic as candidate for wear-resistant tape-bearing surface are tested in form of full-contour dummy-heads. The absence of a second phase eliminates the preferential wear observed at the AI203-TiC surface; very low wear rates and no evidence of brittle fracture are observed.

Statnote 6: post-hoc ANOVA tests

If data are analysed using ANOVA, and a significant F value obtained, a more detailed analysis of the differences between the treatment means will be required. The best option is to plan specific comparisons among the treatment means before the experiment is carried out and test them using ‘contrasts’. In some circumstances, post-hoc tests may be necessary and experimenters should think carefully which of the many tests available should be used. Different tests can lead to different conclusions and careful consideration as to the appropriate test should be given in each circumstance.