Estudo comparativo para avaliação das falhas técnicas em radiografias convencionais de tórax

OBJETIVO: Especificar e quantificar as principais falhas técnicas, sejam elas eletrônicas ou mecânicas, presentes em radiografias convencionais de tórax, com o intuito de melhorar a sua qualidade e reduzir a necessidade da repetição dos exames e, consequentemente, a dose recebida pelo paciente. MATERIAIS E MÉTODOS: Foram selecionadas e avaliadas por um pneumologista 897 radiografias convencionais realizadas ou em projeção posteroanterior ou lateral em cinco instituições de saúde da cidade de São Paulo. Em cada uma delas foram feitas análises das falhas técnicas presentes, as quais foram classificadas de acordo com o erro técnico radiográfico pré-definido e que levou à repetição do exame. RESULTADOS: Os resultados obtidos mostraram que o posicionamento incorreto do paciente (27%), a subexposição (23%) e a superexposição (15%) foram as principais falhas que contribuíram para a repetição dos exames e que apresentaram, na matriz de coeficiente de correlação Pearson, um erro acima de 0,7%, ocasionando aumento da dose recebida pelos pacientes. CONCLUSÃO: Os resultados observados indicaram a necessidade da realização de controle de qualidade dos aparelhos de raios X, a atenção do operador do equipamento, bem como outras abordagens para esclarecer o impacto da necessidade de repetição do exame.

Estimativa dos valores de MSAD em procedimentos de tomografia computadorizada utilizando filmes radiocrômicos

OBJETIVO: Verificar a viabilidade de filmes radiocrômicos como um dosímetro alternativo para estimativa da dose média em cortes múltiplos a partir dos perfis de kerma. MATERIAIS E MÉTODOS: Os filmes foram distribuídos em cilindros posicionados no centro e nas regiões periféricas de um objeto simulador padrão de abdome utilizado para dosimetria em tomografia computadorizada. RESULTADOS: Os valores de dose média em cortes múltiplos calculados foram 13,6 ± 0,7, 13,5 ± 0,7 e 18,7 ± 1,0 mGy para os valores de passo (pitch) de 0,75, 1,00 e 1,50, respectivamente. CONCLUSÃO: Apesar de os resultados mostrarem valores menores que o nível de referência de radiodiagnóstico de 25 mGy estabelecido pela legislação brasileira para exames de abdome, eles sugerem que há espaço para otimização dos procedimentos e uma revisão do valor para o nível de referência de radiodiagnóstico brasileiro.

Estimativa da entalpia reticular (Dm Hmº) de adutos através de termogravimetria: uso de uma equação empírica

An empirical equation: DMHmº = t i/b (where t i is the Kelvin temperature of the beginning of the thermal decomposition obtained from the thermogravimetry of the adducts; b is an empirical parameter wich depends on the metal halide and on the number of ligands) was obtained and tested for 53 adducts MX2.nL (where MX2 is a metal halide from the zinc group). The difference between experimental and calculated values was less than 6% for 22 adducts. To another 22 adducts, that difference was less than 10%. Only for 4 compounds the difference between experimental and calculated values exceeds 15%.

Estimativa por infravermelho da concentração da unidade estrutural b-O-4 em ligninas de angiospermas tropicais

Five Björkman lignins, codified as AM, LL, GG, PP and AP, were isolated from wood species of Aspidosperma macrocarpum Mart., Lophanthera lactescens Ducke, Gallesia gorazema (Vell.) Miq., Peltogyne paniculata Bth. and Aspidosperma polyneuron Muell. Arg., respectively. Analyses of the lignins were carried out by Fourier transformed infrared spectroscopy using an experimental technique, Diffusely Reflected Infrared Fourier Transformed (DRIFT), admitting in the original spectra a band at 1500 cm-1 as an internal reference. Application of a deconvolution technique made possible to estimate the percentage per mol of b-O-4 unit content around 65.5% to AM, 68.0% to LL, 71.0% to GG. 73.4% to PP and 75.0% to AP, toward AM

Estimativa da entalpia de decomposição (deltaD Hmº) de adutos por termogravimetria

An empirical equation: deltaD HmO = t i/2.2(2-n) is obtained and tested for 102 adducts (mainly adducts with zinc group halides). In the equation, t i is the Kelvin temperature of the beginning of the thermal decomposition of the adduct, (obtained by thermogravimetry), and n is the number of ligands. For 1/3 of the tested adducts the difference between experimental and calculated values was less than 5%. For about 1/3 of the adducts that difference exceeds 15%.

Estimativa da entalpia reticular de adutos (DM Hm o ) utilizando-se formas modificadas da equação de Kapustinskii

In this work are presented two modified forms of Kapustinskii equation that could be used to estimate the values of the lattice enthalphies for adducts: DM Hm o=(-n.z+ .z- .10(2)/D).(1-d*/D) .K and DM Hm o=(-n.z+ .z-.10(2)/d).(1-d*/d).K.d. Two new parameters related with steric effects and donor power of the ligands, J anddare introduced. The proposed equations were tested for 49 adducts (mainly from the zinc group halides). The difference between experimental (calorimetric) and calculated values (using the proposed equations) values are less than 5% for 41 of the tested adducts.

Transporte de massa em polímeros intrinsecamente condutores: importância, técnicas e modelos teóricos

In this work we discuss the aspects related to the phenomenon of mass transport in thin electroactive polymer films. Such phenomenon must be considered because the properties and consequent applications of these materials largely depend on the movement of charge carriers, i.e. ions, electrons or holes. The most recent majority of the techniques, methods and theoretical models used in this type of study are gathered and discussed, providing an easy and critical way for choosing the methodology for an investigation.

Estimativa por DSC das entalpias de sublimação da etilenouréia e da propilenouréia: algumas correlações empíricas envolvendo amidas e tioamidas

By using DSC data, the enthaplies of sublimation for ethyleneurea and propyleneurea, are calculated as 84 and 89 kJ mol-1 respectively. Using the vaporization enthalpy values for dimethylethyleneurea and dimethylprophyleneurea, as obtained from literature, the empirical relation: Dcrg Hmo (1)/ Dcrg Hmo (2) = Dlg Hmo (1)/ Dlg Hmo(2) = constant, that relate sublimation or vaporization enthalpies of two different substances and of its methylated derivatives, is obtained. Correlations like that are found to another ureas and thioureas.

Métodos analíticos ultrasensíveis: lente térmica e técnicas correlatas

Among the emergent laser based spectrometric methods, thermal lensing and other photothermal techniques present a great potential for solving a variety of problems in the fields of chemistry, physics and biology. Their main advantages are high concentration sensitivity, sensibility to physical-chemical properties of the medium, excellent spatial resolution and noninvasive characteristics. In this article, theoretical principles, main applications and practical hints as well as fundamental limitations of these techniques will be carefully described. It is hoped that this will give the reader a clear picture of this field of investigation as well as provide to the ones who are not specialists in the area, the necessary background to understand, implement and use photothermal techniques. In the final sections the development frontiers of photothermal spectrometry will be discussed.

Sobre a aplicabilidade da termogravimetria para a estimativa de parâmetros termoquímicos de compostos de coordenação: os elementos lantanídicos

By using thermochemical data reported for a series of chelates of the type [Ln(thd)3], thd = 2, 2, 6, 6 ­ tetramethyl- 3,5-heptanedione and Ln = La, Pr, Nd, Sm, Gd, Tb, Ho, Er, Tm and Yb, empirical correlations were found involving thermochemical parameters (e.g. dissociation enthalpy) and the thermodynamic temperatures of the beginning of thermal degradation of the chelates, t i. It is shown that t i values are of capital importance in the study of this all class of coordination compounds. Among others, the empirical equation is obtained: r3+ = (-0,013.Z + 1,36)/0,005, that relates the lanthanide cation radius (pm) with the atomic number of the element. The remarkable fact is that this equation is achieved by using thermogravimetric and calorimetric parameters. Is also shown that t i values are related with the P(M) function values, which are very close related with the energy difference, deltaE, between the lowest electronic energy level of the f n s²d¹ configuration and the lowest energy level of the f n+1s² configuration in the neutral gaseous atoms.

Técnicas in situ de baixo custo em eletroquímica: a microbalança a cristal de quartzo

Among in situ techniques, the electrochemical quartz crystal microbalance (EQCM) is a powerful tool for the study of electrochemical reactions that produce mass changes in the electrode/solution interface. This review present some systems in which the EQCM combined with classical electrochemical techniques, gives relevant information for understanding the charge transport process at a molecular level. The aim of this review is to do a brief description of experimental arrangements, with emphasis on some special cares that must be considered by the users. Secondly, some chosen electrochemical systems where the technique was successfully applied are discussed. Finally, a brief analysis of electroacoustic impedance experiments was done in order to show when the Sauerbrey equation can be used.