Magnetic-Resonance-Based Electrical Property Mapping Using Global Maxwell Tomography With an 8-Channel Head Coil at 7 Tesla: A Simulation Study.

OBJECTIVE: Global Maxwell Tomography (GMT) is a recently introduced volumetric technique for noninvasive estimation of electrical properties (EP) from magnetic resonance measurements. Previous work evaluated GMT using ideal radiofrequency (RF) excitations. The aim of this simulation study was to assess GMT performance with a realistic RF coil. METHODS: We designed a transmit-receive RF coil with 8 decoupled channels for 7T head imaging. We calculated the RF transmit field ( B1+) inside heterogeneous head models for different RF shimming approaches, and used them as input for GMT to reconstruct EP for all voxels. RESULTS: Coil tuning/decoupling remained relatively stable when the coil was loaded with different head models. Mean error in EP estimation changed from [Formula: see text] to [Formula: see text] and from [Formula: see text] to [Formula: see text] for relative permittivity and conductivity, respectively, when changing head model without re-tuning the coil. Results slightly improved when an SVD-based RF shimming algorithm was applied, in place of excitation with one coil at a time. Despite errors in EP, RF transmit field ( B1+) and absorbed power could be predicted with less than [Formula: see text] error over the entire head. GMT could accurately detect a numerically inserted tumor. CONCLUSION: This work demonstrates that GMT can reliably reconstruct EP in realistic simulated scenarios using a tailored 8-channel RF coil design at 7T. Future work will focus on construction of the coil and optimization of GMT's robustness to noise, to enable in-vivo GMT experiments. SIGNIFICANCE: GMT could provide accurate estimations of tissue EP, which could be used as biomarkers and could enable patient-specific estimation of RF power deposition, which is an unsolved problem for ultra-high-field magnetic resonance imaging.

Adoecimento bancário: construção de estratégias individuais e coletivas para o enfrentamento do desgaste mental relacionado ao trabalho / Bank workers' mental strain: building confrontation strategies

Resumo Este relato visa apresentar e discutir o embasamento, o desenvolvimento e os resultados de um grupo de enfrentamento organizado com trabalhadores bancários adoecidos. A atividade foi realizada pelo Núcleo de Ação em Saúde do Trabalhador (NAST), em parceria com o Sindicato dos Bancários de Limeira. Partindo da trajetória profissional dos trabalhadores, o objetivo foi o de problematizar as características da organização do trabalho contemporâneo nesse setor. O grupo realizou oito encontros de aproximadamente duas horas na sede do sindicato, em Limeira. Nos encontros, os trabalhadores relataram situações laborais adversas determinantes no processo saúde-doença. Grande parte das queixas dos trabalhadores estava relacionada ao desgaste mental ocasionado pela pressão sofrida para alcançar metas superdimensionadas, levando ao estresse -, dentre outras formas de adoecimento -, inclusive pela falta de reconhecimento por parte dos gestores e usuários da instituição. O grupo se mostrou dispositivo potente de enfrentamento e ferramenta importante ao dar espaço de voz para trabalhadores se articularem na construção de estratégias individuais e coletivas para promoção da saúde no local de trabalho.

Abstract This report aims to present and discuss the basis, development and results of a support group constituted with sick bank workers. The activity was carried out by the Núcleo de Ação em Saúde do Trabalhador - NAST (Workers' Health Action Center) in partnership with the Bank Workers' Union of Limeira, state of São Paulo, Brazil. Starting from the workers' professional life, the objective was to query the current labor organization in this sector. The group held eight meetings of approximately two hours each at the union headquarters in Limeira. During the meetings, workers reported adverse work situations that were determinant in their health-disease process. Most of the workers' complaints were related to the mental strain caused by pressure to achieve oversized goals, and by the lack of recognition by the institution managers and users. The support group proved to be a powerful confrontation device and an important tool in providing a voice space for workers to articulate the construction of individual and collective strategies for health promotion in the workplace.

Computation of ultimate SAR amplification factors for radiofrequency hyperthermia in non-uniform body models: impact of frequency and tumour location.

PURPOSE: We introduce a method for calculation of the ultimate specific absorption rate (SAR) amplification factors (uSAF) in non-uniform body models. The uSAF is the greatest possible SAF achievable by any hyperthermia (HT) phased array for a given frequency, body model and target heating volume. METHODS: First, we generate a basis-set of solutions to Maxwell's equations inside the body model. We place a large number of electric and magnetic dipoles around the body model and excite them with random amplitudes and phases. We then compute the electric fields created in the body model by these excitations using an ultra-fast volume integral solver called MARIE. We express the field pattern that maximises the SAF in the target tumour as a linear combination of these basis fields and optimise the combination weights so as to maximise SAF (concave problem). We compute the uSAFs in the Duke body models at 10 frequencies in the 20-900 MHz range and for twelve 3 cm-diameter tumours located at various depths in the head and neck. RESULTS: For both shallow and deep tumours, the frequency yielding the greatest uSAF was ∼900 MHz. Since this is the greatest frequency that we simulated, we hypothesise that the globally optimal frequency is actually greater. CONCLUSIONS: The uSAFs computed in this work are very large (40-100 for shallow tumours and 4-17 for deep tumours), indicating that there is a large room for improvement of the current state-of-the-art head and neck HT devices.