On the Vanishing of the t-term in the Short-Time Expansion of the Diffusion Coefficient for Oscillating Gradients in Diffusion NMR

Nuclear magnetic resonance (NMR) diffusion measurements can be used to probe porous structures or biological tissues by means of the random motion of water molecules. The short-time expansion of the diffusion coefficient in powers of t1/2, where t is the diffusion time related to the duration of the diffusion-weighting magnetic field gradient profile, is universally connected to structural parameters of the boundaries restricting the diffusive motion. The t1/2-term is proportional to the surface to volume ratio. The t-term is related to permeability and curvature. The short time expansion can be measured with two approaches in NMR-based diffusion experiments: First, by the use of diffusion encodings of short total duration and, second, by application of oscillating gradients of long total duration. For oscillating gradients, the inverse of the oscillation frequency becomes the relevant time scale. The purpose of this manuscript is to show that the oscillating gradient approach is blind to the t-term. On the one hand, this prevents fitting of permeability and curvature measures from this term. On the other hand, the t-term does not bias the determination of the t1/2-term in experiments

Análise de timol em cera de abelha por micro-extracção em fase sólida (SPME)

A aplicação contínua de acaricídas lipofílicos sintéticos no tratamento das abelhas conduz a uma acumulação que depende da frequência, lipofilicidade e quantidade de princípio activo utilizada. Este efeito é mais acentuado na cera de abelha que no mel, no entanto, e porque a persistência destes resíduos é elevada, provoca o aparecimento de resistências e a perda do seu efeito acaricida.[1] Esta razão levou à pesquisa de outros compostos alternativos não tóxicos e não persistentes, com efeito sobre o ácaro das abelhas, Varroa Jacobsoni. Entre estes compostos encontra-se o timol, um composto fenólico, volátil, presente no tomilho. Dos diversos componentes dos óleos essenciais este é sem dúvida o que demonstrou maior efeito acaricida, utilizando-se no tratamento das abelhas directamente ou como componente de diversas formulações.[2] Em Portugal, foi introduzido muito recentemente sob a forma comercial de APIGUARD: um gel, à base de timol, que controla termicamente a libertação do princípio activo. O controlo dos resíduos de timol na cera de abelha e no mel é assim um desafio actual quer do ponto de vista sanitário quer de qualidade alimentar. A micro-extracção em fase sólida (SPME) é uma técnica de preparação de amostras que se baseia na sorção de analítos no revestimento de uma fibra de sílica fundida e posterior desorção térmica no injector de um cromatógrafo em fase gasosa (GC). Para além de combinar num único processo etapas de extracção, purificação e concentração dos analitos, a técnica de SPME apresenta uma série de vantagens relativamente às técnicas de extracção convencionais, como a extracção líquido-líquido e extracção em fase sólida, nomeadamente a sua relativa simplicidade e rapidez, reduzido custo e não utilização de solventes para a extracção de analitos, para além de permitir a extracção por imersão directa na amostra gasosa ou líquida e extracção por amostragem do espaço-de-cabeça da amostra líquida ou sólida.[3] Ao contrário das técnicas tradicionais, que permitem uma extracção quantitativa dos analitos, a técnica de SPME baseia-se num equilíbrio de partição do analito. Esta particularidade torna a técnica de SPME bastante sensível a parâmetros experimentais que possam afectar os coeficientes de partição dos analitos e, consequentemente, a sensibilidade e reprodutibilidade dos resultados.[4] O objectivo deste trabalho é o desenvolvimento de uma metodologia para a análise de timol em ceras contaminadas, utilizando como padrão interno a benzofenona. Em primeiro lugar, procedeu-se à optimização da técnica através da determinação da quantidade de cera, temperatura de análise e período de contacto da fibra com o espaço-de-cabeça da amostra mais adequados para o caso em estudo. Numa segunda fase, procedeu-se à análise de diversas lâminas de cera contaminadas propositadamente com timol e sujeitas a diferentes condições de armazenamento: em frio, ao ar e em estufa. Finalmente, procedeu-se à construção da curva de calibração e quantificação do timol presente nas diversas amostras de cera analisadas. Considerando-se os resultados, para os níveis de contaminação avaliados, as condições analíticas mais adequadas ocorrem com a utilização de 1 g de cera, mantendo-se a fibra em contacto com o espaço-de-cabeça durante 40 minutos a uma temperatura de 60 ºC. Nestas condições experimentais foi possível obter uma boa correlação linear (r2=0,990) no intervalo de concentrações [3,5-14 mg/g]. A quantidade de timol encontrada nas amostras é significativamente inferior à colocada durante o processo de fabrico das lâminas, pelo que o processo de conservação não é o mais adequado, sendo evidente uma menor quantidade de timol quando a lâmina de cera é colocada na estufa

Improved Visualization of Prostate Cancer Using Multichannel Computed Diffusion Images: Combining ADC and DWI

(1) Background: For the peripheral zone of the prostate, diffusion weighted imaging (DWI) is the most important MRI technique; however, a high b-value image (hbDWI) must always be evaluated in conjunction with an apparent diffusion coefficient (ADC) map. We aimed to unify the important contrast features of both a hbDWI and ADC in one single image, termed multichannel computed diffusion images (mcDI), and evaluate the values of these images in a retrospective clinical study; (2) Methods: Based on the 2D histograms of hbDWI and ADC images of 70 patients with histologically proven prostate cancer (PCa) in the peripheral zone, an algorithm was designed to generate the mcDI. Then, three radiologists evaluated the data of 56 other patients twice in three settings (T2w images +): (1) hbDWI and ADC; (2) mcDI; and (3) mcDI, hbDWI, and ADC. The sensitivity, specificity, and inter-reader variability were evaluated; (3) Results: The overall sensitivity/specificity were 0.91/0.78 (hbDWI + ADC), 0.85/0.88 (mcDI), and 0.97/0.88 (mcDI + hbDWI + ADC). The kappa-values for the inter-reader variability were 0.732 (hbDWI + ADC), 0.800 (mcDI), and 0.853 (mcDI + hbDWI + ADC). (4) Conclusions: By using mcDI, the specificity of the MRI detection of PCa was increased at the expense of the sensitivity. By combining the conventional diffusion data with the mcDI data, both the sensitivity and specificity were improved

3T vs. 7T fMRI: capturing early human memory consolidation after motor task utilizing the observed higher functional specificity of 7T

ObjectiveFunctional magnetic resonance imaging (fMRI) visualizes brain structures at increasingly higher resolution and better signal-to-noise ratio (SNR) as field strength increases. Yet, mapping the blood oxygen level dependent (BOLD) response to distinct neuronal processes continues to be challenging. Here, we investigated the characteristics of 7 T-fMRI compared to 3 T-fMRI in the human brain beyond the effect of increased SNR and verified the benefits of 7 T-fMRI in the detection of tiny, highly specific modulations of functional connectivity in the resting state following a motor task.Methods18 healthy volunteers underwent two resting state and a stimulus driven measurement using a finger tapping motor task at 3 and 7 T, respectively. The SNR for each field strength was adjusted by targeted voxel size variation to minimize the effect of SNR on the field strength specific outcome. Spatial and temporal characteristics of resting state ICA, network graphs, and motor task related activated areas were compared. Finally, a graph theoretical approach was used to detect resting state modulation subsequent to a simple motor task.ResultsSpatial extensions of resting state ICA and motor task related activated areas were consistent between field strengths, but temporal characteristics varied, indicating that 7 T achieved a higher functional specificity of the BOLD response than 3 T-fMRI. Following the motor task, only 7 T-fMRI enabled the detection of highly specific connectivity modulations representing an “offline replay” of previous motor activation. Modulated connections of the motor cortex were directly linked to brain regions associated with memory consolidation.ConclusionThese findings reveal how memory processing is initiated even after simple motor tasks, and that it begins earlier than previously shown. Thus, the superior capability of 7 T-fMRI to detect subtle functional dynamics promises to improve diagnostics and therapeutic assessment of neurological diseases

Image quality assessment using deep learning in high b-value diffusion-weighted breast MRI

AbstractThe objective of this IRB approved retrospective study was to apply deep learning to identify magnetic resonance imaging (MRI) artifacts on maximum intensity projections (MIP) of the breast, which were derived from diffusion weighted imaging (DWI) protocols. The dataset consisted of 1309 clinically indicated breast MRI examinations of 1158 individuals (median age [IQR]: 50 years [16.75 years]) acquired between March 2017 and June 2020, in which a DWI sequence with a high b-value equal to 1500 s/mm2 was acquired. From these, 2D MIP images were computed and the left and right breast were cropped out as regions of interest (ROI). The presence of MRI image artifacts on the ROIs was rated by three independent observers. Artifact prevalence in the dataset was 37% (961 out of 2618 images). A DenseNet was trained with a fivefold cross-validation to identify artifacts on these images. In an independent holdout test dataset (n = 350 images) artifacts were detected by the neural network with an area under the precision-recall curve of 0.921 and a positive predictive value of 0.981. Our results show that a deep learning algorithm is capable to identify MRI artifacts in breast DWI-derived MIPs, which could help to improve quality assurance approaches for DWI sequences of breast examinations in the future.</jats:p

Germany's journey toward 14 Tesla human magnetic resonance

Multiple sites within Germany operate human MRI systems with magnetic fields either at 7 Tesla or 9.4 Tesla. In 2013, these sites formed a network to facilitate and harmonize the research being conducted at the different sites and make this technology available to a larger community of researchers and clinicians not only within Germany, but also worldwide. The German Ultrahigh Field Imaging (GUFI) network has defined a strategic goal to establish a 14 Tesla whole-body human MRI system as a national research resource in Germany as the next progression in magnetic field strength. This paper summarizes the history of this initiative, the current status, the motivation for pursuing MR imaging and spectroscopy at such a high magnetic field strength, and the technical and funding challenges involved. It focuses on the scientific and science policy process from the perspective in Germany, and is not intended to be a comprehensive systematic review of the benefits and technical challenges of higher field strengths

Function based Risk Assessment and Failure Prediction for Unmanned Space Missions

A strong need has emerged in the aerospace industry for a well-founded and effective failure prevention technique or process that can be employed during the conceptual design of high-risk aerospace systems. In this paper, we describe a methodology to support risk assessment and failure prevention during the earliest stages of spacecraft design and mission planning. The three-step procedure, an extension of the Function-Failure Design method, utilizes detailed information from existing subsystems and systematically abstracts this information to a level that can be used during conceptual design. During this process, we address the issue concerning the level at which systems containing a combination of electrical and mechanical components should be functionally modeled. The complete method is described in general before being applied to two major unmanned spacecraft subsystems

Failure Analysis in Subsystem Design for Space Missions

In order for the Function-Failure Design method to be applicable to modern conceptual design, the method needs to be extended from the mechanical domain to include the electrical domain as very few modern systems are purely mechanical in nature. Towards this goal, we supplement previous efforts describing a standardized vocabulary for mechanical failures by presenting the current state of an electrical and a mechanical failure mode taxonomy. Failure is defined in terms of the cause of the failure mode, the failure mode, and the effect of the failure mode that renders a mechanical, electrical, or electromechanical device incapable of satisfactorily performing its intended function under normal usage conditions. We utilize an elemental physics of failure approach to define failure mode and then use this definition and a variety of resources to develop the electrical failure modes presented in the taxonomy. The list of proposed electrical failure modes is tested against a set of NASA problem reports before being revised to include additional failure modes encountered in space applications. The resulting taxonomy is summarized in the form of 38 electrical failure modes organized into 13 categories. The final version of the mechanical and electrical failure mode taxonomy will be combined with a functional modeling approach to predict potential failures during the conceptual stages of design