Correcting saturation effects of the arterial input function in dynamic susceptibility contrast-enhanced MRI: a Monte Carlo simulation

To prevent systematic errors in quantitative brain perfusion studies using dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI), a reliable determination of the arterial input function (AIF) is essential. We propose a novel algorithm for correcting distortions of the AIF caused by saturation of the peak amplitude and discuss its relevance for longitudinal studies. The algorithm is based on the assumption that the AIF can be separated into a reliable part at low contrast agent concentrations and an unreliable part at high concentrations. This unreliable part is reconstructed, applying a theoretical framework based on a transport-diffusion theory and using the bolus-shape in the tissue. A validation of the correction scheme is tested by a Monte Carlo simulation. The input of the simulation was a wide range of perfusion, and the main aim was to compare this input to the determined perfusion parameters. Another input of the simulation was an AIF template derived from in vivo measurements. The distortions of this template was modeled via a Rician distribution for image intensities. As for a real DSC-MRI experiment, the simulation returned the AIF and the tracer concentration-dependent signal in the tissue. The novel correction scheme was tested by deriving perfusion parameters from the simulated data for the corrected and the uncorrected case. For this analysis, a common truncated singular value decomposition approach was applied. We find that the saturation effect caused by Rician-distributed noise leads to an overestimation of regional cerebral blood flow and regional cerebral blood volume, as compared to the input parameter. The aberration can be amplified by a decreasing signal-to-noise ratio (SNR) or an increasing tracer concentration. We also find that the overestimation can be successfully eliminated by the proposed saturation-correction scheme. In summary, the correction scheme will allow DSC-MRI to be expanded towards higher tracer concentrations and lower SNR and will help to increase the measurement to measurement reproducibility for longitudinal studies.     

Anti-Inflammatory Activities of the Ethanol Extract of Prasiola japonica,an Edible Freshwater Green Algae,and Its Various Solvent Fractions in LPS-Induced Macrophages and Carrageenan-Induced Paw Edema via the AP-1 Pathway

Prasiola japonica possesses several biological activities. However, reports on the anti-inflammatory activities and molecular mechanisms of its different solvent fractions remain limited. In this study, we investigated the potential anti-inflammatory activities of P. japonica ethanol extract (Pj-EE) and four solvent fractions of Pj-EE made with hexane (Pj-EE-HF), chloroform (Pj-EE-CF), butanol (Pj-EE-BF), or water (Pj-EE-WF) in both in vitro (LPS-induced macrophage-like RAW264.7 cells) and in vivo (carrageenan-induced acute paw edema mouse models) experiments. The most active solvent fraction was selected for further analysis. Various in vitro and in vivo assessments, including nitric oxide (NO), cytokines, luciferase assays, real-time polymerase chain reactions, and immunoblotting analyses were performed to evaluate the underlying mechanisms. In addition, the phytochemical constituents were characterized by Liquid chromatography-tandem mass spectrometry. In in vitro studies, the highest inhibition of NO production was observed in Pj-EE-CF. Further examination revealed that Pj-EE-CF decreased the expression of inflammation-related cytokines in LPS-induced RAW264.7 cells and suppressed subsequent AP-1-luciferase activity by inhibition of phosphorylation events in the AP-1 signaling pathway. Pj-EE-CF treatment also demonstrated the strongest reduction in thickness and volume of carrageenan-induced paw edema, while Pj-EE-BF showed the lowest activity. Furthermore, Pj-EE-CF also reduced gene expression and cytokines production in tissue lysates of carrageenan-induced paw edema. These findings support and validate the evidence that Pj-EE, and especially Pj-EE-CF, could be a good natural source for an anti-inflammatory agent that targets the AP1 pathway.     

同步辐射X射线成像技术在脑成像研究中的应用

脑疾病的诊疗、 探索高级脑功能机制和理解意识本源对脑科学研究具有重要意义. 成像技术在阐明脑科学神经系统结构和功能中发挥了重要作用. 迄今, 核磁共振成像、 光学成像和电子显微镜成像技术已为脑科学研究提供了强有力的手段, 取得了突出的进展. 同步辐射X射线显微成像技术具有高分辨率、 快成像速度和高穿透深度等优点, 是一类与已有技术互补的新型脑成像技术. 本文介绍了核磁共振波谱、 光学显微镜和电子显微镜等成像方法在脑成像领域中的应用, 重点阐述了同步辐射X射线成像的优势以及在脑结构成像和功能成像中的应用. 在此基础上, 展望了同步辐射X射线成像应用于脑科学研究的未来发展方向, 讨论了该技术在绘制人脑联接图谱中的优势及可行性.     

Micellar capillary electrophoresis – Electrochemical detection of neurochemicals from Drosophila

The fruit fly is one of the most heavily studied model organisms for genetics research and has significantly contributed to the molecular, cellular, and evolutionary understandings of human behavior. Recent research in the analytical chemistry of the fruit fly has focused on developing methods to obtain highly sensitive chemical quantification information of Drosophila melanogaster, especially looking at the nervous system. We provide a brief overview of work in the area of CE of the fly head and brain.     

High-resolution MR venography of cerebral arteriovenous malformations

The purpose of this study was to evaluate the diagnostic potential of a high-resolution magnetic resonance (MR) venography technique in patients with cerebral arteriovenous malformations (AVMs). A high-resolution 3D gradient echo sequence was used with a long echo time TE to obtain venous information down to sub-pixel sized vessel diameters of several hundred microns. The method is based on the paramagnetic property of deoxyhemoglobin, and the resulting developing phase difference between veins and brain parenchyma at long echo times which leads to signal cancellation. The reconstructed venograms were compared with time-of-flight (TOF)-MR angiography using qualitative and quantitative criteria with the conventional digital subtraction angiography serving as the reference gold standard. In 17 patients with angiographically proven cerebral AVMs, the method indicates its potential in clinical applications. Venography was able to detect all AVMs whereas TOF-MRA failed in three patients. In the delineation of venous drainage patterns MR venography was superior to TOF-MRA, however, the method failed in the detection of about half of the main feeding arteries, as expected. Due to susceptibility artifacts at air/tissue boundaries and interference with paramagnetic hemosiderin, venography was limited with respect to the delineation of the exact nidus sizes and shapes in ten patients with AVMs located close to the skull base or having suffered from previous bleeding. Although the visualization of draining veins represents an important prerequisite in the surgical and radiosurgical treatment planning of cerebral AVMs, application of high resolution MR venography may be limited in the diagnostic work-up in some of these patients. On the other hand, it may be of special importance in the early detection and assessment of small AVMs that are difficult to diagnose with other MR methods.     

The use of multivariate MR imaging intensities versus metabolic data from MR spectroscopic imaging for brain tumour classification

This study investigated the value of information from both magnetic resonance imaging and magnetic resonance spectroscopic imaging (MRSI) to automated discrimination of brain tumours. The influence of imaging intensities and metabolic data was tested by comparing the use of MR spectra from MRSI, MR imaging intensities, peak integration values obtained from the MR spectra and a combination of the latter two. Three classification techniques were objectively compared: linear discriminant analysis, least squares support vector machines (LS-SVM) with a linear kernel as linear techniques and LS-SVM with radial basis function kernel as a nonlinear technique. Classifiers were evaluated over 100 stratified random splittings of the dataset into training and test sets. The area under the receiver operating characteristic (ROC) curve (AUC) was used as a global performance measure on test data. In general, all techniques obtained a high performance when using peak integration values with or without MR imaging intensities. For example for low- versus high-grade tumours, low- versus high-grade gliomas and gliomas versus meningiomas, the mean test AUC was higher than 0.91, 0.94, and 0.99, respectively, when both MR imaging intensities and peak integration values were used. The use of metabolic data from MRSI significantly improved automated classification of brain tumour types compared to the use of MR imaging intensities solely.     

Initial attempts at directly detecting alpha wave activity in the brain using MRI

The “direct detection” of neuronal activity by MRI could offer improved spatial and temporal resolution compared to the blood oxygenation level-dependent (BOLD) effect. Here we describe initial attempts to use MRI to detect directly the neuronal currents resulting from spontaneous alpha wave activity, which have previously been shown to generate the largest extracranial magnetic fields. Experiments were successfully carried out on four subjects at 3 T. A single slice was imaged at a rate of 25 images per second under two conditions. The first (in darkness with eyes-closed) was chosen to promote alpha wave activity, while the second (eyes-open viewing a visual stimulus) was chosen to suppress it. The fluctuations of the phase and magnitude of the resulting MR image data were frequency analysed, and tested for the signature of both alpha wave activity and neuronal activity evoked by the visual stimulus.

Regions were found that consistently showed elevated power in fluctuations of the phase of the MR signal, in the frequency range of alpha waves, during the eyes-closed condition. It was conservatively assumed that if oscillations occurred at the same frequency in the magnitude signal from the same region or at the same frequency in the phase or magnitude signal from other regions overlying large vessels or cerebrospinal fluid (CSF), then the phase changes were not due to neuronal activity related to alpha waves. Using these criteria the data obtained were consistent with direct detection of alpha wave activity in three of the four volunteers. No significant MR signal fluctuations due to evoked activity were identified.