Diffusion-weighted magnetic resonance imaging（d MRI） is widely used to study white and gray matter（GM） micro-organization and structural connectivity in the brain. Super-resolution track-density imaging（TDI） is ...Diffusion-weighted magnetic resonance imaging（d MRI） is widely used to study white and gray matter（GM） micro-organization and structural connectivity in the brain. Super-resolution track-density imaging（TDI） is an image reconstruction method for d MRI data, which is capable of providing spatial resolution beyond the acquired data, as well as novel and meaningful anatomical contrast that cannot be obtained with conventional reconstruction methods. TDI has been used to reveal anatomical features in human and animal brains. In this study, we used short track TDI（st TDI）, a variation of TDI with enhanced contrast for GM structures, to reconstruct directionencoded color maps of fixed tree shrew brain. The results were compared with those obtained with the traditional diffusion tensor imaging（DTI） method. We demonstrated that fine microstructures in the tree shrew brain, such as Baillarger bands in the primary visual cortex and the longitudinal component of the mossy fibers within the hippocampal CA3 subfield, were observable with st TDI,but not with DTI reconstructions from the same d MRI data.The possible mechanisms underlying the enhanced GM contrast are discussed.展开更多
Deep brain stimulation (DBS) is a non-pharmacological treatment for Parkinson’s disease (PD), and its efficacy depends largely on which anatomical structure (target) is stimulated. The subthalamic nucleus (STN) is on...Deep brain stimulation (DBS) is a non-pharmacological treatment for Parkinson’s disease (PD), and its efficacy depends largely on which anatomical structure (target) is stimulated. The subthalamic nucleus (STN) is one of the most commonly used targets, but stimulation of new targets within the posterior sub-thalamic area (PSA), comprising a group of white matter fibers known as prelemniscal radiations (Raprl), as well as the caudal zonaincerta nucleus (Zic), have proven to be superior at improving certain clinical symptoms. Despite their clinical usefulness, their anatomical connectivity has not been completely described in humans. We performed constrained spherical deconvolution of the signal in diffusion-weighted images and subsequent tractography as a means to non-invasively define the connectivity of the Raprl and Zic in a group of five patients with PD. Further, we used track-density imaging, a novel method to improve the spatial resolution of the acquired images, in order to visualize the small subregions that comprise the PSA with a voxel resolution of 0.2 × 0.2 × 0.2 mm3. Both Raprl and Zic demonstrated high probability of connectivity with the dorsal brainstem, cerebellum, subcortical nuclei (globus pallidum ventral, lateral thalamic nuclei), and cortical areas (orbitofrontal cortex, primary and supplementary motor cortex areas). The connectivity patterns were re-producible between patients and were discretely organized as the tracts entered/exited the PSA, depending on their end points. These findings indicate that the PSA is part of the neuronal circuitry controlling movement, and the precise characterization of its connectivity will aid in our understanding of the net-works involved in PD and how they can be modulated with DBS in order to alleviate symptoms.展开更多
In the metrology of radon, an environmental lung carcinogen, the integrated measurements necessary for epidemiological studies are made very often using the tracks detector LR 115 type 2. For dosimetric analysis, the ...In the metrology of radon, an environmental lung carcinogen, the integrated measurements necessary for epidemiological studies are made very often using the tracks detector LR 115 type 2. For dosimetric analysis, the etched tracks from radon alpha particles on this detector are usually counted by means of an optical microscope or a spark counter. An optimal reading of the track densities which must be converted into radon concentrations, can’t be done without a good mastery of the mode of operation and use of these devices. Furthermore, investigations to know as to whether or not each of those can be used to determine radon concentration are necessary. These are the objectives of the present work in which LR 115 samples exposed to radon for at least 3 months, were chemically developed under standard conditions and read. The track densities obtained with the microscope are very much higher than those of the counter for each sample. These results are consistent with those published by other authors. However, each of these devices can be used interchangeably for alpha tracks counting, as both provide radon concentrations with a very good linear correlation coefficient of 0.95 taking into account their respective calibration factors for the reading of this detector. In addition, the saturation phenomenon for the spark counter reading of LR 115 detector occurs beyond 11,000 tr/cm<sup>2</sup>, a density never reached during our environmental radon measurements.展开更多
The Maxianshan area is rich in fluorite resources, the fluoritation was apparently controlled by the stratum, structure and the petrography and possesses the characteristics of the strata-bound deposit. The controllin...The Maxianshan area is rich in fluorite resources, the fluoritation was apparently controlled by the stratum, structure and the petrography and possesses the characteristics of the strata-bound deposit. The controlling stratum is AnZmx2-3 and Z1xn4. The country rocks are mainly migmatite, and secondly, the migmatic granite,展开更多
基金supported by grants from the National Basic Research Development Program of China (2011CB707800)the National Natural Science Foundation of China (21790390, 21790392, and 61371014)
文摘Diffusion-weighted magnetic resonance imaging（d MRI） is widely used to study white and gray matter（GM） micro-organization and structural connectivity in the brain. Super-resolution track-density imaging（TDI） is an image reconstruction method for d MRI data, which is capable of providing spatial resolution beyond the acquired data, as well as novel and meaningful anatomical contrast that cannot be obtained with conventional reconstruction methods. TDI has been used to reveal anatomical features in human and animal brains. In this study, we used short track TDI（st TDI）, a variation of TDI with enhanced contrast for GM structures, to reconstruct directionencoded color maps of fixed tree shrew brain. The results were compared with those obtained with the traditional diffusion tensor imaging（DTI） method. We demonstrated that fine microstructures in the tree shrew brain, such as Baillarger bands in the primary visual cortex and the longitudinal component of the mossy fibers within the hippocampal CA3 subfield, were observable with st TDI,but not with DTI reconstructions from the same d MRI data.The possible mechanisms underlying the enhanced GM contrast are discussed.
基金supported by the National Council of Science and Technology in Mexico(CONACyT)from grant 0114218-2009a CONACyT scholarship to GGMG(CVU 468870).
文摘Deep brain stimulation (DBS) is a non-pharmacological treatment for Parkinson’s disease (PD), and its efficacy depends largely on which anatomical structure (target) is stimulated. The subthalamic nucleus (STN) is one of the most commonly used targets, but stimulation of new targets within the posterior sub-thalamic area (PSA), comprising a group of white matter fibers known as prelemniscal radiations (Raprl), as well as the caudal zonaincerta nucleus (Zic), have proven to be superior at improving certain clinical symptoms. Despite their clinical usefulness, their anatomical connectivity has not been completely described in humans. We performed constrained spherical deconvolution of the signal in diffusion-weighted images and subsequent tractography as a means to non-invasively define the connectivity of the Raprl and Zic in a group of five patients with PD. Further, we used track-density imaging, a novel method to improve the spatial resolution of the acquired images, in order to visualize the small subregions that comprise the PSA with a voxel resolution of 0.2 × 0.2 × 0.2 mm3. Both Raprl and Zic demonstrated high probability of connectivity with the dorsal brainstem, cerebellum, subcortical nuclei (globus pallidum ventral, lateral thalamic nuclei), and cortical areas (orbitofrontal cortex, primary and supplementary motor cortex areas). The connectivity patterns were re-producible between patients and were discretely organized as the tracts entered/exited the PSA, depending on their end points. These findings indicate that the PSA is part of the neuronal circuitry controlling movement, and the precise characterization of its connectivity will aid in our understanding of the net-works involved in PD and how they can be modulated with DBS in order to alleviate symptoms.
文摘In the metrology of radon, an environmental lung carcinogen, the integrated measurements necessary for epidemiological studies are made very often using the tracks detector LR 115 type 2. For dosimetric analysis, the etched tracks from radon alpha particles on this detector are usually counted by means of an optical microscope or a spark counter. An optimal reading of the track densities which must be converted into radon concentrations, can’t be done without a good mastery of the mode of operation and use of these devices. Furthermore, investigations to know as to whether or not each of those can be used to determine radon concentration are necessary. These are the objectives of the present work in which LR 115 samples exposed to radon for at least 3 months, were chemically developed under standard conditions and read. The track densities obtained with the microscope are very much higher than those of the counter for each sample. These results are consistent with those published by other authors. However, each of these devices can be used interchangeably for alpha tracks counting, as both provide radon concentrations with a very good linear correlation coefficient of 0.95 taking into account their respective calibration factors for the reading of this detector. In addition, the saturation phenomenon for the spark counter reading of LR 115 detector occurs beyond 11,000 tr/cm<sup>2</sup>, a density never reached during our environmental radon measurements.
文摘The Maxianshan area is rich in fluorite resources, the fluoritation was apparently controlled by the stratum, structure and the petrography and possesses the characteristics of the strata-bound deposit. The controlling stratum is AnZmx2-3 and Z1xn4. The country rocks are mainly migmatite, and secondly, the migmatic granite,
