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2019-03-07 READ MORE

2019年伊始,张孝通副研究员课题组在《IEEE Transactions on Biomedical Engineering》与《Physics in Medicine and Biology杂志陆续发表了其在7T磁共振平台开展的最新研究成果,两篇论文的第一作者分别为课题组硕士研究生王品一与博士研究生高阳


发表在《IEEE Transactions on Biomedical Engineering》的研究题“Evaluation of Submillimeter Diffusion Imaging of the Macaque Brain Using Readout-Segmented EPI at 7T”。弥散张量成像是当前一种能有效观察和追踪大脑白质纤维束的非侵入性检查方法主要用于研究人类和非人类灵长类动物大脑内的白质结构通路和结构连接模式。在临床上,毫米级的弥散张量成像广泛应用于检测超早期脑梗死、阿尔兹海默病、癫痫和脑肿瘤等疾病。但是由于扫描时间过长,图像畸变等因素的存在,因而制约了弥散张量成像的亚毫米级成像研究。近年来,超高场(7特斯拉及以上)磁共振系统的迅速发展,为亚毫米级别的大脑弥散张量成像提供了无限可能,亚毫米级图像不仅能更清晰地显示大脑白质纤维束,还能显示神经与邻近组织结构之间的空间关系,但直至目前,无论是在临床还是科研上,尚未有一种亚毫米级弥散张量成像的标准方法出现。本研究在西门子人体用7特斯拉超高场磁共振系统平台上,运用先进的西门子RESOLVE技术,在3只麻醉猕猴大脑上进行弥散张量图像的采集。通过设置RESOLVE序列中不同的扫描参数采集到不同的毫米级的弥散图像,进而通过一些列对图像信噪比和几何畸变程度的评估,得出最优的成像参数,从而寻找一种用于亚毫米级空间分辨率的弥散张量成像的最优扫描方案;同时,本研究利用这套最优扫描方案进行亚毫米级的弥散张量图像采集,获得了高质量的0.8 mm各向同性空间分辨率弥散张量图像数据,且与1mm各向同性空间分辨率弥散张量图像数据比较发现,亚毫米级弥散张量图像可以更好描绘大脑白质纤维束走向和通路结构,证实了超高场条件下亚毫米级空间分辨率弥散张量成像的可行性,为临床高分辨率弥散张量成像提供了有益的技术参考。

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原文链接:https://ieeexplore.ieee.org/document/8641295


发表在《Physics in Medicine and Biology》的研究题“A Surface Loop Array for in vivo Small Animal MRI/fMRI on 7T Human Scanners” 基于动物模型的实验一直在神经科学研究中具有不可替代的作用。由于动物专用磁共振系统一般无法容纳大动物,且在同一台磁共振系统上开展动物和人的神经功能比较研究有助于消除不同系统带来的诸多混淆因素影响,因而在人体用磁共振系统上开展大动物研究有其必要性。但是人体用磁共振系统所装配的梯度性能要远低于动物专用磁共振系统,尤其是梯度切换速率限制了对动物进行高分辨率功能磁共振成像的研究,因而制约了高分辨率小动物功能成像研究。本研究在西门子7特斯拉超高场磁共振平台上,提出了一种结合小尺寸发射线圈和多通道接收线圈的新型磁共振射频线圈设计,利用其小范围信号激励能力缩小成像区域,同时结合多通道接收阵列的并行加速能力,最大程度减小图像编码矩阵的尺寸,同时减轻高分辨率功能成像对梯度线圈的性能要求,使得在人用磁共振系统上开展小动物成像研究成为可能。同时本研究的结果证实了低负载的小尺寸表面接收线圈阵列可以提高功能磁共振成像的时域信噪比,为优化功能磁共振成像信号采集的射频线圈设计开拓了新思路。

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2019-02-22 READ MORE

2019年伊始,张孝通副研究员课题组在《IEEE Transactions on Biomedical Engineering》与《Physics in Medicine and Biology杂志陆续发表了其在7T磁共振平台开展的最新研究成果,两篇论文的第一作者分别为课题组硕士研究生王品一与博士研究生高阳


发表在《IEEE Transactions on Biomedical Engineering》的研究题“Evaluation of Submillimeter Diffusion Imaging of the Macaque Brain Using Readout-Segmented EPI at 7T”。弥散张量成像是当前一种能有效观察和追踪大脑白质纤维束的非侵入性检查方法, 主要用于研究人类和非人类灵长类动物大脑内的白质结构通路和结构连接模式。在临床上,毫米级的弥散张量成像广泛应用于检测超早期脑梗死、阿尔兹海默病、癫痫和脑肿瘤等疾病。但是由于扫描时间过长,图像畸变等因素的存在,因而制约了弥散张量成像的亚毫米级成像研究。近年来,超高场(7特斯拉及以上)磁共振系统的迅速发展,为亚毫米级别的大脑弥散张量成像提供了无限可能,亚毫米级图像不仅能更清晰地显示大脑白质纤维束,还能显示神经与邻近组织结构之间的空间关系,但直至目前,无论是在临床还是科研上,尚未有一种亚毫米级弥散张量成像的标准方法出现。本研究在西门子人体用7特斯拉超高场磁共振系统平台上,运用先进的西门子RESOLVE技术,在3只麻醉猕猴大脑上进行弥散张量图像的采集。通过设置RESOLVE序列中不同的扫描参数采集到不同的毫米级的弥散图像,进而通过一些列对图像信噪比和几何畸变程度的评估,得出最优的成像参数,从而寻找一种用于亚毫米级空间分辨率的弥散张量成像的最优扫描方案;同时,本研究利用这套最优扫描方案进行亚毫米级的弥散张量图像采集,获得了高质量的0.8 mm各向同性空间分辨率弥散张量图像数据,且与1mm各向同性空间分辨率弥散张量图像数据比较发现,亚毫米级弥散张量图像可以更好描绘大脑白质纤维束走向和通路结构,证实了超高场条件下亚毫米级空间分辨率弥散张量成像的可行性,为临床高分辨率弥散张量成像提供了有益的技术参考。

图片1.png

原文链接:https://ieeexplore.ieee.org/document/8641295


发表在《Physics in Medicine and Biology》的研究题“A Surface Loop Array for in vivo Small Animal MRI/fMRI on 7T Human Scanners” 基于动物模型的实验一直在神经科学研究中具有不可替代的作用。由于动物专用磁共振系统一般无法容纳大动物,且在同一台磁共振系统上开展动物和人的神经功能比较研究有助于消除不同系统带来的诸多混淆因素影响,因而在人体用磁共振系统上开展大动物研究有其必要性。但是人体用磁共振系统所装配的梯度性能要远低于动物专用磁共振系统,尤其是梯度切换速率限制了对动物进行高分辨率功能磁共振成像的研究,因而制约了高分辨率小动物功能成像研究。本研究在西门子7特斯拉超高场磁共振平台上,提出了一种结合小尺寸发射线圈和多通道接收线圈的新型磁共振射频线圈设计,利用其小范围信号激励能力缩小成像区域,同时结合多通道接收阵列的并行加速能力,最大程度减小图像编码矩阵的尺寸,同时减轻高分辨率功能成像对梯度线圈的性能要求,使得在人用磁共振系统上开展小动物成像研究成为可能。同时本研究的结果证实了低负载的小尺寸表面接收线圈阵列可以提高功能磁共振成像的时域信噪比,为优化功能磁共振成像信号采集的射频线圈设计开拓了新思路。

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2019-02-22 READ MORE
2019-01-16 READ MORE

In a recent study published in Journal of Comparative Neurology entitled “Long‐term histological changes in the macaque primary visual cortex and the lateral geniculate nucleus after monocular deprivation produced by early restricted retinal lesions and diffuser induced form deprivation”, Dr. Toru Takahata and his colleagues reported changes in the lateral geniculate nucleus (LGN) and striate cortex (V1) of 7 monkeys that had partial retinal lesion and lens-induced form deprivation in one of the eyes since infancy.

    Ocular dominance (OD) plasticity has been extensively studied in various mammalian species. While robust OD shifts are typically observed after monocular eyelid suture, relatively poor OD plasticity is observed for early eye removal or after tetrodotoxin (TTX) injections in mice. Hence, abnormal binocular signal interactions in the visual cortex may play a critical role in eliciting OD plasticity.

In this research, we examined the histochemical changes in the lateral geniculate nucleus (LGN) and the striate cortex (V1) in macaque monkeys that experienced two different monocular sensory deprivations in the same eye beginning at 3weeks of age: restricted laser lesions in macular or peripheral retina and form deprivation induced by wearing a diffuser lens during the critical period. The monkeys were subsequently reared for 5 years under a normal visual environment. In the LGN, atrophy of neurons and a dramatic increase of GFAP expression were observed in the lesion projection zones (LPZs). In V1, although no obvious shift of the LPZ border was found, the ocular dominance columns (ODCs) for the lesioned eye shrunk and those for the intact eye expanded over the entirety of V1. This ODC size change was larger in the area outside the LPZ and in the region inside the LPZ near the border compared to that in the LPZ center.

These developmental changes may reflect abnormal binocular interactions in V1 during early infancy. Our observations provide insights into the nature of degenerative and plastic changes in the LGN and V1 following early chronic monocular sensory deprivations.

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Below is the link to access the article: https://onlinelibrary.wiley.com/doi/10.1002/cne.24494


2018-12-14 READ MORE

In a recent study published in Journal of Comparative Neurology entitled “Long‐term histological changes in the macaque primary visual cortex and the lateral geniculate nucleus after monocular deprivation produced by early restricted retinal lesions and diffuser induced form deprivation”, Dr. Toru Takahata and his colleagues reported changes in the lateral geniculate nucleus (LGN) and striate cortex (V1) of 7 monkeys that had partial retinal lesion and lens-induced form deprivation in one of the eyes since infancy.

    Ocular dominance (OD) plasticity has been extensively studied in various mammalian species. While robust OD shifts are typically observed after monocular eyelid suture, relatively poor OD plasticity is observed for early eye removal or after tetrodotoxin (TTX) injections in mice. Hence, abnormal binocular signal interactions in the visual cortex may play a critical role in eliciting OD plasticity.

In this research, we examined the histochemical changes in the lateral geniculate nucleus (LGN) and the striate cortex (V1) in macaque monkeys that experienced two different monocular sensory deprivations in the same eye beginning at 3weeks of age: restricted laser lesions in macular or peripheral retina and form deprivation induced by wearing a diffuser lens during the critical period. The monkeys were subsequently reared for 5 years under a normal visual environment. In the LGN, atrophy of neurons and a dramatic increase of GFAP expression were observed in the lesion projection zones (LPZs). In V1, although no obvious shift of the LPZ border was found, the ocular dominance columns (ODCs) for the lesioned eye shrunk and those for the intact eye expanded over the entirety of V1. This ODC size change was larger in the area outside the LPZ and in the region inside the LPZ near the border compared to that in the LPZ center.

These developmental changes may reflect abnormal binocular interactions in V1 during early infancy. Our observations provide insights into the nature of degenerative and plastic changes in the LGN and V1 following early chronic monocular sensory deprivations.

image.png 

    Below is the link to access the article: https://onlinelibrary.wiley.com/doi/10.1002/cne.24494


2018-12-14 READ MORE

Brain active transmembrane water cycling measured by MR is associated with neuronal activity(2018). DOI: 10.1002/mrm.27473CV.pdf


Ruiliang Bai,Charles S. Springer Jr.,Dietmar Plenz, Peter J. Basser

 

Significance

We found that neurons absorb and release water when they relay messages throughout the brain. Tracking this water movement with imaging technology may one day provide valuable information on normal brain activity, as well as how injury or disease affect brain function.

Current functional magnetic resonance imaging (fMRI) technologies measure neuronal activity indirectly by tracking changes in blood flow and blood oxygen levels. Neurons communicate with each other by a process known as firing. In this process, they emit a slight electrical charge as an enzyme moves positively charged molecules — potassium and sodium ions — through the cell membrane. In the current study, when we stimulated cell cultures of rat neurons to fire, we found that the exchanges of potassium and sodium ions was accompanied by an increase in the number of water molecules moving into and out of the cell.

We noted that our method works only in cultures of neurons and additional studies are necessary to advance the technology so that it can be used to monitor neuronal firing in living organisms.

Abstract

Purpose: fMRI is widely used to study brain activity. Unfortunately, conventional fMRI methods assess neuronal activity only indirectly, through hemodynamic coupling. Here, we show that active, steadystate transmembrane water cycling (AWC) could serve as a basis for a potential fMRI mechanism for direct neuronal activity detection.

Methods: AWC and neuronal actitivity in rat organotypic cortical cultures were simultaneously measured with a hybrid MRfluorescence system. Perfusion with a paramagnetic MRI contrast agent, Gadoteridol, allows NMR determination of the kinetics of transcytolemmal water exchange. Changes in intracellular calcium concentration, [Cai2+] were used as a proxy of neuronal activity and were monitored by fluorescence imaging.

Results: When we alter neuronal activity by titrating with extracellular [K+] near the normal value, we see an AWC response resembling Na+K+ATPase (NKA) MichaelisMenten behavior. When we treat with the voltagegated sodium channel inhibitor, or with an excitatory postsynaptic inhibitor cocktail, we see AWC decrease by up to 71%. AWC was found also to be positively correlated with the basal level of spontaneous activity, which varies in different cultures.

Conclusions: These results suggest that AWC is associated with neuronal activity and NKA activity is a major contributor in coupling AWC to neuronal activity. Although AWC comprises steadystate, homeostatic transmembrane water exchange, our analysis also yields a simultaneous measure of the average cell volume, which reports any slower net transmembrane water transport.

Keywords

active, fMRI, functional MRI, membrane, transcytolemmal, Na+/K+ ATPase, neuronal activity, pump, water exchange

Online paper: https://doi.org/10.1002/mrm.27473

2018-10-18 READ MORE

Brain active transmembrane water cycling measured by MR is associated with neuronal activity(2018). DOI: 10.1002/mrm.27473CV.pdf


Ruiliang Bai,Charles S. Springer Jr.,Dietmar Plenz, Peter J. Basser

 

Significance

We found that neurons absorb and release water when they relay messages throughout the brain. Tracking this water movement with imaging technology may one day provide valuable information on normal brain activity, as well as how injury or disease affect brain function.

Current functional magnetic resonance imaging (fMRI) technologies measure neuronal activity indirectly by tracking changes in blood flow and blood oxygen levels. Neurons communicate with each other by a process known as firing. In this process, they emit a slight electrical charge as an enzyme moves positively charged molecules — potassium and sodium ions — through the cell membrane. In the current study, when we stimulated cell cultures of rat neurons to fire, we found that the exchanges of potassium and sodium ions was accompanied by an increase in the number of water molecules moving into and out of the cell.

We noted that our method works only in cultures of neurons and additional studies are necessary to advance the technology so that it can be used to monitor neuronal firing in living organisms.

Abstract

Purpose: fMRI is widely used to study brain activity. Unfortunately, conventional fMRI methods assess neuronal activity only indirectly, through hemodynamic coupling. Here, we show that active, steadystate transmembrane water cycling (AWC) could serve as a basis for a potential fMRI mechanism for direct neuronal activity detection.

Methods: AWC and neuronal actitivity in rat organotypic cortical cultures were simultaneously measured with a hybrid MRfluorescence system. Perfusion with a paramagnetic MRI contrast agent, Gadoteridol, allows NMR determination of the kinetics of transcytolemmal water exchange. Changes in intracellular calcium concentration, [Cai2+] were used as a proxy of neuronal activity and were monitored by fluorescence imaging.

Results: When we alter neuronal activity by titrating with extracellular [K+] near the normal value, we see an AWC response resembling Na+K+ATPase (NKA) MichaelisMenten behavior. When we treat with the voltagegated sodium channel inhibitor, or with an excitatory postsynaptic inhibitor cocktail, we see AWC decrease by up to 71%. AWC was found also to be positively correlated with the basal level of spontaneous activity, which varies in different cultures.

Conclusions: These results suggest that AWC is associated with neuronal activity and NKA activity is a major contributor in coupling AWC to neuronal activity. Although AWC comprises steadystate, homeostatic transmembrane water exchange, our analysis also yields a simultaneous measure of the average cell volume, which reports any slower net transmembrane water transport.

Keywords

active, fMRI, functional MRI, membrane, transcytolemmal, Na+/K+ ATPase, neuronal activity, pump, water exchange

Online Paper: https://doi.org/10.1002/mrm.27473

2018-10-18 READ MORE

Functionally specific optogenetic modulation in primate visual cortex

Mykyta M. Chernov, Robert M. Friedman, Gang Chen, Gene R. Stoner, and Anna Wang Roe/ PNAS October 9, 2018 115 (41) 10505-10510; published ahead of print September 26, 2018 https://doi.org/10.1073/pnas.1802018115 

 

Significance

Primate visual cortex is organized into columns that process different features of a visual scene, such as color, orientation preference, and ocular dominance. Until now, their small size has made it difficult to modulate them directly. Here, we report for the first time that focal targeting of light-sensitive ion channels (channelrhodopsins) in macaques using lentiviral vectors allows one to stimulate functional domains. We show that such targeted stimulation leads to selective activation of anatomically connected neighboring domains with similar function. Such a fine-scale optical stimulation approach is capable of mapping functionally specific domain-based neuronal networks. Its potential for linking such networks to optogenetic modulation of perception and behavior opens doors for developing targeted, domain-based neuroprosthetics.

Abstract

In primates, visual perception is mediated by brain circuits composed of submillimeter nodes linked together in specific networks that process different types of information, such as eye specificity and contour orientation. We hypothesized that optogenetic stimulation targeted to cortical nodes could selectively activate such cortical networks. We used viral transfection methods to confer light sensitivity to neurons in monkey primary visual cortex. Using intrinsic signal optical imaging and single-unit electrophysiology to assess effects of targeted optogenetic stimulation, we found that (i) optogenetic stimulation of single ocular dominance columns (eye-specific nodes) revealed preferential activation of nearby same-eye columns but not opposite-eye columns, and (ii) optogenetic stimulation of single orientation domains increased visual response of matching orientation domains and relatively suppressed nonmatching orientation selectivity. These findings demonstrate that optical stimulation of single nodes leads to modulation of functionally specific cortical networks related to underlying neural architecture.

Link: http://www.pnas.org/content/115/41/10505

2018-10-18 READ MORE
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