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实时交互式经颅磁刺激功能磁共振成像技术的应用与进展

Application and Progress of Real-time Interleaved Transcranial Magnetic Stimulation Functional Magnetic Resonance Imaging

  • 摘要: 经颅磁刺激(TMS)作为一项非侵入性神经调控技术,在研究大脑功能定位、调控认知功能、诊治神经/精神疾病等方面取得了一定成效,但其作用机制和生理效应未明确。血氧水平依赖的功能性磁共振成像(BOLD-fMRI)能反映脑组织的功能活动。实时交互式经颅磁刺激功能磁共振成像(TMS-fMRI)结合了TMS和BOLD-fMRI两种技术的优势,能够监测TMS刺激部位和与其存在功能连接的远端脑区兴奋性的改变。本文对实时交互式TMS-fMRI的应用和技术的进展、局限性和未来发展方向进行了综述。从应用上看,在大脑功能连接网络研究领域,TMS-fMRI能够显示在不同的实验中TMS对远端脑区产生的影响,并以100 ms的分辨率观察大脑网络间的动态连接,这是在探索时间特异性脑区功能连接方面取得的重要进展,但利用TMS-fMRI对脑区功能连接的空间特异性研究尚有不足,可以作为未来的研究方向;在脑区之间的相互作用探究中,TMS-fMRI能评估TMS对大脑皮层产生的影响以及脑区间的相互作用,帮助我们理解注意力控制背后的神经机制,研究大脑对躯体感觉的处理,但TMS-fMRI只能观察到TMS作用下不同脑区兴奋性之间的关联,而导致这一现象的机制以及脑区之间的关联有无特异性还待进一步研究;TMS-fMRI还能用于研究神经、精神疾病的发病机制和治疗效果,研究精神活性化合物对大脑区域影响,但目前TMS-fMRI还难以在临床中普及,下一步研究者们需要将目光放在TMS-fMRI临床适应症的研究当中。TMS-fMRI的一个主要技术难题是TMS线圈难以在MRI扫描仪内准确定位以刺激大脑皮层的特定区域,另一个重要问题是TMS线圈对静磁场产生影响造成图像伪影,导致回波平面图像的空间畸变和局部信号丢失。研究者们通过持续技术更新逐渐解决了线圈定位和图像伪影两大问题,但TMS-fMRI技术在参数设置、用户体验、应用的简便性和普适性等方面仍存在问题,这是未来的技术进步方向。

     

    Abstract: Transcranial magnetic stimulation (TMS), as a non-invasive neuromodulation technique, has achieved certain results in the study of brain function localization, treatment of nervous and mental diseases, but its mechanism of action and physiological effects are difficult to be clarified. The signals in blood oxygenation level dependent functional magnetic resonance imaging (BOLD-fMRI) is capable of reflecting the activities of brain tissue neurons. TMS-fMRI combines the advantages of two techniques to monitor changes in excitability of the TMS stimulation site and the distal brain region with which it is functionally linked. In this review, we elaborates the advances, limitations and future expectations of real-time interleaved TMS-fMRI. From the perspective of application progress, in the field of brain functional connectivity network research, TMS-fMRI can observe the dynamic connection between brain networks with a resolution of 100 ms, which is an important progress in the exploration of time-specific functional connectivity of brain regions. However, the TMS-fMRI on spatial specificity of functional connectivity of brain regions is still unclear, and future studies can focus on this aspect. In addition, TMS-fMRI can assess the effect of TMS on the cerebral cortex and the interaction between brain regions, help us understand the neural mechanism behind attention control, and study the brain's processing of somatosensory sensation. Nevertheless, TMS-fMRI can only observe the correlation between excitability of different brain regions under the stimulation of TMS, but the mechanism of this phenomenon and whether the correlation between brain regions is specific needs more research. Futhermore, TMS-fMRI can also be used to study the pathogenesis and therapeutic effect of neurological and psychiatric diseases, and the effects of psychoactive compounds on brain regions. Nonetheless, currently TMS-fMRI is still difficult to be widely used in clinical practice, so more efforts are needed in the study of clinical indications of TMS-fMRI. There are two major technical problems of TMS-fMRI. One major problem is that it is difficult for TMS coils to accurately position specific areas of cerebral cortex in MRI scanner. Another major problem is that TMS coils affect the static magnetic field (B0), resulting in image artifacts, spatial distortion and local signal loss of echo-Planar (EP) images. Nowadays, researchers have solved the two major problems through continuous technical updates, but TMS-fMRI still has problems in parameter setting, user experience, simplicity and universality of application and other aspects, which is the direction of future technological progress.

     

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