BOLD-fMRI联合DTI技术在神经解剖学中的应用

<正>1基本原理1.1 BOLD-fMRI成像原理功能磁共振成像(functional magnetic resonance imaging,fMRI)是以血氧水平依赖效应(blood oxygenation level dependent,BOLD)为核心检测和定位脑功能的一种成像技术。它是利用内源性血红蛋白作为对比剂,通过血氧饱和度的变化实现的成像方法,反映了神     

血氧水平依赖脑功能磁共振在精神障碍疾病中的应用

脑功能磁共振成像(fMRI)最主要的形式是血氧水平依赖磁共振成像(】BOLD-fMRI),根据神经元兴奋后局部氧耗与血流增幅不一致,用BOLD效应机制成像,间接显示神经元活动。BOLD-fMRI通过静息态和任务态两种模式,对精神疾病的研究已经不仅局限于研究特定脑区激活程度的差异,更逐渐关注分析各脑区间的神经环路和功能网络连接的变化。本文综述BOLD-fMRI成像原理、应用模式及在研究精神分裂症等常见精神障碍疾病脑区神经活动的相关性及功能连接。     

-Part I:A Review in Principal

这是脑功能磁共振成像(fMRI)的一篇综述文章。广泛使用的血氧水平依赖性磁共振功能成像(BOLD fMRI)技术在不需要射线或对比照影剂或者放射性同位素示踪的情况下,可以观测大脑皮层血流中合氧和去氧血红蛋白的很小浓度变化,这个浓度变化间接地放映了脑神经的活动程度。fMRI分空间分辨率在毫米量级而时间分辨率在秒的量级。神经科学家可以使用这些成像技术可以无创伤地得到脑激活地图分布和试验他们关于脑功能机制的各种假说     

融合白质fMRI的dMRI纤维追踪重建研究

基于弥散磁共振成像(dMRI)的纤维束重建,是分析大脑白质结构的主要工具.现有的纤维追踪成像算法受dMRI分辨率及成像机理约束,在构建大脑白质灰质边界区域的纤维时成像性能和准确性大大下降.为克服该缺陷,提出一种结合功能磁共振成像(fMRI)的新型dMRI纤维追踪成像算法.该算法引入表征白质中fMRI信号各向异性的空间相...     

血氧水平依赖磁共振脑功能成像

磁共振脑功能成像(fMRI)是通过刺激特定感官,引起大脑皮层相应部位的神经活动(功能区激活),并通过磁共振图像来显示的一种研究方法.     

脑成像与脑连接

美国NIH在2009年发布了人脑连接组计划(HCP),该计划的实施将主要依赖三大关键技术:脑电与功能磁共振(fMRI)信息的融合技术、静息态fMRI技术、脑纤维束成像等脑结构分析技术.文中简要介绍了相关技术的研究现状,以及未来的主要发展方向.     

老化与帕金森病基底核的磁共振成像研究进展

随着神经成像技术的不断进步，人们对正常老化和帕金森病(PD)的脑成像改变有了进一步认识。由于磁共振成像(MRI)技术在神经成像方面有其独特的用途和优势，尤其是功能磁共振成像(functional MRI，fMRI)具有很高的空间和时间分辨力，能将解剖和功能图像融为一体，因此在老化与PD基底核研究中MRI的应用越来越多。为进一步开展老化与PD基底核的MRI研究，现将有关文献综述如下：     

用MRI直接检测神经电磁场的研究

随着医学影像学的发展,基于脑内血氧水平变化的功能磁共振成像(fMRI)技术逐渐成为研究人脑功能的最主要的手段之一,但它的时间分辨率低.近年提出的神经电流磁共振成像(nc-MRI)是一种利用磁共振成像(MRI)技术对神经活动产生的电磁场直接成像的新方法.在原理上,nc-MRI是一种无创伤且同时具有高时间和空间分辨率特性的技术.因此,它的出现有可能会极大地推进脑功能的研究.探讨了nc-MRI信号的产生机制,包括神经磁场的理论模型和nc-MRI信号源及nc-MRI信号的模拟计算,其中包括对树突分支磁场的模拟以及nc-MRI的实验研究进展:展望了nc-MRI的未来发展方向.     

血氧水平依赖功能磁共振成像的发展状况

自从上个世纪90年代初，首次引入血氧水平依赖功能磁共振成像(BOLD-fMRI)技术以来，用BOLD-fMRI技术研究人脑的生理功能机制取得了很大的进展。本的目的是概述10多年来BOLD-fMRI的研究和发展状况，并描述研究中发现的一些热点问题，最后展望BOLD-fMRI新的临床应用。     

脑功能成像研究进展

功能磁共振成像、正电子发射计算机断层显像、单光子发射机断层显像和内禀光学成像等断层影像技术能直视活体脑的解剖和功能变化,能在屏幕上看到人脑的思维活动,从而将我们推向了绘制人类思维图像(mapping the human mind)的时代。 1 常用的脑功能成像技术 1.1 功能磁共振成像(functional magnetic resonance imaging,fMRI);依成像原理,fMRI可分为三类:第一类,灌注基础上的fMRI,以示踪剂在脑内的时间过程来计算脑血流。第二类,血流基础上的fMRI,可探查大血管里的血流变化。第三类,磁敏感对照基础上的fMRI,如血氧水平依赖性(blood oxygenation level dependent,BOLD)方法。BOLD fMRI对神经元活动的敏感性是第一、二类fMRI的2～3     

Quantitative study of changes in oxidative metabolism during visual stimulation using absolute relaxation rates

In the context of quantitative functional MRI (fMRI), deoxyhemoglobin (dHb) content is the essential physiological parameter for calibrating the blood oxygenation level-dependent (BOLD) signal. In studies on humans, the baseline dHb content or its equivalent has been evaluated indirectly by means of carbon dioxide breathing as a physiological reference condition. In this study with normal volunteers, quantitative mapping of baseline dHb content was performed in a direct manner by measuring the reversible contribution of the effective transverse relaxation rate. The BOLD signal change in the visual cortex during 8 Hz flicker visual stimulation was calibrated based on the quantitative map of baseline dHb content. The calibrated relaxation rate change that represents the stimulation-induced fractional change of dHb content decreased by 14% within the activated visual cortex. Simultaneous measurement of cerebral blood flow (CBF) with BOLD showed an increase of 59%. From the calibrated relaxation rate and CBF changes, the cerebral metabolic rate of oxygen (CMRO2) was calculated to increase by 19-28% within the activated visual cortex. The ratio of the CBF increase to the CMRO2 increase was 2-3:1, which agreed well with results of similar quantitative fMRI studies for humans. The method proposed here for quantitative evaluation of the BOLD signal may be applicable not only to fMRI for normal human subjects, but also to physiologically altered or diseased states, because it requires no physiological perturbation.     

Relationship of visual cortex function and visual acuity in anisometropic amblyopic children

Purpose: To detect the functional deficit of the visual cortex in anisometropic amblyopia children using functional magnetic resonance imaging (fMRI) technique, and investigate the relationship between visual acuity and visual cortex function.Methods: Blood oxygenation level-dependent fMRI (BOLD-fMRI) was performed in ten monocular anisometropic amblyopia children and ten normal controls. fMRI images were acquired in two runs with visual stimulation delivered separately through the sound and amblyopic eyes. Measurements were performed in cortical activation of striate and extrastriate areas at the occipital lobe. The relationship between cortex function and visual acuity was analyzed by Pearson partial analysis.Results: The activation areas of both the striate and extrastriate cortices in the amblyopic eyes were significantly lower than that of the sound fellow eyes. No relationship was found between the striate and extrastriate cortex activation. No relationship was found between the visual cortical activation of striate, extrastriate areas and visual acuity of anisometropic amblyopes.Conclusions: BOLD-fMRI revealed the independent striate and extrastriate cortical deficits in anisometropic amblyopes. In addition, the visual acuity lesion and the striate and extrastriate cortical deficits were not parallel, and results of fMRI examination have much potential value in the evaluation of amblyopia.     

血氧水平依赖功能磁共振成像的发展状况

自从上个世纪90年代初,首次引入血氧水平依赖功能磁共振成像(BOLD-fMRI)技术以来,用BOLD-fMRI技术研究人脑的生理功能机制取得了很大的进展。本文的目的是概述10多年来BOLD-fM-RI的研究和发展状况,并描述研究中发现的一些热点问题,最后展望BOLD-fMRI新的临床应用。     

Optimization of flow‐sensitive alternating inversion recovery (FAIR) for perfusion functional MRI of rodent brain

Arterial spin labeling (ASL) MRI provides a noninvasive method to image perfusion, and has been applied to map neural activation in the brain. Although pulsed labeling methods have been widely used in humans, continuous ASL with a dedicated neck labeling coil is still the preferred method in rodent brain functional MRI (fMRI) to maximize the sensitivity and allow multislice acquisition. However, the additional hardware is not readily available and hence its application is limited. In this study, flow‐sensitive alternating inversion recovery (FAIR) pulsed ASL was optimized for fMRI of rat brain. A practical challenge of FAIR is the suboptimal global inversion by the transmit coil of limited dimensions, which results in low effective labeling. By using a large volume transmit coil and proper positioning to optimize the body coverage, the perfusion signal was increased by 38.3% compared with positioning the brain at the isocenter. An additional 53.3% gain in signal was achieved using optimized repetition and inversion times compared with a long TR. Under electrical stimulation to the forepaws, a perfusion activation signal change of 63.7 ± 6.3% can be reliably detected in the primary somatosensory cortices using single slice or multislice echo planar imaging at 9.4 T. This demonstrates the potential of using pulsed ASL for multislice perfusion fMRI in functional and pharmacological applications in rat brain. Copyright © 2012 John Wiley & Sons, Ltd.     

Modeling dynamic cerebral blood volume changes during brain activation on the basis of the blood-nulled functional MRI signal

Recently, vascular space occupancy (VASO) based functional magnetic resonance imaging (fMRI) was proposed to detect dynamic cerebral blood volume (CBV) changes using the blood-nulled non-selective inversion recovery (NSIR) sequence. However, directly mapping the dynamic CBV change by the NSIR signal change is based on the assumption of slow water exchange (SWE) around the capillary regime without cerebral blood flow (CBF) effects. In the present study, a fast water exchange (FWE) model incorporating with flow effects was derived from the Bloch equations and implemented for the quantification of dynamic CBV changes using VASO-fMRI during brain activation. Simulated results showed that only subtle differences in CBV changes estimated by these two models were observed on the basis of previously published VASO results. The influence of related physiological and biophysical factors within typical ranges was evaluated in steady-state simulations. It was revealed that in the transient state the CBV curves could be delayed in comparison with measured NSIR curves owing to the imbalance between the inflowing and outflowing blood signals.     

BOLD fMRI and hemodynamic responses to somatosensory stimulation in anesthetized mice: spontaneous breathing vs. mechanical ventilation

Mouse functional MRI (fMRI) has been of great interest due to the abundance of transgenic models. Due to a mouse's small size, spontaneous breathing has often been used. Because the vascular physiology affecting fMRI might not be controlled normally, its effects on functional responses were investigated with optical intrinsic signal (OIS) imaging and 9.4 T BOLD fMRI. Three conditions were tested in C57BL/6 mice: spontaneous breathing under ketamine and xylazine anesthesia (KX), mechanical ventilation under KX, and mechanical ventilation under isoflurane. Spontaneous breathing under KX induced an average pCO₂ of 83 mmHg, whereas a mechanical ventilation condition achieved a pCO₂ of 37‐41 mmHg within a physiological range. The baseline diameter of arterial and venous vessels was only 7%‐9% larger with spontaneous breathing than with mechanical ventilation under KX, but it was much smaller than that in normocapnic isoflurane‐anesthetized mice. Three major functional studies were performed. First, CBV‐weighted OIS and arterial dilations to 4‐second forepaw stimulation were rapid and larger at normocapnia than hypercapnia under KX, but very small under isoflurane. Second, CBV‐weighted OIS and arterial dilations by vasodilator acetazolamide were measured for investigating vascular reactivity and were larger in the normocapnic condition than in the hypercapnic condition under KX. Third, evoked OIS and BOLD fMRI responses in the contralateral mouse somatosensory cortex to 20‐second forepaw stimulation were faster and larger in the mechanical ventilation than spontaneous breathing. BOLD fMRI peaked at the end of the 20‐second stimulation under hypercapnic spontaneous breathing, and at ~9 seconds under mechanical ventilation. The peak amplitude of BOLD fMRI was 2.2% at hypercapnia and ~3.4% at normocapnia. Overall, spontaneous breathing induces sluggish reduced hemodynamic and fMRI responses, but it is still viable for KX anesthesia due to its simplicity, noninvasiveness, and well‐localized BOLD activity in the somatosensory cortex.     

The impact of restricted diet on brain function using BOLD-fMRI

We investigated the effect of a restricted diet model on activity in the human motor cortex using functional magnetic resonance imaging (fMRI). Two series of blood oxygenation level-dependent (BOLD)-fMRI measurements were made in healthy subjects performing simple motor tasks using their right hands. The first series was done 5–10 days prior to the restricted diet schedule (controls), and the second series was performed after 25–28 days of restricted diet, in the form of a religious fast (Ramadan). The size and intensity of the activated area in the motor cortex increased during the time of restricted diet versus the controls. We conclude that restricted diet has a significant effect on cerebral activity, as shown by BOLD-fMRI, although the exact relationship between the images and neuronal activity due to the restricted diet is still to be determined.     

Evaluation of a quantitative blood oxygenation level-dependent (qBOLD) approach to map local blood oxygen saturation

Blood oxygen saturation (SO(2)) is a promising parameter for the assessment of brain tissue viability in numerous pathologies. Quantitative blood oxygenation level-dependent (qBOLD)-like approaches allow the estimation of SO(2) by modelling the contribution of deoxyhaemoglobin to the MR signal decay. These methods require a high signal-to-noise ratio to obtain accurate maps through fitting procedures. In this article, we present a version of the qBOLD method at long TE taking into account separate estimates of T(2), total blood volume fraction (BV(f)) and magnetic field inhomogeneities. Our approach was applied to the brains of 13 healthy rats under normoxia, hyperoxia and hypoxia. MR estimates of local SO(2) (MR_LSO(2)) were compared with measurements obtained from blood gas analysis. A very good correlation (R(2) = 0.89) was found between brain MR_LSO(2) and sagittal sinus SO(2).     

基于一般线性模型的机器学习方法在BOLD-fMRI脑胶质瘤患者个体化运动功能区定位中的应用价值

目的 探讨基于一般线性模型（GLM）的机器学习方法在血氧水平依赖功能磁共振成像（BOLD-fMRI）定位脑胶质瘤患者个体化运动功能中的应用价值。方法 前瞻性研究。纳入2017年11月—2021年11月西安交通大学第一附属医院神经外科确诊为脑胶质瘤且病灶位于大脑运动功能区的38例患者作为机器学习模型的验证集（男25例、女13例,年龄24~69岁）,同期招募健康志愿者50例作为模型的训练集（男26例、女24例,年龄22~68岁）。采用独立成分分析法（ICA）,随机提取98例人类连接组计划（HCP）受试者的静息态功能核磁共振（rs-fMRI）特征。依据健康志愿者的rs-fMRI和基于任务的功能磁共振（tb-fMRI）的相关性,训练基于GLM的机器学习模型。观察项目：（1）采用Pearson相关系数（CC）分析比较GLM预测的激活与实际激活的相似度。（2）采用Dice系数（DC）作为模型预测效能的定量指标,比较GLM与ICA方法的预测效能。结果 （1）胶质瘤患者基于GLM的机器学习方法所预测的激活与实际tb-fMRI的功能激活相似度高[（89.47% （34/38）的患者CC值>0.30）]。（2）胶质瘤患者GLM预测任务态运动功能激活的效能,DC为0.34（0.27,0.42）,优于ICA方法的效能DC 0.26（0.16,0.30）,差异有统计学意义（Z=-3.88,P<0.001）;GLM在肿瘤半球的预测效能优于ICA方法,DC分别为0.36（0.17,0.48）和0.34（0.04,0.45）,差异有统计学意义（Z=-2.43,P=0.015）;2种方法在非肿瘤半球的预测效果均显著高于肿瘤半球（Z=-4.33、-3.59,P值均<0.001）。结论 基于GLM的机器学习方法能够很好地在术前利用rs-fMRI数据预测出胶质瘤患者的tb-fMRI运动功能激活,且其预测效果好于ICA方法。     

Endogenous functional CBV contrast revealed by diffusion weighting

Functional MRI (fMRI) based on the blood oxygenation level dependent (BOLD) contrast often suffers from a lack of specificity because of the vascular spread of oxygenation changes. It is suggested from the optical imaging and animal fMRI literature that cerebral blood volume (CBV) changes are more closely tied to the smaller vessels. As such, fMRI contrast based on CBV changes will have improved spatial specificity to the neuronal activities as they are immediately adjacent to the smaller vessels. In this paper, an endogenous contrast mechanism based on a diffusion weighting strategy that could detect functional CBV changes is presented. Initially, a theoretical framework is presented to model the functional signal changes as a function of CBV under diffusion weighting, which predicts peak CBV sensitivity at various vessel-tissue mixtures. It was found that a b factor over 1500 s/mm(2) would be necessary to achieve dominant CBV contrast. Further, two sets of experimental results are also presented. In the first experiment, diffusion weighting at a set of b factors ranging from 300 to 600 s/mm(2) was used. The results indicated that while the positive activation (predominantly BOLD signal) continued to reduce in magnitude and spatial extent, the negative activation (predominantly CBV signal) remained virtually constant with increasing b factors. The second experiment used a b factor of 1600 s/mm(2) and showed extensive negative activation in the visual cortex and greatly reduced positive activations compared with images with no diffusion weighting. The time course of negative activation showed a faster time to peak and return to baseline than the positive BOLD activity, consistent with the small vessel origin of the signal changes. These results suggest that appropriate diffusion weighting could be used to measure activation related CBV changes.