T2-weighted magnetic resonance imaging of cerebrovascular reactivity in rat reversible focal cerebral ischemia

Cerebrovascular carbon dioxide (CO₂) reactivity is an important hemodynamic index in cerebrovascular disease. In the present study T2^*-weighted magnetic resonance image (T2^*WI) was evaluated as a non-invasive method to investigate changes in CO₂ reactivity. Fourteen rats were subjected to permanent or, 30 and 90 min of temporary middle cerebral artery occlusion. A series of T2^*WIs and diffusion-weighted magnetic resonance images (DWI) was performed hourly under normo- and hypercapnic conditions. Triphenyltetrazolium chloride (TTC) staining of brain sections was obtained at the end of experiment to evaluate ischemic damage. During ischemia, a 4–6% signal increase upon hypercapnia was observed on T2^*WI in the non-ischemic hemisphere, while no such reactivity was seen in the putamen and cortex ipsilateral to the MCA occlusion. After reperfusion, CO₂ reactivity recovered in the putamen and cortex in the 30 min ischemia group and in the cortex alone of the 90 min ischemia groups. The areas with irreversible CO₂ reactivity dysfunction coincidentally revealed no recovery on DWI and lack of TTC staining. The results indicate that T2^*WI can be used to monitor changes in CO₂ reactivity after various ischemic insults that may indicate tissue viability.     

脑功能磁共振成像研究进展

主要综述fMRI产生的历史、成像原理、成像技术和方法、已经取得的成绩以及将来研究发展的方向等。fMRI产生技术广泛应用的20世纪90年代,主要受快速成像技术的影响,从有创走向无创,从而受到神经、认知和心理科学领域的极大关注。fMRI原理是根据神经元兴奋后局部氧耗与血流增幅不一致,而BOLD效应机制成像,间接显示神经元活动。成像主要采用平面回波成像（EPI）和快速小角度激发（FLASH）技术、二者在时间和空间分辨率上各有优劣。最后几年来,fMRI技术对脑功能的研究已取得了巨大的成绩,估计将在这一领域继续拥有非常重要的地位。将来fMRI可能主要在BOLD效应的生理过程、临床应用以及高场磁体的应用等领域进一步展开。     

磁共振成像在肾上腺脑白质营养不良诊断中的应用

目的 探讨氢质子磁共振波谱成像(1H-MRSI)和弥散张量成像(DTI)在肾上腺脑白质营养不良(ALD)诊断中的价值,并应用弥散张量白质纤维束追踪成像(DTT)技术显示ALD纤维束受累情况.方法 对6例ALD患者行1H-MRSI、DTI和常规影像学检查,比较不同病变区域N-乙酰天冬氨酸(NAA)、胆碱复合物(Cho)、肌酐(cr)、表观扩散系数(ADC)和各向异性分量(FA)的变化及相关性,选择胼胝体和锥体束进行白质纤维束成像.结果 病变起始区域NAA/Cr比值(0.55±0.19),NAA/Cho比值(0.22±0.11)降低(F=7.693、7.751),Cho/Cr比值(2.54±0.37)升高(F=6.348),ADC值最高(1.49±0.36,F=5.226),FA值最低(0.21±0.08,F=5.139,均P＜0.05);病变区域近周NAA/Cr比值(1.16±0.03)和NAA/Cho比值(0.45±0.17)降低较远周明显(t=1.769、1.842,P＜0.05);病变发展区域ADC值(0.89±0.03)低,FA值(0.45±0.07)最高;NAA/Cho与ADC负相关(r=-0.71,P＜0.05),与FA正相关(r=0.31,P＜0.05);DTT结果 显示病变区域胼胝体和锥体束均受累,走行中断或呈不连续碎片样.结论 1H-MRSI和DTI为ALD提供了更多的早期诊断依据,并且可动态监测脑白质病变进展,DTT可直接显示ALD患者纤维束受累情况.     

术中1.5T核磁共振外科治疗难治性癫癎

目的探讨应用术中1.5T核磁共振(MRI)治疗难治性癫癎的手术效果。方法手术治疗难治性癫癎15例,利用术中1.5T核磁共振,术前常规行T1、T2及T1加强,及弥散张量成像,术中切除(切开)后行T1、T2及T1加强及弥散张量成像检查,以确定切除范围及功能区定位,其中5例术中MR检查后扩大切除。结果左侧枕叶局灶性皮质发育异常2例,左侧颞叶海绵状血管瘤4例,左侧颞叶海马硬化1例,右侧额叶胚胎发育不良性神经上皮肿瘤1例,右侧中央前回局灶性皮质发育不良1例,右侧颞叶海马硬化1例,右侧颞叶海绵状血管瘤1例,右侧颞叶胶质瘤1级1例,右侧中央后回海绵状血管瘤1例,胼胝体切开2例,engle分级:Ⅰ级11例,Ⅱ级4例。结论术中1.5T核磁共振对切除(切开)病灶及功能保护有指导意义。     

Myelin deficiencies visualized in vivo: visually evoked potentials and T2-weighted magnetic resonance images of shiverer mutant and wild-type mice

Visually evoked potentials (VEPs) and micro magnetic resonance imaging (micro MRI) are widely used as noninvasive techniques for diagnosis of central nervous system (CNS) diseases, especially myelin diseases, such as multiple sclerosis. Here we use these techniques in tandem to validate the in vivo data in mouse models. We used the shiverer mutant mouse, which has little or no CNS myelin, as a test model. These data show that shiverer (MBP(shi)/MBP(shi)) has a VEP latency that is 30% longer than that of its wild-type sibling. Surprisingly, the heterozygous (MBP(shi)/+) mouse, with apparently normal myelin, nevertheless has a 7% increase in its VEP latency vs. wild type. The micro MRIs of the same animals show that myelinated white matter is hypointense compared with gray matter as a result of the shorter T2 in myelinated regions of the CNS. T2-weighted images of wild-type and heterozygous shiverer mice show regions of hypointensity corresponding to the major myelinated tracts, including the optic nerve and the optic tract of the CNS, whereas shiverer mice have no regions of low intensity and therefore no detectable myelinated areas. In shiverer mice, micro MRI can discern hypomyelination throughout the brain, including the optic tract, and these changes correlate with longer VEP latencies. In addition, VEPs can also detect changes in the molecular make up of myelin that are not discernible with histology or micro MR. These data show the potential of using micro MRI in combination with VEPs to follow changes in both the quality and the quantity of myelin in vivo. These combined methods would be useful for longitudinal studies and therapy testing.     

Inter- and intraoperator reliability of brain tissue measures using magnetic resonance imaging

Abstract. Grey matter, white matter and cerebrospinal volume in the human brain were measured using magnetic resonance image analysis software BRAINS. Ten volunteers were scanned in the MR sequence (3D-SPGR; 1.5-mm slice thickness and T2 images; 3mm slice thickness). Two operators obtained ten volume measures of grey matter,white matter and cerebrospinal fluid (CSF) in the intracranial box, frontal box, temporal box, parietal box and occipital box. The same data set of ten scans was segmented and the volumes measured on a second occasion by one operator using the same procedure. The interoperator and intraoperator reliabilities for measures of the three brain tissues were very good, with reliability coefficients (intraclass correlation coefficients) ranging between 0.971 and 0.999. The segmentation and measurement are useful for volumetric studies in the human brain using BRAINS.     

Setup and data analysis for functional magnetic resonance imaging of awake cat visual cortex

Functional magnetic resonance imaging（fMRI）is one of the most commonly used methods in cognitive neuroscience on humans.In recent decades,fMRI has also been used in the awake monkey experiments to localize functional brain areas and to compare the functional differences between human and monkey brains.Several procedures and paradigms have been developed to maintain proper head fixation and to perform motion control training.In this study,we extended the application of fMRI to awake cats without training,receiving a flickering checkerboard visual stimulus projected to a screen in front of them in a block-design paradigm.We found that body movement-induced non-rigid motion introduced artifacts into the functional scans,especially those around the eye and neck.To correct for these artifacts,we developed two methods：one for general experimental design,and the other for studies of whether a checkerboard task could be used as a localizer to optimize the motioncorrection parameters.The results demonstrated that,with proper animal fixation and motion correction procedures,it is possible to perform fMRI experiments with untrained awake cats.     

低血糖脑病的临床及脑部磁共振特征

目的探讨低血糖脑病的临床及脑部磁共振特征。方法回顾分析69例低血糖昏迷患者的临床、脑磁共振（MRI）成像资料。结果低血糖昏迷诱因较为复杂,常见的为进食减少、腹泻、上呼吸道感染、降糖药物应用不当等。临床表现复杂多样,除意识障碍外,还可表现为偏瘫、四肢瘫、凝视麻痹等,多数伴有Babinski征。69例患者中有18例出现脑MRIDWI异常高信号病灶,病灶主要累及海马、基底节、大脑皮质以及皮质下白质,多为对称性损害。3个月后随访,不伴有脑部MRI损害的患者预后良好率明显高于伴有脑部MRI损害的患者（94．12％对22．22％;P=0．0011）。伴有脑部MRI损害者有10例患者预后不良,其中9例（90％）发生于皮质受累患者。结论低血糖脑病临床表现不具有特异性,对于昏迷患者,应当考虑到低血糖的可能。降糖药物应用不当为低血糖脑病的主要诱发因素。脑部MRI要优于脑部CT检查,其中DWI序列对于检测低血糖所致的脑部损害有着非常重要的意义。皮质受累者预后不良。     

超高场磁共振功能成像辅助切除躯体感觉区胶质瘤(附5例报告)

目的应用超高场磁共振功能成像技术进行手术前后研究脑躯体感觉功能区肿瘤与功能区的定位,辅助切除躯体感觉功能区胶质瘤。方法5例邻近或累及躯体感觉功能区的胶质瘤患者,术前行双手持物对接刺激策略,在3.0T磁共振采用血氧水平依赖(BOLD)原理进行图像采集,经工作站(Leonardo syngo 2003A,Siemens)提供的BOLD功能图像分析软件包进行分析获得脑运动功能区的激活图像,参与神经外科手术方案的制定。所有患者均在唤醒麻醉下进行显微外科手术,在术前脑功能磁共振图像指导下利用皮质直接电刺激定位感觉区与运动区。在保护脑功能区功能不受损的前提下,最大程度地切除胶质瘤。术前、术后均行KPS评分,判断患者的状态。结果(1)5例躯体感觉功能区胶质瘤,通过此项技术获得了较好的BOLD功能磁共振成像感觉功能区激活图像,定位躯体感觉功能区。(2)患者在唤醒麻醉下,在术前脑功能磁共振图像指导下利用直接皮质电刺激快捷、准确进行中央后回定位,两者具有良好的一致性。结论应用3.0T MRI可以于术前更好地利用BOLD技术显示躯体感觉功能区与脑胶质瘤的解剖关系,以指导唤醒麻醉下直接皮质电刺激定位躯体感觉功能区的手术,实现最大程度保护患者重要的功能并最大程度地切除肿瘤。     

Model-based variational smoothing and segmentation for diffusion tensor imaging in the brain

This article applies a unified approach to variational smoothing and segmentation to brain diffusion tensor image data along user-selected attributes derived from the tensor, with the aim of extracting detailed brain structure information. The application of this framework simultaneously segments and denoises to produce edges and smoothed regions within the white matter of the brain that are relatively homogeneous with respect to the diffusion tensor attributes of choice. This approach enables the visualization of a smoothed, scale invariant representation of the tensor data field in a variety of diverse forms. In addition to known attributes such as fractional anisotropy, these representations include selected directional tensor components and additionally associated continuous valued edge fields that might be used for further segmentation. A comparison is presented of the results of three different data model selections with respect to their ability to resolve white matter structure. The resulting images are integrated to provide better perspective of the model properties (edges, smoothed image, and so forth) and their relationship to the underlying brain anatomy. The improvement in brain image quality is illustrated both qualitatively and quantitatively, and the robust performance of the algorithm in the presence of added noise is shown. Smoothing occurs without loss of edge features because of the simultaneous segmentation aspect of the variational approach, and the output enables better delineation of tensors representative of local and long-range association, projection, and commissural fiber systems.     

Registration of in vivo magnetic resonance T1-weighted brain images to triphenyltetrazolium chloride stained sections in small animals

Signal changes observed in high-resolution in vivo magnetic resonance (MR) images acquired during cerebral ischemia in small animal models must be correlated to molecular indicators of tissue damage obtained from digitized histological brain sections. An effective image registration technique that incorporates both a linear and non-linear thin plate spline transform was developed to compensate the distortions that occur in the brain during the extraction, fixation, and staining process. Features in different layers of the brain were utilized in conjunction with a radial guideline-assisted landmark selection method to register tissue layers with few distinguishing characteristics. Quantitative analysis using simulated data demonstrated average registration error of 400 microm (corresponding to approximately 2.5 pixels in the MR images) when > or =50 landmark points are used. Visual agreement was obtained between T(1)-weighted MR images and 2,3,5-triphenyltetrazolium chloride stained histology. These methods will allow accurate registration of in vivo images with histology to correlate in vivo surrogate markers of tissue damage with specific histological indicators of disease.     

Influence of X chromosome and hormones on human brain development: a magnetic resonance imaging and proton magnetic resonance spectroscopy study of Turner syndrome.

BACKGROUND: Women with Turner syndrome (TS; 45,X) lack a normal second X chromosome, and many are prescribed exogenous sex and growth hormones (GH). Hence, they allow us an opportunity to investigate genetic and endocrine influences on brain development. METHODS: We examined brain anatomy and metabolism in 27 adult monosomic TS women and 21 control subjects with volumetric magnetic resonance imaging and magnetic resonance spectroscopy. RESULTS: In TS women, regional gray matter volume was significantly smaller in parieto-occipital cortex and caudate nucleus and larger in cerebellar hemispheres. White matter was reduced in the cerebellar hemispheres, parieto-occipital regions, and splenium of the corpus callosum but was increased in the temporal and orbitofrontal lobes and genui of corpus callosum. Women with TS had a significantly lower parietal lobe concentration of N-acetyl aspartate, and higher hippocampal choline. Also, among women with TS, there were significant differences in regional gray matter volumes and/or neuronal integrity, depending upon parental origin of X chromosome and oxandrolone and GH use. CONCLUSIONS: X chromosome monosomy, imprinting and neuroendocrine milieu modulate human brain development-perhaps in a regionally specific manner.     

Directly mapping magnetic field effects of neuronal activity by magnetic resonance imaging

Magnetic resonance imaging (MRI) of brain functional activity relies principally on changes in cerebral hemodynamics, which are more spatially and temporally distributed than the underlying neuronal activity changes. We present a novel MRI technique for mapping brain functional activity by directly detecting magnetic fields induced by neuronal firing. Using a well-established visuomotor paradigm, the locations and latencies of activations in visual, motor, and premotor cortices were imaged at a temporal resolution of 100 msec and a spatial resolution of 3 mm, and were found to be in consistent with the electrophysiological and functional MRI (fMRI) literature. Signal strength was comparable to traditional event-related fMRI methods: about 1% of the baseline signal. The magnetic-source MRI technique greatly increases the temporal accuracy in detecting neuronal activity, providing a powerful new tool for mapping brain functional organization in human and animals.     

原发性三叉神经痛的磁共振扫描对比研究

目的探讨磁共振对三又神经痛的诊断价值。方法采用3D—FFE序列扫描三叉神经痛60例,患、健侧进行对比,术中进行验证。再与患者配偶60例进行对比。结果磁共振显示研究组患侧明显压迫51例,可疑接触3例,无接触6例,健侧明显压迫14例,可疑接触4例,无接触42例,术中证实患侧都存在明确压迫,其中动脉性压迫57例,静脉性压迫3例。对照组明显压迫15例,可疑接触5例,无接触40例。结论磁共振3D—FFE序列扫描对有三叉神经痛有较高的诊断价值,但对静脉性压迫易漏诊。     

MR序列优化组合在创伤性脑损伤的诊断价值

目的分析MR诊断创伤性脑损伤(TBI)的价值,探讨TBI患者MR一站式诊断的可行性。方法对260例TBI病例进行MR序列组合扫描,包括小角度激发快速梯度回波序列(FLASH)、流动衰减反转恢复序列(FLAIR)、自旋回波(SE)T1WI、快速自旋回波(TSE)T2WI,比较MR序列组合和CT对各种类型TBI诊断的差异。结果脑实质内出血61例,MR显示61例,CT显示53例;硬膜下出血55例,MR显示55例,CT显示49例;硬膜外出血45例,MR显示45例,CT显示40例;脑挫(裂)伤35例,MR显示35例,CT显示25例;蛛网膜下腔出血35例,MR显示31例,CT显示33例;弥漫性轴索损伤29例,MR显示29例,CT显示5例。MR序列组合准确显示病变256例,CT为209例,两者差异有极显著统计学意义(P0.01),MR序列组合总体诊断敏感性高于CT。结论 MR序列组合(FLASH\FLAIR\T1WI\T2WI)诊断创伤性脑损伤明显优于CT,可列为TBI常规检查方法,实行TBI一站式诊断。     

Meta-analysis of magnetic resonance imaging brain morphometry studies in bipolar disorder.

BACKGROUND: Several studies assessing volumetric measurements of regional brain structure in bipolar disorder have been published in recent years, but their results have been inconsistent. Our aim was to complete a meta-analysis of regional morphometry in bipolar disorder as assessed using magnetic resonance imaging (MRI). METHODS: We conducted a systematic literature search of MRI studies of bipolar disorder and identified studies which reported volume measurements in a selected number of regions. Twenty-six studies comprising volumetric measurements on up to 404 independent patients with bipolar disorder were included. A meta-analysis was carried out comparing the volumes of regions in bipolar disorder to comparison subjects using a random effects model. RESULTS: Patients with bipolar disorder had enlargement of the right lateral ventricle, but no other regional volumetric deviations which reached significance. Strong heterogeneity existed for several regions, including the third ventricle, left subgenual prefrontal cortex, bilateral amygdala and thalamus. CONCLUSIONS: Regional volume of most structures we studied is preserved in bipolar disorder as a whole, which was significantly associated only with right-sided ventricular enlargement. However the extensive heterogeneity detected indicates the need for further studies to establish if consistent regional brain volume deviation exists in bipolar disorder or in specific clinical subsets of the illness.     

Lesion localization of global aphasia without hemiparesis by overlapping of the brain magnetic resonance images

Global aphasia without hemiparesis is a striking stroke syndrome involving language impairment without the typically manifested contralateral hemiparesis, which is usually seen in patients with global aphasia following large left perisylvian lesions. The objective of this study is to elucidate the specific areas for lesion localization of global aphasia without hemiparesis by retrospectively studying the brain magnetic resonance images of six patients with global aphasia without hemiparesis to define global aphasia without hemiparesis-related stroke lesions before overlapping the images to visualize the most overlapped area. Talairach coordinates for the most overlapped areas were converted to corresponding anatomical regions. Lesions where the images of more than three patients overlapped were considered significant. The overlapped global aphasia without hemiparesis related stroke lesions of six patients revealed that the significantly involved anatomi- cal lesions were as follows： frontal lobe, sub-gyral, sub-lobar, extra-nuclear, corpus callosum, and inferior frontal gyrus, while caudate, claustrum, middle frontal gyrus, limbic lobe, temporal lobe, superior temporal gyrus, uncus, anterior cingulate, parahippocampal, amygdala, and subcallosal gyrus were seen less significantly involved. This study is the first to demonstrate the heterogeneous anatomical involvement in global aphasia without hemiparesis by overlapping of the brain magnetic resonance images.     

Multimodal biological brain age prediction using magnetic resonance imaging and angiography with the identification of predictive regions

Biological brain age predicted using machine learning models based on high‐resolution imaging data has been suggested as a potential biomarker for neurological and cerebrovascular diseases. In this work, we aimed to develop deep learning models to predict the biological brain age using structural magnetic resonance imaging and angiography datasets from a large database of 2074 adults (21–81 years). Since different imaging modalities can provide complementary information, combining them might allow to identify more complex aging patterns, with angiography data, for instance, showing vascular aging effects complementary to the atrophic brain tissue changes seen in T1‐weighted MRI sequences. We used saliency maps to investigate the contribution of cortical, subcortical, and arterial structures to the prediction. Our results show that combining T1‐weighted and angiography MR data led to a significantly improved brain age prediction accuracy, with a mean absolute error of 3.85 years comparing the predicted and chronological age. The most predictive brain regions included the lateral sulcus, the fourth ventricle, and the amygdala, while the brain arteries contributing the most to the prediction included the basilar artery, the middle cerebral artery M2 segments, and the left posterior cerebral artery. Our study proposes a framework for brain age prediction using multimodal imaging, which gives accurate predictions and allows identifying the most predictive regions for this task, which can serve as a surrogate for the brain regions that are most affected by aging.     

DBSegment: Fast and robust segmentation of deep brain structures considering domain generalization

Segmenting deep brain structures from magnetic resonance images is important for patient diagnosis, surgical planning, and research. Most current state‐of‐the‐art solutions follow a segmentation‐by‐registration approach, where subject magnetic resonance imaging (MRIs) are mapped to a template with well‐defined segmentations. However, registration‐based pipelines are time‐consuming, thus, limiting their clinical use. This paper uses deep learning to provide a one‐step, robust, and efficient deep brain segmentation solution directly in the native space. The method consists of a preprocessing step to conform all MRI images to the same orientation, followed by a convolutional neural network using the nnU‐Net framework. We use a total of 14 datasets from both research and clinical collections. Of these, seven were used for training and validation and seven were retained for testing. We trained the network to segment 30 deep brain structures, as well as a brain mask, using labels generated from a registration‐based approach. We evaluated the generalizability of the network by performing a leave‐one‐dataset‐out cross‐validation, and independent testing on unseen datasets. Furthermore, we assessed cross‐domain transportability by evaluating the results separately on different domains. We achieved an average dice score similarity of 0.89 ± 0.04 on the test datasets when compared to the registration‐based gold standard. On our test system, the computation time decreased from 43 min for a reference registration‐based pipeline to 1.3 min. Our proposed method is fast, robust, and generalizes with high reliability. It can be extended to the segmentation of other brain structures. It is publicly available on GitHub, and as a pip package for convenient usage.