Function and connectivity in human primary auditory cortex: a combined fMRI and DTI study at 3 Tesla

Human primary auditory cortex (PAC) is functionally organized in a tonotopic manner. Past studies have used neuroimaging to characterize tonotopic organization in PAC and found similar organization as that described in mammals. In contrast to what is known about PAC in primates and nonprimates, in humans, the structural connectivity within PAC has not been defined. In this study, stroboscopic event-related functional magnetic resonance imaging (fMRI) was utilized to reveal mirror symmetric tonotopic organization consisting of a high-low-high frequency gradient in PAC. Furthermore, diffusion tensor tractography and probabilistic mapping was used to study projection patterns within tonotopic areas. Based on earlier physiological and histological work in nonhuman PAC, we hypothesized the existence of cross-field isofrequency (homotopic) and within-field non-isofrequency (heterotopic)-specific axonal projections in human PAC. The presence of both projections types was found in all subjects. Specifically, the number of diffusion tensor imaging (DTI) reconstructed fibers projecting between high- and low-frequency regions was greater than those fibers projecting between 2 high-frequency areas, the latter of which are located in distinct auditory fields. The fMRI and DTI results indicate that functional and structural properties within early stages of the auditory processing stream are preserved across multiple mammalian species at distinct evolutionary levels.     

White matter asymmetry in the human brain: a diffusion tensor MRI study

Language ability and handedness are likely to be associated with asymmetry of the cerebral cortex (grey matter) and connectivity (white matter). Grey matter asymmetry, most likely linked to language has been identified with voxel-based morphometry (VBM) using T(1)-weighted images. Differences in white matter obtained with this technique are less consistent, probably due to the relative insensitivity of the T(1) contrast to the ultrastructure of white matter. Furthermore, previous VBM studies failed to find differences related to handedness in either grey or white matter. We revisited these issues and investigated two independent groups of subjects with diffusion-tensor imaging (DTI) for asymmetries in white matter composition. Using voxel-based statistical analyses an asymmetry of the arcuate fascicle was observed, with higher fractional anisotropy in the left hemisphere. In addition, we show differences related to handedness in the white matter underneath the precentral gyrus contralateral to the dominant hand. Remarkably, these findings were very robust, even when investigating small groups of subjects. This highlights the sensitivity of DTI for white matter tissue differences, making it an ideal tool to study small patient populations.     

Quantitative diffusion tensor tractography of association and projection fibers in normally developing children and adolescents

Whole-brain diffusion tensor tractography (DTT) at high signal-to-noise ratio and angular and spatial resolutions were utilized to study the effects of age, sex differences, and lateral asymmetries of 6 white matter pathways (arcuate fasciculus [AF], inferior longitudinal fasciculus, inferior fronto-occipital fasciculus [IFOF], uncinate fasciculus [UF], corticospinal tract [CST], and somatosensory pathway [SS]) in 31 right-handed children (6-17 years). Fractional anisotropy (FA), a measure of the orientational variance in water molecular diffusivity, and the magnitude of water diffusivity (parallel, perpendicular, and mean diffusivity) along the pathways were quantified. Three major patterns of maturation were observed: 1) significant increase in FA with age, accompanied by significant decreases in all 3 diffusivities (e.g., left IFOF); 2) significant decreases in all three diffusivities with age without significant changes in FA (e.g., left CST); and 3) no significant age-related changes in FA or diffusivity (e.g., SS). Sex differences were minimal. Many pathways showed lateral asymmetries. In the right hemisphere, the frontotemporal (FT) segment of AF was not visualized in a substantial (29%) number of participants. FA was higher in the left hemisphere in the FT segment of AF, UF, and CST, whereas it was lower in the frontoparietal segment of AF. This study provides normative data essential for the interpretation of pediatric brain DTT measurements in both health and disease.     

White matter development during childhood and adolescence: a cross-sectional diffusion tensor imaging study

Maturation of brain white matter pathways is an important factor in cognitive, behavioral, emotional and motor development during childhood and adolescence. In this study, we investigate white matter maturation as reflected by changes in anisotropy and white matter density with age. Thirty-four children and adolescents aged 6-19 years received diffusion-weighted magnetic resonance imaging scans. Among these, 30 children and adolescents also received high-resolution T1-weighed anatomical scans. A linear regression model was used to correlate fractional anisotropy (FA) values with age on a voxel-by-voxel basis. Within the regions that showed significant FA changes with age, a post hoc analysis was performed to investigate white matter density changes. With increasing age, FA values increased in prefrontal regions, in the internal capsule as well as in basal ganglia and thalamic pathways, the ventral visual pathways, and the corpus callosum. The posterior limb of the internal capsule, intrathalamic connections, and the corpus callosum showed the most significant overlaps between white matter density and FA changes with age. This study demonstrates that during childhood and adolescence, white matter anisotropy changes in brain regions that are important for attention, motor skills, cognitive ability, and memory. This typical developmental trajectory may be altered in individuals with disorders of development, cognition and behavior.     

White matter anatomy of the human deep brain revisited with high resolution DTI fibre tracking

Background and Purpose

Deep white matter (WM) fascicles play a major, yet poorly understood, role in the overall connectivity of human brain. Better knowledge of their anatomy is requisite to understand the clinical correlates of their lesions and develop targeted treatments. We investigated whether MR-based diffusion tensor imaging (DTI) and fibre tracking could reveal in vivo, in explicit details, the 3D WM architecture within the subthalamic region and the internal capsule.

Methods

High-resolution DTI images were acquired on six healthy volunteers on a three Tesla MR scanner. We studied using single-subject analysis WM fascicles within the subthalamic region and the internal capsule, as follows: DTI deterministic fibre tracking (FT) of fascicles; embedding fascicles in the volume-rendered brain coupled with a triplanar view; rigorous anatomic labelling of each fascicle according to classical knowledge as described by pioneer neuroanatomists. Deterministic FT effects were taken into account.

Results

We charted most of WM fascicles of the deep brain, in particular large and complex fascicles such as the basal forebrain bundle and the ansa lenticularis. A topographic classification of subthalamic fascicles was proposed into three groups: the cerebellorubral, the reticulo-dorsal and the tegmento-peripheral one.

Conclusions

Beyond to demonstrate the feasibility of imaging the deepest WM fascicles in vivo, our results pave the way for a better understanding of the brain connectivity and for developing targeted neuromodulation.     

Connectivity-Based Parcellation of Broca's Area

It is generally agreed that the cerebral cortex can be segregated into structurally and functionally distinct areas. Anatomical subdivision of Broca's area has been achieved using different microanatomical criteria, such as cytoarchitecture and distribution of neuroreceptors. However, brain function also strongly depends upon anatomical connectivity, which therefore forms a sensible criterion for the functio-anatomical segregation of cortical areas. Diffusion-weighted magnetic resonance (MR) imaging offers the opportunity to apply this criterion in the individual living subject. Probabilistic tractographic methods provide excellent means to extract the connectivity signatures from diffusion-weighting MR data sets. The correlations among these signatures may then be used by an automatic clustering method to identify cortical regions with mutually distinct and internally coherent connectivity. We made use of this principle to parcellate Broca's area. As it turned out, 3 subregions are discernible that were identified as putative Brodmann area (BA) 44, BA45, and the deep frontal operculum. These results are discussed in the light of previous evidence from other methods in both human and nonhuman primates. We conclude that plausible results can be achieved by the proposed technique, which cannot be obtained by any other method in vivo. For the first time, there is a possibility to investigate the anatomical subdivision of Broca's area noninvasively in the individual living human subject.     

Diffusion tensor imaging and white matter tractography in patients with brainstem lesions

Summary Background. Diffusion tensor imaging (DTI) and white matter tractography (WMT) are promising techniques for estimating the course, extent, and connectivity patterns of the white matter (WM) structures in the human brain. In this study, we investigated the ability of DTI and WMT to visualize white matter tract involvement for the preoperative surgical planning and postoperative assessment of brainstem lesions. Methods. Preoperative and postoperative DTI data (echo-planar, 1.5T) were retrospectively analyzed in 10 patients with brainstem lesions (3 diffuse, 7 focal). WMT applying a tensor deflection algorithm was used to reconstruct WM tracts adjacent to the lesions. Reconstructed tracts included corticospinal tracts and medial lemnisci. The clinical and imaging follow-up data were also compared and analyzed. Findings. WMT revealed a series of tract alteration patterns including deviation, deformation, infiltration, and apparent tract interruption. WMT reconstructions showed that the major WM tracts were preserved during surgery and improved in position and appearance postoperatively. These findings correlated with the improvement or preservation of neurological function as determined by clinical assessment. Conclusions. Compared with the information provided by conventional MR imaging, DTI and WMT provided superior quantification and visualization of lesion involvement in eloquent fibre tracts of the brainstem. Moreover, DTI and WMT were found to be beneficial for white matter recognition in the neurosurgical planning and postoperative assessment of brainstem lesions.     

三维真稳态进动快速成像序列联合扩散张量神经纤维束示踪成像在腰椎间盘突出症中的应用

目的探讨三维真稳态进动快速成像(3D-Ture FISP)序列联合扩散张量神经纤维束示踪成像(DTT)判定腰椎间盘突症(LDH)所致坐骨神经痛责任神经根的价值。方法分别对40例单侧坐骨神经痛LDH患者(病变组)及40名健康志愿者(对照组)行腰骶部MR检查。将3D-Ture FISP序列与DTT图像融合,于L4～S1椎体水平测量双侧神经根FA及ADC值,结合融合图像所示神经根形态、走行及FA、ADC值判定LDH患者坐骨神经痛责任神经根,并进行统计学分析。结果 3D-True FISP序列与DTT融合图像可清晰显示神经根形态及走行。病变组40例(受累神经根51条,未受累神经根189条)中,37例影像学检查判定的责任神经根与临床症状相符,3例不符。对照组(240条神经根)左侧与右侧神经根FA及ADC值差异均无统计学意义(P均0.05),双侧神经根平均FA值为0.346±0.042,ADC值为(1.296±0.080)mm~2/s。病变组患侧神经根FA值为0.253±0.021,ADC值为(1.743±0.089)mm~2/s;对侧神经根FA值为0.339±0.013,ADC值为(1.297±0.075)mm~2/s。病变组患侧神经根FA值明显低于自身同层面对侧神经根(t=0.806,P=0.038)及对照组神经根(t=0.963,P=0.043),ADC值明显高于自身同层面对侧神经根(t=0.866,P=0.040)及对照组神经根(t=0.921,P=0.042)。病变组对侧神经根FA及ADC值与对照组间差异均无统计学意义(P均0.05)。结论 3D-Ture FLSP序列联合DTT技术可清楚显示神经根解剖形态及走行,结合量化分析判定LDH患者坐骨神经痛责任神经根,为临床提供更多诊疗信息。     

Detection of tumour infiltration in axonal fibre bundles using diffusion tensor imaging

We present a method for the detection and quantification of white matter infiltration from human brain tumours based on Diffusion Tensor Imaging (DTI). Since white matter destruction alters the local diffusion properties, DTI has the potential to sensitively detect tumour infiltration and to quantify the degree thereof. Here, we consider three tumour patients with gliomas, two with and one without contralateral tumour progress. We use DTI to identify specific fibre systems, where infiltration has to be assessed. On this basis, the problem of arbitrary region of interest definition is solved such that tumour infiltration can be reliably quantified in particular fibre bundles. It is demonstrated at the Corpus Callosum (CC) and the Pyramidal Tract (PT) that fibre bundle infiltration can be well detected by specific visualisation techniques of diffusion tensor data. Infiltration of the CC is quantified by using a reliable method for the determination of diffusion properties inside particular fibre bundles. For an age normalised quantification of white matter infiltration we introduce the Integrity Index, which measures the diffusion anisotropy inside an infiltrated fibre bundle normalised by the diffusion anisotropy in a specific region of healthy fibre tissue. It turns out that the quantification of CC infiltration correlates with contralateral tumour progression and has the potential to serve as a surrogate marker for this process, which is crucial for surgical therapy decisions and intervention planning.     

Developmental changes and injury induced disruption of the radial organization of the cortex in the immature rat brain revealed by in vivo diffusion tensor MRI

During brain development, morphological changes modify the cortex from its immature radial organization to its mature laminar appearance. Applying in vivo diffusion tensor imaging (DTI), the microstructural organization of the cortex in the immature rat was analyzed and correlated to neurohistopathology. Significant differences in apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were detected between the external (I-III) and deep (IV-VI) cortical layers in postnatal day 3 (P3) and P6 pups. With cortical maturation, ADC was reduced in both cortical regions, whereas a decrease in FA was only seen in the deep layers. A distinct radial organization of the external cortical layers with the eigenvectors perpendicular to the pial surface was observed at both ages. Histology revealed maturational differences in the cortical architecture with increased neurodendritic density and reduction in the radial glia scaffolding. Early DTI after hypoxia-ischemia at P3 shows reduced ADC and FA in the ipsilateral cortex that persisted at P6. Cortical DTI eigenvector maps reveal microstructural disruption of the radial organization corresponding to regions of neuronal death, radial glial disruption, and astrocytosis. Thus, the combined use of in vivo DTI and histopathology can assist in delineating normal developmental changes and postinjury modifications in the immature rodent brain.     

Somatomotor functional MRI in a hypertensive arachnoid cyst

Summary In this article the authors report the study by functional MRI, before and after surgery, of the motor cerebral cortex surrounding a large hypertensive arachnoid cyst. They stress that the functional modifications due to surgery are more relevant than suggested by the simple morphological data.     

全脑功能连接模式分析研究及临床应用进展

基于功能MRI(fMRI)的功能连接(FC)分析可用于研究大脑功能异常。全脑FC模式具有高度特异性,可如指纹般视为个体识别标记,进而诊断疾病并指导临床治疗。本文对全脑FC模式及其临床应用进展进行综述。     

Diffusion tensor imaging fiber tractography for evaluating diffuse axonal injury

Patients with Diffuse axonal injury (DAI) frequently exhibit cognitive disorders chronically. Radiologic recognition of DAI can help understand the clinical syndrome and to make treatment decisions. However, CT and conventional MRI are often normal or demonstrate lesions that are poorly related to the cognitive disorders. Recently, diffusion tensor imaging (DTI) fiber tractography has been shown to be useful in detecting various types of white matter damage. The aim of this study was to evaluate the feasibility of using DTI fiber tractography to detect lesions in DAI patients, and to correlate the DAI lesions with the cognitive disorders. We investigated two patients with chronic DAI. Both had impaired intelligence, as well as attention and memory disorders that restricted their activities of daily living. In both patients, DTI fiber tractography revealed interruption of the white matter fibers in the corpus collosum and the fornix, while no lesions were found on conventional MRI. The interruption of the fornix which involves the circuit of Papez potentially correlates with the memory disorder. Therefore, DTI fiber tractography may be a useful technique for the evaluation of DAI patients with cognitive disorders.     

Integrated image- and function-guided surgery in eloquent cortex: a technique report

The ability to effectively identify eloquent cortex in close proximity to brain tumours is a critical component of surgical planning prior to resection. The use of electrocortical stimulation testing (ECS) during awake neurosurgical procedures remains the gold standard for mapping functional areas, yet the preoperative use of non-invasive brain imaging techniques such as fMRI are gaining popularity as supplemental surgical planning tools. In addition, the intraoperative three-dimensional display of fMRI findings co-registered to structural imaging data maximizes the utility of the preoperative mapping for the surgeon. Advances in these techniques have the potential to limit the size and duration of craniotomies as well as the strain placed on the patient, but more research accurately demonstrating their efficacy is required. In this paper, we demonstrate the integration of preoperative fMRI within a neuronavigation system to aid in surgical planning, as well as the integration of these fMRI data with intraoperative ECS mapping results into a three-dimensional dataset for the purpose of cross-validation.     

Basal ganglia functional connectivity based on a meta-analysis of 126 positron emission tomography and functional magnetic resonance imaging publications

The striatum receives projections from the entire cerebral cortex. Different, but not mutually exclusive, models of corticostriatal connectivity have been proposed, including connectivity based on proximity, parallel loops, and a model of a tripartite division of the striatum into motor, associative, and limbic areas. All these models were largely based on studies of anatomic connectivity in nonhuman mammals and lesion studies in animals and humans. Functional neuroimaging has the potential to discern patterns of functional connectivity in humans in vivo. We analyzed the functional connectivity between the cortex and the striatum in a meta-analysis of 126 published functional neuroimaging studies. We mapped the peak activations listed in each publication into stereotaxic space and used standard functional imaging statistical methods to determine which cortical areas were most likely to coactivate with different parts of the striatum. The patterns of functional connectivity between the cortex and the different striatal nuclei are broadly consistent with the predictions of the parallel loop model. The rostrocaudal and dorsoventral patterns of corticostriatal functional connectivity are consistent with the tripartite division of the striatum into motor, associative, and limbic zones.     

MR扩散张量成像表观扩散系数和各向异性分数对不同病程颈脊髓压迫症的诊断价值

目的 :探讨MR扩散张量成像(MR-diffusion tensor imaging,MR-DTI)表观扩散系数(ADC)和各向异性分数(FA)对不同病程颈脊髓压迫症的诊断价值。方法:2010年1月~2011年6月经MRI常规检查诊断为颈脊髓压迫症的患者50例,其中急性颈脊髓压迫患者15例(A组),均为外伤患者,在伤后72h内接受MRI检查;慢性颈脊髓压迫23例(B组),均为脊髓型颈椎病患者,病程超过6个月;慢性合并急性颈脊髓压迫12例(C组),均有超过6个月的脊髓型颈椎病病史,且本次MRI检查前72h内受到颈部外伤累及颈髓。15例健康志愿者为对照组(D组),MRI常规检查颈脊髓未见异常。4组均行MR-DTI检查,测量A、B、C组患者颈脊髓受压处及D组C5/6椎间盘平面脊髓的ADC和FA,并行组间比较。结果:A、B、C、D组的ADC分别为(0.712±0.241)×10-3mm2/s、(1.012±0.256)×10-3mm2/s、(0.812±0.125)×10-3mm2/s、(0.823±0.106)×10-3mm2/s,FA分别为0.401±0.098、0.472±0.095、0.496±0.172、0.541±0.158。A组ADC和FA与D组比较均明显降低(P<0.05);B组FA与D组比较明显降低、ADC明显增高(P<0.05);C组ADC与D组比较无显著性差异(P>0.05),FA值低于D组(P<0.05)。A组ADC及FA均低于B、C组(P<0.05);B组ADC高于C组,FA低于C组,组间差异有显著性(P<0.05)。结论:MR-DTI的ADC及FA对不同病程颈脊髓压迫症有诊断价值。