Evaluation of voxel-based group-level analysis of diffusion tensor images using simulated brain lesions

We simulated brain lesions in mean diffusivity (MD) and fractional anisotropy (FA) images of healthy subjects to evaluate the performance of voxel-based analysis (VBA) with SPM2. We increased MD and decreased FA, simulating the most typical abnormalities in brain pathologies, in the superior longitudinal fasciculus (SLF), corticospinal tract (CST), and corpus callosum (CC). Lesion sizes varied from 10 to 400 voxels (10.5 mm³ each) and intensity changes from 10 to 100%. The VBA contained eddy current correction, spatial normalization, smoothing, and statistical analysis.The preprocessing steps changed the intensities of MD and FA lesions from the original values, and many lesions remained undetected. The detection thresholds varied between the three brain areas, and between MD and FA images. Although spatial smoothing often improved the sensitivity, it also markedly enlarged the estimated lesion sizes.Since conventional VBA preprocessing significantly affected the outcome and sensitivity of the method itself, the impact of analysis steps should be verified and considered before interpreting the findings. Our results provide insight into the sizes and intensity changes of lesions that can be detected with VBA applied to diffusion tensor imaging (DTI) data.     

White matter damage of patients with Alzheimer’s disease correlated with the decreased cognitive function

Increasing evidence demonstrates that there is marked damage and dysfunction in the white matter in Alzheimer’s disease (AD). The present study investigates the nature of white matter damage of patients with Alzheimer’s disease with diffusion tensor magnetic resonance imaging (DTI) and analyses the relationship between the white matter damage and the cognition function. DTI, as well as T1 fluid attenuated inversion recovery (FLAIR) and T2-FLAIR, was performed on probable patients of Alzheimer’s disease, and sex and age matched healthy volunteers to measure the fractional anisotropy (FA) and mean diffusivity (MD) in the genu and splenium of the corpus callosum, anterior and posterior limbs of the internal capsule, and the white matter of frontal, temporal, parietal, and occipital lobes. FA was lower in the splenium of corpus callosum, as well as in the white matter of the frontal, temporal, and parietal lobes from patients with Alzheimer’s disease than in the corresponding region from healthy controls and was strongly positive correlated with MMSE scores, whereas FA appeared no different in the anterior and posterior limbs of internal capsule, occipital lobes white matter, and the genu of corpus callosum between the patients and healthy controls. MD was significantly higher in the splenium of corpus callosum and parietal lobes white matter from patients than in that those from healthy controls and was strongly negative correlated with MMSE scores, whereas MD in the anterior and posterior limbs of internal capsule, as well as in frontal, temporal, occipital lobes white matter and the genu of corpus callosum, was not different between the patients and healthy controls. The most prominent alteration of FA and MD was in the splenium of corpus callosum. Our results suggested that white matter of patients with Alzheimer’s disease was selectively impaired and the extent of damage had a strong correlation with the cognitive function, and that selective impairment reflected the cortico–cortical and cortico–subcortical disconnections in the pathomechanism of Alzheimer’s disease. The values of FA and MD in white matter, especially in the splenium of corpus callosum in AD patients, might be a more appropriate surrogate marker for monitoring the disease progression.     

Microstructural changes and atrophy in brain white matter tracts with aging

Diffusion tensor (DT) magnetic resonance imaging (MRI) tractography was used to investigate microstructural and volumetric abnormalities of the major brain white matter (WM) tracts with aging in 84 healthy subjects. Linear relationships were found between age and mean diffusivity (MD) increase and fractional anisotropy (FA) decrease in all WM tracts, except the right cingulum and bilateral uncinate, where a linear correlation with age was found for FA only. Quadratic model fitted better MD and FA values of several tracts, including the corpus callosum, limbic pathways, and bilateral association, and corticospinal tracts. Age-related MD and FA abnormalities were associated with radial diffusivity increase in all WM tracts, while axial diffusivity changes were characterized by a considerable variation from a tract to another. A linear negative relationship with age was found for the volumes of the left cingulum and fornix, while the quadratic model fitted better age-related volume loss of corpus callosum and right inferior fronto-occipital fasciculus. Diffusion tensor magnetic resonance imaging may shed light into the complex pathological substrates of WM changes with aging.     

Abnormal integrity of corticocortical tracts in mild cognitive impairment: a diffusion tensor imaging study

Mild cognitive impairment (MCI) has been defined as a transitional state between normal aging and Alzheimer disease. Diffusion tensor imaging (DTI) can estimate the microstructural integrity of white matter tracts in MCI. We evaluated the microstructural changes in the white matter of MCI patients with DTI. We recruited 11 patients with MCI who met the working criteria of MCI and 11 elderly normal controls. The mean diffusivity (MD) and fractional anisotropy (FA) were measured in 26 regions of the brain with the regions of interest (ROIs) method. In the MCI patients, FA values were significantly decreased in the hippocampus, the posterior limb of the internal capsule, the splenium of corpus callosum, and in the superior and inferior longitudinal fasciculus compared to the control group. MD values were significantly increased in the hippocampus, the anterior and posterior limbs of the internal capsules, the splenium of the corpus callosum, the right frontal lobe, and in the superior and the inferior longitudinal fasciculus. Microstructural changes of several corticocortical tracts associated with cognition were identified in patients with MCI. FA and MD values of DTI may be used as novel biomarkers for the evaluation of neurodegenerative disorders.     

Normal aging in the central nervous system: quantitative MR diffusion-tensor analysis

The purpose of this study is to elucidate changes in mean diffusivity (ADC) and fractional anisotropy (FA) using MR diffusion tensor imaging (DTI) in the central nervous system during normal aging. We studied 50 normal volunteers (30 men, 20 women; mean age 44.8 +/- 14.0; age range, 21-69 years) without disorders affecting the central nervous system. The frontal, parietal white matter, lentiform nucleus, posterior limb of internal capsule, thalamus, genu and splenium of the corpus callosum were selected for investigation. There was no significant difference in ADC or FA between male and female or between the right and left hemisphere. A significant ADC increase with advancing age was observed in frontal white matter (P = 0.010) and lentiform nucleus (P = 0.022). A significant FA decline was found only in the genu of the corpus callosum (P < 0.001) with advancing age. Quantitative diffusion tensor analysis correlate with normal aging and may help in assessing normal age-related changes and serve as a standard for comparison with neurodegenerative disorders.     

White matter integrity affected by depressive symptoms in migraine without aura: a tract‐based spatial statistics study

Previous studies have proven that migraine and depression are bidirectionally linked. However, few studies have investigated white matter (WM) integrity affected by depressive symptoms in patients suffering from migraine without aura (MWoA). Forty patients with MWoA were divided into two groups according to their self‐rating depression scale (SDS) score in the present study, including 20 in the SDS (+) (SDS > 49) group and 20 in the SDS (?) (SDS ≤ 49) group. Forty healthy participants were also recruited as the control group. Tract‐based spatial statistics analyses with multiple diffusion tensor imaging‐derived indices [fractional anisotropy (FA), mean diffusivity (MD), radial diffusivity (RD), axial diffusivity (AD)] were employed collectively to investigate WM integrity between all patients with MWoA and all healthy controls, between each subgroup (SDS (?) group and SDS (+) group) and healthy controls, and between the SDS (?) and SDS (+) groups. Compared with healthy controls, decreased AD was shown in several WM tracts of the whole MWoA group, SDS (?) group and SDS (+) group. In addition, compared with the SDS (?) group, the SDS (+) group showed decreased FA and increased MD and RD, with conserved AD, including the genu, body and splenium of the corpus callosum, bilateral superior longitudinal fasciculi, the right anterior corona radiata and some other WM tracts, similar to previous findings in depression disorder. Furthermore, mean FA and RD in some of the above‐mentioned WM tracts in the SDS (+) group were correlated significantly with SDS scores, including the genu and splenium of the corpus callosum, the right anterior corona radiata and the superior longitudinal fasciculi. Our results suggest that WM integrity may be affected by both depression symptoms (more sensitive as RD) and migraine (more sensitive as AD). The findings may serve as a sensitive biomarker of depression severity in MWoA. Copyright © 2013 John Wiley & Sons, Ltd.     

精神分裂症白质损害与发病年龄的弥散张量成像研究

目的:应用弥散张量成像(DTI)比较精神分裂症患者脑白质与正常人群间的差异,并探究各向异性比值(FA)的改变与发病年龄之间的相关性。方法:纳入27例精神分裂症患者和29名性别、年龄及受教育程度相匹配的健康对照。两组研究对象均接受头颅磁共振检测。患者组按照发病年龄分为早发组(发病年龄18岁)和成年发病组(发病年龄≥18岁)。采用基于体素的分析方法,分别比较患者组和对照组、早发组和成年发病组之间FA值的差异,并在控制性别、病程和药物剂量影响的前提下,分析FA值与患者发病年龄的相关性。结果:与健康对照比较,患者组在右侧上纵束、右侧放射冠上部的FA值降低;患者组中早发组和成年发病组间FA值的差异无显著性。患者组FA值与发病年龄呈正相关的脑区包括右侧放射冠前部(r=0.70,P0.01)、右侧胼胝体膝部(r=0.65,P0.01);未发现呈负相关的脑区。结论:本研究提示精神分裂症患者右侧脑区上纵束及放射冠部位存在白质损害,发病年龄愈早,右侧放射冠及胼胝体膝部白质纤维的受损愈重。这对精神分裂症病理生理改变及脑结构异常的进一步研究具有提示作用。     

Age-related decline in the microstructural integrity of white matter in children with early- and continuously-treated PKU: A DTI study of the corpus callosum

Structural, volumetric, and microstructural abnormalities have been reported in the white matter of the brain in individuals with phenylketonuria (PKU). Very little research, however, has been conducted to investigate the development of white matter in children with PKU, and the developmental trajectory of their white matter microstructure is unknown. In the current study, diffusion tensor imaging (DTI) was used to examine the development of the microstructural integrity of white matter across six regions of the corpus callosum in 34 children (7–18 years of age) with early- and continuously-treated PKU. Comparison was made with 61 demographically-matched healthy control children. Two DTI variables were examined: mean diffusivity (MD) and relative anisotropy (RA). RA was comparable to that of controls across all six regions of the corpus callosum. In contrast, MD was restricted for children with PKU in anterior (i.e., genu, rostral body, anterior midbody) but not posterior (posterior midbody, isthmus, splenium) regions of the corpus callosum. In addition, MD restriction became more pronounced with increasing age in children with PKU in the two most anterior regions of the corpus callosum (i.e., genu, rostral body). These findings point to an age-related decrement in the microstructural integrity of the anterior white matter of the corpus callosum in children with PKU.     

Aging in the CNS: comparison of gray/white matter volume and diffusion tensor data

This study investigated the global and regional effects of aging on brain volume, mean diffusivity (MD), and fractional anisotropy (FA) in 73 normal female subjects using voxel-based analysis. On a global scale, gray matter volume and FA were negatively correlated, whereas MD was positively correlated with age. Voxel-wise analyses showed brain volume and FA were negatively correlated predominantly in anterior structures, whereas MD was positively correlated in the cortical gray matter and periventricular white matter. Volume preservation was observed in the cingulate gyrus and subjacent white matter. FA increase was observed in the putamen. Voxel-based direct comparisons of volume and diffusion properties showed FA was more strongly negatively correlated in the fronto-temporal white matter, compared with volume and MD. Stronger positive correlation of MD was observed in the thalamus, caudate nucleus, and midbrain and stronger negative correlation of brain volume was observed in the frontal lobe and basal ganglia, compared with the other. These results indicate that diffusion properties and brain volume are complementary markers to the effects of aging.     

A comparative study of bone marrow mesenchymal stem cell functionality in C57BL and mdx mice

Abnormalities of the white matter (WM) tracts integrity in brain areas involved in emotional regulation have been postulated in major depressive disorder (MDD). However, there is no diffusion tensor imaging (DTI) study in patients with treatment-responsive MDD at present. DTI scans were performed on 22 patients with treatment-responsive MDD and 19 well-matched healthy subjects. Tract-based spatial statistics (TBSS) approach was employed to analyze the scans. Voxel-wise statistics revealed four brain WM tracts with lower fractional anisotropy (FA) in patients compared to healthy subjects: the bilateral internal capsule, the genu of corpus callosum, the bilateral anterior corona radiata, and the right external capsule. FA values were nowhere higher in patients compared to healthy subjects. Our findings demonstrate that the abnormalities of the WM tracts, major in the projection fibers and corpus callosum, may contribute to the pathogenesis of treatment-responsive MDD.     

Diffusion Tensor Imaging (DTI) Findings Following Pediatric Non-Penetrating TBI: A Meta-Analysis

This study meta-analyzed research examining Diffusion Tensor Imaging following pediatric non-penetrating traumatic brain injury to identify the location and extent of white matter changes. Fractional anisotropy (FA) and apparent diffusion coefficient (ADC) data from 20 studies were analyzed. FA increased and ADC decreased in most white matter tracts in the short-term (moderate-to-large effects), and FA decreased and ADC increased in the medium- to long-term (moderate-to-very-large effects). Whole brain (short-term), cerebellum and corpus callosum (medium- to long-term) FA values have diagnostic potential, but the impact of age/developmental stage and injury severity on FA/ADC, and the predictive value, is unclear.     

Evaluation of voxel-based group-level analysis of diffusion tensor images using simulated brain lesions

We simulated brain lesions in mean diffusivity (MD) and fractional anisotropy (FA) images of healthy subjects to evaluate the performance of voxel-based analysis (VBA) with SPM2. We increased MD and decreased FA, simulating the most typical abnormalities in brain pathologies, in the superior longitudinal fasciculus (SLF), corticospinal tract (CST), and corpus callosum (CC). Lesion sizes varied from 10 to 400 voxels (10.5 mm³ each) and intensity changes from 10 to 100%. The VBA contained eddy current correction, spatial normalization, smoothing, and statistical analysis.The preprocessing steps changed the intensities of MD and FA lesions from the original values, and many lesions remained undetected. The detection thresholds varied between the three brain areas, and between MD and FA images. Although spatial smoothing often improved the sensitivity, it also markedly enlarged the estimated lesion sizes.Since conventional VBA preprocessing significantly affected the outcome and sensitivity of the method itself, the impact of analysis steps should be verified and considered before interpreting the findings. Our results provide insight into the sizes and intensity changes of lesions that can be detected with VBA applied to diffusion tensor imaging (DTI) data.     

White matter alterations in narcolepsy patients with cataplexy: tract‐based spatial statistics

Functional imaging studies and voxel‐based morphometry analysis of brain magnetic resonance imaging showed abnormalities in the hypothalamus–thalamus–orbitofrontal pathway, demonstrating altered hypocretin pathway in narcolepsy. Those distinct morphometric changes account for problems in wake–sleep control, attention and memory. It also raised the necessity to evaluate white matter changes. To investigate brain white matter alterations in drug‐naïve narcolepsy patients with cataplexy and to explore relationships between white matter changes and patient clinical characteristics, drug‐naïve narcolepsy patients with cataplexy (n = 22) and healthy age‐ and gender‐matched controls (n = 26) were studied. Fractional anisotropy and mean diffusivity images were obtained from whole‐brain diffusion tensor imaging, and tract‐based spatial statistics were used to localize white matter abnormalities. Compared with controls, patients showed significant decreases in fractional anisotropy of white matter of the bilateral anterior cingulate, fronto‐orbital area, frontal lobe, anterior limb of the internal capsule and corpus callosum, as well as the left anterior and medial thalamus. Patients and controls showed no differences in mean diffusivity. Among patients, mean diffusivity values of white matter in the bilateral superior frontal gyri, bilateral fronto‐orbital gyri and right superior parietal gyrus were positively correlated with depressive mood. This tract‐based spatial statistics study demonstrated that drug‐naïve patients with narcolepsy had reduced fractional anisotropy of white matter in multiple brain areas and significant relationship between increased mean diffusivity of white matter in frontal/cingulate and depression. It suggests the widespread disruption of white matter integrity and prevalent brain degeneration of frontal lobes according to a depressive symptom in narcolepsy.     

Influence of citalopram and environmental temperature on exercise-induced changes in BDNF

Differences and similarities in microstructural white matter alterations between bipolar I and bipolar II disorder were investigated. Twelve patients with bipolar I disorder, 12 patients with bipolar II disorder and 22 healthy controls underwent diffusion tensor imaging. Fractional anisotropy (FA) and mean apparent diffusion coefficient (ADC) maps were compared between groups using voxel-based whole brain analyses. Both bipolar I and II groups had a FA decrease in the corpus callosum, cingulate and right prefrontal regions, and a ADC increase in the medial frontal, anterior cingulate, insular and temporal regions, compared to controls. The bipolar I group had a FA decrease in the right temporal white matter and a ADC increase in the frontal, temporal, parietal and thalamic regions, compared to the bipolar II group. The results suggest disrupted integrity of commissural fibers and white matter in the anterior paralimbic structures in bipolar disorder. Relative sparing of the dorsal system and long association fibers may differentiate bipolar II from I disorder.     

Can we differentiate true white matter fibers from pseudofibers inside a brain abscess cavity using geometrical diffusion tensor imaging metrics?

High fractional anisotropy (FA) usually reflects the orientation and integrity of white matter (WM) fibers. Other regions of increased FA have been described, such as brain abscesses, developing cortex, and areas of hemorrhage. It may not be possible to differentiate true fibers from the pseudofibers found inside an abscess cavity on the basis of FA and mean diffusivity (MD). The aim of this study was to differentiate true WM fibers from pseudo WM tracts inside the abscess cavity using geometrical diffusion tensor imaging metrics [linear anisotropy (CL), planar anisotropy (CP), and spherical anisotropy (CS)]. Diffusion tensor imaging was performed in 42 patients with brain abscess and 10 age/sex-matched controls. Automated segmentation using Java-based software divided the abscess cavity into two sub-regions with FA < 0.20 and FA > or = 0.20. Quantitation was carried out on the sub-regions of the abscess cavity with FA > or = 0.20. In healthy controls, regions of interest were placed on the corpus callosum, posterior limb of the internal capsule, and periventricular and subcortical WM. Significantly increased CP values were observed inside the abscess cavity compared with various normal WM regions. Significantly increased FA and CL values were observed in the abscess cavity compared with subcortical WM only. However decreased FA and CL values were observed in the cavity compared with the corpus callosum, posterior limb of the internal capsule, and periventricular WM. The 95% confidence intervals of means for the abscess cavity were well separated from those for WM in the case of CL and CP; however, they overlapped in the case of FA, MD, and CS. High CP with low CL inside the abscess cavity suggests that the shape of the diffusion tensor is predominantly planar, whereas it is linear in WM tracts. These geometrical indices may have advantages over FA for differentiating true from pseudo WM tracts inside the abscess cavity.     

Quantitative fiber tracking of lateral and interhemispheric white matter systems in normal aging: relations to timed performance

The integrity of white matter, as measured in vivo with diffusion tensor imaging (DTI), is disrupted in normal aging. A current consensus is that in adults advancing age affects anterior brain regions disproportionately more than posterior regions; however, the mainstay of studies supporting this anterior-posterior gradient is based primarily on measures of the corpus callosum. Using our quantitative fiber tracking approach, we assessed fiber tract integrity of samples of major white matter cortical, subcortical, interhemispheric, and cerebellar systems (11 bilateral and 2 callosal) on DTI data collected at 1.5T magnet strength. Participants were 55 men (age 20-78 years) and 65 women (age 28-81 years), deemed healthy and cognitively intact following interview and behavioral testing. Fiber integrity was measured as orientational diffusion coherence (fractional anisotropy, FA) and magnitude of diffusion, which was quantified separately for longitudinal diffusivity (lambdaL), an index of axonal length or number, and transverse diffusivity (lambdaT), an index of myelin integrity. Aging effects were more evident in diffusivity than FA measures. Men and women, examined separately, showed similar age-related increases in longitudinal and transverse diffusivity in fibers of the internal and external capsules bilaterally and the fornix. FA was lower and diffusivity higher in anterior than posterior fibers of regional paired comparisons (genu versus splenium and frontal versus occipital forceps). Diffusivity with older age was generally greater or FA lower in the superior than inferior fiber systems (longitudinal fasciculi, cingulate bundles), with little to no evidence for age-related degradation in pontine or cerebellar systems. The most striking sex difference emerged for the corpus callosum, for which men showed significant decline in FA and increase in longitudinal and transverse diffusivity in the genu but not splenium. By contrast, in women the age effect was present in both callosal regions, albeit modestly more so in the genu than splenium. Functional meaningfulness of these age-related differences was supported by significant correlations between DTI signs of white matter degradation and poorer performance on cognitive or motor tests. This survey of multiple fiber systems throughout the brain revealed a differential pattern of age's effect on regional FA and diffusivity and suggests mechanisms of functional degradation, attributed at least in part to compromised fiber microstructure affecting myelin and axonal morphology.     

Spatiotemporal microstructural white matter changes in diffusion tensor imaging after transient focal ischemic stroke in rats

Structural reorganization in white matter (WM) after stroke is a potential contributor to substitute or to newly establish the functional field on the injured brain in nature. Diffusion tensor imaging (DTI) is an imaging modality that can be used to evaluate damage and recovery within the brain. This method of imaging allows for in vivo assessment of the restricted movements of water molecules in WM and provides a detailed look at structural connectivity in the brain. For longitudinal DTI studies after a stroke, the conventional region of interest method and voxel‐based analysis are highly dependent on the user‐hypothesis and parameter settings for implementation. In contrast, tract‐based spatial statistics (TBSS) allows for reliable voxel‐wise analysis via the projection of diffusion‐derived parameters onto an alignment‐invariant WM skeleton. In this study, spatiotemporal WM changes were examined with DTI‐derived parameters (fractional anisotropy, FA; mean diffusivity, MD; axial diffusivity, DA; radial diffusivity, RD) using TBSS 2 h to 6 weeks after experimental focal ischemic stroke in rats (N = 6). FA values remained unchanged 2–4 h after the stroke, followed by a continuous decrease in the ipsilesional hemisphere from 24 h to 2 weeks post‐stroke and gradual recovery from the ipsilesional corpus callosum to the external capsule until 6 weeks post‐stroke. In particular, the fibers in these areas were extended toward the striatum of the ischemic boundary region at 6 weeks on tractography. The alterations of the other parameters in the ipsilesional hemisphere showed patterns of a decrease at the early stage, a subsequent pseudo‐normalization of MD and DA, a rapid reduction of RD, and a progressive increase in MD, DA and RD with a decreased extent in the injured area at later stages. The findings of this study may reflect the ongoing processes on tissue damage and spontaneous recovery after stroke.     

Diffusional kurtosis imaging and white matter microstructure modeling in a clinical study of major depressive disorder

Major depressive disorder (MDD) is a globally prevalent psychiatric disorder that results from disruption of multiple neural circuits involved in emotional regulation. Although previous studies using diffusion tensor imaging (DTI) found smaller values of fractional anisotropy (FA) in the white matter, predominantly in the frontal lobe, of patients with MDD, studies using diffusion kurtosis imaging (DKI) are scarce. Here, we used DKI whole‐brain analysis with tract‐based spatial statistics (TBSS) to investigate the brain microstructural abnormalities in MDD. Twenty‐six patients with MDD and 42 age‐ and sex‐matched control subjects were enrolled. To investigate the microstructural pathology underlying the observations in DKI, a compartment model analysis was conducted focusing on the corpus callosum. In TBSS, the patients with MDD showed significantly smaller values of FA in the genu and frontal portion of the body of the corpus callosum. The patients also had smaller values of mean kurtosis (MK) and radial kurtosis (RK), but MK and RK abnormalities were distributed more widely compared with FA, predominantly in the frontal lobe but also in the parietal, occipital, and temporal lobes. Within the callosum, the regions with smaller MK and RK were located more posteriorly than the region with smaller FA. Model analysis suggested significantly smaller values of intra‐neurite signal fraction in the body of the callosum and greater fiber dispersion in the genu, which were compatible with the existing literature of white matter pathology in MDD. Our results show that DKI is capable of demonstrating microstructural alterations in the brains of patients with MDD that cannot be fully depicted by conventional DTI. Though the issues of model validation and parameter estimation still remain, it is suggested that diffusion MRI combined with a biophysical model is a promising approach for investigation of the pathophysiology of MDD.     

基于纤维束空间统计学的吸烟成瘾青少年左右脑白质不对称研究

目的:观察吸烟成瘾青少年左右脑白质结构的不对称性变化。 方法:采用基于纤维束空间统计（TBSS）的分析方法,对23名青少年吸烟成瘾者的脑白质弥散张量成像（DTI）数据进行处理,观察分析出现左右脑白质结构异常不对称的脑区。 结果:通过分析,我们发现青少年成瘾者的脑白质在胼胝体部、胼胝体膝部、胼胝体压部、前放射冠、内囊前肢等脑区处的左右脑白质不对称差异值较大（FWE校正后P<0.05）。Pearson相关分析显示在胼胝体部（r=0.431, P=0.040）、胼胝体膝部（r=0.429, P=0.041）、前放射冠（r=0.477, P=0.021）这些脑区的轴向弥散率（AD）与尼古丁依赖量表（FTND）程度分数呈显著正相关,胼胝体压部与FTND呈显著负相关（r=-0.450, P=0.031）。胼胝体膝部的分数各向异性与FTND呈现显著正相关（r=0.678, P=0.000）。前放射冠的AD与吸烟指数包年（pack-year）呈现显著正相关（r=0.493, P=0.017）。 结论:青少年吸烟成瘾者的胼胝体,前放射冠等脑区的脑白质表现出了异常的左右不对称。     

Diffusion tensor imaging and Tract-Based Spatial Statistics in Alzheimer's disease and mild cognitive impairment

We aimed to explore the changes in fractional anisotropy (FA) in subjects with mild cognitive impairment (MCI) and Alzheimer's disease (AD) by analyzing diffusion tensor imaging (DTI) data using the Tract-Based Spatial Statistics (TBSS). DTI data were collected from 17 AD patients, 27 MCI subjects and 19 healthy controls. Voxel-based analysis with TBSS was used to compare FA among the three groups. Additionally, guided by TBSS findings, a region of interest (ROI)-based analysis along the TBSS skeleton was performed on group-level and the accuracy of the method was assessed by the back-projection of ROIs to the native space FA. Neurofiber tracts with decreased FA included: the parahippocampal white matter, cingulum, uncinate fasciculus, inferior and superior longitudinal fasciculus, corpus callosum, fornix, tracts in brain stem, and cerebellar tracts. Quantitative ROI-analysis further demonstrated the significant decrease on FA values in AD patients relative to controls whereas FA values of MCI patients were found in between the controls and AD patients. We conclude that TBSS is a promising method in examining the degeneration of neurofiber tracts in MCI and AD patients.