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1.  White matter correlates of cognitive domains in normal aging with diffusion tensor imaging 
The ability to perform complex as well as simple cognitive tasks engages a network of brain regions that is mediated by the white matter fiber bundles connecting them. Different cognitive tasks employ distinctive white matter fiber bundles. The temporal lobe and its projections subserve a variety of key functions known to deteriorate during aging. In a cohort of 52 healthy subjects (ages 25–82 years), we performed voxel-wise regression analysis correlating performance in higher-order cognitive domains (executive function, information processing speed, and memory) with white matter integrity, as measured by diffusion tensor imaging (DTI) fiber tracking in the temporal lobe projections [uncinate fasciculus (UF), fornix, cingulum, inferior longitudinal fasciculus (ILF), and superior longitudinal fasciculus (SLF)]. The fiber tracts were spatially registered and statistical parametric maps were produced to spatially localize the significant correlations. Results showed that performance in the executive function domain is correlated with DTI parameters in the left SLF and right UF; performance in the information processing speed domain is correlated with fractional anisotropy (FA) in the left cingulum, left fornix, right and left ILF and SLF; and the memory domain shows significant correlations with DTI parameters in the right fornix, right cingulum, left ILF, left SLF and right UF. These findings suggest that DTI tractography enables anatomical definition of region of interest (ROI) for correlation of behavioral parameters with diffusion indices, and functionality can be correlated with white matter integrity.
PMCID: PMC3595518  PMID: 23493587
magnetic resonance imaging; diffusion tensor imaging; executive function; information processing speed; memory; aging; white matter; temporal lobe
2.  Reading impairment in a patient with missing arcuate fasciculus 
Neuropsychologia  2008;47(1):180-194.
We describe the case of a child (“S”) who was treated with radiation therapy at age 5 for a recurrent malignant brain tumor. Radiation successfully abolished the tumor but caused radiation-induced tissue necrosis, primarily affecting cerebral white matter. S was introduced to us at age 15 because of her profound dyslexia. We assessed cognitive abilities and performed diffusion tensor imaging (DTI) to measure cerebral white matter pathways. Diffuse white matter differences were evident in T1-weighted, T2-weighted, diffusion anisotropy, and mean diffusivity measures in S compared to a group of 28 normal female controls. In addition, we found specific white matter pathway deficits by comparing tensor orientation directions in S’s brain with those of the control brains. While her principal diffusion direction maps appeared consistent with those of controls over most of the brain, there were tensor orientation abnormalities in the fiber tracts that form the superior longitudinal fasciculus (SLF) in both hemispheres. Tractography analysis indicated that the left and right arcuate fasciculus (AF), as well as other tracts within the SLF, were missing in S. Other major white matter tracts, such as the corticospinal and inferior occipitofrontal pathways, were intact. Functional MRI measurements indicated left-hemisphere dominanance for language with a normal activation pattern. Despite the left AF abnormality, S had preserved oral language with average sentence repetition skills. In addition to profound dyslexia, S exhibited visuospatial, calculation, and rapid naming deficits and was impaired in both auditory and spatial working memory. We propose that the reading and visuospatial deficits were due to the abnormal left and right SLF pathways, respectively. These results advance our understanding of the functional significance of the SLF and are the first to link radiation necrosis with selective damage to a specific set of fiber tracts.
PMCID: PMC2671152  PMID: 18775735
3.  Individual structural differences in left inferior parietal area are associated with schoolchildrens' arithmetic scores 
Arithmetic skill is of critical importance for academic achievement, professional success and everyday life, and childhood is the key period to acquire this skill. Neuroimaging studies have identified that left parietal regions are a key neural substrate for representing arithmetic skill. Although the relationship between functional brain activity in left parietal regions and arithmetic skill has been studied in detail, it remains unclear about the relationship between arithmetic achievement and structural properties in left inferior parietal area in schoolchildren. The current study employed a combination of voxel-based morphometry (VBM) for high-resolution T1-weighted images and fiber tracking on diffusion tensor imaging (DTI) to examine the relationship between structural properties in the inferior parietal area and arithmetic achievement in 10-year-old schoolchildren. VBM of the T1-weighted images revealed that individual differences in arithmetic scores were significantly and positively correlated with the gray matter (GM) volume in the left intraparietal sulcus (IPS). Fiber tracking analysis revealed that the forceps major, left superior longitudinal fasciculus (SLF), bilateral inferior longitudinal fasciculus (ILF) and inferior fronto-occipital fasciculus (IFOF) were the primary pathways connecting the left IPS with other brain areas. Furthermore, the regression analysis of the probabilistic pathways revealed a significant and positive correlation between the fractional anisotropy (FA) values in the left SLF, ILF and bilateral IFOF and arithmetic scores. The brain structure-behavior correlation analyses indicated that the GM volumes in the left IPS and the FA values in the tract pathways connecting left IPS were both related to children's arithmetic achievement. The present findings provide evidence that individual structural differences in the left IPS are associated with arithmetic scores in schoolchildren.
PMCID: PMC3854708  PMID: 24367320
arithmetical skill; left intraparietal sulcus; structure-behavior correlation; voxel-based morphometry; fiber tracking
4.  Neuroradiological and Neurophysiological Characteristics of Patients With Dyskinetic Cerebral Palsy 
Annals of Rehabilitation Medicine  2014;38(2):189-199.
To investigate neuroradiological and neurophysiological characteristics of patients with dyskinetic cerebral palsy (CP), by using magnetic resonance imaging (MRI), voxel-based morphometry (VBM), diffusion tensor tractography (DTT), and motor evoked potential (MEP).
Twenty-three patients with dyskinetic CP (13 males, 10 females; mean age 34 years, range 16-50 years) were participated in this study. Functional evaluation was assessed by the Gross Motor Functional Classification System (GMFCS) and Barry-Albright Dystonia Scale (BADS). Brain imaging was performed on 3.0 Tesla MRI, and volume change of the grey matter was assessed using VBM. The corticospinal tract (CST) and superior longitudinal fasciculus (SLF) were analyzed by DTT. MEPs were recorded in the first dorsal interossei, the biceps brachii and the deltoid muscles.
Mean BADS was 16.4±5.0 in ambulatory group (GMFCS levels I, II, and III; n=11) and 21.3±3.9 in non-ambulatory group (GMFCS levels IV and V; n=12). Twelve patients showed normal MRI findings, and eleven patients showed abnormal MRI findings (grade I, n=5; grade II, n=2; grade III, n=4). About half of patients with dyskinetic CP showed putamen and thalamus lesions on MRI. Mean BADS was 20.3±5.7 in normal MRI group and 17.5±4.0 in abnormal MRI group. VBM showed reduced volume of the hippocampus and parahippocampal gyrus. In DTT, no abnormality was observed in CST, but not in SLF. In MEPs, most patients showed normal central motor conduction time.
These results support that extrapyramidal tract, related with basal ganglia circuitry, may be responsible for the pathophysiology of dyskinetic CP rather than CST abnormality.
PMCID: PMC4026605  PMID: 24855613
Cerebral palsy; Diffusion tensor imaging; Motor evoked potentials; Magnetic resonance imaging
5.  White Matter Tracts Associated with Set-Shifting in Healthy Aging 
Neuropsychologia  2009;47(13):2835-2842.
Attentional set-shifting ability, commonly assessed with the Trail Making Test (TMT), decreases with increasing age in adults. Since set-shifting performance relies on activity in widespread brain regions, deterioration of the white matter tracts that connect these regions may underlie the age-related decrease in performance. We used an automated fiber tracking method to investigate the relationship between white matter integrity in several cortical association tracts and TMT performance in a sample of 24 healthy adults, 21 – 80 years. Diffusion tensor images were used to compute average fractional anisotropy (FA) for five cortical association tracts, the corpus callosum (CC), and the corticospinal tract (CST), which served as a control. Results showed that advancing age was associated with declines in set-shifting performance and with decreased FA in the CC and in association tracts that connect frontal cortex to more posterior brain regions, including the inferior fronto-occipital fasciculus (IFOF), uncinate fasciculus (UF), and superior longitudinal fasciculus (SLF). Declines in average FA in these tracts, and in average FA of the right inferior longitudinal fasciculus (ILF), were associated with increased time to completion on the set-shifting subtask of the TMT but not with the simple sequencing subtask. FA values in these tracts were strong mediators of the effect of age on set-shifting performance. Automated tractography methods can enhance our understanding of the fiber systems involved in performance of specific cognitive tasks and of the functional consequences of age-related changes in those systems.
PMCID: PMC2749901  PMID: 19540862
6.  A Comprehensive Reliability Assessment of Quantitative Diffusion Tensor Tractography 
NeuroImage  2011;60(2):1127-1138.
Diffusion tensor tractography is increasingly used to examine structural connectivity in the brain in various conditions, but its test-retest reliability is understudied. The main purposes of this study were to evaluate 1) the reliability of quantitative measurements of diffusion tensor tractography and 2) the effect on reliability of the number of gradient sampling directions and scan repetition. Images were acquired from ten healthy participants. Ten fiber regions of nine major fiber tracts were reconstructed and quantified using six fiber variables. Intra- and inter-session reliabilities were estimated using intraclass correlation coefficient (ICC) and coefficient of variation (CV), and compared to pinpoint major error sources. Additional pairwise comparisons were made between the reliability of images with 30 directions and NEX 2 (DTI30-2), 30 directions and NEX 1 (DTI30-1), and 15 directions and NEX 2 (DTI15-2) to determine whether increasing gradient directions and scan repetition improved reliability. Of the 60 tractography measurements, 43 showed intersession CV ≤ 10%, ICC ≥ .70, or both for DTI30-2, 40 measurements for DTI30-1, and 37 for DTI15-2. Most of the reliable measurements were associated with the tracts corpus callosum, cingulum, cerebral peduncular fibers, uncinate fasciculus, and arcuate fasciculus. These reliable measurements included factional anisotropy (FA) and mean diffusivity of all 10 fiber regions. Intersession reliability was significantly worse than intra-session reliability for FA, mean length, and tract volume measurements from DTI15-2, indicating that the combination of MRI signal variation and physiological noise/change over time was the major error source for this sequence. Increasing the number of gradient directions from 15 to 30 while controlling the scan time, significantly affected values for all six variables and reduced intersession variability for mean length and tract volume measurements. Additionally, while increasing scan repetition from 1 to 2 had no significant effect on the reliability for DTI with 30 directions, this significantly reduced the upward bias in FA values from all 10 fiber regions and fiber count, mean length, and tract volume measurements from 5-7 fiber regions. In conclusion, diffusion tensor tractography provided many measurements with high test-retest reliability across different fiber variables and various fiber tracts even for images with 15 directions (NEX 2). Increasing the number of gradient directions from 15 to 30 with equivalent scan time reduced variability whereas increasing repetition from 1 to 2 for 30-direction DTI improved the accuracy of tractography measurements.
PMCID: PMC3468740  PMID: 22227883
reliability; diffusion tensor imaging; tractography; variability; white matter; fiber tracts
7.  Quantifying diffusion MRI tractography of the corticospinal tract in brain tumors with deterministic and probabilistic methods☆ 
NeuroImage : Clinical  2013;3:361-368.
Diffusion MRI tractography has been increasingly used to delineate white matter pathways in vivo for which the leading clinical application is presurgical mapping of eloquent regions. However, there is rare opportunity to quantify the accuracy or sensitivity of these approaches to delineate white matter fiber pathways in vivo due to the lack of a gold standard. Intraoperative electrical stimulation (IES) provides a gold standard for the location and existence of functional motor pathways that can be used to determine the accuracy and sensitivity of fiber tracking algorithms. In this study we used intraoperative stimulation from brain tumor patients as a gold standard to estimate the sensitivity and accuracy of diffusion tensor MRI (DTI) and q-ball models of diffusion with deterministic and probabilistic fiber tracking algorithms for delineation of motor pathways.
We used preoperative high angular resolution diffusion MRI (HARDI) data (55 directions, b = 2000 s/mm2) acquired in a clinically feasible time frame from 12 patients who underwent a craniotomy for resection of a cerebral glioma. The corticospinal fiber tracts were delineated with DTI and q-ball models using deterministic and probabilistic algorithms. We used cortical and white matter IES sites as a gold standard for the presence and location of functional motor pathways. Sensitivity was defined as the true positive rate of delineating fiber pathways based on cortical IES stimulation sites. For accuracy and precision of the course of the fiber tracts, we measured the distance between the subcortical stimulation sites and the tractography result. Positive predictive rate of the delineated tracts was assessed by comparison of subcortical IES motor function (upper extremity, lower extremity, face) with the connection of the tractography pathway in the motor cortex.
We obtained 21 cortical and 8 subcortical IES sites from intraoperative mapping of motor pathways. Probabilistic q-ball had the best sensitivity (79%) as determined from cortical IES compared to deterministic q-ball (50%), probabilistic DTI (36%), and deterministic DTI (10%). The sensitivity using the q-ball algorithm (65%) was significantly higher than using DTI (23%) (p < 0.001) and the probabilistic algorithms (58%) were more sensitive than deterministic approaches (30%) (p = 0.003). Probabilistic q-ball fiber tracks had the smallest offset to the subcortical stimulation sites. The offsets between diffusion fiber tracks and subcortical IES sites were increased significantly for those cases where the diffusion fiber tracks were visibly thinner than expected. There was perfect concordance between the subcortical IES function (e.g. hand stimulation) and the cortical connection of the nearest diffusion fiber track (e.g. upper extremity cortex).
This study highlights the tremendous utility of intraoperative stimulation sites to provide a gold standard from which to evaluate diffusion MRI fiber tracking methods and has provided an object standard for evaluation of different diffusion models and approaches to fiber tracking. The probabilistic q-ball fiber tractography was significantly better than DTI methods in terms of sensitivity and accuracy of the course through the white matter. The commonly used DTI fiber tracking approach was shown to have very poor sensitivity (as low as 10% for deterministic DTI fiber tracking) for delineation of the lateral aspects of the corticospinal tract in our study. Effects of the tumor/edema resulted in significantly larger offsets between the subcortical IES and the preoperative fiber tracks. The provided data show that probabilistic HARDI tractography is the most objective and reproducible analysis but given the small sample and number of stimulation points a generalization about our results should be given with caution. Indeed our results inform the capabilities of preoperative diffusion fiber tracking and indicate that such data should be used carefully when making pre-surgical and intra-operative management decisions.
•Diffusion MRI tractography is used for presurgical brain mapping.•We use intraoperative electric stimulation as a gold standard.•We delineate motor tracts with deterministic and probabilistic DTI and q-ball models.•Probabilistic q-ball has the best sensitivity (79%).•Probabilistic q-ball fiber tracks had the smallest offset to the subcortical IES.
PMCID: PMC3815019  PMID: 24273719
Diffusion MRI Tractography; Corticospinal tract; q-Ball; DTI; Brain tumor; Intraoperative electrical stimulation (IES)
8.  Cerebral White Matter Integrity Mediates Adult Age Differences in Cognitive Performance 
Journal of cognitive neuroscience  2009;21(2):289-302.
Previous research has established that age-related decline occurs in measures of cerebral white matter integrity, but the role of this decline in age-related cognitive changes is not clear. To conclude that white matter integrity has a mediating (causal) contribution, it is necessary to demonstrate that statistical control of the white matter-cognition relation reduces the magnitude of age-cognition relation. In this research, we tested the mediating role of white matter integrity, in the context of a task switching paradigm involving word categorization. Participants were 20 healthy, community-dwelling older adults (60–85 years), and 20 younger adults (18–27 years). From diffusion tensor imaging (DTI) tractography, we obtained fractional anisotropy (FA) as an index of white matter integrity in the genu and splenium of the corpus callosum and the superior longitudinal fasciculus (SLF). Mean FA values exhibited age-related decline consistent with a decrease in white matter integrity. From a model of reaction time distributions, we obtained independent estimates of the decisional and nondecisional (perceptual-motor) components of task performance. Age-related decline was evident in both components. Critically, age differences in task performance were mediated by FA in two regions: the central portion of the genu, and splenium-parietal fibers in the right hemisphere. This relation held only for the decisional component and was not evident in the nondecisional component. This result is the first demonstration that the integrity of specific white matter tracts is a mediator of age-related changes in cognitive performance.
PMCID: PMC2676336  PMID: 18564054
9.  Longitudinal diffusion tensor imaging and neuropsychological correlates in traumatic brain injury patients 
Traumatic brain injury (TBI) often involves focal cortical injury and white matter (WM) damage that can be measured shortly after injury. Additionally, slowly evolving WM change can be observed but there is a paucity of research on the duration and spatial pattern of long-term changes several years post-injury. The current study utilized diffusion tensor imaging to identify regional WM changes in 12 TBI patients and nine healthy controls at three time points over a four year period. Neuropsychological testing was also administered to each participant at each time point. Results indicate that TBI patients exhibit longitudinal changes to WM indexed by reductions in fractional anisotropy (FA) in the corpus callosum, as well as FA increases in bilateral regions of the superior longitudinal fasciculus (SLF) and portions of the optic radiation (OR). FA changes appear to be driven by changes in radial (not axial) diffusivity, suggesting that observed longitudinal FA changes may be related to changes in myelin rather than to axons. Neuropsychological correlations indicate that regional FA values in the corpus callosum and sagittal stratum (SS) correlate with performance on finger tapping and visuomotor speed tasks (respectively) in TBI patients, and that longitudinal increases in FA in the SS, SLF, and OR correlate with improved performance on the visuomotor speed (SS) task as well as a derived measure of cognitive control (SLF, OR). The results of this study showing progressive WM deterioration for several years post-injury contribute to a growing literature supporting the hypothesis that TBI should be viewed not as an isolated incident but as a prolonged disease state. The observations of long-term neurological and functional improvement provide evidence that some ameliorative change may be occurring concurrently with progressive degeneration.
PMCID: PMC3378081  PMID: 22723773
traumatic brain injury; diffusion tensor imaging; longitudinal; neuropsychology; recovery; DTI; TBI
10.  Altered brain morphometry in carpal tunnel syndrome is associated with median nerve pathology☆☆☆ 
NeuroImage : Clinical  2013;2:313-319.
Carpal tunnel syndrome (CTS) is a common median nerve entrapment neuropathy characterized by pain, paresthesias, diminished peripheral nerve conduction velocity (NCV) and maladaptive functional brain neuroplasticity. We evaluated structural reorganization in brain gray matter (GM) and white matter (WM) and whether such plasticity is linked to altered median nerve function in CTS.
We performed NCV testing, T1-weighted structural MRI, and diffusion tensor imaging (DTI) in 28 CTS and 28 age-matched healthy controls (HC). Voxel-based morphometry (VBM) contrasted regional GM volume for CTS versus HC. Significant clusters were correlated with clinical metrics and served as seeds to define associated WM tracts using DTI data and probabilistic tractography. Within these WM tracts, fractional anisotropy (FA), axial (AD) and radial (RD) diffusivity were evaluated for group differences and correlations with clinical metrics.
For CTS subjects, GM volume was significantly reduced in contralesional S1 (hand-area), pulvinar and frontal pole. GM volume in contralesional S1 correlated with median NCV. NCV was also correlated with RD and was negatively correlated with FA within U-fiber cortico-cortical association tracts identified from the contralesional S1 VBM seed.
Our study identified clear morphometric changes in the CTS brain. This central morphometric change is likely secondary to peripheral nerve pathology and altered somatosensory afference. Enhanced axonal coherence and myelination within cortico-cortical tracts connecting primary somatosensory and motor areas may accompany peripheral nerve deafferentation. As structural plasticity was correlated with NCV and not symptomatology, the former may be a better determinant of appropriate clinical intervention for CTS, including surgery.
► CTS demonstrated reduced GM volume in S1, pulvinar, and frontal pole. ► GM volume in S1 was significantly correlated with median nerve conduction velocity. ► Median nerve velocity was linked to WM microstructure in tracts connected to S1.
PMCID: PMC3689649  PMID: 23799199
CTS, carpal tunnel syndrome; NCV, nerve conduction velocity; GM, gray matter; WM, white matter; DTI, diffusion tensor imaging; VBM, voxel-based morphometry; FA, fractional anisotropy; AD, axial diffusivity; RD, radial diffusivity; S1, primary somatosensory cortex; M1, primary motor cortex; Nerve conduction velocity (NCV); Diffusion tensor imaging (DTI); Voxel-based morphometry (VBM); Fractional anisotropy (FA); Axial diffusivity (AD); Radial diffusivity (RD)
11.  Topological correlations of structural and functional networks in patients with traumatic brain injury 
Despite an increasing amount of specific correlation studies between structural and functional connectivity, there is still a need for combined studies, especially in pathological conditions. Impairments of brain white matter (WM) and diffuse axonal injuries are commonly suspected to be responsible for the disconnection hypothesis in traumatic brain injury (TBI) patients. Moreover, our previous research on TBI patients shows a strong relationship between abnormalities in topological organization of brain networks and behavioral deficits. In this study, we combined task-related functional connectivity (using event-related fMRI) with structural connectivity (derived from fiber tractography using diffusion MRI data) estimates in the same participants (17 adults with TBI and 16 controls), allowing for direct comparison between graph metrics of the different imaging modalities. Connectivity matrices were computed covering the switching motor network, which includes the basal ganglia, anterior cingulate cortex/supplementary motor area, and anterior insula/inferior frontal gyrus. The edges constituting this network consisted of the partial correlations between the fMRI time series from each node of the switching motor network. The interregional anatomical connections between the switching-related areas were determined using the fiber tractography results. We found that graph metrics and hubs obtained showed no agreement in both groups. The topological properties of brain functional networks could not be solely accounted for by the properties of the underlying structural networks. However, combining complementary information from both imaging modalities could improve accuracy in prediction of switching performance. Direct comparison between functional task-related and anatomical structural connectivity, presented here for the first time in TBI patients, links two powerful approaches to map the patterns of brain connectivity that may underlie behavioral deficits in brain-injured patients.
PMCID: PMC3817367  PMID: 24204337
functional connectivity; structural connectivity; brain networks; graph theoretical analysis; brain injury
12.  White Matter Integrity in Physically Fit Older Adults 
NeuroImage  2013;0:510-516.
White matter (WM) integrity declines with normal aging. Physical activity may attenuate age-related WM integrity changes and improve cognitive function. This study examined brain WM integrity in Masters athletes who have engaged in life-long aerobic exercise training. We tested the hypothesis that life-long aerobic training is associated with improved brain WM integrity in older adults.
Ten Masters athletes (3 females, age=72.2±5.3yrs, endurance training>15yrs) and 10 sedentary older adults similar in age and educational level (2 females, age=74.5±4.3yrs) participated. MRI fluid-attenuated-inversion-recovery (FLAIR) images were acquired to assess white matter hyper intensities (WMH) volume. Diffusion tensor imaging (DTI) was performed to evaluate the WM microstructural integrity with a DTI-derived metric, fractional anisotropy (FA) and mean diffusivity (MD).
After normalization to whole-brain volume, Masters athletes showed an 83% reduction in deep WMH volume relative to their sedentary counterparts (0.05 ± 0.05% vs. 0.29 ± 0.29%, p<0.05). In addition, we found an inverse relationship between aerobic fitness (VO2max) and deep WMH volume (r=−0.78, p<0.001). Using TBSS, Masters athletes showed higher FA values in the right superior corona radiata (SCR), both sides of superior longitudinal fasciculus (SLF), right inferior fronto-occipital fasciculus (IFO), and left inferior longitudinal fasciculus (ILF). In addition, Masters athletes also showed lower MD values in the left posterior thalamic radiation (PTR) and left cingulum hippocampus.
These findings suggest that life-long exercise is associated with reduced WMH and may preserve WM fiber microstructural integrity related to motor control and coordination in older adults.
PMCID: PMC3759589  PMID: 23769914
Aging; white matter disease; MRI; exercise; plasticity
13.  Altered brain morphometry in carpal tunnel syndrome is associated with median nerve pathology 
NeuroImage : clinical  2013;2:313-319.
Carpal tunnel syndrome (CTS) is a common median nerve entrapment neuropathy characterized by pain, paresthesias, diminished peripheral nerve conduction velocity (NCV) and maladaptive functional brain neuroplasticity. We evaluated structural reorganization in brain gray (GM) and white (WM) matter and whether such plasticity is linked to altered median nerve function in CTS.
We performed NCV testing, T1-weighted structural MRI, and diffusion tensor imaging (DTI) in 28 CTS and 28 age-matched healthy controls (HC). Voxel-based morphometry (VBM) contrasted regional GM volume for CTS versus HC. Significant clusters were correlated with clinical metrics and served as seeds to define associated WM tracts using DTI data and probabilistic tractography. Within these WM tracts, fractional anisotropy (FA), axial (AD) and radial (RD) diffusivity were evaluated for group differences and correlations with clinical metrics.
For CTS subjects, GM volume was significantly reduced in contralesional S1 (hand-area), pulvinar and frontal pole. GM volume in contralesional S1 correlated with median NCV. NCV was also correlated with RD and was negatively correlated with FA within U-fiber cortico-cortical association tracts identified from the contralesional S1 VBM seed.
Our study identified clear morphometric changes in the CTS brain. This central morphometric change is likely secondary to peripheral nerve pathology and altered somatosensory afference. Enhanced axonal coherence and myelination within cortico-cortical tracts connecting primary somatosensory and motor areas may accompany peripheral nerve deafferentation. As structural plasticity was correlated with NCV and not symptomatology, the former may be a better determinant of appropriate clinical intervention for CTS, including surgery.
PMCID: PMC3689649  PMID: 23799199
nerve conduction velocity (NCV); diffusion tensor imaging (DTI); voxel-based morphometry (VBM); fractional anisotropy (FA); axial diffusivity (AD); radial diffusivity (RD)
14.  The occipitofrontal fascicle in humans: A quantitative, in vivo, DT-MRI study 
NeuroImage  2007;37(4):1100-1111.
Since the existence of the occipitofrontal fascicle (OFF) in humans has remained controversial, we utilized diffusion tensor imaging (DT-MRI)-based segmentation and tractography to investigate its trajectory in vivo in the human. We found that the OFF is distinct from the subcallosal fasciculus or Muratoff’s bundle (MB) and extends from the dorsal and medial parts of the occipital lobe as well as the dorsal, medial and inferior parietal lobules to the dorsal and medial part of the prefrontal and premotor regions. In most of its course, it remains parallel to the corpus callosum, the caudate nucleus and the lateral ventricle. In the coronal plane, the OFF is discerned in the core of the white matter medial to the corona radiata and the superior longitudinal fascicle II (SLF II) and lateral to MB and the corpus callosum. The volumetric measurements of the stem portion of the OFF indicate that the OFF is smaller than the SLF II and the cingulum bundle. Since DT-MRI allows the visualization of OFF fibers leading to the projection areas but not to the origin or termination of these fibers, this has been extrapolated from the experimental data in non-human primates. The OFF may have a role in visual spatial processing along with SLF II.
PMCID: PMC3769215  PMID: 17681797
DT-MRI; Segmentation; Tractography; Occipitofrontal fascicle; Fronto-occipital fascicle
15.  Superior longitudinal fasciculus and cognitive dysfunction in adolescents born preterm and at term 
To understanding the relation between cognition and white matter structure in adolescents born preterm without obvious brain injury.
Thirty-two adolescents were selected based on birth risk (Full-term: M:F=8:5, Median (Interquartile Range) Age=16.1(.8); Low-risk preterm: M:F=4:5, Age=16.0(.3); High-risk preterm: M:F=3:7, Age=16.2(1.2)) and reading ability (Good-readers: M:F=3:8, Age=16.0(.6); Average-readers, M:F=6:3, Age=16.8(1.0); Poor-readers M:F=6:6, Age=16.0(.5)) from a longitudinal study on child development. Preterm birth was defined as a gestational age ≤36 weeks and a birth weight <=1600g. All participants demonstrated normal clinical neuroimaging. We examined fractional anisotropy (FA), radial diffusivity and volume of three major white matter fasciculi. The relations between structural measures and birth risk, hemisphere and cognitive ability (attention, lexical and sublexical decoding, auditory phonological awareness and processing speed) were analyzed using mixed-model regression.
Left superior longitudinal fasciculus (SLF) FA and radial diffusivity was related to reading-related skills while right SLF FA was related to attention skills. SLF volume decreased as these skills declined for adolescents born preterm, but not those born at term.
The relation between cognitive skills and SLF volume suggests that cryptic white matter injury may exist, possibly related to oligodendrocyte or axonal loss, despite normal clinical neuroimaging in adolescents born preterm.
PMCID: PMC2910222  PMID: 20187879
Diffusion Tensor Imaging; Prematurity; Cognitive dysfunction
16.  White matter integrity assessed by diffusion tensor tractography in a patient with a large tumor mass but minimal clinical and neuropsychological deficits 
Functional Neurology  2013;27(4):239-246.
Diffusion tensor imaging (DTI) tractography and image registration were used to investigate a patient with a massive left-sided brain tumor, whose size was largely disproportionate to his subtle neurological deficits. MRI was obtained from the patient and his healthy identical twin, who acted as anatomical reference for DTI and as a control for quantitative measures. To compensate for the patient’s altered anatomy, seed and way points for probabilistic tractography were drawn on the color-coded direction maps of the healthy twin. Registration, based on the combination of b0-images, T2-weighted and T1-weighted images, was used to identify the corresponding regions in the patient. The corticospinal tract (CST), the superior longitudinal fasciculus (SLF), and the cingulum bundle (CB) showed displaced anatomy. A significant difference was found between fractional anisotropy distribution along the left SLF and CB, but not along the CST. These findings fit well with the patient’s substantial preservation of his motor abilities, while abnormalities of the SLF and CB could explain the subtle but detectable cognitive deficits.
PMCID: PMC3861348  PMID: 23597438
brain lesion; cognition; DTI; image registration; tractography
17.  White Matter Development in Adolescence: Diffusion Tensor Imaging and Meta-Analytic Results 
Schizophrenia Bulletin  2012;38(6):1308-1317.
In light of the evidence for brain white matter (WM) abnormalities in schizophrenia, study of normal WM maturation in adolescence may provide critical insights relevant to the neurodevelopment of the disorder. Voxel-wise diffusion tensor imaging (DTI) studies have consistently demonstrated increases in fractional anisotropy (FA), a putative measure of WM integrity, from childhood into adolescence. However, the WM tracts that show FA increases have been variable across studies. Here, we aimed to assess which WM tracts show the most pronounced changes across adolescence.
DTI was performed in 78 healthy subjects aged 8–21 years, and voxel-wise analysis conducted using tract-based spatial statistics (TBSS). In addition, we performed the first meta-analysis of TBSS studies on WM development in adolescence.
In our sample, we observed bilateral increases in FA with age, which were most significant in the left superior longitudinal fasciculus (SLF), inferior longitudinal fasciculus, inferior fronto-occipital fasciculus, and anterior thalamic radiation. These findings were confirmed by the meta-analysis, and FA increase in the bilateral SLF was the most consistent finding across studies. Moreover, in our sample, FA of the bilateral SLF showed a positive association with verbal working memory performance and partially mediated increases in verbal fluency as a function of increasing age.
These data highlight increasing connectivity in the SLF during adolescence. In light of evidence for compromised SLF integrity in high-risk and first-episode patients, these data suggest that abnormal maturation of the SLF during adolescence may be a key target in the neurodevelopment of schizophrenia.
PMCID: PMC3494037  PMID: 22499780
adolescence; development; diffusion tensor imaging; superior longitudinal fasciculus; verbal fluency; working memory
18.  Longitudinal changes of structural connectivity in traumatic axonal injury 
Neurology  2011;77(9):818-826.
To identify structural connectivity change occurring during the first 6 months after traumatic brain injury and to evaluate the utility of diffusion tensor tractography for predicting long-term outcome.
The participants were 28 patients with mild to severe traumatic axonal injury and 20 age- and sex-matched healthy control subjects. Neuroimaging was obtained 0–9 days postinjury for acute scans and 6–14 months postinjury for chronic scans. Long-term outcome was evaluated on the day of the chronic scan. Twenty-eight fiber regions of 9 major white matter structures were reconstructed, and reliable tractography measurements were determined and used.
Although most (23 of 28) patients had severe brain injury, their long-term outcome ranged from good recovery (16 patients) to moderately (5 patients) and severely disabled (7 patients). In concordance with the diverse outcome, the white matter change in patients was heterogeneous, ranging from improved structural connectivity, through no change, to deteriorated connectivity. At the group level, all 9 fiber tracts deteriorated significantly with 7 (corpus callosum, cingulum, angular bundle, cerebral peduncular fibers, uncinate fasciculus, and inferior longitudinal and fronto-occipital fasciculi) showing structural damage acutely and 2 (fornix body and left arcuate fasciculus) chronically. Importantly, the amount of change in tractography measurements correlated with patients' long-term outcome. Acute tractography measurements were able to predict patients' learning and memory performance; chronic measurements also determined performance on processing speed and executive function.
Diffusion tensor tractography is a valuable tool for identifying structural connectivity changes occurring between the acute and chronic stages of traumatic brain injury and for predicting patients' long-term outcome.
PMCID: PMC3162636  PMID: 21813787
19.  Brain networks of spatial awareness: evidence from diffusion tensor imaging tractography 
Left unilateral neglect, a dramatic condition which impairs awareness of left-sided events, has been classically reported after right hemisphere cortical lesions involving the inferior parietal region. More recently, the involvement of long-range white matter tracts has been highlighted, consistent with the idea that awareness of events occurring in space depends on the coordinated activity of anatomically distributed brain regions. Damage to the superior longitudinal fasciculus (SLF), linking parietal to frontal cortical regions, or to the inferior longitudinal fasciculus (ILF), connecting occipital and temporal lobes, have been described in neglect patients. In this study four right-handed patients with right-hemisphere strokes were submitted to a high-definition anatomical MRI with diffusion tensor imaging (DTI) sequences and to a paper-and-pencil neglect battery. We used DTI tractography to visualize the SLF, the ILF and the inferior fronto-occipital fasciculus (IFOF), a pathway running in the depth of the temporal lobe, not hitherto associated with neglect. Two patients with cortical involvement of the inferior parietal and superior temporal regions, but intact and symmetrical fasciculi, showed no signs of neglect. The other two patients with signs of left neglect had superficial damage to the inferior parietal cortex and white matter damage involving the IFOF. These findings suggest that superficial damage to the inferior parietal cortex per se may not be sufficient to produce visual neglect. In some cases, a lesion to the direct connections between ventral occipital and frontal regions (i.e. IFOF) may contribute to the manifestation of neglect by impairing the top-down modulation of visual areas from frontal cortex.
PMCID: PMC2386830  PMID: 17991702
Aged; 80 and over; Awareness; physiology; Cerebral Cortex; physiopathology; Diffusion Magnetic Resonance Imaging; Dominance; Cerebral; physiology; Female; Humans; Image Processing; Computer-Assisted; Imaging; Three-Dimensional; Kinesthesis; physiology; Male; Middle Aged; Nerve Fibers; Myelinated; physiology; Nerve Net; physiopathology; Perceptual Disorders; diagnosis; physiopathology; Stroke; complications; physiopathology
20.  Inter-hemispheric functional connectivity disruption in children with prenatal alcohol exposure 
MRI studies, including recent diffusion tensor imaging (DTI) studies, have shown corpus callosum abnormalities in children prenatally exposed to alcohol, especially in the posterior regions. These abnormalities appear across the range of Fetal Alcohol Spectrum Disorders (FASD). Several studies have demonstrated cognitive correlates of callosal abnormalities in FASD including deficits in visual-motor skill, verbal learning, and executive functioning. The goal of this study was to determine if inter-hemispheric structural connectivity abnormalities in FASD are associated with disrupted inter-hemispheric functional connectivity and disrupted cognition.
Twenty-one children with FASD and 23 matched controls underwent a six minute resting-state functional MRI scan as well as anatomical imaging and DTI. Using a semiautomated method, we parsed the corpus callosum and delineated seven inter-hemispheric white matter tracts with DTI tractography. Cortical regions of interest (ROIs) at the distal ends of these tracts were identified. Right-left correlations in resting fMRI signal were computed for these sets of ROIs and group comparisons were done. Correlations with facial dysmorphology, cognition, and DTI measures were computed.
A significant group difference in inter-hemispheric functional connectivity was seen in a posterior set of ROIs, the para-central region. Children with FASD had functional connectivity that was 12% lower than controls in this region. Sub-group analyses were not possible due to small sample size, but the data suggest that there were effects across the FASD spectrum. No significant association with facial dysmorphology was found. Para-central functional connectivity was significantly correlated with DTI mean diffusivity, a measure of microstructural integrity, in posterior callosal tracts in controls but not in FASD. Significant correlations were seen between these structural and functional measures and Wechsler perceptual reasoning ability.
Inter-hemispheric functional connectivity disturbances were observed in children with FASD relative to controls. The disruption was measured in medial parietal regions (para-central) that are connected by posterior callosal fiber projections. We have previously shown microstructural abnormalities in these same posterior callosal regions and the current study suggests a possible relationship between the two. These measures have clinical relevance as they are associated with cognitive functioning.
PMCID: PMC3083458  PMID: 21303384
Fetal alcohol (FAS, FASD); Brain; functional MRI (fMRI); resting-state, connectivity; neuropsychological
21.  Fiber Pathways of Attention Subnetworks Revealed with Tract-Based Spatial Statistics (TBSS) and Probabilistic Tractography 
PLoS ONE  2013;8(11):e78831.
It has been widely accepted that attention can be divided into three subnetworks - alerting, orienting and executive control (EC), and the subnetworks of attention are linked to distinct brain regions. However, the association between specific white matter fibers and the subnetworks of attention is not clear enough. Using diffusion tensor imaging (DTI), the white matter connectivity related to the performance of attention was assessed by attention network test (ANT) in 85 healthy adolescents. Tract-based spatial statistics (TBSS) and probabilistic diffusion tractography analysis demonstrated that cerebellothalamic tract was involved in alerting, while orienting depended upon the superior longitudinal fasciculus (SLF). In addition, EC was under the control of anterior corona radiata (ACR). Our findings suggest that different fiber pathways are involved in the three distinct subnetworks of attention. The current study will yield more precise information about the structural substrates of attention function and may aid the efforts to understand the neurophysiology of several attention disorders.
PMCID: PMC3817088  PMID: 24223852
22.  Improved Sensitivity to Cerebral White Matter Abnormalities in Alzheimer’s Disease with Spherical Deconvolution Based Tractography 
PLoS ONE  2012;7(8):e44074.
Diffusion tensor imaging (DTI) based fiber tractography (FT) is the most popular approach for investigating white matter tracts in vivo, despite its inability to reconstruct fiber pathways in regions with “crossing fibers.” Recently, constrained spherical deconvolution (CSD) has been developed to mitigate the adverse effects of “crossing fibers” on DTI based FT. Notwithstanding the methodological benefit, the clinical relevance of CSD based FT for the assessment of white matter abnormalities remains unclear. In this work, we evaluated the applicability of a hybrid framework, in which CSD based FT is combined with conventional DTI metrics to assess white matter abnormalities in 25 patients with early Alzheimer’s disease. Both CSD and DTI based FT were used to reconstruct two white matter tracts: one with regions of “crossing fibers,” i.e., the superior longitudinal fasciculus (SLF) and one which contains only one fiber orientation, i.e. the midsagittal section of the corpus callosum (CC). The DTI metrics, fractional anisotropy (FA) and mean diffusivity (MD), obtained from these tracts were related to memory function. Our results show that in the tract with “crossing fibers” the relation between FA/MD and memory was stronger with CSD than with DTI based FT. By contrast, in the fiber bundle where one fiber population predominates, the relation between FA/MD and memory was comparable between both tractography methods. Importantly, these associations were most pronounced after adjustment for the planar diffusion coefficient, a measure reflecting the degree of fiber organization complexity. These findings indicate that compared to conventionally applied DTI based FT, CSD based FT combined with DTI metrics can increase the sensitivity to detect functionally significant white matter abnormalities in tracts with complex white matter architecture.
PMCID: PMC3432077  PMID: 22952880
NeuroImage  2008;42(2):1032-1044.
We investigated the relation between cognitive processing speed and structural properties of white matter pathways via convergent imaging studies in healthy and brain-injured groups. Voxel-based morphometry (VBM) was applied to diffusion tensor imaging data from thirty-nine young healthy subjects in order to investigate the relation between processing speed, as assessed with the Digit-Symbol subtest from WAIS-III, and fractional anisotropy, an index of microstructural organization of white matter. Digit-Symbol performance was positively correlated with fractional anisotropy of white matter in the parietal and temporal lobes bilaterally and in the left middle frontal gyrus. Fiber tractography indicated that these regions are consistent with the trajectories of the superior and inferior longitudinal fasciculi. In a second investigation, we assessed the effect of white matter damage on processing speed using voxel-based lesion symptom mapping (VLSM) analysis of data from seventy-two patients with left hemisphere strokes. Lesions in left parietal white matter, together with cortical lesions in supramarginal and angular gyri were associated with impaired performance. These findings suggest that cognitive processing speed, as assessed by the Digit-Symbol test, is closely related to the structural integrity of white matter tracts associated with parietal and temporal cortices and left middle frontal gyrus. Further, fiber tractography applied to VBM results and the patient findings suggest that the superior longitudinal fasciculus, a major tract subserving fronto-parietal integration, makes a prominent contribution to processing speed.
PMCID: PMC2630965  PMID: 18602840
Cognitive processing speed; diffusion tensor imaging; individual differences; magnetic resonance imaging; neural pathways; neuropsychology
24.  Global Tractography with Embedded Anatomical Priors for Quantitative Connectivity Analysis 
Tractography algorithms provide us with the ability to non-invasively reconstruct fiber pathways in the white matter (WM) by exploiting the directional information described with diffusion magnetic resonance. These methods could be divided into two major classes, local and global. Local methods reconstruct each fiber tract iteratively by considering only directional information at the voxel level and its neighborhood. Global methods, on the other hand, reconstruct all the fiber tracts of the whole brain simultaneously by solving a global energy minimization problem. The latter have shown improvements compared to previous techniques but these algorithms still suffer from an important shortcoming that is crucial in the context of brain connectivity analyses. As no anatomical priors are usually considered during the reconstruction process, the recovered fiber tracts are not guaranteed to connect cortical regions and, as a matter of fact, most of them stop prematurely in the WM; this violates important properties of neural connections, which are known to originate in the gray matter (GM) and develop in the WM. Hence, this shortcoming poses serious limitations for the use of these techniques for the assessment of the structural connectivity between brain regions and, de facto, it can potentially bias any subsequent analysis. Moreover, the estimated tracts are not quantitative, every fiber contributes with the same weight toward the predicted diffusion signal. In this work, we propose a novel approach for global tractography that is specifically designed for connectivity analysis applications which: (i) explicitly enforces anatomical priors of the tracts in the optimization and (ii) considers the effective contribution of each of them, i.e., volume, to the acquired diffusion magnetic resonance imaging (MRI) image. We evaluated our approach on both a realistic diffusion MRI phantom and in vivo data, and also compared its performance to existing tractography algorithms.
PMCID: PMC4233943  PMID: 25452742
diffusion MRI; global tractography; spline; brain connectivity; MCMC; anatomical priors
25.  Mapping of Functional Areas in the Human Cortex Based on Connectivity through Association Fibers 
Cerebral Cortex (New York, NY)  2008;19(8):1889-1895.
In the human brain, different regions of the cortex communicate via white matter tracts. Investigation of this connectivity is essential for understanding brain function. It has been shown that trajectories of white matter fiber bundles can be estimated based on orientational information that is obtained from diffusion tensor imaging (DTI). By extrapolating this information, cortical regions associated with a specific white matter tract can be estimated. In this study, we created population-averaged cortical maps of brain connectivity for 4 major association fiber tracts, the corticospinal tract (CST), and commissural fibers. It is shown that these 4 association fibers interconnect all 4 lobes of the hemispheres. Cortical regions that were assigned based on association with the CST and the superior longitudinal fasciculus (SLF) agreed with locations of their known (CST: motor) or putative (SLF: language) functions. The proposed approach can potentially be used for quantitative assessment of the effect of white matter abnormalities on associated cortical regions.
PMCID: PMC2705697  PMID: 19068488
Brodmann area; cortical connectivity; diffusion tensor imaging; fiber tracts; tractography; white matter atlas

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