Fiber Assignment Research Articles

A study on the correlation between the local topological properties of the brain structural networks in depression and the severity of the disease

Objective To explore the differences of the connectivity strength, the clustering coefficient and the local efficiency of the nodes in the brain structural networks in the depression and healthy subjects and then analyze the mode of the local connections of the brain regions and their local efficiency of the transmission of information and their relationship with the severity of the disease in the depression. Methods The Diffusion Tensor Imaging data were obtained from 24 depression patients and 25 healthy controls. The whole cerebral cortex was parcellated into 90 regions by the anatomical label map. Tractography was performed in the whole cerebral cortex of each subject to reconstruct white matter tracts of the brain using the fiber assignment by continuous tracking (FACT) algorithm. And then the brain structural networks were constructed using the complex network theory. The local topological properties of the brain structural networks of the depression and healthy were examined by two sample t-test. Results The local efficiency of the nodes of the networks in depression decreased significantly (the left middle frontal gyrus (orbital part): 0.64±0.30, the left hippocampus: 0.57±0.07, the right parahippocampal gyrus: 0.50±0.15) compared with the healthy (0.88±0.10, 0.64±0.06, 0.66±0.13 respectively, P=0.00098, 0.00039, 0.00017, survived critical FDR threshold for multiple comparisons); and the clustering coefficient of the nodes of the networks in depression (the left middle frontal gyrus (orbital part): 0.14±0.07) decreased significantly when compared with the healthy (0.22±0.06, P=0.000030, survived critical FDR threshold for multiple comparisons). Significant negative correlation was found between the local efficiency of the left middle frontal gyrus (orbital part) and the total scores of HAMD-17 in the depression (r=-0.48, P=0.02). Conclusion The degree of the localization and the local efficiency of the information transmission of the frontal lobe are decreased. The local efficiency in the information transmission in the hippocampal is also decreased. And the local efficiency of the frontal lobe is negatively related with the severity of the disease in the depression. Key words: Depression; Diffusion Tensor Imaging; Brain structural network; Local topological properties

DTI of the visual pathway - white matter tracts and cerebral lesions.

DTI is a technique that identifies white matter tracts (WMT) non-invasively in healthy and non-healthy patients using diffusion measurements. Similar to visual pathways (VP), WMT are not visible with classical MRI or intra-operatively with microscope. DIT will help neurosurgeons to prevent destruction of the VP while removing lesions adjacent to this WMT. We have performed DTI on fifty patients before and after surgery between March 2012 to January 2014. To navigate we used a 3DT1-weighted sequence. Additionally, we performed a T2-weighted and DTI-sequences. The parameters used were, FOV: 200 x 200 mm, slice thickness: 2 mm, and acquisition matrix: 96 x 96 yielding nearly isotropic voxels of 2 x 2 x 2 mm. Axial MRI was carried out using a 32 gradient direction and one b0-image. We used Echo-Planar-Imaging (EPI) and ASSET parallel imaging with an acceleration factor of 2 and b-value of 800 s/mm². The scanning time was less than 9 min. The DTI-data obtained were processed using a FDA approved surgical navigation system program which uses a straightforward fiber-tracking approach known as fiber assignment by continuous tracking (FACT). This is based on the propagation of lines between regions of interest (ROI) which is defined by a physician. A maximum angle of 50, FA start value of 0.10 and ADC stop value of 0.20 mm²/s were the parameters used for tractography. There are some limitations to this technique. The limited acquisition time frame enforces trade-offs in the image quality. Another important point not to be neglected is the brain shift during surgery. As for the latter intra-operative MRI might be helpful. Furthermore the risk of false positive or false negative tracts needs to be taken into account which might compromise the final results.

Decoding the superior parietal lobule connections of the superior longitudinal fasciculus/arcuate fasciculus in the human brain

The temporo-parietal (TP) white matter connections between the inferior parietal lobule and superior temporal gyrus as part of the superior longitudinal fasciculus/arcuate fasciculus (SLF/AF) or middle longitudinal fasciculus (MdLF) have been studied in prior diffusion tensor tractography (DTT) studies. However, few studies have been focusing on the higher TP connections of the superior parietal lobule with the temporal lobe. These higher TP connections have been shown to have a role in core processes such as attention, memory, emotions, and language. Our most recent study, for the first time, hinted to the possibility of a long white matter connection interconnecting the superior parietal lobule (SPL) with the posterior temporal lobe in human brain which we call the SLF/AF TP-SPL and for a shorter abbreviation, the TP-SPL. We decided to further investigate this white matter connection using fiber assignment by continuous tracking deterministic tractography and high spatial resolution diffusion tensor imaging on 3T. Five healthy right-handed men (age range 24–37years) were studied. We delineated the SPL connections of the SLF/AF TP bilaterally in five normal adult human brains. Using a high resolution DTT technique, we demonstrate for the first time, the trajectory of a long fiber bundle connectivity between the SPL and posterior temporal lobe, called the SLF/AF TP-SPL (or the TP-SPL), bilaterally in five healthy adult human brains. We also demonstrate the trajectory of the vertically oriented posterior TP connections, interconnecting the inferior parietal lobule (IPL) with the posterior temporal lobe (TP-IPL) in relation to the TP-SPL, arcuate fasciculus and other major language pathways. In the current study, for the first time, we categorized the TP connections into the anterior and posterior connectivity groups and subcategorized each one into the SPL or IPL connections.

Brief meditation increases fiber wiring between striatum and corona radiata

White matter tractography has becoming increasingly useful for the visualization and measurement of brain anatomical structures and connections in both cortical and subcortical regions. Our previous studies using Diffusion Tensor Imaging have revealed the changes of white matter indexes including fractional anisotropy, axial diffusivity, and radial diffusivity at the corona radiata, an important white matter tract connecting the anterior cingulate cortex (ACC) to other structures including striatum after brief meditation training - integrative body-mind training (IBMT) in healthy college students [1,2]. Since ACC and striatum involve in self-control networks, here we seek to further investigate the mechanism of white matter changes by employing an innovative tracking method and targeting specific fiber bundle connecting ACC and striatum after 2-week of IBMT. Fourteen healthy undergraduates were recruited at campus and received 30 min of IBMT for 2-wk, with a total of five hours training. IBMT involves body relaxation, mental imagery, and mindfulness training, accompanied by selected music background and guided by IBMT coach [1,2]. DTI scans were preformed before and after 2-wk IBMT with a Philips 3T Achieva. DTIstudio was used for preprocessing that includes motion and eddy current correction, coregistration, and subsequent calculation of diffusion tensors and FA maps. Fiber Assignment by Continuous Tractography (FACT) method was then used with FA threshold set at 0.2 and principal eigenvector set at 45° for fiber tracking. Normalization was carried out with DiffeoMap to normalize subject images to atlas by linear and non-linear transformation. With the inverse linear and non-linear transformation matrices, the atlas, a brain parcellation map with 130 segmented ROI objects, was warped to the individual data space for each subject. ROIs in the left anterior corona radiata (ACR) and striatum were then defined by ROIeditor [3]. We focused on the number of fibers for the fiber bundle between striatum and left ACR, and compared within-group changes before and after 2-wk training. We found increased number of fibers penetrating both striatum and left ACR after 2-wk IBMT (P=0.000).

Distinguishing and quantification of the human visual pathways using high-spatial-resolution diffusion tensor tractography

Quantification of the living human visual system using MRI methods has been challenging, but several applications demand a reliable and time-efficient data acquisition protocol. In this study, we demonstrate the utility of high-spatial-resolution diffusion tensor fiber tractography (DTT) in reconstructing and quantifying the human visual pathways. Five healthy males, age range 24–37years, were studied after approval of the institutional review board (IRB) at The University of Texas Health Science Center at Houston. We acquired diffusion tensor imaging (DTI) data with 1-mm slice thickness on a 3.0-Tesla clinical MRI scanner and analyzed the data using DTT with the fiber assignment by continuous tractography (FACT) algorithm. By utilizing the high-spatial-resolution DTI protocol with FACT algorithm, we were able to reconstruct and quantify bilateral optic pathways including the optic chiasm, optic tract, optic radiations free of contamination from neighboring white matter tracts.

Selective verbal memory impairment due to left fornical crus injury in a patient with intraventricular hemorrhage.

Selective verbal memory impairment due to left fornical crus injury in a patient with intraventricular hemorrhage.

Unusual neural connection between injured cingulum and brainstem in a patient with subarachnoid hemorrhage.

Unusual neural connection between injured cingulum and brainstem in a patient with subarachnoid hemorrhage.

Recovery of the corticospinal tracts injured by subfalcine herniation: a diffusion tensor tractography study.

Recovery of the corticospinal tracts injured by subfalcine herniation: a diffusion tensor tractography study.

White matter abnormalities in 22q11.2 deletion syndrome: Preliminary associations with the Nogo-66 receptor gene and symptoms of psychosis

BackgroundThis study utilized diffusion tensor imaging (DTI) to analyze white matter tractography in the anterior limb of the internal capsule (ALIC), fornix, and uncinate fasciculus (UF) of individuals with 22q11.2 deletion syndrome and controls. Aberrations in these tracts have been previously associated with schizophrenia. With up to 25% of individuals with 22q11.2DS developing schizophrenia in adulthood, we hypothesized reduction in structural integrity of these tracts, including an association with prodromal symptoms of psychosis. We further predicted an association between allelic variation in a functional polymorphism of the Nogo-66 receptor gene and 22q11.2DS white matter integrity. MethodsTractography was conducted using fiber assignment by streamline tracking algorithm in DTI Studio. Subjects were genotyped for the rs701428 SNP of the Nogo-66 receptor gene, and assessed for presence of prodromal symptoms. ResultsWe found significant group differences between 22q11.2DS and controls in DTI metrics for all three tracts. DTI metrics of ALIC and UF were associated with prodromal symptoms in 22q11.2DS. Further, ALIC DTI metrics were associated with allelic variation of the rs701428 SNP of the Nogo-66 receptor gene in 22q11.2DS. ConclusionsAlterations in DTI metrics suggest white matter microstructural anomalies of the ALIC, fornix, and UF in 22q11.2DS. Structural differences in ALIC appear to be associated with the Nogo-66 receptor gene, which has been linked to myelin-mediated axonal growth inhibition. Moreover, the association between psychosis symptoms and ALIC and UF metrics suggests that the Nogo-66 receptor gene may represent a susceptibility gene for psychosis through its disruption of white matter microstructure and myelin-associated axonal growth.

Walk the Line: From Diffusion Imaging to the Microstructure of the Brain

tracking is superior. For the clinician, this means that one has to select the appropriate method for each problem, in other words, “to walk the line”—not only along the fibers. Diffusion kurtosis Imaging is one of the recent developments of the past decade in diffusion tensor imaging [19]. It is based on the measurement of different b-values and allows the assessment of the diffusion-weighted signal that has statistically a non-Gaussian distribution (kurtosis). In this signal, different contributions from intracellular and extracellular space and bound and free water (compartments being not necessarily restricted to anatomical borders) are mirrored. This means that a higher kurtosis is associated with higher diffusion heterogeneity and a lower kurtosis with reduced diffusion heterogeneity, such as restricted diffusion. By this means it is possible to find more subtle changes of the integrity of white matter than by the diffusion metrics derived from the Gaussian distribution such as fractional anisotropy and mean, axial and radial diffusivity alone. In this issue, Zhang, Yang, and coworkers reported on the use of diffusion kurtosis imaging in 15 patients with presumably genetic (formerly called idiopathic) epilepsies. Compared with controls, mean kurtosis differed in the white matter of both frontal lobes, and in the gray and white matter of the right parietal lobe. Even if we do not know what it exactly means, it is another hint for an altered microstructure in a diseased brain. In any case, more information is added for the evaluation of the brain’s microstructure and the specific damages being not seen on conventional MR images. The selection of appropriate measurements and theoretically and practically correct evaluation tools is crucial to approach the histological truth of the pathologies. So we also have to “walk the line” for an adequate research in neuroradiology. Diffusion-weighted imaging taught us in the 1990s to identify acute stroke on diffusion-weighted images as diffusion restriction being attributed to pathophysiological changes of the underlying microstructure such as intracellular edema [1–4]. At the same time, the anisotropic orientation of water diffusion being also dependent on the microstructure of the brain was addressed [5] and expressed as self-diffusion tensor [6]. Soon, several tracking methods for fiber tracking were proposed (for a review, see [7]). The most famous and commonly used tracking algorithms are fiber assignment by continuous tracking (FACT) [8–10] and probabilistic tracking [11–15]. Especially FACT algorithm is widely used and has been implemented in commercial neurosurgical planning devices. Why now adding a new tracking method such as global tracking [16–17] to so many others? They all have their disadvantages and limitations. Where is the truth—the ground truth? Global tracking won the award of the “MICCAI 2009 Fiber Cup: Reconstructing Fibers from the Phantom Data.” It was the method that reconstructed best the ground truth of a phantom [18] with given fiber bendings and crossings and different anisotropies. How does it perform in the living and diseased brain? This topic is addressed in this issue entitled as “Global Tracking in human gliomas: a comparison with established tracking methods” by Nguyen Thanh et al. The advantage of global tracking is the resolution of fiber crossings and the continuation of the fibers distally to it. On the other hand, the adaptation to the globally estimated fiber tracts leads to a certain rigidity of the reconstruction, so that some strongly bended fibers are not fully accounted for. In this case, probabilistic

Reproducibility of corticospinal diffusion tensor tractography in normal subjects and hemiparetic stroke patients

PurposeThe reproducibility of corticospinal diffusion tensor tractography (DTT) for a guideline is important before longitudinal monitoring of the therapy effects in stroke patients. This study aimed to establish the reproducibility of corticospinal DTT indices in healthy subjects and chronic hemiparetic stroke patients. Materials and methodsWritten informed consents were obtained from 10 healthy subjects (mean age 25.8±6.8 years), who underwent two scans in one session plus the third scan one week later, and from 15 patients (mean age 47.5±9.1 years, 6–60 months after the onset of stroke, NIHSS scores between 9 and 20) who were scanned thrice on separate days within one month. Diffusion-tensor imaging was performed at 3T with 25 diffusion directions. Corticospinal tracts were reconstructed using fiber assignment by continuous tracking without and with motion/eddy-current corrections. Intra- and inter-rater as well as intra- and inter-session variations of the DTT derived indices (fiber number, apparent diffusion coefficient (ADC), and fractional anisotropy (FA)) were assessed. ResultsIntra-session and inter-session coefficients of variations (CVs) are small for FA (1.13–2.09%) and ADC (0.45–1.64%), but much larger for fiber number (8.05–22.4%). Inter-session CVs in the stroke side of patients (22.4%) are higher than those in the normal sides (18.0%) and in the normal subjects (14.7%). Motion/eddy-current correction improved inter-session reproducibility only for the fiber number of the infarcted corticospinal tract (CV reduced from 22.4% to 14.1%). ConclusionThe fiber number derived from corticospinal DTT shows substantially lower precision than ADC and FA, with infarcted tracts showing lower reproducibility than the healthy tissues.

Diffusion tensor imaging fiber tracking with reliable tracking orientation and flexible step size.

We propose a method of reliable tracking orientation and flexible step size fiber tracking. A new directional strategy was defined to select one optimal tracking orientation from each directional set, which was based on the single-tensor model and the two-tensor model. The directional set of planar voxels contained three tracking directions: two from the two-tensor model and one from the single-tensor model. The directional set of linear voxels contained only one principal vector. In addition, a flexible step size, rather than fixable step sizes, was implemented to improve the accuracy of fiber tracking. We used two sets of human data to assess the performance of our method; one was from a healthy volunteer and the other from a patient with low-grade glioma. Results verified that our method was superior to the single-tensor Fiber Assignment by Continuous Tracking and the two-tensor eXtended Streamline Tractography for showing detailed images of fiber bundles.

Global Tracking in Human Gliomas: A Comparison with Established Tracking Methods

PurposeGlobal tracking (GT) is a recently published fibre tractography (FT) method that takes simultaneously all fibres into account during their reconstruction. The purpose of this study was to compare this new method with fibre assignment by continuous tracking (FACT) and probabilistic tractography (PT) for the detection of the corticospinal tract (CST) in patients with gliomas.MethodsTractography of the CST was performed in 17 patients with eight low grade and nine anaplastic astrocytomas located in the motor cortex or the corticospinal tract. Diffusions metrics as fractional anisotropy (FA), mean (MD), axial (AD) and radial diffusivity (RD) were obtained. The methods were additionally applied on a physical phantom to assess their accuracy.ResultsPT was successful in all (100 %), GT in 16 (94 %) and FACT in 15 patients (88 %). The case where GT and FACT, both, missed the CST showed the highest AD and RD, whereas the one where FACT algorithm, alone, was not successfully showed the lowest AD and RD of the group. FA was reduced on the pathologic side (FApath 0.35 ± 0.16 (mean ± SD) versus FAcontralateral 0.51 ± 0.15, p corr < 0.03). RD was increased on the pathologic side (RDpath 0.67 ± 0.29 × 10− 3 mm2/s versus RDcontralateral 0.46 ± 0.08 × 10− 3 mm2/s, p corr < 0.03). In the phantom measurement, only GT did not detect false positive fibres at fibre crossings.ConclusionPT performed well even in areas of increased diffusivities indicating a severe oedema or disintegration of tissue. FACT was also susceptible to a decrease of diffusivities and to a susceptibility artefact, where GT was robust.

Diffusion tensor tractography of the arcuate fasciculus in patients with brain tumors: Comparison between deterministic and probabilistic models.

The purpose of this study was to compare the deterministic and probabilistic tracking methods of diffusion tensor white matter fiber tractography in patients with brain tumors. We identified 29 patients with left brain tumors <2 cm from the arcuate fasciculus who underwent pre-operative language fMRI and DTI. The arcuate fasciculus was reconstructed using a deterministic Fiber Assignment by Continuous Tracking (FACT) algorithm and a probabilistic method based on an extended Monte Carlo Random Walk algorithm. Tracking was controlled using two ROIs corresponding to Broca's and Wernicke's areas. Tracts in tumoraffected hemispheres were examined for extension between Broca's and Wernicke's areas, anterior-posterior length and volume, and compared with the normal contralateral tracts. Probabilistic tracts displayed more complete anterior extension to Broca's area than did FACT tracts on the tumor-affected and normal sides (p < 0.0001). The median length ratio for tumor: normal sides was greater for probabilistic tracts than FACT tracts (p < 0.0001). The median tract volume ratio for tumor: normal sides was also greater for probabilistic tracts than FACT tracts (p = 0.01). Probabilistic tractography reconstructs the arcuate fasciculus more completely and performs better through areas of tumor and/or edema. The FACT algorithm tends to underestimate the anterior-most fibers of the arcuate fasciculus, which are crossed by primary motor fibers.

An improved fiber tracking algorithm based on fiber assignment using the continuous tracking algorithm and two-tensor model.

This study tested an improved fiber tracking algorithm, which was based on fiber assignment using a continuous tracking algorithm and a two-tensor model. Different models and tracking decisions were used by judging the type of estimation of each voxel. This method should solve the cross-track problem. This study included eight healthy subjects, two axonal injury patients and seven demyelinating disease patients. This new algorithm clearly exhibited a difference in nerve fiber direction between axonal injury and demyelinating disease patients and healthy control subjects. Compared with fiber assignment with a continuous tracking algorithm, our novel method can track more and longer nerve fibers, and also can solve the fiber crossing problem.

Impairment-Aware Design of Translucent DWDM Networks Based on the k-Path Connectivity Graph

In this paper we propose a design procedure based on comprehensive integer linear programing (ILP) for translucent optical transport networks (OTNs), exploiting an extended version of the so-called “connectivity graph.” For the first time to the best of our knowledge, we propose a mathematical approach that covers the manifold challenges of a realistic optical layer OTN design, jointly solving the regenerator placement problem (RPP) and the routing, fiber and wavelength assignment with regenerator problem (RFWA-RP). As a first contribution, we extend the concept of the connectivity graph to a k-path (k-p) connectivity graph. Second, the formulation addresses the problem of planning the number of dense wavelength division multiplexing systems, jointly solving the RPP and placing transponders. Third, we consider regeneration devices as wavelength converters also, showing the benefits arising from that aspect disregarded in the existing impairment-aware (IA) ILP formulations based on the connectivity graph. Finally we compare over different networks the results of our design procedure with those achieved by a hybrid method that combines a simplified IA-ILP formulation with a greedy heuristic. Moreover, an analytical framework to evaluate the network cost in terms of capital expenditure and operational expenditure is also presented. We show that the k-p connectivity graph represents a cost-effective tool for network design, as it allows one to greatly reduce the number of resources needed in both the protected and the unprotected scenarios.

Topography of the Chimpanzee Corpus Callosum

The corpus callosum (CC) is the largest commissural white matter tract in mammalian brains, connecting homotopic and heterotopic regions of the cerebral cortex. Knowledge of the distribution of callosal fibers projecting into specific cortical regions has important implications for understanding the evolution of lateralized structures and functions of the cerebral cortex. No comparisons of CC topography in humans and great apes have yet been conducted. We investigated the topography of the CC in 21 chimpanzees using high-resolution magnetic resonance imaging (MRI) and diffusion tensor imaging (DTI). Tractography was conducted based on fiber assignment by continuous tracking (FACT) algorithm. We expected chimpanzees to display topographical organization similar to humans, especially concerning projections into the frontal cortical regions. Similar to recent studies in humans, tractography identified five clusters of CC fibers projecting into defined cortical regions: prefrontal; premotor and supplementary motor; motor; sensory; parietal, temporal and occipital. Significant differences in fractional anisotropy (FA) were found in callosal regions, with highest FA values in regions projecting to higher-association areas of posterior cortical (including parietal, temporal and occipital cortices) and prefrontal cortical regions (p<0.001). The lowest FA values were seen in regions projecting into motor and sensory cortical areas. Our results indicate chimpanzees display similar topography of the CC as humans, in terms of distribution of callosal projections and microstructure of fibers as determined by anisotropy measures.

Arcuate Fasciculus Abnormalities and Their Relationship with Psychotic Symptoms in Schizophrenia

Disruption of fronto-temporal connections involving the arcuate fasciculus (AF) may underlie language processing anomalies and psychotic features such as auditory hallucinations in schizophrenia. No study to date has specifically investigated abnormalities of white matter integrity at particular loci along the AF as well as its regional lateralization in schizophrenia. We examined white matter changes (fractional anisotropy (FA), axial diffusivity (AD), asymmetry indices) along the whole extent of the AF and their relationship with psychotic symptoms in 32 males with schizophrenia and 44 healthy males. Large deformation diffeomorphic metric mapping and Fiber Assignment Continuous Tracking were employed to characterize FA and AD along the geometric curve of the AF. Our results showed that patients with schizophrenia had lower FA in the frontal aspects of the left AF compared with healthy controls. Greater left FA and AD lateralization in the temporal segment of AF were associated with more severe positive psychotic symptoms such as delusions and hallucinations in patients with schizophrenia. Disruption of white matter integrity of the left frontal AF and accentuation of normal left greater than right asymmetry of FA/AD in the temporal AF further support the notion of aberrant fronto-temporal connectivity in schizophrenia. AF pathology can affect corollary discharge of neural signals from frontal speech/motor initiation areas to suppress activity of auditory cortex that may influence psychotic phenomena such as auditory hallucinations and facilitate elaboration of delusional content.

Fibre assignment in next-generation wide-field spectrographs

We present an optimized algorithm for assigning fibres to targets in next-generation fibre-fed multi-object spectrographs. The method, which we have called the draining algorithm, ensures that the maximum number of targets in a given target field is observed in the first few tiles. Using randomly distributed targets and mock galaxy catalogues, we have estimated that the gain provided by the draining algorithm, compared to a random assignment, can be as much as 2 per cent for the first tiles. For a survey such as the Baryon Oscillation Spectroscopic Survey (BigBOSS), this would imply saving for observation several hundred thousand objects or, alternatively, reducing the covered area in ∼350 deg2. An important advantage of this method is that the fibre collision problem can be solved easily and in an optimal way. We also discuss the additional optimizations of the fibre-positioning process. In particular, we show that if we allow for the rotation of the focal plane, we can improve the efficiency of the process by ∼3.5–4.5 per cent, even if only small adjustments are permitted (up to 2°). For instruments that allow large rotations of the focal plane, the expected gain increases to ∼5–6 per cent. Therefore, these results strongly support the use of focal plane rotation in future spectrographs, as far as the efficiency of the fibre-positioning process is concerned. Finally, we discuss the implications of our optimizations and provide some basic hints for an optimal survey strategy, based on the number of targets per positioner.

Corpus Callosum and Cingulum Tractography in Parkinson's Disease

In Parkinson's disease (PD) cell loss in the substantia nigra is known to result in motor symptoms; however widespread pathological changes occur and may be associated with non-motor symptoms such as cognitive impairment. Diffusion tensor imaging is a quantitative imaging method sensitive to the micro-structure of white matter tracts. To measure fractional anisotropy (FA) and mean diffusivity (MD) values in the corpus callosum and cingulum pathways, defined by diffusion tensor tractography, in patients with PD, PD with dementia (PDD) and controls and to determine if these measures correlate with Mini-Mental Status Examination (MMSE) scores in parkinsonian patients. Patients with PD (17 Males [M], 12 Females [F]), mild PDD (5 M, 1 F) and controls (8 M, 7 F) underwent cognitive testing and MRI scans. The corpus callosum was divided into four regions and the cingulum into two regions bilaterally to define tracts using the program DTIstudio (Johns Hopkins University) using the fiber assignment by continuous tracking algorithm. Volumetric MRI scans were used to measure white and gray matter volumes. Groups did not differ in age or education. There were no overall FA or MD differences between groups in either the corpus callosum or cingulum pathways. In PD subjects the MMSE score correlated with MD within the corpus callosum. These findings were independent of age, sex and total white matter volume. The data suggest that the corpus callosum or its cortical connections are associated with cognitive impairment in PD patients.