DTI reveals hypothalamic and brainstem white matter lesions in patients with idiopathic narcolepsy

Symptomatic narcolepsy is often related to hypothalamic, pontine, or mesencephalic lesions. Despite evidence of disturbances of the hypothalamic hypocretin system in patients with idiopathic narcolepsy, neuroimaging in patients with idiopathic narcolepsy revealed conflicting results and there is limited data on possible structural brain changes that might be associated with this disorder.

New evidence for involvement of the entorhinal region in schizophrenia: a combined MRI volumetric and DTI study

Postmortem examinations and magnetic resonance imaging (MRI) studies suggest involvement of the entorhinal cortex (EC) in schizophrenic psychoses. However, the extent and nature of the possible pathogenetical process underlying the observed alterations of this limbic key region for processing of multimodal sensory information remains unclear. Three-dimensional high-resolution MRI volumetry and evaluation of the regional diffusional anisotropy based on diffusion tensor imaging (DTI) were performed on the EC of 15 paranoid schizophrenic patients and 15 closely matched control subjects. In schizophrenic patients, EC volumes showed a slight, but not significant, decrease. However, the anisotropy values, expressed as inter-voxel coherences (COH), were found to be significantly decreased by 17.9% (right side) and 12.5% (left side), respectively, in schizophrenics. Reduction of entorhinal diffusional anisotropy can be hypothesized to be functionally related to disturbances in the perforant path, the principal efferent EC fiber tract supplying the limbic system with neuronal input from multimodal association centers. Combinations of different MRI modalities are a promising approach for the detection and characterization of subtle brain tissue alterations.

Alterations of white matter integrity related to the season of birth in schizophrenia: a DTI study

In schizophrenia there is a consistent epidemiological finding of a birth excess in winter and spring. Season of birth is thought to act as a proxy indicator for harmful environmental factors during foetal maturation. There is evidence that prenatal exposure to harmful environmental factors may trigger pathologic processes in the neurodevelopment, which subsequently increase the risk of schizophrenia. Since brain white matter alterations have repeatedly been found in schizophrenia, the objective of this study was to investigate whether white matter integrity was related to the season of birth in patients with schizophrenia. Thirty-four patients with schizophrenia and 33 healthy controls underwent diffusion tensor imaging. Differences in the fractional anisotropy maps of schizophrenia patients and healthy controls born in different seasons were analysed with tract-based spatial statistics. A significant main effect of season of birth and an interaction of group and season of birth showed that patients born in summer had significantly lower fractional anisotropy in widespread white matter regions than those born in the remainder of the year. Additionally, later age of schizophrenia onset was found in patients born in winter months. The current findings indicate a relationship of season of birth and white matter alterations in schizophrenia and consequently support the neurodevelopmental hypothesis of early pathological mechanisms in schizophrenia.

Image registration for triggered and non-triggered DTI of the human kidney: Reduced variability of diffusion parameter estimation

BACKGROUND: To investigate if non-rigid image-registration reduces motion artifacts in triggered and non-triggered diffusion tensor imaging (DTI) of native kidneys. A secondary aim was to determine, if improvements through registration allow for omitting respiratory-triggering. METHODS: Twenty volunteers underwent coronal DTI of the kidneys with nine b-values (10-700 s/mm2 ) at 3 Tesla. Image-registration was performed using a multimodal nonrigid registration algorithm. Data processing yielded the apparent diffusion coefficient (ADC), the contribution of perfusion (FP ), and the fractional anisotropy (FA). For comparison of the data stability, the root mean square error (RMSE) of the fitting and the standard deviations within the regions of interest (SDROI ) were evaluated. RESULTS: RMSEs decreased significantly after registration for triggered and also for non-triggered scans (P < 0.05). SDROI for ADC, FA, and FP were significantly lower after registration in both medulla and cortex of triggered scans (P < 0.01). Similarly the SDROI of FA and FP decreased significantly in non-triggered scans after registration (P < 0.05). RMSEs were significantly lower in triggered than in non-triggered scans, both with and without registration (P < 0.05). CONCLUSION: Respiratory motion correction by registration of individual echo-planar images leads to clearly reduced signal variations in renal DTI for both triggered and particularly non-triggered scans. Secondarily, the results suggest that respiratory-triggering still seems advantageous.J. Magn. Reson. Imaging 2014. (c) 2014 Wiley Periodicals, Inc.

DTI and VBM reveal white matter changes without associated gray matter changes in patients with idiopathic restless legs syndrome

BACKGROUND AND PURPOSE We evaluated cerebral white and gray matter changes in patients with iRLS in order to shed light on the pathophysiology of this disease. METHODS Twelve patients with iRLS were compared to 12 age- and sex-matched controls using whole-head diffusion tensor imaging (DTI) and voxel-based morphometry (VBM) techniques. Evaluation of the DTI scans included the voxelwise analysis of the fractional anisotropy (FA), radial diffusivity (RD), and axial diffusivity (AD). RESULTS Diffusion tensor imaging revealed areas of altered FA in subcortical white matter bilaterally, mainly in temporal regions as well as in the right internal capsule, the pons, and the right cerebellum. These changes overlapped with changes in RD. Voxel-based morphometry did not reveal any gray matter alterations. CONCLUSIONS We showed altered diffusion properties in several white matter regions in patients with iRLS. White matter changes could mainly be attributed to changes in RD, a parameter thought to reflect altered myelination. Areas with altered white matter microstructure included areas in the internal capsule which include the corticospinal tract to the lower limbs, thereby supporting studies that suggest changes in sensorimotor pathways associated with RLS.

Eye movement and diffusion tensor imaging analysis of treatment effects in a Niemann-Pick Type C patient

New treatment options for Niemann-Pick Type C (NPC) have recently become available. To assess the efficiency and efficacy of these new treatment markers for disease status and progression are needed. Both the diagnosis and the monitoring of disease progression are challenging and mostly rely on clinical impression and functional testing of horizontal eye movements. Diffusion tensor imaging (DTI) provides information about the microintegrity especially of white matter. We show here in a case report how DTI and measures derived from this imaging method can serve as adjunct quantitative markers for disease management in Niemann-Pick Type C. Two approaches are taken--first, we compare the fractional anisotropy (FA) in the white matter globally between a 29-year-old NPC patient and 18 healthy age-matched controls and show the remarkable difference in FA relatively early in the course of the disease. Second, a voxelwise comparison of FA values reveals where white matter integrity is compromised locally and demonstrate an individualized analysis of FA changes before and after 1year of treatment with Miglustat. This method might be useful in future treatment trials for NPC to assess treatment effects.

Alterations of white matter integrity related to motor activity in schizophrenia

Altered structural connectivity is a key finding in schizophrenia, but the meaning of white matter alterations for behavior is rarely studied. In healthy subjects, motor activity correlated with white matter integrity in motor tracts. To explore the relation of motor activity and fractional anisotropy (FA) in schizophrenia, we investigated 19 schizophrenia patients and 24 healthy control subjects using Diffusion Tensor Imaging (DTI) and actigraphy on the same day. Schizophrenia patients had lower activity levels (AL). In both groups linear relations of AL and FA were detected in several brain regions. Schizophrenia patients had lower FA values in prefrontal and left temporal clusters. Furthermore, using a general linear model, we found linear negative associations of FA and AL underneath the right supplemental motor area (SMA), the right precentral gyrus and posterior cingulum in patients. This effect within the SMA was not seen in controls. This association in schizophrenia patients may contribute to the well known dysfunctions of motor control. Thus, structural disconnectivity could lead to disturbed motor behavior in schizophrenia.

Combined use of pulsed arterial spin-labeling and susceptibility-weighted imaging in stroke at 3T

Background and Purpose: In acute stroke it is no longer sufficient to detect simply ischemia, but also to try to evaluate reperfusion/recanalization status and predict eventual hemorrhagic transformation. Arterial spin labeling (ASL) perfusion may have advantages over contrast-enhanced perfusion-weighted imaging (cePWI), and susceptibility weighted imaging (SWI) has an intrinsic sensitivity to paramagnetic effects in addition to its ability to detect small areas of bleeding and hemorrhage. We want to determine here if their combined use in acute stroke and stroke follow-up at 3T could bring new insight into the diagnosis and prognosis of stroke leading to eventual improved patient management. Methods: We prospectively examined 41 patients admitted for acute stroke (NIHSS >1). Early imaging was performed between 1 h and 2 weeks. The imaging protocol included ASL, cePWI, SWI, T2 and diffusion tensor imaging (DTI), in addition to standard stroke protocol. Results: We saw four kinds of imaging patterns based on ASL and SWI: patients with either hypoperfusion and hyperperfusion on ASL with or without changes on SWI. Hyperperfusion was observed on ASL in 12/41 cases, with hyperperfusion status that was not evident on conventional cePWI images. Signs of hemorrhage or blood-brain barrier breakdown were visible on SWI in 15/41 cases, not always resulting in poor outcome (2/15 were scored mRS = 0–6). Early SWI changes, together with hypoperfusion, were associated with the occurrence of hemorrhage. Hyperperfusion on ASL, even when associated with hemorrhage detected on SWI, resulted in good outcome. Hyperperfusion predicted a better outcome than hypoperfusion (p = 0.0148). Conclusions: ASL is able to detect acute-stage hyperperfusion corresponding to luxury perfusion previously reported by PET studies. The presence of hyperperfusion on ASL-type perfusion seems indicative of reperfusion/collateral flow that is protective of hemorrhagic transformation and a marker of favorable tissue outcome. The combination of hypoperfusion and changes on SWI seems on the other hand to predict hemorrhage and/or poor outcome.

Forensic application of postmortem diffusion-weighted and diffusion tensor MR imaging of the human brain in situ

DWI and DTI of the brain have proved to be useful in many neurologic disorders and in traumatic brain injury. This prospective study aimed at the evaluation of the influence of the PMI and the cause of death on the ADC and FA for the application of DWI and DTI in forensic radiology.

Diffusion tensor imaging in episodic cluster headache

Cluster headache (CH) is a rare headache disorder with severe unilateral headache bouts and autonomic symptoms. The pathophysiology of CH is not completely understood. Using a voxel-based morphometric paradigm or functional imaging, a key role of the hypothalamus and the pain matrix could be demonstrated during CH episodes. However, there are no diffusion tensor imaging (DTI) data investigating the white matter microstructure of the brain in patients with CH. Therefore, we used DTI to delineate microstructural changes in patients with CH in a headache-free state.

Optic radiation fiber tracking using anteriorly angulated diffusion tensor imaging: a tested algorithm for quick application

Fiber tracking (FT) of the optic pathways (OPs) is difficult because there is no standard for the parameters of diffusion tensor imaging (DTI), placement of seed volumes, or interpreting the results.

Callosal connections of primary visual cortex predict the spatial spreading of binocular rivalry across the visual hemifields

In binocular rivalry, presentation of different images to the separate eyes leads to conscious perception alternating between the two possible interpretations every few seconds. During perceptual transitions, a stimulus emerging into dominance can spread in a wave-like manner across the visual field. These traveling waves of rivalry dominance have been successfully related to the cortical magnification properties and functional activity of early visual areas, including the primary visual cortex (V1). Curiously however, these traveling waves undergo a delay when passing from one hemifield to another. In the current study, we used diffusion tensor imaging (DTI) to investigate whether the strength of interhemispheric connections between the left and right visual cortex might be related to the delay of traveling waves across hemifields. We measured the delay in traveling wave times (ΔTWT) in 19 participants and repeated this test 6 weeks later to evaluate the reliability of our behavioral measures. We found large interindividual variability but also good test-retest reliability for individual measures of ΔTWT. Using DTI in connection with fiber tractography, we identified parts of the corpus callosum connecting functionally defined visual areas V1-V3. We found that individual differences in ΔTWT was reliably predicted by the diffusion properties of transcallosal fibers connecting left and right V1, but observed no such effect for neighboring transcallosal visual fibers connecting V2 and V3. Our results demonstrate that the anatomical characteristics of topographically specific transcallosal connections predict the individual delay of interhemispheric traveling waves, providing further evidence that V1 is an important site for neural processes underlying binocular rivalry.

Examining the gateway to the limbic system with diffusion tensor imaging: the perforant pathway in dementia

Current treatments for Alzheimer's disease (AD) are only able to slow the progression of mental deterioration, making early and reliable diagnosis an essential part of any promising therapeutic strategy. In the initial stages of AD, the first neuropathological alterations occur in the perforant pathway (PP), a large neuronal fiber tract located at the entrance to the limbic system. However, to date, there is no sensitive diagnostic tool for performing in vivo assessments of this structure. In the present bimodal magnetic resonance imaging (MRI) study, we examined 10 elderly controls, 10 subjects suffering from mild cognitive impairment (MCI), and 10 AD patients in order to evaluate the sensitivity of diffusion tensor imaging (DTI), a new MRI technique, for detecting changes in the PP. Furthermore, the diagnostic explanatory power of DTI data of the PP should be compared to high-resolution MRI volumetry and intervoxel coherences (COH) of the hippocampus and the entorhinal cortex, two limbic regions also involved in the pathophysiology of early AD. DTI revealed a marked decrease in COH values in the PP region of MCI (right side: 26%, left side: 29%, as compared to controls) and AD patients (right side: 37%, left side: 43%, as compared to controls). Reductions in COH values of the PP region were significantly correlated with cognitive impairment. DTI data of the PP zone were the only parameter differing significantly between control subjects and MCI patients, while the volumetric measures and the COH values of the hippocampus and the entorhinal cortex did not. DTI of medial temporal brain regions is a promising non-invasive tool for the in vivo diagnosis of the early/preclinical stages of AD.