Neuro-cognitive effects of degraded visibility on illusory body ownership.

Based on visuo-tactile stimulation, the rubber hand illusion induces a sense of ownership for a dummy hand. Manipulating the visibility of the dummy hand during the stimulation influences cognitive aspects of the illusion, suggesting that the related brain activity may be influenced too. To test this, we analyzed brain activity (fMRI), subjective ratings, and skin conductance from 45 neurotypical participants undergoing a modified rubber hand illusion protocol where we manipulated the visibility (high, medium, and low) of a virtual hand, not the brush (virtual hand illusion; VHI). To further investigate the impact of visibility manipulations on VHI-related secondary effects (i.e. vicarious somatosensation), we recorded brain activity and skin conductance during a vicarious pain protocol (observation of painful stimulations of the virtual hand) that occurred after the VHI procedure. Results showed that, during both the VHI and vicarious pain periods, the activity of distinct visual, somatosensory, and motor brain regions was modulated by (i) visibility manipulations, (ii) coherence between visual and tactile stimulation, and (iii) time of visuo-tactile stimulation. Accordingly, embodiment-related subjective ratings of the perceived illusion were specifically influenced by visibility manipulations. These findings suggest that visibility modifications can impact the neural and cognitive effects of illusory body ownership, in that when visibility decreases the illusion is perceived as weaker and the brain activity in visual, motor, and somatosensory regions is overall lower. We interpret this evidence as a sign of the weight of vision on embodiment processes, in that the cortical and subjective aspects of illusory body ownership are weakened by a degradation of visual input during the induction of the illusion.

Subacute changes in brain functional network connectivity after nocturnal sodium oxybate intake are associated with anterior cingulate GABA.

Sodium oxybate (γ-hydroxybutyrate, GHB) is an endogenous GHB/GABAB receptor agonist, clinically used to promote slow-wave sleep and reduce next-day sleepiness in disorders such as narcolepsy and fibromyalgia. The neurobiological signature of these unique therapeutic effects remains elusive. Promising current neuropsychopharmacological approaches to understand the neural underpinnings of specific drug effects address cerebral resting-state functional connectivity (rsFC) patterns and neurometabolic alterations. Hence, we performed a placebo-controlled, double-blind, randomized, cross-over pharmacological magnetic resonance imaging study with a nocturnal administration of GHB, combined with magnetic resonance spectroscopy of GABA and glutamate in the anterior cingulate cortex (ACC). In sum, 16 healthy male volunteers received 50 mg/kg GHB p.o. or placebo at 02:30 a.m. to maximize deep sleep enhancement and multi-modal brain imaging was performed at 09:00 a.m. of the following morning. Independent component analysis of whole-brain rsFC revealed a significant increase of rsFC between the salience network (SN) and the right central executive network (rCEN) after GHB intake compared with placebo. This SN-rCEN coupling was significantly associated with changes in GABA levels in the ACC (pall < 0.05). The observed neural pattern is compatible with a functional switch to a more extrinsic brain state, which may serve as a neurobiological signature of the wake-promoting effects of GHB.

Illusory Body Ownership Affects the Cortical Response to Vicarious Somatosensation.

Fundamental human feelings such as body ownership ("this" body is "my" body) and vicariousness (first-person-like experience of events occurring to others) are based on multisensory integration. Behavioral links between body ownership and vicariousness have been shown, but the neural underpinnings remain largely unexplored. To fill this gap, we investigated the neural effects of altered body ownership on vicarious somatosensation. While recording functional brain imaging data, first, we altered participants' body ownership by robotically delivering tactile stimulations ("tactile" stroking) in synchrony or not with videos of a virtual hand being brushed ("visual" stroking). Then, we manipulated vicarious somatosensation by showing videos of the virtual hand being touched by a syringe's plunger (touch) or needle (pain). Only after the alteration of body ownership (synchronous visuo-tactile stroking) and specifically during late epochs of vicarious somatosensation, vicarious pain was associated with lower activation in premotor and anterior cingulate cortices with respect to vicarious touch. At the methodological level, the present study highlights the importance of the neural response's temporal evolution. At the theoretical level, it shows that the higher-level (cognitive) impact of a lower-level (sensory) body-related processing (visuo-tactile) is not limited to body ownership but also extends to other psychological body-related domains, such as vicarious somatosensation.

Gamma-hydroxybutyrate increases brain resting-state functional connectivity of the salience network and dorsal nexus in humans.

According to the triple network hypothesis the brain is equipped with three core neurocognitive networks: the default mode (DMN), the salience (SN), and the central executive (CEN) network. Moreover, the so called dorsal nexus, has met growing interest as it is a hub region connecting these three networks. Assessment of resting-state functional connectivity (rsFC) of these networks enables the elucidation of drug-induced brain alterations. Gamma-hydroxybutyrate (GHB) is a GHB/GABA-B receptor agonist that induces a paradoxical state of mixed stimulation and sedation at moderate doses, which makes it a valuable tool to investigate neural signatures of subjective drug effects. Employing a placebo-controlled, double-blind, randomized, cross-over design, we assessed the effects of GHB (35 mg/kg p. o.) in 19 healthy male subjects on DMN-, SN-, CEN-, and dorsal nexus-rsFC measured by functional magnet resonance imaging and applying independent component as well as seed-based analyses, while subjective drug effects were investigated using visual analog scales (VAS). Subjectively, GHB increased VAS ratings of a general drug effect, stimulation, and sedation. Intrinsic DMN-, and CEN-rsFC remained largely unchanged under GHB, but the drug increased SN-DMN-rsFC and SN-dorsal nexus-rsFC, while dorsal nexus-rsFC was reciprocally increased to both the SN (right anterior insula) and to the CEN (right middle frontal gyrus). Increased sedation significantly predicted the observed SN-dorsal nexus-rsFC. In conclusion, GHB generates a unique stimulant/sedative subjective state that is paralleled by a complex pattern of increased functional connectivity encompassing all three core neurocognitive networks of the brain, while increased SN-dorsal nexus-rsFC was demonstrated to be a potential signature of the sedative component of the drug effect.

Prohedonic properties of gamma-hydroxybutyrate are associated with changes in limbic resting-state functional connectivity.

OBJECTIVE: Gamma-hydroxybutyrate (GHB) is an endogenous GHB-/GABA-B receptor agonist and a narcolepsy treatment. However, GHB is also abused for its prohedonic effects. On a neuronal level, it was shown that GHB increases regional cerebral blood flow in limbic areas such as the right anterior insula (rAI) and the anterior cingulate cortex (ACC). We aimed to further explore the association between the subjective and neuronal signatures of GHB. METHOD: We assessed subjective effects and resting-state functional connectivity (rsFC) of an rAI- and an ACC-seed in 19 healthy male subjects after GHB (35 mg/kg p.o.) using a placebo-controlled, double-blind, randomized, cross-over functional magnet resonance imaging design. RESULTS: GHB increased subjective ratings for euphoria (p < 0.001) and sexual arousal (p < 0.01). Moreover, GHB increased rAI-rsFC to the right thalamus and the superior frontal gyrus and decreased ACC-rsFC to the bilateral paracentral lobule (all p < 0.05, cluster corrected). Moreover, GHB-induced euphoria was associated with rAI-rsFC to the superior frontal gyrus (p < 0.05, uncorrected). CONCLUSIONS: GHB induces prohedonic effects such as euphoria and sexual arousal and in parallel modulates limbic rsFC with areas linked to regulation of mood, cognitive control, and sexual experience. These results further elucidate the drug's effects in neuropsychiatric disorders and as drug of abuse.

Two dose investigation of the 5-HT-agonist psilocybin on relative and global cerebral blood flow.

Psilocybin, the active compound in psychedelic mushrooms, is an agonist of various serotonin receptors. Seminal psilocybin positron emission tomography (PET) research suggested regional increases in glucose metabolism in frontal cortex (hyperfrontality). However, a recent arterial spin labeling (ASL) study suggests psilocybin may lead to hypo-perfusion in various brain regions. In this placebo-controlled, double-blind study we used pseudo-continuous ASL (pCASL) to measure perfusion changes, with and without adjustment for global brain perfusion, after two doses of oral psilocybin (low dose: 0.160 mg/kg; high dose: 0.215 mg/kg) in two groups of healthy controls (n = 29 in both groups, total N = 58) during rest. We controlled for sex and age and used family-wise error corrected p values in all neuroimaging analyses. Both dose groups reported profound subjective drug effects as measured by the Altered States of Consciousness Rating Scale (5D-ASC) with the high dose inducing significantly larger effects in four out of the 11 scales. After adjusting for global brain perfusion, psilocybin increased relative perfusion in distinct right hemispheric frontal and temporal regions and bilaterally in the anterior insula and decreased perfusion in left hemispheric parietal and temporal cortices and left subcortical regions. Whereas, psilocybin significantly reduced absolute perfusion in frontal, temporal, parietal, and occipital lobes, and bilateral amygdalae, anterior cingulate, insula, striatal regions, and hippocampi. Our analyses demonstrate consistency with both the hyperfrontal hypothesis of psilocybin and the more recent study demonstrating decreased perfusion, depending on analysis method. Importantly, our data illustrate that relative changes in perfusion should be understood and interpreted in relation to absolute signal variations.

Conflict monitoring and error processing: new insights from simultaneous EEG-fMRI.

Error processing and conflict monitoring are essential executive functions for goal directed actions and adaptation to conflicting information. Although medial frontal regions such as the anterior cingulate cortex (ACC) and the pre-supplementary motor area (pre-SMA) are known to be involved in these functions, there is still considerable heterogeneity regarding their spatio-temporal activations. The timing of these functions has been associated with two separable event-related potentials (ERPs) usually localized to the medial frontal wall, one during error processing (ERN--error related negativity) and one during conflict monitoring (N2). In this study we aimed to spatially and temporally dissociate conflict and error processing using simultaneously recorded EEG and fMRI data from a modified Flanker task in healthy adults. We demonstrate a spatial dissociation of conflict monitoring and error processing along the medial frontal wall, with selective conflict level dependent activation of the SMA/pre-SMA. Activation to error processing was located in the ACC, rostral cingulate zone (RCZ) and pre-SMA. The EEG-informed fMRI analysis revealed that stronger ERN amplitudes are associated with increased activation in a large coherent cluster comprising the ACC, RCZ and pre-SMA, while N2 amplitudes increased with activation in the pre-SMA. Conjunction analysis of EEG-informed fMRI revealed common activation of ERN and N2 in the pre-SMA and divergent activation in the RCZ. No conjoint activation between error processing and conflict monitoring was found with standard fMRI analysis along the medial frontal wall. Our fMRI findings clearly demonstrate that conflict monitoring and error processing are spatially dissociable along the medial frontal wall. Moreover, the overlap of ERN- and N2-informed fMRI activation in the pre-SMA provides new evidence that these ERP components share conflict related processing functions and are thus not completely separable.

Investigating functional brain connectivity patterns associated with two hypnotic states.

While there's been clinical success and growing research interest in hypnosis, neurobiological underpinnings induced by hypnosis remain unclear. In this fMRI study (which is part of a larger hypnosis project) with 50 hypnosis-experienced participants, we analyzed neural and physiological responses during two hypnosis states, comparing them to non-hypnotic control conditions and to each other. An unbiased whole-brain analysis (multi-voxel- pattern analysis, MVPA), pinpointed key neural hubs in parieto-occipital-temporal areas, cuneal/precuneal and occipital cortices, lingual gyri, and the occipital pole. Comparing directly both hypnotic states revealed depth-dependent connectivity changes, notably in left superior temporal/supramarginal gyri, cuneus, planum temporale, and lingual gyri. Multi-voxel- pattern analysis (MVPA) based seeds were implemented in a seed-to-voxel analysis unveiling region-specific increases and decreases in functional connectivity patterns. Physiologically, the respiration rate significantly slowed during hypnosis. Summarized, these findings foster fresh insights into hypnosis-induced functional connectivity changes and illuminate further knowledge related with the neurobiology of altered consciousness.

Investigation of Cerebral White Matter Changes After Spinal Cord Injury With a Measure of Fiber Density.

Remote neurodegenerative changes in supraspinal white matter (WM) can manifest after central lesions such as spinal cord injury (SCI). The majority of diffusion tensor imaging (DTI) studies use traditional metrics such as fractional anisotropy (FA) and mean diffusivity (MD) to investigate microstructural changes in cerebral WM after SCI. However, interpretation of FA readouts is often challenged by inherent limitations of the tensor model. Recent developments in novel diffusion markers, such as fiber density (FD), allows more accurate depictions of WM pathways and has shown more reliable quantification of WM alterations compared to FA in recent studies of neurological diseases. This study investigated if FD provides useful characterization of supraspinal WM integrity after SCI in addition to the traditional DTI readouts. FA, MD, and FD maps were derived from diffusion datasets of 20 patients with chronic SCI and compared with 19 healthy controls (HC). Group differences were investigated across whole brain WM using tract-based spatial statistics and averaged diffusion values of the corticospinal tract (CST) and thalamic radiation (TR) were extracted for comparisons between HC and SCI subgroups. We also related diffusion readouts of the CST and TR with clinical scores of sensorimotor function. To investigate which diffusion markers of the CST and TR delineate HC and patients with SCI a receiver operating characteristic (ROC) analysis was performed. Overall, patients with an SCI showed decreased FA of the TR and CST. ROC analysis differentiated HC and SCI based on diffusion markers of large WM tracts including FD of the TR. Furthermore, patients' motor function was positively correlated with greater microstructural integrity of the CST. While FD showed the strongest correlation, motor function was also associated with FA and MD of the CST. In summary, microstructural changes of supraspinal WM in patients with SCI can be detected using FD as a complementary marker to traditional DTI readouts and correlates with their clinical characteristics. Future DTI studies may benefit from utilizing this novel marker to investigate complex large WM tracts in patient cohorts with varying presentations of SCI or neurodegenerative diseases.

Impact of fMRI-guided advanced DTI fiber tracking techniques on their clinical applications in patients with brain tumors.

INTRODUCTION: White matter tractography based on diffusion tensor imaging has become a well-accepted non-invasive tool for exploring the white matter architecture of the human brain in vivo. There exist two main key obstacles for reconstructing white matter fibers: firstly, the implementation and application of a suitable tracking algorithm, which is capable of reconstructing anatomically complex fascicular pathways correctly, as, e.g., areas of fiber crossing or branching; secondly, the definition of an appropriate tracking seed area for starting the reconstruction process. Large intersubject, anatomical variations make it difficult to define tracking seed areas based on reliable anatomical landmarks. An accurate definition of seed regions for the reconstruction of a specific neuronal pathway becomes even more challenging in patients suffering from space occupying pathological processes as, e.g., tumors due to the displacement of the tissue and the distortion of anatomical landmarks around the lesion. METHODS: To resolve the first problem, an advanced tracking algorithm, called advanced fast marching, was applied in this study. The second challenge was overcome by combining functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) in order to perform fMRI-guided accurate definition of appropriate seed areas for the DTI fiber tracking. In addition, the performance of the tasks was controlled by a MR-compatible power device. RESULTS: Application of this combined approach to eight healthy volunteers and exemplary to three tumor patients showed that it is feasible to accurately reconstruct relevant fiber tracts belonging to a specific functional system. CONCLUSION: fMRI-guided advanced DTI fiber tracking has the potential to provide accurate anatomical and functional information for a more informed therapeutic decision making.

Uniformity and Deviation of Intra-axonal Cross-sectional Area Coverage of the Gray-to-White Matter Interface.

Diffusion magnetic resonance imaging (dMRI) is a compelling tool for investigating the structure and geometry of brain tissue based on indirect measurement of the diffusion anisotropy of water. Recent developments in global top-down tractogram optimizations enable the estimation of streamline weights, which characterize the connection between gray matter areas. In this work, the intra-axonal cross-sectional area coverage of the gray-to-white matter interface was examined by intersecting tractography streamlines with cortical regions of interest. The area coverage is the ratio of streamline weights divided by the surface area at the gray-to-white matter interface and assesses the estimated percentage which is covered by intra-axonal space. A high correlation (r = 0.935) between streamline weights and the cortical surface area was found across all regions of interest in all subjects. The variance across different cortical regions exhibits similarities to myelin maps. Additionally, we examined the effect of different diffusion gradient subsets at a lower, clinically feasible spatial resolution. Subsampling of the initial high-resolution diffusion dataset did not alter the tendency of the area coverage at the gray-to-white matter interface across cortical areas and subjects. However, single-shell acquisition schemes with lower b-values lead to a steady increase in area coverage in comparison to the full acquisition scheme at high resolution.

Fiber up-sampling and quality assessment of tractograms - towards quantitative brain connectivity.

BACKGROUND AND PURPOSE: Diffusion MRI tractography enables to investigate white matter pathways noninvasively by reconstructing estimated fiber pathways. However, such tractograms remain biased and nonquantitative. Several techniques have been proposed to reestablish the link between tractography and tissue microstructure by modeling the diffusion signal or fiber orientation distribution (FOD) with the given tractogram and optimizing each fiber or compartment contribution according to the diffusion signal or FOD. Nevertheless, deriving a reliable quantification of connectivity strength between different brain areas is still a challenge. Moreover, evaluating the quality of a tractogram and measuring the possible error sources contained in a specific reconstructed fiber bundle also remains difficult. Lastly, all of these optimization techniques fail if specific fiber populations within a tractogram are underrepresented, for example, due to algorithmic constraints, anatomical properties, fiber geometry or seeding patterns. METHODS: In this work, we propose an approach which enables the inspection of the quality of a tractogram optimization by evaluating the residual error signal and its FOD representation. The automated fiber quantification (AFQ) is applied, whereby the framework is extended to reflect not only scalar diffusion metrics along a fiber bundle, but also directionally dependent FOD amplitudes along and perpendicular to the fiber direction. Furthermore, we also present an up-sampling procedure to increase the number of streamlines of a given fiber population. The introduced error metrics and fiber up-sampling method are tested and evaluated on single-shell diffusion data sets of 16 healthy volunteers. RESULTS AND CONCLUSION: Analyzing the introduced error measures on specific fiber bundles shows a considerable improvement in applying the up-sampling method. Additionally, the error metrics provide a useful tool to spot and identify potential error sources in tractograms.

In human non-REM sleep, more slow-wave activity leads to less blood flow in the prefrontal cortex.

Cerebral blood flow (CBF) is related to integrated neuronal activity of the brain whereas EEG provides a more direct measurement of transient neuronal activity. Therefore, we addressed what happens in the brain during sleep, combining CBF and EEG recordings. The dynamic relationship of CBF with slow-wave activity (SWA; EEG sleep intensity marker) corroborated vigilance state specific (i.e., wake, non-rapid eye movement (NREM) sleep stages N1-N3, wake after sleep) differences of CBF e.g. in the posterior cingulate, basal ganglia, and thalamus, indicating their role in sleep-wake regulation and/or sleep processes. These newly observed dynamic correlations of CBF with SWA - namely a temporal relationship during continuous NREM sleep in individuals - additionally implicate an impact of sleep intensity on the brain's metabolism. Furthermore, we propose that some of the aforementioned brain areas that also have been shown to be affected in disorders of consciousness might therefore contribute to the emergence of consciousness.

Gamma-Hydroxybutyrate Increases Resting-State Limbic Perfusion and Body and Emotion Awareness in Humans.

Gamma-hydroxybutyrate (GHB) is a GHB-/GABA-B receptor agonist inducing a broad spectrum of subjective effects including euphoria, disinhibition, and enhanced vitality. It is used as treatment for neuropsychiatric disorders including narcolepsy and alcohol withdrawal, but is also a drug of abuse. Non-medical users report enhancement of body and emotion awareness during intoxication. However, the neuronal underpinnings of such awareness alterations under GHB are unknown so far. The assessment of regional cerebral blood flow (rCBF) by pharmacological magnetic resonance imaging (phMRI) enables the elucidation of drug-induced functional brain alterations. Thus, we assessed the effects of GHB (35 mg/kg p.o.) in 17 healthy males on rCBF and subjective drug effects, using a placebo-controlled, double-blind, randomized, cross-over design employing arterial spin labeling phMRI. Compared to placebo, GHB increased subjective ratings for body and emotion awareness, and for dizziness (p<0.01-0.001, Bonferroni-corrected). A whole-brain analysis showed increased rCBF in the bilateral anterior cingulate cortex (ACC) and the right anterior insula under GHB (p<0.05, cluster-corrected). ACC and insula rCBF are correlated with relaxation, and body and emotion awareness (p<0.05-0.001, uncorrected). Interaction analyses revealed that GHB-induced increase of body awareness was accompanied by increased rCBF in ACC, whereas relaxation under GHB was accompanied by elevated rCBF in right anterior insula (p<0.05, uncorrected). In conclusion, enhancement of emotion and body awareness, and increased perfusion of insula and ACC bears implications both for the properties of GHB as a drug of abuse as well as for its putative personalized potential for specific therapeutic indications in affective disorders.

Neural underpinnings of prosexual effects induced by gamma-hydroxybutyrate in healthy male humans.

Gamma-hydroxybutyrate (GHB) is a GHB-/GABAB-receptor agonist currently used as treatment for narcolepsy but also as a drug of abuse. Non-medical GHB users have repeatedly reported prosexual effects including libido-enhancement and lowering of attractiveness standards for partner selection. Here, we examined the putative prosexual effects of oral GHB in healthy males in two experiments both employing randomized, placebo-controlled, double-blind, balanced, and cross-over study designs. In experiment I, subjective effects of 20 and 35mg/kg GHB vs. placebo were tested in 32 participants using the Sexual Arousal and Desire Inventory. In experiment II, brain reactivity towards erotic vs. neutral pictures was investigated in 15 participants using functional magnetic resonance imaging after 35mg/kg GHB vs. placebo. In experiment I, prosexual effects of GHB were shown by increased SADI ratings regarding physiological, evaluative, and motivational aspects of sexual arousal. In experiment II, erotic visual stimuli activated the bilateral insula, nucleus accumbens (NAcc), fusiform gyrus, thalamus, and left occipital pole under placebo. After GHB administration, even sexually neutral pictures of persons induced subjective sexual arousal and increased activation of the bilateral NAcc and right anterior cingulate cortex, which significantly correlated (left NAcc by trend). Moreover, a psychophysiological interaction analysis showed that GHB increased connectivity between NAcc and ventromedial prefrontal cortex during processing of visual erotic cues, i.e., in the condition in which subjective sexual arousal was highest. Our data show that GHB stimulates hedonic sexual functioning and lowers the threshold for erotic perception, which is related to increased susceptibility of mesolimbic reward pathways.

Three-dimensional fiber architecture of the nonpregnant human uterus determined ex vivo using magnetic resonance diffusion tensor imaging.

The global muscle and collagen fiber orientation in the human uterus has been analyzed hitherto by various standard microscopic techniques. However, no widely accepted model of the fiber architecture of the myometrium could be acquired. The purpose of the present study was to investigate the uterus by magnetic resonance (MR) diffusion tensor imaging (DTI) in a 3D macroscopic approach. Ex vivo MR DTI measurements were performed on five uteri from nonpregnant patients. The main diffusion directions reflecting the orientation of directional structures in the examined tissues were determined from diffusion-weighted spin-echo measurements. A fiber tracking algorithm was used to extrapolate the fiber architecture. The method was validated against histological slides and indirectly through the analysis of leiomyomas, which exhibit less anisotropy than normal myometrium. Significant anisotropy was found in most regions of all examined nonpregnant human uteri. But only two systems of fibers were found running circularly along the intramural part of the uterine tubes. They merged caudally and built a close fitting envelope of circular layers around the uterine cavity. On the cervix, circular fibers were observed in the outer part as well as mostly longitudinal fibers in the inner part. These results confirm the existence of directional structures in the complex fiber architecture of the human uterus. They also indicate that MR DTI is a beneficial and complementary tool to standard microscopic techniques to determine the intrinsic fiber architecture in human organs.

Construction of a temperature-controlled diffusion phantom for quality control of diffusion measurements.

PURPOSE: To construct a temperature-controlled diffusion phantom with known diffusion properties and geometry in order to facilitate the comparison and optimization of diffusion sequences with the objective of increasing the precision of experimentally derived diffusion parameters. MATERIALS AND METHODS: A temperature-stabilized diffusion phantom made up of two crossing strands of hydrophobic polyethylene fibers was constructed. Reproducibility and temperature dependence of several diffusion parameters was investigated and compared with computer simulations. Furthermore, in order to stimulate actual use, the precision of measurement of different diffusion-encoding schemes was compared using bootstrap analysis. RESULTS: The measured values of the diffusion parameters are highly reproducible and feature strong temperature dependence which is reproduced in simulations, underlining the necessity of a temperature-stabilized environment for quality control. The exemplary application presented here demonstrates that the phantom allows comparing and optimizing different diffusion sequences with regard to their measurement precision. CONCLUSION: The present work demonstrates that the diffusion phantom facilitates and improves the comparison and quality control of diffusion sequences and the ensuing parameters. The results show that an accurate temperature control is a vital prerequisite for highly reproducible calibration measurements. As such, the phantom might provide a valuable calibration tool for clinical studies.

Reconstruction of the human visual system based on DTI fiber tracking.

PURPOSE: To apply and to evaluate the newly developed advanced fast marching algorithm (aFM) in vivo by reconstructing the human visual pathway, which is characterized by areas of extensive fiber crossing and branching, i.e., the optic chiasm and the lateral geniculate nucleus (LGN). MATERIALS AND METHODS: Diffusion tensor images were acquired in 10 healthy volunteers. Due to the proximity to bony structures and air-filled spaces of the optic chiasm, a high sensitivity encoding (SENSE) reduction factor was applied to reduce image distortions in this area. To reconstruct the visual system, three different seed areas were chosen separately. The results obtained by the aFM tracking algorithm were compared and validated with known anatomy. RESULTS: The visual system could be reconstructed reproducibly in all subjects and the reconstructed fiber pathways are in good agreement with known anatomy. CONCLUSION: The present work shows that the advanced aFM, which is especially designed for overcoming tracking limitations within areas of extensive fiber crossing, handles the fiber crossing and branching within the optic chiasm and the LGN correctly, thus allowing the reconstruction of the entire human visual fiber pathway, from the intraorbital segment of the optic nerves to the visual cortex.