Reliability of graph analysis of resting state fMRI using test-retest dataset from the Human Connectome Project.

The exploration of brain networks with resting-state fMRI (rs-fMRI) combined with graph theoretical approaches has become popular, with the perspective of finding network graph metrics as biomarkers in the context of clinical studies. A preliminary requirement for such findings is to assess the reliability of the graph based connectivity metrics. In previous test-retest (TRT) studies, this reliability has been explored using intraclass correlation coefficient (ICC) with heterogeneous results. But the issue of sample size has not been addressed. Using the large TRT rs-fMRI dataset from the Human Connectome Project (HCP), we computed ICCs and their corresponding p-values (applying permutation and bootstrap techniques) and varied the number of subjects (from 20 to 100), the scan duration (from 400 to 1200 time points), the cost and the graph metrics, using the Anatomic-Automatic Labelling (AAL) parcellation scheme. We quantified the reliability of the graph metrics computed both at global and regional level depending, at optimal cost, on two key parameters, the sample size and the number of time points or scan duration. In the cost range between 20% to 35%, most of the global graph metrics are reliable with 40 subjects or more with long scan duration (14min 24s). In large samples (for instance, 100 subjects), most global and regional graph metrics are reliable for a minimum scan duration of 7min 14s. Finally, for 40 subjects and long scan duration (14min 24s), the reliable regions are located in the main areas of the default mode network (DMN), the motor and the visual networks.

Brain responses to uncertainty about upcoming rectal discomfort in quiescent Crohn's disease - a fMRI study.

BACKGROUND: Patients with Crohn's disease (CD) in remission are exposed to chronic psychological distress, due to the constant risk of relapse. This permanent situation of anticipation and uncertainty can lead to anxiety, which may, in turn, trigger relapse. We aimed to investigate the effects of uncertainty on behavioral and brain responses to anticipation of visceral discomfort in quiescent CD patients. METHODS: Barostat-controlled rectal distensions were preceded by cued uncertain or certain anticipation in nine CD patients and nine matched healthy volunteers. Brain responses obtained before distension across the different anticipation conditions in regions of interest (ROI) involved in (anticipation of) pain were measured using functional magnetic resonance imaging and compared between CD and controls. The association between anxiety-related psychological variables and cerebral anticipatory activity was tested. KEY RESULTS: During uncertainty, CD patients had significantly stronger activations than controls in the cingulate cortex, insula, amygdala, and thalamus with trends in the hippocampus, prefrontal, and secondary somatosensory cortex. In patients, brain responses to uncertainty in the majority of ROI correlated positively with gastrointestinal symptom-specific anxiety, trait-anxiety, and intolerance of uncertainty. CONCLUSIONS & INFERENCES: In a context of uncertainty regarding occurrence of uncomfortable visceral sensations, CD is associated with excessive reactivity in brain regions known to be involved in sensory, cognitive and emotional aspects of pain processing and modulation, and threat appraisal. Our findings contribute to a better understanding of the role of emotional and cognitive processes in CD. This may, in turn, lead to the development of new (psycho)therapeutic approaches for management of symptoms and related anxiety.

[Functional magnetic resonance imaging. What are the benefits expected in hand surgery?]. / IRM fonctionnelle. Quels apports en chirurgie de la main ?

Functional MRI (fMRI) allowed considerable advances upon understanding of cerebral functioning. Cortical plasticity, which allows the voluntary command of a restored function by a transferred muscle remains to be investigated in its intimacy. The authors present here the round table held at the 48th annual meeting of the French Society for Surgery of the Hand on December 22nd, 2012. It tries to review the analysis of the phenomenon observed during multiple tendinous transfers for restoration of proximal radial nerve palsy. Were successively approached: 1) Methods of acquisition and analysis of the signals (C. D-M.); 2) Movement reorganization (O.M.); 3) Motor plasticity after hand allograft (A. S.); 4) The potential interest of the fMRI in hand rehabilitation (F. D.); 5) The analysis of cerebral plasticity in general (H. B.). A rather philosophical conclusion opens other fields to f MRI (A.M.).

Local landmark alignment for high-resolution fMRI group studies: toward a fine cortical investigation of hand movements in human.

Converging evidence conclusively demonstrates the robust relationship between anatomical landmarks and underlying functional organization in primary cortical regions. In consequence, a precise alignment across subjects of such specific individual landmarks should improve the overlap of the corresponding functional areas and thus the detection of active clusters at the group level. In an effort to define a dedicated processing pipeline for a fine non-invasive exploration of the motor cortex in human, we evaluated four recent non-linear registration methods based on anatomical and functional indexes. We used high-resolution functional MRI data to finely reveal the impact of the registration on the cortical assignment of the detected clusters. Our results first demonstrate that the quality of registration strongly affects the statistical significance and the assignment of activated clusters to specific anatomical regions, here in the primary motor area. Our results also illustrate the bias induced by the chosen reference template on the detected clusters. The analysis of the Jacobian of the deformation field informs us about how each method deforms the anatomical structures and functional maps. The methodology we propose, combining high resolution fMRI and non-linear registration method, allows a robust non-invasive exploration of the motor cortex.

Global Functional Disconnections in Post-anoxic Coma Patient.

Disorders of consciousness have been related to different disconnection patterns as assessed by neuroimaging tools such as PET or fMRI. In this report, we use resting-state functional MRI acquisition and a functional connectivity analysis by graph of brain networks, to investigate the global residual connection pattern in a patient with consciousness disorders following post-anoxic injury. We then compare this pattern with those of a group of twenty controls. We observed that the patient's graph presents multiple disconnections in primary areas and in high-order associative areas. This pattern is consistent with a vegetative state, as reported by other groups. Further, the informations conveyed by this approach are consistent with those provided by PET, fMRI and EP. This new approach presents a very strong potential for diagnosis for consciousness disorder patients since it is applicable very early after the insult.

Usefulness of functional MRI associated with PET scan and evoked potentials in the evaluation of brain functions after severe brain injury: preliminary results.

OBJECTIVE: To evaluate the feasability and the potential usefulness of functional MRI (fMRI) for the evaluation of brain functions after severe brain injury, when compared to a multimodal approach (evoked potentials [EP] and Positron Emission Tomography [PET] examinations). MATERIAL AND METHODS: Seven patients (mean age: 49 years [23-73], three males, four females) presenting with coma after acute severe brain injuries underwent fMRI (auditive, visual, somesthesic), (18)F-FDG PET and EP (auditive, visual, somesthesic) within a 3-day period of time in a mean of 120 days after initial brain injury. fMRI activations in somesthesic, visual and auditive cortical areas were compared to EP (28 possible comparisons) and to the metabolic activity on PET examination in the same anatomical areas (21 possible comparisons). RESULTS: In case of availability, results were concordant between fMRI and PET in 10 comparisons but not in one, and between fMRI and EP in 11 comparisons but not in four. CONCLUSIONS: In many patients, there is a good concordance between fMRI and brain functions suggested by EP and metabolic activity demonstrated with PET. In few others, fMRI can be integrated in the early evaluation of brain functions to further augment our capacity for a proper evaluation of brain functions in critically ill patients.

Sequence of pattern onset responses in the human visual areas: an fMRI constrained VEP source analysis.

We measured the timing of activity in distinct functional areas of the human visual cortex after onset of a visual pattern. This is not possible with visual evoked potentials (VEPs) or magnetic fields alone, and direct combination of functional magnetic resonance imaging (fMRI) with electromagnetic data has turned out to be difficult. We tested a relatively new approach, where both position and orientation of the active cortex was given to the VEP source model. Subjects saw the same visual patterns flashed ON and OFF, both when recording VEPs and fMRI responses. We identified the positions and orientations of the activated cortex in four retinotopic areas in each individual, and the corresponding dipoles were seeded to model the individual evoked potential data. Unexplained variance, comprising signals from other areas, was inversely modeled. Despite the partially a priori fixed model and optimized signal-to-noise ratio of VEP data, full separation of retinotopic areas was only seldom possible due to crosstalk between the adjacent sources, but separation was usually possible between areas V1 and V3/V3a. Whereas the latencies generally followed the hierarchical organization of cortical areas (V1-V2-V3), with around 25 ms between the strongest responses, an early activation emerged 10-20 ms after V1, close to the temporo-occipital junction (LO/V5) and with an additional 20-ms latency in the corresponding region of the opposite hemisphere. Our approach shows that it is feasible to directly seed information from fMRI to electromagnetic source models and to identify the components and dynamics of VEPs in different retinotopic areas of a human individual.

Timing of interactions across the visual field in the human cortex.

While it is generally believed that interactions across long distances in the visual field occur only in the higher-order cortical areas, other results suggest that such interactions are processed very early. In the preceding paper, we identified the latencies within a subset of cortical areas in the human visual system. In the present study, we test in which areas and at which latencies the responses to two visual patterns start interacting. We used functional magnetic resonance imaging directly combined with visual-evoked potential source analysis. Interactions appeared first anterolaterally to the retinotopic areas, at 80 ms for two stimuli presented in the left lower visual quadrant and at 100 ms for symmetrical stimulation of both lower quadrants. In the lateral occipital-V5 region (LOV5), two patterns presented simultaneously in one quadrant elicited a response with shorter latency and infra-linear addition of the amplitudes compared with the patterns presented separately. For bilateral stimulation, the timing of the LOV5 response coincided with the response to contralateral stimulation alone. Other visual areas showed interactions appearing later than within LOV5: starting at 150 ms in V1, at 120 ms in V3-V3a for the left visual hemifield stimulation and at 160 ms for both visual hemifields stimulation. Our data show that distinct patterns in the visual field interact first in LOV5, suggesting that this region must be the first to pool spatial information across the whole visual field.

fMRI retinotopic mapping--step by step.

fMRI retinotopic mapping provides detailed information about the correspondence between the visual field and its cortical representation in the individual subject. Besides providing for the possibility of unambiguously localizing functional imaging data with respect to the functional architecture of the visual system, it is a powerful tool for the investigation of retinotopic properties of visual areas in the healthy and impaired brain. fMRI retinotopic mapping differs conceptually from a more traditional volume-based, block-type, or event-related analysis, in terms of both the surface-based analysis of the data and the phase-encoded paradigm. Several methodological works related to fMRI retinotopic mapping have been published. However, a detailed description of all the methods involved, discussing the steps from stimulus design to the processing of phase data on the surface, is still missing. We describe here step by step our methodology for the complete processing chain. Besides reusing methods proposed by other researchers in the field, we introduce original ones: improved stimuli for the mapping of polar angle retinotopy, a method of assigning volume-based functional data to the surface, and a way of weighting phase information optimally to account for the SNR obtained locally. To assess the robustness of these methods we present a study performed on three subjects, demonstrating the reproducibility of the delineation of low order visual areas.

Does perception of biological motion rely on specific brain regions?

Perception of biological motions plays a major adaptive role in identifying, interpreting, and predicting the actions of others. It may therefore be hypothesized that the perception of biological motions is subserved by a specific neural network. Here we used fMRI to verify this hypothesis. In a group of 10 healthy volunteers, we explored the hemodynamic responses to seven types of visual motion displays: drifting random dots, random dot cube, random dot cube with masking elements, upright point-light walker, inverted point-light walker, upright point-light walker display with masking elements, and inverted point-light walker display with masking elements. A gradient in activation was observed in the occipitotemporal junction. The responses to rigid motion were localized posteriorly to those responses elicited by nonrigid motions. Our results demonstrate that in addition to the posterior portion of superior temporal sulcus, the left intraparietal cortex is involved in the perception of nonrigid biological motions.

Moving illusory contours activate primary visual cortex: an fMRI study.

Identifying the cortical areas activated by illusory contours provides valuable information on the mechanisms of object perception. We applied functional magnetic resonance imaging to identify the visual areas of the human brain involved in the perception of a moving Kanizsa-type illusory contour. Our results indicate that, in addition to other cortical regions, areas V5 and V1 are activated. Activity in area V1 was particularly prominent.

MRI measurement of the functional blood flow changes in a large superficial vein draining the motor cortex.

In this study, phase-contrast MR techniques are applied in order to measure the blood flow changes induced by a motor task in a large superficial vein draining the motor cortex. The measurements were applied to six healthy volunteers, in motor rest conditions and during performance of a motor task. The latter consisted of sequential finger-to-thumb opposition. The task was actually executed and mentally simulated. Significant blood flow increases were found when changing from from mental simulation to actual execution of the motor task (increases ranging between 1.6 and 10.3 ml/min, i.e. 9% and 45%, respectively) and from resting conditions to actual execution of the motor task (increases ranging between 1.7 and 14.0 ml/min, i.e. 32% and 72%, respectively).

Possible involvement of primary motor cortex in mentally simulated movement: a functional magnetic resonance imaging study.

The role of the primary motor cortex (M1) during mental simulation of movement is open to debate. In the present study, functional magnetic resonance imaging (fMRI) signals were measured in normal right-handed subjects during actual and mental execution of a finger-to-thumb opposition task with either the right or the left hand. There were no significant differences between the two hands with either execution or simulation. A significant involvement of contralateral M1 (30% of the activity found during execution) was detected in four of six subjects. Premotor cortex (PM) and the rostral part of the posterior SMA were activated bilaterally during motor imagery. These findings support the hypothesis that motor imagery involves virtually all stages of motor control.

[Organ cryopreservation: current status of research carried out in Grenoble]. / Cryopréservation d'organes: etat actuel des recherches développées à Grenoble.

After discussing the problem of organ cryopreservation and reviewing the current data available on this subject, the Grenoble project is presented. Physical and biological studies have been combined with experimentation of autologous renal transplantation in rabbits to assess the functional value of the retransplanted organ after treatment and cooling. Renal resistances are measured during perfusion of the kidney with the cryoprotective solution. In order to verify the homogeneity of the cryoprotector concentration in the organ, on NMR spectral imaging test has been developed. A new rapid imaging method now allows real time monitoring of concentration variations during perfusion. In addition to concentration and homogeneity, analysis of local spectra also provides information about the local temperature de the kidney.

Intracranial gradient-echo and spin-echo functional MR angiography in humans.

PURPOSE: To investigate the predominance of venous signal intensity at 1.5-T gradient-echo (GRE) functional magnetic resonance (MR) imaging of motor activity and to demonstrate the contribution from task-induced changes in flow velocity to the functional MR imaging signal intensity. MATERIALS AND METHODS: Functional MR imaging of motor activity was performed in healthy volunteers. In a first examination, conventional two-dimensional GRE blood oxygenation level-dependent (BOLD) functional MR imaging techniques were used, and the image planes were carefully positioned with respect to the veins that responded to the motor task. In a second examination, two-dimensional spin-echo (SE) techniques were used, and the image planes were oriented axially and measured in a sequential multisection manner. The areas of hyperintensity on functional MR images were eventually processed by means of maximum intensity projection. RESULTS: Functional MR angiograms were obtained in both examinations. The possibility to generate SE functional MR angiograms demonstrates that venous inflow effects may contribute substantially to signal intensity in conventional two-dimensional GRE BOLD functional MR imaging of motor activity. CONCLUSION: Veins have a substantial role in BOLD functional MR imaging of motor activity.

Venous thrombosis generation by means of high-intensity focused ultrasound.

Sclerotherapy of superficial varicose veins is now performed with chemical agents since physical agents have given only poor clinical results. We investigated the possibility of using high intensity focused ultrasound energy to achieve this goal in an animal model, the rat femoral vein. A specially designed probe delivering ultrasonic energy at a central frequency of 7.31 MHz was constructed and evaluated. Femoral veins of six rats were surgically exposed to a set of between four and seven 3-s exposures at 1-mm increments at a power level of 167 W/cm2. At 2 days following the irradiation, control veins were patent while occlusive thrombus was documented by Doppler flow and histological studies in all six of the irradiated veins. No damage to the surrounding soft tissues was noted. We concluded that high-intensity focused ultrasound can be used to induce thrombosis in this animal model.