A framework based on sulcal constraints to align preterm, infant and adult human brain images acquired in vivo and post mortem.

Robust spatial alignment of post mortem data and in vivo MRI acquisitions from different ages, especially from the early developmental stages, into standard spaces is still a bottleneck hampering easy comparison with the mainstream neuroimaging results. In this paper, we test a landmark-based spatial normalization strategy as a framework for the seamless integration of any macroscopic dataset in the context of the Human Brain Project (HBP). This strategy stems from an approach called DISCO embedding sulcal constraints in a registration framework used to initialize DARTEL, the widely used spatial normalization approach proposed in the SPM software. We show that this strategy is efficient with a heterogeneous dataset including challenging data as preterm newborns, infants, post mortem histological data and a synthetic atlas computed from averaging the ICBM database, as well as more commonly studied data acquired in vivo in adults. We then describe some perspectives for a research program aiming at improving folding pattern matching for atlas inference in the context of the future HBP's portal.

Spherical wavelet transform for ODF sharpening.

The choice of local HARDI reconstruction technique is crucial for discerning multiple fiber orientations, which is itself of substantial importance for tractography, and reliable and accurate assessment of white matter fiber geometry. Due to the complexity of the diffusion process and its milieu, distinct diffusion compartments can have different frequency signatures, making the HARDI signal spread over multiple frequency bands. Therefore, we put forth the idea of multiscale analysis with localized basis functions, ensuring that different frequency ranges are probed. With the aim of truthful recovery of fiber orientations, we reconstruct the orientation distribution function (ODF), by incorporating a spherical wavelet transform (SWT) into the Funk-Radon transform. First, we apply and validate our proposed SWT method on real physical phantoms emulating fiber bundle crossings. Then, we apply the SWT method to a real brain data set. The analysis of the real data set suggests that different angular frequencies may capture different information, thus stressing the importance of multiscale analysis. For both phantom and real data, we compare the SWT reconstruction with state-of-the-art q-ball imaging and spherical deconvolution reconstruction methods. We demonstrate the algorithm efficiency in diffusion ODF denoising and sharpening that is of particular importance for applications to fiber tracking (especially for probabilistic approaches), and brain connectome mapping. Also, the algorithm results in considerable data compression that could prove beneficial in applications to fiber bundle segmentation, and for HARDI based white matter morphometry methods.

Real-time MR diffusion tensor and Q-ball imaging using Kalman filtering.

Magnetic resonance diffusion imaging (dMRI) has become an established research tool for the investigation of tissue structure and orientation. In this paper, we present a method for real time processing of diffusion tensor and Q-ball imaging. The basic idea is to use Kalman filtering framework to fit either the linear tensor or Q-ball model. Because the Kalman filter is designed to be an incremental algorithm, it naturally enables updating the model estimate after the acquisition of any new diffusion-weighted volume. Processing diffusion models and maps during ongoing scans provides a new useful tool for clinicians, especially when it is not possible to predict how long a subject may remain still in the magnet.

Automatic inference of sulcus patterns using 3D moment invariants.

The goal of this work is the automatic inference of frequent patterns of the cortical sulci, namely patterns that can be observed only for a subset of the population. The sulci are detected and identified using brainVISA open software. Then, each sulcus is represented by a set of shape descriptors called the 3D moment invariants. Unsupervised agglomerative clustering is performed to define the patterns. A ratio between compactness and contrast among clusters is used to select the best patterns. A pattern is considered significant when this ratio is statistically better than the ratios obtained for clouds of points following a Gaussian distribution. The patterns inferred for the left cingulate sulcus are consistent with the patterns described in the atlas of Ono.

Brain morphometry using 3D moment invariants.

This paper advocates the use of shape descriptors based on moments of 3D coordinates for morphometry of the cortical sulci. These descriptors, which have been introduced more than a decade ago, are invariant relatively to rotations, translations and scale and can be computed for any topology. A rapid insight into the derivation of these invariants is proposed first. Then, their potential to characterize shapes is shown from a principal component analysis of the 12 first invariants computed for 12 different deep brain structures manually drawn for 7 different brains. Finally, these invariants are used to find some correlates of handedness and sex among the shapes of 116 different cortical sulci automatically identified in each of 142 brains of the ICBM database.

Clinical characteristics and topography of lesions in movement disorders due to thalamic lesions.

OBJECTIVE: To determine which thalamic subnuclei are involved in symptomatic unilateral movement disorders due to localized thalamic infarction, and the clinical characteristics of these abnormal movements. METHODS: The authors studied 22 patients with thalamic infarcts for their clinical presentation and the topography of the lesions, using three-dimensional T1-weighted MRI sequencing and stereotaxic analysis of the lesions. RESULTS: Patients were divided into four groups: 1) absence of abnormal involuntary movements (AIM) (nine patients); 2) isolated dystonic posture (two patients); 3) myoclonic dystonia (five patients); and 4) tremor or myoclonus (six patients). In patients with AIM, thalamic lesions were contralateral to the abnormal movements, involving the thalamogeniculate territory, centered on the ventral intermediate (Vim) and ventral caudal (Vc) nuclei. No significant difference in the volumes or center of mass of the lesions was found between patients with tremor and myoclonus and patients with dystonia, although the central nucleus and the internal part of the Vim nucleus were more consistently damaged in dystonic patients. CONCLUSION: Movement disorders related to thalamic lesions included: 1) myoclonic dystonia with predominating myoclonus and "thalamic" hand associating dystonic posture and slow, pseudo-athetoid movements, both related to lesions in the Vim and Vc nuclei of the thalamus; and 2) postural and action tremor, also related to lesions in the Vim, similar to tremor associated with midbrain lesions, as a result of abnormal functioning of the cerebello-thalamic pathways.

Role of the supplementary motor area in motor deficit following medial frontal lobe surgery.

OBJECTIVE: Patients undergoing surgical resection of medial frontal lesions may present a transient postoperative deficit that remains largely unpredictable. The authors studied the role of the supplementary motor area (SMA) in the occurrence of this deficit using fMRI. METHODS: Twenty-three patients underwent a preoperative fMRI before resection of medial frontal lesions. Tasks included self-paced flexion/extension of the left and right hand, successively. Preoperative fMRI data were compared with postoperative MRI data and with neurologic outcome. RESULTS: Following surgery, 11 patients had a motor deficit from which all patients recovered within a few weeks or months. The deficit was similar across patients, consisting of a global reduction in spontaneous movements contralateral to the operated side with variable severity. SMA activation was observed in all patients. The deficit was observed when the area activated in the posterior part of the SMA (SMA proper) was resected. CONCLUSIONS: fMRI is able to identify the area at risk in the SMA proper whose resection is highly related to the occurrence of the motor deficit. The clinical characteristics of this deficit support the role of the SMA proper in the initiation and execution of the movement.

Clinical severity in CADASIL related to ultrastructural damage in white matter: in vivo study with diffusion tensor MRI.

BACKGROUND AND PURPOSE: CADASIL is a newly recognized cause of subcortical ischemic strokes that progressively leads to dementia associated with pseudobulbar palsy and severe motor disability. This deleterious progression and the severity of clinical presentation are widely variable among affected subjects. The exact role played by MRI white-matter abnormalities, a hallmark of the disease, in the severity of the clinical phenotype remains poorly understood. METHODS: To address this issue, we used diffusion tensor imaging (DTI), a new MRI technique highly sensitive to white-matter microstructural changes, in 16 symptomatic patients and 10 age-matched controls. Mean diffusivity and anisotropy of diffusion were measured within hyperintensities identified on T2-weighted images (T2WI) and outside these lesions on 4 slices at the level of centrum semiovale. RESULTS: We found a 60% increase of water mean diffusivity and a parallel loss of diffusion anisotropy in hyperintensities identified on T2WI. The same pattern of diffusion changes, but of lesser intensity, was found in the normal-appearing white matter on T2WI. Mean diffusivity in regions with increased signal on T2WI was higher in patients with severe clinical disability compared with those with no or mild deficit (1.33+/-0.11 versus 1.13+/-0.11 10(-3) mm(2)/s, P<0.01). Furthermore, diffusion measured within T2 hyperintensities correlated with both the Mini-Mental State Examination and Rankin scale scores. In patients with a severe clinical status, the increase of water diffusion in these regions exceeded 70% in comparison with values obtained in the normal white matter in control subjects. CONCLUSIONS: These results indicate that DTI is able to detect important ultrastructural changes in regions with increased signal on T2WI and within the normal-appearing white matter in CADASIL. The diffusion changes might be related to both neuronal loss and demyelination. The degree of the underlying ultrastructural alterations is related to the severity of the clinical status with a possible threshold level of white-matter damage above which severe neurological impairment may occur in this disease. DTI appears to be a promising technique for monitoring disease progression in CADASIL.