Cortical activation resulting from the stimulation of periodontal mechanoreceptors measured by functional magnetic resonance imaging (fMRI).

OBJECTIVE: To describe the normal cortical projections of periodontal mechanoreceptors. MATERIAL AND METHODS: A device using von Frey filaments delivered 1-Hz punctate tactile stimuli to the teeth during fMRI. In a block design paradigm, tooth (T) 11 and T13 were stimulated in ten volunteers and T21 and T23 in ten other subjects. Random-effect group analyses were performed for each tooth, and differences between teeth were examined using ANOVA. RESULTS: The parietal operculum (S2) was activated bilaterally for all teeth; the postcentral gyrus (S1) was activated bilaterally for T21 and T23 and contralaterally for T11 and T13. In the second-level analysis including the four teeth, we found five clusters: bilateral S1 and S2, and left inferior frontal gyrus, with no difference between teeth in somatosensory areas. However, the ANOVA performed on the S1 clusters found separately in each tooth showed that S1 activation was more contralateral for the canines. CONCLUSION: One-hertz mechanical stimulation activates periodontal mechanoreceptors and elicits bilateral cortical activity in S1 and S2, with a double representation in S2, namely in OP1 and OP4. CLINICAL RELEVANCE: The cortical somatotopy of periodontal mechanoreceptors is poorly described. These findings may serve as normal reference to further explore the cortical plasticity induced by periodontal or neurological diseases.

White matter anatomy of the human deep brain revisited with high resolution DTI fibre tracking.

BACKGROUND AND PURPOSE: Deep white matter (WM) fascicles play a major, yet poorly understood, role in the overall connectivity of human brain. Better knowledge of their anatomy is requisite to understand the clinical correlates of their lesions and develop targeted treatments. We investigated whether MR-based diffusion tensor imaging (DTI) and fibre tracking could reveal in vivo, in explicit details, the 3D WM architecture within the subthalamic region and the internal capsule. METHODS: High-resolution DTI images were acquired on six healthy volunteers on a three Tesla MR scanner. We studied using single-subject analysis WM fascicles within the subthalamic region and the internal capsule, as follows: DTI deterministic fibre tracking (FT) of fascicles; embedding fascicles in the volume-rendered brain coupled with a triplanar view; rigorous anatomic labelling of each fascicle according to classical knowledge as described by pioneer neuroanatomists. Deterministic FT effects were taken into account. RESULTS: We charted most of WM fascicles of the deep brain, in particular large and complex fascicles such as the basal forebrain bundle and the ansa lenticularis. A topographic classification of subthalamic fascicles was proposed into three groups: the cerebellorubral, the reticulo-dorsal and the tegmento-peripheral one. CONCLUSIONS: Beyond to demonstrate the feasibility of imaging the deepest WM fascicles in vivo, our results pave the way for a better understanding of the brain connectivity and for developing targeted neuromodulation.

Intraoperative 3T MR imaging for spinal cord tumor resection: feasibility, timing, and image quality using a "twin" MR-operating room suite.

We assessed feasibility, safety, and timing of an original intraoperative MR procedure in 3 cases of resection of spinal cord glioma by using a clinical 3T MR system connected to an adjacent operating room in a design being coined "twin" or "dual" MR-operating room suite.

Hyperacute intraventricular hemorrhage: detection and characterization, a comparison between 5 MRI sequences.

We aimed to evaluate the diagnostic accuracy of MRI for detecting early intraventricular hemorrhage (IVH) (within 6 hours after hemorrhage and to describe the MR features that allow diagnosis. For this purpose, MR data of 22 patients with hyperacute intraparenchymal hemorrhage were independently rated as negative or positive for IVH by two observers, in a blind, retrospective study taking computed tomography (CT) as providing the correct diagnosis of IVH. Sensitivity, specificity, intra- and interobserver agreement were assessed. On FSE-FLAIR, EPI-GRE-T2* and DWI images, all cases of IVH were correctly rated (sensitivity of 100%). For b0 EPI images, obtained from diffusion-weighted echo planar sequences, one case of IVH was missed by one reader (sensitivity of 88%). For T1 images, one patient was incorrectly rated negative for IVH by the two readers (sensitivity of 90%). Three forms of IVH were described, including clotted hematoma, layered hemorrhage and red blood cell deposit. When CT images were obtained within a time span of less than 3 hours after MRI, volume was assessed. Volume of hemorrhage on CT correlated best with DWI images but was underestimated on EPI-GRE T2* images.

Calculation of the renal perfusion and glomerular filtration rate from the renal impulse response obtained with MRI.

The aim of this study was to assess the importance of deconvolution for the calculation of renal perfusion and glomerular filtration rate (GFR) on the basis of concentration-time curves as measured with perfusion MRI. Six rabbits were scanned dynamically after injection of a gadolinium chelate. Concentration-time curves were generated by manually drawing regions of interest in the aorta and the renal cortex. To remove the dependency on the arterial input function, a regularized structured total least-squares deconvolution algorithm was used to calculate the renal impulse response. This curve was fitted by the sum of two gamma variate functions, corresponding to the passage of the contrast agent in the glomeruli and the proximal convoluted tubules. Tracer kinetics models were applied to these two functions to obtain the renal perfusion and GFR. For comparison, these two parameters were also calculated on the basis of the renal concentration-time curve before deconvolution. The renal perfusion values correlated well (r = 0.9, P = 0.014) with the values calculated by a validated upslope method. The GFR values correlated well (r = 0.9, P = 0.014) with the values obtained from the clearance of (51)Cr-EDTA. A comparison of the values obtained with and without deconvolution demonstrated the necessity of deconvolution.