Line Garnero

Influence of skull anisotropy for the forward and inverse problem in EEG : Simulation studies using FEM on realistic head models

For the sake of realism in the description of conduction from primary neural currents to scalp potentials, we investigated the influence of skull anisotropy on the forward and inverse problems in brain functional imaging with EEG. At present, all methods available for cortical imaging assume a spherical geometry, or when using realistic head shapes do not consider the anisotropy of head tissues. However, to our knowledge, no study relates the implication of this simplifying hypothesis on the spatial resolution of EEG for source imaging.

Somatosensory cortical remodelling after rehabilitation and clinical benefit of in writer's cramp

In order to explore the pathophysiological basis of a new rehabilitation therapy in writers cramp (WC), healthy controls, untreated WC patients and WC patients who recovered a legible handwriting after rehabilitation were explored using magnetoencephalography, and the somatosensory evoked fields of fingers I, II, III and V in the sensory cortex were studied. In the cortex controlling the dystonic limb, the size of the hand representation in the trained patients was similar to that of healthy controls, and significantly different from that of untrained patients. Trained patients exhibited ‘super-normal’ reorganisation of the finger maps. In the cortex controlling the non-dystonic limb, there was little difference between trained and untrained patients, and the hand representation was enlarged and disorganised. The authors hypothesise that prolonged tailored rehabilitation in WC may induce long-term plasticity phenomena, lateralised to the cortex controlling the dystonic hand.

Off-axis multi-slit coding for tomographic x-ray imaging of microplasma

Abstract Off-axis multi-slit coding is proposed for the imaging of X-rays emitted by laser-produced microplasmas. Unlike usual coding aperture techniques based on a two-dimensional reconstruction, our code allows a reconstruction with a mainly one-dimensional algorithm, without loosing the tomographical capability, which is provided by the off-axis location of slits in the coding mask.

Non-iterative, Limited-angle Tomographic Imaging Using Eigenfunctions Adapted to Space-limited Objects

A non-iterative approach is taken to the problem of tomographic imaging with a limited angle of view, based on a priori knowledge of the finite extent of the objects to be reconstructed. This method consists of finding, for an object of given spatial extent, a set of expansion functions adapted to this constraint. This set of basis functions is then used to relate the object to its available projections, in order to reconstruct the object distribution from the incomplete data; that is, to recover the object from limited projection data. The corresponding matrix inversion, computed before recording the data, is performed with a regularization procedure. Numerical results prove the stability of this approach in the presence of noise.

Analyse du codage de l'information en tomographie longitudinale a haute resolution

Abstract Using a 3-D Fourier analysis, we investigate the nature of the informations contained in the high resolution motion pinhole recordings. We show that these images can be interpreted as parallel projections of a distorted 3-D emitting object. Thus, the use of the 3-D central slice theorem and the circular motion of the pinhole show that a 3-D Fourier region remains unexplored. Such a fact leads to a notable degradation of objects containing only very low spatial frequencies. But, in other cases, this degradation is generally less important (heart imaging for instance) and the improvement in resolution of this method proves to be appreciable when analysing local defects of fixation in nuclear medicine.

Improved Tomographic X-Ray Microimaging Of Laser Plasmas By Double Multislit Coding Cameras

A tri-dimensional microimaging system was developed for X-rays emitted by laser induced plasmas. It uses a multislit coding mask and linear CCD detectors perpendicular to each slit, in order to provide real time 3-D imaging. However, the aperture upon the object is too small to expect a very good separation in depth ; but improvement can be brought by using simultaneously two such multi-slit cameras in different directions of space. Numerical simulations already show the interest of this double coding.

Three Dimensional Limited Angle Tomographic Imaging Using Constrained Natural Pixels

We present in this paper a method for 2-D or 3-D tomographic reconstruction, when the angle of view of the projections is limited. This method uses a decomposition into constrained natural pixels which incorporates a priori information and a fast iterative inversion process. Numerical simulations show the importance of the added constraints, and prove the stability of the method in the presence of noisy data.

Technical problems in emission computed axial tomography

Abstract The different problems of positional inaccuracy of the recording system in emission computed axial tomography are studied. Mathematical analysis and experimental results show the artefacts due to these misadjustments, which appear in the reconstructed images. Some threshold tolerable values for these adjustments are given.