Pascal Desbarats

Propagation beam consideration for 3D THz computed tomography

In this paper, a model of the beam propagation is developed according to the physical properties of THz waves used in THz computed tomography (CT) scan imaging. This model is first included in an acquisition simulator to observe and estimate the impact of the Gaussian beam intensity profile on the projection sets. Second, the model is introduced in several inversion methods as a convolution filter to perform efficient tomographic reconstructions of simulated and real acquired objects. Results obtained with three reconstruction methods (BFP, SART and OSEM) are compared to the techniques proposed in this paper. We will demonstrate an increase of the overall quality and accuracy of the 3D reconstructions.

Impairment of GABAB receptor dimer by endogenous 14‐3‐3ζ in chronic pain conditions

In the central nervous system, the inhibitory GABAB receptor is the archetype of heterodimeric G protein‐coupled receptors (GPCRs). However, the regulation of GABAB dimerization, and more generally of GPCR oligomerization, remains largely unknown. We propose a novel mechanism for inhibition of GPCR activity through de‐dimerization in pathological conditions. We show here that 14‐3‐3ζ, a GABAB1‐binding protein, dissociates the GABAB heterodimer, resulting in the impairment of GABAB signalling in spinal neurons. In the dorsal spinal cord of neuropathic rats, 14‐3‐3ζ is overexpressed and weakens GABAB inhibition. Using anti‐14‐3‐3ζ siRNA or competing peptides disrupts 14‐3‐3ζ/GABAB1 interaction and restores functional GABAB heterodimers in the dorsal horn. Importantly, both strategies greatly enhance the anti‐nociceptive effect of intrathecal Baclofen in neuropathic rats. Taken together, our data provide the first example of endogenous regulation of a GPCR oligomeric state and demonstrate its functional impact on the pathophysiological process of neuropathic pain sensitization.

Mojette reconstruction from noisy projections

Apart from the usual methods based on the Radon theorem, the Mojette transform proposes a specific algorithm called Corner Based Inversion (CBI) to reconstruct an image from its projections. Contrary to other transforms, it offers two interesting properties. First, the acquisition follows discrete image geometry and resolves the well-known irregular sampling problem. Second, it updates projection values during the reconstruction such that the sinogram contains only data for not yet reconstructed pixels. Unfortunately, the CBI algorithm is noise sensitive and reconstruction from corrupted data fails. In this paper, we develop a new noise-robust CBI algorithm based on data redundancy and noise modelling in the projections. This algorithm is applied in discrete tomography from a Radon acquisition. Reconstructed image results are discussed and applications in usual tomography are detailed.

A new processing sequence to assess airways using 3D CT-scan

Accurate measurement of physiological parameters such as the bronchial lumen and bronchial wall areas helps in the diagnosis of lung diseases. Algorithms allowing such measures are the result of complex processing sequences composed of (i) bronchial volume extraction (ii) bronchial volume skeletonization (iii) wall extraction. The proposed sequences however still show weaknesses in terms of precision, extent and automation. In this paper we address various problems encountered at each step of the processing sequence and propose a new sequence for measuring lumen on bronchial section. Finally, this sequence is tested on two datasets of 10 anonymous exams1 collected from 10 different healthy volunteers and 10 different patients suffering from asthma that were attended by different practitioners.

A Preliminary Study to Reduce the Missing Wedge Effect by Using a Noise Robust Mojette Reconstruction

Apart from the usual methods based on the Radon theorem, the Mojette transform proposes a specific algorithm called Corner Based Inversion (CBI) to reconstruct an image from its projections. Contrary to other transforms, it offers two interesting properties. First, the acquisition follows discrete image geometry and resolves the well-known irregular sampling problem. Second, it updates projection values during the reconstruction such that the sinogram contains only data for not yet reconstructed pixels. These properties could be a solution to reduce the missing wedge effect in tomography. Unfortunately, the CBI algorithm is noise sensitive and reconstruction from corrupted data fails. In this paper, we first develop and optimize a noise-robust CBI algorithm based on data redundancy and noise modelling in the projections. Afterwards, this algorithm is applied in discrete tomography from a specific Radon acquisition. Reconstructed image results are discussed and applications and perspectives to reduce the missing wedge effect are also developed.

Segmentation of left ventricle on dynamic MRI sequences for blood flow cancellation in Thermotherapy

Abstract In this paper, we develop a new semi-automated segmentation method to cancel the unstable blood flow within the left ventricle (LV) in cardiac magnetic resonance (MR) images with parallel imaging. The segmentation is performed using a deformable model driven by a new external energy based on estimated probability density function (pdf) of the MR signal in the LV. The use of signal distribution through the data allows us both to pull the contour towards the myocardium edges and to ensure the smoothness of the curve. Since data for each slice are acquired with the GRAPPA parallel imaging technique, the spatial segmentation is followed by a temporal propagation to improve the convergence in terms of quality and rapidity. Experiments demonstrate that the proposed model provides better results than the results of three state-of-the art methods based on Active Contour Model, which should facilitate the use of the method for clinical purposes.

Segmentation of left ventricle on MRI sequences for blood flow cancelation in thermotherapy

In this paper, we develop a new semi-automated segmentation method to cancel the chaotic blood flow signal within the left ventricle (LV) in cardiac magnetic resonance (MR) images with parallel imaging. The segmentation is performed using a deformable model driven by a new external energy based on estimated probability density function (pdf) of the MR signal in the LV. The use of noise distribution through the data allows us both to pull the contour towards the myocardium edges and to ensure the smoothness of the curve. Since data for each slice are acquired with the GRAPPA parallel imaging technique, the spatial segmentation is followed by a temporal propagation to improve the convergence in terms of quality and rapidity. Experiments demonstrate that the proposed model provides better results than those obtained from the standard Active Contour, which should facilitate the use of the method for clinical purposes.

Influence of the acquisition method on terahertz tomography

Terahertz tomography is a technique used in the field of contact-free and non destructive testing [1][2]. It can be achieved using a raster scanning system with three axes or two axes and a rotation stage. The setup uses a Gunn diode working at a frequency of 84 GHz as a source and a Schottky diode or pyroelectric element for the detection. A tripler can be added to the source to obtain a frequency of 252 GHz. The sample is hold on a rotating stage θ mounted on a two axis (X, Y) scanner. We propose to characterize the origin of the electronic noise induced by fluctuations in the detector and analyze the influence of the acquisition method on the reconstructed image in tomography.

A step towards planification of focused ultrasound thermoablation

Focused ultrasound devices are used in thermal ablation therapy. Their utilization implies to planify the focal point trajectory before the intervention. Our final objtective is to provide clinicians with a planification tool. In this article, different methods for trajectory planification are presented and then evaluated on 3D synthetic objects taking into account the total intervention duration. Finally, a discussion on the efficiency of the methods in clinical use is proposed.