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Aymeric RESHEF
État académique
Thèse en cours...
Sujet: Nouvelle chaine d'acquisition et de reconstruction tomographiques sur arceau interventionnel
Direction de thèse:
Encadrement de thèse:
Ellipse bleue: doctorant, ellipse jaune: docteur, rectangle vert: permanent, rectangle jaune: HDR. Trait vert: encadrant de thèse, trait bleu: directeur de thèse, pointillé: jury d'évaluation à mi-parcours ou jury de thèse.
Productions scientifiques
Dual-rotation C-arm cone-beam computed tomography to increase low-contrast detection
International audience
Purpose: This paper investigates the capabilities of a dual-rotation C-arm cone-beam computed tomography (CBCT) framework to improve non-contrast-enhanced low-contrast detection for full volume or volume-of-interest (VOI) brain imaging.Method: The idea is to associate two C-arm short-scan rotational acquisitions (spins): one over the full detector field of view (FOV) at low dose, and one collimated to deliver a higher dose to the central densest parts of the head. The angular sampling performed by each spin is allowed to vary in terms of number of views and angular positions. Collimated data is truncated and does not contain measurement of the incoming X-ray intensities in air (air calibration). When targeting full volume reconstruction, the method is intended to act as a virtual bow-tie. When targeting VOI imaging, the method is intended to provide the minimum full detector FOV data that sufficiently corrects for truncation artifacts. A single dedicated iterative algorithm is described that handles all proposed sampling configurations despite truncation and absence of air calibration.Results: Full volume reconstruction of dual-rotation simulations and phantom acquisitions are shown to have increased low-contrast detection for less dose, with respect to a single-rotation acquisition. High CNR values were obtained on 1% inserts of the Catphanmath formula 515 module in 0.94 mm thick slices. Image quality for VOI imaging was preserved from truncation artifacts even with less than 10 non-truncated views, without using the sparsity a priori common to such context.Conclusion: A flexible dual-rotation acquisition and reconstruction framework is proposed that has the potential to improve low-contrast detection in clinical C-arm brain soft-tissue imaging.
ISSN: 0094-2405 Medical Physics https://hal.archives-ouvertes.fr/hal-01587006 Medical Physics, American Association of Physicists in Medicine, 2017, Advances and trends in image formation in X-ray CT, 44 (9), pp.e164-e173. <http://onlinelibrary.wiley.com/doi/10.1002/mp.12247/full>. <10.1002/mp.12247> http://onlinelibrary.wiley.com/doi/10.1002/mp.12247/fullARRAY(0x7f4f390ec658) 2017-09-13
Reconstruction tomographique 2D : une nouvelle méthode de rétro-projection filtrée
National audience
En reconstruction tomographique 2D, le terme de « rétro-projection filtrée » est ambigu, car les projections sont d’abord filtrées puis rétro-projetées dans le plan image. Si l’inversion des opérations est possible mathématiquement, elle n’est jamais appliquée en pratique. Cet article présente un moyen de calculer la rétro-projection filtrée avec la même précision numérique quel que soit l’ordre des opérations. Une illustration dans le cadre de la reconstruction de régions d’intérêt démontre la versatilité de la méthode.
Actes du XXVIe colloque GRETSI XXVIe colloque GRETSI https://hal.archives-ouvertes.fr/hal-01587192 XXVIe colloque GRETSI, Sep 2017, Juan-les-Pins, France. Actes du XXVIe colloque GRETSI, 2017ARRAY(0x7f4f38d73e38) 2017-09-05
Nonlinear diffusion constraints for reconstructing subsampled rotational angiography data
International audience
Interventional imaging with cone-beam C-arm CT often lacks sufficient sampling. Compressed sensing based reconstruction algorithms have shown promising results to improve image quality in this context using sparsity constraints. Compressed sensing theory by itself assumes random measurements and l1 penalties. In practice, benefits are seen with uniform subsampling patterns. Here, we investigate substituting l1 total variation with a nonlinear diffusion constraint and show on a clinical data set that image quality is also improved. This result adds flexibility to the design of CS-based algorithms as C-arm CT images may not be so well approximated by piecewise constant functions.
The 12th International Meeting on Fully Three-Dimensional Image Reconstruction in Radiology and Nuclear Medicine Fully3D 2013 https://hal-supelec.archives-ouvertes.fr/hal-00933983 Fully3D 2013, Jun 2013, Lake Tahoe, California, United States. pp.38-41Conference papers 2013-06-16
Compressed-sensing-based content-driven hierarchical reconstruction: Theory and application to C-arm cone-beam tomography
International audience
Purpose: This paper addresses the reconstruction of x-ray cone-beam computed tomography (CBCT) for interventional C-arm systems. Subsampling of CBCT is a significant issue with C-arms due to their slow rotation and to the low frame rate of their flat panel x-ray detectors. The aim of this work is to propose a novel method able to handle the subsampling artifacts generally observed with analytical reconstruction, through a content-driven hierarchical reconstruction based on compressed sensing.Methods: The central idea is to proceed with a hierarchical method where the most salient features (high intensities or gradients) are reconstructed first to reduce the artifacts these features induce. These artifacts are addressed first because their presence contaminates less salient features. Several hierarchical schemes aiming at streak artifacts reduction are introduced for C-arm CBCT: the empirical orthogonal matching pursuit approach with the ℓ0 pseudonorm for reconstructing sparse vessels; a convex variant using homotopy with the ℓ1-norm constraint of compressed sensing, for reconstructing sparse vessels over a nonsparse background; homotopy with total variation (TV); and a novel empirical extension to nonlinear diffusion (NLD). Such principles are implemented with penalized iterative filtered backprojection algorithms. For soft-tissue imaging, the authors compare the use of TV and NLD filters as sparsity constraints, both optimized with the alternating direction method of multipliers, using a threshold for TV and a nonlinear weighting for NLD.Results: The authors show on simulated data that their approach provides fast convergence to good approximations of the solution of the TV-constrained minimization problem introduced by the compressed sensing theory. Using C-arm CBCT clinical data, the authors show that both TV and NLD can deliver improved image quality by reducing streaks.Conclusions: A flexible compressed-sensing-based algorithmic approach is proposed that is able to accommodate for a wide range of constraints. It is successfully applied to C-arm CBCT images that may not be so well approximated by piecewise constant functions.
ISSN: 0094-2405 Medical Physics https://hal.archives-ouvertes.fr/hal-01230277 Medical Physics, American Association of Physicists in Medicine, 2015, 42 (9), <http://scitation.aip.org/content/aapm/journal/medphys/42/9>. <10.1118/1.4928144> http://scitation.aip.org/content/aapm/journal/medphys/42/9ARRAY(0x7f4f390deb38) 2015-08-13
Dual-rotation C-arm cone-beam computed tomography to increase low-contrast resolution
International audience
Interventional imaging with C-arm Cone-Beam Computed Tomography (CBCT) lacks low-contrast resolution. The use of bow-tie filters is common in diagnostic Computed Tomography (CT), as they reduce both patient dose and the dynamic range of the signal at the detector. Without a bowtie filter, a single-rotation acquisition results either in underexposed areas where the object is thick, or in over-exposed areas where the object is thin. Here, we propose to acquire two rotations in order to compensate for the absence of a bowtie filter: an un-truncated acquisition at low exposure and a truncated acquisition at higher exposure. We allow the rotations not to be acquired at the exact same positions, and introduce a reconstruction strategy to make full use of our redundant data and reconstruct the full field-of-view. The method is extended to volume-of-interest tomography. Results on a quality assurance phantom show that an angularly finely sampled acquisition of truncated intensity projections increases low-contrast resolution of C-arm CBCT, when combined with a (sub)set of un-truncated, low-intensity projections. Depending on the angular sampling of the un-truncated data, improvement is observed either over the entire field-of-view or over the truncated field-of-view.
4th International Conference on Image Formation in X-Ray Computed Tomography https://hal.archives-ouvertes.fr/hal-01351563 4th International Conference on Image Formation in X-Ray Computed Tomography, Jul 2016, Bamberg, GermanyARRAY(0x7f4f390de7d8) 2016-07-18