[Building the scientific commons. Conflictualities and pluralism in the light of clinical trials Covid-19]. / Faire du commun dans les sciences - Conflictualités et pluralisme à l'épreuve des essais cliniques COVID-19.

TITLE: Faire du commun dans les sciences - Conflictualités et pluralisme à l'épreuve des essais cliniques COVID-19. ABSTRACT: La crise de la COVID-19 s'est ouverte sur un déficit de moyens thérapeutiques permettant de lutter efficacement contre cette maladie pour les cas les plus graves et sur de nombreuses initiatives visant à mettre en évidence un traitement efficace. Si différentes options ont été explorées, parmi lesquelles la transfusion de plasma de patients guéris, la lutte contre les mécanismes immunitaires déclenchant une réponse trop forte (les orages cytokiniques) ou, à moyen terme, la vaccination, ce sont dans un premier temps surtout les médicaments antiviraux qui ont nourri les espoirs. Après l'identification d'un certain nombre de principes actifs montrant des effets in vitro, il s'agissait d'obtenir rapidement des réponses quant à leurs effets bénéfiques in vivo et aux risques induits. Aussi, s'est-on senti en droit d'attendre que la science nous apporte les connaissances nécessaires sur ces médicaments, qu'elle nous parle, une fois sollicitée, de manière claire et d'une seule voix ; et cela, dans une situation d'urgence où la synchronisation des rythmes de la recherche et du soin n'a rien d'une évidence.

SPECT low-field MRI system for small-animal imaging.

UNLABELLED: Localization of regions with increased uptake of radiotracer in small-animal SPECT is greatly facilitated when using coregistration with anatomic images of the same animal. As MRI has several advantages compared with CT (soft-tissue contrast and lack of ionizing radiation) we developed a SPECT/low-field MRI hybrid device for small-animal imaging. METHODS: A small-animal single-pinhole gamma-camera (pinhole, 1.5 mm in diameter and 12 cm in focal length) adjacent to a dedicated low-field (0.1 T) small MR imager (imaging volume, 10 x 10 x 6 cm(3)) was used. The animal was placed in a warmed nonmagnetic polymethyl methacrylate imaging cell for MR acquisition, which was followed immediately by SPECT after translation of the imaging cell from one modality to the other. 3-Dimensional T1-weighted sequences were used for MRI. Phantom studies enabled verification of a low attenuation (10%) for (99m)Tc and (201)Tl and a very slight increase in Compton scattering due to the radiofrequency coil and polymethyl methacrylate imaging cell. RESULTS: SPECT/MRI data acquisition and image coregistration of selected examples using different radiotracers for lungs, kidneys, and brain were obtained in 3 nude mice with isotropic spatial resolutions of 0.5 x 0.5 x 0.5 mm(3) for MRI and 1 x 1 x 1 mm(3) for SPECT. The total acquisition time for combined SPECT and MRI lasted 1 h 45 min. CONCLUSION: A low-magnetic-field strength of 0.1 T is a simple and useful solution for a small-animal dual-imaging device combining pinhole SPECT with the adjacent MR imager.

Pinhole SPECT imaging: compact projection/backprojection operator for efficient algebraic reconstruction.

We describe the efficient algebraic reconstruction (EAR) method, which applies to cone-beam tomographic reconstruction problems with a circular symmetry. Three independant steps/stages are presented, which use two symmetries and a factorization of the point spread functions (PSFs), each reducing computing times and eventually storage in memory or hard drive. In the case of pinhole single photon emission computed tomography (SPECT), we show how the EAR method can incorporate most of the physical and geometrical effects which change the PSF compared to the Dirac function assumed in analytical methods, thus showing improvements on reconstructed images. We also compare results obtained by the EAR method with a cubic grid implementation of an algebraic method and modeling of the PSF and we show that there is no significant loss of quality, despite the use of a noncubic grid for voxels in the EAR method. Data from a phantom, reconstructed with the EAR method, demonstrate 1.08-mm spatial tomographic resolution despite the use of a 1.5-mm pinhole SPECT device and several applications in rat and mouse imaging are shown. Finally, we discuss the conditions of application of the method when symmetries are broken, by considering the different parameters of the calibration and nonsymmetric physical effects such as attenuation.

A prospective study on algorithms adapted to the spatial frequency in tomography.

The use of iterative algorithms in tomographic reconstruction always leads to a frequency adapted rate of convergence in that low frequencies are accurately reconstructed after a few iterations, while high frequencies sometimes require many more computations. In this paper, we propose to build frequency adapted (FA) algorithms based on a condition of incomplete backprojection and propose an FA simultaneous algebraic reconstruction technique (FA-SART) algorithm as an example. The results obtained with the FA-SART algorithm demonstrate a very fast convergence on a highly detailed phantom when compared to the original SART algorithm. Though the use of such an FA algorithm may seem difficult, we specify in which case it is relevant and propose several ways to improve the reconstruction process with FA algorithms.

Assessment of left ventricular perfusion, volumes, and motion in mice using pinhole gated SPECT.

UNLABELLED: Quantitative functional normal data should be a prerequisite before applying SPECT in murine models of cardiac disease. Therefore, we investigated the capability of in vivo pinhole gated SPECT for establishment of a reference database for left ventricular myocardial perfusion, volumes, and motion in normal mice. METHODS: A small-animal dedicated pinhole gamma-camera with a field of view of 17 cm and a focal distance of 12 cm was used with a 1.5-mm pinhole and a 2.5-cm radius of rotation. Phantoms were designed to test spatial resolution and microvolume measurements of accuracy. Eight adult normal mice (CD1) were studied using a heated mixture of air (0.3 L/min) and 1.5%-2.5% isoflurane for anesthesia. For myocardial perfusion, 350-450 MBq of (99m)Tc-tetrofosmin were used in 0.15-0.25 mL. Gated acquisitions (8 or 10 time bins per cardiac cycle) were obtained using a 180 degrees circular arc and 48 anterior projections of 300 R-R intervals. Image reconstruction was done using a specific Algebraic Reconstruction Technique (ART) cone-beam algorithm. For quantification, reconstructed images were processed using standard nuclear medicine software. RESULTS: Millimetric spatial resolution and volume calibration linear relationships (r(2) = 0.99) in the 10- to 100-muL range were obtained in phantoms and used to scale in vivo volume values. In mice, left ventricular perfusion was lower in the apex (65% +/- 6%) versus lateral (72% +/- 5%), inferior (74% +/- 5%), septum (75% +/- 4%), and anterior (74% +/- 2%) walls. The left ventricular ejection fraction was 60% +/- 9%, end-diastolic volume was 50 +/- 8 muL, end-systolic volume was 20 +/- 6 muL, stroke volume was 29.5 +/- 6 muL, and cardiac output was 9.6 +/- 1.6 mL/min. Wall thickening was higher in the apex (47% +/- 12%) versus lateral (30% +/- 9%), inferior (33% +/- 8%), septum (37% +/- 10%), and anterior (33% +/- 10%) walls. CONCLUSION: This work shows that in vivo pinhole gated SPECT can be used for assessment of left ventricular perfusion, volumes, and cardiac function in normal mice.