Jean-Pierre Tasu

Multidimensional MR mapping of multiple components of velocity and acceleration by fourier phase encoding with a small number of encoding steps

Previous studies have shown that the multi‐step approach of velocity or acceleration encoding is highly efficient in terms of the signal‐to‐noise ratio per unit time. This work describes a multidimensional extension of this method for simultaneously measuring multiple components of velocity and acceleration with a few encoding steps. N flow dimensions were encoded with an ND‐matrix, obtained by combining the various flow‐encoding gradients. The small matrix obtained with as few as two encoding steps can be extended by zero‐filling in all N dimensions and using ND‐Fourier transformation to obtain the maximum of the resulting peak in the ND‐matrix, which gives simultaneously all the components of velocity and/or acceleration. The processing time was shortened by using a method of phase computation that gives the same precision as Fourier transformation, but is much faster. A rotating disk was used to show that the velocity‐to‐noise ratio increases with the number of dimensions acquired, demonstrating the efficiency of multidimensional flow measurements. The feasibility of the method is illustrated by 3D maps of the myocardium velocity, and 2D measurement of velocity and acceleration in the ascending aorta—both obtained by multidimensional phase encoding in volunteers. Magn Reson Med 44:723–730, 2000.

Precision of magnetic resonance velocity and acceleration measurements: Theoretical issues and phantom experiments

Magnetic resonance (MR) sequences have been developed for acquiring multiple components of velocity and/or acceleration in a reasonable time and with a single acquisition. They have many parameters that influence the precision of measurements: NS, the number of flow‐encoding steps; NEX, the number of signal accumulations; and ND, the number of dimensions. Our aims were to establish a general relationship revealing the precision of these measurements as a function of NS, ND, and NEX and to validate it by experiments using phantoms. Previous work on precision has been restricted to two‐step (NS = 2) or 1D (ND = 1) MR velocity measurements. We describe a comprehensive approach that encompasses both multistep and multidimensional strategies. Our theoretical formula gives the precision of velocity and acceleration measurements. It was validated experimentally with measurements on a rotating disk phantom. This phantom was much easier to handle than fluid‐based phantoms. It could be used to assess both velocity and acceleration sequences and provided accurate and precise assessments over a wide, adjustable range of values within a single experiment. Increasing each of the three parameters, NS, ND, and NEX, improves the precision but makes the acquisition time longer. However, if only one parameter is to be assessed, maximizing the number of steps (NS) is the most efficient way of improving the precision of measurements; if several parameters are of interest, they should be measured simultaneously. By contrast, increasing the number of signals accumulated (NEX) is the least efficient strategy. J. Magn. Reson. Imaging 2001;13:445–451.

From flow to pressure: estimation of pressure gradient and derivative by MR acceleration mapping

A non-invasive method for estimating deep pressures would be of great value in tile clinical management of cardiovascular disease because of the cost and risk associated with invasive methods of measuring blood pressure [1]. The velocity derivatives versus time and space are solutions of the Navier-Stokes equation, assuming that the flowing medium is a Newtonian fluid. MR velocity imaging has been used by many authors to estimate small pressure gradients in steady [2] and pulsatile [3] laminar flow. However, these authors used the velocity derivative versus time, which does not take into account the geometrical term of acceleration and, furthermore, considerably increases noise. We previously proposed and validated a method for measuring the total acceleration using MR Fourier encoding [4]. We present here two methods to compute respectively space and time derivatives of the pressure from MR acceleration maps.

Estimation of left ventricular performance through temporal pressure variations measured by MR velocity and acceleration mappings

To describe a method for assessing pressure variation vs. time (dp/dt) using blood flow acceleration measured by MRI, and to demonstrate its applicability in estimating left ventricular (LV) function.

Impact of the global outflow angle on recanalization after endovascular treatment of middle cerebral artery bifurcation aneurysms

Background and purpose Intracranial aneurysm recanalization after endovascular treatment (EVT) remains a major problem. The goal of this study was to find new predictive factors of recanalization after EVT of middle cerebral artery (MCA) bifurcation aneurysms. Methods 96 MCA bifurcationaneurysms, ruptured or unruptured, treated by EVT between Septembre 2009 and December 2014, were retrospectively included. Clinical parameters and aneurysm characteristics were recorded. From the initial three-dimensional DSA, spatial coordinates found on parent and daughter arteries of MCA bifurcations gave four different flow angle values; inflow, outflows 1 and 2, and the global outflow angle (the sum of the two outflow angles). Inter- and intra-observer reproducibilities of three-dimensional angle value measurements were performed. Results Recanalization occurred in 25 cases (26%) and retreatment was performed in 11 cases (11%). Only 1 patient (1%) had rebleeding. Univariate analysis established the following as predictive factors of recanalization: high blood pressure (P=0.014), aneurysm height (P<0.001), aneurysm width (P<0.001), neck size (P<0.001), postoperative occlusion class (P=0.040), percentage of packing volume (P<0.001), as well as the two outflow angles (P=0.006 and 0.045), and the global outflow angle (P<0.001). Multivariate analysis revealed two independent risk factors for recanalization: the global outflow angle (OR=1.05; 95% CI 1.02 to 1.08; P<0.002) and aneurysm width (OR=0.67; 95% CI 0.46 to 0.96; P=0.031). A global outflow angle threshold <192° was found to be a risk factor for recanalization (OR=13.75; 95% CI 4.46 to 42.44), with a sensitivity of 80% and specificity of 77%. Conclusions This study emphasizes that a new parameter, the global outflow angle, can be predictive of recanalization for MCA bifurcation aneurysms treated by EVT.

LBA-001Efficacy, tolerability and impact on quality of life of selective internal radiation therapy (with yttrium-90 resin microspheres) or sorafenib in patients with locally advanced hepatocellular carcinoma: The SARAH trial

Bouattour Mohamed, Assenat Eric, Guiu Boris, Ilonca Alina Diana, Pageaux Georges-Philippe, Sibert Annie, Lebtahi Rachida, Allaham Wassim, Barraud Hélène, Laurent Valérie, Mathias Elodie, Bronowicki Jean-Pierre , Tasu Jean-Pierre, Perdrisot Rémy, Silvain Christine, Gerolami René, Mundler Olivier , Seitz Jean-Francois, Vidal Vincent, Aubé Christophe, Oberti Frédéric, Couturier Olivier, Brenot-Rossi Isabelle, Raoul Jean-Luc, Sarran Anthony, Costentin Charlotte, Itti Emmanuel, Luciani Alain, Adam René, Lewin Maı̈té, Samuel Didier, Ronot Maxime , Dinut Aurelia, Pereira Helena, Castera Laurent, Chatellier Gilles, Vilgrain Valérie, and the SARAH Trial Group Assistance Publique Hôpitaux de Paris, Hôpitaux Universitaires Paris Nord Val de Seine, Hôpital Beaujon, Clichy, France, Centre Hospitalier Universitaire de Montpellier, Hôpital Saint Eloi, Montpellier, France, Centre Hospitalier Universitaire de Montpellier, Hôpital Gui de Chauliac, Montpellier, France, Centre Hospitalier Universitaire de Nancy, Hôpital de Brabois, Vandoeuvre-lès-Nancy, France, Centre Hospitalier Universitaire de Poitiers, Poitiers, France, Assistance Publique Hôpitaux de Marseille, Hôpital de la Timone, Marseille, France, Université de la Méditerranée, Marseille, France, Université Aix-Marseille, Marseille, France, Centre Hospitalier Universitaire d’Angers, Angers, France, Institut Paoli Calmettes, Marseille, France, Assistance Publique Hôpitaux de Paris, Hôpital Henri Mondor, Créteil, France, Université Paris Est Créteil, Faculté de Médecine, Créteil, France, INSERM IMRB U955 Equipe 18, Créteil, France, Assistance Publique Hôpitaux de Paris, Hôpital Paul Brousse, Villejuif, France, Assistance Publique Hôpitaux de Paris, Hôpital Européen Georges-Pompidou, Unité de Recherche Clinique, Paris, France, INSERM, Centre d’Investigation Clinique 1418 (CIC1418), Paris, France, Université Paris Diderot, Sorbonne Paris Cité, Faculté de Médecine, Paris, France, INSERM U1149, Centre de Recherche de l’Inflammation (CRI), Paris, France, Université Paris-Descartes, Sorbonne Paris Cité, Faculté de Médecine, Paris, France