Jean-Louis Barat

A validation of a flow quantification by MR phase mapping software

AIM We evaluated a Siemens software of flow quantification (FQ) by MR phase mapping, in the framework of a common practical use. METHODS Experiments with a laminar flow phantom and in vivo pulsatile flow were performed. In particular, FQ in ascending aorta was investigated in healthy volunteers. RESULTS AND CONCLUSION Flow phantom experiments reveal that the FQ slightly underestimates (8% on the average) actual velocities (mean velocities over a vessel area), and also that velocity uncertainties are related to the encoding velocity value, whatever the measured velocity. Furthermore, using well characterized working criteria, we found low intraobserver variability and negligible interobserver variability in ascending aorta FQs. The role played by the choice of reference area in FQ accuracy is emphasized. When recording several cardiac cycles during the same acquisition, it is shown that the FQ software may provide erroneous results. Several comments for FQ software use in the ascending aorta are added.

Assessment of brain natriuretic peptide in patients with suspected heart failure: comparison with radionuclide ventriculography data

BACKGROUND The aim of the study was to prospectively evaluate patients with suspected or known heart disease using plasma brain natriuretic peptide (BNP) measurement and radionuclide ventriculography to examine whether left ventricular dysfunction is associated with an abnormal rise of BNP concentration. METHODS Patients (n=153) and controls (n=14) underwent radionuclide ventriculography to determine Left ventricular Ejection Fraction (LVEF) and measurement of plasma BNP concentration using a commercial kit. RESULTS Plasma BNP concentration in controls was significantly lower than that in patients whatever the stage of the disease, significantly lower than that of patients with normal LVEF (LVEF>55%); than that of patients with altered LVEF (LVEF< or =40%); and than that of patients with moderately reduced LVEF (40%<LVEF< or =5%). Comparisons between groups of patients showed that the more severe the disease, the higher the BNP level. From the ROC curve, a plasma BNP concentration of 52 pg/ml was attached to a 85% sensitivity and 82% specificity in identifying patients with LVEF< or =40%. CONCLUSIONS Plasma BNP concentration provides a reliable and sensitive marker of LV systolic dysfunction evaluated by a nuclear medicine technique, and could be a potential screening test to identify patients for additional investigations.

Characterisation, cloning and sequencing of a conformation-dependent monoclonal antibody to the α IIb β 3 integrin: interest for use in thrombus detection

The detection of newly formed thrombi is of primary importance in clinical medicine. The activated platelet is a potential target for the localization of thrombotic lesions in arteries. The integrin f IIb g 3 membrane changes conformation upon activation. A novel anti- f IIb g 3 monoclonal antibody (MAb), XIIF9, is described which recognizes an epitope whose expression was enhanced by activation. Radioiodinated XIIF9 bound to a single class of sites on the g 3 subunit, with 13600 - 2000 molecules bound per unstimulated platelet and a K d of 34.5 nM. Platelets stimulated with 0.5 U/ml of thrombin bound 66000 - 4000 molecules/cell ( K d = 51.6 nM). Moreover, XIIF9 binding to unstimulated platelets could be increased 4-fold by treatment of the f IIb g 3 complex with 5 mM EDTA. Thus, XIIF9 recognized an epitope on the g 3 subunit whose accessibility was increased upon thrombin activation or EDTA treatment. Sequence analysis of the gene segment encoding the XIIF9 heavy chain revealed interesting motifs shared with cyclic CX6-7C anti- f IIb g 3 peptides or with AC7, a published MAb specific for activated f IIb g 3 . In vivo experiments in atherosclerotic rabbits followed by immunohistological analysis, revealed a specific binding of XIIF9 on platelets engaged in thrombus formation, demonstrating real clinical potential for such MAbs in imaging.

A human monoclonal antibody obtained from EBV‐transformed B cells with specificity for myosin

Summary. We describe the preparation of a stable human lymphoblastoid cell line obtained during ex vivo studies in which peripheral blood lymphocytes of a Glanzmanns thrombasthenia patient were transformed with Epstein‐Barr virus. Somatic hybrids secreted an IgM monoclonal antibody (B7) that reacted with the myosin heavy chain of human platelets by immunoblotting. Flow cytometry showed that B7 barely recognized unstimulated intact platelets, but bound abundantly after permeabilization of fixed cells with Triton X‐100. The reactivity of the antibody on thin sections of human myocardium and aorta was studied by immunohistochemistry. B7 specifically stained myosin of myocytes, but there was no labelling of aortic smooth muscle cells. The epitope was conserved in cardiac or skeletal myosin prepared from pig or rabbit. Measurement of the dissociation constant in a competitive ELISA showed that B7 bound with high affinity (10−8 M). Purified Fab fragments retained their ability to bind to myosin, suggesting that B7 may be useful in the imaging of myocardial necrosis after myocardial infarction, myocarditis, cardiac drug toxicosis or graft rejection. This work also shows that EBV transformation of B cells may uncover naturally occurring autoantibodies which under normal circumstances are inhibited by the immune surveillance system.

Feasibility of endocardial edge detection by using an inversion recovery artifact.

An inversion recovery (IR) artifact was used to delineate the blood/wall boundary in left ventricles. The artifact consisted of a hypointensity signal in pixels located at the boundary of two contiguous tissues with different T1 relaxation times. The feasibility of measuring the ejection fraction using the artifact was tested in ten healthy volunteers, with two IR snapshot‐FLASH sequences possessing different times of repetition (TR = 11msec and TR = 3.5msec) and appropriate times of inversion. The comparison with a cine‐MRI sequence showed that ejection fraction measurements are feasible when performed with a snapshot‐FLASH sequence that has a sufficiently short TR (3.5msec). J. Magn. Reson. Imaging 2001;13:461–466.

Automatic outlining of the left ventricular cavity in magnetic resonance imaging. Comparison with manual outlining

The purpose of this work was to build an automatic outlining algorithm of the left ventricular cavity. This algorithm is based on Mathematical Morphology. The main tool of segmentation is nammed Watersheds and Geodesic Reconstruction algorithms. For this study, we Implemented an uptodate version of the algorithm by means of Hiearchic FIFO. On the native magnetic resonance image, we studied the reproducibility of human manual tracking. We obtained correct automatic outlines of the left ventricule for 21 prospectively examined subjects. This study demonstrates the advantage of an automatic approach according to the important variability in manual tracing and to the big number of images to study.