[Dose reduction during CT coronary angiography]. / La réduction de dose en coroscanographie.

Dose delivery during CT coronary angiography with retrospective ECG gating is high especially due to the important slice overlapping. Optimization of the acquisition parameters is necessary to reduce patient exposure. First, the height of the scan field should be limited to the heart. Both kV and mA should be adjusted based on patient morphology. ECG gated exposure modulation with mA reduction during systole, a technique most applicable for patients with slow and regular heart rate, can result in a dose reduction up to 50%. The use of prospective ECG gating can also reduce patient dose. This technique also requires patients with slow and regular heart rate.

Influence of kinetic parameters of high pressure processing on bacterial inactivation in a buffer system.

High pressure processing is recently applied in the food industry to inactivate spoilage and pathogenic microorganisms. Bacterial cells exhibit various barosensibility, and the role of pressurization, depressurization and constant pressure stage remain unknown. We investigated the effect of high pressure processing on Salmonella typhimurium and Listeria monocytogenes cells at 400 and 500 MPa respectively in buffer pH 7 at 20 degrees C. We applied various pressurization/depressurization kinetic rates (1, 5 and 10 MPa/s for pressurization and 250, 20 and 5 MPa/s for depressurization), and various pulse series or pressure holding times. Results show that high pressure pulses reduced linearly the number of bacterial cells according to the product of pressure and time: we defined this product as a Barometric Power (BP). Reduction of both microorganisms increased when holding time increased from 5 to 20 min, and better results were obtained when the rate of pressurization and depressurization were increased.

[Acute coronary syndromes and myocardial perfusion. Cardiac magnetic resonance imaging and ultrafast CT]. / Syndromes coronaires aigus et perfusion myocardique. Les acquis de l'IRM cardiaque, les perspectives du scanner multibarrettes.

Imaging myocardial perfusion is essential in the management of acute coronary syndromes without ST elevation (ACS ST-) confirming the diagnosis of coronary lesions and quantifying the myocardial ischaemia, an important factor in the stratification of coronary risk. In ACS ST-, perfusion imaging allows evaluation of myocardial viability, diagnosis of residual ischaemia and also the detection of no-reflow phenomena after reperfusion procedures. Although myocardial scintigraphy is the reference method in clinical practice, it has many limitations such as its spatial resolution, its irradiation, its attenuation artefacts, and also the fact that it does not visualise the coronary arteries. This has led to the rapid development of two new non-invasive imaging techniques: cardiac MRI and ultrafast CT. The major advantage of MRI is the possibility of associating analysis of myocardial perfusion with that of cardiac muscle function by investigating right and left ventricular function at rest and during myocardial ischaemia stress tests and by analysis of myocardial viability. More recently, ultrafast CT has been clinically validated for coronary imaging. However, analysis of myocardial perfusion and ventricular function by CT scan is still only at the research stage.

[Intra-aortic balloon pumping and variations in flow in the dilated coronary artery in acute myocardial infarction]. / Contrepulsion intra-aortique et variation du flux de l'artère coronaire dilatée à la phase aiguë de l'infarctus du myocarde.

The object of this study of acute anterior myocardial infarction uncomplicated by cardiogenic shock, a context in which the role of intra-aortic balloon pumping (IABP) remains controversial, was to analyse the effects of IABP on coronary flow in the culprit artery. Twenty-one patients admitted for angioplasty in the acute phase of anterior myocardial infarction were included. The IABP was performed in 6 patients (Group 1) because of clinical signs of cardiac failure. Fifteen patients (Group 2) had no signs of cardiac failure. Coronary flow velocity was recorded by a Doppler catheter after successful angioplasty. The following parameters were analysed: average peak velocity (APV), average diastolic peak velocity (ADPV), average systolic peak velocity (ASPV), diastolic to systolic velocity ratio (DSVR) and maximum peak velocity (MPV). Intra-aortic balloon pumping was associated with an increase in the diastolic indices (APV 17.9 +/- 3.5 vs 14.9 +/- 3.6 cm/s; p < 0.05; ADPV 27.6 +/- 5.2 vs 19.7 +/- 4.7 cm/s; p < 0.05), and a decrease in the systolic index ASVP (3.8 +/- 1.3 vs 7.6 +/- 2.6 cm/s; p < 0.05). The diastolic indices recorded with IABP did not change in Group 2. The velocity spectra changed with the appearance of abnormalities usually described in the presence of microcirculatory abnormalities ("no reflex" phenomenon): decrease in anterograde systolic flow, rapid deceleration of diastolic velocities with appearance of a retrograde systolic flow. The authors conclude that IABP increases diastolic velocities of coronary flow in the acute phase of revascularised anterior myocardial infarction complicated by left ventricular failure but does not seem to be accompanied by improved myocardial perfusion.

[Loffler's fibroblastic endocarditis. A report of a case complicating toxocarosis]. / Endocardite fibroblastique de Löffler. A propos d'un cas compliquant une toxocarose.

The authors report a case of Löffler's fibroblastic endocarditis complicating a toxocarosis infection. Parasitic infestation with toxocara canis is usually asymptomatic, but this was a very rare observation of cerebral involvement associated with symptomatic Löffler's endocarditis. This is an unusual form of restrictive cardiac disease constantly accompanied by prolonged hypereosinophilia. In addition to the classical signs of cardiac failure, an acute febrile illness imitating a connective tissue disease may be observed. Echocardiography helps diagnosis by showing endomyocardial fibrosis and adherent thrombosis at one or both ventricular apices. The management of cardiac failure should include, whenever possible, radical treatment of the hypereosinophilia. At an advanced stage, surgical endocardial decortication is the only means of improving symptoms and the prognosis of these patients.

[MRI quantification of regional variations of left ventricular parietal stress in normal subjects]. / Quantification par imagerie par résonance magnétique des variations régionales de la contrainte pariétale du ventricule gauche chez le sujet normal.

The object of this study was to analyse regional variations in end systolic left ventricular wall stress in normal subjects using three-dimensional magnetic resonance imaging (MRI) with excellent spatial resolution. Eight to 12 contiguous short axis sections of the left ventricle were acquired from the apex to the base in apnoea with a rapid echo-gradient sequence in 15 healthy volunteers. The end systolic wall stress was calculated by three methods: Grossman's formula (CR) using the wall thickness and radius of curvature, Janz's formula (CS) using the surfaces, and a three-dimensional approach (C3D) providing a precise calculation of the radius of curvature. The values of wall stress obtained by CS and CR were lower (p < 0.001) at the apex (3.2 and 3.3 10(3) newton/m2 respectively) than at the base (6.9 and 7.1 10(3) newton/m2). There was no difference between the base and apex with the C3D method (8.0 and 9.0 10(3) newton/m2 respectively, NS). The same results were observed at the inferior, lateral, anterior and septal segments with an increase at the base using the CS and CR formulae, the C3D remaining homogeneous in the left ventricle except for the interventricular septum. The lateral wall stress was significantly lower with respect to the interventricular septum in all sections from the apex to the base, irrespective of the method of calculation used. The differences in regional wall stress from the base to the apex reported in healthy subjects seem to be related to an underestimation of left ventricular wall thickness and an underestimation of the radius of curvature rather than to a physiological phenomenon.

Regional assessment of wall curvature and wall stress in left ventricle with magnetic resonance imaging.

Left ventricular functional abnormalities are associated with regional increases of wall stress and modifications of wall curvature. This study describes the integration of the short-axis and long-axis wall curvatures for determining peak systolic wall stress. Quantification was realized with cine magnetic resonance imaging (MRI) from the location of the endocardial and epicardial borders of the left ventricle on pairs of consecutive short-axis sections. Fifteen normal volunteers were subjected to cine MRI, and different methods of calculating peak systolic wall stress were compared. A short-axis analysis showed a 55 +/- 13% increase of the circumferential mean of the peak systolic wall stress between apical and basal sections. Regarding the curvature, no significant increase of wall stress was observed except on the septal wall (31 +/- 18%). Short-axis studies proved to be insufficient for determining the regional variations of left ventricular wall stress and for providing normal reference values for the location of abnormal regions in patients.

Global left ventricular cardiac function: comparison between magnetic resonance imaging, radionuclide angiography, and contrast angiography.

RATIONALE AND OBJECTIVES: Cardiac magnetic resonance imaging (MRI) has been shown to be a robust and noninvasive method to assess left ventricular (LV) cardiac function. This study sought to assess volumes and mass calculated with MRI using fast techniques for acquisition and postprocessing, and to compare results in terms of cost-effectiveness with those of radionuclide angiography (RNA) or contrast angiography (CA). METHODS: Thirty-five patients and 15 healthy volunteers were studied. All patients underwent an MRI examination during the same period that they underwent ventriculography (26 patients) or radiography (25 patients). From 7 to 11 short-axis slices were acquired with a breath-hold fast-gradient echo-segmented sequence from apex to base. Contours were drawn with an automated border detection software. RESULTS: Ejection fraction (EF) correlated well between modalities (r = 0.77, P<0.001, for MRI and RNA; r = 0.72, P< 0.001, for MRI and CA). CONCLUSIONS: Cardiac MRI is a fast and accurate technique for estimation of LV volumes, EF, and mass.

The self catalytic enzyme inactivation induced by solvent stirring: a new example of protein conformational change induction.

This article gives a new example of the protein conformational change induction. A well known example widely described in the literature is the prion, a protein whose the pathologic form, PrPsc, induces a conformational change of the normal form, PrPc, by interaction with it. This work highlights the existence of a self-catalytic conformation change for lysozyme. The functional modification of this protein is analysed in terms of irreversible loss of activity. Our experiments and the kinetic model derived from our results show that lysozyme inactivation is catalyzed by the inactivated lysozyme molecules; the lysozyme molecules with modified conformation induce a conformational change of native lysozyme molecules that in turn become inactive. This phenomenon is enhanced by stirring, which increases the probability and the efficiency of collisions between enzyme molecules. Furthermore, the self-catalytic inactivation kinetics of lysozyme is increased when salts are dissolved in the enzyme solution. Under these conditions, the protective effect due to the addition of salts, reported in previous literature, disappear. Salt-induced lysozyme destabilization effect can be observed. The salts enhance the aggregation of inactive enzyme molecules. A kinetic model of self catalytic inactivation of the enzyme has been developed, taking into account the results obtained with and without the addition of salts in aqueous solution.