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J Chambron

Publications and source records attributed to J Chambron.

At least 37 records · Page 2Linked to original sources
PubMed1993

Oxygen imaging in perfused hearts by dynamic nuclear polarization.

The feasibility of localized oximetry by dynamic nuclear polarization (DNP) imaging is demonstrated on perfused sheep hearts. DNPI is a magnetic, double resonance technique, in which the electron paramagnetic resonance (EPR) of a free radical dissolved in a perfusion medium is saturated, while the nuclear magnetic resonance (NMR) of water protons is used to perform conventional NMR imaging. The presence of oxygen reduces the enhancement of the NMR signal induced by DNP. The oxygen content of sheep heart tissues was detected by the subtraction of the DNP image of the heart, perfused with a nitrogen-equilibrated solution, from an image obtained when the heart was perfused with an oxygen-equilibrated solution. This result was obtained with extreme oxygen partial pressure, and the discussion presents physical and chemical means for improving the DNP imaging method. Physical means include field cycling, electron paramagnetic rotary saturation, and the use of a 180 degrees NMR pulse before EPR irradiation. The chemical means discussed are deuterium substitution in nitroxides and the potential use of solid, free radical probes. It is suggested to use the perfused heart model for comparing the numerous methods available to measure the oxygen content of tissues.

Animals↗
PubMed1993

An evaluation of the significance of areas of intense signal in the MR brain images of patients with multiple sclerosis.

This study evaluates the distribution of areas of intense signal (AIS) in 189 patients with multiple sclerosis (MS) and 83 patients presenting high-risk factors of cerebrovascular injuries. Two multivariate statistical analyses (multifactorial discriminant analysis and logistic regression analysis) with two AIS scores and several subpopulations of patients (according to age and/or the number of AIS) were tested. The results of these analyses were expressed with the usual screening test. The results obtained in this study even without the help of any clinical information are very promising, since they established that the specificity of MRI could be improved by using the distribution of the AIS in the various anatomical areas as a criterion. Five regions of the brain display were particularly significant in the discrimination between MS and non-MS patients: In decreasing order we found that the temporal, occipital, brain stem, and parietal regions were more specific with respect to the diagnosis of MS, while only the basal ganglia could account for non-MS patients. With multifactorial discriminant analysis and logistic regression analysis respectively, 78.9 (+/- 2.8)% and 85.1 (+/- 2.8)% of the patients were correctly classified by MRI. The results obtained on the main group were confirmed by a predictive test carried out on an other population of 40 patients, which produced similar results. The comparison between our method and Fazekas's imaging criteria showed a 20% improvement in favour of our approach and it is hoped that it will contribute to make the most of MRI as a tool for the diagnosis of MS.

Adolescent↗
PubMed1993

Quantitative cerebral magnetic resonance imaging during ACTH treatment of multiple sclerosis.

Serial MR scans were performed with the 2DFT imaging method and the filtered backprojection imaging method on 12 patients with multiple sclerosis in acute phase, 4 in a relapsing/remitting form, and 8 in a progressive form, before, during and after ACTH treatment. Both T1 and T2mono relaxation times, obtained by fitting transverse magnetization decay curves with a monoexponential function within the apparently normal white matter and the areas of increased signal, were measured. With the backprojection method it was possible to fit the transverse magnetization decay curve with a biexponential function and obtain T2long and T2short relaxation times. The T2mono and T1 relaxation times of the apparently normal white matter were significantly different from those obtained for volunteers, but no significant differences were found before, during, or after treatment. The transverse magnetization decay curves of the areas of increased signal were better fitted by a biexponential function. No significant changes in these relaxation times were observed after ACTH treatment. These results argue against an anti-oedematous action of ACTH and may suggest that it has an immunosuppressant effect.

Adrenocorticotropic Hormone↗
PubMed1993

Blood-brain barrier breakdown in MBP-specific T cell induced experimental allergic encephalomyelitis. A quantitative in vivo MRI study.

Blood--brain barrier permeability in myelin basic protein (MBP)-specific T cell induced experimental allergic encephalomyelitis (EAE) was studied by magnetic resonance imaging (MRI) in Lewis rats. Myelin basic protein-specific T cells of different specificity and/or purified protein derivative (PPD)-specific T cells were used. During the course of EAE, the volume of the lesions and the T1 and T2 relaxation times were recorded and evaluated with respect to the clinical signs. The results showed that the severity of abnormalities seen on MRI, corresponding to the blood--brain barrier breakdown and cerebral oedema depended on the following two factors: (i) the specificity of the MBP-specific T cells used; (ii) the number of MBP-specific T cells transferred. It was also shown that the more specific the cells were, the less severe the cerebral blood--brain barrier rupture. Moreover, the blood--brain barrier breakdown increased when the number of cells increased. Our results demonstrated that a synergy exists between MBP and PPD-specific T cells which seems to result in an increase in central nervous system inflammation. This helps to explain the role of Mycobacterium tuberculosis in the induction of EAE.

Animals↗
PubMed1993

[Evaluation of sensitivity of an assay: application to a third-generation thyrotropin (TSH) assay].

The concentration-specific smallest detectable difference (D) between two concentrations (i.e., the sensitivity) was determined from the results of within-run and run-to-run reproducibility studies of a third-generation thyrotropin assay. Only low concentrations were considered (range 0-0.3 m U/l). Assays were performed in singlet or in duplicate. Findings confirmed the value of the assay: the analytic detection limit approximated 0.005 mU/l and the functional detection limit was around 0.01 mU/l. Expressed as a percentage of the concentration, D% was under 20% for levels of less than 0.02 mU/l in within-run studies or of less than 0.03 mU/l in run-to-run studies. With concentrations in excess of 0.05 mU/l, D% was under 10% in within-run studies and slightly above 10% in run-to-run studies. These new detection thresholds for this assay should be taken into account when interpreting clinical results from a single run (TRH test) or from several runs (hormone replacement therapy or suppression test).

Humans↗
PubMed1993

[Free triiodothyronine assays using labeled antibody: evaluation and comparison with an analog labeled assay].

We evaluated analytically and clinically two new one-step labelled antibody assays for measuring free triiodothyronine (FT3): the first, radiolabelled with 125I, Amerlex-MAB (MAB) from Kodak Diagnostic, and the second, labelled with peroxidase, Enzymun-test FT3 (BM) from Boehringer Mannheim adapted for the Boehringer ES 600 analyser. The clinical results were compared with those obtained with a radiolabelled analog tracer kit, Amerlex-M (M) from Kodak Diagnostic. The latter kit is known to give low FT3 results in sera with low albumin concentrations. Analytical performances of the automated method (BM) were better than those obtained with the manual method (MAB): intra-assay reproducibility (CV < 3% vs CV about 5%), inter-assay reproducibility (CV < 4% vs CV between 4 and 8%) and mean drift (+1.25% vs -4.3%). The detection limit was low for both kits (< 1 pmol/l). In the euthyroid reference group (n = 98) we observed a significant difference between outpatient and hospitalized patient FT3 concentrations as measured with the M kit only. The reference range was 3.2-6.5 pmol/l for the MAB kit vs 5.4-9.2 pmol/l for the BM kit. This result underlines the problem of standardisation with the FT3 assays. Clinical sensitivity for hyperthyroidism (n = 38) was better for the MAB (92%) than for the BM kit (76%). Specificity in euthyroid L-thyroxine (T4) treated patients (n = 26) was good for both kits (MAB: 92%; BM: 88%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

[Dynamic cartography of flow patterns by cine-MRI. Presentation of the technique and preliminary results for major vessels].

The authors report the principles, experimental evaluation and clinical approach of a method for dynamic imaging of flow patterns by NMRI, based upon the phase modulation technique. The imaging method is based upon gradient echo, functioning in "cine" and "flow compensated" mode. Modifications in this sequence enable attribution to the moving spins phase of a value which is considered to be proportional to the flow rate. A map of rates is then obtained from the phase image. Calibration of this sequence in vitro has shown excellent correlations between flow rate and the phase information thus obtained: r always > 0.98 for rates up to m/s. The first results obtained in vivo for the thoracic and abdominal aorta, in 11 control subjects, show that the technique is suitable for the study of pulsatile blood flow, providing very detailed information concerning the spatial distribution of flow rates. Mean flow in the suprarenal abdominal aorta (4.6 +/- 1.6 l/min) is 32% greater than that in the inferior vena cava (3.1 +/- 1 l/min), corresponding to an estimation of portal vein flow of 1.5 l/min. Practical limitations related to the use of a resistive magnet are nevertheless stressed and the authors list the technical aspects necessary for the better clinical utilisation of this non-invasive flowmetric technique. A review of the current literature forms the basis for an assessment of the potential importance of dynamic and quantitative NMRI of flow patterns in the cardiovascular area.

Aorta↗
PubMed1992

In vivo dynamic MR imaging of MBP-induced acute experimental allergic encephalomyelitis in Lewis rat.

A dynamic in vivo study by MRI consisting of the measurement of relaxation times and in the visualization of the BBB permeability by Gd-DOTA was performed in an MBP-induced acute EAE model of Lewis rat. Fourteen rats were immunized with an MBP/CFA mixture, eight by CFA alone, and three control rats were used to test the harmless effect of repeatedly performed MRI examinations. Beginning on the 8th or 9th days and in parallel with the emergence of clinical signs, rats immunized by the MBP/CFA mixture showed slight increases of relaxation times and of the BBB permeability. These abnormalities, which always remain localized in the periventricular regions, become more pronounced toward the 10th and 11th days, just before (or at the same time) as paraplegia manifestations. After a plateau of a few days, they diminish with the clinical signs. This close correlation found in vivo establishes the essential role of BBB in the pathogenesis of clinical signs of this EAE model.

Animals↗
PubMed1992

Viscosity of water in hibernating and nonhibernating mammals estimated by proton NMR relaxation times.

Longitudinal (T1) and transverse (T2) nuclear magnetic resonance relaxation times were measured in vitro at 37, 30, 25, 15, and 5 degrees C on serum, brain, liver, kidney, and heart samples from a hibernator, the European hamster, active in summer (SA), active in winter, or in the hibernating state in winter; from a less efficient hibernator, the golden hamster; and from a homeotherm, the rat. T1 and T2 relaxation times varied between species and in the European hamster between the active and hibernating subjects. Despite the major relaxation time differences between the organs, NMR relaxation time measurements showed a general trend to an increase in the viscosity of water for the European hamster in the active state. Although these modifications were not directly related to the process of hibernation itself, the relaxation times observed in the hibernating animals were closer to those seen in the rat. This evidenced that changes of physical properties of water reflect a better adaptation to low temperatures of the hamster, as compared to the nonhibernator, given that the low water viscosity of SA hamster allows the decrease of the viscosity with temperature during the hibernating state. These in vitro studies permit the study the viscosity which is an important physicochemical parameter involved in NMR longitudinal relaxation time of water proton. More detailed studies of other physiological parameters must be undertaken by further in vivo measurements.

Animals↗
PubMed1992

Photoacoustic detection of triplet state and singlet oxygen in highly absorbing samples.

A photoacoustic (PA) effect theory taking into account two heat sources corresponding to the radiationless relaxation processes of two states of different lifetimes and to the heat diffusion across the sample is herewith presented. Results obtained demonstrate that the amplitude and the phase of the PA signal depend on the sample's thermal properties, on its optical absorption coefficient, on the lifetime of the long-lived excited state, and on the ratio of the two heat sources. This ratio can be expressed as a function of the product of the energy of the excited state times the quantum yield of its production. Simulations of PA amplitude and phase variations vs light modulation frequency exhibit new features of the PA signal:phase inversion and fast decrease of the amplitude. Experimental verifications were carried out on solutions and gels. Fitting of the amplitude and phase variations allow us to measure the lifetime and conversion yield of the intermediate state which can be a triplet state or singlet oxygen, O2(1 delta g). The addition of an acceptor, specific to O2(1 delta g), induces changes in the amplitude of the PA signal which can be used to study the production and deactivation of this excited form of oxygen. This work demonstrates the usefulness of PA in the detection of metastable excited states such as the triplet state and singlet oxygen and in their quantitative analysis.

Coloring Agents↗
PubMed1991

Nuclear magnetic resonance T2 relaxation times in multiple sclerosis.

An original method was used to carry out the mathematical analysis of T2 transverse magnetization decay curves and the measure of T2 relaxation times on multiple sclerosis (MS) patients. The presumably normal white matter (WM) of these patients presented higher T2 relaxation times (98.6 msec), in comparison with that found in a population sample (88 msec). In this case, magnetization decay curves remain mostly monoexponential and are characterized by a single T2. On the other hand, areas of increased signal (AIS) curves are always better fitted by a biexponential function characterized by a short (82 msec) and a long (greater than 200 msec) T2. The spreading out of long T2 varies from one AIS to another in the same patient and among different patients; values of long T2 also vary with time, but without any correlation with the clinical state. In fact, no correlation was been established between relaxation times and clinical parameters. Quantitative MRI therefore enables a different approach to interpret MRI images; results suggest that several histobiochemical parameters play a role in the pathogenesis of an AIS and that MS is a dynamic and constantly evolving disease.

Adult↗
PubMed1991

In vivo determination of multiexponential T2 relaxation in the brain of patients with multiple sclerosis.

In vivo measurement of T2 relaxation times in multiple sclerosis (MS) lesions by magnetic resonance imaging (MRI) is potentially useful for the evaluation of the disease activity. Seven patients with definite MS were investigated over a period of three years (19 examinations), using a whole-body MRI scanner operating at 0.15 T with a specially designed high-power radio-frequency head coil. A modified CPMG sequence with a 180 degree pulse interval of TE = 6 msec and 128 echoes was used for the T2 relaxation measurement of the areas of increased signal (AIS) and white matter (WM). A biexponential T2 analysis of each pixel of the spin-echo images was computed. The T2 relaxation processes were found to be a monoexponential function in WM. The T2 relaxation times of apparently normal white matter in MS patients was significantly longer than in control subjects. The T2 relaxation curves of the AIS were found in most cases to fit a biexponential function characterized by a short and a long T2. T2 long relaxation times of AIS were spread out over a wide range (150-560 msec). The study of T2 long histograms shows that some AIS can be divided into two or three parts depending on the T2 long values. Each of these parts may correspond to a pathological process such as edema, demyelination and gliosis. Evolution of T2 relaxation times over a period of time cannot as yet be correlated with modifications in the clinical state.

Adult↗
PubMed1991

Left ventricular ejection fraction in obstructive sleep apnea. Effects of long-term treatment with nasal continuous positive airway pressure.

The effects of treatment with nasal continuous positive airway pressure (CPAP) on left ventricular ejection fraction (LVEF) were assessed in 29 patients with obstructive sleep apnea (OSA) in a prospective study using multiple gated equilibrium radionuclide angiocardiography. All patients were evaluated before CPAP treatment was initiated and were reevaluated after one year (mean +/- SE, 415 +/- 6 days), of home treatment with nasal CPAP. The mean LVEF increased from 59 +/- 1 percent to 63 +/- 1 percent (p less than 0.005). The degree of improvement in LVEF was correlated with baseline LVEF (r = 0.54; p less than 0.003), meaning that the lower the baseline value, the greater the increase with treatment. The changes were not different when subgroups of medicated and unmedicated patients were considered separately. These results show that long-term nasal CPAP treatment results in improved left ventricular function in OSA.

Evaluation Studies as Topic↗
PubMed1990

Analytical and clinical evaluation of a new one-step non-analogue radioimmunoassay for serum-free thyroxine.

We evaluated analytically and clinically the new one-step non-analogue free thyroxine (FT4) assay (Amerlex-MAB from Amersham), using a labelled monoclonal thyroxine-specific antibody as tracer, in comparison with the Gammacoat two-step FT4 kit (Baxter). Analytical performances of the new kit were excellent: within and between run coefficients of variation were less than 5% in the working range. Clinical sensitivities for hypo- and hyperthyroidism were comparable for both kits (FT4 Amerlex-MAB 95% confidence interval: 12-25 pM). When serum was supplemented with albumin we observed a slight decrease in FT4 values measured by both kits. When oleate was added to serum we noted a moderate increase with the Amerlex-MAB kit up to 10 mM oleate added and a much more marked increase with the two-step kit. Results obtained with patients from particular euthyroid populations, known to have low albumin or high free fatty acids concentrations or to have perturbed FT4 results when measured by an analogue-based method, agreed with those of the in vitro studies. With these patients the specificity of the Amerlex-MAB FT4 results was good but slightly decreased compared with the two-step FT4 method, except for heparin-treated patients who were all classified according to their euthyroidal status (17/17 instead of 13/17 with the two-step kit).

Antibodies, Monoclonal↗
PubMed1990

In vitro and in vivo effects of increased concentrations of free fatty acids on free thyroxin measurements as determined by five assays.

To compare in vitro and in vivo effects of increased concentrations of free fatty acids (FFA) on free thyroxin (FT4) values, we measured FT4 in three pooled sera supplemented with oleate and in serum from 18 euthyroid patients before and after an infusion of fat emulsion (Intralipid). We used five FT4 RIA kits: two two-step methods [Gammacoat, Baxter (GC); Ria-gnost, Behring (RG)], two analog RIAs [Amerlex-M, Amersham (AM); Coat-Ria, BioMérieux (CR)], and one kit with labeled antibodies [Amerlex-MAB*, Amersham (AA)]. In vitro, at the maximum oleate addition of 5 mmol/L, FT4 increased when measured by the GC and RG kits, decreased by the AM kit, and showed no significant change by the CR and AA kits. In vivo, post-Intralipid, FFA concentrations rose significantly and the FT4 changes agreed with the results of the in vitro experiments, except for the RG kit, for which FT4 increased in only nine patients. We conclude that in vitro oleate addition is useful to predict the in vivo effect of increased FFA on FT4 values; moreover, in serum from euthyroid subjects with high concentrations of FFA, FT4 analyzed with the CR or AA kits should better agree with normal results for thyrotropin than FT4 values measured with the other kits.

Chromatography, Gas↗
PubMed1990

[MRI study of hypoplasia of the abdominal aorta in a 3-month-old infant].

The authors report coarctation of the abdominal aorta in an infant aged three months. A complete study of the lesion was made by magnetic resonance imaging (MRI), which confirmed involvement of the renal and iliac arteries, dilatation of the celiac trunk and of the superior mesenteric artery, and the absence of visualization of the inferior mesenteric artery. MRI is seen to be a valuable tool for monitoring this type of anomaly and allows angiography to be avoided.

Aorta, Abdominal↗