[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).

Photoacoustic detection of photosensitized oxygenations in highly absorbing samples

A photoacoustic (PA) study of the relaxation processes of the excited states of photosensitizers in the presence of oxygen and chemical acceptors is described. It has been predicted theoretically that the ratio of PA amplitudes with and without acceptor depends on two parameters alpha and beta, related to the sensitizer and to the acceptor properties, respectively. Experimental studies were carried out on solutions of hematoporphyrin IX and methylene blue. The addition of an acceptor, specific to the singlet oxygen, like tetramethyl ethylene or furfuryl alcohol, appears to decrease significantly the photoacoustic signal amplitude within the band of absorption.

[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.

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.

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.

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.

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.

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.

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.

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.

Changes in serum testosterone levels after myocardial infarction

To evaluate the effect of a severe non-endocrine disease on testosterone levels we determined the total testosterone (T), free testosterone (fT), myoglobin and myosin plasmatic levels in 18 men at the time of hospitalization for acute myocardial infarction (AMI), and 1, 3, 7 and 21 days later. Five different methods for determining fT were applied and compared; 1) radioimmunoassay after ultrafiltration, 2) direct analogue based radioimmunoassay (RIA), 3) calculation from total T, sex-hormone-binding globulin (SHBG) and albumin concentrations, 4) calculation from total T, SHBG concentrations with albuminemia fixed at 40 g/L, and 5) evaluation by the (total T)/(SHBG) ratio (fT index). After AMI the total T and fT decreased rapidly (minimum at day 1) and then increased until day 21. While a lower sensitivity in detecting small changes was noted for the direct analogue based fT RIA and for the calculation using a fixed albuminemia, the evolving pattern of the 5 different fT determinations was similar despite different absolute values. However, there was a wide scattering in the results from the different methods used to determine fT. Compared to ultrafiltration, the fT values were lower by direct analogue based assay and higher by calculation. There was a trend of correlation between changes in total T and the maximum myosin concentration (r = 0.557, p = 0.02), showing a relationship between the hormonal changes and the severity of the myocardial infarction.

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.

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.

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.

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.

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.

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).

[Value of cine magnetic resonance imaging in the diagnosis and quantification of valvular regurgitation. Comparison with angiography and Doppler echocardiography]

Thirty-three patients presenting with regurgitation of the mitral valve (19 cases), tricuspid valve (14 cases) or aortic valve (11 cases) documented by angiography (n = 20) and/or doppler-echocardiography (n = 28) were examined by cine-MRI in order to test this method in valvular regurgitation. Sixteen ECG-synchronized cine-MRI images were acquired by the GRASS technique every 40 ms on appropriate projections, with a resistive 0.28 Tesla Bruker magnet. The semiology of normal and pathological blood flow images at cine-MRI is described. Valvular regurgitations present as "signal void" jets the chronology and spatial extension of which depend on the severity of the lesion. The differential diagnosis with physiological flows is discussed. The diagnostic sensitivity of the method was 29/29 when compared with angiography and 29/33 when compared with doppler-echocardiography (2 cases of 1/4 mitral regurgitation and 2 cases 1/4 tricuspid regurgitation were not visible at cine-MRI). The specificity of this method, as can be judged from 104 patients explored, also seems to be satisfactory. The severity of regurgitation was graded from 1 to 4 with the three methods, on the basis of strict criteria. The differences in grade evaluation exceeded +/- 1 point in only one case of mitral regurgitation which was greatly underestimated by the doppler method as compared with angiography and cine-MRI. Thus, cine-MRI is a reliable method to evaluate valvular regurgitations and their severity. It solves the practical problem raised by non-echogenic patients when catheterization is to be postponed or avoided.

Myocardial gated tomoscintigraphy with 99Tcm-methoxy-isobutyl-isonitrile (MIBI): regional and temporal activity curve analysis

Myocardial gated tomoscintigraphy with hexakis-(2 methoxy-isobutyl-isonitrile) labelled with 99Tcm, is more suitable to resolve precisely the size of myocardial infarct than nongated 201Tl tomoscintigraphy. Gated tomography gives short axis slices at eight points in the cardiac cycle. A quantitative method to analyse heart wall activity and its motion is proposed. In two groups of patients, one with inferior infarct and the other with anterior infarct, the time-activity curves show a maximum in systole for healthy regions and a flattened curve in akinetic regions. Gated tomoscintigraphy assesses more accurately the size of the injured regions because there is no averaging between systolic and diastolic activity as in 201Tl tomoscintigraphy. This method should permit a better follow-up of patients with myocardial infarct.

[Familial hyperthyroxinemia with dysalbuminemia: screening of 21,000 patients at the occasion of thyroid evaluation]

Serum samples from 21,342 patients undergoing evaluation of thyroid status were screened for familial dysalbuminemic hyperthyroxinemia (FDH) using a specific test based on the measure of charcoal uptake of 125I thyroxine (T4) from serum diluted 1:100 with addition of unlabelled 10(-6) M T4. We found 17 cases of FDH: a higher incidence (8:10,000) than previously reported in the general population (1:10,000). The results of thyroid function tests of patients with FDH are presented: total T4 concentration is increased in only 14 subjects; thyrotropin and free T4 measured by an immunoextraction method are the most useful assays to evaluate the clinical status of these patients.

[Comparison of the left ventricular stroke volume and fraction measured with MRI and contrast ventriculography]

27 patients who underwent a contrast ventriculography in right anterior oblique at 30 degrees (for various cardiopathies) were studied by MRI with a mean delay of 5.7 +/- 6.2 days. After location of the medio-ventricular area, a diastolic horizontal section (apex of the R wave) and a systolic section (descending portion of the T wave) are carried out using the spin ultrasound technique. The same calculations are used for MRI au X-Ray contours (modified area-length method) by two strictly independent operators. With MRI, the LVSF is under estimated (40.4 +/- 19%) as compared angiography (46.1 +/- 18%). The linear correlation is 0.79 and in half of the patients (13 in 27) the deviation of the LVSF exceeds 10 p. cent. The volumes also tend to be underestimated with MRI (97 +/- 50 and 64 +/- 51 ml for the diastole and systole respectively) compared with angiography (123 +/- 66 and 73 +/- 62 ml), but the difference is only significant for the diastole and the linear correlation coefficients are improved at 0.82 and 0.90. Underestimation of the parameters measured with MRI is the consequence of multiple factors including the imprecise determination of the true telesystole, the marked effect of the partial volume related to the thickness of the section, and especially the obliquity of the plane studied on MRI, compared with the long axis of the heart. The error made by using a calculation algorithm, conceived for projective methods showing the long axis of the modeled ellipsoid, also explains the underestimation of volumes obtained with MRI, tomographic method. The simple technique used here seems especially interesting in the analysis of segmental contraction. Finally, the development of cine-MRI will undoubtedly be extremely beneficial in the study of ventricular contraction and relaxation.