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A Syrota

Publications and source records attributed to A Syrota.

At least 73 records · Page 4Linked to original sources

Movement- and task-related activations of motor cortical areas: a positron emission tomographic study.

Using repeated measurements of regional cerebral blood flow with positron emission tomography, we investigated the regional cortical activations induced in 10 normal subjects, by two different finger motor tasks, i.e., a repeated flexion-extension of all fingers and a repeated flexion-extension of the middle finger. The all-finger movement only activated the primary sensorimotor cortex (SM) and the supplementary motor area (SMA) contralateral to the movement. However, the activation of the SMA was clearly task related during this motor task, because it was only observed when the movement was triggered by an auditory cue but not when it was self-paced. The middle finger movement was performed during self-paced conditions. It induced a much more complex pattern of activation than the all-finger movement, characterized by a high degree of SM and SMA activation contralateral to the side of the movement, as well as a slight ipsilateral activation of these areas. We suggest that this pattern of cortical activation may reflect the process of individuating finger movement or the early stages of motor learning of this unusual and technically difficult movement. Our data also confirm that the SM activation is closely linked to the intrinsic parameters of the movement; while the SMA may be activated by different aspects of the movement realization and preparation.

Adult↗

Canine myocardial dihydropyridine binding sites: a positron emission tomographic study with the calcium channel inhibitor 11C-S11568.

The in vivo determination of the density of dihydropyridine (DHP) binding sites will allow the assessment of pathophysiological changes associated with heart disease. The calcium channel antagonist S 11568: (+/-)(amino-7 dioxa-2,5 heptyl)-2(dichloro -2,3 phenyl) -4 methyl-6dihydro -1,4 pyridine has an in vitro profile of high potency and of high selectivity for the L-type Ca2+ channel. S 11568 was labelled by a reaction between 11C-diazomethane and the precursor 6-(7-amino-2,5-dioxa heptyl)-4-(2,3-dichloro phenyl)-5-(ethoxycarbonyl)-2 methyl-1,4 dihydro nicotinic acid. (+)-PN 200 110, a DHP with in vitro high affinity for the L-type Ca2+ channel, was also radiolabeled. Positron emission tomographic (PET) studies of both 11C-DHP myocardial uptake were performed in Beagle dogs. 11C-(+)-PN 200 110 had a rapid wash-out from myocardium. In contrary, after a bolus injection, 11C-S 11568 myocardial concentration increased to reach a maximum in 1-2 minutes and then remained in a plateau with a slight downslope while the blood concentration fell rapidly. Myocardial uptake was 2 to 4 fold higher than lung uptake, leading to a good contrast on PET images. Pre-treatment with unlabeled S 11568 (2 mumol/kg or 6 mumol/kg over 15 minutes) reduced myocardial uptake by 60% and 80%, respectively. Specific binding was estimated during a displacement experiment: bolus of unlabeled S 11568: 1 mumol/kg followed by a continuous infusion of 3 mumol/kg over 2 hours. It was found to represent 80% of the total binding. To assess influence of S 11568 on coronary blood flow and therefore on the myocardial tracer delivery, coronary blood flow was measured using 15O-H2O and PET at baseline and following bolus injections of 0.4, 0.8, 2 mumol/kg of S 11568. Only the higher dose increased coronary blood flow. This is the in vivo demonstration of the binding characteristics to myocardial tissue of a DHP ligand. Such properties make S 11568 suitable for PET experiments. The studies of DHP binding sites will provided new insights concerning physiological situations as well as heart disease.

Animals↗

Preparation and pharmacological characterization of [76Br]-meta-bromobenzylguanidine ([76Br]MBBG).

[76Br]-meta-Bromobenzylguanidine ([76Br]MBBG) was prepared from the iodinated analog (MIBG) and [76Br]NH4 using a Cu(+)-assisted halogen exchange reaction. [76Br]MBBG was produced in a 60-65% radiochemical yield with a specific activity of 20 MBq/nmol. In rats, biodistribution kinetic studies showed a high uptake of [76Br]MBBG in heart tissues with its maximum of 5% ID/S at 2 h p.i.; whereas 4 h p.i., the maximum of the heart-to-lung concentration ratio of 8 was observed. Metabolic studies in rats indicated that [76Br]MBBG was rapidly metabolized in plasma. However in heart tissue, 25 h p.i., 85% of the radioactivity still represented unchanged radiotracer. Pharmacological studies in rats showed that the myocardial uptake of [76Br]MBBG was similar to that of norepinephrine. After pretreatment of the rats, the uptake of [76Br]MBBG was reduced 4 h p.i. to the following values: after desipramine (DMI) to 37%, after dexamethasone (DXM) to 88% and after 6-hydroxydopamine (6-OHDA) to 16%. These preliminary results suggest that [76Br]MBBG can be useful for the assessment of heart catecholamine reuptake disorders with PET.

Animals↗

In vivo quantification of myocardial muscarinic receptors in heart transplant patients.

BACKGROUND: Decreased myocardial adenylate cyclase activity in response to guanine nucleotide stimulation has been recently demonstrated in denervated myocardium of transplant patients, suggesting that changes in left ventricular muscarinic receptors may occur. METHODS AND RESULTS: The concentration and affinity constants of myocardial muscarinic receptors were determined by positron emission tomography with 11C-labeled methylquinuclidinyl benzilate (MQNB), a specific hydrophilic antagonist, in six transplant patients 4.7 +/- 2.3 months after surgery and in six normal subjects. Patients had no sign of cardiac rejection at endomyocardial biopsy. After intravenous injections of MQNB, time-activity curves were obtained over different regions of interest and were fitted to a nonlinear mathematical model. No difference in the concentration of muscarinic receptors was found in transplant patients compared with control subjects: 24 +/- 4 versus 26 +/- 7 pmol/mL tissue, respectively (P = NS). The association rate constant k+1, the dissociation rate constant k-1, and thus the equilibrium-dissociation constant Kd were the same in transplant patients compared with control subjects. CONCLUSIONS: Despite known decreased GTP-stimulated adenylate cyclase activity in transplant patients, the density and affinity constants of myocardial muscarinic receptors are not altered. This suggests abnormalities of the signal-transduction function, such as a change in the guanine nucleotide binding proteins.

Adult↗

Central D2 receptors and negative symptoms of schizophrenia.

Most in vivo studies of striatal D2 receptor (SD2R) density with positron emission tomography in schizophrenia have attempted to relate this variable to the diagnosis of the illness. In the present study, a relationship between SD2R and clinical dimensions of this psychosis was searched for in a highly selected group of young negative schizophrenics (8 drug-naïve and 2 drug-free). The SD2R density index measured in vivo using 76Br-bromolisuride and PET correlated negatively (r = 0.80, P < 0.01) with a psychomotor dimension of schizophrenia involving blunted affect and alogia. The mean SD2R index of the patients did not differ from that of age-matched control subjects. Therefore, this behavioural dimension accounts for the variance of the SD2R, suggesting that the striatal dopamine system modulates symptoms such as flattened affect and alogia.

Adolescent↗

Amygdala atrophy in Alzheimer's disease. An in vivo magnetic resonance imaging study.

OBJECTIVES: To study the ability of magnetic resonance imaging to measure the volume of the amygdala and detect amygdala atrophy in patients with early Alzheimer's disease. DESIGN: Prospective case-control study and "blind" measurements. SETTING: Subjects were ambulatory outpatients selected from an institutional practice in Paris, France. PATIENTS: We studied 11 patients with probable Alzheimer's disease according to National Institute of Neurologic and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA) and Consortium to Establish a Registry for Alzheimer's Disease (CERAD) inclusion and exclusion criteria, as well as six age-matched control subjects. INTERVENTION: None. MAIN OUTCOME MEASURE: A 1.5-T magnetic resonance imager was used to acquire the images. Two neuroradiologists independently and blindly measured the volume of the right and left amygdalas on high-resolution contiguous slices. In addition, other cerebral structures, ie, the sylvian fissures, temporal lobes, lateral and third ventricles, corpus callosum, and hippocampal formation, were measured on a single slice. RESULTS: The values obtained by the two observers correlated highly (r = .90), and interrater variability was 13%. The Alzheimer's disease group showed significant (33%, P < .0001) atrophy of the amygdala when compared with the control group. The other structures showed less variation. CONCLUSION: Significant amygdala atrophy can be detected in vivo in patients with early Alzheimer's disease by means of standard magnetic resonance imaging. This technique may be useful in the early diagnosis of Alzheimer's disease.

Aged↗

Simultaneous temperature and regional blood volume measurements in human muscle using an MRI fast diffusion technique.

The thermal dependence of the translational diffusion coefficient and of the regional blood volume was investigated in vivo by using a special MR pulsed gradient technique with reduced sensitivity to bulk tissue motion. Measurements were done at 0.5 T, using a small gradient insert. The diffusion coefficient of muscle water was calibrated against thermocouple-measured temperature in vitro, both with the muscle fibers parallel and perpendicular to the diffusion gradient. The maximum muscle temperature variation obtained by percutaneous conduction was -8.8 +/- 1.6 degrees C under cooling and +3.7 +/- 1.6 degrees C under heating, from basal state. Simultaneously the fractional regional blood volume decreased by a factor of 3.5 under cooling and increased by a factor of 2.7 under heating. Due to the interdependence of microcirculation and tissue temperature, this technique may be used to follow heat production or deposition in living tissue (muscle exercise, electromagnetic irradiation, etc.).

Artifacts↗

Modeling analysis of [11C]flumazenil kinetics studied by PET: application to a critical study of the equilibrium approaches.

The multi-injection modeling approach was used for the in vivo quantitation of benzodiazepine receptors in baboon brain using positron emission tomography (PET) and [11C]flumazenil (RO 15-1788) as a specific ligand. The model included three compartments (plasma, free, and bound ligand) and five parameters (including the benzodiazepine receptor concentration). The plasma concentration after correction for the metabolites was used as the input function. The experimental protocol consisted of four injections of labeled and/or unlabeled ligand. This protocol allows the evaluation, from a single experiment, of the five model parameters in various regions of interest. For example, in the temporal cortex, the concentration of receptor sites available for binding (B'max) and the equilibrium dissociation constant (Kd) were estimated to be 70 +/- 15 pmol/ml and 15.8 +/- 2.2 nM, respectively. The validity of the equilibrium approach, which is the most often used quantitation method, has been studied from simulated data calculated using these model parameters. The equilibrium approaches consist of reproducing in PET studies the experimental conditions that permit the use of the usual in vitro methods such as Scatchard analysis. These approaches are often open to criticism because of the difficulty of defining the notion of equilibrium in in vivo studies. However, it appears that the basic relation of Scatchard analysis is valid over a broader range of conditions than those normally used, such as the requirement of a constant bound/free ratio. Simulations showed that the values of the receptor concentration (B'max) and the equilibrium dissociation constant (Kd) found using Scatchard analysis are always underestimated. These simulations also suggest an explanation concerning the dependency of B'max and Kd on the time point employed for the Scatchard analysis, a phenomenon found by several authors. To conclude, we propose new protocols that allow the estimation of the B'max and Kd parameters using a Scatchard analysis but based on a protocol including only one or two injections. These protocols being entirely noninvasive, it thus becomes possible to investigate possible changes in receptor density and/or affinity in patients.

Animals↗

Positron emission tomography with 11C CGP-12177 to assess beta-adrenergic receptor concentration in idiopathic dilated cardiomyopathy.

BACKGROUND: Positron emission tomography (PET) with 11C-labeled CGP-12177 (CGP) has been shown to have the potential to noninvasively measure beta-adrenergic receptor concentration in dog heart. The present study was undertaken to evaluate the clinical value of this technique. METHODS AND RESULTS: Eight normal subjects and 10 patients with heart failure related to an idiopathic cardiomyopathy were studied. Estimation of beta-receptor concentration was based on a graphic method applied on myocardial PET time-concentration curves obtained after an intravenous injection of 11C-CGP followed 30 minutes later by a coinjection of labeled and unlabeled CGP. The clinical tolerance of these injections was good. Left ventricular concentration of beta-receptors was decreased in patients compared with controls (3.12 +/- 0.51 versus 6.60 +/- 1.18 pmol/mL, respectively; p < 0.001). This 53% decrease agrees with previous in vitro data. In eight of the 10 patients, the beta-receptor concentration obtained from PET was compared with the beta-receptor density determined on left ventricular endomyocardial biopsy samples by in vitro binding technique using 3H-CGP-12177. Results obtained with both techniques were correlated (r = 0.79, p = 0.019). Moreover, decreased beta-receptor concentration correlated with the beta-contractile responsiveness to intracoronary dobutamine infusion (r = 0.83, p = 0.003), indicating a direct link between changes in the receptor number and its biological function. CONCLUSIONS: PET appears to be a safe and reliable method of assessing in vivo changes in the number of left ventricular beta-adrenergic receptor sites of patients with idiopathic cardiomyopathy.

Adrenergic beta-Antagonists↗

MR imaging as a potential diagnostic test for metabolic myopathies: importance of variations in the T2 of muscle with exercise.

OBJECTIVE: Most metabolic myopathies (like glycogenoses and mitochondrial myopathies) are related to inborn errors of muscle energy metabolism and often present clinically as exercise intolerance (inability to sustain normal exercise). We investigated whether the previously observed absence of normal exercise-induced variation in the T2 of muscle in McArdle's disease (a metabolic myopathy caused by muscle phosphorylase deficiency) was specific for this disease and whether the variations in T2 could be used for screening patients suspected of having metabolic myopathy. SUBJECTS AND METHODS: Exercise-induced variations in proton MR signal and in intracellular pH were studied in the forearm flexor muscles of nine healthy subjects and 49 patients with exercise intolerance due to muscle pain, suggesting a metabolic myopathy. The relative increase in T2, delta T2/T2, was measured from MR spin-echo images before and after exercise. Phosphocreatine (used as a control of the degree of exercise) and intracellular pH were measured from phosphorus-31 spectra before and during exercise. The progressive 4.5-min handgrip exercise reached maximal exertion capability at the end of exercise and decreased phosphocreatine to less than 50% of its rest value. RESULTS: Variations in T2 and end-exercise pH were correlated. The nine healthy subjects showed a delta T2/T2 ranging from +19% to +44% (but little T1 variation). Ten patients with McArdle's disease showed only slight delta T2/T2 (0-10%). There was no overlap with values for healthy subjects, but there was some with values for other patients. Of the 21 subjects with a delta T2/T2 less than 19%, 19 had a metabolic myopathy. The other two had a congenital neuromuscular disorder (one central core disease, one nemaline myopathy) with type I fiber predominance (type I muscle fibers are characterized by a high oxidative metabolism and a low lactic acid production). CONCLUSION: The altered increase in T2 was sensitive but not specific for McArdle's disease. However, as variations in T2 reflect variations in pH, they seem to be specific for myopathies in which there is little exercise-induced decrease in pH (some metabolic myopathies and congenital neuromuscular disorders with type I fiber predominance) among patients in whom exercise intolerance is the main symptom. Our results suggest that MR imaging might be useful as a screening test for these diseases.

Adolescent↗

Assessment of coronary reserve in man: comparison between positron emission tomography with oxygen-15-labeled water and intracoronary Doppler technique.

This study compared positron emission tomography (PET) using oxygen-15-labeled water for measurement of coronary reserve with intracoronary Doppler in patients with left anterior descending artery stenosis and patients with no coronary lesion and a coronary reserve 3 as assessed by the invasive technique. To determine whether PET measurement of coronary reserve is altered by partial volume effect, patients with left ventricular dysfunction due to idiopathic cardiomyopathy were studied with both techniques. Direct ultrasonic measurement of coronary reserve was performed the day prior to the PET study: a Doppler catheter was placed in the proximal left anterior descending artery; mean velocity was recorded at baseline and after dipyridamole administration. Using a time-of-flight PET system, patients underwent: (1) an intravenous bolus of oxygen-15-labeled water at baseline and 4 to 6 min after intravenous infusion of dipyridamole using the same protocol as for Doppler study and (2) a 18F-fluorodeoxyglucose (FDG) myocardial imaging. Oxygen-15 time-activity curves were recorded in myocardial regions of interest (ROIs) drawn on a static FDG image. Using the left ventricular time-activity curve as an input function, a standard model with a single-tissue compartment was fitted to the PET data; myocardial blood flow was estimated as the blood-to-tissue transfer rate constant. Coronary reserve measured by PET was well correlated with the measured by intracoronary Doppler (r = 0.98, p < 0.001 for global population). This PET method is an accurate and reliable tool to noninvasively measure coronary reserve in patients, even in those with left ventricular dysfunction.

Blood Flow Velocity↗

Correction of attenuation in SPECT with an attenuation coefficient map: a new method.

Attenuation coefficient (mu) maps, measured from transmission scan, are now becoming available. A simple method of attenuation correction is needed for routine implementation, however. Significant attenuation compensation can be mathematically obtained by dividing each actual pixel value of emission projections by the average of all the attenuation factors [exp (-sigma mu)] of all voxels along the same projection ray. This simple method, compatible with filtered back projection algorithms, was tested on simulations of cardiac and cerebral transaxial images on a Vax computer using the RECLBL library. In the models, the different structures received different activity and mu values. Three types of emission projections were generated: the ideal projections obtained by summation of the activity along each projection ray, the corresponding attenuated projections, and the projections corrected for attenuation. Comparison of projections on a pixel by pixel basis showed differences of less than 20% between the corrected and ideal projections. After reconstruction, both absolute and relative quantification were greatly improved by the correction of attenuation. Further validation of the method is in progress with actual patient data.

Algorithms↗

Dopaminergic D2 receptor SPECT imaging in Rett syndrome: increase of specific binding in striatum.

A dopamine deficiency has been implicated in Rett syndrome, a progressive encephalopathy in girls that involves movement, tonus and cognitive disorders. To test the hypothesis that striatal D2 receptors increase in number in early stages of the disease, we measured the binding potential of 123I-Iodolisuride, a specific D2 ligand, in eleven Rett children aged 4-15 yr (7.9 +/- 3.5 yr) (mean +/- s.d.) and eight control subjects aged 3.5-13 yr (8.1 +/- 3.8 yr) who exhibited other neurological disorders. Regional cerebral blood flow (rCBF) was also measured with SPECT using 133Xe. The binding potential for 123I-ILIS and D2 receptors was significantly higher in Rett (0.45) than in controls (0.23) (p < 0.01). An increase in 123I-ILIS binding due to increased rCBF in patients' striata was excluded. Our results are consistent with a higher density of D2 receptors in young patients suffering from Rett syndrome because of reduced dopaminergic neurotransmission.

Adolescent↗

Bromine-76-metabromobenzylguanidine: a PET radiotracer for mapping sympathetic nerves of the heart.

Iodine-123-metaiodobenzylguanidine (MIBG) is used to qualitatively assess heart innervation with single-photon emission computed tomography (SPECT). This approach is clinically useful in the prognostic evaluation of congestive heart failure. To improve quantification of uptake of the tracer using positron emission tomography (PET), we studied the characteristics of the bromoanalog of MIBG. Bromine-76-metabromobenzylguanidine (76Br-MBBG) was prepared from a heteroisotopic exchange between radioactive bromine atoms (noncarrier-added (76Br) BrNH4) and the cold iodine atoms of the precursor metaiodobenzylguanidine. Biodistribution was studied in rats and PET cardiac imaging performed in dogs. Myocardial uptake was high and prolonged in both species (mean half-life in dogs: 580 min). In rats, myocardial uptake was inhibited by desipramine by 64%, whereas after pretreatment with 6-hydroxydopamine uptake was reduced by 84%. In dogs pretreated with 6-hydroxydopamine or with desipramine, a steep washout of the tracer occurred (mean half-life: 136 min and 118 min, respectively). The non-specific uptake plus the passive neuronal diffusion of the tracer could be estimated at about 25%-30% of the total fixation. In dogs, analysis of unchanged 76Br-MBBG in plasma showed that radiotracer metabolism was slow: 60 min after injection, 80% of the radioactivity was related to unchanged 76Br-MBBG. These preliminary findings suggest that 76Br-MBBG could be used to quantitatively assess adrenergic innervation in heart disease using PET. When combined with use of 11C-CGP 12177, cardiac adrenergic neurotransmission can be assessed.

3-Iodobenzylguanidine↗

Quantification of myocardial muscarinic receptors with PET in humans.

The potential for noninvasive quantification of myocardial muscarinic receptors using PET data, a mathematical model, multi-injection protocols and 11C-labeled methylquinuclidinyl benzilate (MQNB) as a radioligand was previously demonstrated in dogs. The present study examines the possibility of optimizing the experimental protocol to make this approach suitable for human studies. For six normal subjects, the protocol included three injections: a tracer injection, followed 30 min later by an injection of an excess of unlabeled MQNB (displacement) and then 30 min later by a simultaneous injection of unlabeled and labeled MQNB (coinjection). The model input function was estimated from the PET data corresponding to the left ventricular cavity. This protocol enables a separate evaluation of all parameters of a ligand-receptor model which includes three compartments and seven parameters. The complexity of this three-injection protocol, however, appears to be inconvenient for clinical use. A simplified two-injection protocol (tracer injection and coinjection) was evaluated in five other normal subjects and the results were compared to those obtained with the three-injection protocol. In regions of interest over the left ventricle, the mean value of the receptor concentration B'max and the equilibrium dissociation constant Kd were 26 +/- 7 pmole/ml tissue and 2.0 +/- 0.5 pmole/ml tissue, respectively. The possible existence of nonspecific binding was studied in two subjects using a double-displacement protocol. The corresponding rate constant was found to be very low (0.03 min-1).

Adult↗

Carbon 13 NMR study of glycogen metabolism in the baboon liver in vivo.

In vivo glycogen metabolism was investigated at 2 Tesla by 13C NMR in the baboon liver. Two concentric surface coils were used for 13C observation and proton decoupling, respectively. Spectra were acquired in 2 to 10 minutes with a 60 ms repetition time. After 3 hours of glucose infusion in the 48 hr fasted animal, 3 g of 99%-enriched [1-13C]glucose were injected. The distribution of the label on C-1 and also C-2, C-5 and C-6 of glycogen indicated 65% and 35% contributions of the direct and indirect pathways to glycogen synthesis from glucose, respectively. The results show that hepatic metabolic pathways and rates can be followed in vivo in large animals by 13C NMR at 2 Tesla.

Animals↗

In vivo 13C-NMR evaluation of glycogen content in a patient with glycogen storage disease.

Glycogen storage disease was suspected in a 10-month-old boy. Initial technical problems did not permit the determination of the precise enzyme, deficiency, and type VI glycogen storage disease was only diagnosed at the age of 2 years. In the mean time, natural abundance 13C nuclear magnetic resonance evaluation of muscular and hepatic glycogen content indicated normal muscular glycogen and increased hepatic glycogen in our patient, a finding which strongly argued for the diagnosis of type VI glycogen storage disease. Even though the use of nuclear magnetic resonance might seem, in this situation, a somewhat circuitous means of reaching the diagnosis, it appears that nuclear magnetic resonance could provide a useful tool for a non-invasive diagnosis of glycogen storage diseases.

Creatine↗

Beta-adrenergic contractile reserve as a predictor of clinical outcome in patients with idiopathic dilated cardiomyopathy.

To examine the ability of beta-adrenergic contractile reserve assessment to predict the outcome of patients with heart failure, a prospective study was undertaken in 35 patients with idiopathic dilated cardiomyopathy and radionuclide ejection fraction below 40%. During right- and left-sided catheterization, right atrial and left ventricular (LV) pressures, peak positive LV dp/dt, cardiac index, and plasma norepinephrine and epinephrine concentrations were measured at baseline. After a left main intracoronary infusion of dobutamine (25 to 200 micrograms.min-1), beta-adrenergic contractile responsiveness was assessed as the net increase in peak positive LV dp/dt (delta LV dp/dt). After the initial examination, patients were treated with diuretics, digitalis, and angiotensin converting enzyme inhibitors and then followed-up. After a mean follow-up period of 13 +/- 7 months, two groups of patients were distinguished: those who responded to medical therapy (group A, n = 26) and those with clinical deterioration (group B, n = 9) leading to death (n = 4) or heart transplantation (n = 5). Initial peak positive LV dp/dt, LV end-diastolic pressure, cardiac index, and LV ejection fraction were better in group A than in group B (p less than 0.001). Initial plasma norepinephrine and epinephrine concentrations were significantly higher and delta LV dp/dt was lower in group B than in group A (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗