Intracellular Phosphate and ATP Depletion Measured by Magnetic Resonance Spectroscopy in Patients Receiving Maintenance Hemodialysis.

Background: The precise origin of phosphate that is removed during hemodialysis remains unclear; only a minority comes from the extracellular space. One possibility is that the remaining phosphate originates from the intracellular compartment, but there have been no available data from direct assessment of intracellular phosphate in patients undergoing hemodialysis.

Methods: We used phosphorus magnetic resonance spectroscopy to quantify intracellular inorganic phosphate (Pi), phosphocreatine (PCr), and ATP.

Oxytocin and Serotonin Brain Mechanisms in the Nonhuman Primate.

Oxytocin (OT) is increasingly studied for its therapeutic potential in psychiatric disorders, which are associated with the deregulation of several neurotransmission systems. Studies in rodents demonstrated that the interaction between OT and serotonin (5-HT) is critical for several aspects of social behavior. Using PET scan in humans, we have recently found that 5-HT 1A receptor (5-HTR) function is modified after intranasal oxytocin intake.

Studying the neural bases of prism adaptation using fMRI: A technical and design challenge.

Prism adaptation induces rapid recalibration of visuomotor coordination. The neural mechanisms of prism adaptation have come under scrutiny since the observations that the technique can alleviate hemispatial neglect following stroke, and can alter spatial cognition in healthy controls. Relative to non-imaging behavioral studies, fMRI investigations of prism adaptation face several challenges arising from the confined physical environment of the scanner and the supine position of the participants.

Imaging Dopamine and Serotonin Systems on MPTP Monkeys: A Longitudinal PET Investigation of Compensatory Mechanisms.

Unlabelled: It is now widely accepted that compensatory mechanisms are involved during the early phase of Parkinson's disease (PD) to delay the expression of motor symptoms. However, the neurochemical mechanisms underlying this presymptomatic period are still unclear. Here, we measured in vivo longitudinal changes of both the dopaminergic and serotonergic systems in seven asymptomatic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated monkeys (when motor symptoms are less apparent) using PET.

A lesion detection observer study comparing 2-dimensional versus fully 3-dimensional whole-body PET imaging protocols.

Unlabelled: We compared the impact of 2-dimensional (2D) and fully 3-dimensional (3D) acquisition modes on the performance of human observers in detecting and localizing tumors in whole-body (18)F-FDG images.

Methods: We selected protocols based on noise equivalent count (NEC) rates derived from a series of 2D and fully 3D whole-body patient and phantom acquisitions on a dual-mode PET scanner. The fully 3D peak NEC value for a standard 70-kg patient was achieved for an injected dose of approximately 444 MBq (12 mCi) assuming a 90-min delay before acquisition, whereas the 2D peak value was never reached.

Myocardial perfusion and glucose uptake coupling in CAD patients.

Purpose: To evaluate coronary artery disease (CAD) patients regarding to their perfusion-glucose uptake relationship at rest for all myocardial regions and to determine whether this evaluation could typify patients with different positron emission tomography (PET)-pattern proportions and pathophysiological characteristics.

Methods: Rest/dipyridamole H(15)2O and 18FDG PET studies were performed in 23 patients with left ventricular dysfunction. Regional index (relative perfusion, %H(15)2O; relative glucose uptake, %18FDG) allowed to detect PERFUSION-metabolism mismatch (i.

A reduced extracellular serotonin level increases the 5-HT1A PET ligand 18F-MPPF binding in the rat hippocampus.

Unlabelled: 4,2'-(Methoxyphenyl)-1-[2'-(N-2"-pyridinyl)-p-fluorobenzamido]ethylpiperazine ((18)F-MPPF) is a radiotracer used in clinical PET studies for the visualization of serotonin-1A (5-HT(1A)) receptors. In a previous study, we demonstrated that a rapid enhancement of extracellular serotonin concentrations influences (18)F-MPPF-specific binding. Because endogenous serotonin is significantly decreased in some pathologies, the aim of this study was to determine whether (18)F-MPPF is sensitive to depletion of this neurotransmitter.

Modeling [18 F]MPPF positron emission tomography kinetics for the determination of 5-hydroxytryptamine(1A) receptor concentration with multiinjection.

The selectivity of [18F]MPPF (fluorine-18-labeled 4-(2;-methoxyphenyl)-1-[2;-(N-2"-pirydynyl)-p-fluorobenzamido]ethylpiperazine) for serotonergic 5-hydroxytryptamine(1A) (5-HT1A) receptors has been established in animals and humans. The authors quantified the parameters of ligand-receptor exchanges using a double-injection protocol. After injection of a tracer and a coinjection dose of [18F]MPPF, dynamic positron emission tomography (PET) data were acquired during a 160-minute session in five healthy males.

Factor analysis of medical image sequences improves evaluation of first-pass MR imaging acquisitions for myocardial perfusion.

Rationale And Objectives: Factor analysis of medical image sequences (FAMIS) applied to gadolinium chelate-enhanced subsecond magnetic resonance (MR) imaging was evaluated as a postprocessing method for assessing myocardial perfusion in coronary artery disease (CAD).

Materials And Methods: To assess the accuracy of motion correction, five normal volunteers underwent MR imaging at rest. Thirteen patients with well-documented CAD and no myocardial infarction underwent MR imaging at rest and after dipyridamole administration.

SIC, an intracerebral beta(+)-range-sensitive probe for radiopharmacology investigations in small laboratory animals: binding studies with (11)C-raclopride.

Unlabelled: Our aim was to show the ability of a recently developed beta(+)-range-sensitive intracerebral probe (SIC) to measure, in vivo, the binding of radioligands in small animals.

Methods: The potential of the device for pharmacokinetic studies was evaluated by measurement of the dynamic striatal binding of (11)C-raclopride, a well-documented D(2) dopaminergic receptor ligand, in rat brain after intravenous injection of the labeled compound. The effects of preinjection of the unlabeled ligand (raclopride, 2 mg/kg intravenously) and of increasing the synaptic dopamine level (amphetamine treatment, 1 mg/kg intravenously) or of depleting synaptic dopamine (reserpine pretreatment, 5 mg/kg intraperitoneally) on in vivo (11)C-raclopride binding were monitored by SIC.

Brain processing of visual sexual stimuli in human males.

Despite its critical sociobiological importance, the brain processing of visual sexual stimuli has not been characterized precisely in human beings. We used Positron Emission Tomography (PET) to investigate responses of regional cerebral blood flow (rCBF) in nine healthy males presented with visual sexual stimuli of graded intensity. Statistical Parametric Mapping was used to locate brain regions whose activation was associated with the presentation of the sexual stimuli and was correlated with markers of sexual arousal.

Perfusion-MVO2 mismatch during inotropic stress in CAD patients with normal contractile function.

With the use of[11C]acetate, positron emission tomography (PET) permits exploration of myocardial blood flow (MBF) and oxidative metabolism (MVo2) coupling. PET imaging was performed at rest and under dobutamine infusion in 8 normal subjects and 10 coronary artery disease (CAD) patients with significant single-vessel left anterior descending (LAD) stenosis (> 70%) and normal regional left contractile function at rest. Resting MBF and MVo2 were similar in remote and LAD regions of normal subjects and patients.

Parameter and index images of benzodiazepine receptor concentration in the brain.

Unlabelled: In vivo studies of ligand-receptor interactions with PET data are based on different approaches that provide either quantitative results (receptor density and affinity) or indices that are assumed to be correlated with the receptor concentration. The aims of this study are to obtain parametric images of benzodiazepine receptor concentration and of flumazenil affinity and to study the validity of two receptor concentration indexes.

Methods: A three-compartment ligand-receptor model, [11C]flumazenil, and experimental data obtained using a three-injection protocol in human volunteers were used to acquire parametric images.

Effects of GABAA receptors activation on brain glucose metabolism in normal subjects and temporal lobe epilepsy (TLE) patients. A positron emission tomography (PET) study. Part I: Brain glucose metabolism is increased after GABAA receptors activation.

Though gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the human central nervous system, the metabolic response to GABA system activation remains imperfectly known. We studied in vivo with positron emission tomography (PET) the variations of glucose metabolism in the human brain after stimulation of the GABAA receptors by systemic administration of the specific GABAA agonist, 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP). These investigations were performed in three normal volunteers and as part of presurgical evaluation for temporal lobe epilepsy in six patients.