Synthetic exposure with a CMOS camera for multiple exposure speckle imaging of blood flow.

Speckle contrast imaging is an established technique to obtain relative blood flow maps over wide fields of view. A major improvement of the method relies on the acquisition of raw speckle images at different exposure times but requires simultaneous modulation of a laser pulse in duration and intensity and precise synchronization with a camera. This complex instrumentation has limited the use of multiple exposure speckle imaging. We evaluate here the use of a CMOS camera for a simplified approach based on synthetic exposure images created from the sum of successive frames acquired at a 1 ms exposure time. Both methods have been applied to evaluate controlled flows in micro-channels. The contribution of noises to the speckle contrast have been quantified and compared. Dark, readout and shot noise contributions to the total contrast remain constant for modulated exposure, while all these contributions decrease with increasing exposure time for synthetic exposure. The relative contribution of noises to speckle contrast depends on the level of illumination and the exposure time. Guidelines for flow measurements and limitations of the use of a CMOS camera with a limited frame rate for synthetic exposure acquisition scheme are discussed. The synthetic exposure method is simple to implement and should facilitate the translation of multiple exposure speckle imaging to clinical set-ups.

Optical and thermal simulations for the design of optodes for minimally invasive optogenetics stimulation or photomodulation of deep and large cortical areas in non-human primate brain.

The use of optogenetics or photobiomodulation in non-human primate (NHP) requires the ability to noninvasively stimulate large and deep cortical brain tissues volumes. In this context, the optical and geometrical parameters of optodes are critical. Methods and general guidelines to optimize these parameters have to be defined. OBJECTIVE: We propose the design of an optode for safe and efficient optical stimulation of a large volume of NHP cortex, down to 3-5 mm depths without inserting fibers into the cortex. APPROACH: Monte Carlo simulations of optical and thermal transport have been carried out using the Geant4 application for tomographic emission (GATE) platform. Parameters such as the fiber diameter, numerical aperture, number of fibers and their geometrical arrangement have been studied. Optimal hardware parameters are proposed to obtain homogeneous fluence above the fluence threshold for opsin activation without detrimental thermal effects. MAIN RESULTS: The simulations show that a large fiber diameter and a large numerical aperture are preferable since they allow limiting power concentration and hence the resulting thermal increases at the brain surface. To obtain a volume of 200-500 mm3 of brain tissues receiving a fluence above the opsin activation threshold for optogenetics or below a phototocixity threshold for photobiomodulation, a 4 fibers configuration is proposed. The optimal distance between the fibers was found to be 4 mm. A practical implementation of the optode has been performed and the corresponding fluence and thermal maps have been simulated. SIGNIFICANCE: The present study defines a method to optimize the design of optode and the choice of stimulation parameters for optogenetics and more generally light delivery to deep and large volumes of tissues in NHP brain with a controlled irradiance dosimetry. The general guidelines are the use of silica fibers with a large numerical aperture and a large diameter. The combination of several fibers is required if large volumes need to be stimulated while avoiding thermal effects.

Optogenetic Tractography for anatomo-functional characterization of cortico-subcortical neural circuits in non-human primates.

Dissecting neural circuitry in non-human primates (NHP) is crucial to identify potential neuromodulation anatomical targets for the treatment of pharmacoresistant neuropsychiatric diseases by electrical neuromodulation. How targets of deep brain stimulation (DBS) and cortical targets of transcranial magnetic stimulation (TMS) compare and might complement one another is an important question. Combining optogenetics and tractography may enable anatomo-functional characterization of large brain cortico-subcortical neural pathways. For the proof-of-concept this approach was used in the NHP brain to characterize the motor cortico-subthalamic pathway (m_CSP) which might be involved in DBS action mechanism in Parkinson's disease (PD). Rabies-G-pseudotyped and Rabies-G-VSVg-pseudotyped EIAV lentiviral vectors encoding the opsin ChR2 gene were stereotaxically injected into the subthalamic nucleus (STN) and were retrogradely transported to the layer of the motor cortex projecting to STN. A precise anatomical mapping of this pathway was then performed using histology-guided high angular resolution MRI tractography guiding accurately cortical photostimulation of m_CSP origins. Photoexcitation of m_CSP axon terminals or m_CSP cortical origins modified the spikes distribution for photosensitive STN neurons firing rate in non-equivalent ways. Optogenetic tractography might help design preclinical neuromodulation studies in NHP models of neuropsychiatric disease choosing the most appropriate target for the tested hypothesis.

Optimization and characterization of nonlinear excitation and collection through a gradient-index lens for high-resolution nonlinear endomicroscopy.

We report a study of gradient index (GRIN) lenses as a miniaturized micro-objective for in vivo imaging in the context of the development of a nonlinear endomicroscope. A numerical study of the parameters influencing the lateral resolution, excitation, and collection efficiency, when GRIN lens is coupled with a double clad fiber (DCF), is exposed. Four commercial DCFs, previously identified from the literature as potential endoscopic fibers, are simulated. Then, an experimental study characterizes two GRIN lenses (one commercial, one homemade) by their dispersion and nonlinear effects, potential intrinsic fluorescence, and use for fluorescence lifetime measurements. Images of neural cells from brain tissues of mice through a GRIN lens are presented.

PIXSIC, a pixelated ß⁺-sensitive probe for radiopharmacological investigations in rat brain: binding studies with [¹8F]MPPF.

PURPOSE: The aim of this work was to demonstrate the pharmacokinetic potential of a wireless pixelated ß(+)-sensitive probe (PIXSIC). PROCEDURES: The binding of 2'-methoxyphenyl-(N-2'-pyridinyl)-p-[(18)F]fluoro-benzamidoethylpiperazine ([(18)F]MPPF), a 5-HT1A serotonin receptor radiopharmaceutical, was measured in anesthetized rats and compared to microPET data. The effects of a 5-HT1A antagonist injection on in vivo [(18)F]MPPF binding were monitored by PIXSIC. RESULTS: PIXSIC allowed differentiating the radioactive kinetics according to the location of its pixels in the hippocampus, cortex, corpus callosum, and cerebellum. The device accurately detected the changes in [(18)F]MPPF binding, after 5-HT1A antagonist blockade. The time-activity curves were reproducible and consistent with kinetics obtained simultaneously with a microPET camera. CONCLUSIONS: These results demonstrate the ability of the PIXSIC device to record reliably the binding of PET ligands, with a high spatiotemporal resolution in anesthetized rodents. These first in vivo results are a key stage on the path to its implementation in awake freely moving animals.

Functional ultrasound imaging reveals different odor-evoked patterns of vascular activity in the main olfactory bulb and the anterior piriform cortex.

Topographic representation of the outside world is a key feature of sensory systems, but so far it has been difficult to define how the activity pattern of the olfactory information is distributed at successive stages in the olfactory system. We studied odor-evoked activation patterns in the main olfactory bulb and the anterior piriform cortex of rats using functional ultrasound (fUS) imaging. fUS imaging is based on the use of ultrafast ultrasound scanners and detects variations in the local blood volume during brain activation. It makes deep brain imaging of ventral structures, such as the piriform cortex, possible. Stimulation with two different odors (hexanal and pentylacetate) induced the activation of odor-specific zones that were spatially segregated in the main olfactory bulb. Interestingly, the same odorants triggered the activation of the entire anterior piriform cortex, in all layers, with no distinguishable odor-specific areas detected in the power Doppler images. These fUS imaging results confirm the spatial distribution of odor-evoked activity in the main olfactory bulb, and furthermore, they reveal the absence of such a distribution in the anterior piriform cortex at the macroscopic scale in vivo.

A wireless beta-microprobe based on pixelated silicon for in vivo brain studies in freely moving rats.

The investigation of neurophysiological mechanisms underlying the functional specificity of brain regions requires the development of technologies that are well adjusted to in vivo studies in small animals. An exciting challenge remains the combination of brain imaging and behavioural studies, which associates molecular processes of neuronal communications to their related actions. A pixelated intracerebral probe (PIXSIC) presents a novel strategy using a submillimetric probe for beta(+) radiotracer detection based on a pixelated silicon diode that can be stereotaxically implanted in the brain region of interest. This fully autonomous detection system permits time-resolved high sensitivity measurements of radiotracers with additional imaging features in freely moving rats. An application-specific integrated circuit (ASIC) allows for parallel signal processing of each pixel and enables the wireless operation. All components of the detector were tested and characterized. The beta(+) sensitivity of the system was determined with the probe dipped into radiotracer solutions. Monte Carlo simulations served to validate the experimental values and assess the contribution of gamma noise. Preliminary implantation tests on anaesthetized rats proved PIXSIC's functionality in brain tissue. High spatial resolution allows for the visualization of radiotracer concentration in different brain regions with high temporal resolution.

Visualizing odor representation in the brain: a review of imaging techniques for the mapping of sensory activity in the olfactory glomeruli.

The brain transforms clues from the external world, the sensory stimuli, into activities in neuroglial networks. These circuits are activated in specialized sensory cortices where specific functional modules are responsible for the spatiotemporal coding of the stimulus. A major challenge in the neuroscience field has been to image the spatial distribution and follow the temporal dynamics of the activation of such large populations in vivo. Functional imaging techniques developed in the last 30 years have enabled researchers to solve this critical issue, and are reviewed here. These techniques utilize sources of contrast of radioisotopic, magnetic and optical origins and exploit two major families of signals to image sensory activity: the first class uses sources linked to cellular energy metabolism and hemodynamics, while the second involves exogenous indicators of neuronal activity. The whole panel of imaging techniques has fostered the functional exploration of the olfactory bulb which is one of the most studied sensory structures. We summarize the major results obtained using these techniques that describe the spatial and temporal activity patterns in the olfactory glomeruli, the first relay of olfactory information processing in the main olfactory bulb. We conclude this review by describing promising technical developments in optical imaging and future directions in the study of olfactory spatiotemporal coding.

A method based on Monte Carlo simulations and voxelized anatomical atlases to evaluate and correct uncertainties on radiotracer accumulation quantitation in beta microprobe studies in the rat brain.

The beta-microprobe is a simple and versatile technique complementary to small animal positron emission tomography (PET). It relies on local measurements of the concentration of positron-labeled molecules. So far, it has been successfully used in anesthetized rats for pharmacokinetics experiments and for the study of brain energetic metabolism. However, the ability of the technique to provide accurate quantitative measurements using (18)F, (11)C and (15)O tracers is likely to suffer from the contribution of 511 keV gamma rays background to the signal and from the contribution of positrons from brain loci surrounding the locus of interest. The aim of the present paper is to provide a method of evaluating several parameters, which are supposed to affect the quantification of recordings performed in vivo with this methodology. We have developed realistic voxelized phantoms of the rat whole body and brain, and used them as input geometries for Monte Carlo simulations of previous beta-microprobe reports. In the context of realistic experiments (binding of (11)C-Raclopride to D2 dopaminergic receptors in the striatum; local glucose metabolic rate measurement with (18)F-FDG and H(2)O(15) blood flow measurements in the somatosensory cortex), we have calculated the detection efficiencies and corresponding contribution of 511 keV gammas from peripheral organs accumulation. We confirmed that the 511 keV gammas background does not impair quantification. To evaluate the contribution of positrons from adjacent structures, we have developed beta-Assistant, a program based on a rat brain voxelized atlas and matrices of local detection efficiencies calculated by Monte Carlo simulations for several probe geometries. This program was used to calculate the 'apparent sensitivity' of the probe for each brain structure included in the detection volume. For a given localization of a probe within the brain, this allows us to quantify the different sources of beta signal. Finally, since stereotaxic accuracy is crucial for quantification in most microprobe studies, the influence of stereotaxic positioning error was studied for several realistic experiments in favorable and unfavorable experimental situations (binding of (11)C-Raclopride to D2 dopaminergic receptors in the striatum; binding of (18)F-MPPF to 5HT1A receptors in the dorsal raphe nucleus).

Simultaneous in vivo magnetic resonance imaging and radioactive measurements with the beta-MicroProbe.

PURPOSE: Multimodal instrumentation is a new technical approach allowing simultaneous and complementary in vivo recordings of complementary biological parameters. To elucidate further the physiopathological mechanisms in intact small animal models, especially for brain studies, a challenging issue is the actual coupling of magnetic resonance imaging (MRI) techniques with positron emission tomography (PET): it has been shown that running the technology for radioactive imaging in a magnet alters the spatiotemporal performance of both modalities. Thus, we propose an alternative coupling of techniques that uses the beta-MicroProbe instead of PET for local measurements of radioactivity coupled with MRI. METHODS: We simultaneously recorded local radioactivity due to [(18)F]MPPF (a 5-HT(1A) receptor PET radiotracer) binding in the hippocampus with the beta-MicroProbe and carried out anatomical MRI in the same anaesthetised rat. RESULTS: The comparison of [(18)F]MPPF kinetics obtained from animals in a magnet with kinetics from a control group outside the magnet allowed us to determine the stability of tracer biokinetic measurements over time in the magnet. We were thus able to show that the beta-MicroProbe reliably measures radioactivity in rat brains under an intense magnetic field of 7 Tesla. CONCLUSION: The biological validation of a beta-MicroProbe/MRI dual system reported here opens up a wide range of future multimodal approaches for functional and pharmacological measurements by the probe combined with various magnetic resonance technologies, including anatomical MRI, functional MRI and MR spectroscopy.

The potential of the beta-Microprobe, an intracerebral radiosensitive probe, to monitor the [(18)F]MPPF binding in the rat dorsal raphe nucleus.

The aim of this study was to demonstrate the ability of a recently developed beta(+)-range sensitive intracerebral probe (beta-Microprobe) to measure the binding kinetics of [(18)F]MPPF, a well-documented 5-HT(1A) serotoninergic receptor ligand, in the dorsal raphe nucleus (DRN) of the anaesthetised rat. This midbrain nucleus presents a high concentration of 5-HT(1A) receptors known to be implicated in the effects of antidepressants. The difficulty confronting this study lay in the fact that the dimensions of the DRN are smaller than the detection volume of the beta-Microprobe. In the first part of the study, we studied the feasibility of this measurement from a theoretical point of view by autoradiography and a Monte Carlo simulation. We determined the optimal beta-Microprobe location close to the DRN and verified that this configuration allowed accurate determination of [(18)F]MPPF specific binding in the nucleus. In the second part of our study, we measured the in vivo time-concentration curves of [(18)F]MPPF binding in the DRN in comparison with the cerebellum. The specificity of [(18)F]MPPF binding in the DRN was confirmed by its displacement after non-labelled 5-HT(1A)antagonist injection (MPPF or WAY-100635). Moreover, we verified the feasibility of using beta-Microprobe monitoring and simultaneous validation by microdialysis to study the effect of an increase in extracellular serotonin, induced by fenfluramine injection, on [(18)F]MPPF binding in the DRN. Our theoretical simulations, confirmed by our experimental results, demonstrate the ability of this new device to monitor in vivo the binding of [(18)F]MPPF in the DRN of anaesthetised rodents.

[Cervical lymph node inflammation in children]. / Adénophlegmons cervicaux de l'enfant.

One hundred and twenty seven cases of cervical lymph node infection were seen between 1974 and 1986 in children aged between 1 month and 10 years. The point of origin of the infection wa identified in 30% of cases and was, in decreasing order: cutaneous, in the cervico-cephalic region; pharyngo-tonsillar via the lymphatic structures of the pharynx or by direct effraction of the buccopharyngeal mucosa; and, finally, dental. The site of the secondary lymph node infection was generally below and behind the angle of the jaw and in some cases submandibular. Two thirds of cases progressed to suppuration and were evaluated bacteriologically. Four organisms were identified: Staphylococcus, very much in the majority. The origin of the infection was almost always cutaneous. There was a predilection for the child aged under 5 with a majority under 2. The streptococcus was in second place far behind the staphylococcus. The origin of the infection was pharyngo-tonsillar, with the beta-haemolytic streptococcus predominant, bucco-dental, with the alpha-haemolytic predominant, and a very small number of cases with a cutaneous origin. The age of these children was greater than in the staphylococcal infection group: the great majority were over 2 and all cases with a dental origin were aged over 5. There were a small number of anaerobic infections. In 2 of the 3 bacteriologically confirmed cases, the origin was pharyngo-tonsillar and development was obviously favored by the initial antibiotics prescribed. Management took into account the predominance of the staphylococcus, the resistance of this organism to penicillin G and its usual sensitivity to methicillin.(ABSTRACT TRUNCATED AT 250 WORDS)

[Sudden deafness. Critical study of a series of 118 cases]. / Surdités brusques. Etude critique d'une série de 118 cas.

The different types of sudden deafness have been the subject of considerable research, particularly in respect of their definition and etiopathogenic mechanisms. The concept of a vascular disorder has acquired a predominant place that is open to discussion; very little attention has been paid to the very different ages of the patients, their sex distribution, and the varying course of sudden deafness with age. It is in this respect that the original nature of this study lies.

[Hemangiopericytoma of the parotid in the child (author's transl)]. / Un hémangiopéricytome de la parotide chez l'enfant.

A very rare case of localization in a large salivary gland (parotid) of a hemangiopericytoma in a 9 and 1/2 year old child. Detailed and discussed histopathological examinations resulted in a diagnosis of hemangiopericytoma (Nézelof, Gérard-Marchant). Despite wide excision by parotidectomy, there was a local recurrence two years later.