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At least 271 records · Page 15Linked to original sources
PubMed2006

Optical images of dose distributions in Gel-Fricke: dosimetric performances of the gel.

The purpose of this work was to examine the dosimetric performances of the radiochromic Fricke-Agarose-Xylenol Orange gel by optical measurements in order to perform dose reconstructions, in view of a future development for 3-D maps. Optical images and dose-response curves of the gel were obtained by a CCD-based device, originally designed for reading radiochromic films, that was modified to meet the optical properties of the dosemeter. With a resolution of 0.18 x 0.18 mm the optimum range of doses in which per cent uncertainty is lower than 2% was 3-10 Gy. The minimum detectable dose, estimated as the absorbed dose corresponding to 3 SD above background, was 0.1 Gy. With a resolution of 1.98 x 1.98 mm the optimum range of doses in which per cent uncertainty is lower than 2% was 0.3-10 Gy. The minimum detectable dose, estimated as the absorbed dose corresponding to 3 SD above background, was 0.015 Gy. The comparison with alanine dosemeters in the dose range 7-10 Gy showed agreement within a few per cent and the same agreement was observed for the comparison with TLD in the range 1-3 Gy.

Dose-Response Relationship, Radiation↗
PubMed2003

Optical imaging of the retinotopic organization of V1 in the common marmoset.

We examined the retinotopic mapping of the visual world in the primary visual cortex of the marmoset monkey using differential optical imaging. Two sets of complementary stripe-like locations were visually stimulated in turn. Their difference depicts the cortical representations of continuous bands of visual space. By rotating the sets of stripe-like locations it is possible to map different spatial axes. Analogous to the macaque we found that the V1/V2 border represented the vertical meridian, while horizontal, 45-, and 135-degree angled stripes of space were also represented in a continuous manner. We developed a new automatic method of calculating local measures of cortical magnification from our optical retinotopic maps. Using this method we found no evidence of any local anisotropies in cortical representation. Overall our results indicate that space is mapped isotropically in the primary visual cortex of the common marmoset.

Algorithms↗
PubMed2002

Optical imaging fiber-based single live cell arrays: a high-density cell assay platform.

A high-density, ordered array containing thousands of microwells is fabricated on an optical imaging fiber. Each individually addressable microwell is used to accommodate a single living cell. A charged coupled device (CCD) detector is employed to monitor and spatially resolve the fluorescence signals obtained from each individual cell, allowing simultaneous monitoring of cellular responses of all the cells in the array using reporter genes (lacZ, EGFP, ECFP, DsRed) or fluorescent indicators. Yeast and bacteria cell arrays were fabricated and used to perform multiplexed cell assays with resolution at the single-cell level. Monitoring gene expression in single yeast cells carrying a two-hybrid system was used to detect in vivo protein-protein interactions. The single-cell array technology provides a new platform for monitoring the unique multiple responses of large populations of individual cells from different strains or cell lines. The rich data acquired by the cell array has the potential to be employed as a new tool for cell biology research as well as to improve cell-based high-throughput screening (HTS) applications, such as the validation of new disease-associated cellular targets and the early-stage evaluation of potential drug candidates.

Escherichia coli↗
PubMed2005

Massively parallel manipulation of single cells and microparticles using optical images.

The ability to manipulate biological cells and micrometre-scale particles plays an important role in many biological and colloidal science applications. However, conventional manipulation techniques--including optical tweezers, electrokinetic forces (electrophoresis, dielectrophoresis, travelling-wave dielectrophoresis), magnetic tweezers, acoustic traps and hydrodynamic flows--cannot achieve high resolution and high throughput at the same time. Optical tweezers offer high resolution for trapping single particles, but have a limited manipulation area owing to tight focusing requirements; on the other hand, electrokinetic forces and other mechanisms provide high throughput, but lack the flexibility or the spatial resolution necessary for controlling individual cells. Here we present an optical image-driven dielectrophoresis technique that permits high-resolution patterning of electric fields on a photoconductive surface for manipulating single particles. It requires 100,000 times less optical intensity than optical tweezers. Using an incoherent light source (a light-emitting diode or a halogen lamp) and a digital micromirror spatial light modulator, we have demonstrated parallel manipulation of 15,000 particle traps on a 1.3 x 1.0 mm2 area. With direct optical imaging control, multiple manipulation functions are combined to achieve complex, multi-step manipulation protocols.

B-Lymphocytes↗
PubMed2007

Depth-resolved optical imaging and microscopy of vascular compartment dynamics during somatosensory stimulation.

The cortical hemodynamic response to somatosensory stimulus is investigated at the level of individual vascular compartments using both depth-resolved optical imaging and in-vivo two-photon microscopy. We utilize a new imaging and spatiotemporal analysis approach that exploits the different characteristic dynamics of responding arteries, arterioles, capillaries and veins to isolate their three-dimensional spatial extent within the cortex. This spatial delineation is validated using vascular casts. Temporal delineation is supported by in-vivo two-photon microscopy of the temporal dynamics and vascular mechanisms of the arteriolar and venous responses. Using these techniques we have been able to characterize the roles of the different vascular compartments in generating and controlling the hemodynamic response to somatosensory stimulus. We find that changes in arteriolar total hemoglobin concentration agree well with arteriolar dilation dynamics, which in turn correspond closely with changes in venous blood flow. For 4-s stimuli, we see only small changes in venous hemoglobin concentration, and do not detect measurable dilation or ballooning in the veins. Instead, we see significant evidence of capillary hyperemia. We compare our findings to historical observations of the composite hemodynamic response from other modalities including functional magnetic resonance imaging. Implications of our results are discussed with respect to mathematical models of cortical hemodynamics, and to current theories on the mechanisms underlying neurovascular coupling. We also conclude that our spatiotemporal analysis approach is capable of isolating and localizing signals from the capillary bed local to neuronal activation, and holds promise for improving the specificity of other hemodynamic imaging modalities.

Animals↗
PubMed2004

Biomedical applications of optical imaging.

Developments in imaging offer real-time visualisation of biological processes at the cellular and molecular level. This article considers how micro- and nanotechnology may enhance the application of optical imaging for in vivo and in vitro diagnostics.

Biomedical Engineering↗
PubMed1995

Coherent spatiotemporal patterns of ongoing activity revealed by real-time optical imaging coupled with single-unit recording in the cat visual cortex.

1. We examined the spatiotemporal organization of ongoing activity in cat visual areas 17 and 18, in relation to the spontaneous activity of individual neurons. To search for coherent activity, voltage-sensitive dye signals were correlated with the activity of single neurons by the use of spike-triggered averaging. In each recording session an area of at least 2 x 2 mm of cortex was imaged, with 124 diodes. In addition, electrical recordings from two isolated units, the local field potential (LFP) from the same microelectrodes, and the surface electroencephalogram (EEG) were recorded simultaneously. 2. The optical signals recorded from the dye were similar to the LFP recorded from the same site. Optical signals recorded from different cortical sites exhibited a different time course. Therefore real-time optical imaging provides information that is equivalent in many ways to multiple-site LFP recordings. 3. The spontaneous firing of single neurons was highly correlated with the optical signals and with the LFP. In 88% of the neurons recorded during spontaneous activity, a significant correlation was found between the occurrence of a spike and the optical signal recorded in a large cortical region surrounding the recording site. This result indicates that spontaneous activity of single neurons is not an independent process but is time locked to the firing or to the synaptic inputs from numerous neurons, all activated in a coherent fashion even without a sensory input. 4. For the cases showing correlation with the optical signal, 27-36% of the optical signal during spike occurrence was directly related to the occurrence of spontaneous spikes in a single neuron, over an area of 2 x 2 mm. In the same cortical area, 43-55% of the activity was directly related to the visual stimulus. 5. Surprisingly, we found that the amplitude of this coherent ongoing activity, recorded optically, was often almost as large as the activity evoked by optimal visual stimulation. The amplitude of the ongoing activity that was directly and reproducibly related to the spontaneous spikes of a single neuron was, on average, as high as 54% of the amplitude of the visually evoked response that was directly related to optimal sensory stimulation, recorded optically. 6. Coherent activity was detected even at distant cortical sites up to 6 mm apart.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1997

Optical imaging in medicine: I. Experimental techniques.

The overwhelming scatter which occurs when optical radiation propagates through tissue severely limits the ability to image internal structure using measurements of transmitted intensity. A broad range of methods has been proposed during the past decade or so in order to improve imaging performance. Direct methods involve isolating an unscattered or least-scattered component of transmitted scattered light. Indirect methods generally involve measuring some characteristic of the temporal distribution of transmitted light, or an equivalent in the frequency domain, and obtaining a computational solution to the inverse problem. In this paper, we review the experimental techniques which have been proposed in order to explore both direct and indirect imaging. The relative merits and limitations of the various experimental methods are discussed, and we consider the future directions and likelihood of success of optical imaging in medicine.

Diagnostic Imaging↗
PubMed1997

Neuronal synchronization and ionic mechanisms for propagation of excitation in the functional network of immortalized GT1-7 neurons: optical imaging with a voltage-sensitive dye.

Immortalized gonadotropin releasing hormone (GnRH) neurons (GT1 cell line) in culture release GnRH in a pulsatile manner, suggesting that GT1 cells form a functional neuronal network. Optical imaging techniques and a voltage-sensitive fluorescent dye (RH795) were used to study the mechanism of neuronal synchronization and intercellular communication in cultured GT1-7 cells (one of the subclones of the GT1 cell line). The majority (79%) of GT1-7 cells in contact with one another revealed synchronized fluctuations in spontaneous neuronal activity. When a cell in contact with other cells was electrically stimulated, the evoked excitation was propagated to neighbouring cells. The ionic mechanisms involved in the propagation of electrical signals between interconnected GT1-7 cells were investigated using various blockers of Na+, Ca2+ and K+ channels. The propagation of stimulus-evoked excitation was prevented by the voltage-dependent Na+ channel blocker tetrodotoxin. It was also prevented by the voltage-dependent Ca2+ channel blockers, Ni+ (nonselective), nimodipine (L-type) and flunarizine (T-type > L-type), but not apparently affected by omega-agatoxin IVA (P- and Q-type) and omega-conotoxin MVIIA (N-type). The propagation was not influenced by the K+ channel blockers, quinine, tetraethylammonium and Ba2+, but in some cases, it was enhanced by 4-aminopyridine (4-AP) and prevented by apamin. These results suggest that voltage-dependent Na+ channels and L- and T-type Ca2+ channels are involved in the propagation of electrical signals in the GT1-7 neuronal network. Ionic mechanisms, through 4-AP- or apamin-sensitive K+ channels, also seem to be involved in the regulation of signal propagation. These mechanisms may underlie the functioning of the neuronal network formed by immortalized GnRH neurons.

Animals↗
PubMed2006

Interaction of scanning probes with semiconductor nanocrystals; physical mechanism and basis for near-field optical imaging.

We investigate the modification of photoluminescence (PL) from single semiconductor nanocrystal quantum dots (NCs) in the proximity of metal and semiconducting atomic force microscope (AFM) tips. The presence of the tip alters the radiative decay rate of an emitter via interference and opens efficient nonradiative decay channels via energy transfer to the tip material. These effects cause quenching (or enhancement) of the emitter's PL intensity as a function of its distance from the interacting tip. We take advantage of this highly distance-dependent effect to realize a contrast mechanism for high-resolution optical imaging. AFM tips are optimized as energy acceptors by chemical functionalization with InAs NCs to achieve optical resolution down to 30 nm. The presented experimental scheme offers high-resolution optical information while maintaining the benefits of traditional AFM imaging. We directly measure the PL intensity of single NCs as a function of the tip distance. Our results are in good agreement with calculations made by a classical theoretical model describing an oscillating dipole interacting with a planar mirror.

Journal Article↗
PubMed1994

Optical imaging of the in vitro guinea pig piriform cortex activity using a voltage-sensitive dye.

The spatio-temporal patterns of signal processing in guinea pig piriform cortex (PC) slices were analyzed by optical imaging using a voltage-sensitive dye. Slices (400 microns thick) were cut in a plane parallel to the lateral olfactory tract and perpendicular to the cortical surface. In all the anterior PC and the majority of the posterior PC preparations, neural activity elicited by electrical stimulation of layer Ia propagated along the same layer, then it invaded into layers II and III and propagated along them. In addition to the above pattern, invasion of activity into the deeper area than layer III was observed in some posterior PC preparations. Real-time imaging of an active zone evoked by Ia shocks and its spatio-temporal behavior will contribute to resolving olfactory information processing.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed2005

Optical imaging of epileptiform activity in experimentally induced cortical malformations.

Electrophysiological studies of human cortical dysplasia and rodent models revealed widespread hyperexcitability in the malformation itself as well as in its vicinity. We here analyzed the initiation of paroxysmal epileptiform activity using optical imaging of neuronal activity in rats with cortical malformations induced by neonatal freeze lesions. Brain slice preparations were incubated with the voltage-sensitive dye RH795 and neuronal activity was monitored using a fast-imaging photodiode array combined with standard field potential recordings. Spontaneous paroxysmal epileptiform activity emerged in all slices from animals with cortical malformations and sham-operated controls 20-40 min after omission of extracellular Mg(2+). Following electrophysiological and optical recordings, slices were histochemically processed. Using this approach, the present study demonstrated that in animals with freeze-lesion-induced focal cortical malformations, paroxysmal epileptiform activity always emerged from the dysplastic cortex and then spread to adjacent areas through superficial layers. This distribution of initiation sites was significantly different to sham-operated controls in which epileptogenic foci were located in various cytoarchitectonic areas. The present study indicates that following global changes in excitability, the dysplastic cortex itself is the main initiation site of paroxysmal epileptiform activity in animals with focal cortical malformations.

Animals↗
PubMedDate not supplied

Optical imaging of Renilla luciferase, synthetic Renilla luciferase, and firefly luciferase reporter gene expression in living mice.

We have recently demonstrated that Renilla luciferase (Rluc) is a promising bioluminescence reporter gene that can be used for noninvasive optical imaging of reporter gene expression in living mice, with the aid of a cooled charged couple device (CCD) camera. In the current study, we explore the expression of a novel synthetic Renilla luciferase reporter gene (hRluc) in living mice, which has previously been reported to be a more sensitive reporter than native Rluc in mammalian cells. We explore the strategies of simultaneous imaging of both Renilla luciferase enzyme (RL) and synthetic Renilla luciferase enzyme (hRL):coelenterazine (substrate for RL/hRL) in the same living mouse. We also demonstrate that hRL:coelenterazine can yield a higher signal when compared to Firefly luciferase enzyme (FL): D-Luciferin, both in cell culture studies and when imaged from cells at the surface and from lungs of living mice. These studies demonstrate that hRluc should be a useful primary reporter gene with high sensitivity when used alone or in conjunction with other bioluminescence reporter genes for imaging in living rodents.

Animals↗
PubMed1997

Optical imaging of cat auditory cortical organization after electrical stimulation of a multichannel cochlear implant: differential effects of acute and chronic stimulation.

OBJECTIVE: To study the effects of electrical stimulation on cortical activation patterns. MATERIALS AND METHODS: Optical imaging of auditory cortex in cats that are acutely and chronically electrically stimulated with cochlear implants. RESULTS: Chronic electrical stimulation results in expansion of cortical territory and overlap. CONCLUSION: Effects of chronic electrical stimulation are comparable to use-dependent cortical plastic reorganization.

Animals↗
PubMed2005

Optical imaging of respiratory neuron activity from the dorsal view of the lower brainstem.

1. We visualized respiratory-related neuron network activity in the dorsal part of the pons and medulla of an in vitro preparation from newborn rats by optical recordings using a voltage-sensitive dye. We measured optical signals from several seconds before to several seconds after the inspiratory phase using the inspiratory motor nerve discharge as the trigger signal and we averaged the optical signals of 20-50 respiratory cycles to obtain an optical image correlating specifically to inspiratory activity. 2. Four areas that were excited or inhibited corresponding to the respiratory cycles were detected. (i) The most rostral activity was in the rostral and lateral parts of the pons, with activity mainly in the inspiratory phase, corresponding to the pontine-respiratory group. (ii) In the midpontine level, inspiratory activity followed by long-lasting hyperpolarization appeared in the midlateral parts. This part was presumed to reflect activity in the locus coeruleus. The hyperpolarization became almost negligible after treatment with the alpha-adrenergic antagonist, phentolamine. (iii) In the dorsal medulla, the predominantly inspiratory activity was detected at the rostral level of the area postrema. This part was considered to reflect activity mainly of the hypoglossal nucleus. (iv) At a similar level, we also detected weak and disperse inspiratory activity extending more laterally and caudally than that of the hypoglossal nucleus activity. This might reflect activity of the dorsal respiratory group. 3. In conclusion, the present optical recording study revealed that the dorsal part of the lower brainstem in the in vitro preparation is noticeably active as well as the ventral part shown in the previous study. This method is very useful for analysis of pharmacological properties, as well as the spatio-temporal pattern of respiratory-related network activity in the brainstem.

Animals↗
PubMed2004

Diffusion of epidermal growth factor in rat brain extracellular space measured by integrative optical imaging.

Epidermal growth factor (EGF) stimulates proliferation, process outgrowth, and survival in the CNS. Understanding the actions of EGF necessitates characterizing its distribution in brain tissue following drug delivery or release from cellular sources. We used the integrative optical imaging (IOI) method to measure diffusion of fluorescently labeled EGF (6,600 Mr; 4 microg/ml) in the presence of excess unlabeled EGF (90 microg/ml) to compete off specific receptor binding and reveal the "true" EGF diffusion coefficient following injection in rat brain slices (400 microm). The effective diffusion coefficient was 5.18 +/- 0.16 x 10(-7) (SE) cm2/s (n = 22) in rat somatosensory cortex and the free diffusion coefficient, determined in dilute agarose gel, was 16.6 +/- 0.12 x 10(-7) cm2/s (n = 27). Tortuosity (lambda), a parameter representing the hindrance imposed on EGF by the convoluted brain extracellular space (ECS), was 1.8, the lowest yet measured by IOI for a protein in brain. Control experiments with fluorescent dextran of similar molecular weight and tetramethylammonium confirmed EGF did not affect local ECS structure. We conclude that transport of smaller growth factors such as EGF through brain ECS is less hindered than that of larger proteins (>10,000 Mr, e.g., nerve growth factor) where typically lambda > 2.1. Modeling was used to predict that low lambda will allow EGF sources in the brain to be further from target cells and still elicit a biological response. High lambda values for larger growth factors imply more constrained local biological effects than with smaller proteins such as EGF.

Amino Acid Sequence↗
PubMed2006

Depression of presynaptic excitation by the activation of vanilloid receptor 1 in the rat spinal dorsal horn revealed by optical imaging.

In this study, we show that capsaicin (CAP) depresses primary afferent fiber terminal excitability by acting on vanilloid receptor 1 (TRPV1 channels) of primary afferent fibers in adenosine 5'-triphosphate (ATP)- and temperature-dependent manner using two optical imaging methods. First, transverse slices of spinal cord were stained with a voltage-sensitive dye and the net excitation in the spinal dorsal horn was recorded. Prolonged treatment (>20 min) with the TRPV1 channel agonist, CAP, resulted in a long-lasting inhibition of the net excitation evoked by single-pulse stimulation of C fiber-activating strength. A shorter application of CAP inhibited the excitation in a concentration-dependent manner and the inhibition was reversed within several minutes. This inhibition was Ca(++)-dependent, was antagonized by the TRPV1 channel antagonist, capsazepine (CPZ), and the P(2)X and P(2)Y antagonist, suramin, and was facilitated by the P(2)Y agonist, uridine 5'-triphosphate (UTP). The inhibition of excitation was unaffected by bicuculline and strychnine, antagonists of GABA(A) and glycine receptors, respectively. Raising the perfusate temperature to 39 degrees C from 27 degrees C inhibited the excitation (-3%/ degrees C). This depressant effect was antagonized by CPZ and suramin, but not by the P(2)X antagonist, 2', 3'-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate (TNP-ATP). Second, in order to record the presynaptic excitation exclusively, we stained the primary afferent fibers anterogradely from the dorsal root. CAP application and a temperature increase from 27 degrees C to 33 degrees C depressed the presynaptic excitation, and CPZ antagonized these effects. Thus, this study showed that presynaptic excitability is modulated by CAP, temperature, and ATP under physiological conditions, and explains the reported central actions of CAP. These results may have clinical importance, especially for the control of pain.

Adenosine Triphosphate↗
PubMed2003

Advances in optical imaging of the newborn infant brain.

New methods of imaging the oxygenation, hemodynamics, and metabolism of the newborn infant brain are being developed, based on illumination of the head with near-infrared light. Techniques known as optical topography and optical tomography have the potential to provide valuable information about the function of the normal brain, and about a variety of cerebral pathology such as hypoxic-ischemia. Optical methods provide a unique means of monitoring brain oxygenation safely in an intensive care environment without interference with the normal handling of the infant. Studies on infants have focused on the assessment of steady-state regional cerebral perfusion and tissue oxygenation, as well as monitoring hemodynamic changes in response to sensory stimulation. Recent technological and methodological advances in this research field are reviewed, and the likely impact of optical imaging methods on the care of newborn infants is assessed.

Brain↗