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At least 451 records · Page 25Linked to original sources
PubMed1993

Mapping cone photopigment optical density.

The distribution of cone photopigment across the retina affects the amount of light captured by cones at each retinal location. Cone photopigment optical density is measured in two ways, with reflectometry and/or with color matching. Color matching measures a higher optical density than does reflectometry. Control experiments confirm that large-field color matches measure photopigment optical density toward their outer edge. There is qualitative agreement as to photopigment distribution from both techniques near the fovea. Beyond 1 deg, color matching indicates little decrease in photopigment with increasing eccentricity, whereas retinal densitometry shows a steep decline in photopigment. The decrease in perifoveal optical density measured with reflectometry is attributed to the decrease in cone coverage from fovea to perifovea as rods and interphotoreceptor spaces increase. Differences among subjects in photopigment distribution near the fovea, measured with both techniques, reflect differences in the specialization of the foveal center for cone length and/or photopigment concentration per cone, which are factors influencing results from both techniques.

Adult↗
PubMed2004

Corroded surface roughness of copper analyzed by Fourier transform infrared mapping microscopy and optical profilometric study.

This study shows the effects of roughness on infrared spectra shapes of thin corrosion products on metallic substrates. The calculated spectra show that the baseline is mainly affected by increasing roughness and that such effects do not shift the position of the absorption bands. The model obtained has been used to extract data of artificial patina on a copper surface. Surface defects of copper substrates can be distinguished on the whole surface, from the morphological and chemical points of view, using optical profilometry and infrared microspectroscopy. An homogeneous layer of cuprite covers the surface except in the linear defects. Fourier transform infrared (FT-IR) analysis indicates that a mixture of atacamite and clinoatacamite is mainly located in these scratches. The width of these particular areas is in good agreement with profilometric observations.

Journal Article↗
PubMed1980

Specification of retinotectal connexions during development of the toad Xenopus laevis.

The specification of central connexions of retinal ganglion cells was studied in Xenopus laevis. In one series of experiments, the right eye primordium was rotated 180 degrees at embryonic stages 24-32. In the other series, the left eye was transplanted into the right orbit, and vice versa, with either 0 degrees or 180 degrees rotation. After metamorphosis the visual projections from the operated eye to the contralateral optic tectum were mapped electrophysiologically and compared with the normal retinotectal map. In all cases the visual projection map was rotated through the same angle as was indicated by the position of the choroidal fissure. The left eye exchanged into the right orbit retained its original axes and projected to the contralateral tectum. These results suggest that retinal ganglion cell connexions are specified before stage 24.

Animals↗
PubMed2001

Physical and transcript map of the dominant optic atrophy (OPA1) gene critical region at 3q28-q29.

The dominant optic atrophy gene (OPA1) has previously been mapped to chromosome 3q28-q29. We have now constructed a physical and transcriptional map across the OPA1 critical region between markers D3S3557 and D3S3346. It comprises 21 sequence-tagged sites (STSs), 4 single nucleotide polymorphisms, 29 expressed sequence tags, 2 known genes, and 12 newly generated STSs anchored onto 21 yeast artificial chromosome, 22 bacterial artificial chromosome, 48 P1 phage artificial chromosome, and 42 cosmid overlapping clones spanning 2.5 Mb. The map has allowed us to order many of the markers hitherto only roughly defined and to exclude 23 of the putative candidate genes assigned to the region. We found the OPA1 critical interval to be 450-550 kb. It contains 2 known genes, RPL35a and SDHA, which thus constitute candidate genes.

Chromosomes, Human, Pair 3↗
PubMed2006

Chemical shift anisotropic mapping of a coherent optical absorber using magnetic field induced quantum beats.

A new method for mapping the spatial structure of optical coherent materials which relies on imposing a set of linear orthogonal gradient magnetic fields for a controlled hyperfine splitting of energy levels to create characteristic quantum beats when illuminated with a laser pulse with sufficient bandwidth to excite these levels is proposed. In this approach, a spectroscopic fingerprint of the dopant sites due to concentration and field susceptibilities in the sample is achieved through a Fourier decomposition of the radiative relaxation decay in an approach analogous to nuclear magnetic resonance spectroscopy due to the imposition of a controlled spatial-spectral encoding scheme. A three pulse sequence necessary to interrogate a gradient resolved voxel is also discussed. This three pulse approach can be combined with the conventional confocal imaging technique to provide information about the underlying chemistry of dopant distribution along each imaging plane which is useful in guiding the design and manufacturing process of optical crystals. In combination with gradient induced quantum beats, the entire inhomogeneous bandwidth can be interrogated. The proposed approach would scan this entire bandwidth at much faster rate enabling characterization of a large number of crystals than is currently possible through mechanical scanning with a confocal microscopy based spectroscopic technique as well as providing functional dopant profiling which is not currently possible with conventional approaches.

Journal Article↗
PubMed1999

Large-scale synaptic errors during map formation by regeneration optic axons in the goldfish.

During the formation of visual maps, growing axons initially form a map by using topographically distributed cues that direct their growth and branching to the appropriate target region. This initial map is typically roughly retinotopic and is subsequently refined through activity-dependent rearrangement or cell death. Although synaptic connections are thought to be rearranged during the later refinement phase, there is no clear evidence that synapses are being formed during the initial targeting phase of development. Also, because optic fiber growth can be accurately directed during normal development, it is unclear whether regenerative fibers that have more pathway disorder would behave similarly. This issue was addressed by using optic fibers of goldfish that have the capacity to regenerate a retinotopic projection and can reestablish a rough retinotopic order without impulse activity. The optic nerve of goldfish was crushed, and at various times later, a small number of optic fibers in ventronasal retina was labeled with wheatgerm agglutinin-horseradish peroxidase. The tectum was then processed for electron microscopy to look at the distribution of labeled synapses during regeneration. At 3 weeks, synapses were observed at the far anterior end of the tectum and none were yet seen at the correct posterior retinotopic position. At 4-5 weeks, synapses were seen in nearly equal numbers at the incorrect anterior end and at both correct (retinotopic) and incorrect posterior positions. At late stages of regeneration, synapses were restricted to their correct posterior retinotopic position in the tectum, as they were in normal fish. These findings show that the formation of global retinotopic order entails the formation and subsequent elimination of a large number of highly ectopic synapses. Synaptic rearrangement is a major feature of targeting in this system and may be required for the regeneration of a retinotopic projection.

Animals↗
PubMed1983

Early auditory experience aligns the auditory map of space in the optic tectum of the barn owl.

Auditory and visual space are mapped in the optic tectum of the barn owl. Normally, these maps of space are in close mutual alignment. Ear plugs inserted unilaterally in young barn owls disrupted the binaural cues that constitute the basis of the auditory map. Yet when recordings were made from the tecta of these birds as adults, the auditory and visual maps were in register. When the ear plugs were removed from these adult birds and binaural balance was restored, the auditory maps were shifted substantially relative to the visual maps and relative to the physical borders of the tecta. These results demonstrate that the neural connectivity that gives rise to the auditory map of space in the optic tectum can be modified by experience in such a way that spatial alignment between sensory modalities is maintained.

Acoustic Stimulation↗
PubMed1998

Dominant optic atrophy: exclusion and fine genetic mapping of the candidate gene, HRY.

Autosomal dominant optic atrophy (OPA1) maps to Chromosome (Chr) 3q28, and the disease interval has been refined to within 1.4 cM, flanked by the markers D3S3669 and D3S3562. HRY, the human homolog of the Drosophila segmentation gene, hairy, maps by in situ hybridization to the chromosomal region 3q28-q29. We screened for mutations in HRY in 36 patients from 18 pedigrees with dominant optic atrophy and a group of normal control individuals. Heteroduplex mutation analysis and direct sequencing of all four coding exons and one upstream putative untranslated exon were performed. No disease-associated sequence alterations were identified. A polymorphism in the untranslated region of exon 2 was found, with four alleles. PCR amplification of this part of exon 2 in four of the pedigrees affected by autosomal dominant optic atrophy mapping to chromosome 3q, followed by haplotype analysis, showed recombination between HRY and OPA1 in one pedigree. This allows us to genetically position HRY in relation to known microsatellite markers in the region, placing HRY telomeric to marker D3S3562 and centromeric to D3S1305. This is outside the published critical disease interval for dominant optic atrophy. We have, therefore, excluded HRY as the gene for dominant optic atrophy by sequence analysis, mapped it genetically, and identified a polymorphism in our population.

Animals↗
PubMed2006

Independence of calibration curves for EBT Gafchromic films of the size of high-energy X-ray fields.

The EBT Gafchromic radiochromic film is a relatively new product designed specifically for dosimetry in radiation therapy. Due to the weak dependence of its response on the photon energy (variations are below 10% in the 50 kVp-10 MVp range), the film is ideal for dosimetry when the photon energy spectrum may be changing or unknown. In order to convert a map of optical densities into a map of absorbed radiation doses, a calibration curve constructed on the basis of standard calibration films is necessary. Our results have shown that, with the EBT Gafchromic film, one can use the same calibration curve for 6-MV X-ray fields of any size in the range from 5 x 5 cm(2) up to 40 x 40 cm(2). This is not the case for radiographic films, such as Kodak X-Omat V, whose response to the same dose varies approximately by 10% depending on the field size in this range. This insensitivity of the EBT Gafchromic film to size of the radiation field makes it possible to assess doses delivered by small radiation fields. With the help of this film, it was shown that the output factor for a 0.5 x 0.5 cm(2) field is 0.60+/-0.03 (2SD) relative to the 10 x 10 cm(2) field.

Calibration↗
PubMed2004

Optical imaging of breast tumor through temporal log-slope difference mappings.

A novel optical temporal log-slope difference mapping approach is proposed for cancerous breast tumor detection. In this method, target tissues are illuminated by near-infrared (700-1000 nm) ultrashort laser pulses from various surface source points, and backscattered time-resolved light signals are collected at the same surface points. By analyzing the log-slopes of decaying signals over all points on the source-detection grid, a log-slope distribution on the surface is obtained. After administration of absorption contrast agents, the presence of cancerous tumors increases the decaying steepness of the transient signals. The mapping of log-slope difference between native tissue and absorption-enhanced cancerous tissue indicates the location and projection of tumors on the detection surface. In this paper, we examine this method in the detection of breast tumors in two model tissue phantoms through computer simulation. The first model has a spherical tumor of 6mm in diameter embedded at the tissue center. The second model is a large tissue phantom embedded with a non-centered spherical tumor 8mm in diameter. Monte Carlo methods were employed to simulate the light transport and signal measurement. It is shown that the tumor in both the tissue models will be accurately projected on the detection surface by the proposed log-slope difference mapping method. The image processing is very fast and does not require any inverse optimization in image reconstruction.

Breast Neoplasms↗
PubMed2005

Two-dimensional mapping of electro-optic phase retardation in lithium niobate crystals by digital holography.

We demonstrate accurate two-dimensional mapping of the phase retardation induced by the electro-optic effect in lithium niobate crystals. Off-axis digital holography is used to investigate congruent z-cut crystals. The spatially resolved optical path difference is interferometrically measured while a linearly rising voltage ramp is applied to the crystal. This procedure provides information on the uniformity of crystals' electro-optic properties and offers the ability to detect the presence of defects that is of fundamental importance for reliable processing of photonic devices.

Journal Article↗
PubMedDate not supplied

The temporal/spatial evolution of optical signals in human cortex.

Intraoperative measures of functioning brain are an important aspect to understanding normal and diseased cortical response. Previous studies, in animal models, have used optical reflectance maps to illustrate the location and timing of functional activity. We used optical reflectance mapping in patients undergoing parietal tumor resection to reveal the temporal/spatial evolution of perfusion and other related metabolic responses of sensorimotor cortex to peripheral somesthetic stimulation. The somatosensory cortex of seven anesthetized patients was mapped in response to transcutaneous electrical median and ulnar nerve stimulation using optical reflectance imaging. The time course and spatial extent of this response were measured and correlated with evoked potential maps collected during the same conditions. Observable signals first appeared within 1-2 sec, peaked at 3 sec, and disappeared by 9 sec. These signals colocalized with the largest evoked potentials in both the sensory and motor regions and demonstrated topological specificity with median and ulnar nerve stimulation. Maps of this temporal/spatial resolution illustrate the integrative and dynamic nature of the neuronal, vascular, and metabolic responses of human cortex. These data also provide insight to the mechanisms responsible for signals obtained using other brain imaging techniques such as PET and fMRI.

Brain Mapping↗
PubMed2002

ADC mapping of the human optic nerve: increased resolution, coverage, and reliability with CSF-suppressed ZOOM-EPI.

The mean apparent diffusion coefficient (ADC) of the human optic nerve (ON) has been quantified in vivo, and mean ADC maps are shown along the complete length of the nerve from the globe to the optic chiasm. The mean ADC, over the whole nerve, is shown to be 1058 x 10(-6) mm(2) s(-1) (standard deviation (SD), over nine 3-mm slices, 101x10(-6) mm(2) s(-1); range (833-1178)x10(-6) mm(2) s(-1)). The robustness of the method relies on acquisition of high-resolution coronal images of the ON using the ZOOM-EPI technique, which makes use of a shortened echo train length for increased resolution with decreased susceptibility-induced distortions. Suppression of the cerebrospinal fluid (CSF) and fat signals from tissues that surround the ON also helps successful identification and delineation of the nerve. Averaging of magnitude images is used to compensate for the inherently low signal-to-noise ratio (SNR) of the acquired images; the effects of the Rayleigh distributed noise in such images are allowed for during ADC calculations.

Cerebrospinal Fluid↗
PubMed2003

New paradigm for optical imaging: temporally encoded maps of intrinsic signal.

We present a new technique for acquiring and analyzing intrinsic signal optical images of brain activity, using continuous stimulus presentation and data acquisition. The main idea is to present a temporally periodic stimulus and to analyze the component of the response at the stimulus frequency. Advantages of the new technique include the removal of heart, respiration, and vasomotor artifacts, a dramatic increase in spatial resolution, and a 30-fold or greater reduction in acquisition time. We also present a novel approach to localizing instantaneous neuronal responses using time-reversed stimuli that is widely applicable to brain imaging. To demonstrate the power of the technique, we present high-resolution retinotopic maps of five visual areas in mouse cortex and orientation maps in cat visual cortex.

Animals↗
PubMed2001

The cortical representation of the hand in macaque and human area S-I: high resolution optical imaging.

High-resolution images of the somatotopic hand representation in macaque monkey primary somatosensory cortex (area S-I) were obtained by optical imaging based on intrinsic signals. To visualize somatotopic maps, we imaged optical responses to mild tactile stimulation of each individual fingertip. The activation evoked by stimulation of a single finger was strongest in a narrow transverse band ( approximately 1 x 4 mm) across the postcentral gyrus. As expected, a sequential organization of these bands was found. However, a significant overlap, especially for the activated areas of fingers 3-5, was found. Surprisingly, in addition to the finger-specific domains, we found that for each of the fingers, weak stimulation activated also a second "common patch" of cortex, located just medially to the representation of the finger. These results were confirmed by targeted multiunit and single-unit recordings guided by the optical maps. The maps remained very stable over many hours of recording. By optimizing the imaging procedures, we were able to obtain the functional maps extremely rapidly (e.g., the map of five fingers in the macaque monkey could be obtained in as little as 5 min). Furthermore, we describe the intraoperative optical imaging of the hand representation in the human brain during neurosurgery and then discuss the implications of the present results for the spatial resolution accomplishable by other neuroimaging techniques, relying on responses of the microcirculation to sensory-evoked electrical activity. This study demonstrates the feasibility of using high-resolution optical imaging to explore reliably short- and long-term plasticity of cortical representations, as well as for applications in the clinical setting.

Action Potentials↗
PubMed1998

Synchronizing retinal activity in both eyes disrupts binocular map development in the optic tectum.

Spatiotemporal correlations in the pattern of spontaneous and evoked retinal ganglion cell (RGC) activity are believed to influence the topographic organization of connections throughout the developing visual system. We have tested this hypothesis by examining the effects of interfering with these potential activity cues during development on the functional organization of binocular maps in the Xenopus frog optic tectum. Paired recordings combined with cross-correlation analyses demonstrated that exposing normal frogs to a continuous 1 Hz of stroboscopic illumination synchronized the firing of all three classes of RGC projecting to the tectum and induced similar patterns of temporally correlated activity across both lobes of the nucleus. Embryonic and eye-rotated larval animals were reared until early adulthood under equivalent stroboscopic conditions. The maps formed by each RGC class in the contralateral tectum showed normal topography and stratification after strobe rearing, but with consistently enlarged multiunit receptive fields. Maps of the ipsilateral eye, formed by crossed isthmotectal axons, showed significant disorder and misalignment with direct visual input from the retina, and in the eye-rotated animals complete compensatory reorientation of these maps usually induced by this procedure failed to occur. These findings suggest that refinement of retinal arbors in the tectum and the ability of crossed isthmotectal arbors to establish binocular convergence with these retinal afferents are disrupted when they all fire together. Our data thus provide direct experimental evidence that spatiotemporal activity patterns within and between the two eyes regulate the precision of their developing connections.

Aging↗
PubMed2003

Shedding light on brain mapping: advances in human optical imaging.

Several functional brain imaging techniques have been used to study human cortical organization. Optical imaging of intrinsic signals (OIS) offers perhaps the best combination of spatial coverage, resolution and speed for mapping the functional topography of human cortex. In this review, we discuss recent advances in optical imaging technology and methodology that have made human OIS easier to implement and more accessible, including improvements in detector characteristics and the development of sophisticated algorithms for reducing motion artifact. Moreover, we discuss how these advances have helped enhance our understanding of the functional organization of the human brain. We also review newly developed analyses for interpreting and validating optical signals, including refined signal analysis techniques and multimodality comparisons. Combined, these advances have enabled the study of not only primary sensory and motor cortices, but also higher cognitive processes such as language production and comprehension. Continued improvement and implementation of this technique promises to shed new light on the functional organization of human cortex.

Algorithms↗