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Results for “Optical imaging”

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At least 937 records · Page 52Linked to original sources
PubMed2006

Elimination of depth degeneracy in optical frequency-domain imaging through polarization-based optical demodulation.

A novel optical frequency-domain imaging system is demonstrated that employs a passive optical demodulation circuit and a chirped digital acquisition clock derived from a voltage-controlled oscillator. The demodulation circuit allows the separation of signals from positive and negative depths to better than 50 dB, thereby eliminating depth degeneracy and doubling the imaging depth range. Our system design is compatible with dual-balanced and polarization-diverse detection, important techniques in the practical biomedical application of optical frequency-domain imaging.

Analog-Digital Conversion↗
PubMed2002

Multiwavelength optical intrinsic signal imaging of cortical spreading depression.

Cortical spreading depression (CSD) is an important disease model for migraine and cerebral ischemia. In this study, we exploit the high temporal and spatial resolution of optical imaging to characterize perfusion-dependent and -independent changes in response to CSD and to investigate the etiology of reflectance changes during CSD. In this experiment, we characterized the optical response to CSD at wavelengths that emphasize perfusion-related changes (610 and 550 nm), and we compared these results with 850 nm and blood volume data. Blood volume changes during CSD were recorded using an intravascular fluorescent dye, Texas Red dextran. We observed triphasic optical signals at 850 and 550 nm characterized by spreading waves of increased, decreased, then increased reflectance (Fig. 1) which expanded at a rate of approximately 3-5 mm/min. The signal at 610 nm had a similar initial phase, but the phase 2 response was slightly more complex, with a parenchymal decrease in reflectance but a vascular increase in reflectance. Reflectance values decreased in phase three. Blood volume signals were delayed relative to the optical intrinsic signals and corresponded temporally to phases 2 and 3. This is the first study to characterize optical imaging of intrinsic signal responses to CSD, in vivo, at multiple wavelengths. The data presented here suggest that changes in light scattering precede perfusion responses, the blood volume increase (phase 2) is accompanied by a reduction in deoxyhemoglobin, and the blood volume decrease (phase 3) is accompanied by an increase in deoxyhemoglobin. Previous studies have suggested the oligemia of spreading depression was a result of decreased metabolic demand. This study suggests that during the oligemic period there is a greater reduction in oxygen delivery than in demand.

Animals↗
PubMed2006

Overcoming photodamage in second-harmonic generation microscopy: real-time optical recording of neuronal action potentials.

Second-harmonic generation (SHG) has proven essential for the highest-resolution optical recording of membrane potential (Vm) in intact specimens. Here, we demonstrate single-trial SHG recordings of neuronal somatic action potentials and quantitative recordings of their decay with averaging at multiple sites during propagation along branched neurites at distances up to 350 mum from the soma. We realized these advances by quantifying, analyzing, and thereby minimizing the dynamics of photodamage (PD), a frequent limiting factor in the optical imaging of biological preparations. The optical signal and the PD during SHG imaging of stained cultured Aplysia neurons were examined with intracellular electrode recordings monitoring the resting Vm variations induced by laser-scanning illumination. We found that the PD increased linearly with the dye concentration but grew with the cube of illumination intensity, leading to unanticipated optimization procedures to minimize PD. The addition of appropriate antioxidants in conjunction with an observed Vm recovery after termination of laser scanning further refined the imaging criteria for minimization and control of PD during SHG recording of action potentials. With these advances, the potential of SHG as an effective optical tool for neuroscience investigations is being realized.

Action Potentials↗
PubMedDate not supplied

Multipixel techniques for frequency-domain photon migration imaging.

The ability to map interior optical properties of a highly scattering medium from exterior measurements of light propagation is afforded by optical tomography. In this communication, we describe the problem of optical tomography, the techniques of photon migration measurements necessary to accomplish it, and the development of multipixel measurements for rapid collection of optical signals. These multipixel measurements are shown to provide detection of contrast owing to the optical properties of absorption and fluorescence associated with dye-laden heterogeneities embedded in a tissue-like scattering medium. From these rapid measurements, successful reconstruction of an interior optical property map may now be possible with clinically realistic data acquisition times. Applications for the technology arise for biomedical optical imaging for the in vivo detection of disease and the diagnosis of tissue (bio-) chemistry.

Absorption↗
PubMedDate not supplied

Optimal design of structured nanospheres for ultrasharp light-scattering resonances as molecular imaging multilabels.

Optical molecular imaging could potentially enable noninvasive high-resolution characterization and diagnosis of living tissue. The capability to image multiple molecular targets simultaneously is particularly important. Currently this task cannot be achieved using conventional optical contrast agents, due to their broad spectral responses (approximately 80 to 200 nm). Developments in research on semiconductor nanocrystals (quantum dots) provide one possible solution. We describe a different concept of multilabel molecular imaging that utilizes resonant light-scattering spectroscopy of multilayered nanospheres to achieve tunable ultrasharp resonance peaks with widths as narrow as 10 nm. Our theoretical study demonstrates that dozens of molecular targets can potentially be imaged simultaneously using this approach.

Equipment Design↗
PubMed2006

Recent developments in optical coherence tomography for imaging the retina.

Optical coherence tomography (OCT) was introduced in ophthalmology a decade ago. Within a few years in vivo imaging of the healthy retina and optic nerve head and of retinal diseases was a fact. In particular the ease with which these images can be acquired considerably changed the diagnostic strategy used by ophthalmologists. The OCT technique currently available in clinical practice is referred to as time-domain OCT, because the depth information of the retina is acquired as a sequence of samples, over time. This can be done either in longitudinal cross-sections perpendicular to, or in the coronal plane parallel to the retinal surface. Only recently, major advances have been made as to image resolution with the introduction of ultrahigh resolution OCT and in imaging speed, signal-to-noise ratio and sensitivity with the introduction of spectral-domain OCT. Functional OCT is the next frontier in OCT imaging. For example, polarization-sensitive OCT uses the birefringent characteristics of the retinal nerve fibre layer to better assess its thickness. Blood flow information from retinal vessels as well as the oxygenation state of retinal tissue can be extracted from the OCT signal. Very promising are the developments in contrast-enhanced molecular optical imaging, for example with the use of scattering tuneable nanoparticles targeted at specific tissue or cell structures. This review will provide an overview of these most recent developments in the field of OCT imaging focussing on applications for the retina.

Humans↗
PubMed2003

Effect of dextran-induced changes in refractive index and aggregation on optical properties of whole blood.

The purpose of the present study is to investigate systematically the mechanisms of alterations in the optical properties of whole blood immersed in the biocompatible agent dextran, and to define the optimal concentration of dextrans required for blood optical clearing in order to enhance the capability of light penetration depth for optical imaging applications. In the experiments, dextrans with different molecular weights and various concentrations were employed and investigated by the use of the optical coherence tomography technique. Changes in light attenuation, refractive index and aggregation properties of blood immersed in dextrans were studied. It was concluded from the results that the mechanisms for blood optical clearing are characteristic of the types of dextrans employed, their concentrations and the application stages. Among the substances applied, Dx500 at a concentration at 0.5 g dl(-1) gives the best result in improving light penetration depth through the blood. The increase of light transmission at the beginning of the addition of dextrans is mainly attributed to refractive index matching between the scattering centres and the ground matter. Thereafter, the transmission change is probably due to a dextran-induced aggregation-disaggregation effect. Overall, light scattering in the blood could be effectively reduced by the application of dextrans. It represents a promising approach to increasing the imaging depth for in vivo optical imaging of biological tissue, for example optical coherence tomography.

Adult↗
PubMed2006

[Influence of "optical illusion" on detectability in diagnosis for head CT images: participation of optical illusion of light perception in medical image reading and diagnosis].

Even if the visual impression of the photographic density of the brain in head CT images is shown as physically the same, it is known that optical illusions of lightness perception (assimilation, contrast, picture frame effect, etc.) occur and that practical density can be observed psychologically differently, according to differences in the color of the skull and background, and differences in cases (differences in picture pattern). Therefore, in this study, in order to clarify the influence of optical illusion on detectability in diagnosis, the author attempted to compare detectability in four sample cases, consisting of acute cerebral infarction (1), acute epidural hematoma (1), and chronic subdural hematoma (2), using visual subjective evaluation. In the case of acute cerebral infarction, there was no significant difference in detectability between the original image and the virtual images. Further, it clarified that the original head CT image (acute epidural hematoma) with the high-density hematoma recognized at the marginal limited part of the brain was inferior to virtual images in detectability, while it clarified that the original head CT image (chronic subdural hematoma) with the low-density hematoma was superior to virtual images in detectability, because of visual psychological emphasis on the difference of the film contrast between the hematoma and white skull.

Brain↗