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Results for “Optical imaging”

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At least 145 records · Page 8Linked to original sources
PubMed1997

Identification of functioning cortex using cortical optical imaging.

OBJECTIVE: The purpose of this study was to evaluate the technique of cortical optical imaging (COI) of intrinsic cortical optical signals related to neuronal activation. The specific goals of the study were to evaluate some of the technical aspects of COI and thus maximize the intensity of the image of this intrinsic signaling process and to determine the physiological reliability of COI in a well-defined animal system. METHODS: The intrinsic optical signal of activated whisker barrel cortex of rat was imaged using a computer-based technique for rapid acquisition of enhanced images. Single-unit microelectrode recordings of cortical neuronal responses to whisker movement were used to confirm the locations of the whisker barrels. RESULTS: Narrow band incident light at 600- to 610-nm wavelength was most effective for producing optical images. Images could be obtained during activation by a single long (40 s) stimulus or by averaging the signal generated by repeated shorter (1-8 s) stimuli. Focusing slightly below the cortical surface, minimizing movement, and abolishing extraneous light were all important in increasing the signal-to-noise ratio. The locations of whisker movement-evoked cortical activity determined using COI are consistent with the known functional anatomy of rat whisker barrel cortex. The images obtained with this experimental arrangement are shown to be accurate predictors of the location of neuronal activity determined by comparing the locations of active sites identified with COI with locations of areas of neuronal activity determined using single-cell recording techniques. CONCLUSIONS: COI is able to rapidly identify areas of cortex containing elicited neuronal activity. The technique allows cortical activation maps to be made rapidly with a very high degree of spatial resolution. COI is reliable and consistent over time. COI, if used carefully, holds promise as an intraoperative technique to study both human and experimental animal cortical function.

Animals↗
PubMed2000

[Basic principles of physics in optical imaging of the human eye].

Creation of a real picture of the observed object on the retina by optical system of the eye is the primary physical condition of the visual perception. Absorption of the light energy initiates the sequence of further physicochemical, biochemical and psychophysiological events partially taking place already in the retina but mostly in the higher cerebral and spinal centres. So the visual perception and its final evaluation is the result of a complicated complex of processes where the optical imaging itself plays the role of the starting factor. In the publication particularly the physical substance of the optical imaging on refraction surfaces between media with different refraction index has been accentuated. The laws of reflection and refraction and their origin are derived in the terms of the physical (Maxwell equations) and geometrical (Fermat principle, principle of the mutual independence of light beams) optics. In the adequate extent the development and structure of the eye and the whole visual complex, the bases of the quantification of the visual perception and contemporary opinions on mechanisms of the colour vision (trichromatic theory) have been described. The publication is completed by a mathematical appendix explaining some relations usually absent in the biomedical literature.

Electromagnetic Phenomena↗
PubMed2002

Optical imaging of intrinsic signals in ferret auditory cortex: responses to narrowband sound stimuli.

This paper describes optical imaging of the auditory cortex in the anesthetized ferret, particularly addressing optimization of narrowband stimuli. The types of sound stimuli used were tone-pip trains and sinusoidal frequency and amplitude modulated (SFM and SAM) tones. By employing short illumination wavelengths (546 nm), we have successfully characterized the tonotopic arrangement, in agreement with the well-established electrophysiological tonotopic maps of the ferret auditory primary field (AI). The magnitude of the optical signal increased with sound level, was maximal for a modulation frequency (MF) of 2-4 Hz, and was larger for tone-pip trains and SFM sounds than for SAM sounds. Accordingly, an optimal narrowband stimulus was defined. Thus optical imaging can be used successfully to obtain frequency maps in auditory cortex by an appropriate choice of stimulus parameters. In addition, background noise consisting of 0.1-Hz oscillations could be reduced by introduction of blood pressure enhancing drugs. The optical maps were largely independent of 1) the type of narrowband stimulus, 2) the sound level, and 3) the MF. This stability of the optical maps was not predicted from the electrophysiological literature.

Acoustic Stimulation↗
PubMed2002

Hemodynamic response in the unanesthetized rat: intrinsic optical imaging and spectroscopy of the barrel cortex.

Optical imaging spectroscopy was used to measure the hemodynamic response of somatosensory cortex to stimulation of the whiskers. Responses to brief puffs of air were compared in anesthetized and unanesthetized rats. The hemodynamic response was approximately four times larger in the unanesthetized animal than the corresponding anesthetized animal. In unanesthetized animals, a short-latency (approximately 400 milliseconds) short-duration (approximately 300 milliseconds) hemodynamic startle response was observed. General linear model analysis was used to extract this component from the time series, and revealed an underlying short-latency increase in deoxygenated hemoglobin in response to somatosensory stimulation. It is proposed that anesthesia can have a marked affect on the relation between changes in blood volume and blood flow. This work represents a step in the development of an experimental model that can be used to investigate fundamental neurologic processes in the awake-behaving rodent.

Anesthesia↗
PubMed2006

Tissue engineering scaffolds based on photocured dimethacrylate polymers for in vitro optical imaging.

Model tissue engineering scaffolds based on photocurable resin mixtures with sodium chloride have been prepared for optical imaging studies of cell attachment. A photoactivated ethoxylated bisphenol A dimethacrylate was mixed with sieved sodium chloride (NaCl) crystals and photocured to form a cross-linked composite. Upon soaking in water, the NaCl dissolved to leave a porous scaffold with desirable optical properties, mechanical integrity, and controlled porosity. Scaffolds were prepared with salt crystals that had been sieved to average diameters of 390, 300, 200, and 100 microm, yielding porosities of approximately 75 vol %. Scanning electron microscopy and X-ray microcomputed tomography confirmed that the pore size distribution of the scaffolds could be controlled using this photocuring technique. Compression tests showed that for scaffolds with 84% (by mass fraction) salt, the larger pore size scaffolds were more rigid, while the smaller pore size scaffolds were softer and more readily compressible. The prepared scaffolds were seeded with osteoblasts, cultured between 3 and 18 d, and examined using confocal microscopy. Because the cross-linked polymer in the scaffolds is an amorphous glass, it was possible to optically image cells that were over 400 microm beneath the surface of the sample.

Animals↗
PubMed2007

Diffuse optical imaging and spectroscopy for cancer.

Visible light and near infrared light interact with biological tissue by absorption and scattering. Diffuse optical imaging and spectroscopy reconstructs tissue physiologic parameters based on noninvasive measurement of tissue optical properties. This technology can be used to differentiate physiologic and molecular signatures of both malignant and benign tissues, as they relate to the area of cancer research. Major advantages are the use of non-ionizing radiation, real-time continuous data acquisition, low cost, and portability. Limitations include low spatial resolution and limited reproducibility. This paper reviews the currently available state-of-the-art technologies for diffuse optical imaging and spectroscopy and their applications in cancer research.

Biomedical Technology↗
PubMed2006

Fetal gene transfer using lentiviral vectors: in vivo detection of gene expression by microPET and optical imaging in fetal and infant monkeys.

Fetal intraperitoneal administration of human immunodeficiency virus (HIV)-l-derived lentiviral vectors (10(7) infectious particles/fetus) has consistently shown high levels of transduction and gene expression in the omentum, peritoneum, and diaphragm when assessed by polymerase chain reaction (PCR) and whole tissue fluorescence. In vivo imaging techniques were explored with early-gestation long-tailed macaques that were administered the vesicular stomatitis virus-glycoprotein (VSV-G)-pseudotyped HIV-1-derived lentiviral vector expressing a mutant herpes simplex virus type 1 thymidine kinase (HSV-1-sr39tk) and firefly luciferase under the control of the cytomegalovirus (CMV) promoter. Fetuses were monitored sonographically and twice during gestation 9-[4-[18F]Fluoro-3-(hydroxymethyl)butyl]guanine (18F-FHBG) was injected into the fetal circulation under ultrasound guidance in preparation for microPET imaging. All newborns were delivered at term by cesarean section and raised in the nursery for postnatal studies. At 2 months postnatal age, animals were imaged and biodistribution was assessed. Optical imaging for firefly luciferase expression was also performed every 2 months postnatal age. Under all imaging conditions gene expression was observed in the abdominal region, and closely paralleled findings from prior studies based on whole tissue fluorescence. These investigations have shown that HSV-1-sr39tk and firefly luciferase can be used to safely detect transgene expression at multiple time points in fetal and infant monkeys in vivo and without evidence of adverse effects.

Animals↗
PubMed2005

In vivo optical imaging of human adenoid cystic carcinoma cell metastasis.

A noninvasive, whole-body, real-time fluorescence optical imaging of stable high-level green fluorescent protein (GFP)-expressing human adenoid cystic carcinoma (ACC-M-GFP) was demonstrated for in vivo visualization of metastatic behavior in nude mice. Five-week-old female nude mice were injected with ACC-M-GFP in the primary organ: submandibular gland. Metastases were only visualized by GFP expression in the lung. However, metastatic lesions of ACC-M-GFP in the lung, muscle, bladder and bony were found by imaging of GFP expression in intact mice through tail vein injection of ACC-M-GFP cells. The construction of highly fluorescent and stable GFP transfectants of ACC-M has revealed the multi-organ metastatic capability of ACC-M cells through this optical imaging.

Animals↗
PubMed1999

Optical images of visible and invisible percepts in the primary visual cortex of primates.

We optically imaged a visual masking illusion in primary visual cortex (area V-1) of rhesus monkeys to ask whether activity in the early visual system more closely reflects the physical stimulus or the generated percept. Visual illusions can be a powerful way to address this question because they have the benefit of dissociating the stimulus from perception. We used an illusion in which a flickering target (a bar oriented in visual space) is rendered invisible by two counter-phase flickering bars, called masks, which flank and abut the target. The target and masks, when shown separately, each generated correlated activity on the surface of the cortex. During the illusory condition, however, optical signals generated in the cortex by the target disappeared although the image of the masks persisted. The optical image thus was correlated with perception but not with the physical stimulus.

Animals↗
PubMed2004

Optical imaging of visually evoked responses in prosimian primates reveals conserved features of the middle temporal visual area.

Optical imaging of intrinsic cortical responses to visual stimuli was used to characterize the organization of the middle temporal visual area (MT) of a prosimian primate, the bush baby (Otolemur garnetti). Stimulation with moving gratings revealed a patchwork of oval-like domains in MT. These orientation domains could, in turn, be subdivided into zones selective to directional movements that were mainly orthogonal to the preferred orientation. Similar, but not identical, zones were activated by movements of random dots in the preferred direction. Orientation domains shifted in preference systematically either around a center to form pinwheels or as gradual linear shifts. Stimuli presented in different portions of the visual field demonstrated a global representation of visual space in MT. As optical imaging has revealed similar features in MT of New World monkeys, MT appears to have retained these basic features of organization for at least the 60 million years since the divergence of prosimian and simian primates.

Animals↗
PubMed2003

Near-infrared optical imaging of proteases in cancer.

Near-infrared optical imaging is a newer imaging technique that, coupled with sensitive enzymatically specific fluorescent beacons, shows much promise for earlier detection of many cancers and their in situ characterization. On the basis of animal studies demonstrating visualization of micrometastasis-sized tumors and the ability to evaluate therapeutic enzyme inhibition real-time, such imaging may be incorporated in the clinical imaging paradigm in the future, both to improve cancer screening as well as for monitoring therapy in individual patients. This review details some of the related biology, optical probe design, and required hardware, with in vivo cathepsin and matrix metalloprotinease imaging used as examples.

Animals↗
PubMed1999

Optical imaging technology in minimally invasive surgery. Current status and future directions.

Optical engineering and imaging technology have played a major role in the evolving field of minimally invasive surgery (MIS) by making it possible to visualize the manipulation of tissue at remote internal sites. We assess and review the optical imaging technology used during a variety of MIS procedures from an engineering perspective. The field of MIS is evolving rapidly. Optic-based technologies have the potential to further improve diagnostic capabilities of MIS. Optical imaging technologies and instrument designs are discussed in relation to their current and future use in MIS procedures. Technical limitations in imaging technology are described, along with potential solutions. We review the current status and future role of optical imaging technology in MIS. In the future, synergistic benefits from engineering, imaging technology, and MIS are likely to improve diagnostic ability and patient care.

Equipment Design↗
PubMed2004

In vivo optical imaging of tone-evoked activity in the dorsal cochlear nucleus with a voltage sensitive dye.

We investigated the use of optical imaging for observing the spatial patterns of neural activation in the dorsal cochlear nucleus (DCN) of hamsters during tonal stimulation. The patterns of activation were studied in the DCN, in vivo, following application of a voltage sensitive dye, Di-2-ANEPEQ, to the DCN surface. Beginning 60-90 min following dye application, tones were presented to the ipsilateral ear. Electrophysiological recordings after dye application revealed no significant toxicity of Di-2-ANEPEQ that affected the frequency-tuning properties of DCN neurons. We examined areas of activation in response to each of a series of test stimuli consisting of pure tones ranging in frequency from 2 to 20 kHz. For each stimulus condition, images were collected over a stimulus interval of 400 msec and averaged over 32 stimulus repetitions. These images revealed areas of activation with definable epicenters. The epicenters shifted from lateral to more medial locations on the DCN surface with increases in stimulus frequency. Comparison with electrophysiological data indicated a close parallel between the tonotopic gradient defined by optical imaging and that defined by the distribution of characteristic frequencies. The principal temporal and spatial features of these optical responses are described.

Acoustic Stimulation↗
PubMed2001

Whole-body and intravital optical imaging of angiogenesis in orthotopically implanted tumors.

The development of drugs for the control of tumor angiogenesis requires a simple, accurate, and economical assay for tumor-induced vascularization. We have adapted the orthotopic implantation model to angiogenesis measurement by using human tumors labeled with Aequorea victoria green fluorescent protein for grafting into nude mice. The nonluminous induced capillaries are clearly visible against the very bright tumor fluorescence examined either intravitally or by whole-body luminance in real time. The orthotopic implantation model of human cancer has been well characterized, and fluorescence shadowing replaces the laborious histological techniques for determining blood vessel density. Intravital images of orthotopically implanted human pancreatic tumors clearly show angiogenic capillaries at both primary and metastatic sites. A quantitative time course of angiogenesis was determined for an orthotopically growing human prostate tumor periodically imaged intravitally in a single nude mouse over a 19-day period. Whole-body optical imaging of tumor angiogenesis was demonstrated by injecting fluorescent Lewis lung carcinoma cells into the s.c. site of the footpad of nude mice. The footpad is relatively transparent, with comparatively few resident blood vessels, allowing quantitative imaging of tumor angiogenesis in the intact animal. Capillary density increased linearly over a 10-day period as determined by whole-body imaging. Similarly, the green fluorescent protein-expressing human breast tumor MDA-MB-435 was orthotopically transplanted to the mouse fat pad, where whole-body optical imaging showed that blood vessel density increased linearly over a 20-week period. These powerful and clinically relevant angiogenesis mouse models can be used for real-time in vivo evaluation of agents inhibiting or promoting tumor angiogenesis in physiological microenvironments.

Animals↗
PubMed2005

Molecular optical imaging: applications leading to the development of present day therapeutics.

A number of advances in the molecular imaging field have led to the sensing of specific molecular targets and pathways in living animals. In the optical imaging field, these include the designing of biocompatible near-infrared fluorochromes, development of targeted and activatable "smart" imaging probes, and engineering of activatable fluorescent and bioluminescent proteins. The current advances in molecular optical imaging will help in early disease diagnoses, functioning of a number of pathways and finally help speed drug discovery. In this review, we will describe the near infrared fluorescent and bioluminescence imaging modalities and how these techniques have been employed in current research. Furthermore, we will also shed some light on the use of these imaging modalities in neurotherapeutics, for example imaging different parameters of vector-mediated gene expression in glioma tumors and stem cell tracking in vivo.

Animals↗
PubMed1992

Intrinsic signal optical imaging in the forepaw area of rat somatosensory cortex.

The responses of somatosensory cortex (S-I) to tactile stimulation of the forepaw were assessed by intrinsic signal optical imaging. The tips of digits two or five were alternately touched with mechanical tappers while video photographs were taken of S-I illuminated by an 800-nm light source. The resulting images showed two highlighted areas about 300 microns in diameter and 500 microns apart. Generation of these images required less than 1 hr. Electrode penetrations placed in the areas highlighted during stimulation provided multiunit recordings with receptive fields appropriate for the stimulated digit and not the other digit. Penetrations between the high-lighted areas yielded receptive fields on intervening digits. These results demonstrate that intrinsic signal optical images are obtainable in S-I and confirm the functional somatotopy previously reported using electrical recording. Furthermore, the short time required to produce the images and the obtainable spatial resolution suggest that optical recording could be employed for the study of cortical reorganization in this brain region.

Animals↗
PubMed1998

Functional architecture in monkey inferotemporal cortex revealed by in vivo optical imaging.

To investigate the functional organization in the monkey inferotemporal cortex, which is the last exclusively visual area along the ventral visual cortical pathway, optical imaging based on intrinsic signals was carried out. We first conducted single-cell recordings with microelectrodes and determined the features critical for the activation of single cells. For the subsequent optical imaging, each critical feature was presented, which evoked multiple dark spots. Individual spots were approximately 0.5 mm in diameter and one of them covered the site of the electrode penetration at which the particular critical feature had been determined. The degree of stimulus selectivity varied from spot to spot, and from region to region even within a spot. Some regions were activated only by one of 12- 16 stimuli, while others by more than three stimuli. There were spots specifically activated by faces, and the position of activation spot changed gradually along the cortical surface as the stimulus face was rotated in depth. The length of the overall region along the direction of shift of these spots was approximately 1 mm. These results confirm the regional clustering of cells with similar stimulus selectivity and suggest larger units in which some parameters of object features are continuously mapped.

Animals↗
PubMed1999

Orientation topography of layer 4 lateral networks revealed by optical imaging in cat visual cortex (area 18).

The functional specificity of corticocortical connections with respect to the topography of orientation selectivity was studied by optical imaging of intrinsic signals and bulk injections of fluorescent latex beads (green and red) and biocytin into layer 4. The distributions of retrogradely labelled cells and anterogradely labelled axon terminals were histologically reconstructed from all cortical laminae, and the resulting anatomical maps compared with the optically imaged functional maps. Layer 4 injections produced extensive horizontal labelling up to 2-3 mm from the injection centres albeit without the clear patchy pattern described after layer 2/3 injections (Gilbert & Wiesel 1989, J. Neurosci., 9, 2432-2442; Kisvárday et al. 1997, Cerebral Cortex, 7, 605-618). The functional (orientation) distribution of the labelled projections was analysed according to laminar location and lateral spread. With regard to the former, no major difference in the orientation topography between supragranular- (upper tier), granular- (middle tier) and infragranular (lower tier) layers was seen. Laterally, proximal and distal projections were distinguished and further dissected into three orientation categories, iso- (+/- 30 degrees ), oblique- (+/- 30-60 degrees ) and cross-orientations (+/- 60-90 degrees ) with respect to the orientation preference at the injection sites. The majority of distal connections (retrograde and anterograde) was equally distributed across orientations (35.4% iso-, 33.7% oblique-, and 30.9% cross-orientations) that are equivalent with a preponderance to dissimilar orientations (oblique- and cross-orientations, 64.6%). In one case, distal excitatory and inhibitory connections could be morphologically distinguished. For both categories, a marked bias to dissimilar orientations was found (excitatory, 63.7%; inhibitory, 86.6%). Taken together, these results suggest that the long-range layer 4 circuitry has a different functional role from that of the iso-orientation biased (52.9%, Kisvárday et al. 1997, Cerebral Cortex, 7, 605-618) layer 2/3 circuitry, and is perhaps involved in feature difference-based mechanisms, e.g. figure ground segregation.

Animals↗