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PubMed1996

Dynamic optical imaging.

The main direction in modern imaging is increasing the spatial resolution and selectivity for pathology pattern recognition at the microscale. Dynamic optical imaging (DOl) has enormous potential in the selectivity of description of living tissue state at cellular and subcellular levels. However, multiple light scattering creates considerable difficulties in revealing the tissue microstructure in its depth. On the other hand, along with changes in the microstructure, pathology should also manifest itself in the integral macroscopic pattern of the tissue. Actually, living tissue, as a distributed active media with well-developed reception and self-regulation, is characterized by a high spatial synergy. In such a media, even morphologically small pathology could disturb tissue functioning in a rather extended area. As a result, after some definite time, a diffuse "field" of the pathological phenomena appears even in the morphological image. Since optical contrast is determined by tissue components (such as blood), which actively participate in physiological functioning, the distributed functional pattern of the tissue is reflected in optical images in the form of spatiotemporal modulation of the optical density. This observation opens up the possibility of investigating the diffuse pattern of the pathology at the functional stage of its development, even before the actual appearance of noticeable morphological changes .

Journal Article↗
PubMedDate not supplied

Suprathreshold auditory cortex activation visualized by intrinsic signal optical imaging.

The suprathreshold tonotopic organization of rat and guinea pig auditory cortex was investigated using intrinsic signal optical imaging through a thinned skull. Optical imaging revealed that suprathreshold pure sine wave tone stimulation (25-80 dB) evoked activity over large cortical areas that were tonotopically organized. Three-dimensional surface plots of the activated areas revealed "patchy' auditory-evoked activity consisting of numerous local peaks and valleys building to a maximum. Subsequent detailed electrophysiological mapping in the same subjects confirmed the localization of auditory-evoked activity based on optical imaging, including responses to a test frequency at cortical loci more than 2 octaves away from the threshold-defined isofrequency contour. The success of this technique in visualizing auditory cortex functional organization at suprathreshold stimulus levels will allow for future investigations of auditory cortex frequency representation, including representational plasticity induced by a variety of experimental manipulations.

Acoustic Stimulation↗
PubMed1994

Enhanced optical imaging of rat gliomas and tumor margins.

Current intraoperative methods used to maximize the extent of tumor removal are limited to intraoperative biopsies, ultrasound, and stereotactic volumetric resections. A new technique involving the optical imaging of an intravenously injected dye has the potential to localize tumors and their margins with a high degree of accuracy. In a rat glioma model, enhanced optical imaging was performed and indocyanine green was used as the contrast-enhancing agent. In all 22 animals, the peak optical change in the tumor was greater than in the ipsilateral brain around the tumor and the contralateral normal hemisphere. The clearance of the dye was significantly delayed to a greater extent in the tumor than in the brain around the tumor and the normal brain. After attempts were made at complete microscopic resection, enhanced optical imaging of the tumor margins and the histological samples demonstrated a specificity of 93% and a sensitivity of 89.5%. Enhanced optical imaging was capable of outlining the tumor even when the imaging was done through the cranium. The optical imaging of rat gliomas with a contrast-enhancing dye is able to differentiate between normal brain and tumor tissue both at the cortical surface and at the tumor margins. The application of these studies in an intraoperative clinical setting may allow for the more accurate determination of tumor margins and may increase the extent of tumor removal.

Animals↗
PubMedDate not supplied

An in-line optical image translator with applications in x-ray videography.

Many applications in radiography require, or would benefit from, the ability to translate, i.e. move, an optical image in the detector plane. In this paper, we describe the design and characterization of a prism-based optical image translator for insertion into existing XRII-video imaging systems. A pair of prisms rotatable about the optical axis form a very compact in-line optical image translator for installation in the parallel light path between an x-ray image intensifier and its video camera. Rotation of the prisms translates the XRII optical image on the camera target. With the addition of x-ray and light collimators to limit the image to a single video line, x-ray streak images may be acquired. By rotating an object in the x-ray beam during a streak, a complete computed tomography (CT) data set may be acquired. This image translator can translate an image anywhere in the focal plane of a 50-mm-output lens within a 40-mm-diam circle. The prisms have an aperture of 50 mm, permitting an optical speed of F/2 with a 50-mm output lens. The design is insensitive to angular alignment errors. This image translator is achromatic, since the spectral width of the output phosphorus of image intensifiers is sufficient to introduce blurring in a nonacrhomatic design. A prism-based image translator introduces image distortion, since the prisms do not operate at minimum deviation. The distortion is less than 4% over all parts of a typical detector area, and less than 1% in the central region of the image.(ABSTRACT TRUNCATED AT 250 WORDS)

Biophysical Phenomena↗
PubMed1997

Multianalyte biosensors on optical imaging bundles.

We present an optical biosensor design that expands the utility of enzyme biosensors. These biosensors are fabricated by site-selective photodeposition of analyte-sensitive polymer matrices on optical imaging fibres. These dual-analyte arrays allow for the simultaneous, independent measurement of the analyte of interest and the transducing analyte. The first integrated optical-biosensors using this design have been prepared that allow both the dependent and independent analytes to be measured simultaneously, for example penicillin and pH (Healey & Walt, 1995) or glucose and O2 (Li & Walt, 1995). Independent measurement of the transducing analyte allows penicillin or glucose to be quantitated in the presence of a concurrent pH or O2 change, respectively. Penicillin can be measured in the range 0.25-10.0 mM in the pH range 6.2-7.5. Glucose can be measured in the range 0.6-20.0 mM in the O2 range 20-100%. The utility of the sensor design was demonstrated by using the penicillin-dual-analyte biosensor to quantitate penicillin produced during a Penicillium chrysogenum fermentation.

Biosensing Techniques↗
PubMedDate not supplied

Optical imaging of intrinsic signals in chinchilla auditory cortex.

We have assessed sound frequency and intensity responses in primary auditory cortex of the (ketamine) anesthetized chinchilla using optical imaging of intrinsic signals. Temporal cortex was exposed via a 10-mm craniotomy and a windowed chamber was mounted. A 4-second period of gated tones (10 ms rise/fall; 50 ms plateau; 10/s) was presented to the contralateral ear at levels between 0 and 80 dB SPL. The cortical surface was illuminated with 540 nm light and video images captured in 0.5-second bins for 7.5 s (Imager 2001; Optical Imaging). Intrinsic signals were first apparent 0.5-1 s after stimulus onset, and were maximal after 3-4 s; they decayed over several seconds. The cortical area in which intrinsic activity was detected corresponded closely with electrophysiologically defined AI cortex. Intrinsic signals can reliably be detected to stimuli at 30-40 dB SPL, and in general, the area of intrinsic signal activity tends to expand with increasing stimulation level. Using stimulation levels of 80 dB SPL, we show that low-frequency stimuli (0.5-1 kHz) evoke intrinsic signals in anterior areas whilst posterior areas are activated by high-frequency stimuli (e.g. 16 kHz). Thus a low- to high-frequency tonotopic organization is seen along this axis.

Animals↗
PubMed1995

The spatial resolution performance of a time-resolved optical imaging system using temporal extrapolation.

Optical imaging methods are being explored as a potential means of screening for breast cancer. Previous investigations of time-resolved imaging techniques have suggested that due to the lack of photons with sufficiently small pathlengths, the spatial resolution achievable through a human breast would be unlikely to be better than a centimeter. Experimental results presented here indicate, however, that higher resolution may be achieved by extrapolating the measured temporal distribution of transmitted photons. This is performed using a least-squares fit between data and an analytic model of photon transport. The spatial resolution of a time-resolved imaging system was evaluated by measuring the edge response produced by an opaque mask embedded in the center of a 51-mm-thick, very highly scattering medium. The limiting spatial resolution was improved from about 13 mm to about 5 mm.

Breast Neoplasms↗
PubMed1990

Functional organization of primate visual cortex revealed by high resolution optical imaging.

A high spatial resolution optical imaging system was developed to visualize cerebral cortical activity in vivo. This method is based on activity-dependent intrinsic signals and does not use voltage-sensitive dyes. Images of the living monkey striate (VI) and extrastriate (V2) visual cortex, taken during visual stimulation, were analyzed to yield maps of the distribution of cells with various functional properties. The cytochrome oxidase--rich blobs of V1 and the stripes of V2 were imaged in the living brain. In V2, no ocular dominance organization was seen, while regions of poor orientation tuning colocalized to every other cytochrome oxidase stripe. The orientation tuning of other regions of V2 appeared organized as modules that are larger and more uniform than those in V1.

Action Potentials↗
PubMed2000

Principal component analysis and blind separation of sources for optical imaging of intrinsic signals.

The analysis of data sets from optical imaging of intrinsic signals requires the separation of signals, which accurately reflect stimulated neuronal activity (mapping signal), from signals related to background activity. Here we show that blind separation of sources by extended spatial decorrelation (ESD) is a powerful method for the extraction of the mapping signal from the total recorded signal. ESD is based on the assumptions (i) that each signal component varies smoothly across space and (ii) that every component has zero cross-correlation functions with the other components. In contrast to the standard analysis of optical imaging data, the proposed method (i) is applicable to nonorthogonal stimulus-conditions, (ii) can remove the global signal, blood-vessel patterns, and movement artifacts, (iii) works without ad hoc assumptions about the data structure in the frequency domain, and (iv) provides a confidence measure for the signals (Z score). We first demonstrate on orientation maps from cat and ferret visual cortex, that principal component analysis, which acts as a preprocessing step to ESD, can already remove global signals from image stacks, as long as data stacks for at least two-not necessarily orthogonal-stimulus conditions are available. We then show that the full ESD analysis can further reduce global signal components and-finally-concentrate the mapping signal within a single component both for differential image stacks and for image stacks recorded during presentation of a single stimulus.

Animals↗
PubMed2006

A hyperspectral fluorescence system for 3D in vivo optical imaging.

In vivo optical instruments designed for small animal imaging generally measure the integrated light intensity across a broad band of wavelengths, or make measurements at a small number of selected wavelengths, and primarily use any spectral information to characterize and remove autofluorescence. We have developed a flexible hyperspectral imaging instrument to explore the use of spectral information to determine the 3D source location for in vivo fluorescence imaging applications. We hypothesize that the spectral distribution of the emitted fluorescence signal can be used to provide additional information to 3D reconstruction algorithms being developed for optical tomography. To test this hypothesis, we have designed and built an in vivo hyperspectral imaging system, which can acquire data from 400 to 1000 nm with 3 nm spectral resolution and which is flexible enough to allow the testing of a wide range of illumination and detection geometries. It also has the capability to generate a surface contour map of the animal for input into the reconstruction process. In this paper, we present the design of the system, demonstrate the depth dependence of the spectral signal in phantoms and show the ability to reconstruct 3D source locations using the spectral data in a simple phantom. We also characterize the basic performance of the imaging system.

Animals↗
PubMedDate not supplied

Diagnosis of peritonitis using near-infrared optical imaging of in vivo labeled monocytes-macrophages.

Peritonitis is an inflammatory process characterized by massive monocytes-macrophages infiltration. Since early diagnosis is important for a successful therapeutic outcome, the feasibility for a selective labeling and imaging of macrophages for highly sensitive optical imaging was assessed. After in vitro incubation of mouse macrophages J774A.1 with the far-red/near-infrared fluorochrome DY-676, distinct fluorescence intensities (1026+/-142 a.u.) were detected as compared to controls (552+/-54 a.u.) using a whole-body small animal near-infrared fluorescence (NIRF) imaging system. Macrophage labeling was confirmed by confocal laser scanning microscopy (CLSM) and fluorescence-activated cell sorting, (FACS). The fluorochrome was also found to be predominantly distributed within compartments in the cytoplasm. Additionally, peritonitis was induced in mice by intraperitoneal injection of zymosanA. After intravenous injection of fluorochrome (55 nmol/kg) and using whole-body fluorescence imaging, higher fluorescence intensities (869+/-151 a.u.) were detected in the peritoneal area of diseased mice as compared to controls (188+/-41 a.u.). Furthermore, cells isolated from peritoneal lavage revealed the presence of labeled monocytes-macrophages. The results indicate that in vivo diagnosis of peritonitis by near-infrared optical imaging of labeled monocytes-macrophages is feasible. Possibly, early stages of other inflammatory diseases could also be detected by the proposed diagnostic method in the long term.

Animals↗
PubMed2002

Intraoperative intrinsic optical imaging of neuronal activity from subdivisions of the human primary somatosensory cortex.

We performed intrinsic optical imaging of neuronal activity induced by peripheral stimulation from the human primary somatosensory cortex during brain tumor surgery for 11 patients. After craniotomy and dura reflection, the cortical surface was illuminated with a xenon light through an operating microscope. The reflected light passed through a bandpass filter, and we acquired functional images using an intrinsic optical imaging system. Electrical stimulation of the median nerve, or the first and fifth digits, induced biphasic intrinsic optical signals which consisted of a decrease in light reflectance followed by an increase. The decrease in light reflectance was imaged, and we identified a neural response area within the crown of the postcentral gyrus. In experiments on first and fifth digit stimulation, we identified optical responses in separated areas within the crown of the postcentral gyrus, i.e. near the central sulcus and near the postcentral sulcus. In the former response area, separate representations of the two fingers were observed, whereas in the latter response area, the two fingers were represented in the same region. A similar somatotopic representation was observed with electrical stimulation of the first and third branches of the trigeminal nerve. These results seem to support the hypothesis of hierarchical organization in the human primary somatosensory cortex.

Adult↗
PubMed2000

Probing physiology and molecular function using optical imaging: applications to breast cancer.

The present review addresses the capacity of optical imaging to resolve functional and molecular characteristics of breast cancer. We focus on recent developments in optical imaging that allow three-dimensional reconstruction of optical signatures in the human breast using diffuse optical tomography (DOT). These technologic advances allow the noninvasive, in vivo imaging and quantification of oxygenated and deoxygenated hemoglobin and of contrast agents that target the physiologic and molecular functions of tumors. Hence, malignancy differentiation can be based on a novel set of functional features that are complementary to current radiologic imaging methods. These features could enhance diagnostic accuracy, lower the current state-of-the-art detection limits, and play a vital role in therapeutic strategy and monitoring.

Breast Neoplasms↗
PubMed2002

Optical imaging spectroscopy in the unanaesthetised rat.

We describe a method for imaging the local cortical haemodynamic response to whisker stimulation in the rat without use of anaesthetic or paralytic agents. Female Hooded Lister rats were anaesthetised and a section of skull overlying somatosensory cortex thinned to translucency. A stainless steel chamber was then secured over the thin cranial window. Following recovery, animals were supported in a harness whilst the head was held by the implanted chamber using a pneumatically driven clamp. Optical imaging and optical imaging spectroscopy (OIS) of somatosensory cortex were performed whilst the contralateral whiskers were stimulated using a computer controlled air-puffer. Imaging sessions lasted approximately 15 min and data were collected for at least three consecutive days. Experiments were then repeated with the animals under urethane anaesthesia. Spectral analysis revealed qualitatively similar haemodynamic response functions across both anaesthetic states. However, our results indicate that the cortical haemodynamic response to somatosensory stimulation is larger by a factor of approximately 5 in the unanaesthetised rat compared with the anaesthetised rat. This preparation may make possible the investigation of the haemodynamic correlates of a broad range of neurological processes in the awake, behaving rodent.

Animals↗
PubMed2002

Optical imaging combined with targeted electrical recordings, microstimulation, or tracer injections.

To facilitate the combination of optical imaging with various electrode-based techniques, we have designed and produced a skull-mounting "sliding-top cranial window" and a removable "electrode positioner microdrive". These new devices were used to study sensory processing in chronic and acute experiments in the cerebral cortices of cats and monkeys. This assembly allows simultaneous optical imaging of intrinsic signals or voltage-sensitive dyes combined with extracellular recording (single and multiple unit recording and local field potential), intracellular recording, microstimulation, or targeted injection of tracers. After the functional architecture is determined by optical imaging, electrodes are targeted into a selected cortical site under full visual control, at a variety of penetration angles (30-90 degrees ), accessing a large cortical area. The device consists of three parts: (1) a skull-mounting chamber, (2) a sliding cap, and (3) a microdrive. The microdrive can easily be removed and the cranial window is then sealed and covered with a flat protective cover. For chronic experiments, this arrangement allows the animal to be handled over a long period while fitted with a sealed cranial window of minimal volume and weight, and with negligible risk of accidental damage or infection.

Action Potentials↗
PubMed1990

Cortical functional architecture and local coupling between neuronal activity and the microcirculation revealed by in vivo high-resolution optical imaging of intrinsic signals.

We have shown previously the existence of small, activity-dependent changes in intrinsic optical properties of cortex that are useful for optical imaging of cortical functional architecture. In this study we introduce a higher resolution optical imaging system that offers spatial and temporal resolution exceeding that achieved by most alternative imaging techniques for imaging cortical functional architecture or for monitoring local changes in cerebral blood volume or oxygen saturation. In addition, we investigated the mechanisms responsible for the activity-dependent intrinsic signals evoked by sensory stimuli, and studied their origins and wavelength dependence. These studies enabled high-resolution visualization of cortical functional architecture at wavelengths ranging from 480 to 940 nm. With the use of near-infrared illumination it was possible to image cortical functional architecture through the intact dura or even through a thinned skull. In addition, the same imaging technique proved useful for imaging and discriminating sensory-evoked, activity-dependent changes in local blood volume and oxygen saturation (oxygen delivery). Illumination at 570 nm allowed imaging of activity-dependent blood volume increases, whereas at 600-630 nm, the predominant signal probably originated from activity-dependent oxygen delivery from capillaries. The onset of oxygen delivery started prior to the blood volume increase. Thus, optical imaging based on intrinsic signals is a minimally invasive procedure for monitoring short- and long-term changes in cerebral activity.

Animals↗
PubMed2001

Optical imaging of matrix metalloproteinase-2 activity in tumors: feasibility study in a mouse model.

PURPOSE: To develop an optical imaging method to determine the expression level of tumoral matrix metalloproteinase-2 (MMP-2) in vivo. MATERIALS AND METHODS: An optical contrast agent was developed that was highly activatable by means of MMP-2-induced conversion. Signal characteristics of the probe were quantified ex vivo with a recombinant enzyme. Animal tumor models were established with MMP-2-positive (human fibrosarcoma cell line, n = 4) and MMP-2-negative (well-differentiated mammary adenocarcinoma, n = 4) tumor cell lines. Both tumors were implanted into nude mice and were optically imaged after intravenous administration of the MMP-2-sensitive probe. RESULTS: The MMP-2-sensitive probe was activated by MMP-2 in vitro, producing up to an 850% increase in near-infrared fluorescent signal intensity. This activation could be blocked by MMP-2 inhibitors. MMP-2-positive tumors were easily identified as high-signal-intensity regions as early as 1 hour after intravenous injection of the MMP-2 probe, while contralateral MMP-2-negative tumors showed little to no signal intensity. A nonspecific control probe showed little to no activation in MMP-2-positive tumors. CONCLUSION: It is feasible to image MMP-2 enzyme activity in vivo by using near-infrared optical imaging technology and "smart" matrix metalloproteinase-sensitive probes.

Animals↗
PubMed1999

Optical imaging of functional domains in the cortex of the awake and behaving monkey.

As demonstrated by anatomical and physiological studies, the cerebral cortex consists of groups of cortical modules, each comprising populations of neurons with similar functional properties. This functional modularity exists in both sensory and association neocortices. However, the role of such cortical modules in perceptual and cognitive behavior is unknown. To aid in the examination of this issue we have applied the high spatial resolution optical imaging methodology to the study of awake, behaving animals. In this paper, we report the optical imaging of orientation domains and blob structures, approximately 100-200 micrometer in size, in visual cortex of the awake and behaving monkey. By overcoming the spatial limitations of other existing imaging methods, optical imaging will permit the study of a wide variety of cortical functions at the columnar level, including motor and cognitive functions traditionally studied with positron-emission tomography or functional MRI techniques.

Animals↗