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PubMed1997

Optical considerations in digital imaging.

The topic of optics and its effect in ultimate rendered image quality has largely been underemphasized for medical imaging systems. In actuality, adequate attention to optical issues is essential in ensuring that image quality is optimal. Generally, optical issues can be divided into two broad categories: optical interface optimization and lighting optimization. Although these issues deal with disparate aspects of optical physics, they are covered within a single article because they both apply to the common goal of generating superior medical images.

Diagnostic Imaging↗

PubMed2004

Ophthalmic imaging by spectral optical coherence tomography.

PURPOSE: To demonstrate two novel ophthalmic imaging techniques based on fast Spectral Optical Coherence Tomography (SOCT). DESIGN: Prospective observation case report. METHODS SETTING: Research laboratory. STUDY POPULATION: A normal human subject. MAIN OUTCOME MEASURES: Correlation of an optical coherence retinal tomogram with known retinal anatomy, reduction of eye exposure to the probing light beam during Optical Coherence Tomography (OCT) examination. RESULTS: High resolution (3- x 20-microm) cross-sectional 2-dimensional images of the human retina in vivo have been obtained with only 0.1-second total illumination time (for 1024 A-scans), and approximately 200- microW eye exposure. Details of the optic disk in vivo have been visualized at a rate of eight frames per second, which is sufficient to provide real time analysis. The 3-dimensional images of the optic nerve correspond to the images obtained from a fundus camera. CONCLUSIONS: Because of its short acquisition time and high sensitivity, SOCT uses a 100 times lower exposure/A-scan to obtain images of comparable quality to those obtained by the commercial instrument based on traditional time-domain OCT. Spectral Optical Coherence Tomography therefore provides a much wider safety margin than the traditional method and allows relaxation of the current safety precautions forbidding more than 10 minutes/day scanning of the same location of a retina. As a result of the high speed offered by the new technique, the 3-dimensional tomograms, which allow a surgeon access to a comprehensive and detailed view of relevant pathologies, are obtained in a much shorter, clinically more reasonable time.

Adult↗

PubMed1989

Constraints on passive spatial coherence filtering of imaging systems due to properties of the impulse response.

Properties of the amplitude and intensity impulse responses of passive optical imaging systems have consequences for the spatial coherence filtering properties of such systems. It is shown that imaging systems that have both space-invariant impulse responses and truncating pupil functions have no capability to block spatially coherent sources while imaging those that are incoherent. However, examples of systems with space-variant impulse responses with approximately such capabilities appear to be realizable for a certain range of parameters. However, even space-variant systems cannot block unresolved coherent sources while retaining the capability of imaging those that are spacially incoherent for the same range of source-plane coordinates.

Humans↗

PubMed1991

Magnetic resonance imaging signs of optic nerve gliomas in neurofibromatosis 1.

We reviewed the magnetic resonance images of four children with neurofibromatosis 1 and orbital optic gliomas. The images showed double-intensity tubular thickening characteristic of perineural arachnoidal gliomatosis, elongation of the nerves, and downward kinking of the nerves in the midorbit. We believe these findings typify the orbital gliomas in patients with this disease.

Adolescent↗

PubMed1996

Concurrent reflectance imaging and microdialysis in the freely behaving cat.

We present a method to perform simultaneous microdialysis with light reflectance imaging of neural activity in a discrete brain region of the freely behaving animal. We applied this method to the dorsal hippocampus of freely behaving cats to (1) measure extracellular glutamate and reflectance variations across a sleep-waking cycle, (2) assess spatially coherent neural activity changes accompanying local perfusion of cocaine and (3) measure local changes in cell volume induced by infusion of hyper- and hypo-osmotic solutions. Higher extracellular glutamate concentrations corresponded to higher imaged neural activity. Sequential images showed that cocaine perfusion elicited a propagating reflectance change as cocaine reached the tissue. Microperfusion of hypo-osmotic solution ( - 100 mOsm), which increases cell volume, decreased reflectance. Microperfusion of hyperosmotic sucrose solutions, which reduce cell volume, increased reflectance in a dose-dependent manner. The data indicate that reflectance imaging can measure changes in cell volume, and could, thus, measure neural activity through activity/cell volume corollaries. Combining microdialysis and optical imaging enables investigation of the neurochemical bases of spontaneous neural activity patterns within discrete brain nuclei.

Animals↗

PubMed1990

[Measurements of reversibility of optic disc cupping in glaucoma using a computerized videographic image analyzer].

Optic disc changes were studied in young and elderly glaucoma patients who underwent reduction of intraocular pressure (IOP) by filtrating surgery. A computerized videographic image analysis system (Optic Nerve Head Analyzer, Rodenstock) was used to measure the cup/disc-ratio, the ratio of the rim area over the disc area (rim area/disc area-ratio), and the ratio of the cup volume over the disc area (cup volume/disc area-ratio) before and after filtrating surgery. Each parameter was assessed as total and quadrantal values. Materials consisted of 19 eyes of 15 patients (8 eyes of 5 patients with primary open angle glaucoma, 2 eyes of 2 patients with secondary glaucoma, and 9 eyes of 7 patients with developmental glaucoma). Sixteen eyes (84%) of 12 patients showed a decrease of the total cup/disc-ratio after operation. In this group, the patients had a decrease in IOP of 18.9 +/- 10. 6mmHg (mean +/- SD) after the operation. Among 16 eyes that had a decreased total cup/disc-ratio, statistically significant decrease of the cup/disc-ratio (p less than 0.01) and statistically significant increase of the rim area/disc area-ratio (p less than 0.01) were noted in total and for all quadrants except for the temporal. The greatest improvement of cupping was seen in the nasal quadrant. With regard to cup volume/disc area-ratio, a statistically significant decrease was observed in total and in all quadrants (p less than 0.01). The IOP change correlated linearly with that of the total cup volume/disc area-ratio (R = 0.51, p less than 0.05). No statistically significant linear correlation was noted between age and the change in any disc parameter.

Adolescent↗

PubMed2005

Remote NADH imaging through an ordered array of electrochemiluminescent nanoapertures.

In this report, we present an ordered array comprising thousands of nanoapertures for the electrochemiluminescent (ECL) detection of NADH. It was fabricated on the distal face of a coherent optical fiber bundle. Such a high-density array of nanoapertures combines optical, imaging and electrochemical properties. Indeed, each nanoaperture is surrounded by a gold nanoring, which acts as an electrode material. The behavior of the array was characterized by cyclic voltammetry and it shows excellent electrochemical performances. NADH is the analyte, which is measured in presence of Ru(bpy)3(2+). The ruthenium complex mediates the NADH oxidation and this coenzyme acts as a co-reactant in the ECL mechanism. ECL light is generated at the distal face of the array by each gold ring electrode. A fraction of this ECL light is collected by the corresponding nanoaperture, transmitted through the optical fiber bundle and finally imaged on the proximal face with a CCD camera. In this work, we show that NADH concentration is remotely detected by an oxidative-reductive ECL mechanism. We present also some preliminary results about the ECL process of NADH with Ru(bpy)3(2+). The ECL behavior of NADH on gold surface is reported. The influence of the applied potential on the collected light intensity was investigated. The variation of the ECL intensity measured through the nanoaperture array with NADH concentration is linear. Remote ECL detection of NADH is spatially resolved over a large area with a micrometer resolution through the array. Therefore, such array integrates several complementary functions: ECL light generation, collection, transmission and remote imaging in an array format.

Electrochemistry↗

PubMed1997

Simultaneous detection of near-field topographic and fluorescence images of human chromosomes via scanning near-field optical/atomic-force microscopy (SNOAM).

Scanning near-field optical/atomic-force microscopy (SNOAM) provided us with simultaneous topographical and optical images of human chromosomes using a sharp and bent optical fiber as a near-field optical probe. Native chromosomes were spread out onto a coverslip using the surface-spreading whole-mount method. The SNOAM system does not need pretreatment of samples such as metal coating or chemical immobilization. Near-field topographic and fluorescence images provided useful information on native chromosome structure.

B-Lymphocytes↗

PubMed1992

SIMS microscopy in the biomedical field.

We attempted to indicate the requirements for biomedical applications of SIMS microscopy. Sample preparation methodology should preserve both the structural and the chemical integrity of the tissue. Furthermore, it is often necessary to correlate ionic and light microscope images. This implies a common methodological approach to sample preparation for both microscopes. The use of low or high mass resolution depends on the elements studied and their concentrations. To improve the acquisition and processing of images, digital imaging systems have to be designed and require both ionic and optical image superimposition. However, the images do not accurately reflect element concentration; a relative quantitative approach is possible by measuring secondary ion beam intensity. Using an internal reference element (carbon) and standard curves the results are expressed in micrograms/mg of tissue. Despite their limited lateral resolution (0.5 microns) the actual SIMS microscopes are very suitable for the resolution of biomedical problems posed by action modes and drug localization in human pathology. SIMS microscopy should provide a new tool for metabolic radiotherapy by facilitating dose evaluation. The advent of high lateral resolution SIMS imaging (less than 0.1 microns) should open up new fields in biomedical investigation.

Animals↗

PubMed1999

Imaging cortical dynamics at high spatial and temporal resolution with novel blue voltage-sensitive dyes.

Conventional imaging techniques have provided high-resolution imaging either in the spatial domain or in the temporal domain. Optical imaging utilizing voltage-sensitive dyes has long had the unrealized potential to achieve high resolution in both domains simultaneously, providing subcolumnar spatial detail with millisecond precision. Here, we present a series of developments in voltage-sensitive dyes and instrumentation that make functional imaging of cortical dynamics practical, in both anesthetized and awake behaving preparations, greatly facilitating exploration of the cortex. We illustrate this advance by analyzing the millisecond-by-millisecond emergence of orientation maps in cat visual cortex.

Animals↗

PubMed2002

Small animal imaging. current technology and perspectives for oncological imaging.

Advances in the biomedical sciences have been accelerated by the introduction of many new imaging technologies in recent years. With animal models widely used in the basic and pre-clinical sciences, finding ways to conduct animal experiments more accurately and efficiently becomes a key factor in the success and timeliness of research. Non-invasive imaging technologies prove to be extremely valuable tools in performing such studies and have created the recent surge in small animal imaging. This review is focused on three modalities, PET, MR and optical imaging which are available to the scientist for oncological investigations in animals.

Animals↗

PubMed2003

Imaging of angiogenesis: from microscope to clinic.

Advances in imaging are transforming our understanding of angiogenesis and the evaluation of drugs that stimulate or inhibit angiogenesis in preclinical models and human disease. Vascular imaging makes it possible to quantify the number and spacing of blood vessels, measure blood flow and vascular permeability, and analyze cellular and molecular abnormalities in blood vessel walls. Microscopic methods ranging from fluorescence, confocal and multiphoton microscopy to electron microscopic imaging are particularly useful for elucidating structural and functional abnormalities of angiogenic blood vessels. Magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET), ultrasonography and optical imaging provide noninvasive, functionally relevant images of angiogenesis in animals and humans. An ongoing dilemma is, however, that microscopic methods provide their highest resolution on preserved tissue specimens, whereas clinical methods give images of living tissues deep within the body but at much lower resolution and specificity and generally cannot resolve vessels of the microcirculation. Future challenges include developing new imaging methods that can bridge this resolution gap and specifically identify angiogenic vessels. Another goal is to determine which microscopic techniques are the best benchmarks for interpreting clinical images. The importance of angiogenesis in cancer, chronic inflammatory diseases, age-related macular degeneration and reversal of ischemic heart and limb disease provides incentive for meeting these challenges.

Angiogenesis Inhibitors↗

PubMed1998

Phase-contrast X-ray CT image of breast tumor.

Phase-contrast X-ray CT images generated by differences in refractive indices can be used to visualize the internal structures of soft tissues without contrast enhancement. In this study, imaging of human breast tumor was performed on formalin-fixed samples. Experiments were carried out at the synchrotron source of the Photon Factory, Tsukuba, Japan. The X-ray energy was adjusted to 17.7 keV. Phase-contrast X-ray CT images revealed various structures of human breast tumor as clearly as optical images.

Journal Article↗

PubMed2003

Assessment of an in situ temporal calibration method for time-resolved optical tomography.

A 32-channel time-resolved optical imaging device is developed at University College London to produce functional images of the neonatal brain and the female breast. Reconstruction of images using time-resolved measurements of transmitted light requires careful calibration of the temporal characteristics of the measurement system. Since they can often vary over a period of time, it is desirable to evaluate these characteristics immediately after, or prior to, the acquisition of image data. A calibration technique is investigated that is based on the measurement of light back-reflected from the surface of the object being imaged. This is facilitated by coupling each detector channel with an individual source fiber. A Monte Carlo model is employed to investigate the influence of the optical properties of the object on the back-reflected signal. The results of simulations indicate that their influence may be small enough to be ignored in some cases, or could be largely accounted for by a small adjustment to the calibrated data. The effectiveness of the method is briefly demonstrated by imaging a solid object with tissue-equivalent optical properties.

Brain↗

PubMed2001

Autofluorescence imaging to optimize 5-ALA-induced fluorescence endoscopy of bladder carcinoma.

OBJECTIVES: To design an optical system for detecting autofluorescence (AF) of bladder tumors and to determine the success of reducing the false-positive rate of 5-aminolevulinic acid-induced fluorescence endoscopy (AFE). AFE provides significantly higher sensitivity in detecting and localizing bladder carcinoma compared with white light endoscopy. The specificity of AFE is equivalent to white light endoscopy, mostly because of the false-positive fluorescence of chronic cystitis lesions. Laser-induced spectral autofluorescence detection is also an efficient method in the diagnosis of bladder carcinoma. METHODS: Bladder tissue was excited to AF using the D-Light (375 to 440 nm) after regular AFE with detection of fluorescence-positive areas. The optical image was produced using a special RGB camera. Biopsies were taken from AFE-positive areas, the peritumoral edges, and normal bladder mucosa. The AF images of the suspicious areas were compared with the AFE images and the histologic results. RESULTS: A total of 43 biopsies were histologically examined (24 benign and 19 neoplastic). AF imaging showed contrast differences between papillary tumors, flat lesions, and normal mucosa. The combination of AFE with AF raised the specificity of AFE alone from 67% to 88%. CONCLUSIONS: AF imaging is possible. The value of the method in reducing the false-positive rate of the highly sensitive AFE needs to be validated with higher numbers. The combination of AF with AFE had a 20% higher specificity than AFE alone in our study.

Administration, Intravesical↗

PubMed1999

Image processing of collagen: role in medicine.

This article describes how quantitative studies of electron-optical images from collagen fibrils, used as a model system can provide information not only about the molecular architecture of the fibril but also about the structural alterations produced by a treatment or disorder.

Animals↗

PubMed2005

Computations of the acoustically induced phase shifts of optical paths in acoustophotonic imaging with photorefractive-based detection.

Acoustophotonic imaging uses ultrasound-modulated scattered light to improve the quality of optical imaging in diffusive media. Experiments that use photorefractive-crystal-based detection have shown that there is a large dc shift in the acoustically modulated or ac optical signal, which could be utilized to further improve optical imaging resolution. We report that photon paths in a diffusive medium were generated by a Monte Carlo simulation, and the optical phase shifts of the various photons induced by the presence of a realistic focused ultrasound beam were calculated. Quantities that characterize the ac and dc signal components were evaluated by use of the calculated phase shifts. It was confirmed that the dc component dominates owing to coherent summation of the contributions from all the photons.

Acoustics↗

PubMed2000

Evaluation of the adaptive speckle suppression filter for coronary optical coherence tomography imaging.

During the last few years, optical coherence tomography (OCT) has demonstrated considerable promise as a method of high-resolution intravascular imaging. The goal of this study was to apply and to test the applicability of the rotating kernel transformation (RKT) technique to the speckle reduction and enhancement of OCT images. The technique is locally adaptive. It is based on sequential application of directional masks and selection of the maximum of all outputs. This method enhances the image features by emphasizing thin edges while suppressing a noisy background. Qualitatively, the RKT algorithm provides noticeable improvement over the original image. All processed images are smoother and have better-defined borders of media, intima, and plaque. The quantitative evaluation of RKT performance showed that in terms of average contrast-to-noise ratio, there is a significant improvement in image quality between original and enhanced images. The RKT image enhancement technique shows great promise in improving OCT images for superior boundary identification.

Coronary Angiography↗