Quasielastic scattering of coherent light in tissue can be utilized to probe the superficial blood flow of the skin and other organs. This fundamental principle has been employed in the construction of laser Doppler tissue perfusion monitors and imagers, intended for experimental and clinical investigations of tissue blood flow. In this paper, the theory of laser Doppler equipment is discussed. The measuring depth can be estimated by Monte Carlo simulation, while the dynamic light scattering (light scattering including Doppler effects) can be modeled by autocorrelation techniques. Based on these techniques estimators for tissue perfusion and tissue blood cell concentration are derived. The operating principle of the laser Doppler monitor is described in detail, with special reference to the design of probes. This monitor is useful for tracking temporal changes in tissue perfusion at a single point. The principle of a recently developed laser Doppler perfusion imager is reviewed. This imager is useful in mapping the spatial variations in tissue perfusion. Different ways of evaluating the performances of the monitor and imager in both mechanical flow simulators and in-vivo studies are discussed. Finally a brief overview is made of some fields of application in which the laser Doppler technique for measurement of tissue perfusion has been successfully used.
Laser based techniques are in continuous development in medical research, diagnostics, and therapeutics. For example, in ophthalmology these techniques are ranging from a well established technique such as photocoagulation of retinal vessels with blue light from continuous emitting argon ion lasers, to the more recently developed technique with pulsed infrared emission from neodymium-yttrium-aluminum-garnet lasers for posterior capsulectomy and to the more experimental modalities such as photorefractive keratectomy utilizing excimer lasers with ultraviolet emission. This paper will give a brief discussion of the basic principles of light propagation in tissue together with a presentation of the basic interaction mechanisms between laser emission and living tissues.
Lasers are being increasingly used in bioptics and in life sciences in general, especially for medical applications for therapy and diagnostics. Lasers are also broadly used in environment sciences to monitor atmospheric parameters and concentrations of molecular species of natural origin or coming from human activities such as the various kind of pollutants. The peculiar features of lasers exploited in these areas are mainly the capability of developing an action or performing a measurement without physical contact with the target and, if required, from a remote position with the assistance of suitable beam delivery systems such as telescopes, microscopes, or optical fibers. These features are directly related to the space and time coherence of the laser light and to the energy storage capability of the laser material which allow an extremely effective concentration of the beam energy in space, direction frequency, or time. A short description of the principle of operation and relevant properties of lasers are given and the most significant properties of the laser emission are briefly reviewed. Lasers for medical applications (mainly for therapy) will be mentioned, pointing out the specific property exploited for the various applications. Finally, examples of laser applications to the environmental sciences will be reported. A summary of the properties exploited in the various bio-optical applications is shown.
Holographic interferometry is well adapted for the determination of 2D strain fields in osseous structures. The knowledge of those strain fields is important for the understanding of structure behavior such as arthrosis.
General scalar diffraction theory forms the basis for providing use with a description of wave propagation for various coherent input field distributions. This theory leads to the development of the Fresnel and Fraunhofer approximations, which are the starting point for our treatment of optical Fourier image processing. Presented are imaging techniques used to record optical Fourier transforms of various input field distributions. Also presented are methods used to record optical matched spatial filters used in pattern recognition applications. Examples are given of optical Fourier transforms for different input fields, correlations resulting from pattern recognition studies, and designs of optical hybrid systems used in image processing and pattern recognition.
Optical fiber sensors based on the amplitude modulation technique are discussed. According to their basic working principle, these sensors are classified into three classes: spectrometric, transducer, and all-fiber sensors. Examples of fiber-optic sensors developed for biomedical and environmental applications are given. Typical parameters of biomedical interest, which are conveniently monitored by fiber-sensors, are: temperature, pressure, blood flow, pH, pO2, pCO2, glucose, and immunological parameters. Other parameters of interest for environmental monitoring are CH4, other hydrocarbons polluting air and water, and trichloroethylene and chloroform.
A Monte Carlo model of light transport in tissue is presented and used to calculate fluence rates within beef liver. The optical coefficients of beef liver used in these calculations have been determined experimentally on both fresh and laser coagulated tissue samples. Coagulation was found to increase the scattering, but left the absorption little changed. Using these measured optical coefficients, the model showed that the light distribution in the tissue was changed significantly following coagulation. The fluence rates in the coagulated tissue were found to be more diffuse than in the fresh tissue.
We report here the experience of our multidisciplinary group that has been working since 1986 on excimer laser angioplasty. After having selected the excimer laser between the available sources because of the negligible lesions left on the residual tissue, we had the purpose to develop a suitable laser and catheter system. Neglecting here all the preliminary studies, we outline only a typical phenomenon related to the energy delivery and useful for the comprehension of the recanalization process. The energy emitted by every single fiber determines, under a certain threshold, independent recanalized channels in the plaque with residual flaps. At a higher energy level the overposition of the lobes, due to the intrinsic divergence, up to the recanalization in a single large channel. In our opinion this condition is crucial in the design of the catheters to obtain an optical instead of a mechanical recanalization. The biological experimentation conducted during the preliminary tests on human hearts obtained from transplants or cadavers, convinced us that the correct goal to pursue was unique laser angioplasty without the need for further balloon dilation.
Several substances, e.g., hematoporphyrin derivatives (HpD), dihematoporphyrin ether/ester (DHE), phthalocyanines, porphycenes, and other drugs are known to be temporarily and selectively stored in tumors after systematic application. This transient marking opens up new perspectives for diagnostic and therapeutic procedures. The marker most commonly used today is DHE intravenously injected at doses of 0.2 up to 3.0 mg/kg bodyweight for diagnosis and therapy respectively. The corresponding clearance intervals after injection of DHE range from 3 - 48 h and 25 - 75 h. The highly sensitive two-wavelength laser excitation method with computerized fluorescence imaging offers great advantages for the detection of photosensitized tumors and adds support to conventional diagnostic techniques. Photoinduced production of singlet oxygen is said to be the initial process leading to tumor destruction. Homogeneous irradiation of the area to be treated and a reliable light dosimetry are prerequisites for an effective tumor therapy. Standard instruments for a routine application so far do not exist. Integral irradiation techniques and special laser fiber modifications, however, are under development, which guarantee a uniform distribution of light on the area to be treated. Positive results are such treatments--especially in urology, pneumology, and otorhinolaryngology--indicate the future potential of photodynamic therapy of tumors.
In the confocal scanning light microscope a specific volume is sampled during the imaging process. The physical process is explained, together with how the size of the pinholes used affect the actual size of this volume. The thus produced 3-D imaging is of high quality but subject to a number of limitations. A novel (bilateral scanning) arrangement is presented that may relieve some of these. In this approach, a double-sided scanning mirror element and a charge coupled device (CCD for image collection) are used.
Remote sensing is one means to obtain objective and repetitive information about our fast- changing and endangered environment on a regional and global scale. It has the capability to strengthen our awareness about the present situation on the earth''s surface. Earth observation offers the possibility to gather information for a large variety of application and to describe inter-relationships and consequences of human activities. Observational possibilities and needs are explained and listed.
New promising medical applications of IR lasers can be much wider with flexible cables and catheters for laser power delivery. Special super-dry silica fiber allow catheters to be designed for promising Ho and Tm lasers at wavelengths about 2 micrometers . But for longer wavelengths of Er:, CO- and CO2-lasers, other fibers should be used--polycrystalline silver halide fibers, singlecrystalline sapphire fibers, and hollow metal waveguides. Optical parameters of such fibers are under discussion alongside a design of special optical connectors, efficient coupling units, and optics at distal end. Applications of cables and catheters for laser therapy and medical diagnostics are analyzed.
Lasers are now commonly accepted and widely used surgical instruments in otorhinolaryngology. There have been a great number of technological advances with lasers that have contributed to the expansion of this new surgical modality with an increased number of medical applications. Surgical strategies have also changed and are more favorable toward conservative surgery in which less tissues is removed than with more radical resections. This combination of improving technology and medical attitudes has changed the field of otorhinolaryngology, and resulted in an expanding use of laser surgery. Since 1973 we have been using the carbon dioxide laser in the treatment of diseases of the upper aero digestive systems, learning this new surgical technique from the pioneer work of Strong, Jako, and Vaughan. It is our conviction that a laser surgeon must have a thorough knowledge of laser biophysics, instrumentation, safety protocols, and surgical indications, and have the technical skills to perform laser surgery. Laser technology continues to improve at an increased speed, and it is imperative to update knowledge of current and potential applications of lasers in our specialty. It is the purpose of this article to present our clinical experience of 18 years with the use of lasers in surgery of ORL, emphasizing the carbon dioxide laser.
The basic properties of the laser speckle wave are briefly reviewed. Studies and measurements of test objects are possible by observing either the direct displacement of the speckles (speckle photography) or interferometric variations of brightness by adding a reference wave (speckle interferometry). Speckle interferometry becomes a particularly useful tool combined with direct video-recording and electronic processing. The resulting system--TV-holography (ESPI) is described in greater detail as it is potentially useful for many biomedical applications. It is shown how image processing can be used to increase the measuring accuracy and aid the interpretation of fringe patterns.
Major environmental problems all over the world require immediate action. Often a quantitative observation of the environmental effects on natural or man-made systems is asked for. Useful information about the object is collected in the speckle fields produced by scattered coherent light. Object changes are detected by correlation of corresponding speckle fields. Optical methods are employed for this task: holography, holographic interferometry, double- exposure speckle photography, speckle correlation, or electronic speckle pattern interferometry. Modifications of these techniques are adapted to on-site and real-time applications in environmental diagnostics. Practical results are presented in examples from the study of plants and the monitoring of climatic effects on cultural stone monuments.
Since Hippocrates, physicians have three weapons to fight malignant diseases of the human body: Quae medicamenta non sanat, ferrum sanat; quae ferrum non sanat, ignis sanat; and quae vero ignis non sanat, insanabilia reputari oportet. Today there are various possibilities to use the ''fire'': electrical and optical cauterization; mono- and bipolar rf-surgery; ionizing radiation for tumor treatment; and last but not least, the laser of laser tissue interactions, all can be used to remove malignant tissue either by biological digestion or immediate ablation, i.e., photovaporization or photodecomposition. This paper will discuss a semiempirical theory of the so-called photoablation process and the thermal side effects of the surrounding tissue. The term ''Photoablation; has to be well differentiated with the terms photovaporization, photodisruption and photofragmentation. As will be shown in this paper, photoablation is a microscale fast thermal explosion.
The clinical application of lasers in ophthalmology is schematized, showing for each anatomic eye structure, pathologies that may be treated through this procedure. In the cornea, the unusual laser practice for suture removals and the promising possibility of the excimer laser in refractive surgery are discussed. In the iris, the camerular angle, and the ciliary body, the laser application is essentially used to treat the glaucoma and other situations that are not so frequent. The capsulotomy with YAG LASER is used in the treatment of structures related with crystalline and, at least, the treatment of the retina and choroid pathology is expanded. A. A. explained the primordial interest and important of laser in the diabetic retinopathy treatment and some results in patients with more than 5 years of evolution are: 55 of the patients with proliferative diabetic retinopathy (RDP) treated for more than 5 years noticed their vision improved or stabilized; 5 years after treating patients with PDR, 49.3 had their vision stabilized or even improved, provided the diabetics had declared itself more than 20 years ago, versus 61.7 provided the diabetics had declared itself less than 20 years before; finally, 53.8 of the patients under 40-years-old when the diabetics was diagnosed, had their vision improved or at least stabilized 5 years after the beginning of the treatment. On the other side, when patients were over 40 years old when the diabetics was diagnosed percentage increased to 55.9. This study was established in the follow-up of 149 cases over 10 years.
Diabetes Mellitus is a chronic disease that is revealed with a lot of alterations due to factors such as an absolute or relative reduction of the insulin. It is usually accompanied by generalized arteriosclerosis and prepares for certain microvasculares pathologies such as retinopathy, nefropathy, and neuropathy. The first effects of diabetes in the retina seem to act on the capillaries. The functional modifications of the retinal circulation appear before the structural ones. These consist of the blood flux damage and the obligation of the hematorretinal barrier with extravasacy as can be proved in the fluorophotometry of the vitreous humor. Nowadays, medical treatments are more effective and only vitrectomy and photocoagulation are used in diabetic retinopathy. For that, the argon laser and the xenon arch are used. The treatment is usually spread panretine, with coagulation in a grid pattern around the eye, avoiding the macula and other vital structures, and treating the neoformed blood vessels. The rate of grave visual loss in the studies carried out with there techniques was 12 in relation to 28 in the non-treated cases. The most important factors of risk found, were the discal neoformed blood vessels and the hemorrhage of the vitreous humor. Adverse effects were found such as the reduction of visual sharpness and the contrition of the visual field, these are greater in patients treated with the xenon arch than in those treated with the argon laser.
Laser ranging to satellites is one of the most precise methods for positio ning on the surface of the Earth. Reference is made to the need for precise posi tioning and to the improvement brought by the use of space techniques. Satellite Laser Ranging system is then described and in view of the high precision of the results derived from its measurements comments are made to some of the more important applications: high precision networks tectonic plate motion polar motion and earth''s rotation. Finally plans for system improvement in the near future are also presented.
Portuguese coastal wetlands are located in estuaries and coastal lagoons. Due to physiographic patterns of tidal flats and salt-marshes and the geometric resolution of the pixels of the multispectral scanning system (MSS) and the thematic mapper (TM) Landsat imagery, only the large estuarine intertidal systems of Aveiro and Ria Formosa provide carthographic documents for land use planning. The wetlands systems and the water turbidity were classified using digital processing of the radiometric responses of the vegetation, the soils, and the water. The procedures of the digital processing were filtering, contrast enhancements, vegetation ratios, principal components analysis, and unispectral and multispectral rectangular classifications.
Dynamic measurement of force distribution concerning foot-loading during walking were made with a novel automatic image processing system. The operation principle, associated practical problems, and clinical applications are described.
Surface topographic measurement in the shape of the human back is demonstrated by an automatic method. A linear grating is projected and a corresponding deformed pattern casted on the backs is processed, sending the 3D shape. An algorithm for phase detection over the spatial pattern is the selected method. Theoretical background, experimental results, and clinical implications are reported.