The contribution of water to the quantitative determination of hemoglobin concentration and saturation by near-infrared spectroscopy in turbid media was investigated. The study consisted of in vitro measurements of an aqueous suspension containing Liposyn, bovine blood, and yeast buffered at pH 7.2. The optical coefficients of the medium (μ_a~0.03 to 0.08 cm^-1, μ_s' ~ 6 cm^-1 at wavelengths of 715 and 825 nm) were similar to those of biological tissue in the near-infrared, and the hemoglobin concentration was about 23 μM. It was possible to reversibly saturate and desaturate hemoglobin in the full range of 0 to 100% by flowing either oxygen or nitrogen through the suspension. In these experimental conditions, water absorption must be taken into account to obtain accurate oxyhemoglobin concentrations and low hemoglobin saturation values. By contrast, the water correction has a small effect on the determination of deoxyhemoglobin concentration and high hemoglobin saturation values. By extrapolating the result to physiological conditions, where water content is lower and hemoglobin content is higher than in the experimental conditions, it was concluded that water absorption should have a smaller effect on the determination of hemoglobin concentrations and saturation in tissues at the wavelengths used in this study. In particular, for hemoglobin concentrations larger than 100 μM, the water correction is less than 5% at saturation values higher than 50%.

A portable tissue oximeter that uses light-emitting diodes and two-wavelength near infrared spectroscopy has been developed. The tissue oximeter is compact enough to be portable and it is therefore expected to make better use of the advantages of NIRS-based oximetry and to expand the scope of applications of monitoring tissue oxygen. The algorithm for this instrument was deduced through systematic experiments by varying blood volume and scattering intensity in a tissuelike phantom. The experimental results were compared with theoretical results obtained from diffusion theory. Experimentally determined coefficients of the algorithm were in close agreement with the theoretically derived coefficients. From evaluation tests of the algorithm applied to in vitro and in vivo measurements, it was confirmed that a good linear response to the concentration of oxygenated and deoxygenated blood can be obtained by this algorithm within a range of about a 50% change in concentration from an initial state.

Near infrared spectroscopy (NIRS) is an optical technique that provides information on cerebral tissue oxygenation and hemodynamics on a continuous, direct, and noninvasive basis. It is used to determine cerebral blood volume (CBV) and cerebrovascular CO₂ reactivity during normoxic hyper- and hypocapnia in a group of 28 healthy volunteers aged 20 to 83 years. The main focus is on to the age dependency of the measured variables. The influence of changes in minute ventilation during normocapnia on the cerebral oxygenation was also studied. The mean CBV (±SD) in age was, for 20 to 30 years, 2.14±0.51 ml/100 g of brain tissue; for 45 to 50 years, 1.92±0.40 ml/100 g; and for 70 to 83 years, 1.47±0.55 ml/100 g. The CBV showed a significant decrease with advancing age. No influence was found for a change in minute ventilation on cerebral oxygenation. During hypercapnia cerebral blood flow (CBF) significantly increased in all age groups, with a factor of 1.31±0.17 kPa^-1, 1.64±1.39 kPa^-1, and 2.4±1.7 kPa^-1, respectively, for the three age groups. The difference in change among the age groups was not statistically significant (p=0.09). The trend seen was an increased change in CBF with advancing age. During hypocapnia, the CBF significantly decreased in all age groups, with a factor of 0.89±0.08 kPa^-1, 0.89±0.04 kPa^-1, and 0.85±0.11 kPa^-1, respectively. There was no significantdifference among the age groups (p=0.50).

Near infrared spectroscopy (NIRS) was used to measure oxygen consumption (VO₂) in the human forearm with two different methods.VO₂ was measured in ten patients, first by inducing a forearm venous occlusion and then an ischemia. The mean value of VO₂ was 3.3 ± 1.1 μMO₂ × 100 g^-1×min^-1 during venous occlusion and 2.9±0.9 μMO₂ × 100 g^-1×min^-1 during ischemia. The difference between the two means was 0.4 μMO₂ × 100 g^-1×min^-1. A good agreement between the two methods was demonstrated. The results showed that NIRS is a useful tool for the measurement of VO₂. The venous occlusion method was the method of choice because it could be easily repeated at the bedside without causing any discomfort to the patient.

Moiré topography is a valuable technique for studying the shape and deformation of delicate biological structures such as the tympanic membrane. A projection moiré method is described that can produce both shape and deformation fringes in real time, at a rate of 25 interferograms per second. The apparatus is based on electronic subtraction of the projected grating line image of the object and a reference grating line image stored in digital memory. The image field and fringe plane distance can be adjusted to the object dimensions. Using a fringe plane distance of 82 μm, a precision of 5 μm over a measuring depth of 0.4 mm is demonstrated by measurements on a spherical calibration object. The application to in vitro shape and deformation measurements of the gerbil tympanic membrane is demonstrated.

The utility of 2',7'-bis-(carboxyethyl)-5-(6')-carboxyfluorescein (BCECF) for the execution of the structuredness of the cytoplasmic matrix (SCM) measurement for lymphocyte activation is investigated. Cells were incubated with BCECF/AM [2',7'-bis-(carboxyethyl)-5(6')-carboxyfluorescein acetoxymethylester], a nonfluorescent lipophilic acetoxymethylester that readily enters cells and is enzymatically hydrolyzed to fluorescent BCECF once inside. Leakage of BCECF out of cells is negligible in comparison to that observed with fluorescein, greatly reducing one source of background fluorescence. However, spontaneous hydrolysis of BCECF/AM in aqueous solution does contribute significant background fluorescence, which can be minimized by staining at relatively high concentrations of cells and subsequent dilution. As is the case with fluorescein, the polarization spectrum of intracellular BCECF shows a wavelength dependence not seen in the spectrum of the dye in homogeneous media of various viscosities. The more pronounced wavelength dependence of the polarization observed with BCECF compared with fluorescein suggests that BCECF might be preferable to fluorescein as a marker for the SCM test.

The initial experimental results of a new hybrid digital and analog design for retinal tracking and laser beam control are described. The results demonstrate tracking rates that exceed the equivalent of 60 deg per second in the eye, with automatic creation of lesion patterns and robust loss of lock detection. Robotically assisted laser surgery to treat conditions such as diabetic retinopathy and retinal tears can soon be realized under clinical conditions with requisite safety using standard video hardware and inexpensive optical components.

The ablation depth and collateral thermal damage for pulsed infrared photoablation as a function of wavelength with the free-electron laser (FEL) at 10.1, 11.8, 12.8, and 14.5 mm wavelengths is investigated. FEL data are compared with the blow-off and the continuous ablation models. Porcine cadaver corneas were used as target material. [Ablation depth per pulse as well as collateral thermal damage (extension of eosinophilic zone at the excision base beyond the irradiated surface) were measured by histologic micrometry.] The experimental data are compared with theoretical calculations for both models. At low water absorption (10.1 mm) the additional absorption of the cornea was taken into account. FEL data were: energy per pulse between 15.6 and 17.8 mJ, ablation zone around 0.2 mm2, and pulse length 4 ms (macropulse). In this wavelength range an effective photoablation of biological materials with a high water content can be achieved. The measured FEL data of ablation depth fail to confirm the blow-off model; they are 3 to 5 times higher than predicted. However, they are in agreement with the continuous ablation model, describing ablation depth sufficiently well (610%). The wavelength range from 11.8 to 14.5 mm is dominated by water absorption; here the ablation depth depends on the water absorption coefficient only, if other parameters are kept constant. At a 10.1 mm wavelength, collagen absorption contributes to the overall absorption of corneal tissue. The ablation depth can only be described by the continuous ablation model; however, the collateral thermal damage pattern can be described by both models (deviation of data 610–25%).

An automatic threshold selection method is proposed for biomedical image analysis based on a histogram coding scheme. The threshold values can be determined based on the well-known Lloyd–Max scalar quantization rule, which is optimal in the sense of achieving minimum mean-square-error distortion. An iterative self-organizing learning rule is derived to determine the threshold levels. The rule does not require any prior information about the histogram, hence is fully automatic. Experimental results show that this new approach is easy to implement yet is highly efficient, robust with respect to noise, and yields reliable estimates of the threshold levels.

In order to evaluate the use of low level light (LLL) indocyanine green angiography in the diagnosis and treatment of central serous choroidopathy (CSC), a new system for LLL infrared videoangiography is described. The system was coupled with a standard fundus camera employing a low-power continuous light source. The system consists of a cooled charge-coupled device (CCD) camera and a third-generation image intensifier. The CCD camera investigates the pathologies of choroidal images with very good performance in terms of spatial resolution, dynamic range, and signal-to-noise ratio. The image intensifier carries out the choroidal angiography in real time. The results of 48 cases of CSC demonstrated the following ICGV features: focal RPE leakage; hyperfluorescent areas appearing in late phases and underlying the focal leakage or pigment epithelium detachment (PED); PED in the guise of early hyperfluorescent areas; delays in choroidal filling. The findings support the hypothesis that CSC originates in the choroid with localized hyperpermeability. The system described minimized retinal illumination and demonstrated increased angiographic resolution and contrast compared with conventional ICG angiographic systems.

Optical low-coherence reflectometry and confocal microscopy images were taken of the rat dorsal skin flap window model. Blood vessel depths and diameters measured with the two techniques, and preparation thickness determined from reflectometry images, are in reasonable agreement with measurements from histologic sections. Blood vessels appear as areas of low signal when constant-depth reflectometry images are taken at a depth near the center of a vessel, whereas they appear bright when taken close to the blood–dermis boundary. Doppler shift plus increased light absorption in blood, and the blood–dermis index of refraction mismatch, are discussed as possible causes of the dark- and bright-appearing vessels, respectively. One reflectometry image was used to generate an input grid for a novel Monte Carlo analysis program that is capable of determining the light distribution and heat generation [J/m³] within complex blood vessel geometries. The feasibility of imaging skin blood vessel accurately with optical low-coherence tomography, and using the acquired knowledge of blood vessels structure to create more realistic Monte Carlo analyses is demonstrated by the results of the study.

Hollow waveguides (WG) made of plastic, silica, and metals have been developed for mid-IR spectrum transmission and are already being used, mainly in medical applications, in laser surgery and treatments. Characterization of these fibers is one of the important steps that enables further understanding of newly developed methods of preparation or applications. Scattering and beam profile measurements are discussed which have provided new data that may be used for future improvement or applications of these types of waveguides. Data on the roughness of the tube walls of WGs were obtained from backscattering measurements before and after deposition of the guiding layers. This is important for developing WGs for the shorter wavelengths in the mid-IR range (e.g., Er:YAG lasers, λ=2.94 nm). Measurements under various bending, radii have made it possible to calculate the contribution of scattering as well as absorption and changes in modes of propagation. Beam profile measurements have supplied data on the contribution of coupling to the mode of propagation, and the dependence of delivered energy to a target at a distance on the coupled value of energy. The conditions under which a whisper gallery mode of propagation appears as a function of the radius of bending and the angle of incidence to the normal of the inner wall, were found.