This PDF file contains the editorial “Editorial: The year 1992 in review: part II” for OE Vol. 32 Issue 02

The heating of tissue by microwave radiation has attained a place of importance in various medical fields, such as the treatment of malignancies, urinary retention, and hypothermia. Accurate temperature measurements in these treated tissues is important for treatment planning and for the control of the heating process. It is also important to be able to measure spacial temperature distribution in the tissues because they are heated in a nonuniform way by the microwave radiation. Conventional temperature sensors used today are inaccurate in the presence of microwave radiation and require contact with the heated tissue. Fiber optic radiometry makes it possible to measure temperatures accurately in the presence of microwave radiation and does not require contact with the tissue. Accurate temperature measurements of tissues heated by microwave was obtained using a silver halide optic radiometer, enabling control of the heating process in other regions of the tissue samples. Temperature mappings of the heated tissues were performed and the nonuniform temperature distributions in these tissues was demonstrated.

The skin erythema meter is a fiber optic, dual-wavelength reflectance meter that measures the reflectance of the skin on two wavelengths, one the blood/hemoglobin absorption band (555 nm) and another a reference (660 nm). The instrument consists of a fiber optic sensor head, a microprocessor-based control and analysis unit, and a plotter, and it presents the relation between the measured reflectance results in terms of a reflectance index [R(555 nm):R(660 nm)]. The measurement cycle, including printing, takes 5 s. Stability tests on the erythema meter (constant distance, reference object) showed the standard deviation of the reflectance index to be ± 0.1%, whereas that in repeatability tests was less than ± 0.5% for skin and less than ± 0.2% for paper with handheld positioning and repetition. The dynamic change in the reflectance index was about 30% with strong irritation. Results of various irritation test series on human skin are also presented. Finally, the performance and applicability of the skin erythema meter with respect to allergy test procedures, irritancy testing, and measurement of uv-induced erythema are discussed.

Modified (sculpted) optical fiber tips for medical delivery systems are described. Tips have aspherical profiles (parabolic, hyperbolic, etc.) Light distributions of modified silica (n = 1.457) tips were calculated using a 3-D ray-tracing program in air and water. It was found that the focusing effects of aspherical tips are from 2.5 to 3.0 times better than those of spherical tips. It is possible to increase the irradiance of tissue in water by about 6 to 9 times using normal silica fiber with high efficiency (without total internal reflection). Experiments were performed in air and water, using registration of light distribution with a CCD-camera, and confirmed the theoretical predictions.

A lensless backscatter fiber optic probe is used to measure the size distribution of protein molecules inside an excised, but intact, human eye lens. The fiber optic probe, about 5 mm in diameter, can be positioned arbitrarily close to the anterior surface of the eye; it is a transreceiver, which delivers a Gaussian laser beam into a small region inside the lens and provides a coherent detection of the laser light scattered by the protein molecules in the backward direction. Protein sizes determined from the fast and slow diffusion coefficients show good correlation with the age of the lens and cataractogenesis.

The fluorescein derivatives are now commonly used for measuring intracellular pH. Cytoplasmic pH is estimated from the shape of the pH-dependent excitation spectrum of the trapped fluorescent marker. The ability of 2',7'-bis-(2 carboxyethyl)-5-(and-6)-carboxyfluorescein as a fluorescent probe for pH monitoring in vivo is evaluated and the in vitro pH sensitivity ofthis fluorescent probe is investigated. In vivo experiments were carried out on tumor-grafted mice. Dyes were injected intraperitoneally and fluorescence emission spectra were collected at different excitation wavelengths by an adapted system bearing optic fibers. Ratios were calculated on the basis of maximum emission wavelength fluorescence intensities at retained excitation wavelengths. The choice of wavelength excitation was restricted to 465 nm because the 450-nm excitation wavelength leads to problems of autofluorescence and tissue penetration of light. At a 500/465 ratio, the pH sensitivity is greatly reduced. Kinetic profiles of fluorescence intensities show low tissue and tumoral uptake with a plateau phase 100 mm after dye injection. Ratio values reach a steady state 30 mm after dye injection and remain stable during the whole experiment. The results clearly indicate differences in ratio values for tumoral and normal tissues (p < 0.005). The tumoral ratio (1.88 ± 0.07) is always lower than normal tissue ratio (2.45 ± 0.09).

The validity of the similarity parameter ∑^'_s ≡ ∑_s(1 - g), the reduced scattering coefficient, where g is the average cosine of the scattering phase function is investigated. Attenuation coefficients α and diffusion patterns are obtained from solutions of the transport equation for isotropic scattering and Rayleigh-Gans scattering, applied to infinite media. Similarity is studied for the attenuation coefficient α, as well as for the Kubelka-Munk absorption and backscattering coefficients in the positive and negative directions, and for predictions of the internal reflection at interfaces. Similarity between solutions of the Boltzmann equation for highly forward scattering and isotropic scattering (g = 0) exist only when ∑_a << ∑_s(l - g). However, because similarity between results, both with g > 0.9, is independent of the value of the absorption coefficient, it is advantageous to simulate highly forward scattering media like biological tissues with g > 0.9, e.g., by Monte Carlo simulations, instead of using isotropic scattering or diffusion theory. Monte Carlo simulations on slabs confirm the deviations from the diffusion approximation and show the behavior near boundaries. Application of similarity may save calculation time in Monte Carlo simulations, because simulation with a lower value for g will increase the mean free path.

An in vitro model is developed for application in studies of the optical and physical characteristics of flowing blood in rigid and flexible tubes (artificial vessels). The results indicate that both transmission and reflection of light are dependent on blood volume changes and orientation as well as the deformability of the red blood cells. Light transmission and reflection in human blood shows a parabolic behavior at hematocrit levels greater than 40%, when plotted against blood flow. At both low and high flow rates, the light transmission increases when compared to an intermediate flow where the transmission shows a minimum. The optical wavelength used also affects the light transmission and reflection in moving blood. The results of studies of blood in flow-through models are important for the understanding of the optical mechanisms behind the signal generation in photometrical measurement techniques.

The optical properties of brain tissues have been evaluated by measuring the phase velocity and attenuation of harmonically modulated light. The phase velocity for photon density waves at 650-nm wavelength has been found to be in the range of 5 to 12% of the corresponding velocity in a nonscattering medium, and the optical penetration depth was in the range 2.9 to 5.2 mm. These results are used to predictthe resolution of optical imaging of deep tissue structures by diffusely propagating incoherent photons. The results indicate that structures of a few millimeters in linear dimension can be identified at 10 mm depth provided that proper wavelength and time resolution are selected. This depth can possibly be enlarged to 30 mm in the case of tissues with very low scattering such as in the case of the neonatal human brain.

A holographic continuous exposure method is proposed for studying the dynamic and structural characteristics of the Brownian motion of unicellular algae. The measured algae velocity and size distribution functions are reported.

Based on previous studies from this laboratory that demonstrated degradation of cholesterol crystals ingested by macrophages in a cell culture system and indicated that intracellular phospholipids could play an important role in mobilization of crystalline cholesterol, the role of each of the three major intracellular phospholipid species in degradation of crystals is further explored. Fluorescently labeled cholesterol crystals are incubated with phospholipids over a period of 5 d. Morphological changes in crystals are monitored using digital imaging fluorescence microscopy, fluorescence redistribution after photobleaching, confocal microscopy, and epifluorescent and phase contrast microscopy. Results clearly demonstrate that all three phospholipids are able to mobilize crystalline cholesterol. However, the mechanisms by which they exert mobilization are different. Sphingomyelin and phosphatidylcholine are found to cause gradual and uniform dissolution of crystals, more or less preserving their original shape. Phosphatidylethanolamine appear to penetrate into the crystal, causing its fragmentation and solubilization. In the mixture of all three phospholipids representing the composition found in macrophages, both of the described mechanisms are working simultaneously.

Laser speckle limits the resolution that can be achieved in holography. Time-varying speckle, caused by scattering from moving objects, is even more troublesome. It can destroy the correlation needed to obtain fringes in holographic interferometry and even, ifthe fluctuations are rapid compared with the exposure time needed, the coherence needed to record a hologram. These problems are discussed, with particular reference to biomedical holography, and suggestions are made for minimizing their effect. Some positive aspects of time-varying speckle are also discussed. The fluctuations obey the same statistics as the spatial variations of a stationary speckle pattern. These statistics can be used to measure the movement of the scattering particles, a technique of particular value in biomedical science. Potential applications include monitoring blood flow, motility, and intracellular activity.

Alterations in plasma membrane structure and function are considered of primary importance in the pathogenesis of cell injury. Multiple microscopic techniques are employed to detail alterations in plasma membrane lipid structure during hypoxic injury in individual rat hepatocytes. Multiparameter digitized video microscopy, fluorescence quenching imaging, and fluorescence resonance energy transfer imaging are used to measure and monitor lipid domain formation and topography; laser tweezers are used to monitor the plasma membrane viscoelasticity. These microscopic techniques indicate that hypoxic injury in hepatocytes leads to alterations in plasma membrane lipid topography with the eventual formation of lipid domains. In concert with previous data generated with digitized fluorescence polarization microscopy and fluorescence recovery after photobleaching (FRAP), a model is proposed where formation of the distinct lipid domains promotes loss of the plasma membrane permeability barrier and cell death.

A model that predicts temperature fields in C02-laser-irradiatedtissue is applied in search of the optimal irradiation conditions or the general purpose of soft tissue removal. In a series of single pulse simulations and pulse train simulations the effect of parameters such as pulse durations, irradiance during a pulse, and the repetition rate of pulses are studied. The simulations are carried out for two basic beam profiles: Gaussian and rectangular. As a result, a range of preferred values for each parameter is obtained. The rectangular profile exhibits a far better behavior in the sense that lateral thermal damage is highly reduced compared to the Gaussian profile. Ablation thresholds and efficiencies are calculated for both profiles as a by-product. Results are in good agreement with other reported studies.

The surface temperature profiles of human enamel blocks following laser irradiation are examined using a mathematical model. A physical model for calculating this surface temperature is developed and then solved by the Laplace transform technique. The enamel block is modeled as a homogeneous cylinder in one dimension with the entiresurface exposed to laser beam irradiation. Both the photon absorption/transmission and convective heat loss are taken into consideration in the proposed model. This model allows the surface temperature to be calculated under arbitrary combinations of laser wavelength, pulse pattern, and energy density. Results indicate that (1) surface temperature depends on the wavelength, energy density, and duration of the pulse; (2) high surface temperatures (~ 300°C) can be achieved with associated inside temperature changes of less than 5°C; and (3) the surface temperature depends strongly on the environmental heat transfer coefficients. These results will facilitate the rational development of lasers as potential tools in preventive dentistry.

The rapid motion of microscopic features such as the cross striations of single contracting muscle cells are difficult to capture with conventional optical microscopes, video systems, and image processing approaches. An integrated digital video imaging microscope system specifically designed to capture images from single contracting muscle cells at speeds of up to 240 Hz and to analyze images to extract features critical for the understanding of muscle contraction is described. This system consists of a brightfield microscope with immersion optics coupled to a high-speed charge-coupled device (CCD) video camera, super-VHS (S-VHS) and optical media disk video recording (OMDR) systems, and a semiautomated digital image analysis system. Components are modified to optimize spatial and temporal resolution to permit the evaluation of submicrometer features in real physiological time. This approach permits the critical evaluation of the magnitude, time course, and uniformity of contractile function throughout the volume of a single living cell with higher temporal and spatial resolutions than previously possible.

Tunable, pulsed radiation sources in the ultraviolet, visible, and infrared wavelength ranges offer novel opportunities for investigating laser-induced biomedical effects. Free-electron lasers (FELs) deliver continuously tunable, pulsed radiation in the infrared, providing the capability to selectively target radiation into the vibrational modes of water or other biopolymers. Experimental techniques for measuring the absorption spectra of biological samples are described. These spectra indicate wavelengths that potentially serve as the basis for laser-induced biomedical effects. Some practical considerations for infrared, visible, and UV spectroscopy of biological samples are summarized, and the connection between biomedical research and more fundamental investigations of vibrational energy transfer are emphasized.

novel approach is proposed for fluorescence imaging of biological substrates. Discrimination among the contributions of different fluorophores is achieved in the time domain, taking advantage of the differences in decay times of exogenous versus endogenous fluorescences. The experimental setup relies on an intensified video camera and on a subnanosecond dye laser used for the excitation. The video camera has an electronic shutter that provides exposure times as short as 5 ns. A detailed description of the apparatus is reported with an analysis of performances. The time-gated technique is especially attractive for tumor detection in combination with photosensitizing drugs. Experiments performed on a murine tumor have shown interesting results that make this technique promising for a future application in the clinical diagnosis.

The influence of β-carotene content on laser-induced total fluorescence is evaluated in vitro, using human arteries at 488-nm excitation. The investigation demonstrates that the β-carotene content in normal arteries increases with a longer period of incubation in β-carotene solution. This is associated with a decrease in the total fluorescence emission at 488-nm excitation. A decrease of 52% in the total fluorescence emitted from the arterial tissue is noted with the increased β-carotene deposition after incubation. The experimental data are highly correlated with theoretical analyses, derived by using the Kubelka-Munk and Lambert-Beer models, which incorporate parameters of β-carotene content in arterial tissue (r = 0.94 and r = 0.91 , respectively). Total fluorescence from 138 samples of various types of atherosclerotic plaques is compared with that from normal arteries used as controls. Total fluorescence gradually decreases with longer incubation periods in β-carotene solution. For all atherosclerotic plaques, the normalized fluorescence of 0.30 ± 0.16 at initial incubation decreases to 0.23 ± 0.12 after 6 d of incubation (p < 0.005). The value then decreases to 0.19 ± 0.10 after 12 d of incubation (p < 0.005 compared to the initial and 6 d of incubation). Seventy-nine plaques with surface fissures exhibited an accelerated reduction in total fluorescence when compared to nonfissured plaque.

The large number of new materials such as amalgams and the variety of techniques for finishing and polishing in operative dentistry has stimulated interest in simple, nondestructive methods of surface roughness evaluation. We studied an optical method based on the scattering of reflected coherent light on prepared samples of composite resins submitted to different surface treatments. The method should be able to measure the degree of flatness of the samples, thus enabling a classification procedure according to a figure of merit to be defined. The diffraction properties of such moderately rough surfaces has been correlated with mechanical profilometer measurements of the residual granular structure after polishing. Different surface treatments of composite resins result in distinctive levels of surface flatness, and it is shown that a relation between the intensity of the normalized specular reflection of a beam of coherent light and the rms surface roughness can be established for characterization purposes.

The recently synthesized photosensitizer 9-acetoxy-tetra-npropylporphycene (ATPPn), a compound of the group of porphycenes,was tested for photodynamic therapy on a human bladder carcinoma cell line. Because of the hydrophobic character of the molecules, ATPPn was incorporated into soya phosphatidylcholine liposomes for administration. Bladder carcinoma cells were incubated for 60 mm at 37°C with the liposomes containing 0.5-μg ATPPn ad 1.5-ml medium. Using these concentrations, no dark toxicity and no phospholipid cytotoxicity were evident. Fluorescence measurements were made to show intracellular uptake of the photosensitizer. For the irradiation treatment, cells were exposed to coherent light delivered by a dye laser at a power density of 30 mW/cm². Irradiation with 1, 3, 6, 12, 24, and 48 J/cm² resulted in an increasing photokilling effect in correspondence to a decreasing survival rate of 93.0, 75.9, 60.1, 43.5, 28.3, and 11.3%, respectively. The results do encourage further investigations that include in vivo studies.

The Na⁺, K⁺-adenosine triphosphatase (ATPase) in microsomal membrane vesicles is covalently labeled with the triplet probe eosin 5'-isothiocyanate. Rotational mobility of the protein is investigated by measuring the time-resolved depolarization of the emitted phosphorescence from the triplet state of eosin, induced by a laser pulse. The probe is attached either nonspecifically to the protein or under conditions where the eosin is attached specifically to a lysine residue located atthe putative ATP binding site. The total anisotropy of the emission is found to be almost constant when measured over the temperature range 10 to 25°C. The anisotropy value is relatively small when the label is bound nonspecifically to the binding sites of the protein, but markedly increases when specifically bound to the protein, suggesting that the independent motion of the probe is constrained at this site. The anisotropy decay curve obtained from the specifically labeled protein shows a clearly biphasic character, and is composed of a rapidly rotating component with a rotational correlation time of 20 to 5 μs and a slower rotating component with a rotational correlation time of 250 to 90 μs in the temperature range 10 to 25°C. These motions are individually assigned to the segmental motion of the polypeptide chain and rotation of the whole protein about its axis normal to the plane of the membrane, respectively. It is estimated that about 80% ofthe total anisotropy signal is contributed by the fast rotation, and the remainder results from slow rotation.

A technique for the sequential measurement of fluorescence and phosphorescence depolarization is reported. The technique is based on a newly developed photomultiplier gain-suppression technique. The gain-suppression characteristics of the circuit are studied by applying a constant level of incident light. To demonstrate this new technique, a solid sample ofthetriplet probe eosin is excited by a pulsed, frequency-doubled Nd:YAG laser; the resulting orthogonally polarized emissions are collected by two balanced photomultipliers (PMT5). The gains of the PMTs are suppressed for the duration of the fluorescence emission, and subsequently returned to normal, to maintain the fluorescence and phosphorescence signals at the same level. The suppression of the gain is controlled by a specially designed dual-channel PMT gain-suppression circuit. The signals from the PMTs are recorded by two digital oscilloscopes, one set at a fast sampling rate to measure the static fluorescence anisotropy, the other set at a slow sampling rate to measure the slow phosphorescence depolarization. The anisotropy values can then be deduced from the two sets of recordings.

Results of the application of a tunable diode laser (TDL) to determining the trace gas components of human exhalation are presented. The analyzer is specially developed to measure both carbonoxides (CO and C0₂) in expired air. A few results illuminating possible applications of TDLs in high-sensitivity medical diagnostics have been obtained. For nonsmokers, expired concentrations of CO are slightly higher than those in inhaled air. The specific surplus value seems to be independent of the ambient atmospheric CO content. The surplus CO content increases by more than an order of magnitude just after intensive exercises, e.g., jogging. For smokers, the pharmacokinetic of abundant CO removal from the organism could be investigated by this technique, which provides quick and reliable measurements of smoking status. Breath-holding synchronous measurements of CO and CO₂ in exhalation demonstrate behavior that is different with breath-holding time. The method seems useful for the investigation of phenomena such as molecular pulmonary diffusion through the alveolar-capillary membrane and an organism's adaptation to oxygen shortage. Prospects for the development and application of diode laser spectroscopy to trace gas analysis in medicine are also discussed.

Two finite element-based methods for calculating Fresnel region and near-field region intensities resulting from diffraction of light by two-dimensional apertures are presented. The first is derived using the Kirchhoff area diffraction integral and the second is derived using a displaced vector potential to achieve a line integral transformation. The specific form of each ofthese formulations is presented for incident spherical waves and for Gaussian laser beams. The geometry of the twodimensional diffracting aperture(s) is based on biquadratic isoparametric elements, which are used to define apertures of complex geometry. These elements are also used to build complex amplitude and phase functions across the aperture(s), which may be of continuous or discontinuous form. The finite element transform integrals are accurately and efficiently integrated numerically using Gaussian quadrature. The power of these methods is illustrated in several examples which include secondary obstructions, secondary spider supports, multiple mirror arrays, synthetic aperture arrays, apertures covered by screens, apodization, phase plates, and off-axis apertures. Typically, the finite element line integral transform results in significant gains in computational efficiency over the finite element Kirchhoff transform method, but is also subject to some loss in generality.

The optical cavity of the Boeing free-electron laser (FEL) was reconfigured as a semiconfocal ring resonator with two glancing incidence hyperboloid-paraboloid telescopes. The challenge for this experiment was the complexity of the ring resonator compared to the simplicity of a concentric cavity. The ring resonator's nonspherical mirror surfaces, its multiple elements, and the size of the components contributed to the problems of keeping the optical mode of the resonator matched to the electron beam in the wiggler. Several new optical diagnostics were developed to determine when the optical mode in the FEL was spatially and temporally matched to the electron beam through the wiggler. These included measurements of the focus position and Rayleigh range of the ring resonator optics to determine the spatial match of the optical mode through the wiggler, and a measurement of the position of the optical axis for multiple passes around the ring resonatorto determine the stability of the resonator alignment. This paper also describes the optical measurements that were necessary to achieve reliable lasing. The techniques for measuring ring resonator Rayleigh range and focus position, multiple pass alignment, cavity length, optical energy per micropulse, peak power, optical extraction, small signal gain, ringdown loss, lasing wavelength, electron bunch pulse width, and energy slew are discussed.

method for measuring the modulation transferfunction (MTF) of a detector array from zero spatial frequency to twice the Nyquist frequency is presented. Laser speckle with a tunable, narrow spatial-frequency bandpass is used. The MTF measured with this method is compared to the MTF measured using sine targets. The results of the two methods agree to within 2%.

Interferometric measurements of real surfaces are combined with computed optical design analyses. To accomplish this, a special software interface driver was developed to accept serial optical path difference (OPD) data from a Zygo Mark III interferometer, to apply standard algorithms, and convert the measured data into a CODE V readable file. Analysis is conducted on a large-aperture developmental optical system containing a fold mirror of eggcrate construction. MTF performance of the entire system is computed as are the contributions of individual measured surfaces to overall optical quality. Diffraction effects resulting from the rib structure of the eggcrate mirror are isolated in the analysis, as are the effects of gravity and figure components of the wavefront. The hybrid analysis demonstrates the usefulness of coupling interferometry with an optical design program in the analysis of complex optical systems.

There has been much recent interest in the application of optical tomography to the study of transport phenomena and chemical reactions in transparent fluid flows. An example is the use of multidirectional holographic interferometry and computed tomography for the study of crystal growth from solution under microgravity conditions. A critical part of any such measurement system is the computed tomography program used to convert the measured interferometric data to refractive index distributions in the object under study. Several of the most promising computed tomography algorithms for this application are presented and compared. Because of the practical difficulty of making multidirectional interferometric measurements, these measurements generally provide only limited amounts of data. Recent studies have indicated that of the several classes of reconstruction algorithms applicable in the limited-data situation, those based on the multiplicative algebraic reconstruction technique (MART) are the fastest, most flexible, and most accurate. Several MART-type algorithms have been proposed in the literature. The performance of state-of-the-art implementations of four such algorithms under conditions of interest to those reconstructing multidirectional interferometric data are compared. The algorithms are tested using numerically generated data from two phantom objects, with two levels of added noise and with two different imaging geometries. A reconstruction of real data from a multidirectional holographic interferometer using the best of the algorithms is shown.

A rotating wafer scanner is designed and developed to determine its operational feasibility and advantages over a linear wafer scanner. The scanner is designed to operate at atmosphere. Each of its constituent parts were independently tested, and when the assembled system was evaluated, 0.2-μm-diam particle detectivity was observed.

This PDF file contains the editorial “Book Rvw: Fiber Optic Networks," by Paul E. Green, Jr. for OE Vol. 32 Issue 02

This PDF file contains the editorial “Book Rvw: Particle Field Holography," by Chandra S. Vikram for OE Vol. 32 Issue 02