J774 is a cell line derived from Balb/c mice that in vitro behaves as macrophages (including scavenger-receptor expression) and has been widely used to study macrophage cell biology. In vivo it produces histiocytic lymphoma tumors that are invasive and metastatic. We report here on the response of subcutaneous J774 tumors to photodynamic therapy with scavenger-receptor targeted chlorin(e6). Bovine serum albumin was covalently conjugated with chlorin(e6), maleylated and purified by acetone precipitation and both this and free chlorin(e6) were injected IV into mice at 2 mg/kg. When tumors were illuminated with 665 nm laser-light after 24 hours there was a highly significant response (tumor volume and growth rate) for the conjugate, but this led to a relatively small survival increase due to the highly metastatic nature of the tumor. The free chlorin(e6) gave very little tumor response. When light was delivered 3 hours after injection the response from the conjugate disappeared due to insufficient time for the tumor cells to take up the photosensitizer by receptor-mediated endocytosis. Free chlorin(e6) at 3 hours, however, produced a total regression of the tumors due to a primarily vascular effect, but the mice died sooner than control animals. When J774 tumors were surgically removed at different times after implantation the mouse survival was proportional to the length of time they had had the tumor. We interpret this data to show that mice with J774 tumors slowly develop concomitant immunity and a PDT regimen that swiftly ablates the tumor will give worse survival results than a regimen with a slower tumor response.

Tumor cell destruction usually induces host immune responses, such as local inflammation and increased activities of macrophages and neutrophils. Use of immunoadjuvant can usually enhance such immune activities. Laser immunotherapy is designed to use the combination of laser photothermal and immunological interactions to induce long-term antitumor immunity with the help of immunoadjuvant. It uses a selective hyperthermia for acute tumor destruction through an intratumor administration of indocyanine green and a noninvasive irradiation by an 805-nm laser. The concurrent in situ administration of immunoadjuvant helped achieve the desired effect: tumor eradication and antitumor immunity. The current study further explores the function of immunoadjuvants in laser immunotherapy by testing four different adjuvants: glycated chitosan, complete Freund's adjuvant, incomplete Freund's adjuvant, and c-parvum. Each adjuvant provided long-term tumor cure in the treatment of a metastatic mammary tumor model in rats. However, glycated chitosan and complete Freund's adjuvant were most effective with 25% and 18% long- term cure rates, respectively. Different concentrations of glycated chitosan were also used in treatment of rats bearing metastatic breast tumors.

Photothermal interaction of an 805-nm diode laser with an absorptive dye, indocyanine green (ICG), has been shown to be an efficacious therapy for metastatic breast tumors in a rat model when combined with immunoadjuvant. When ICG solution was injected into the target tissue, selective tissue destruction can be achieved. To study the selective photothermal interaction, temperature change in irradiated tissue was achieved. To study the selective photothermal interaction, temperature change in irradiated tissue was studied using chicken breast tissue and phantom composed of gelatin and intralipid. ICG solution was mixed with gel phantom to simulate dye-enhanced target tissue. The target gel was then embedded in chicken breast tissue. The temperature change of irradiated chicken and gel phantom was measured by needle temperature probes at different tissue depths and radii from the center of the laser beam to construct a two-dimensional array of temperature change in a cylindrical coordinate system. It was shown that it is possible to selectively raise the temperature of deep target tissue while not substantially heating nontargeted tissue. A Nd:YAG laser was also used to irradiate the tissue-gel system and the photothermal results were compared with that using the 805-nm laser.

Significant damage to rabbit corneal tissue was produced by a single pulse, in vitro exposure of 1540 m infrared laser light operating in either millisecond or nanosecond pulse widths. Millisecond pulse widths of infrared laser light produced a marked coagulative necrosis of both the corneal epithelium and stroma. We also noted histologic alterations in the stromal matrix within the beam path that we interpreted as matrix remodeling. To test this interpretation, we used an indirect immunohistochemical procedure to detect Matrix Metalloproteinase-2 (MMP-2) activity. Immunohistochemistry revealed that the MMP-2 reaction was mostly limited to the margins of the beam path. In addition, the MMP-2 reaction was less intense than expected given the significant tissue changes observed in the histologic sections. Exposure of rabbit corneal tissue to the nanosecond pulse widths produced a less severe coagulative necrosis of the tissue when compared to the millisecond exposures. However, a markedly stronger immunohistochemical pattern than would have been predicted from the histologic sections was observed, with approximately half of the beam path filled with MMP-2 reaction product. These data suggest an association between infrared laser pulse width and the degree of extracellular matrix remodeling in rabbit corneal tissue.

Threshold, median effective dose, and the mechanism of laser-tissue interaction are not well defined at the 1318-nm wavelength for human corneal exposures. The goals of this research effort are to identify at-risk groups, characterize the lesions imposed, and establish the ED₅₀ for single pulse 1318-nm laser exposures on the cornea. A Neodymium: Yttrium Aluminum Garnet (Nd:YAG) laser was used to deliver 1318-nm wavelength pulses to the corneas of ten female Dutch Belted rabbits (Oryctolagus cuniculus). Single pulses of 0.5-ms duration and radiant beam energy ranging from 116 to 2250 joules/per square centimeter (J/cm²) were used. Exposure sites were clinically evaluated acutely, one hour and twenty-four hours post-exposure for the presence of a lesion. Results from the twenty-four hour evaluation were used to determine the ED₅₀. Grossly, the lesions appeared as small, circular, well-demarcated, white, opaque lesions. Histologically, the lesions appeared as conical shaped coagulative necrosis with the base of the lesion at the epithelial surface of the cornea and extending to the apex at the endothelial border of the cornea. The ED50 for 1318-nm exposures to the rabbit cornea was determined to be 383 J/cm² for a 0.1-mm spot size as measured at 1/e².

We demonstrate application of a thermal wave imaging technique to determine the physical dimensions and position of laser-heated chromophores in tissue. We demonstrate that utilization of a periodically modulated laser source for thermal wave excitation and coherent detection applied to each pixel may be used to compute images of thermal wave amplitude and phase at the laser modulation frequency and significantly improve quality of recorded radiometric images. A theoretical analysis utilizes solution of the three-dimensional heat conduction equation to simulate thermal wave images of amplitude and phase. Effects of non- specific laser excitation on the recorded thermal wave images have been analyzed. Results of numerical simulations are compared to that obtained from tissue phantoms and in- vivo samples.

Cartilage laser thermoforming, also known as laser reshaping, is a new surgical procedure that allows in-situ treatment of deformities in the head and neck with less morbidity than traditional approaches. During laser irradiation, cartilage becomes sufficiently subtle or deformable for stretching and shaping into new stable configurations. This study describes the experimental and theoretical characterization of the thermal response of porcine cartilage to laser irradiation (Nd:YAG). The surface temperature history of cartilage specimens was monitored during heating and thermal relaxation; using laser exposure times ranging between 1 and 15 s and laser powers of 1 to 10 W. The experimental results were then used to validate a finite element model, which accounts for heat diffusion, light propagation in tissue, and heat loss due to water evaporation. The simultaneous solution of the energy and mass diffusion equations resulted in predictions of temperature distribution in cartilage that were in good agreement with experiments. The model simulations will provide insights to the relationship between the laser treatment parameters (exposure time, laser beam diameter, and power) and the onset of new molecular arrangements and cell thermal injury in the material, thus conceiving basic guidelines of laser thermoforming.

The effect of water content on specific heat capacity was examined using temperature modulated Differential Scanning Calorimetry (TMDSC). This research was motivated in part by the development laser cartilage reshaping operations, which use photothermal heating to accelerate stress relaxation and shape change. Deposition of thermal energy leads to mechanical stress relaxation and redistribution of cartilage internal stresses, which may lead to a permanent shape change. The specific heat of cartilage specimens (dia: 3 mm and thickness 1-2 mm) was measured using a heating rate of 2 degree(s)C/min for conventional DSC and 2 degree(s)C/min with an amplitude 0.38-0.45 degree(s)C and a period 60-100 sec for TMDSC. The amount of water in cartilaginous tissue was determined using thermogravimetry analysis (TGA) under ambient conditions. In order to correlate changes in heat flow with alterations in cartilage mechanical behavior, dynamic mechanical temperature analysis (DMTA) was used to estimate the specific transition temperatures where stress relaxation occurs. With decreasing water content, we identified a phase transition that shifted to a higher temperature after 35-45% water content was measured. The phase transition energy increased from 0.12 J/g to 1.68 J/g after a 45% weight loss. This study is a preliminary investigation focused on understanding the mechanism of the stress relaxation of cartilage during heating. The energy requirement of such a transition estimated using TMDSC and temperature range, where cartilage shape changes likely occur, was estimated.

The response of cartilage tissue to thermal stress can be investigated indirectly by measuring changes in optical properties during heating. Temperature distributions in cartilage depend on the mode of heating. Laser irradiation of thick cartilage specimens results in non-uniform heating, causing asynchronous stress relaxation in different regions of the tissue. In contrast, slow heating of cartilage in a Rose chamber results in more uniform temperature profiles. In addition, the heating of tissue in a saline- (or mineral oil) filled Rose chamber eliminates dehydration effects that are commonly encountered during laser heating. The purpose of this investigation was to measure diffuse reflectance and diffuse transmittance of porcine septal cartilage tissue during slow heating. Diffuse reflectance and transmittance were measured using integrating sphere and lock-in detection techniques. Cartilage surface temperatures were estimated using a thermocouple and cold-junction compensator. Diffusely transmitted light was observed to decrease, plateau, and then increase, whereas diffusely reflected light was observed to increase, plateau, and then decrease. The change in slope for both transmitted and reflected light occurred at cartilage front surface temperatures of between 45 and 50 degree(s)C. The results suggest that changes in the optical properties of cartilage tissue occur due to a phase transformation during heating.

Laser thermal therapy (LTT) is a minimally invasive surgical technique used to destroy solid tumors while minimizing damage to adjacent normal tissues. Optical energy, delivered through fibers implanted into the target volume, raises tissue temperatures above 60 degree(s)C resulting in coagulative necrosis (thermal damage). Thermal damage volumes, however, can be irregular and unpredictable, resulting from dynamic changes in the tissue properties during treatment. A closed-loop feedback fuzzy logic controller for LTT was developed with the tissue treated as a black-box system. Preliminary testing was conducted for simulated LTT with a single spherically emitting source fiber at the center of 5 mm and 10 mm diameter target tissues. Dynamic changes in blood perfusion and tissue optical properties due to heating were incorporated into the LTT simulator. Input laser power was modulated to control the temperature field in an attempt to reach target temperatures at the source (90 degree(s)C to avoid tissue charring) and at the target boundary (55 degree(s)C). In all simulations, thermal damage based on Arrhenius formulation ((Omega) equals 1) was reached at the target boundary. The controller also responded efficiently to unexpected, rapid temperature changes.

Sub-ablative thermal exposure is applied clinically to stabilize joints by taking advantage of the fact that such heating causes collagenous tissues to shrink. Unfortunately heating also generally causes tissue material properties to degrade, owing to the denaturation of the collagen network. The literature reveals that different modalities of heating such as laser and radio frequency modes create different amounts of shrinkage and varying levels of thermal damage (mechanical property degradation) within the target tissue. The relationship between shrinkage and denaturation is poorly understood, limiting the rational design of such thermal therapies. In the present research, a preliminary thermomechanical modeling capable of predicting the final state of a collagenous tissue undergoing sub-ablative heating is presented. The hybrid methodology utilized includes in-vitro experimentation and finite element analysis. It has been shown that the proposed methodology has excellent potential as a tool in simulating and determining the optimal responses of collagenous tissues when they are subjected to sub-ablative thermal treatments.

Large thermal damage zones have been observed after application of free-running holmium laser pulses inside the human body as, for example, for arthroscopic surgery. The aim of our study is to reduce thermal damage by increasing the ablation efficiency, and to achieve a smooth surface of the ablated tissue. For that purpose we use a multiply Q- switched thulium laser ((lambda) equals 2.0 micrometers , acousto- optical QS) that emits pulse series consisting of a pre- pulse of 40 mJ energy and up to 6 ablation pulses of 100 mJ each, separated by time intervals of 60 microsecond(s) . Q-switched laser pulses explosively ablate the target material. In a liquid environment, this leads to the formation of cavitation bubbles and to mechanical damage of the surrounding tissue. The pre-pulse of 40 mJ serves to minimize the cavitation effects, as it produces a small cavity that is then filled by the ablation products created by the burst of 100-mJ pulses. The pre-pulse creates, furthermore, a channel between fiber tip and target that reduces absorption losses in the liquid. Reduction of cavitation effects and channel formation are demonstrated by time-resolved photography. The use of a thulium laser instead of a holmium laser contributed to the desired reduction of thermal damage, because the penetration depth of the thulium laser light in cartilage (approximately 170 micrometers ) is only half as large as with the holmium laser.

Cavitation bubbles accompany explosive evaporation of water after pulsed energy deposition during endosurgery. Bubbles collapsing at the time of an endo-probe produce a powerful and damaging water jet propagating forward in the axial direction of the probe. We demonstrate that formation of this flow and associated tissue damage can be prevented by application of the concave probes that slow the propagation of the back boundary of the bubble. A similar effect can be achieved by positioning an obstacle to the flow, such as a ring or a pick tip in a close proximity to the back, side or front of the tip. Dependence of the flow dynamics on geometry of the probe was studied using fast flash photography and particle velocimetry. With a flat tip a maximal jet velocity of 80 m/s is achieved at a pulse energy of 0.12 mJ, while with an optimized concave probe the jet is completely stopped. The maximal distance between the probe and the tissue at which cells were affected by the water jet was measured using choriallantoic membrane of a chick embryo and Propidium Iodide staining. Changing the tip geometry from flat or convex to an optimized concave shape resulted in reduction of the damage distance by a factor of 4 with pulse energies varying from 0.02 to 0.75 mJ. Elimination of the water jet dramatically improves precision and safety of the pulsed endosurgery reducing the axial damage zone to a size of the cavitation bubble at its maximal expansion.

We developed a medical surgical system with function variability and flexible delivery of dual-wavelength infrared fiber laser that simultaneously oscillated 3 and 2 micrometers radiation. We studied the function variability (cutting/coagulation) of this fiber laser using a specially designed filter which contained two adjacent areas with different transmission for 2 micrometers radiation. When the power of 3 micrometers radiation was set to 0.6 W and the power of 2 micrometers radiation was changed from 0 W to 0.77 W using this filter at the beam traveling speed of 0.25 mm/s, the cutting groove formed in myocardium tissue increased from 0.80 mm to 0.89 mm and the coagulation layer thickness increased from 0.41 mm to 0.85 mm. We successfully developed a filter system that could continuously control coagulation layer thickness with cutting capability constant. We studied a flexible beam delivery using a single crystal sapphire fiber. The transmission efficiency per meter for 3 and 2 micrometers radiation using a 200-micrometers core-diameter sapphire fiber was 58.0% and 60.4%, respectively. The bending loss at 3-cm loop radius was 5.6%. The high flexibility and low bending loss of the sapphire fiber might make it possible to apply the dual-wavelength infrared fiber laser to endoscopic treatment. In summary, these results may encourage the possibility for practical use of the fiber laser.

Laser use is pervasive and steadily expanding both in the private sector and the Department of Defense (DoD). For more than 20 years, Rockwell Laser Industries, the U.S. Army, and the Food and Drug Administration's Center for Devices and Radiological Health have separately collected data on injuries occurring during, or resultant from, the use of lasers. However, data from these sources is incomplete and has not recently undergone a thorough compiling, statistical analysis, review and summarization. It is our belief that in order to evaluate current related medical surveillance, safety and training procedures, this data needs such an examination. Persons maintaining these databases were contacted and any available data on laser injury was collected. The data was analyzed and examined for pertinent similarities and differences among a wide range of parameters. We summarize these findings in this paper and also comment on the injuries, current safety measures and injury reporting protocols associated with laser use.

We have previously demonstrated that retinal damage thresholds can vary as a function of ultrashort laser pulse chirp. Computations and in-vivo experiments have both demonstrated such results. Here, we present a study of the computation of damage thresholds as functions of laser wavelength, pulse duration, and chirp. Damage threshold trends are explored and related to current and future laser safety exposure limits.

Hydrogen peroxide (H₂O₂) in situ synthesis within cultures of retinal pigment epithelial cells exposed to near-IR (NIR) continuous wave (CW) and mode-locked lasers is investigated. Any production of H₂O₂ as a consequence of NIR laser exposure is indicative of a multiphoton absorption event, resulting in an intracellular photochemical reaction. Comparisons of mode-locked and CW laser threshold energies required for the photo-oxidative reaction provide support for an enhancement in multiphoton absorption in tissues exposed to the high peak powers inherent in mode-locked laser beams. Due to different fluorescent staining properties our results indicate different mechanisms for oxidative stress from CW and mode- locked laser exposure.

We have previously shown that minimum visible lesions (MVL) generated in vivo by exposures at threshold energies are not ophthalmoscopically visible at one hour, but become visible 24 hours post-exposure. Our preliminary studies toward understanding this phenomenon at the molecular level are presented. We provide threshold data relating cytotoxicity with energy for acute laser exposures in cultured retinal pigment epithelial cells. Rapid loss of cell viability is used as an initial endpoint of analysis. Comparisons of damage efficiency for continuous wave and mode-locked lasers are presented.

Recent theoretical and experimental findings have produced wide ranges of absorption coefficients for melanin in the visible and near-infrared wavelength ranges. These values have been reported for a variety of laser pulse durations, from less than one nanosecond to CW exposures of several seconds. Here we present the findings of non-linear absorption studies in melanin-doped samples in an effort to reconcile bioeffects experiments and theory across a wide variety of irradiance levels. These studies are of particular interest to laser bioeffects in the retina, for which melanin plays a key role in the absorption of laser energy.

Previously, we reported that ultrashort, near infrared (NIR) laser pulses caused more DNA breakage in cultured retinal pigment epithelial (RPE) cells than did CW, NIR laser radiation delivering a similar radiant exposure. We hypothesized that this difference was due to multiphoton absorption in an intracellular chromophore such as the RPE melanin. We investigated two-photon excitation of fluorescence in a suspension of isolated bovine RPE melanosomes exposed to a 1-KHz train of approximately 50- fsec laser pulses at 810 nm from a Ti:Sapphire laser, and compared this to the fluorescence excited by CW exposures at 406 nm from a Krypton ion laser. Fluorescence was measured with a PC-based spectrometer. The CW sources excited fluorescence with a peak at 525 nm. The fluorescence intensity depended on the irradiance of the sample, as well as the melanosome concentration. Peak fluorescence was obtained with a suspension of ~2 x 10⁷ melanin granules/ml. The 810-nm, ultrashort pulses also excited fluorescence, but with a broader, lower-amplitude peak. The weaker fluorescence signal excited by the 810-nm ultrashort pulse laser for a given melanosome concentration, compared to 406-nm CW excitation, is possibly due to the smaller two- photon absorption cross-section. These results indicate the involvement of multiphoton absorption in DNA damage.

To explore the polarization-dependent optical properties of skeletal muscle tissues, we calibrated the extinction coefficients of the polarization components parallel with and perpendicular to chicken breast tissue filaments and the cross-polarized intensity coupling coefficients between the two polarization components, based on the measured quasi- coherent photons. The calibrated values of these coefficients were quite consistent with previously reported. The extinction coefficient in the polarization along tissue filaments was significantly higher than that of the other polarization. Also, the cross-polarized coupling coefficient of the coupling from the polarization of tissue filaments into the other was stronger than that of inverse coupling.

We present a fiber optic spectral polarimeter, an instrument that allows measurement of the spectrally resolved Stokes parameters. The instrument consists of a pair of polarization maintaining (PM) fibers spliced at 45 degree(s) with respect to each other in line with a polarizer module whose transmission axis is aligned to the fast axis of the first PM fiber. The generated spectrum is composed of three quasi- cosinusoidal components, which carry information required to reconstruct the spectrally resolved Stokes parameters of incident light. Fourier transform of the measured spectrum provides the significant parameters for determination of the spectrally resolved Stokes parameters of light. The performance of the fiber optic spectral polarimeter is demonstrated by the computer simulation and experiments with input light of known polarization states. A unique characteristic of this instrument is that the spectrally resolved polarization state of incident light can be determined from one spectral measurement without any mechanical movement. Moreover, the instrument can be incorporated into a tomographic imaging system such as a conventional microscopy system. Polarization based microscopy combined with a fiber optic spectral polarimeter will provide measurements that allow better understanding of depolarization process of light passing through biological materials for diagnostic imaging.

A multiple-channel polarization-sensitive system based on optical coherence tomography was built to measure the Mueller matrix of scattering biological tissue. The Jones matrix of a sample can be determined with a single scan and subsequently converted into an equivalent non-depolarizing Mueller matrix. As a result, the system can be used to measure the Mueller matrix of soft tissue. Birefringence, axis orientation, and diattenuation can be extracted.

This paper presents our study of time-resolved propagation of polarized light in scattering media. Monte Carlo simulated time-resolved Stokes vectors of transmitted light were compared with the experimental results. A satisfying match has been obtained.

In this investigation, a polarization-based imaging system is developed and described that measures the two-dimensional effective backscattering Mueller matrix of a sample in near real-time. As is well known, a Mueller matrix can provide considerable information on the makeup and optical characteristics of a sample and also directly describes how the sample transforms an incident light beam. The ability to measure the two-dimensional Mueller matrix of a biological sample, therefore, can provide considerable information on the sample composition as well as the potential to reveal significant structural information that normally would not be visible through standard imaging techniques. Additional information can also be obtained through the application of image-processing, decomposition, and reconstruction techniques that operate directly on the 2D Mueller matrix. Using the developed system, it is shown how the induction of internal strain within the sample coupled with image reconstruction and decomposition techniques can further improve image contrast and aid in the detection of boundaries between tissues of different biomechanical and structural properties. The studies presented were performed with both rat tissue and a melanoma-based tissue culture. The results demonstrate how these techniques could provide information that may be of diagnostic value in the physical detection of malignant lesion boundaries.

Single electrical stimulation of the cervical sympathetic trunk elicits in the ganglion cells an excitatory postsynaptic potential (EPSP) or multiple EPSPs of varying latencies, among which a fast excitatory postsynaptic potential (f-EPSP) is the main type of ganglionic transmission in the sympathetic neurons. In previous work, we studied the effects of Helium-Neon laser with wavelength 632.8 nm on membrane conductance of neurons with stable f- EPSP in isolated rat superior cervical ganglia. The aim of this study is to further measure the effect of Helium-Neon Laser with wavelength 632.8 nm on fast excitatory postsynaptic potential of postganglionic neurons in the isolated rate superior cervical ganglia by means of intracellular recording techniques. The neurons with fast excitatory postsynaptic potential were irradiated by different power densities (1 and 5 mW/cm²), pulse frequency of 1 Hz laser. Irradiated by the 2 mW/cm² laser, the amplitude of the f-EPSP could augment (P<0.05) and even caused action potential (AP) at the end of the first 1-2 minute, the F-EPSP could descend and lasted for 3- 8 minutes later.

We present preliminary experimental data that enable us to suggest that heat transfer in cellular tissue under local strong heating is a more complex phenomenon than a simple heat diffusion. Namely, we demonstrate that under local strong heating of a muscle tissue heat transfer in it exhibits substantial anisotropy unexplained in the context of the standard diffusion model. The observed temperature dynamics is also characterized by nonlinear behavior as well as by a certain repeat reversibility. The latter means that the time variations in the temperature of a cellular tissue undergoing repeated acts of heating go in the same way at least approximately. We explain the observed anomalous properties of heat transfer by suggesting the flow of the interstitial liquid to appear due to nonuniform heating which, in turn, affects the heat transfer. A possible mechanism responsible for this effect is discussed.

We analyze the necrosis growth due to thermal coagulation induced by laser light absorption and limited by heat diffusion into the surrounding live tissue. The tissue is assumed to contain a certain tumor in the undamaged tissue whereof the blood perfusion rate does not change during the action. By contrast, the normal tissue responds strongly to increase in the tissue temperature and the blood perfusion rate can grow by tenfold. We study in detail the necrosis formation under conditions typical for a real course of thermal therapy treatment, the duration of the action is taken about 5 minutes when a necrosis domain of size about or above 1 cm is formed. In particular, if the tumor size is sufficiently large, it is about 1 cm, and the tissue response is not too delayed, the delay time does not exceed 1 min, then there are conditions under which the relative volume of the damaged normal tissue is small in comparison with the tumor volume after the tumor is coagulated totally.

The structure of the regional lymph nodes and the thymus was studied in the experiments upon the mice of the line C57BL with the subcutaneous interwoven melanoma B₁₆ in the periods from one hour to 12 days after the radiation of melanoma with one irradiation impulse of the Nd laser with the energy density of 400 J/cm². During the first 3 days after the irradiation of tumor with laser radiation the impoverishment of lymph nodes and thymus with lymphocytes takes place because of their intensified migration from these organs to the blood channel. Then one can see the restoration of the lymph nodes and thymus structure. The restoration of lymphopoiesis in the lymph nodes went on in the first place because of the poiesis in the follicles which consist of B-lymphocytes. Consequently, the lymphoid tissue plays a great role in the reorganization of the immunological status of the organism. Reorganization can be seen during the treatment of tumors with laser radiation, and it takes place in the first instance because of the reinforcement of the humoral immunity.

Among different problems in different theories of laser light propagation and scattering in biological tissues there is one (especially for laser illumination), which is now not yet widely discussed in application to biomedical optics - the effect of boundary roughnesses. But this effect can have potentially a strong influence on a total light field into a tissue. So the development of different theoretical methods and models to calculate a surface scattering is the important problem in biomedical optics. One of such theoretical approach can be based on the electromagnetic wave diffraction theory (EWDT) if the peculiarities of optical waveband will be taken into account. The basis exact EWDT allows to determine the scattering field from the perfectly conducting rough surfaces in relative units or in the terms of radiophysical cross section. For light wavelengths in biomedical optics, another conducting boundary condition is needed, and the result must be presented in optical terms and absolute units. The use of EWDT in application to the biomedical optics becomes possible by means of exact comparative analysis of the essential conceptions of the photometry and diffraction theories, which has been made in this work.

The rapidly advancing field of tissue engineering requires innovative approaches to characterize the changing properties of engineered constructs. Nondestructive evaluations of mechanical properties are a critical portion of this. Tissue engineers must have the ability to dynamically evaluate the growth of cells on material scaffolds producing engineered tissues. We have developed an acoustic method to stress the surface of tissues, and using optical techniques we are able to noninvasively measure the properties of the tissue. This method is compared to traditional uniaxial tensile mechanical testing. This new methodology provides a minimally invasive technique to strain tissues and noninvasively measure the mechanical properties of the material.

The study of optical clearing dynamics of various connective tissues was carried out by means of polarization microscopy. Rate difference of optical clearing of such types of tissues as cartilage, meniscus, nasal septum tissues, sclera and tunica testis was found. The areas of unidirectional orientation of collagen fibers in cartilage and tunica testis were determined.

A means of assessing the internal structure of teeth based upon use of high frequency, highly localized ultrasound (acoustic waves) generated by a short laser pulse is discussed. Some key advantages of laser-generated ultrasound over more traditional contact transducer methods are that it is noncontact and nondestructive in nature and requires no special surface preparation. Optical interferometric detection of ultrasound provides a complementary nondestructive, noncontact technique with a very small detection footprint. This combination of techniques, termed laser-based ultrasonics, holds promise for future in-vivo diagnostics of tooth health. In this paper, initial results using laser-based ultrasound for assessment of dental structures are presented on an extracted human incisor. Results show the technique to be sensitive to the enamel/dentin, dentin/pulp, and dentin/cementum junctions as well as a region of dead tracts in the dentin.

Laser irradiation may stimulate chondrocytes proliferation in the peripheral region surrounding a photothermally-heated area in rabbit nasal septal cartilage. In this study, ex- vivo rabbit nasal septal cartilages maintained in culture were irradiated with an Nd:YAG laser ((lambda) equals1.32 micrometers , 4-16 sec, 10-45 W/cm²) to examine the relationship between the diameter of replicating cells and irradiation time. Also, this study investigated whether proliferation occurs following heating (by immersion in hot saline baths, with a heated metal rod, and a soldering iron) and mechanical modification (crushing with a metal stamp and scoring with a scalpel). Replicating chondrocytes were identified using a Bromodeoxyuridine (BrdU) double antibody detection system in whole mount tissue. Light microscopy was used to confirm the presence of BrdU stained chondrocytes. The mechanical and thermal stressors used failed to produce a proliferative response in chondrocytes as previously seen with laser irradiation. We suspect that chondrocyte proliferation may be induced as a response to alteration in matrix structure produced by photothermal, thermal, or mechanical modification of the matrix. Heat generated by a laser to stimulate chondrocyte proliferation may lead to new treatment options for degenerative articular diseases and disorders. Laser technology can be adapted for use with minimally invasive surgical instrumentation to deliver light into otherwise inaccessible regions of the body.

Selective targeting the retinal pigment epithelium (RPE) while sparing adjacent tissue such as the photoreceptors has been demonstrated by repetitively irradiating the fundus with a train of green microsecond(s) -laser pulses. The aim of this study was to investigate selective RPE effects alternatively by means of rapidly scanning a cw-laser beam across the RPE to obtain the required microsecond(s) -illumination times. The radiation of an Ar⁺ laser (514 nm) was transmitted through a 25-micrometers core diameter fiber to a scanner unit. The fiber tip was imaged onto the object plane with a magnification of 0.75. The beam was repetitively scanned across porcine RPE samples in vitro providing an irradiation time of 1.6 microsecond(s) . Cell damage was investigated with a fluorescence viability assay.

The origin of cell damage due to irradiation of the retina with microsecond laser pulses is most likely the disintegration of retinal pigment epithelial cells, which is caused by the formation of microbubbles around the strongly absorbing melanosomes within the cell. In order to get a more detailed understanding of the laser tissue interaction in the retinal pigment epithelium we irradiated a suspension of porcine melanosomes, which served as a model system, by a frequency doubled Nd:YLF laser emitting at 527 nm. We used pulse durations of 500 ns and 3.5 microsecond(s) . The formation of microbubbles around isolated melanosomes was imaged directly on a microscopic level by fast flash light photography. Near threshold radiant exposure for bubble formation, we found transient bubbles with diameters below 1 micrometers and lifetimes below 500 ns. Applying super-threshold irradiation stable bubbles with diameters up to 7 micrometers and lifetimes in the millisecond time regimen were observed. This can be explained by production of stable gas inside the melanosome due to laser heating.

Though allowable (safe) energy doses of pulsed laser radiation have been determined in the central retina, the sensitivity of the peripheral retina to damage must also be assessed. We used results from ray-tracing in an eye model to estimate laser spot size at the retina and recent thermal model computations of damage thresholds to predict off-axis retinal injury from laser irradiation. The predictions were made for threshold exposures with a 532-nm, 10-ns, Nd:YAG laser beam that filled the dilated pupil (7-mm diameter). Results were compared to previously published measured energy doses at the cornea needed to produce a minimally visible lesion (MVL) in the peripheral retina of rhesus subjects. We predicted the threshold for injury at the macula, and at selected portions of peripheral retina out to 60 degree(s) from the fovea. Both predictions and measured data were normalized to their respective macula values. Normalized predicted thresholds in the peripheral retina increased as a function of angular distance from the macula. This varied from the measured data which, on the other hand, were relatively insensitive to angular position in the peripheral retina. The difference is likely due to improvements in methods of assessing retinal injury that have been incorporated into the model.