The purpose of this study was to investigate the induction of anti-tumor immunity by photodynamic therapy (PDT). We used EMT-6 mammary sarcoma, a moderately immunogenic tumor, with 10(6) cells injected s.c. in thighs of immunocompetent Balb/c mice. Mice were treated 10 days later when tumors were 6-mm diameter. Two PDT regimens were equally effective in curing tumors: 1-mg/kg of liposomal benzoporphyrin derivative (BPD) followed after 15 min by 150 J/cm² 690 nm light or 10-mg/kg chlorin(e6) (ce6) followed after 6 hours by 150 J/cm² 665 nm light. BPD-PDT produced a black eschar 24-48 hours after treatment with no visible tumor, followed by healing of the lesion. By contrast ce6-PDT showed no black eschar, but a slow disappearance of tumor over 5-7 days. When cured mice were rechallenged with 10(6) EMT-6 cells in the opposite thigh, all ce6-PDT cured mice rejected the challenge, but BPD-PDT cured mice grew tumors in a proportion of cases. When mice were cured by amputation of the tumor bearing leg, all mice subsequently grew tumors upon rechallenge. Mice were given two EMT6 tumors (1 in each leg) and the mouse was injected with ce6 or BPD but only one tumor was treated with light. Both tumors (PDT-treated and contralateral) regressed at an equal rate until they became undetectable, but in some mice the untreated tumor recurred. Those mice cured of both tumors rejected a subsequent EMT6 rechallenge. Amputation of the tumor bearing leg did not lead to regression of the contralateral tumor. Mice that rejected an EMT6 rechallenge failed to reject a subsequent cross-challenge with J774 reticulum cell sarcoma (an alternative Balb/c murine tumor). These data show that PDT generates a tumor-specific memory immune response, and in addition an active tumoricidal immune response capable of destroying distant established tumors. We hypothesize that ce6-PDT is more effective than BPD-PDT due to more necrotic rather than apoptotic cell death and/or generation of heat-shock proteins that are known for efficient presentation of tumor antigens via dendritic cells to cytotoxic T-cells. PDT could be used to treat a locally advanced tumor while at the same time destroying distant metastases via an induced immune response.

Upon giving an outline on vaccines in general, their history and priorities for future development, this paper gives a brief summary of the advances in the generation of cancer vaccines from the first attempts made over 100 years ago to those currently evaluted in clinical trials. This is followed by discussing hte intitial achievements in the investigation of cancer vaccines generated by photodynamic therapy (PDT). Recent contributions from our research to the understanding of how PDT-generated cancer vaccines work and their advantages compared to other types of cancer vaccines are discussed.

Laser immunotherapy is a novel method developed to treat metastatic tumors. The selective photothermal interaction using a near-infrared laser and indocyanine green destroys living tumor cells while preserving antigenic tissue derived protein. The treated tumor remained in the host as a source of exposed tumor antigens. Working in tandem with the applications of immunoadjuvant, laser immunotherapy has shown to induce an anti-tumor immunity in a metastatic mammary tumor model in rats. To further study the effect of laser immunotherapy, the immunogenicity of the rat model, DMBA-4, was investigated through surgical removal or primary tumors and by tumor immunization using freeze-thaw tumor cell lysates. The surgical removal of the primary tumors did not have any effect on the recurrence of the tumors at the primary sites. The metastases at remote sites also developed after the surgery. In the tumor challenges following the immunization, the immunized rats only had delayed emergence of the primary tumors and the metastases. All the immunized rats died with multiple tumors. The laser immunotherapy cured rats, on the other hand, showed strong tumor resistance in repeated tumor rechallenges. Our results showed that the laser immunotherapy could induce a strong anti-tumor immunity in a poorly immunogenic tumor model. Furthermore, the effect of laser immunotherapy on the metastases at remote sites indicated that this novel method could become an effective method in treating the metastatic tumors.

Laser immunotherapy, a novel therapy for breast cancer, utilizes selective photothermal interaction to raise the temperature of tumor tissue above the cell damage threshold. Photothermal interaction is achieved with intratumoral injection of a laser absorbing dye followed by non-invasive laser irradiation. When tumor heating is used in combination with immunoadjuvant to stimulate an immune response, anti-tumor immunity can be achieved. In our study, gelatin phantom simulations were used to optimize therapy parameters such as laser power, laser beam radius, and dye concentration to achieve maximum heating of target tissue with the minimum heating of non-targeted tissue. An 805-nm diode laser and indocyanine green (ICG) were used to achieve selective photothermal interactions in a gelatin phantom. Spherical gelatin phantoms containing ICG were used to simulate the absorption-enhanced target tumors, which were embedded inside gelatin without ICG to simulate surrounding non-targeted tissue. Different laser powers and dye concentrations were used to treat the gelatin phantoms. The temperature distributions in the phantoms were measured, and the data were used to determine the optimal parameters used in selective hyperthermia (laser power and dye concentration for this case). The method involves an optimization coefficient, which is proportional to the difference between temperatures measured in targeted and non-targeted gel. The coefficient is also normalized by the difference between the most heated region of the target gel and the least heated region. A positive optimization coefficient signifies a greater temperature increase in targeted gelatin when compared to non-targeted gelatin, and therefore, greater selectivity. Comparisons were made between the optimization coefficients for varying laser powers in order to demonstrate the effectinvess of this method in finding an optimal parameter set. Our experimental results support the proposed use of an optimization coefficient to find optimal parameters for selective hyperthermia.

Positive results of Laser-Assisted Cancer Immunotherapy (LACI) have been reported previously in the irradiation of superficial tumors. This paper reports the effect of LACI using laser interstitial therapy approach. We hypothesize that the maximum immuno response depends on laser induced tumor temperature. The measurement of tumor temperature is crucial to ensure necrosis by thermal damage and immuno response. Wister Furth female rats in this study were inoculated with 13762 MAT B III rat mammary adinocarcinoma. LACI started seven to ten days following inoculation. Contrary to surface irradation, we applied laser interstitial irradiation of tumor volume to maximize the energy deposition. A diode laser with a wavelength of 805 nm was used for tumor irradiation. The laser energy was delivered inside the tumor through a quartz fiber. Tumor temperature was measured with a micro thermocouple (interstitial), while the tumor surface temperature was controlled with an IR detector. The temperature feedback demonstrates that it is possible to maintain the average tumor temperature at the same level with reasonable accuracy in the desired range from 65°C-85°C. In some experiments we used microwave thermometry to control average temperature in deep tissue for considerable period of time, to cause maximum thermal damage to the tumor. The experimental set-up and the different temperature measurement techniques are reported in detail, including the advantages and disadvantages for each method.

We investigated the mechanisms of material ejection in Q-switched Er:YAG laser tissue ablation. Q-switched laser ablation at moderate and high radiant exposrues is associated with very high volumetric energy densities in the target material. For water, an initial phase of nonequilibrium surface vaporization of the entire liquid volume. The ablation of deeper layers with lower peak temperatures proceeds as phase explosion. For mechanically strong tissues, the nonequilibrium surface vaporization is followed by a vapor explosion coupled with thermal dissociation of the biomolecules into volatile products. In deeper layers, ablation proceeds as confined boiling with mechanical tearing of the tissue matrix by the vapor pressure. The recoil stress induced by the primary material ejection at a radiation exposure of 5 J/cm² is in the order of 500-900 MPa. For water and soft tissues such as liver, the recoil causes a powerful secondary material expulsion. For mechanically stronger tissues such as skin, nosecondayr expulsion was observed even though the recoil stress largely exceeeds the static tensile strength of the tissue. Recoil-induced material expulsion results in an increase of both ablation efficiency and mechanical side effects of ablation that becomes ever more pronounced with decreasing pulse duration. Neither the succession of phases in nanosecond-laser tissue ablation nor recoil-induced material expulsion have yet been modeled theoretically even though they are of great importance for the efficiency and precision of ablation. Their consideration remains a major challenge for future work.

We investigated the mechanisms of material ejection in IR laser tissue ablation using free-running Er:YAG laser pulses. We found that for water and soft tissues such as liver the primary mechanism for material ejection is a phase explosion within the target material. The recoil induced by the primary material ejection causes a secondary material expulsion that largely increases the ablation efficiency. For mechanically stronger tissues such as skin, the material ejection is driven by confined boiling, and recoil-induced expulsion plays no role. The high efficiency of recoil-induced material expulsion is associated with a loss in ablation precision and an increase of mechanical side effects that needs to be considered for an appropriate choice of laser parameters.

Currently ultra short pulses with pluse duration close to 100 fs are investigated for tissue ablation to perform laser surgery in a microscopic scale without any damage to the remaining tissue. Several groups showed already that the risk of thermal damage can be avoided; however the ablated material leaves the surface with a high velocity which leads to significant recoil momentum to the tissue. This paper focuses on the experimental set-up to measure this momentum transfer. Various set-ups had been developd over the last years like a pendulum that is highly senstive but cannot ensure that in a train of pulses each pulse will impact at exactly the same spot. A sliding rod in a glass tube ensured the constant impact point but is sensitive to several environmental conditions, which are hard to control. Recently, special swing plates were designed as vibration disks. The small sample was mounted in the center of this plate and exposed by fs pulses of a TiSa laser. The beam of a laser Doppler vibrometer was focused onto the backside of the plate monitored its motion. This set-up enabled us to measure the recoil momentum. While the total momentum transfer could be well determined to Δp=6 10^-3 g mm/s, the question about a mechanical damage, for example for hair cells in the inner ear is much more difficult to answer, since this depends on the time in which the ablated materials leaves the surface. Evaporation times of 40 ps would lead to serious risk ofhar cell damage.

Yucatan mini-pigs and Yorkshire pigs were exposed on their flanks to 1318 nm, 0.5 ms laser pulses. Injuries were readily visible on the Yorkshire pigs immediately, one hour, and 24 hours post exposure but difficult to locate at 3 days post exposure. The Yucatan mini-pig injuries were not seen immediately or at one-hour post exposure, but at 24 hours and three days post exposure they were easily identified. The Yorkshire injuries were round red, well demarcated, with a circular pink area of edema. It is hypothesized that skin pigmentation has an effect on the mechanism of 1318 nm laser energy absorption in skin. Pigmentation may have a significant effect on how infrared laser injuries present, develop and heal.

Yucatan Mini-pigs were exposed on their flank to 0.5 milli second 1318 nm pulses of laser light. The ED50 damage threshold was determined for this laser exposure combination. The skin was assessed for injury immediately, at 1 hour, 24 hours and three days post exposure. Generally, at least 24 hours was required for visible lesions to form. It was found that as the duration between exposure and assessment expanded the injury was more easily visualized. Tissue samples were collected for histology at one hour, 24 hours and three days. Histologic sections will be presented in future work. It was also found that the topical application of mineral oil to the area of interest was found to greatly increase the ease of identification of injuries.

An increasing number of industries, to include military, medicinal, and technological arenas, are using 1.3 micron laser systems for which current skin and eye guidelines are identical. No skin threshold, ED50 or exposure data are available. The mechanisms of laser-tissue interaction with skin at 1.3 microns are unknown. Together, these facts necessitate increased research to prevent future laser accidents and injuries. This study examines the method of interaction of 1.3 microns laser light with tissue in the Yorkshire pig. Our research addresses laser-tissue interaction through delivery using a Nd:YAG with an intracavity filter producing 1.3 micron light at 0.5 millisecond exposure time and in the range of 137 to 475 J/cm². Laser exposure to Yorkshire pigs was evaluated for dermal lesion development. Lesions were appraised for acute, one-hour and 24-hour post exposure presentation.

A thermal model was used to calculate the skin temperature rise in porcine skin and predict the damage thresholds in terms of laser power for various wavelengths, pulse durations, skin parameters and laser spot sizes. Laser exposures of 1.54 μm, 0.60 ms in duration and using a 0.7 mm spot size were applied to the porcine skin. The damage thresholds were determined at 1-hour and 24-hour post exposures using probit analysis. Only one subject was exposed giving adequate fiducial limits at the 95% confidence level. The ED50 for these 72 exposures was determined to be 58 mJ, giving a radiant exposure of 15 Jcm^-2. The damage threshold is compared with model predictions, with work previously published in the literature and with the ANSI Standard’s MPE for 1540 nm lasers at 0.60 ms.

Our research into laser bioeffects has increasingly focused on cytotoxic mechanisms affecting genomic expression and programmed cellular stress responses. In the context of DNA damage, we previously reported that more DNA strand breaks were produced in cultured retinal pigment epithelium (RPE) cells exposed to ultrashort pulse, than to CW, near-infrared (NIR) laser radiation. To test the hypothesis that RPE melanin was the cellular chromophore responsible for mediating this damage, the experiments were repeated with a line of human-derived RPE cells that could be grown in culture expressing varying levels of pigmentation. Lightly-pigmented cells were either unexposed, or exposed to the output of a Ti:Sapphire laser producing 810 nm light in mode-locked pulses (48-fsec at 80 MHz), or as CW radiation. Cells were irradiated at 160 W/cm² or 80 W/cm² (the estimated ED50 or half-ED50 for a retinal lesion). Immediately following the laser exposure, cells were processed for the comet assay. Longer "comet" tails and larger "comet" areas indicated more DNA strand breaks. In lightly-pigmented RPE cells, the overall comet assay differences among the laser-exposed groups were smaller than those observed in our earlier experiments which utilized highly pigmented primary cells. The comet tail lengths of cells exposed to the mode-locked pulses at the ED50, however, were significantly longer than those of the controls or the CW-exposed cells. The other comet assay parameters examined (tail moment, comet area) did not show consistent differences among the groups. While these results support the involvement of melanin in the ultrashort pulse laser-induced damage to DNA, they do not exclude the involvement of other cellular chromophores. Some preliminary experiments describing other measures of cellular stress responses to laser-induced oxidative stress are described.

In order to estimate the optimum laser conditions for efficient dissociation of cholesterol ester in an arteriosclerotic region of blood vessels, we have invstigated the relationship between laser wavelength and power density on cholesterol ester dissociation using a mid infrared free electron laser (MIR-FEL). In this study, cholesteryl oleate, which is a typical cholesterol ester found in arteriosclerotic regions, was irradited with 5.75-μm-FELs, which cause vibration of ester bonds. Two results were obtained. (1) Ester dissociated depending on the absorption coefficient, and the macropulse duration was shorter than the thermal relaxation time, showing that ester bonds dissociated into carboxylic acid and cholesterol by macropulse-induced thermal effects without accompanying thermal diffusion, (2) Using a wavelength of 5.75-μm the maximum ester dissociation ratio was achieved under the optimum laser conditions of a macropulse energy density of 0.4-1.0 J/cm². We conclude that MIR pulsed-lasers with a wavelegnth of 5.75 μm can be useful for removal of cholesteryl lester in an arteriosclerotic region of blood vessels.

The objective of this study was to model the optical profile of a proprietary light source in various simulated biological tissues using Monte Carlo based raytracing software. The proprietary light source, built by Light Sciences Corporation, has an LED array at its distal end and is being evaluated for use as an intratumoral PDT treatment device. The light source was scanned in a goniometer to characterize its optical geometry in air and this data provided the basis for an optical model of the device. The bulk scattering effect of the model in biological tissue was then simulated using the raytracing software. The simulated results were further verified with experimental measurements in phantom medium. The simulated results indicated a non-uniform light distribution along the LED array axis in air. In addition, the light distribution at cross section normal to the LED array axis is "butterfly" in shape with the differences of the peak to average approximately ±42%. However, the optical profile of the light source in a bulk scattering tissue became much more uniform than those in air, with a peak to average spread in cross section of ±15%.

Biological tissue scatters light mainly in the forward direction where the scattering phase function has a narrow peak. This peak makes it difficult to solve the radiative transport equation. However, it is just for forward peaked scattering that the Fokker-Planck equation provides a good approximation, and it is easier to solve than the transport equation. Furthermore, the modification of the Fokker-Planck equation by Leakeas and Larsen provides an even better approximation and is also easier to solve. We demonstrate the accuracy of these two approximations by solving the problem of reflection and transmission of a plane wave normally incident on a slab composed of a uniform scattering medium.

To examine the phenomenon of polarization memory, we examine time resolved backscattering of circularly polarized plane waves normally incident on a slab containing a random distribution of latex spheres in water. For large spheres polarization memory occurs a short time after first order scattering and before depolarization. It is the result of successive near forward scattering events that maintain the incident wave's helicity. For moderately large scatterers, it exhibits a simple dependence on the anisotropy factor. For larger spheres or those with higher refractive indices, it also depends on complicated angular and polarization characteristics of backscattering given by Mie theory.

In this paper we present experimental results demonstrating processing techniques developed in our laboratory that can be utilized to decode or extract useful information from two-dimensional Mueller matrices of turbid media. Through the use of these methods, involving the partial least squares technique, it is shown how scattering coefficient contributions as a function of particle size can be estimated for a given sample. Furthermore, we demonstrate how a spatial selection algorithm known as "chain select" can be used to help facilitate the interpretation of the measured Mueller matrix images. The samples utilized in this investigation were comprised of polystyrene spheres with diameters ranging from 200 nm to 2000 nm and analyzed with 514 nm light. At this wavelength, both Rayleigh and Mie-types of scattering are observed.

The Mueller matrix describes all the polarizing properties of a sample, and therefore the optical differences between cancerous and non-cancerous tissue should be present within the matrix elements. We present in this paper the Mueller matrices of three types of tissue; normal, benign mole, and malignant melanoma on a Sinclair swine model. Feature extraction is done on the Mueller matrix elements resulting in the retardance images, diattenuation images, and depolarization images. These images are analyzed in an attempt to determine the important factors for the identification of cancerous lesions from their benign counterparts. In addition, the extracted features are analyzed using statistical processing to develop an accurate classification scheme and to identify the importance of each parameter in the determination of cancerous versus non-cancerous tissue.

In hyperthermia, the accurate measurement of blood flow is regarded as a key footstep to describe physiological status of subjects since blood flow serves both to deliver oxygen and the metabolic substrates, and to carry away heat and the waste products of metabolism. To facilitate these issues we put forward a simple optical method to measure dynamical change of blood volume combining laser speckle measurement and CCD microscopic imaging technique. In this study, at first we selected six different temperatures (31°C, 33°C, 35°C, 37°C, 38°C, 39°C), followed variations of blood velocity and diameter in microvessels (15~50μm) on rat’s mesentery after 30 minutes at each temperature. Furthermore, during heated at seven higher different temperatures (41°C, 43°C, 45°C, 46°C, 49°C, 51°C, 54°C) for 30 minutes respectively, diameter and velocity were measured in vivo and real time. The results showed that changes of blood volume ranged from 68~110% when temperature altered, and the relationship between the constant value and the temperature approximated linear (k=0.05±0.005). While heated at 41°C~46°C for 30 min, velocity increased slightly but diameter and blood volume increased markedly and finally got to constants. The value of velocity increased to maximum when microvessels were heated with 49°C for 12 min. At this temperature, diameter and blood volume increased during the first 14 min, but began to decrease when heated longer. When temperature is higher than 49°C, 51°C, 54°C, velocity ,diameter and blood volume all increased at first and then decreased during 30 min and at the end of heating they were all far lower than control value. We draw our conclusion that the critical temperature is 49°C for intestine microcirculation with heating for 30 min. And the rates of thermal damage are proportion to temperature for the same heating time.

The optical properties of porcine liver were studied during the dehydration process at different constant temperature (37°C, 40°C,43°C, 46°C, 50°C). Each time after porcine liver samples were placed in thermostat for a different period, the weight of samples were recorded by a precise electronic scale, and the optical properties of corresponding samples were measured by a double integrating sphere system. The results showed that the absorption coefficient mainly depended on dehydration level of tissue. In contrast, the reduced scattering coefficient had more complex relation with the dehydration process, which depended on both temperature and heating time. There is not obvious relation between the reduced scattering coefficient and dehydration level. This study implies that dehydration, temperature and teim are important factors altering optical properties of tissue.

In present work an analysis of the existing experimental data has been carried out on the ablation of biological tissue (skin, cornea, bone) under high-irradiance laser beam ~109W/cm² at different wavelengths λ = 0.266, 0.532, 1,064, 2.7, 2.8, 2.9 μm. Comparison of the dependence of the ablation threshold values versus the intensity and wavelength of the single incident pulse to the data obtained in experiments on hgih power pulses interaction with organic low-density targets of agar-agar allows to reveal some common mechanisms. For the above threshold intensities, the temporal pulse shape becomes decisive and together with tissue transmittacne at a definite wavelength determines the depth and character of tissue disruption and may be changed according to therapeutic destination.

Assessment of laser tissue damage is not complete without an investigation into the cellular effects that are induced. In the past, tissue damage was quantified by such macroscopically visual results as tissue mass removal, carbonization, and melting. In this research, we used heat shock protein (hsp70) transcription, to track cellular response to laser injury. A stable cell line was generated containing the luciferase reporter gene attached to the heat shock protein (Hsp70) promoter. After thermal injury with a Holmium:YAG pulsed laser (wavelength= 2.1 μm, pulsetime = 250 μs, 30 pulses, 3 Hz), luciferase is produced upon hsp70 activation and emits bioluminescence at 563 nm. The luminescence was quantified with a liquid nitrogen cooled CCD camera. A minimum pulse energy (65 mJ/pulse, 2.0 mJ/mm²) was needed to activate the hsp70 response and a higher energy (103 mJ/pulse, 3.2 mJ/mm²) was associated with a reduction in hsp70 response. Bioluminescence levels correlated well to actual hsp70 protein concentrations as determined by ELISA assay. Photon counts were normalized to the percentage of live cells by means of a flow cytometry cell viability assay. The hsp70 response followed an Arrhenius relationship in nature when constant temperature water bath and constant area laser experiments were carried out.

Soft tissues of human and animals are composite, typically being made up of the collagen and elastin fibres with high water contents. The strain measurement in soft tissues has proven to be a difficult task. Digital Speckle Method, an optical measurement method combining with computer image processing technique, has many advantages like full-field, non-contact and high measuring accuracy. Two main techniques, the Digital Speckle Correlation Method (DSCM) and Electric Speckle Pattern Interferometry (ESPI), have been developed and applied on many aspects. Using these two methods, the strain measurements caused by the continual deformation of soft tissues under pure tensile loading are completed and presented in this paper. Experiments are performed under the conditions of constant temperature and necessitate humidity with smart sensor. After capture a series of speckle patterns in continual time period, the displacement and strain distribution of soft tissues can be obtained by two improved techniques (Improved DSCM and Time-Sequence ESPI). Thus, the tensile modulus and Poisson ratio of soft tissues will be extracted.

Presented herein is a maximum likelihood (ML) estimator for assessing small motions in speckle patterns. Estimators of this kind are important in a variety of speckle techniques used in non-destructive evaluation. These speckle patterns can be two-dimensional (one spatial dimension and one temporal dimension) as obtained in objective speckle techniques or three-dimensional (two spatial dimensions and one temporal dimension) as seen in subjective (imaged) speckle methods. The specific estimator discussed herein is appropriate for assessing strain in two dimensional subjective patterns. We demonstrate good performance of this estimator for speckle motions of a small portion of a pixel. Beyond this point, more conventional approaches (e.g., correlation) have been shown to perform well. This maximum likelihood estimator can be implemented easily with simple linear image processing filtering techniques.

A multiphysics approach, combining acoustics, optics, and mechanics can be used to detect regions of skin with distinct mechanical behavior that may indicate a pathology, such as a cancerous skin lesion. Herein, an acousto-optical approach to evaluating the viscoelastic behavior of superficial skin layers will be presented. The method relies upon inducing low frequency guided surface waves in the skin and detecting these waves by monitoring the shift in the backscattered laser speckle pattern created by illuminating a small region of the skin with coherent light. Artificial lesions in the form of chemical cross-linking and chemical softening were induced in superficial porcine skin layers and detected based upon variations in local mechanical behavior. The lesions affect not only the time-of-flight of the guided surface waves, but also change the relative phase of the acoustic waves as determined optically. The method may be applicable in the study and diagnosis of superficial skin lesions.

We have demonstrated a capability of biomechanical characterization by photoacoustic measurement using various concentraiton gelatins as tissue pahntom. We have also evaluated the viscoelasticity of the cartilages tissue-engineered under the different culture conditions. Structural tissues, such as cartilage, bone, tendon, and muscle require time-dependent mechanical responses (viscoelastic properties) to describe their mechanical behavior. However, non-invasive measurement of tissue viscoelastic has not been developed; such measurement is necessary for tissue engineering applications on weight-bearing tissues. As tissue viscoelasticity affects the propagation and attenuation of the stress waves generated in the tissue, their relaxation times which are defined as the time for the stress wave amplitude to decrease by a factor of 1/e, give the viscosity-elasticity ratio of the tissue. In this study, stress waves (photoacoustic waves) which were induced by 250-nm, 6-ns, light pulses from an OPO were detected by a piezoelectric transducer. The relaxation time of the photoacoustic wave was measured for various concentrations of gelatins which had been measured their viscoelastic properties by a conventional method. Consequently, the relaxation time corresponded to the known viscosity-elasticity ratio of the gelatins. For the tissue-engineered cartileges, photoacoustic measurements were performed under the different cultured conditions. The relaxation time of the cartilages closely correlated with the viscosity-elasticity ratio measured by a convetional method. Therefore, the photoacoustic measurement is one of the qualified candidates for a non-invasive viscoelastic measurement of tissue.

Dental health care and research workers require a means of imaging the structures within teeth in vivo. One critical need is the detection of tooth decay in its early stages. If decay can be detected early enough, the process can be monitored and interventional procedures, such as fluoride washes and controlled diet, can be initiated to help re-mineralize the tooth. Currently employed x-ray imaging is limited in its ability to visualize interfaces and incapable of detecting decay at a stage early enough to avoid invasive cavity preparation followed by a restoration. To this end, non-destructive and non-contact in vitro measurements on extracted human molars using laser-based ultrasonics are presented. Broadband ultrasonic waves are excited in the extracted sections by using a pulsed carbon-dioxide (CO₂) laser operating in a region of high optical absorption in the dental hard tissues. Optical interferometric detection of the ultrasonic wave surface displacements in accomplished with a path-stabilized Michelson-type interferometer. Results for bulk and surface in-vitro characterization of caries are presented on extracted molars with pre-existing caries.

High resolution SEM, light microscopy, and non-invasive CT/MRI imaging can produce 3D views of anatomy and generate computational tissue models for many biomedical and tissue engineering applications. Recently, the integration of image processing with computer-aided design (CAD), computer aided manufacturing (CAM), and solid freeform fabrication technology has achieved a remarkable advance in the field of computer-aided tissue engineering (CATE). This paper presents an overview of CATE, including its application in computer-aided tissue modeling, computer-aided tissue informatics, and computer-aided tissue scaffold design and manufacturing. An image-based 3D reconstruction approach, along with a discussion of various enabling reverse engineering techniques for structural representation and CAD based modeling of tissue anatomy will be introduced. An example of biomimetic modeling and design of 3D heterogeneous bony tissue structures under anatomical, biological, and mechanical constraints will also be presented.

We present the theoretical operation and experimental results of a fiber optic interferometer, which we have used to measure the surface displacement of a collagen gel. Dispersed within the collagen gel are fibroblast cells. We describe a measurement system to assist in the detailed study of the biochemical and mechanical processes involved in fibroblast cell contraction. The interferometric system is non-contacting and offers a large dynamic range of measurement. Digital demodulation of a phase generated carrier results in an experimental sensitivity limit on the order of tens of nanometers with a measurement range of up to 2 mm. Computer-controlled data acquisition allows measurement of the contracting gel host over a period of several hours. We describe the optical interferometric system and present experimental results on a contracting collagen gel.

Time-Resolved Laser-Induced Fluorescence Spectroscopy (TR-LIFS) represents a potential tool for the in-situ characterization of bioengineered tissues. In this study, we evaluate the application of TR-LIFS to non-intrusive monitoring of matrix composition during osteogenetic differentiation. Human adipose-derived stem cells, harvested from 3 patients, were induced in osteogenic media for 3, 5, and 7 weeks. Samples were subsequently collected and probed for time-resolved fluorescence emission with a pulsed nitrogen laser. Fluorescence parameters, derived from both spectral- and time-domain, were used for sample characterization. The samples were further analyzed using Western blot analysis and computer-based densitometry. A significant change in the fluorescence parameters was detected for samples beyond 3 weeks of osteogenic differentiation. The spectroscopic observations: 1) show increase of collagen I when contrasted against the time-resolved fluorescence spectra of commercially available collagens; and 2) are in agreement with Western blot analysis that demonstrated significant increase in collagen I content between 3- vs. 5-weeks and 3- vs. 7-weeks and no changes for collagens III, IV, and V. Our results suggest that TR-LIFS can be used as a non-invasive means for the detection of specific collagens in maturing connective tissues.

We review the mechanisms underlying material ejection in pulsed laser ablation of biological tissues, with special emphasis on the thermodynamics and kinetics of phase transitions and their modifications arising from the presence of a tissue matrix.