Measuring tissue heat penetration by scattered light measurements.

BACKGROUND AND OBJECTIVES: The monitoring of tissue morphological changes during clinical procedure such as laser thermotherapy, laser hair removal and others is important in order to prevent damage to healthy tissue. An optical system and method for the assessment of real time in vivo tissue morphological changes is proposed. MATERIALS AND METHODS: We used ex vivo chicken breast as tissue samples. The samples were irradiated by CO(2) laser to create thermal structural changes. The optical properties of the tissue samples were measured using an integrating sphere method. We measured the tissue heat penetration and the scattered light from the tissue and compared the results to Monte-Carlo simulation. RESULTS: Thermal interaction causes structural changes in the tissue. Therefore changing (increasing) the scattering properties of the tissue. We relate the structural changes to the scattered light pattern and proposed a method for controlling the thermal interaction. CONCLUSION: It is possible to design a real time in vivo controlling system for laser tissue thermal interaction that utilizes the changes in the scattered light pattern.

Broad band and low loss mid-IR flexible hollow waveguides.

This paper introduces a deposition method to create a multilayered waveguide with alternating layers of high index of refraction contrast. A very thin Ag layer, practically transparent in the mid-IR radiation wavelengths of CO(2) and Er-YAG lasers, was created. This enabled a good contrast of the indices of refraction of silver/silver iodide. Theoretical calculations as well as experiments have shown that transmission was higher at these wavelengths for two pair layers, in comparison to one pair of silver/silver iodide. Windows of transmittance and small sensitivity to bending were demonstrated for those two pair layer waveguides. This method could be extended to an increased number of pairs to configure a true photonic band gap waveguide.

Laser activated fluorescence measurements and morphological features: an in vivo study of clearance time of fluorescein isothiocyanate tagged cell markers.

Fourteen BALB/c mice were divided into two groups. One group served as the control and the second group was injected with a squamous cell carcinoma cell line to the tongue. After tumor development (1-4 weeks), mice were injected with a FITC conjugated CD3 marker to their tongues. Immediately after the marker injection, the clearance of the marker was measured using a laser spectroscopy system. The markers were excited by an argon laser at 488 nm and the fluorescence signal was measured as a function of time. A biopsy was taken from every mouse after the procedure and the excised tissue was histologically evaluated. Analysis of clearance times revealed a second order exponential decay for both groups with a slower pace of signal clearance for the sick mice.

Optical simulations of a noninvasive technique for the diagnosis of diseased salivary glands in situ.

A simulation experiment for three-dimensional (3D) imaging of exogenous fluorescinated antibodies that specifically bind to infiltrating lymphocytes in minor salivary glands was carried out. Small (approximately 1 mm3 volume) rhodamine targets, which mimic diseased minor salivary glands labeled with fluorescent antibodies to infiltrating lymphocytes in Sjøgren's syndrome, were embedded in a highly scattering tissue phantom consisting of a thick Delrin disk covered by index matched Delrin slabs of various thickness. In this way the variation of fluorescence profiles on the surface of tissue could be examined corresponding to the range of depths of the salivary glands in vivo. Surface images were obtained for different target depths and radial distances from laser excitation to target fluorophore. These images were analyzed and compared to calculations based on random walk theory in turbid media, using previously determined scattering and absorption coefficients of the Delrin. Excellent agreement between the surface profiles experimentally measured and those predicted by our random walk theory was obtained. Derivation of these theoretical expressions is a necessary step toward devising an inverse algorithm which may have the potential expressions to perform 3D reconstruction of the concentration distribution of fluorescent labels within tissue.

Flexible waveguides for Er-YAG laser radiation delivery.

Flexible plastic waveguides (FPW) were devised for the delivery of Er-YAG laser radiation. The FPW characteristics were studied under various conditions. In vitro studies were carried out to explore the drilling procedure on extracted teeth and the FPW-tissue mutual effects. The results which were obtained proved that the FPW as a delivery device might be a substitute hand applicator for the pneumatic turbine for drilling in teeth.

Tumor localization using magnetic nanoparticle-induced acoustic signals.

Cancer is a major public health problem worldwide, especially in developed countries. Early detection of cancer can greatly increase both survival rates and quality of life for patients. A magnetoacoustic-based method had been previously proposed for early tumor detection, in a minimal invasive procedure, using magnetic nanoparticles (MNPs). This paper presents a supporting localization algorithm that can provide the clinician with essential tumor location data and could enable a sequential biopsy. It provides localization algorithm development, as well as its validation in both computerized simulations and in vitro experiments. Three-dimensional (3-D) tumor localization is demonstrated with an error of 2.14 mm and an overlapping volume of 84% of the actual tumor. The obtained results are promising and prove the feasibility of tumor localization using a time difference of arrival algorithm along with a magnetoacoustic detection scheme.

Modeling and simulations of the pharmacokinetics of fluorophore conjugated antibodies in tumor vicinity for the optimization of fluorescence-based optical imaging.

BACKGROUND AND OBJECTIVES: One of the methods to detect and localize tumors in tissue is to use fluorophore conjugated specific antibodies as tumor surface markers. The goals of this study are to understand and quantify the pharmacokinetics of fluorophore conjugated antibodies in the vicinity of a tumor. This study concludes another stage of the development of a non-invasive fluorescenated antibody-based technique for imaging and localization of tumors in vivo. STUDY DESIGN/MATERIALS AND METHODS: A mathematical model of the pharmacokinetics of fluorophore conjugated antibodies in the vicinity of a tumor was developed based on histological staining experiments. We present the model equations of concentrations of antibodies and free binding sites. We also present a powerful simulation tool that we developed to simulate the imaging process. We analyzed the model and studied the effects of various independent parameters on the imaging result. These parameters included initial volume of markers (injected volume), total number of binding sites, tumor size, binding and dissociation rate constants, and the diffusion coefficient. We present the relations needed between these parameters in order to optimize the imaging results. RESULTS AND CONCLUSIONS: A powerful and accurate tool was developed which may assist in optimizing the imaging system results by setting the injection volume and concentration of fluorophore conjugated antibodies in tissue and approximating the time interval where maximum specific binding occurs and the tumor can be imaged.

Characterization of hollow fibers for the transmission of infrared radiation.

Plastic hollow fibers were made from plastic tubes covered on the internal wall with a metal layer (a-type) or a metal layer and dielectric layer on top of it (b-type). The CO(2) laser energy transmission through the hollow fiber was measured as a function of the radius of curvature and the coupling lens (focal length at a constant fiber length). The yield of the transmission decreased in subtle curvatures (radius of curvature up to 100 cm) and remained almost constant as the curvature became sharper (down to radius of curvature of 13 cm). For the a-type fibers, the characteristics of attenuation depended on the focal length of the coupling lenses. The energy distribution at the output was measured and mapped. The experimental results showed that the maximum of the energy distribution is asymetrically positioned relative to the center and closer to the internal wall at a smaller bending radius. This was predicted in our previous theoretical calculation. The value of transmitted power attenuation was up to 1.4 dB/m. Maximum power at the output was 30 W, for a fiber of 50-cm length and a cross-sectional diameter of 1.9 mm. These types of hollow fiber have already been used in surgical experiments on dogs.

Subjects' dissimilarity in the analysis of laser-tissue dose-response experiments: a potential cause for puzzling results.

The in vivo dose-response laser-tissue experiment is usually performed on several subjects, each exposed several times at different tissue sites. The collected data are then unified into a single statistical batch and analysed under the tacit assumption that the tolerances of all the subjects are similar. However, if this assumption is incorrect the data unification may lead to very biased results. This study reanalyses a raw data set measured by the US Army Medical Research Detachment Walter Reed Army Institute of Research (USAMRD-WRAIR), which was used to study the influence of the laser wavelength on the energy threshold of retinal injury. The USAMRD-WRAIR report reveals a significant variation of threshold with small changes in wavelength. Despite an extensive study, performed by the USAMRD-WRAIR researchers, which included possible lasers variations, many aspects of experimental technique and biological absorption properties of the eye, a cause for the threshold variation was not found. Our current results suggest that unaccounted specimen's dissimilarity might be the cause for this unclear threshold variations.

Broadband flexible waveguides for free-electron laser radiation.

We refined flexible waveguides previously developed for CO(2) and Er:YAG laser radiation to transmit free-electron-laser (FEL) radiation. One can tune this laser over several segments of the radiation spectrum. This laser has a high peak power of as much as 10 MW with pulse energy of as much as 100 mJ. We made the waveguides of either Teflon or fused-silica tubes internally coated with metal and dielectric layers. We optimized the internal coatings specifications for transmission of various radiation wavelengths in the mid-IR range and enabled transmission of high-peak radiation. We performed experiments in three major FEL sites in the United States over a more than 1-year period when we measured and examined various characteristics of transmission. We used the analysis of these experiments as feedback to further improve these waveguides. The good preliminary results encourage us to invest more effort to further develop these waveguides until a suitable waveguide is obtained for this type of laser and make possible its introduction to the medical field where its characteristics can be exploited in surgical applications.

Flexible waveguides for IR laser radiation and surgery applications.

Flexible plastic waveguides were developed to deliver IR radiation, especially at 10.6 microns, which is the CO2 laser radiation wavelength. The waveguide is made from teflon tube with the inner wall coated with a metal layer and a dielectric overlayer. The internal diameter (ID) is 1.0 mm, length 1.0-1.2 m, and the distal tip decreases moderately to ID approximately 0.6 mm. The distal part on the last 10 centimeters is coated externally with a metal layer. Maximum power that can be delivered at the outlet is approximately 30 W and 10.6 x 10(3) W/cm2. This type of waveguide was used in several medical operations to evaluate its cutting characteristics and the resistances to heat reflection from the tissue while operating in orifices containing liquid substances.

Increase in immune cell infiltration with progression of oral epithelium from hyperkeratosis to dysplasia and carcinoma.

In the present study, epithelium derived lesions of various pathological manifestations were examined histologically and immunohistochemically for mononuclear cell infiltration. The infiltrate under the transformed epithelium of oral lesions, was examined for differences in the composition of immune mononuclear cells as the epithelium moves from hyperkeratosis through various degrees of dysplasia to squamous cell carcinoma. The study was performed on 53 human tongue tissues diagnosed as hyperkeratosis (11 cases), mild dysplasia (nine cases), moderate and severe dysplasia (14 cases) and squamous cell carcinoma (19 cases). A similar analysis was performed on 30 parotid gland tissues diagnosed as pleomorphic adenoma (14 cases) and carcinoma ex-pleomorphic adenoma (16 cases). Immunohistochemical analysis of various surface markers of the tumour infiltrating immune cells was performed and correlated with the transformation level as defined by morphology and the expression of p53 in the epithelium. The results revealed that, in the tongue lesions, the changes in the epithelium from normal appearance to transformed were accompanied by a corresponding increase in the infiltration of CD4, CD8, CD14, CD19+20, and HLA/DR positive cells. The most significant change was an increase in B lymphocytes in tongue lesions, that was in accordance with the transformation level (P<0.001). In the salivary gland, a significant number of cases did not show an infiltrate. In cases where an infiltrate was present, a similar pattern was observed and the more malignant tissues exhibited a higher degree of immune cell infiltration.

Experimental surgery on dog's stomach and liver using CO 2 laser plastic hollow fibers: technical method.

Plastic hollow fibers for the transmission of CO 2 laser energy in curved paths were produced by plating the inner surface of plastic tubes with a metal film and dielectric film upon it. These fibers can transmit high power up to 40 W at the outlet, with high transmission yield even through several bendings. A three-dimensional simulator was built to simulate paths in the dog's body and the outlet power was measured. From the achieved data the expected transmitted power during real surgery was appreciated. The fibers were checked for their influence on live tissues of dogs. Incisions were made in the liver and ulcers in the dogs' stomachs were treated. The fibers were inserted into the stomach through the dogs' esophagus. Complete healing was observed after four weeks.

Analytical solutions for time-resolved fluorescence lifetime imaging in a turbid medium such as tissue.

An analytical solution is developed to quantify a site-specific fluorophore lifetime perturbation that occurs, for example, when the local metabolic status is different from that of surrounding tissue. This solution may be used when fluorophores are distributed throughout a highly turbid media and the site of interest is embedded many mean scattering distances from the source and the detector. The perturbation in lifetime is differentiated from photon transit delays by random walk theory. This analytical solution requires a priori knowledge of the tissue-scattering and absorption properties at the excitation and emission wavelengths that may be obtained from concurrent time-resolved reflection measurements. Additionally, the solution has been compared with the exact, numerically solved solution. Thus the presented solution forms the basis for practical lifetime imaging in turbid media such as tissue.

Preliminary experiments of possible uses in medicine of novel plastic hollow fibers for transmission of CO2 radiation.

Plastic hollow fibers for the transmission of CO2 laser energy in curved paths were produced by plating the inner surface of plastic tubes with a metal film and dielectric film upon that. These fibers can transmit high power, up to 40 W at the outlet, with high transmission yield even through several bendings. To demonstrate a possible use of the fibers, they were checked for their influence on live tissues of dogs. Incisions were made in the liver, and ulcers in the dogs' stomachs were treated. The fibers were inserted into the stomach through the esophagus. Complete healing was observed after 4 weeks.