Published papers

© 2018 by the authors. Licensee MDPI, Basel, Switzerland. To evaluate the effectiveness of photodynamic therapy occurring in the interstitial space of the myocardium, we estimated the interstitial concentration of talaporfin sodium in the canine myocardium by constructing a three-compartment pharmacokinetic model based on measured changes in talaporfin sodium plasma concentration and myocardial fluorescence. Differential rate equations of talaporfin sodium concentration in the plasma, interstitial space, and cell compartment were developed with individual compartment volume, concentration, and rate constants. Using measured volume ratios based on histological examinations, we defined that the myocardial fluorescence consisted of the linear addition of fluorescence generated from these three compartments. The rate constants were obtained by fitting to minimize the sum of the squared errors between the measured talaporfin sodium concentrations and the calculated concentrations divided by the number of data points using the conjugate gradient method in MATLAB. We confirmed that this fitting operation may be appropriate, because a coefficient of determination between the measured talaporfin sodium changes and the calculated concentrations using our equations was 0.99. Consequently, to estimate the interstitial concentration in the canine myocardium, we propose a three-compartment pharmacokinetic model construction methodology using measured changes in talaporfin sodium plasma concentration and changes in myocardial fluorescence.

© 2018 SPIE. To avoid an instability of the optical coefficient measurement using sliced tissue preparation, we proposed the combination of light intensity measurement through an optical fiber puncturing into a bulk tissue varying field of view (FOV) and ray tracing calculation using Monte-Carlo method. The optical coefficients of myocardium such as absorption coefficient μa, scattering coefficient μs, and anisotropic parameter g are used in the myocardium optical propagation. Since optical coefficients obtained using thin sliced tissue could be instable because they are affected by dehydration and intracellular fluid effusion on the sample surface, variety of coefficients have been reported over individual optical differences of living samples. The proposed method which combined the experiment using the bulk tissue with ray tracing calculation were performed. In this method, a 200 μmΦ high-NA silica fiber installed in a 21G needle was punctured up to the bottom of the myocardial bulk tissue over 3 cm in thickness to measure light intensity changing the fiber-tip depth and FOV. We found that the measured attenuation coefficients decreased as the FOV increased. The ray trace calculation represented the same FOV dependence in above mentioned experimental result. We think our particular fiber punctured measurement using bulk tissue varying FOV with Inverse Monte-Carlo method might be useful to obtain the optical coefficients to avoid sample preparation instabilities.

© 2018 SPIE. To study a mechanism of phrenic nerve preservation phenomena during a photosensitization reaction, we investigated an uptake of talaporfin sodium and photosensitization reaction effect on an electric propagation. Right phrenic nerve was completely preserved after superior vena cava isolations using the photosensitization reaction in canine animal experiments, in spite of adjacent myocardium was electrically blocked. We predicted that low drug uptake and/or low photosensitization reaction effect on the nerve might be a mechanism of that phenomena. To investigate uptake to various nerve tissue, a healthy extracted crayfish ventral nerve cord and an extracted porcine phrenic nerve were immersed in 20 μg/ml talaporfin sodium solution for 0-240 min. The mean talaporfin sodium fluorescence brightness increased depending on the immersion time. This brightness saturated around the immersion time of 120 min. We found that talaporfin sodium uptake inside the perineurium which directly related to the electric propagation function was lower than that of outside in the porcine phrenic nerve. To investigate photosensitization reaction effect on electric propagation, the crayfish nerve was immersed into the same solution for 15 min and irradiated by a 663 nm laser light with 120 mW/cm2. Since we found the action potential disappeared when the irradiation time was 25-65 s, we consider that the crayfish nerve does not tolerant to the photosensitization reaction on electric propagation function at atmospheric pressure. From these results, we think that the low uptake of talaporfin sodium inside the perineurium and low oxygen partial pressure of nerve might be the possible mechanism to preserve phrenic nerve in vivo.

Copyright © 2018 SPIE. We studied the dependence of a perpendicular pressure to the luminal surface on the heating drug delivery performance using a laser-mediated thermal balloon with porcine carotid artery walls ex vivo. We proposed the combination use of our laser-mediated thermal balloon and drug coated balloon (DCB) to enhance a drug delivery performance. We prospected that the perpendicular pressure, which was applied directly to the luminal surface by balloon dilatation, would enhance the quantity of DCB drug delivered into artery wall. To simulate our laser thermal balloon heating, 63°C preheated artery samples were prepared by heated saline dropping for 15 s, and then these samples were dipped in 37°C saline for 15 s. Non-heated artery samples were prepared by dipping in 37°C saline for 30 s. The perpendicular pressure up to 10 atm corresponding to DCB dilatation pressure was added directly to these artery samples by fluorescence Rhodamine B solution for 30 s. The quantity of drug delivered was microscopically measured with fluorescence brightness in the cross-section of the drug delivered artery samples. We found drastic drug delivery increase at 8 atm using the pre-heated artery sample. Delamination of intima layer was observed by EVG stained cross-sectional specimens with 8 atm in the pre-heated artery sample. We think this drastic pressure dependence on the heating drug delivery performance might be corresponding to increase in permeability of drug into the artery wall originated to morphology change in intima.

© 2018 SPIE. To investigate hemolysis phenomena during a photosensitization reaction with the reaction condition continuously and simultaneously for a safety assessment of hemolysis side effect, we constructed an optical system to measure blood sample absorption spectrum during the reaction. Hemolysis degree might be under estimated in general evaluation methods because there is a constant oxygen pressure assumption in spite of oxygen depression take place. By investigating hemoglobin oxidation and oxygen desorption dynamics obtained from the contribution of the visible absorption spectrum and multiple regression analysis, both the hemolysis phenomena and its oxygen environment might be obtained with time. A 664 nm wavelength laser beam for the reaction excitation and 475-650 nm light beam for measuring the absorbance spectrum were arranged perpendicularly crossing. A quartz glass cuvette with 1×10 mm in dimensions for the spectrum measurement was located at this crossing point. A red blood cells suspension medium was arranged with low hematocrit containing 30 μg/ml talaporfin sodium. This medium was irradiated up to 40 J/cm2. The met-hemoglobin, oxygenatedhemoglobin, and deoxygenated-hemoglobin concentrations were calculated by a multiple regression analysis from the measured spectra. We confirmed the met-hemoglobin concentration increased and oxygen saturation decreased with the irradiation time, which seems to indicate the hemolysis progression and oxygen consumption, respectively. By using our measuring system, the hemolysis progression seems to be obtained with oxygen environment information.

© 2018 SPIE. We studied collagen reversible denaturation by a weak near-infrared laser light irradiation for vascular softening. Balloon angioplasty induced about 60% restenosis rate for superficial femoral artery at 6 months after the balloon dilatation originated from mechanical injuries in vascular wall. We anticipated that mechanical injuries can be prevented by softening of the collagen fibers in vascular wall. Collagen softening is resulted from dissociation of a few hydrogen bonds in collagen molecules in general. We estimated that hydrogen bonds can be dissociated by near-infrared photon energy with less heat production because hydrogen bond energy is about 30 kJ/mol corresponding to about 4 μm in wavelength. We studied collagen denaturation by a weak near-infrared laser light irradiation from mechanical and optical characteristic changes. A collagen film derived from bovine dermis was irradiated with 980 nm wavelength semiconductor laser under the condition that temperature rise was kept under 4.1°C. To evaluate collagen denaturation from mechanical characteristic change, the elastic modulus was analyzed from the stress-strain curve of the irradiated collagen film. Stress of the collagen film was measured with a load cell when 0.25%/s strain was loaded with a rack-andpinion automatic stage. Infrared absorption spectrum peak in 3300 cm-1 band of the collagen film, which is originated from hydrogen bonds, was measured to evaluate collagen denaturation from optical characteristic change. We found that the collagen film was 12% softened by a particular laser light irradiance.

© 2018 SPIE. To avoid the instability of an optical coefficient measurement using sliced tissue preparation, an attenuation coefficient measurement by puncturing an optical fiber in bulk tissue have been reported. We proposed a modified puncturing method to obtain an absorption coefficient and scattering coefficient by increasing optical information. We used the light intensity measurement through a single high-NA fiber puncturing into an optically thick bulk tissue varying detection parameters, the depth and field of view (FOV), at the tip. The light intensity measurement and ray trace calculation using the Monte Carlo method (inverse or normal) were employed. We constructed the measurement system which can change the FOV at the fiber tip inside the bulk tissue using the variable aperture outside the bulk tissue. A 200 μmΦ NA:0.5 fiber installed in a 21G needle was punctured down to surface of the bulk tissue to measure light intensity in the bulk tissue. Using homogeneous optical model solution, the accuracy about attenuation coefficients of the constructed experimental system was confirmed. The error in the attenuation coefficient was up to 1.4%. We demonstrated the optical coefficient measurement of porcine myocardium using the proposed method. To fit dependence of the measured attenuation coefficients on FOV, we decided that the absorption coefficient, the scattering coefficient, and anisotropic parameter were 0.2 mm-1, 10 mm-1, and 0.96, respectively. We proposed modified puncturing optical coefficient measurement varying depth and FOV. We demonstrated its usefulness on myocardium.

© Copyright 2018, Mary Ann Liebert, Inc. 2018. Background: It has been reported that the oxygen pressure of a photosensitizer medium decreases during an irradiation leading to decrease in the efficacy of the photosensitization reaction against the target cell in vitro. Objective: The aim of this study was to obtain solutions with high dissolved oxygen levels in cultivated wells with perceiving oxygen environment and photosensitizer bleaching for photosensitization reaction studies. Materials and methods: We used a 10-mm-wide optical cell cuvette with a 1-mm optical path length as the well. A red blood cell (RBC) suspension with a hematocrit level of 0.625% was employed as the optical sample. The photosensitizer talaporfin sodium was added to a concentration of 30 μg/mL. The optical sample was irradiated by a 663-nm diode laser at 120 mW/cm2, for a total radiant exposure of 0-20 J/cm2, to induce a photosensitization reaction. Absorption spectra of the samples in the range of 475-700 nm were measured before and after each irradiation condition. Visible spectroscopy was selected to distinguish between the major three hemoglobin (Hb) types: oxygenated Hb, deoxygenated Hb, and met Hb. Also, this wavelength range was selected to investigate photobleaching using the Q band absorption peak. Each Hb concentration was estimated using a multiple regression analysis applied to the obtained absorption spectra. Results: The relationship between oxygen saturation and the absorption peak in the Q band from the talaporfin sodium dynamics with increasing radiant exposure was revealed by our method with approximately twofold oxygen-dissolved solution. Conclusions: We could perceive the oxygen environment and the photosensitization reaction progression simultaneously with increasing dissolved oxygen by adding RBCs to the cell medium and measuring the absorption spectrum of it.

© 2019 SPIE. We studied the necessary time for cell necrosis on myocardial cells against a photodynamic reaction using talaporfin sodium with various drug contact time in vitro. We have developed a new methodology of cardiac catheter ablation for tachyarrhythmia using a photodynamic reaction. To realize an immediate electrical conduction block within a few minutes, we intended to occur the photodynamic reaction outside the cells by using a short drug contact time. In a clinical situation, the drug distribution around the cells changes continuously after the drug administration. To study the change of electrical conduction block performance with these drug distribution change, we measured the necessary time for myocardial cell necrosis with various drug contact time. The concentration of intracellular Ca2+ ion was measured by Fluo-4 AM fluorescence dye during the photodynamic reaction with excitation light of 663 nm in wavelength under a confocal microscope. The time for myocardial cell necrosis was evaluated using a decrease of Ca2+ ion after the cell membrane rupture. The drug contact time for myocardial cells was varied 1-60 min. We obtained that the necessary time for myocardial cell decreased until around 10 min of drug contact time, and it increased after around 20 min of drug contact time. We suggest that the drug contact time within 10-20 min would the most effective timing to minimize the necessary time for myocardial cell necrosis using photodynamic reaction since the oxidative stress during uptake process would be high.

© 2019, Japanese Society for Medical and Biological Engineering. All rights reserved. We investigated the delivery of rhodamine B and Oregon Green®-labeled paclitaxel (OGLP) in ex vivo porcine carotid artery wall (CAW) samples after heating the reagents to 50–70°C for 15 s. When the isolated CAW samples were placed in the heated fluorophore solutions, the penetration depth of the hydrophobic rhodamine B increased significantly compared with reference solution at 37°C. The penetration depth of OGLP also tended to increase upon heating to 70°C for 15 s. We also studied the mechanism of this agent delivery enhancement by observing the inner surface structure and hydrophobicity of the CAW samples after heating. An expanded mesh structure at the inner surface of the heated CAW samples was observed upon heating above 70°C, and the mean hydrophobicity of the media layer also increased significantly. We hypothesize that heating at 60–70°C for 15 s enhances the delivery of fluorophores to CAW samples as a result of an expanded mesh structure at the inner surface of the CAW, along with a simultaneous increase in hydrophobicity.

© 2019, Springer-Verlag London Ltd., part of Springer Nature. To measure the few millimeter–scale macroscopic optical properties of biological tissue, including the scattering coefficient, while avoiding the instability that originates from sample slicing preparation processes, we performed propagated light intensity measurements through an optical fiber that punctures the bulk tissue while varying the fiber tip depth and the field of view (FOV) at the tip; the results were analyzed using the inverse Monte Carlo method. We realized FOV changes at the fiber tip in the bulk tissue using a variable aperture that was located outside the bulk tissue through a short high-numerical aperture (high-NA) multi-mode fiber with a quasi-straight shape. Using a homogeneous optical model solution, we verified the principle and operation of the constructed experimental system. A 200-μm-core-diameter silica fiber with NA of 0.5 and length of 1 m installed in a 21G needle was used. The detection fiber’s shape was maintained over a radius of curvature of 30 cm. The dependences of the detected light intensity on the FOV and the depth showed better than 1.4% accuracy versus calculated dependences based on the measured optical properties of the solution. Adaptation of the method for use with complex structured biological tissue, particularly in the presence of a thick fascia, was not completely resolved. However, we believe that our specific fiber puncture–based measurement method for use in bulk tissue based on variation of the FOV with inverse Monte Carlo method-based analysis will be useful in obtaining optical coefficients while avoiding sample preparation–related instabilities.

© 2018 SPIE. Background: Skin photosensitivity is a major side effect of photodynamic therapy (PDT). It is induced by the photosensitizer remaining in the skin. It is usually rapidly metabolized by the liver, but the pharmacokinetic profile varies widely among individuals. This makes it difficult to predict the incidence of skin photosensitivity. Therefore, we conducted a prospective study to investigate whether the NPe6 fluorescence intensity in skin after NPe6-PDT could be measured safely in human patients using a fluorescence sensing system for judging the risk of skin photosensitivity. Methods: The NPe6 fluorescence measurements using a constructed fluorescence sensing system at the inside of the arm were acquired prior to and 5 and 10 minutes after NPe6 administration as well as at the time of PDT (4-5 hours after administration), at discharge (2 or 3 days after PDT), and at 1 or 2 weeks after PDT. Participants were interviewed as to whether they had any complications at 2 weeks after PDT. Results: Nine male patients and one female patient entered this study. All of the measurements of NPe6 fluorescence in the skin could be obtained without any complications. The spectral peak was detected at the time of discharge (2-3 days after administration) in most cases and it decreased at 1 or 2 weeks after PDT. Conclusions: The fluorescence of NPe6 in the skin could be detected feasibly using the fluorescence sensing system in human patients. Measuring fluorescence intensity in the skin might be useful to predict the incidence of skin photosensitivity after PDT.