Atsuki Komiya

Dimensionless solutions and general characteristics of bioheat transfer during thermal therapy

Abstract The derivation and application of the general characteristics of bioheat transfer for medical applications are shown in this paper. Two general bioheat transfer characteristics are derived from solutions of one-dimensional Pennes’ bioheat transfer equation: steady-state thermal penetration depth, which is the deepest depth where the heat effect reaches; and time to reach steady-state, which represents the amount of time necessary for temperature distribution to converge to a steady-state. All results are described by dimensionless form; therefore, these results provide information on temperature distribution in biological tissue for various thermal therapies by transforming to dimension form.

Rapid yet accurate measurement of mass diffusion coefficients by phase shifting interferometer

The technique of using a phase-shifting interferometer is applied to the study of diffusion in transparent liquid mixtures. A quick method is proposed for determining the diffusion coefficient from the measurements of the location of fringes on a grey level picture. The measurement time is very short (within 100 s) and a very small transient diffusion field can be observed and recorded accurately with a rate of 30 frames per second. The measurement can be completed using less than 0.12 cc of solutions. The influence of gravity on the measurement of the diffusion coefficient is eliminated in the present method. Results on NaCl-water diffusion systems are presented and compared with the reference data.

Measurement of Soret and Fickian diffusion coefficients by orthogonal phase-shifting interferometry and its application to protein aqueous solutions

We have developed a method to measure thermodiffusion and Fickian diffusion in transparent binary solutions. The measuring instrument consists of two orthogonally aligned phase-shifting interferometers coupled with a single rotating polarizer. This high-resolution interferometer, initially developed to measure isothermal diffusion coefficients in liquid systems [J. F. Torres, A. Komiya, E. Shoji, J. Okajima, and S. Maruyama, Opt. Lasers Eng. 50, 1287 (2012)], was modified to measure transient concentration profiles in binary solutions subject to a linear temperature gradient. A convectionless thermodiffusion field was created in a binary solution sample that is placed inside a Soret cell. This cell consists of a parallelepiped cavity with a horizontal cross-section area of 10 × 20 mm(2), a variable height of 1-2 mm, and transparent lateral walls. The small height of the cell reduces the volume of the sample, shortens the measurement time, and increases the hydrodynamic stability of the system. An additional free diffusion experiment with the same optical apparatus provides the so-called contrast factors that relate the unwrapped phase and concentration gradients, i.e., the measurement technique is independent and robust. The Soret coefficient is determined from the concentration and temperature differences between the upper and lower boundaries measured by the interferometer and thermocouples, respectively. The Fickian diffusion coefficient is obtained by fitting a numerical solution to the experimental concentration profile. The method is validated through the measurement of thermodiffusion in the well-known liquid pairs of ethanol-water (ethanol 39.12 wt.%) and isobutylbenzene-dodecane (50.0 wt.%). The obtained coefficients agree with the literature values within 5.0%. Finally, the developed technique is applied to visualize biomolecular thermophoresis. Two protein aqueous solutions at 3 mg∕ml were used as samples: aprotinin (6.5 kDa)-water and lysozyme (14.3 kDa)-water. It was found that the former protein molecules are thermophilic and the latter thermophobic. In contrast to previously reported methods, this technique is suitable for both short time and negative Soret coefficient measurements.

Photothermal therapy of tumors in lymph nodes using gold nanorods and near-infrared laser light with controlled surface cooling

Photothermal therapy (PTT) using near-infrared (NIR) laser light and gold nanorods (GNRs) shows promise as a novel cancer treatment modality. However, the laser intensity required to destroy tumor cells located beneath the skin is greater than the threshold intensity that causes skin damage; thus, irradiation with laser light damages the skin as well as the tumor. Here, we show that a temperature control system allows metastatic lymph nodes (LNs) to be treated by PTT using NIR laser light and GNRs, without skin damage. A mouse model of LN metastasis was developed by injection of tumor cells, and the tumor-bearing proper axillary LN was treated with NIR laser light after injection of GNRs. The skin temperature was maintained at 45 °C during irradiation by using a temperature control system. Bioluminescence imaging revealed that tumor progression was less in LNs exposed to NIR laser light and GNRs than in LNs exposed to NIR laser light alone or controls (no irradiation or GNRs). Furthermore, the skin and LN capsule were macroscopically intact on day 9 after irradiation with NIR laser light, whereas tumor cells within the LN showed apoptosis. A numerical analysis demonstrated that the high-temperature zone and the LN region showing damage were localized to an area up to 3 mm in depth. The proposed novel PTT technique, using NIR laser light and GNRs with controlled surface cooling, could be applied clinically to treat metastatic LNs located within or outside the area accessible for surgical dissection.

Development and estimation of a novel cryoprobe utilizing the Peltier effect for precise and safe cryosurgery

We have developed a novel cryoprobe for skin cryosurgery utilizing the Peltier effect. The four most important parameters for necrotizing tissue efficiently are the cooling rate, end temperature, hold time and thawing rate. In cryosurgery for small skin diseases such as flecks or early carcinoma, it is also important to control the thickness of the frozen region precisely to prevent necrotizing healthy tissue. To satisfy these exacting conditions, we have developed a novel cryoprobe to which a Peltier module was attached. The cryoprobe makes it possible to control heat transfer to skin surface precisely using a proportional-integral-derivative (PID) controller, and because it uses the Peltier effect, the cryoprobe does not need to move during the operation. We also developed a numerical simulation method that allows us to predict the frozen region and the temperature profile during cryosurgery. We tested the performance of our Peltier cryoprobe by cooling agar, and the results show that the cryoprobe has sufficient cooling performance for cryosurgery, because it can apply a cooling rate of more than 250 degrees C/min until the temperature reaches -40 degrees C. We also used a numerical simulation to reconstruct the supercooling phenomenon and examine the immediate progress of the frozen region with ice nucleation. The calculated frozen region was compared with the experimentally measured frozen region observed by an interferometer, and the calculation results showed good agreement. The results of numerical simulation confirmed that the frozen region could be predicted accurately with a margin of error as small as 150 microm during use of the cryoprobe in cryosurgery. The numerical simulation also showed that the cryoprobe can control freezing to a depth as shallow as 300 microm.

Discrete Ordinates Radiation Element Method for Radiative Heat Transfer in Three-Dimensional Participating Media

A new algorithm, the discrete ordinates radiation element method (DOREM), for modeling radiative heat transfer in inhomogeneous three-dimensional participating media is described. The DOREM uses advantages of the both the radiation element method (REM) and the discrete ordinates method. Benchmark comparisons are conducted against several radiation models. The DOREM successfully implements radiative heat transfer simulations precisely, since false scattering never occurs. The DOREM has advantages of computational speed against Monte Carlo, and the CPU time and the memory size of the DOREM are 82 times faster and 767 times smaller at the maximum than that of the REM.

Numerical Study of Non-Gray Radiation and Natural Convection Using the Full-Spectrum k-Distribution Method

The interaction of non-gray radiation and natural convection in a 2-D cavity is studied numerically. The aim of this work is to analyze the thermal and flow behaviors of real cases with a small temperature difference using the full-spectrum k-distribution method. In addition, the results are obtained for different medium assumptions like pure convection, transparent medium, and gray medium to investigate which assumption is appropriate to be used instead of non-gray calculations. The results show that the gray medium assumption for radiative heat transfer is suitable to be used in cavities with normal air mixture at normal room conditions.

Infrared Radiative Properties of Thin Polyethylene Coating Pigmented With Titanium Dioxide Particles

The infrared (IR) radiative properties of TiO 2 pigment particles must be known to perform thermal analysis of a TiO 2 pigmented coating. Resins generally used in making pigmented coatings are absorbing at IR wavelengths, which means that the conventional Mie solution (MS) may not be adequate in this domain. There are two approaches to evaluating radiative properties in an absorbing medium: far field approximation (FFA) and near field approximation (NFA). In this study, after reviewing these two approaches, we evaluated the radiative properties of TiO 2 particles in polyethylene resin as an absorbing matrix in the wavelength range of 1.7-15 μm based on the MS, FFA, and NFA. We then calculated the effective scattering and absorption coefficients for different models. To investigate the effect of the particle size and volume concentration on the transmittance of IR wavelengths, we made a nongray radiative heat transfer in an anisotropic scattering monodisperse pigmented layer, with independent scattering using the radiation element method by the ray emission model. The results showed that all three approaches predicted similar results in the particle size domain and volume fraction range utilized in pigmented coatings.

Description of the adhesive crystal growth under normal and micro-gravity conditions employing experimental and numerical approaches

Investigation of the crystal growth in solutions is closely related to effective and high quality production of medicine, food and new materials. In the present study, experiments and numerical simulations were performed to explain the mechanism of crystal growth from an aqueous solution. In the experiment, transient double diffusion fields were observed by using an accurate optical measuring system. In the numerical simulation, transient double diffusion fields were calculated by a numerical simulation code, applying initial and boundary conditions obtained by experiment. The results of numerical simulation show good agreement with experimental results. Taking these two approaches into consideration, it was considered that adhesive crystal growth was dominated by the temperature dependence of the solutal diffusion coefficient. The microscopic mechanism of adhesive crystal growth is almost the same between micro-gravity and normal gravity conditions; nevertheless, the macroscopic growth rate is different in each situation. Simulation of adhesive crystal growth can be performed easily using appropriate boundary conditions obtained by the present experiments.

Initiation process and propagation mechanism of positive streamer discharge in water

The aim of this study was to clarify the initiation process and the propagation mechanism of positive underwater streamers under the application of pulsed voltage with a duration of 10 μs, focusing on two different theories of electrical discharges in liquids: the bubble theory and the direct ionization theory. The initiation process, which is the time lag from the beginning of voltage application to streamer inception, was found to be related to the bubble theory. In this process, Joule heating resulted in the formation of a bubble cluster at the tip of a needle electrode. Streamer inception was observed from the tip of a protrusion on the surface of this bubble cluster, which acted as a virtual sharp electrode to enhance the local electric field to a level greater than 10 MV/cm. Streak imaging of secondary streamer propagation showed that luminescence preceded gas channel generation, suggesting a mechanism of direct ionization in water. Streak imaging of primary streamer propagation revealed intermitten...