Name: agarose-based tissue mimicking optical phantoms for diffuse reflectance spectroscopy
Uploaded: 2018-08-22T14:00:00
Description: Watch this Scientific Journal Video about Agarose-based Tissue Mimicking Optical Phantoms for Diffuse Reflectance Spectroscopy at JoVE.com

Part of this work was supported by a Grant-in-Aid for Scientific Research (C) from the Japanese Society for the Promotion of Science (25350520, 22500401, 15K06105) and the US-ARMY ITC-PAC Research and Development Project (FA5209-15-P-0175, FA5209-16-P-0132).

1. Construction of a Conventional Diffuse Reflectance and Total Transmittance Spectroscopic System
Note: Construct the measuring systems for the diffuse reflectance and total transmittance spectra using a broadband white light source, a light guide, an achromatic lens, an integrating sphere, a sample holder, an optical fiber, and a multi-channel spectrometer. The role of the light trap is to remove the specular reflection component from the reflectance spectrum. The sample holder of the integrat...

The most critical step in this protocol is the temperature control of the base material. The temperature to maintain the base material ranged from 58 to 60 &#176;C. If the temperature is more than 70 &#176;C, a denaturation of both the lipid emulsion and the whole blood will occur. As a consequence, the optical properties of the phantom will deteriorate. If the temperature is less than 40 &#176;C, the base material will be ununiformly gelled and, thus, the light scattering and absorption agents will be heterogeneously di...

Optical phantoms are objects mimicking the optical properties of biological tissues and have been widely used in the biomedical optics field. They are designed so that the optical properties, such as light scattering and absorption coefficients, match with those of living human and animal tissues. Optical phantoms are generally used for the following purposes: simulating the light transport in biological tissues, calibrating a newly developed optical system design, evaluating the quality and performance of existing systems, comparing the performance between systems, and validating the ability of the optical methods to quantify the optical properties1,2,3,4,5. Therefore, easy-to-get substances, a simple fabrication process, a high reproducibility, and an optical stability are required for making optical phantoms.
Various types of optical phantoms with different base materials such as aqueous suspension6, gelatin gel7, agarose gel8,9,10, polyacrylamide gel11, resin12,13,14,15,16, and room-temperature-vulcanizing silicone17 have been reported in previous literature. It has been reported that gelatin- and alginate-based gels are useful for optical phantoms with heterogeneous structures18. Alginate phantoms have a suitable mechanical and thermal stability for evaluating photothermal effects such as laser ablation studies and laser-based hyperthermia studies18. Agarose gels have the ability to fabricate heterogeneous structures, and their mechanical and physical properties are stable for a long time18. High-purity agarose gels have a very low turbidity and a weak optical absorption. Therefore, optical properties of agarose-based phantoms could easily be designed with the appropriate light scattering and absorbing agents. Recently, styrene-ethylene-butylene-styrene (SEBS) block copolymers19 and polyvinyl chloride (PVC) gels20 have been reported as interesting phantom materials for optical and photoacoustic techniques.
Polymer microspheres7,12,21,22, titanium oxide powder1, and lipid emulsions23,24,25,26 such as milk and lipid emulsion are used as light scattering agents, whereas black ink27,28 and molecular dyes29,30 are used as light absorbers. Diffuse reflectance spectra of most living organs are dominated by the absorption of oxygenated and deoxygenated hemoglobin in red blood cells. Therefore, hemoglobin solutions31,32 and whole blood8,9,10,33,36 are often used as light absorbers in the phantoms for a diffuse reflectance spectroscopy and multispectral imaging.
The method described in this article is used to create an optical phantom mimicking the light transport in biological tissues and to characterize its optical properties. As an example, a two-layered optical phantom mimicking optical properties of human skin tissue is demonstrated. The advantages of this method over alternative techniques are the ability to represent diffuse reflectance spectra of living biological tissues in the visible to near-infrared wavelength region, as well as the simplicity to make it, using easily available materials and conventional optical instruments. Therefore, the optical phantoms made by this method will be useful for the development of optical methods based on diffuse reflectance spectroscopy and multispectral imaging.

<table>
	<tbody>
		<tr>
			<td>150-W halogen-lamp light source</td>
			<td>Hayashi Watch Works Co., Ltd, Tokyo, Japan</td>
			<td>LA-150SAE</td>
			<td></td>
		</tr>
		<tr>
			<td>Light guide</td>
			<td>Hayashi Watch Works Co., Ltd, Tokyo, Japan</td>
			<td>LGC1-5L1000</td>
			<td></td>
		</tr>
		<tr>
			<td>Integrating Sphere</td>
			<td>Labsphere Incorporated, North Sutton, NH, USA</td>
			<td>RT-060-SF</td>
			<td></td>
		</tr>
		<tr>
			<td>Port adapter</td>
			<td>Labsphere Incorporated, North Sutton, NH, USA</td>
			<td>PA-050-SMA-SF</td>
			<td></td>
		</tr>
		<tr>
			<td>Light trap</td>
			<td>Labsphere Incorporated, North Sutton, NH, USA</td>
			<td>LTRP-100-C</td>
			<td></td>
		</tr>
		<tr>
			<td>Spectralon white standard with 99% diffuse reflectance</td>
			<td>Labsphere Incorporated, North Sutton, NH, USA</td>
			<td>SRS-99-020</td>
			<td></td>
		</tr>
		<tr>
			<td>Optical fiber</td>
			<td>Ocean Optics Inc., Dunedin, Florida, USA</td>
			<td>P400-2-VIS-NIR</td>
			<td></td>
		</tr>
		<tr>
			<td>Miniature Fiber Optic Spectrometer</td>
			<td>Ocean Optics Inc., Dunedin, Florida, USA</td>
			<td>USB2000</td>
			<td></td>
		</tr>
		<tr>
			<td>Achromatic lens</td>
			<td>Chuo Precision Industrial Co.,Ltd, Tokyo, Japan</td>
			<td>ACL-50-75M</td>
			<td></td>
		</tr>
		<tr>
			<td>Intralipid</td>
			<td>Fresenius Kabi AB, Uppsala, Sweden</td>
			<td>Intralipid 10%</td>
			<td></td>
		</tr>
		<tr>
			<td>Coffee 
			(Blendy Mocha Blend Regular Coffee)</td>
			<td>Ajinomoto AGF, Inc. Tokyo, Japan</td>
			<td>Unavailable</td>
			<td></td>
		</tr>
		<tr>
			<td>Whole blood</td>
			<td>Nippon Bio-Test Laboratories Inc. Saitama, Japan</td>
			<td>0103-2</td>
			<td></td>
		</tr>
		<tr>
			<td>Agarose</td>
			<td>Nippon Genetics Co., Ltd, Tokyo, Japan</td>
			<td>NE-AG02</td>
			<td></td>
		</tr>
		<tr>
			<td>Cooking heater</td>
			<td>TOSHIBA CORPORATION Tokyo, Japan</td>
			<td>HP-103K</td>
			<td></td>
		</tr>
	</tbody>
</table>

agarose-based tissue mimicking optical phantoms for diffuse reflectance spectroscopy

This protocol describes how to make agarose-based tissue-mimicking phantoms and demonstrates how to determine their optical properties using a conventional optical system with an integrating sphere. Measuring systems for the acquisition of the diffuse reflectance and total transmittance spectra are constructed with a broadband white light source, a light guide, an achromatic lens, an integrating sphere, a sample holder, an optical fiber probe, and a multi-channel spectrometer. An acrylic mold consisting of two rectangular acrylic pieces and a U-shaped acrylic piece is constructed to create an epidermal phantom and a dermal phantom with whole blood. The application of a sodium dithionite (Na2S2O4) solution to the dermal phantom enables the researcher to deoxygenate hemoglobin in red blood cells distributed in the dermal phantom. The inverse Monte Carlo simulation with the diffuse reflectance and total transmittance spectra measured by a spectrometer with an integrating sphere is performed to determine the absorption coefficient spectrum &#181;a(&#955;) and the reduced scattering coefficient spectrum &#181;s&#39;(&#955;) of each layer phantom. A two-layered phantom mimicking the diffuse reflectance of human skin tissue is also demonstrated by piling up the epidermal phantom on the dermal phantom.

Figure 3 shows the representative estimated spectra of the reduced scattering coefficient and the absorption coefficient for the epidermal phantom and dermal phantom. The results shown in Figure 3 are the averages of ten measurements of both reflectance and transmittance spectra. The reduced scattering coefficient &#181;s&#39; has a broad scattering spectrum, exhibiting a higher magnitude at shorter w...

Watch this Scientific Journal Video about Agarose-based Tissue Mimicking Optical Phantoms for Diffuse Reflectance Spectroscopy at JoVE.com

Agarose-based Tissue Mimicking Optical Phantoms for Diffuse Reflectance Spectroscopy

Here, we demonstrate how agarose-based tissue-mimicking optical phantoms are made and how their optical properties are determined using a conventional optical system with an integrating sphere.

This protocol describes how to make agarose-based tissue-mimicking phantoms and demonstrates how to determine their optical properties using a ...

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