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Research paper : Improving the reliability of temperature measurements taken with clinical infrared ear thermometers (J. Ishii)−59−Synthesiology - English edition Vol.1 No.1 (2008) having wide view angles was designed by conducting Monte Carlo simulation, but what is the shape of the cavity recommended by AIST and employed in JIS? Also, what material is used normally to coat the inner wall of cavity of the standard BBR, and what level of intrinsic emissivity does it have in the infrared region?Answer (Juntaro Ishii)Figure c shows the cross sectional view graph of the standard blackbody cavity for calibration of ear thermometer developed by AIST. The material of the blackbody cavity is oxygen-free copper with high thermal conductivity, and the wall of the cavity is designed so its thickness will be 0.5 mm or less. The inner wall of the blackbody cavity must be blackened so it will have high emissivity of 0.95 or more in the infrared wavelength region. AIST measured spectral emissivity for black paint and coating material commercially available in Japan and overseas in the infrared region using the FTIR spectrometer system, and we employed black paint (Nextel’s velvet coatings) with spectral emissivity of 0.96 or more in the 5~12 µm wavelength region.6 History of development of ear thermometerQuestion (Naoto Kobayashi)Ear thermometer is an innovative clinical thermometer that allows non-contact measurement in short time. You mentioned that it was developed by an American company in the 1990s, but was this type of thermometer developed in Japan or other countries at that time? If it was completely original creation by the American company, what is the reason that this company was able to make it while others couldn’t? If it was a result of development competition, why couldn’t the companies of Japan or other countries win this competition?Answer (Juntaro Ishii)The approach of determining temperature of skin and body surface by measuring infrared radiation from human body was a measurement technique available for a long time, and was applied to breast cancer diagnosis using thermography system. Also, measurement of temperature around the tympanic membrane was a subject of “basal body temperature (core temperature)” measurement that was medically important since it was close indication of brain temperature. However, in the conventional method, thin wire temperature sensor such as thermocouple or thermistor was pressed directly against the eardrum, so patients (subjects) felt pain and suffering, and it was a special body temperature measurement method done only by medical specialists.Although I do not know the details of the history of development of current infrared ear thermometer, I guess that there were two technological points in product realization: development of highly sensitive and low cost infrared sensor, and technology for compensation of effect of temperature change in thermometer caused by the temperature fluctuation in surrounding environment and by contact with human body. I think the basic methodology for infrared ear thermometer was already known, and technical development for product realization was in progress not only in the US but also in Europe and Japan. In the US, state-of-art R&D were conducted for infrared sensor and precise infrared measurement as core technologies in defense and space fields, and I think the US was able to lead the world in producing highly practical ear thermometer using these advanced infrared technology. Although this is my guess, the clinical thermometer manufacturers of Japan and Europe, which had manufactured mercury-in-glass and thermistor thermometers but did not have technological foundation for infrared measurement, might have been thinking, “Product realization for low-cost highly reliable clinical infrared thermometer that can compete with thermistor thermometers was far ahead in time”. Then, an American venture company actually developed competitive ear thermometer, and the product won support from users in the American market. I think, only after that, product development by Japanese and European manufacturers has accelerated.7 Performance test of ear thermometer in marketQuestion (Naoto Kobayashi)What is the level of reliability of current ear thermometer in market? In the comparison test (for FY2005) of ear thermometer conducted officially by the National Consumer Affairs Center, measurement variation of 0.5-0.7 °C was reported. Is this result unavoidable in the current situation where there is a maximum 0.4 °C fluctuation in temperature graduation due to insufficient long-term stability, or is it something that can be improved if the traceability for current ear thermometer gets better? These are points of interest and I would like to hear your thoughts.Answer (Juntaro Ishii)For user-level reliability of ear thermometer, I am aware of the fact that it does not completely satisfy the users. I think it is necessary to divide the issue into two parts for consideration: (1) performance of thermometer as a physical measurement instrument (thermometer), and (2) performance of thermometer as a medical equipment whose measurement subject is the human body.For (1), as mentioned in the article, it is possible to verify the reliability of measurement and feed the result back to improve product performance by conducting calibration and conformity assessment using standard BBR traceable to international unit (SI) of temperature for infrared thermometer, and I believe that the result of R&D by AIST is contributing to the improvement of reliability. Some of the products do still have problems of long-term stability, but I think a more stable thermometer will be developed in the future along with verification and assessment using standard BBR and by maintaining traceability.In contrast, (2) is a matter of obtaining reliability in measuring the human body, which is “measurement subject with variation”, and a different approach is necessary from (1). As mentioned in the article, current ear thermometers have different measurement view angles by types, and the measured site is not necessarily “eardrum” itself, and in many cases it measures “interior of ear canal including eardrum”. In general, a nonnegligible temperature difference (temperature distribution) may occur in the eardrum and the surrounding ear canal, and moreover, there may also be differences in emissivity between the eardrum and the skin surface of the surrounding ear canal. Therefore, even if the same subject is repeatedly measured with the ear thermometer, the measured data may show large variation depending on how the ear thermometer probe is inserted into the earhole. Moreover, occurrence of different temperature readings among ear thermometers with different measurement view angles is unavoidable in current circumstances.These issues cannot be necessarily verified by engineering assessment using “physically correct BBR” as in (1), and it is necessary to increase reliability by conducting the clinical assessment with assumed medical knowledge. From the standpoint of developing the ear thermometer, “thermometer that selectively measures eardrum”, and “method of taking repeated number of measurements in one measurement, and then using highest temperature value as measurement result” and “method of displaying values converted to temperature of armpit or oral by processing data based on the characteristics of thermometer and the clinical information rather than using measurement as it” are being researched and developed. On the other hand, in the international standardization (ISO/IEC) which is in progress now, the ear thermometer is categorized as a clinical thermometer

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