土屋 健伸, 清水 一磨, 遠藤 信行

Takenobu TSUCHIYA, Kazuma SHIMIZU, Nobuyuki ENDOH

神奈川大学工学部電気電子情報工学科

Department of Electric, Electronics, and Information Engineering, Faculty of Engineering, Kanagawa University

キーワード : temperature rise in the human body, thermal imaging method, tissue-mimicking phantom, mimicking bone, finite difference time domain method, heat conduction equation method

今日，超音波診断装置は広く普及し，医療現場，特に産婦人科領域では必要不可欠なものとなっている．しかし，診断対象領域の拡大や診断装置の性能を向上する目的での照射超音波の高周波化・高出力化に伴い，超音波装置の安全性を検証するための研究が世界中で実施されている．日本超音波医学会でも機器及び安全に関する委員会を中心に安全性についての検討や実験が実施されており，近年では音響放射圧を用いたイメージング装置の生体への影響について，多方面の検討が実施されている．そこで，本報告では赤外線カメラを用いた熱画像法による測定システムを構築し，IEC 60601-2-37を参考に製作した分割ファントムを用い，その断面の2次元温度分布測定を行った結果について報告する．初めに，温度分布と照射超音波出力の関係性を求めた．さらに，超音波の伝搬方向に擬似骨（アクリル）がある場合とない場合について温度上昇実験を行った．この結果，超音波の反射が骨ならびに骨近傍の温度を上昇させる現象を可視化することができた．次に，従来法の熱電対による測定結果と比較し，熱画像法の妥当性について検討した．さらに，数値シミュレーションを行って熱画像法の測定結果と比較することで，さらなる妥当性を検討した．使用が容易なシミュレーションプログラムを作成することで，臨床医による体内温度分布の予測も可能となり，安全性の確立や啓蒙に役立つと考える．

Currently, ultrasound diagnostic devices are widely used and have become an essential tool in the medical front, particularly in the field of obstetrics and gynecology. These diagnostic devices have high frequencies and a large power of irradiated ultrasound waves for improving their performance and expanding the fields of their application, but lately research is being conducted worldwide to verify the safety of these devices. At the Japan Society of Ultrasonics in Medicine (JSUM), the Ultrasound Equipment and Safety Committee is testing and verifying the safety of these devices. In recent years, JSUM has been examining imaging equipment that use acoustic radiation force from the perspective of their impact on human health. With this background in mind, we developed a thermal imaging-based measurement system that uses infrared cameras to measure the two-dimensional temperature distributions of cross-sections of a phantom prepared following IEC 60601-2-37. We first obtained the relationship between the temperature distribution and irradiated ultrasound output power. We also conducted temperature rise tests on the propagation direction of ultrasound waves for cases with and without a mimicking bone (acrylic). Hence, we were able to visualize the effect of the temperature rise on the bone and neighboring areas caused by the reflection of ultrasonic waves. Next, we examined the validity of thermal imaging by comparing these measurements with those obtained through the conventional thermocouple method. We further examined their validity by conducting numerical simulations and comparing the simulation results with the thermal imaging measurement results. We consider that developing an easy-to-use simulation program will enable technicians to predict the temperature distribution in the body and help raise awareness of safety.