土屋 健伸, 遠藤 信行

Takenobu TSUCHIYA, 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 : thermal effects, numerical simulation, sound wave propagation, heat conduction, heat conduction by thick blood vessel

今日，超音波診断装置は，医療現場に広く普及している．特に産婦人科領域では，必要不可欠な診断技術として確固たる地位を築いている．しかし，近年，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必要とされている．超音波を人体に照射すると，生体に発熱を生じる熱的作用と機械的な振動である非熱的作用が生じる．熱的作用は，生体を伝搬する超音波が減衰することでエネルギーが熱に変換することで生じる作用である．超音波による熱的作用を予測するには，生体中の音波伝搬を解析し，その超音波強度から生体内での発熱量を求め，生体中の熱伝導を解析する必要がある．ここでは，数値シミュレーションによって集束超音波照射時における音波伝搬ならびに熱伝導の解析を行った．さらに生体内の関心領域に太い血管が存在する場合の熱伝導解析を行い，血流による熱拡散の影響について調べた．

Ultrasonic diagnostic equipment is widely used in the medical field today. In particular, it is an established and indispensable diagnostic technology in obstetrics and gynecology. Recently, however, as high-frequency and high-intensity ultrasound is being increasingly used to expand diagnostic target regions and improve the diagnostic performance, it is necessary to validate the safety of ultrasonic diagnostic equipment. The effects of ultrasound radiation on the human body, including thermal effects, which generate heat, and non-thermal effects, which are mechanical oscillations, need to be investigated. Thermal effects occur as the ultrasound propagating in the body is attenuated and the energy is converted to heat. It is important to understand thermal effects when investigating the safety of ultrasonic diagnostic equipment. To predict thermal effects, it is critical to analyze the sound wave propagation inside the living body, obtain the calorific value of the ultrasound intensity, and analyze the heat conduction inside the living body. In this study, we used numerical simulations to analyze sound wave propagation and heat conduction for focused ultrasound irradiation. We also conducted an analysis of sound wave propagation and heat conduction in the presence of a thick blood vessel in the region of interest inside the living body and studied the effect of blood flow on heat diffusion.