新井 竜雄¹, 田中 昭太郎², 大谷 隆彦³

Tatsuo ARAI¹, Shotaro TANAKA², Takahiko OTANI³

¹古野電気株式会社システム機器事業部, ²株式会社デンソーボデー機器技術2 部, ³同志社大学工学部電機工学科

¹System Products Division, Furuno Electric CO., LTD, ²Body Electronics Components Eng. Dept.2, Denso Corporation, ³Department of Electrical Engineering, Faculty of Engineering, Doshisha University

キーワード : heel bone densitometry, speed of sound (SOS), quantitative ultrasound (QUS), temperature characteristics

超音波による骨の評価は踵を測定部位とすることが多く, その指標の一つとして音速(SOS) が用いられる. 物質の音速 は一般に温度の影響を受けるが, 人体の場合は温度は安定していると認識されていた. 踵は末端部であり冬季では体温よ り温度が低くなり音速に影響する. この現象は超音波骨評価装置が普及するにつれて知られるようになったが, これまで の研究では踵の音速と温度の相関を見るか, 脂肪などの一部の組成の温度特性のみの測定であり, 系統立てて関連付けた 研究はなかった. 踵を構成する各生体組織である皮質骨, 骨髄, 海綿骨, 表皮, 筋肉, 脂肪および皮下脂肪の温度特性を ウシから摘出したサンプルを用いて測定した. その結果, 皮質骨, 骨髄, 脂肪の温度係数が大きいのに対し, 筋肉や表皮 の温度係数は小さかった. 皮質骨と骨髄はほぼ同じ温度係数を示したが, 海綿骨の温度係数はその半分程度であった. 各 生体組織の厚さと温度係数を用いて踵の音速を計算し, その温度特性を推定した. 21 名の女性の踵の音速の温度係数を 測定した結果は推定結果と良い一致を得た.

The heel bone is often chosen for ultrasound assessment of bone. Ultrasound velocity generally serves as a diagnostic index and varies with the temperature of the medium. While commercial quantitative ultrasound systems assume that the temperature of the heel is stable, heel bone temperature is influenced more by ambient temperature than by body temperature, especially in the winter. The effect of heel temperature has received more attention as quantitative ultrasound measurement systems have gained wider use. Although the effect of heel temperature has been reported, few studies show a correlation between ultrasound parameters and measured temperature and the temperature characteristics of soft tissue and the like. We determined the temperature characteristics of cortical bone, trabecular bone, bone marrow, superficial skin, muscle, fat, and subcutaneous fat, major components of the heel by using the bovine extirpated samples. While temperature coefficients of muscle and superficial skin were low, those of bone marrow and fat were high. The temperature coefficients of cortical bone and bone marrow were the same, although the temperature coefficient of trabecular bone was half that of cortical bone. We then estimated temperature characteristics and calculated ultrasound velocity in the heel using thickness and the temperature coefficient of each heel component. The estimated temperature characteristics were consistent with those actually observed in 21 women volunteers.