宮本 倫聡¹, 小谷 和彦¹, UURTUYA Shuumarjav¹, 大竹 章文², 曹 景文², 紺野 啓¹, 谷口 信行¹

Michiaki MIYAMOTO¹, Kazuhiko KOTANI¹, Shuumarjav UURTUYA¹, Akifumi OTAKE², Jing-Wen TSAO², Kei KONNO¹, Nobuyuki TANIGUCHI¹

¹自治医科大学臨床検査医学, ²日立アロカメディカル株式会社

¹Department of Clinical Laboratory Medicine, Jichi Medical University, ²Hitachi Aloka Medical, Ltd.

キーワード : Doppler angle, flow velocity errors, spectral broadening, linear-array transducer, carotid arteries

目的：超音波ドプラ法による最大流速測定における計測誤差を回避するため，プローブの補正角度は60度以内に設定する必要があるとされている．しかし，たとえ60度以下の角度補正でも測定値は実際の流速よりも過大評価になってしまうことが指摘されている．今回，我々は角度補正に伴う最大流速測定値の過大評価について追試を行った．方法：糸ファントム駆動装置を水中に設置し，糸ファントムを100cm/sの一定した移動速度で駆動させた．糸ファントムを超音波装置のリニア型プローブを用いて補正角度を45度，50度，60度になるようにした．角度設定の不正確さによる計測誤差が出現しないようにプローブを固定した状態で，各々の補正角度で糸ファントムの移動速度を3回ずつ測定した．結果：各最大移動速度の平均値は補正角度45度で120.1cm/s，50度で124.2cm/s，60度で135.2cm/sであった．補正角度が45度でも約20％の過大評価となり，補正角度が大きくなるにつれて過大評価となった．結語：角度補正が60度以下でも，最大流速の測定値は過大評価になっていると考えられる．

Purpose: Because measurement errors are caused by the Doppler incident angle in ultrasound velocity estimation, it is said that the incident angle should be within 60 degrees. However, previous reports showed that if the incident angle was within 60 degrees or less, the measurements were greater than the actual velocity. We reevaluated overestimation of velocity with the Doppler incident angle. Methods: A string phantom was installed in a water tank and set at a constant speed of 100 cm/s. The ultrasound linear-array transducer was adjusted so that the incident angles were 45 degrees, 50 degrees, and 60 degrees. The transducer was fixed in a state where a measurement error did not appear. The velocities of the string phantom were measured at the Doppler incident angle of 45 degrees, 50 degrees, and 60 degrees three times, respectively. Results: The means of peak velocity at the incident angle of 45 degrees, 50 degrees, and 60 degrees were 120.1 cm/s, 124.2 cm/s, and 135.2 cm/s, respectively. Even with an incident angle of 45 degrees, the overestimation of velocity was approximately 20%. As the incident angle became larger, the overestimation of velocity increased. Conclusion: Even if the incident angle is 60 degrees or less, flow velocity may be overestimated.