澤口 能一, 王 作軍, 古幡 博

Yoshikazu SAWAGUCHI, Zuojun WANG, Hiroshi FURUHATA

東京慈恵会医科大学ME研究室

Medical Engineering Laboratory, Jikei University School of Medicine

キーワード : ultrasound, thrombus, reocclusion, prevention

目的：様々な血流再開通法において血栓再形成による再閉塞は非常に重要な問題である．そのため，新規超音波療法による血栓成長抑制を検証すべく，in vitroにてウシフィブリン血栓と中周波数超音波を用いて検討を行った．超音波による血栓成長抑制効果は超音波の音響強度ごとに定量的に評価を行った．方法：ウシ血漿にCaCl₂（最終濃度：25 mM）を直径15 mm，高さ1.5 mmの円盤状容器に入れ，37℃で30分間放置することで血栓を作製した．そこへ新たに血漿を加え密封した状態で37℃の水浴中で30分間超音波を照射した．血栓成長抑制効果は分光光度計を用いて血栓の増高（mm）を定量化することで評価した．なお，本検討で使用した超音波照射条件は以下の通りである．周波数：500kHz，音響強度：0.07‐0.72W/cm²，振動子直径：10 mm，連続波．結果と考察：超音波照射群と超音波非照射群を比較した結果，音響強度0.28‐0.72 W/cm²において血栓成長を顕著に抑制出来ることを示した（p＜0.05）．また，この血栓抑制効果は音響強度依存的に増強することが示唆された．結論：本検討で見出した低強度の中周波数超音波による新血栓成長抑制効果には，臨床的再開通法に伴う再閉塞リスクを低侵襲的に抑制出来る可能性があると期待された．

Purpose: To prevent reocclusion after various recanalization therapies, we conducted an in vitro experiment using bovine fibrin clot and middle frequency ultrasonication to examine the ultrasonic therapeutic effect suppressing the regrowth of thrombi. Degree of ultrasonic control was quantitatively evaluated according to ultrasound (US) intensity. Methods: Discoidal clots created using bovine plasma with CaCl₂ (final concentration, 25 mM) at 37 degrees C in a circular container 15 mm in diameter and 1.5 mm deep. Fresh bovine plasma was placed on the clot after 30 minuets, and in an another container that was ultrasonicated for 30 minutes in a water bath at 37 degrees C. Growth rate was calculated by measuring change in clot thickness before and after sonication, from changes in optical absorption measured using a new precise optical system. Our new optical system utilized the relationship between spatial clot growth and US spatial intensity distribution on the discoidal clot. US conditions: frequency, 500 kHz; continuous wave intensity, 0.07 to 0.72 W/cm²; and transducer diameter; 10 mm. Results: Suppression of thrombus growth was significantly greater in the US group than in the Non-US group, in which the controlled ratio increased over the intensity range of 0.28 to 0.72 W/cm² (p＜ 0.05). Conclusions: These results suggest that a novel US control effect of thrombus regrowth with a middle frequency and low intensity can serve as a new noninvasive method for preventing thrombotic reocclusion in clinical risks caused by the various recanalization techniques.