古賀 政利

Masatoshi KOGA

国立循環器病センター内科脳血管部門

Cerebrovascular Division, Department of Medicine, National Cardiovascular Center

キーワード : acute ischemic stroke, transcranial Doppler sonography, transcranial color-coded sonography, ischemic penumbra, sonothrombolysis

急性期脳梗塞症例では，経頭蓋超音波ドプラ法（transcranial Doppler: TCD）は主に微小栓子シグナルの評価に有用で，脳梗塞の病態評価や奇異性脳塞栓症診断，及び抗血栓薬の効果の評価に用いられている．経頭蓋カラードプラ法（transcranial color-coded sonography: TCCS）は，主に主幹脳動脈の狭窄・閉塞性病変評価，側副血行の評価に用いられている．TCD/TCCSは非侵襲的検査であり，ベッドサイドで繰り返し簡便に施行出来る．急性期脳梗塞のtherapeutic time window（3‐6時間）に血管の閉塞・開通状態をモニター出来る手段はTCD/TCCSのみである．最近，アルテプラーゼ（rt-PA）静注療法による超急性期血栓溶解療法時にTCDやTCCSを併用することで閉塞血管の再開通率が改善することが報告されsonothrombolysisとして注目されている．rt-PA療法にTCDモニターと超音波造影剤（Levovist^®）を併用すると再開通率がさらに向上することも示唆されている．古幡らは，500 kHzの低周波経頭蓋超音波血栓溶解法の安全性と有効性を前臨床で確認し，その治療ユニットとすでに臨床応用されているTCCS診断ユニットを組み合わせた一体型の新規装置を開発中である．近い将来に，本療法が急性期脳梗塞のさらに有用な治療手段となる可能性がある．

In patients with acute ischemic stroke, transcranial Doppler (TCD) sonography is mainly used to detect microembolic signals with long-term monitoring, and it provides important information for stroke mechanisms and the effectiveness of antithrombotic agents. TCD is also useful to check the presence of right-to-left shunt via heart/lung with intravenous injection of gas microbubbles during the Valsalva maneuver. Transcranial color-coded sonography (TCCS) is mainly used to evaluate occlusive intracranial arteries and collateral cerebral circulation via the circle of Willis. TCD/TCCS are simple and noninvasive procedures that are convenient for repetitive real-time evaluation at the bedside. The therapeutic time window for ischemic stroke is about 3 to 6 hours from onset, and early recanalization of the occluded artery within the time window is strongly associated with a good clinical outcome. TCD/TCCS are the only useful tools to monitor the recanalization status of the occluded artery in the very short time window. The image resolution of TCCS is inferior to that of digital subtraction angiography, 3-dimensional CT angiography, and magnetic resonance angiography, and interpretation of examination results may be affected by the skill of the examiner. Education and training are essential for TCD/TCCS to serve as standard imaging modalities in patients with cerebrovascular disease. Recently, it was reported that the combination of TCD/TCCS with intravenous plasminogen activator (rt-PA) therapy in patients with hyperacute ischemic stroke, i.e., sonothrombolysis, shows promise in terms of improving the recanalization rate of occluded arteries and the clinical outcome. The additional usage of an ultrasound contrast agent (Levovist^®) with rt-PA therapy and TCD may further increase the recanalization rate. In Japan, Furuhata et al. found that 500-kHz continuous wave ultrasound was safe and effective for accelerating clot lysis in in vitro and in vivo experiments. A new integrated device with a commercially available diagnostic unit and a therapeutic unit with a 500-kHz continuous wave probe is already being developed, and a clinical trial for hyperacute ischemic stroke will be conducted in the near future.