南 康範, 工藤 正俊

Yasunori MINAMI, Masatoshi KUDO

近畿大学医学部消化器内科

Department of Gastroenterology and Hepatology, Kindai University Faculty of Medicine

キーワード : contrast-enhanced ultrasound, Contrast Vector Imaging, flash replenishment curve, time intensity curve parameters, wash-in and wash-out curve

造影超音波は高感度に血流シグナルを検出できることから活動性のある腫瘍部位を同定できる有用な検査であるが，組織レベルの血流量や微細な血流速度を定量的に測定することは困難である．そのため，造影超音波による血流定量の試みとしてtime intensity curveのパラメータ比較による報告がなされており，そのtime intensity curve解析の主なものとしてwash-in and wash-out curveとflash replenishment curveがある．ただし，計測で用いる関心領域の位置や大きさによって輝度値が大きく変動することは超音波検査の宿命であり，観察時間の長さによってパラメータに誤差が生じる得るリスクはcurve fittingでは避けられない．さらに，パラメータ比較では実際にどれだけの血流変化を表しているのかを臨床医が想像し難いという根本的な問題がある．一方，新しく発表されたContrast Vector Imaging®は造影剤バブルの軌跡を画像解析することで局所組織における血流速度を直接計測することができる画期的な画像技術である．造影超音波による血流定量の評価法が確立されれば，腫瘍の鑑別診断や化学療法の早期効果予測に大きく貢献するものと期待される．

Contrast-enhanced ultrasound (CEUS) is a powerful tool to detect viable tumor lesions effectively because of the higher diagnostic sensitivity of images; however, it is difficult to evaluate microvascular perfusion quantitatively. Alternatively, time intensity curve (TIC) parameters measured using CEUS have been compared as quantitative analysis for blood perfusion. There are two major analysis methods using TIC: wash-in and wash-out curve and flash replenishment curve. Unfortunately, there is a big fluctuation of intensity in decibel according to the depth and/or size of the region of interest on CEUS, and it is also inevitable that curve fitting analysis runs the risk of error on TIC parameters according to the CEUS examination time. Basically, it is difficult for physicians to identify the degree of change in blood flow based on analysis of TIC parameters. Meanwhile, the epoch-making new technology, Contrast Vector Imaging®, has been launched. It can directly measure microvascular perfusion by quantitative imaging analysis of Sonazoid bubble tracking. Recently, anti-tumor therapeutic strategies have been developed. We need to establish a standard technique for quantitative assessment of microvascular perfusion on CEUS, which is expected to contribute significantly to early tumor response assessment of anti-tumor therapies in the future.