尾上 篤志¹, 秋山 隆弘²

Atsushi ONOUE¹, Takahiro AKIYAMA²

¹長寿クリニック超音波室, ²近畿大学医学部堺病院泌尿器科

¹Chouju Clinic, ²Department of Urology, Kinki University Sakai Hospital

キーワード : contrast ultrasonography, renal tumor, time intensity curve

超音波造影剤の登場により, 従来のカラードプラ(パワードプラ) 法に比べmicro bubbleの単純な反射強度増強効果を利用して血流検出感度の向上がみられたが, 最近ではハーモニック(高調波)信号や擬似ドプラ信号を利用したUSで, micro bubbleから発生する信号のみを分離して検出可能となった. その結果, 組織を還流する遅い血流やtrapされている血流内のmicro bubbleの動態までも可視化できるようになり, 造影CTのように動脈相において腫瘍の動脈血流を評価したり, 実質相において腫瘍のperfusion血流を描出することができるようなった. この新しい造影USを腎腫瘍に適用し, 腫瘍にmicro bubbleが飽和するまでに必要な間歇送信時間を測定すると, 腎細胞癌(N＝20) 4.2±2.2 秒は腎血管筋脂肪腫(N＝6) 21.5±8.4 秒に比べ有意(p＝0.004)に短く, 腫瘍内の還流速度に差があることが証明された. さらに, 透析患者では高率に腎細胞癌を合併し, その早期診断が重要な課題であるが, 造影USは腎細胞癌の早期診断の決めてとして十分な感度を持っているため透析腎の管理に有用である. このように造影USは, ①RCC/AMLの鑑別診断の決め手として有用である, ②CT/MRIで発見困難な透析腎癌のdetectionにも威力を発揮する, など優れた臨床的な成果が得られる検査法である. 本章では, 我々の経験を基に腎腫瘍診断における造影USについて基礎から応用までを解説した. 腎腫瘍診断にとって, 造影USは未だ完成された診断法ではないが, さらに新しい新技術の発展が期待される分野でもあり, 今後の発展に期待したい.

Ultrasound (US) contrast agents containing microbubbles enable color Doppler (power Doppler) ultrasound to detect blood flow in renal masses with greater sensitively and show blood flow and hemodynamics in tumor tissue in solid renal masses. These contrast methods can even detect slow or trapped blood flows by capturing harmonic and pseudo-Doppler signals (loss of correlation). This new method makes it possible to evaluate arterial blood flow in the early (vascular) phase and perfusion blood flow in the late (parenchymal) phase in renal tumors, as is now possible with contrast dynamic CT. Microbubble time intensity curves (TIC) from the region of interest (ROI) can also be derived from this data. Pattern classification may prove useful in characterizing renal tumor tissue. The limited quantity of data based on intensity curves suggests that the time intensity curve may prove useful as a differentiating tool. In addition, such data should enable us to determine the saturation time of microbubble contrast agents, that is, the time required for blood to fill a renal mass, by measuring the minimum intermittent ultrasound emission time necessary to destroy the microbubbles in it. This could enable us to differentially diagnose renal masses of various histologic types. We have already established methods for differentially diagnosing between renal cell carcinoma (N=20) and renal angiomyolipoma (AML) (N=6). Filling times in renal cell carcinoma averaged 4.2賊2.2 seconds in renal cell carcinoma and 21.5賊8.4 seconds in renal angiomyolipoma (significant difference, P=0.004). We have also found that renal cell carcinoma derived from acquired cystic kidneys frequently occurred in patients under long-term maintenance hemodialysis were more easily detected with this method than with CT or MRI. This overview of the principle of conventional color Doppler imaging and our experience using the most recent contrast harmonic ultrasound imaging technology to study renal tumors allows us to suggest that contrast harmonic imaging holds promise as a developing diagnostic method and that further development is warranted.