造影エコー診断の肝癌局所治療への応用―治療効果判定と穿刺ガイド─

抄録

Areas of residual tumors after RFA or PEI therapy are not distinguishable from necrotic tissues on US. The sonographic findings of gray-scale, color Doppler and power Doppler scanning after RFA or PEI therapy do not correlate well with the overall necrotic shape, or with the volume or extent of coagulation necrosis induced. Therefore, contrast-enhanced CT or MRI is generally necessary to assess the efficacy of the treatment. The absence of intensified areas on contrast-enhanced CT indicates the disappearance of the blood supply and, by inference, a successful treatment. Conversely, focal areas of persistent contrast enhancement usually indicate viable tumor cells, and, therefore, warrant further treatment to achieve a complete tumor necrosis.
Harmonic gray-scale images can extract only the blood flow echoes created by destruction of microbubbles, whilst echoes from tissue are effectively cancelled. This mode makes it possible to clearly depict residual blood flow in tumors after therapy. Because contrast-enhanced harmonic sonography is easy to perform and provides real-time needle insertion guidance, it may be favored in monitoring response to localized therapies, obviating unnecessary CT and treatment sessions.
Although contrast-enhanced CT can clearly depict residual areas of tumors after RFA or PEI therapy, it does not make possible real-time guidance in percutaneous therapies. Furthermore, the retention of lipiodol in HCC lesions sometimes makes it difficult to distinguish the hyperattenuating area of contrast enhancement from that of lipiodol when the retention of iodized oil in tumors is incomplete.
Contrast-enhanced harmonic gray-scale images can reveal the tumor vascularity in patients with HCC, after transcatheter arterial embolization and percutaneous therapies, with high sensitivity and accuracy in comparison with dynamic CT. This capability of harmonic imaging for depicting residual cancer cells in HCCs after treatment facilitates a correct guidance for the insertion of a needle on US monitoring, which cannot be achieved by any other imaging modalities including CT and MRI.
The noninvasive vascular technique of contrast-enhanced harmonic imaging is an extremely sensitive tool for detecting the intranodular blood flow in hepatic tumors. This method is drastically changing the diagnostic and therapeutic strategy of hepatic tumors, especially HCC, resulting in an eventual improvement in the prognosis of patients with HCC.