Irreversible electroporation (IRE) is emerging as a new minimally invasive ablation technique for the treatment of a variety of malignant tumors, which has unique aspects that differ from those of conventional ablation therapies such as radiofrequency ablation or cryotherapy. Electroporation means the formation of nanoscale pores in the cell membrane when certain electric fields are applied across the cell. This phenomenon can be reversible or irreversible according to the strength of the electric field. This non-thermal ablation provides entire tumor cell death preserving the surrounding important structures, such as vessels, bile ducts, and nerves. Tissue regeneration speed after the treatment is considerably faster than that of other ablation techniques. IRE could have potential advantages compared with thermal ablative modalities. Various tumors including liver cancer, pancreatic cancer, lung cancer, prostatic cancer and so on may be included in the application. Short-term treatment outcome is satisfactory and continued exploration is needed in human tumors.

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We report a woman in her late 60s with hepatocellular carcinoma in whom the tumor was successfully treated by irreversible electroporation (IRE). Vascular-phase contrast-enhanced US (CEUS) with Sonazoid and dynamic CT at 1 day after treatment showed no tumor enhancement, but the safety margin of ablation appeared to be insufficient. On the other hand, in Kupffer-phase CEUS, the ablation zone showed a clear contrast defect with a sufficient ablation margin, indicating cell death of hepatocytes, cancer cells, and Kupffer cells in this area following IRE treatment. Very similar findings were observed in hepatobiliary-phase Gd-EOB-DTPA-enhanced MRI at 7 days after treatment. These results suggest that both Kupffer-phase CEUS and hepatobiliary-phase Gd-EOB-DTPA-enhanced MRI may be useful for assessing the ablation zone in patients who have undergone IRE.

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IRE（Irreversible electroporation）は，2008年に米国で市販され，軟部組織の悪性腫瘍の治療に広く使われるようになった．中でも膵癌は放射線療法以外によい局所療法がないことから，IREの治療対象として注目されている．IREはnon-thermal ablationの局所治療法であり，胆管，膵管，血管，消化管などの構造を温存して，細胞のみに細胞死を惹起せしめることから，切除不能局所進行膵癌の治療法として期待されている．本稿では，IREの原理から臨床応用まで，膵癌の新治療法について概説する．

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Various ablation therapies, such as cryoablation (CA), radiofrequency ablation (RFA), mi-crowave ablation, irreversible electroporation, and high intensity focused ultrasound, are performed for renal cell carcinoma worldwide. In Japan, of these, only CA is covered by national insurance now and CA and RFA are often performed mainly for non-candidates for surgical resection. These ablation therapies are less invasive than surgery and can be performed per-cutaneously under image guidance and local anesthesia. Both CA and RFA have high technical effectiveness (>90% local tumor control). They are safe and their complications are usually minor and asymptomatic. Complications include bleeding, thermal injury of the surrounding organs, infection, pneumothorax, and dissemination. As another advantage, renal function is less affected by ablation therapies. The opportunities of ablation therapies will increase more in the future.

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画像技術の進歩によって，超音波（US）やコンピューター断層撮影（CT）あるいは磁気共鳴映像法（MRI）から得られた三次元画像データは，超音波プローブの動きと同期してリアルタイムに表示することが可能である．CT/MR-US fusion imagingはUSで描出困難な肝細胞癌（HCC）の視認性を改善し，また病変と肝内脈管との三次元的な位置関係の理解を支援する．穿刺局所療法の「ターゲティング」としてのフュージョン画像の利用によって，描出困難なHCCに対する高い治療成功率（94.4～100％）と低い局所再発率（0～8.3％）が得られたと報告されている．また，フュージョン画像では焼灼治療前後のUS画像同士の比較や重ね合わせ機能も活用することができ，穿刺局所療法の「モニタリング」としての新たな役割が期待される．US-US fusion imagingでは左右対比によって治療部位のUS評価を可能にし，US-US overlay fusionでは焼灼高エコー域への腫瘍像の投影によって焼灼マージンの視覚化が可能となった．US-US overlay fusionを穿刺局所療法に活用することで安定的に安全マージンの確保が行える点で非常に有用であり，その結果局所再発のリスク低減にも貢献できる．本稿では肝癌の穿刺局所療法におけるUSフュージョン画像の治療支援の現状を総括する．

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