玉井 秀幸

Hideyuki TAMAI

和歌山県立医科大学第二内科

Second Department of Internal Medicine Wakayama Medical University

キーワード : ultrasonography, phase inversion, tissue harmonic imaging, tissue characterization

テストファントムを用いてwideband phase inversion tissue harmonic imagingと従来のエコー法を比較検討した結果, 方位, 距離分解能, コントラスト分解能の改善と, アーチファクトの低減効果が得られた. 肝細胞癌, 肝血管腫, 胆石において, エコー輝度から高調波強度の解析を行い, 高エコー型肝細胞癌, 肝血管腫, 純コレステロール胆石から強い高調波の発生がみられ, 組織性状診断における有用性が示唆された. 特に低または等エコー型肝細胞癌ではみられない輝度上昇が, 低または等エコー型肝血管腫で有意にみられ, 質的診断及び鑑別診断に有用な所見と考えられた(感度81.3%, 特異度79.2%). また土屋分類1型胆石(純コレステロール石)でのみ有意な輝度上昇がみられ, 質的診断に有用な所見と考えられた(感度100%, 特異度78.4%). 腹部疾患502例570病変に臨床応用した結果, 深度別での画質改善率は, 浅部領域, 中間領域, 深部領域でそれぞれ89.7%, 91.8%, 83.9%, 新病変検出率はそれぞれ5.7%, 7.0%, 3.6%, 画質悪化率それぞれ0%, 0.7%, 3.6%であり, 病変の深さに関わらず画質が改善した. Wideband phase inversion tissue harmonic imagingは従来のエコー法にとってかわり, 精密検査やスクリーニング検査に広く用いるべき検査である.

A series of experimental studies using a test phantom carried out to compare the basic characteristics of phase inversion tissue harmonic imaging (THI) and conventional sonography (CUS) clearly showed the superiority of tissue harmonic imaging over conventional sonography. Tissue harmonic imaging had higher axial, lateral, and contrast resolution and fewer side-lobe artifacts. Brightness measured to analyze the intensity of harmonics generated by hepatocellular carcinomas (HCC), hepatic hemangiomas, and gall stones in clinical cases clearly showed that hyperechoic hepatocelluar carcinomas, hepatic hemangiomas, and pure cholesterol stones generated more harmonics than adjacent background liver tissue. The brightness of hypoechoic or isoechoic hepatic hemangiomas was significantly increased on tissue harmonic imaging, while that of both hypoechoic and isoechoic hepatocellular carcinomas was not. Sensitivity and specificity in diagnosing hepatic hemangiomas were 81.3% and 79.2%, respectively. Likewise, the brightness of pure cholesterol stones, but not that of other gallstones, was significantly increased on tissue harmonic imaging: sensitivity and specificity for pure cholesterol stones were 100％ and 78.4％, respectively. These results indicate the usefulness of phase inversion tissue harmonic imaging in the tissue characterization. The next series included 502 cases with 570 abdominal nodules. We visualized each lesion at the same slice with both conventional sonography and tissue harmonic imaging and compared their image quality and rate of detection by depth of lesion. Rates of improvement were 89.7％, 91.8％, and 83.9％ in shallow, middle, and deep lesions, respectively. Respective rates of detection of new lesions were 5.7％, 7.0％, and 3.6％. Phase inversion tissue harmonic imaging visualized all lesions examined more clearly than conventional sonography, regardless of location. We thus suggest that phase inversion tissue harmonic imaging will replace conventional sonography as a screening method.