小榑 二世

Kazutoki KOGURE

杏林大学医学部第三内科

Third Department of Internal Medicine, Kyorin University School of Medicine

キーワード : radio-frequency signal, K distribution, hemangioma of the liver, hepatocellular carcinoma, ultrasonography

目的：近年, 超音波診断装置の進歩などにより小さな肝細胞癌を発見することが可能となったが, 典型的な超音波像を呈 さない例も多く, また, 術者による診断能力の差も存在するため客観性の向上のために定量的な診断手法の確立が望まれ ている. 肝腫瘍からのradio-frequency (RF) 信号はK 分布にしたがうことが知られている. K 分布は不均一性部からの 後方散乱信号の統計的性質を特徴づけるために用いられている. そこで肝血管腫, 肝細胞癌よりRF 信号を取得しK 分 布のパラメータであるφ(RF 信号の振幅の二乗平均) とα(有効散乱体個数を算出し肝腫瘍の定量的評価) について検 討した. 対象：肝血管腫10 例10 結節, 肝細胞癌24 例27 結節である. 方法：超音波診断装置はALOKA 社製SSD-1000 を使用した. 肝腫瘍に一致したRF 信号内に279 点よりなる測定単位を設定し, このヒストグラムに最も適合するK 分 布のパラメータをχ²適合度検定を用い算出した. 結果：φは肝血管腫で高値を示し両腫瘍間で有意差が認められた(p＜ 0.05). αは両腫瘍間で有意差は認められなかった. 考察：αは両腫瘍とも同等であったがφは肝血管腫の方が高値であ り肝血管腫の内部には散乱しやすい状況が存在することが推定された. また, これらは従来から報告されてきている病理 学的所見にも一致しておりK 分布のパラメータを用いることで腫瘍の定量的評価が可能と考えられた.

Purpose: In recent years, advances in ultrasonographic techniques have allowed the detection of even small hepatocellular carcinomas. However, many cases do not show distinctive ultrasonographic features. A quantitative ultrasonographic procedure for making the diagnosis would therefore be desirable. It is recognized that radio-frequency (RF) signals from hepatic tumors conform to the K distribution. The K distribution is used for the characterization of the statistical properties of backscattering signals from heterogeneous regions. In this study, RF signals were acquired from hemangioma of the liver (hemangioma) and hepatocellular carcinoma (HCC), and parameters of the K distribution, i.e., φ(the mean square of the amplitude of RF signals) and α(the number of effective scatterers), were calculated for the quantitative ultrasonographic evaluation of hepatic tumors. Methods: This study included 10 nodules of 10 patients with hemangioma and 27 nodules of 24 patients with HCC. The A-mode RF signals passing through the hepatic tumors were acquired with an Aloka SSD-1000 ultrasound system, and measurement units comprising 279 points were set on the RF signals corresponding to the tumor lesion. The parameters of the K distribution that were most consistent with the histogram were calculated and assessed. Results: With regard to φ, the values were high in hemangioma, and there was a significant (P＜0.05) difference in the φ value between hemangioma and HCC. On the other hand, there was no significant difference in the a value between hemangioma and HCC. Conclusion: The α values of hemangioma were equivalent to those of HCC, while the φ values for hemangioma were higher than those for HCC. It was deduced from these observations that a situation in which an electron beam is likely to scatter exists in the tumor. This is also consistent with the pathological findings reported from previous studies. The use of these parameters is expected to allow quantitative ultrasonographic evaluation of hepatic tumors.