Department of Medical Imaging and Radiological Sciences, College of Medicine, Chang Gung University, Taoyuan 33302, Taiwan.
Med Phys. 2013 Jul;40(7):072901. doi: 10.1118/1.4808115.
Radiofrequency ablation (RFA) is a widely used alternative modality in the treatment of liver tumors. Ultrasound B-mode imaging is an important tool to guide the insertion of the RFA electrode into the tissue. However, it is difficult to visualize the ablation zone because RFA induces the shadow effect in a B-scan. Based on the randomness of ultrasonic backscattering, this study proposes ultrasound Nakagami imaging, which is a well-established method for backscattered statistics analysis, as an approach to complement the conventional B-scan for evaluating the ablation region.
Porcine liver samples (n = 6) were ablated using a RFA system and monitored by employing an ultrasound scanner equipped with a 7.5 MHz linear array transducer. During the stages of ablation (0-12 min) and postablation (12-24 min), the raw backscattered data were acquired at a sampling rate of 30 MHz for B-mode, Nakagami imaging, and polynomial approximation of Nakagami imaging. The contrast-to-noise ratio (CNR) was also calculated to compare the image contrasts of the B-mode and Nakagami images.
The results demonstrated that the Nakagami image has the ability to visualize changes in the backscattered statistics in the ablation zone, including the shadow region during RFA. The average Nakagami parameter increased from 0.2 to 0.6 in the ablation stage, and then decreased to approximately 0.3 at the end of the postablation stage. Moreover, the CNR of the Nakagami image was threefold that of the B-mode image, showing that the Nakagami image has a better image contrast for monitoring RFA. Specifically, the use of the polynomial approximation equips the Nakagami image with an enhanced ability to estimate the range of the ablation region.
This study demonstrated that ultrasound Nakagami imaging based on the analysis of backscattered statistics has the ability to visualize the RFA-induced ablation zone, even if the shadow effect exists in the B-scan.
射频消融（RFA）是治疗肝脏肿瘤的一种广泛应用的替代方法。B 型超声成像是引导 RFA 电极插入组织的重要工具。然而，由于 RFA 在 B 扫描中产生阴影效应，因此很难可视化消融区域。基于超声背散射的随机性，本研究提出了超声 Nakagami 成像，这是一种成熟的背散射统计分析方法，作为补充传统 B 扫描评估消融区域的方法。
使用 RFA 系统对猪肝样本（n=6）进行消融，并使用配备 7.5 MHz 线性阵列换能器的超声扫描仪进行监测。在消融（0-12 分钟）和消融后（12-24 分钟）阶段，以 30 MHz 的采样率采集原始背散射数据，用于 B 模式、Nakagami 成像和 Nakagami 成像的多项式逼近。还计算了对比度噪声比（CNR），以比较 B 模式和 Nakagami 图像的图像对比度。
结果表明，Nakagami 图像具有可视化消融区域中背散射统计变化的能力，包括 RFA 期间的阴影区域。消融阶段的平均 Nakagami 参数从 0.2 增加到 0.6，然后在消融后阶段结束时降至约 0.3。此外，Nakagami 图像的 CNR 是 B 模式图像的三倍，表明 Nakagami 图像具有更好的监测 RFA 的图像对比度。具体来说，多项式逼近的使用赋予了 Nakagami 图像增强的估计消融区域范围的能力。
本研究表明，基于背散射统计分析的超声 Nakagami 成像具有可视化 RFA 诱导的消融区域的能力，即使 B 扫描中存在阴影效应。
