School of Microelectronics, Tianjin University, Tianjin, China.
Department of Electrical Engineering, Chang-Gung University, Taoyuan, Taiwan.
Sci Rep. 2020 Mar 25;10(1):5468. doi: 10.1038/s41598-020-62363-7.
High-intensity focused ultrasound (HIFU) is a well-accepted tool for noninvasive thermal therapy. To control the quality of HIFU treatment, the focal spot generated in tissues must be localized. Ultrasound imaging can monitor heated regions; in particular, the change in backscattered energy (CBE) allows parametric imaging to visualize thermal information in the tissue. Conventional CBE imaging constructed in the spatial domain may be easily affected by noises when the HIFU focal spot is visualized. This study proposes frequency-domain CBE imaging to improve noise tolerance and image contrast in HIFU focal spot monitoring. Phantom experiments were performed in a temperature-controlled environment. HIFU of 2.12 MHz was applied to the phantoms, during which a clinical scanner equipped with a 3-MHz convex array transducer was used to collect raw image data consisting of backscattered signals for B-mode, spatial-, and frequency-domain CBE imaging. Concurrently, temperature changes were measured at the focal spot using a thermocouple for comparison with CBE values by calculating the correlation coefficient r. To further analyze CBE image contrast levels, a contrast factor was introduced, and an independent t-test was performed to calculate the probability value p. Experimental results showed that frequency-domain CBE imaging performed well in thermal distribution visualization, enabling quantitative detection of temperature changes. The CBE value calculated in the frequency domain also correlated strongly with that obtained using the conventional spatial-domain approach (r = 0.97). In particular, compared with the image obtained through the conventional method, the contrast of the CBE image obtained using the method based on frequency-domain analysis increased by 2.5-fold (4 dB; p < 0.05). Frequency-domain computations may constitute a new strategy when ultrasound CBE imaging is used to localize the focal spot in HIFU treatment planning.
高强度聚焦超声（HIFU）是一种广泛认可的无创热疗工具。为了控制 HIFU 治疗的质量，必须对组织中产生的焦点进行定位。超声成像是监测加热区域的手段；特别是，背散射能量（CBE）的变化允许参数成像来可视化组织中的热信息。在可视化 HIFU 焦点时，在空间域中构建的传统 CBE 成像可能很容易受到噪声的影响。本研究提出了频域 CBE 成像，以提高 HIFU 焦点监测中的噪声容限和图像对比度。在温度受控的环境中进行了体模实验。应用 2.12MHz 的 HIFU 于体模，在此期间，配备 3MHz 凸阵换能器的临床扫描仪用于收集由背散射信号组成的原始图像数据，用于 B 模式、空间域和频域 CBE 成像。同时，使用热电偶在焦点处测量温度变化，以便通过计算相关系数 r 与 CBE 值进行比较。为了进一步分析 CBE 图像对比度水平，引入了对比度因子，并进行了独立 t 检验以计算概率值 p。实验结果表明，频域 CBE 成像在热分布可视化方面表现良好，能够定量检测温度变化。在频域中计算的 CBE 值与使用传统空间域方法获得的值也具有很强的相关性（r=0.97）。特别是与传统方法获得的图像相比，基于频域分析的方法获得的 CBE 图像的对比度提高了 2.5 倍（4dB；p<0.05）。在使用超声 CBE 成像定位 HIFU 治疗计划中的焦点时，频域计算可能构成一种新策略。
