Rahimian Siavash, Tavakkoli Jahan
Department of Physics, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada.
J Ther Ultrasound. 2013 Sep 2;1:14. doi: 10.1186/2050-5736-1-14. eCollection 2013.
This study investigated the dynamic changes of tissue attenuation coefficients before, during, and after high-intensity focused ultrasound (HIFU) treatment at different total acoustic powers (TAP) in ex vivo porcine muscle tissue. It further assessed the reliability of employing changes in tissue attenuation coefficient parameters as potential indicators of tissue thermal damage.
Two-dimensional pulse-echo radio frequency (RF) data were acquired before, during, and after HIFU exposure to estimate changes in least squares attenuation coefficient slope (Δβ) and attenuation coefficient intercept (Δα 0). Using the acquired RF data, Δβ and Δα 0 images, along with conventional B-mode ultrasound images, were constructed. The dynamic changes of Δβ and Δα 0, averaged in the region of interest, were correlated with B-mode images obtained during the HIFU treatment process.
At a HIFU exposure duration of 40 s and various HIFU intensities (737-1,068 W/cm(2)), Δβ and Δα 0 increased rapidly to values in the ranges 1.5-2.5 dB/(MHz.cm) and 4-5 dB/cm, respectively. This rapid increase was accompanied with the appearance of bubble clouds in the B-mode images. Bubble activities appeared as strong hyperechoic regions in the B-mode images and caused fluctuations in the estimated Δβ and Δα 0 values. After the treatment, Δβ and Δα 0 values gradually decreased, accompanied by fade-out of hyperechoic spots in the B-mode images. At 10 min after the treatment, they reached values in ranges 0.75-1 dB/(MHz.cm) and 1-1.5 dB/cm, respectively, and remained stable within those ranges. At a long HIFU exposure duration of around 10 min and low HIFU intensity (117 W/cm(2)), Δβ and Δα 0 gradually increased to values of 2.2 dB/(MHz.cm) and 2.2 dB/cm, respectively. This increase was not accompanied with the appearance of bubble clouds in the B-mode images. After HIFU treatment, Δβ and Δα 0 gradually decreased to values of 1.8 dB/(MHz.cm) and 1.5 dB/cm, respectively, and remained stable at those values.
Δβ and Δα 0 estimations were both potentially reliable indicators of tissue thermal damage. In addition, Δβ and Δα 0 images both had significantly higher contrast-to-speckle ratios compared to the conventional B-mode images and outperformed the B-mode images in detecting HIFU thermal lesions at all investigated TAPs and exposure durations.
本研究调查了高强度聚焦超声（HIFU）在不同总声功率（TAP）下对离体猪肌肉组织进行治疗前、治疗期间和治疗后的组织衰减系数动态变化。它还进一步评估了将组织衰减系数参数的变化用作组织热损伤潜在指标的可靠性。
在HIFU暴露前、暴露期间和暴露后采集二维脉冲回波射频（RF）数据，以估计最小二乘衰减系数斜率（Δβ）和衰减系数截距（Δα0）的变化。利用采集到的RF数据构建Δβ和Δα0图像以及传统B模式超声图像。在感兴趣区域内平均的Δβ和Δα0的动态变化与HIFU治疗过程中获得的B模式图像相关。
在HIFU暴露持续时间为40秒且HIFU强度各异（737 - 1068 W/cm²）时，Δβ和Δα0迅速增加，分别达到1.5 - 2.5 dB/（MHz·cm）和4 - 5 dB/cm的范围。这种快速增加伴随着B模式图像中气泡云的出现。气泡活动在B模式图像中表现为强高回声区域，并导致估计的Δβ和Δα0值波动。治疗后，Δβ和Δα0值逐渐下降，同时B模式图像中的高回声斑点逐渐消失。治疗后10分钟，它们分别达到0.75 - 1 dB/（MHz·cm）和1 - 1.5 dB/cm的范围，并在这些范围内保持稳定。在HIFU暴露持续时间约为10分钟且HIFU强度较低（117 W/cm²）时，Δβ和Δα0分别逐渐增加到2.2 dB/（MHz·cm）和2.2 dB/cm的值。这种增加并未伴随着B模式图像中气泡云的出现。HIFU治疗后，Δβ和Δα0分别逐渐下降到1.8 dB/（MHz·cm）和1.5 dB/cm的值，并在这些值处保持稳定。
Δβ和Δα0估计均为组织热损伤的潜在可靠指标。此外，与传统B模式图像相比，Δβ和Δα0图像的对比度与斑点比均显著更高，并且在所有研究的TAP和暴露持续时间下，在检测HIFU热损伤方面均优于B模式图像。
