Institute of Biomedical Engineering, Department of Engineering Science, University of Oxford, Oxford, UK.
Ultrasound Med Biol. 2011 Jun;37(6):922-34. doi: 10.1016/j.ultrasmedbio.2011.02.016.
Thermal ablation by high-intensity focused ultrasound (HIFU) shows great promise as a noninvasive cancer therapy. This work proposes a novel method of real-time HIFU treatment monitoring that uses the passively monitored acoustic signal emanating from the focus during HIFU exposure. We performed 212 exposures in seven freshly excised ox livers using 1.067-MHz HIFU at a 95% duty cycle for a range of insonation durations and acoustic intensities. Acoustic emissions were recorded using a 15-MHz passive detector aligned confocally and coaxially with the HIFU transducer. Lesion presence and size were ascertained by slicing the tissue in the transverse and axial focal planes post exposure. Our results demonstrate that successful formation of HIFU lesions in ex vivo ox liver is highly correlated with the presence of pronounced dips in the magnitude of the received signal at integer harmonics of the insonation frequency. A detector based on this observation predicted lesioning with >80% accuracy in regimes that were very likely to create lesions (≥60 J of energy) and had an error rate of <6% for exposures that were too short to cause lesioning (≤1 s long). The overall sensitivity and specificity of the detector were 75.6% and 74.2%, respectively. The proposed detector could therefore provide a low-cost means of effectively monitoring clinical HIFU treatments passively and in real time.
高强度聚焦超声（HIFU）的热消融技术在非侵入性癌症治疗方面显示出巨大的潜力。本工作提出了一种新的实时 HIFU 治疗监测方法，该方法利用 HIFU 辐照期间从焦点发出的被动监测声信号。我们在七个新鲜离体牛肝中进行了 212 次 1.067MHz HIFU 辐照，95%占空比，辐照持续时间和声强范围广泛。使用与 HIFU 换能器共焦共轴的 15MHz 被动探测器记录声发射。辐照后，通过在横切和轴向焦平面上切片确定组织中的损伤存在和大小。我们的结果表明，在离体牛肝中成功形成 HIFU 损伤与接收信号在辐照频率整数谐波处的幅度明显下降的存在高度相关。基于这一观察结果的探测器在非常有可能形成损伤的区域（≥60J 能量）以超过 80%的准确率预测了损伤，并在太短而不会导致损伤的情况下（≤1s）的辐照具有小于 6%的错误率。该探测器的总体灵敏度和特异性分别为 75.6%和 74.2%。因此，该探测器可以提供一种低成本的方法，用于有效地被动和实时监测临床 HIFU 治疗。
