Abstract：
The clinical use of high intensity focused ultrasound (HIFU) therapy for noninvasive tissue ablation has recently gained momentum. Guidance is provided by either magnetic resonance imaging (MRI) or conventional B-mode ultrasound imaging, each with its own advantages and disadvantages. The main limitation of ultrasound imaging is its inability to provide temperature measurements over the ranges corresponding to the target temperatures during ablative thermal therapies (between 55 °C and 70 °C). Here, variations in ultrasound backscattered energy (ΔBSE) were used to monitor temperature increases in liver tissue up to an absolute value of 90 °C during and after HIFU treatment. In vitro experimental measurements were performed in 47 bovine liver samples using a toroidal HIFU transducer operating at 2.5 MHz to increase the temperature of tissues. An ultrasound imaging probe working at 7.5 MHz was placed in the center of the HIFU transducer to monitor the backscattered signals. The free-field acoustic power was set to 9 W, 12 W or 16 W in the different experiments. HIFU sonications were performed for 240 s using a duty cycle of 83 % to allow ultrasound imaging and raw radiofrequency data acquisition during exposures. Measurements showed a linear relationship between ΔBSE (in dB) and temperature (r = 0.94, p < 0.001) over a temperature range from 37 °C to 90 °C, with a high reliability of temperature measurements below 75 °C. Monitoring can be performed at the frame rate of ultrasound imaging scanners with an accuracy within an acceptable threshold of 5 °C, given the temperatures targeted during thermal ablations. If the maximum temperature reached is below 70 °C, ΔBSE is also a reliable approach for estimating the temperature during cooling. Histological analysis shown the impact of the treatment on the spatial arrangement of cells that can explain the observed variation of ΔBSE. These results demonstrate the ability of ΔBSE measurements to estimate temperature in ultrasound images within an effective therapeutic range. This method can be implemented clinically and potentially applied to other thermal-based therapies.
摘要：
高强度聚焦超声（HIFU）治疗用于非侵入性组织消融的临床应用最近获得了动力。通过磁共振成像（MRI）或传统的B型超声成像提供指导，每个人都有自己的优点和缺点。超声成像的主要限制是其不能在消融热治疗期间(在55°C和70°C之间)提供与目标温度相对应的范围内的温度测量。这里,在HIFU治疗期间和之后，使用超声反向散射能量（ΔBSE）的变化来监测肝脏组织的温度升高，直至90°C的绝对值。使用在2.5MHz下操作的环形HIFU换能器在47个牛肝样品中进行体外实验测量以提高组织的温度。将工作在7.5MHz的超声成像探头放置在HIFU换能器的中心以监测反向散射信号。自由场声功率设定为9W,在不同的实验中12W或16W。使用83％的占空比进行HIFU超声处理240s，以允许在曝光期间进行超声成像和原始射频数据采集。测量结果表明，在37°C至90°C的温度范围内，ΔBSE（以dB为单位）与温度（r=0.94，p<0.001）之间呈线性关系，在低于75°C的温度测量具有高可靠性。可以以超声成像扫描仪的帧速率进行监测，精度在5°C的可接受阈值内，给定热消融期间的目标温度。如果达到的最高温度低于70°C，ΔBSE也是用于估计冷却期间的温度的可靠方法。组织学分析显示处理对细胞的空间排列的影响,其可以解释所观察到的ΔBSE的变化。这些结果证明了ΔBSE测量在有效治疗范围内估计超声图像中的温度的能力。该方法可以在临床上实施并且潜在地应用于其他基于热的治疗。
