Purpose

A real-time and non-invasive thermometry technique is essential in thermal therapies to monitor and control the treatment. Ultrasound is an attractive thermometry modality due to its relatively high sensitivity to change in temperature and fast data acquisition and processing capabilities. A temperature-sensitive acoustic parameter is required for ultrasound thermometry in order to track the changes in that parameter during the treatment. Currently, the main ultrasound thermometry methods are based on variation in the attenuation coefficient, the change in backscattered energy of the signal (CBE), the backscattered radio-frequency (RF) echo-shift due to change in the speed of sound and thermal expansion of the medium, and change in the amplitudes of the acoustic harmonics. In this work, an ultrasound thermometry method based on second harmonic CBE (CBE_h2) and combined fundamental and second harmonic CBE (CBE_comb) is used to produce 2D temperature maps, detect localized heated region generated by low intensity focused ultrasound (LIFU), and control temperature in the heated region.

Materials and methods

Ex vivo pork muscle tissue samples were exposed to localized LIFU heating source and 2D temperature maps were produced from the RF data acquired by a 4.2 MHz linear array probe using a Verasonics Vantage™ ultrasound scanner (Verasonics Inc., Redmond, WA) after the exposure. Calibrated needle thermocouples were also placed in the ex vivo tissue sample close to the LIFU focal zone for temperature calibration purposes. The estimated temperature maps were the established echo-shift technique. A tissue motion compensation algorithm was also used to reduce the susceptibility to motion artifacts.

Results

2D temperature maps were generated using CBE of acoustic harmonic and echo-shift techniques. The results show a direct correlation between the CBE of acoustic harmonics and focal tissue temperature for a range of temperatures from 37 °C (baseline) to 47 °C.

Conclusions

The findings of this study show that the CBE of acoustic harmonics technique can be used to noninvasively estimate temperature change in tissue in the hyperthermia temperature range.

中文翻译：

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利用声谐波的反向散射能量进行无创校准的组织温度估算

目的

实时，非侵入性测温技术对于热疗法中的监测和控制治疗至关重要。超声波是一种有吸引力的测温方式，因为它对温度变化具有相对较高的灵敏度，并具有快速的数据采集和处理能力。超声测温需要温度敏感的声学参数，以便跟踪治疗过程中该参数的变化。当前，主要的超声波测温方法是基于衰减系数的变化，信号的背向散射能量（CBE）的变化，由于声速和热膨胀的变化而导致的背向散射射频（RF）回波偏移介质的变化，以及声谐波幅度的变化。在这项工作中，_h2）以及组合的基波和二次谐波CBE（CBE _comb）用于生成2D温度图，检测由低强度聚焦超声（LIFU）生成的局部加热区域，并控制加热区域中的温度。

材料和方法

将离体的猪肌肉组织样品暴露于局部LIFU热源，暴露后，使用Verasonics Vantage™超声扫描仪（Verasonics Inc.，华盛顿州雷德蒙德）通过4.2 MHz线性阵列探针从RF数据获取二维温度图。校准的针型热电偶也放置在离LIFU聚焦区较近的离体组织样本中，以进行温度校准。估计的温度图是已建立的回波偏移技术。组织运动补偿算法也用于减少运动伪影的敏感性。

结果

使用声谐波的CBE和回声偏移技术生成2D温度图。结果表明，在从37°C（基线）到47°C的温度范围内，声谐波的CBE与焦点组织温度之间存在直接相关性。

结论

这项研究的结果表明，声谐波的CBE技术可用于无创地估计高温温度范围内组织的温度变化。