Miller Naomi R, Bograchev Konstantin M, Bamber Jeffrey C
Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Sutton, Surrey, United Kingdom.
Ultrasound Med Biol. 2005 Mar;31(3):401-13. doi: 10.1016/j.ultrasmedbio.2004.11.014.
Ultrasonic temperature imaging is a promising technique for guiding focused ultrasound surgery (FUS). The FUS system is run at an initial, nonablative intensity and a diagnostic transducer images the heat-induced echo strain, which is proportional to the temperature rise. The echo strain image portrays an elliptical "hot spot" corresponding to the focal region of the therapy transducer. It is anticipated that such images will be used to predict the location of the thermal lesion that would be produced at an ablative intensity. We demonstrated in vitro that heat-induced echo strain images can visualize a spatial peak temperature rise of <2 degrees C (starting at room temperature). However, the imaging beam was perpendicular to the treatment beam in these experiments, whereas the most convenient approach in vivo would be to mount the imaging probe within the housing of the therapy transducer such that the two beams are coaxial. A previous simulation experiment predicted that echo strain images would be noisier for the coaxial configuration because sharp lateral gradients in axial displacement cause increased RF signal decorrelation within the beam width. The aim of the current study was to verify this prediction in vitro. We found, that for a temperature rise of approximately 4 degrees C, the mean contrast-to-noise ratio for coaxial and perpendicular echo strain images was 0.37 (+/-0.24) and 2.00 (+/-0.72) respectively. Furthermore, the decorrelation noise seen in the coaxial images obscured the posterior axial border of the hot spot. We conclude that the coaxial configuration will be useful for localizing the hot spot in the lateral direction. However, it may not be able to depict the axial extent of the hot spot or to portray a parameter that is directly related to temperature rise.
超声温度成像是一种用于引导聚焦超声手术（FUS）的很有前景的技术。FUS系统以初始的非消融强度运行，诊断换能器对热诱导的回声应变进行成像，该应变与温度升高成正比。回声应变图像描绘了一个与治疗换能器的焦点区域相对应的椭圆形“热点”。预计此类图像将用于预测在消融强度下产生的热损伤的位置。我们在体外证明，热诱导的回声应变图像可以可视化空间峰值温度升高<2摄氏度（从室温开始）。然而，在这些实验中成像束与治疗束垂直，而在体内最方便的方法是将成像探头安装在治疗换能器的外壳内，使两束光同轴。先前的模拟实验预测，对于同轴配置，回声应变图像会有更多噪声，因为轴向位移中的尖锐横向梯度会导致波束宽度内的射频信号去相关增加。本研究的目的是在体外验证这一预测。我们发现，对于大约4摄氏度的温度升高，同轴和垂直回声应变图像的平均对比度与噪声比分别为0.37（±0.24）和2.00（±0.72）。此外，同轴图像中看到的去相关噪声掩盖了热点的后轴向边界。我们得出结论，同轴配置将有助于在横向方向上定位热点。然而，它可能无法描绘热点的轴向范围或描绘与温度升高直接相关的参数。
