Miller Naomi R, Bamber Jeffrey C, ter Haar Gail R
Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Trust, Sutton, Surrey, UK.
Ultrasound Med Biol. 2004 Mar;30(3):345-56. doi: 10.1016/j.ultrasmedbio.2003.11.016.
Ultrasonic estimation of heat-induced echo strain has been suggested as a noninvasive technique for guiding focused ultrasound (US) surgery (FUS), that is, for predicting the location of the thermal lesion before it is formed. The proposed strategy is to run the FUS system at a nonablative intensity and to use a diagnostic transducer to image the heat-induced echo strain, which, over a sufficiently small temperature range, is proportional to the temperature rise. The principal aim of this in vitro study was to determine if temperature-induced strain imaging is likely to be able to visualise the small (< 0.5%) strains that one would be restricted to in vivo. Temperature rises ranging from approximately 2 degrees C to 15 degrees C (starting at approximately 25 degrees C) were induced in bovine liver samples using an FUS system. The pre- and post-heated US images were processed to produce images of the apparent axial strain. These images were found to possess excellent spatial and contrast resolution, so that the hot spot remained clearly visible even when the spatial peak strain value was approximately 0.2% (corresponding to temperature rises on the order of 2 to 5 degrees C). Good repeatability in the strain images was observed within and between tissue samples. Artefacts due to thermoacoustic refraction were seen distal to the heated region, but they did not reduce hot spot visibility. The length of the hot spot exceeded that of the subsequent ablation (by approximately 200%), which was to be expected given that temperature imaging depicts the entire area over which the temperature has increased relative to the baseline. We conclude that temperature-induced strain imaging for the guidance of FUS in the liver is likely to be feasible, provided that it will be possible either to neglect or to correct for the additional sources of error (such as cardiac-induced motion) that will arise in vivo.
超声估计热诱导回声应变已被提议作为一种用于引导聚焦超声（US）手术（FUS）的非侵入性技术，即用于在热损伤形成之前预测其位置。所提出的策略是使FUS系统以非消融强度运行，并使用诊断换能器对热诱导回声应变进行成像，在足够小的温度范围内，该应变与温度升高成正比。这项体外研究的主要目的是确定温度诱导应变成像是否有可能可视化在体内会受到限制的小应变（<0.5%）。使用FUS系统在牛肝样本中诱导出约2℃至15℃（起始温度约为25℃）的温度升高。对加热前后的超声图像进行处理以生成表观轴向应变图像。发现这些图像具有出色的空间和对比度分辨率，因此即使空间峰值应变值约为0.2%（对应于约2至5℃的温度升高）时，热点仍清晰可见。在组织样本内部和之间观察到应变图像具有良好的重复性。在加热区域远端可见由于热声折射引起的伪像，但它们并未降低热点的可见性。热点的长度超过了随后消融区域的长度（约200%），考虑到温度成像描绘了相对于基线温度升高的整个区域，这是可以预期的。我们得出结论，在肝脏中用于引导FUS的温度诱导应变成像可能是可行的，前提是有可能忽略或校正体内会出现的其他误差来源（如心脏引起的运动）。
