Arthur R M, Straube W L, Trobaugh J W, Moros E G
Department of Electrical and Systems Engineering, Washington University School of Engineering, St. Louis, Missouri, USA.
Int J Hyperthermia. 2005 Sep;21(6):589-600. doi: 10.1080/02656730500159103.
Ultrasound is an attractive modality for temperature monitoring because it is non-ionizing, convenient, inexpensive and has relatively simple signal processing requirements. This modality may be useful for temperature estimation if a temperature-dependent ultrasonic parameter can be identified, measured and calibrated. The most prominent methods for using ultrasound as a non-invasive thermometer exploit either (1) echo shifts due to changes in tissue thermal expansion and speed of sound (SOS), (2) variation in the attenuation coefficient or (3) change in backscattered energy from tissue inhomogeneities. The use of echo shifts has received the most attention in the last decade. By tracking scattering volumes and measuring the time shift of received echoes, investigators have been able to predict the temperature from a region of interest both theoretically and experimentally in phantoms, in isolated tissue regions in vitro and preliminary in vivo studies. A limitation of this method for general temperature monitoring is that prior knowledge of both SOS and thermal-expansion coefficients is necessary. Acoustic attenuation is dependent on temperature, but with significant changes occurring only at temperatures above 50 degrees C, which may lead to its use in thermal ablation therapies. Minimal change in attenuation, however, below this temperature range reduces its attractiveness for use in clinical hyperthermia. Models and measurements of the change in backscattered energy suggest that, over the clinical hyperthermia temperature range, changes in backscattered energy are dependent on the properties of individual scatterers or scattering regions. Calibration of the backscattered energy from different tissue regions is an important goal of this approach. All methods must be able to cope with motion of the image features on which temperature estimates are based. A crucial step in identifying a viable ultrasonic approach to temperature estimation is its performance during in vivo tests.
超声是一种颇具吸引力的温度监测方式，因为它是非电离的、便捷、廉价且信号处理要求相对简单。如果能够识别、测量并校准与温度相关的超声参数，这种方式可能有助于温度估计。将超声用作非侵入式温度计的最主要方法有：（1）利用由于组织热膨胀和声速（SOS）变化引起的回波偏移；（2）利用衰减系数的变化；（3）利用组织不均匀性引起的背向散射能量变化。在过去十年中，回波偏移的应用受到了最多关注。通过跟踪散射体积并测量接收到的回波的时间偏移，研究人员已经能够在体模、体外分离的组织区域以及初步的体内研究中，从理论和实验上预测感兴趣区域的温度。这种用于一般温度监测的方法的一个局限性在于，需要SOS和热膨胀系数的先验知识。声衰减取决于温度，但只有在温度高于50摄氏度时才会发生显著变化，这可能导致其在热消融治疗中的应用。然而，在该温度范围以下，衰减变化极小，这降低了其在临床热疗中的吸引力。背向散射能量变化的模型和测量表明，在临床热疗温度范围内，背向散射能量的变化取决于单个散射体或散射区域的特性。对来自不同组织区域的背向散射能量进行校准是这种方法的一个重要目标。所有方法都必须能够应对温度估计所基于的图像特征的运动。确定一种可行的超声温度估计方法的关键步骤是其在体内测试中的性能。
