Data acquisition and analyses for the development of diagnostic ultrasound safety

描述（由申请人提供）：当声波（例如诊断超声脉冲）通过介质（例如组织）传播时，波的吸收和散射会在介质中产生净力，称为“辐射力”。这个力使介质偏离了它的平衡位置。一种相对较新的成像方法利用这种效应来获得定性的新型诊断信息。被称为声辐射力脉冲成像（ARFI）的辐射力在组织中产生的长，相对高振幅脉冲产生的组织位移与标准成像产生的组织位移完全不同，位移的大小和时间动态提供了组织粘弹性特性的信息。这些技术使临床医生能够区分健康组织与受损或患病组织。然而，与目前用于超声成像的超声脉冲相比，ARFI使用的超声脉冲要长得多，而且通常振幅更高，而且人们担心，由于这些较长的脉冲不符合当前超声安全指标（即热指数（TI）和机械指数（MI））的基本假设，因此ARFI在某些情况下可能是不安全的。越来越需要国家和国际标准来确保ARFI成像期间患者的安全。目前，很少有客观数据可以作为这些必要标准的基础。拟议的研究项目的目标是通过进行一系列专门设计的计算和实验研究，以获取制定此类标准所需的数据，从而提供全面而灵活的安全标准的创建。建议项目的具体目标是：1)确定球形气泡在所有相关条件下的惯性空化阈值（已经确定了6种条件，例如，除了热损伤之外，还适用于机械损伤的阈值标准，使用更长的声脉冲持续时间和双频暴露等），2)确定arfi型脉冲的温度-时间曲线和热剂量（TD）(根据热剂量的使用制定安全标准；而不是目前所做的最大稳态温升，这是本提案的基础),3)根据吸收能量而不是时间来量化热剂量，并将这个新公式发展成普遍适用的超声剂量度量(首先遵循电离辐射成功应用的发展路径，然后研究一个新制定的概念，热作用函数，这类似于经典力学中的作用积分)。前两个目标相对集中，因为它们将提供数据，以支持使用新的成像模式。第三个目标侧重于开发一个暴露度量，以指导使用临床超声诊断和治疗程序的最佳参数选择。

DESCRIPTION (provided by applicant): When acoustic waves, e.g., pulses of diagnostic ultrasound, propagate through a medium, e.g., tissue, absorption and scattering of the wave induce a net force, called a "radiation force", in the medium. This force displaces the medium from its equilibrium position. A relatively new family of imaging methods makes use of this effect to obtain qualitatively new types of diagnostic information. Termed Acoustic Radiation Force Impulse imaging, or ARFI, the radiation force produced in tissue by long, relatively high-amplitude pulses produces tissue displacements that are quite different from those produced by standard imaging, and the magnitude and temporal dynamics of the displacements provide information on the viscoelastic properties of the tissue. These techniques allow the clinician to distinguish healthy from damaged or diseased tissue. However, ARFI employs ultrasound pulses that are much longer, and often of higher amplitude, than those currently used for ultrasound imaging, and there is concern that because these longer pulses do not adhere to the fundamental assumptions underlying the current ultrasound safety indices, i.e., the thermal index (TI) and the mechanical index (MI), ARFI may be unsafe in certain circumstances. There is a growing need for national and international standards to ensure patient safety during ARFI imaging. At present, there are few objective data upon which to base these needed standards. The goal of the proposed research project is to provide for the creation of encompassing yet flexible safety standards by conducting several series of computational and experimental studies specifically designed to acquire the data needed to develop such standards. The Specific Aims of the proposed project are: 1) determine the threshold for inertial cavitation for spherical bubbles under all relevant conditions (6 conditions have been identified, e.g., threshold criteria appropriate for mechanical in addition to thermal damage, use of longer acoustic pulse durations and dual-frequency exposures, etc.), 2) determine the temperature-time profiles and thermal doses (TD) for ARFI-type pulses (development of safety standards based on use of the thermal dose, rather than the maximum steady-state temperature rise as is currently done, is fundamental to this proposal), and 3) quantify the thermal dose in terms of absorbed energy rather than time and develop this new formulation into a universally applicable ultrasound dose metric (first following a development path like that successfully employed with ionizing radiation, then investigating a newly formulated concept, the thermal action function, which is analogous to the action integral of classical mechanics). The first two aims are relatively focused in that they will provide data to support the use of new imaging modalities. The third aim focuses on developing an exposure metric to guide selection of optimal parameters for both diagnostic and therapeutic procedures using clinical ultrasound. PUBLIC HEALTH RELEVANCE: The overall goal of this project is to ensure the safety of diagnostic ultrasound by accomplishing two major objectives: 1) Provide both theoretical and experimental data upon which national and international safety standards for Acoustic Radiation Force Impulse imaging (ARFI) imaging methods can be based, and 2) Develop a new mathematical formula that will allow physicians to determine optimal ultrasound exposure settings for different diagnostic purposes ARFI is a relatively new family of imaging methods in diagnostic ultrasound. These techniques allow the physician to distinguish healthy tissue from tissue that is diseased or injured in some way. However, ARFI may employ ultrasound pulses that are much longer, and often of higher amplitude, than those currently used for ultrasound imaging. Because of this, there is concern that introduction of these techniques into the clinic may jeopardize the stellar safety record that diagnostic ultrasound has maintained over 5 decades of medical practice. This project is designed to provide both theoretical and experimental data upon which appropriate national and international safety standards can be based to help ensure that ultrasound preserves its unique position as the safest of all the imaging methods available to the physician. The second objective of this work is to develop an entirely new mathematical formula that will allow the physician to determine the very best ultrasound exposure settings to obtain the necessary diagnostic information by using the very lowest total energy. The results of this project will advance understanding of medical ultrasound methods and help ensure the safety of diagnostic ultrasound both now and well into the future.