Data acquisition and analyses for the development of diagnostic ultrasound safety

描述(由申请人提供)：当声波(例如诊断超声的脉冲)通过介质(例如组织)传播时，波的吸收和散射在该介质中引起净作用力，该净作用力被称为“辐射力”。这个力使介质从其平衡位置移位。一个相对较新的成像方法家族利用这种效应来获得定性的新类型的诊断信息。被称为声辐射力脉冲成像，或ARFI，由长的、相对高幅度的脉冲在组织中产生的辐射力产生的组织位移与标准成像产生的那些完全不同，并且位移的大小和时间动态提供关于组织的粘弹性属性的信息。这些技术使临床医生能够区分健康和受损或患病的组织。然而，ARFI使用的超声脉冲比目前用于超声成像的超声脉冲要长得多，而且通常幅度更高，而且有人担心，因为这些更长的脉冲不符合当前超声安全指数(即热指数(TI)和机械指数(MI))的基本假设，所以ARFI在某些情况下可能不安全。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，几乎没有客观数据来作为这些所需标准的基础。拟议研究项目的目标是通过开展几系列专门为获取制定此类标准所需的数据而专门设计的计算和实验研究，为建立包容而灵活的安全标准奠定基础。拟议项目的具体目标是：1)确定所有相关条件下球形气泡的惯性空化阈值(已确定6种条件，例如，除热损伤外，适用于机械设备的阈值标准、使用较长的声脉冲持续时间和双频曝光等)，2)确定ArfI类脉冲的温度-时间分布和热剂量(TD)(根据热剂量而不是目前所做的最大稳态温升制定安全标准，这是本提议的基础)，3)用吸收能量而不是时间来量化热剂量，并将这一新公式发展成普遍适用的超声剂量度量(首先遵循与电离辐射成功采用的发展路径，然后研究一个新提出的概念-热作用函数，它类似于经典力学的作用积分)。前两个目标相对集中，因为它们将提供数据来支持使用新的成像模式。第三个目标是开发一种暴露指标，以指导使用临床超声为诊断和治疗程序选择最佳参数。

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.