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传播，例如，在组织中，波的吸收和散射在介质中引起称为“辐射力”的净力。这个力使介质从其平衡位置移动。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型诊断信息。称为声辐射力脉冲成像或ARFI，由长的、相对高振幅的脉冲在组织中产生的辐射力产生与由标准成像产生的组织位移完全不同的组织位移，并且位移的幅度和时间动态提供关于组织的粘弹性性质的信息。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，ARFI采用的超声脉冲比目前用于超声成像的脉冲长得多，并且通常具有更高的幅度，并且存在这样的担忧，即，由于这些较长的脉冲不符合当前超声安全指数的基本假设，即，热指数（TI）和机械指数（MI）ARFI在某些情况下可能不安全。越来越需要制定国家和国际标准，以确保ARFI成像期间的患者安全。目前，作为这些必要标准基础的客观数据很少。拟议研究项目的目标是通过进行几系列专门为获取制定此类标准所需的数据而设计的计算和实验研究，为制定全面而灵活的安全标准做好准备。该项目的具体目标是：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，适用于除热损伤之外的机械损伤、使用较长的声脉冲持续时间和双频暴露等的阈值标准），2)确定ARFI型脉冲的温度-时间曲线和热剂量（制定基于热剂量的安全标准，而不是目前所做的最大稳态温升，是这项建议的基础），以及3）根据吸收的能量而不是时间来量化热剂量，并将这种新的公式发展成普遍适用的超声剂量度量（首先遵循类似于电离辐射成功使用的发展路径，然后研究一个新的概念，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以支持新成像模式的使用。第三个目标侧重于开发一个曝光度量，以指导使用临床超声的诊断和治疗程序的最佳参数的选择。 公共卫生相关性：该项目的总体目标是通过实现两个主要目标来确保诊断超声的安全性：1）提供理论和实验数据，声辐射力脉冲成像（ARFI）成像方法的国家和国际安全标准可以基于这些数据，和2）开发一个新的数学公式，使医生能够确定不同诊断目的的最佳超声暴露设置一个相对较新的家庭的成像方法在诊断超声。这些技术允许医生区分健康组织与患病或以某种方式受伤的组织。然而，ARFI可以采用比当前用于超声成像的超声脉冲长得多并且通常具有更高幅度的超声脉冲。正因为如此，人们担心将这些技术引入临床可能会危及诊断超声在50多年的医疗实践中保持的良好安全记录。该项目旨在提供理论和实验数据，并以此为基础制定适当的国家和国际安全标准，以帮助确保超声保持其作为医生可用的所有成像方法中最安全的独特地位。这项工作的第二个目标是开发一个全新的数学公式，使医生能够确定最佳的超声暴露设置，以获得必要的诊断信息，通过使用最低的总能量。该项目的结果将促进对医学超声方法的理解，并有助于确保现在和未来诊断超声的安全性。

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.