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An Overview of Ultrasonic Exposimetry and its Clinical Relevance
Published in Marvin C. Ziskin, Peter A. Lewin, Ultrasonic Exposimetry, 2020
Peter A. Lewin, Marvin C. Ziskin
Also, this chapter discusses the potential for in vivo cavitation, its detection, and its predictability using the newly developed mechanical index. The mechanical index is based on the evidence indicating that the ratio of the peak negative pressure squared and the frequency is constant for cavitation thresholds under pulsed ultrasound exposure. Both thermal and mechanical indices are intended to provide users with the most meaningful information about the potential occurrence of an adverse biological effect. These indices are developed for on-screen display, so that users of ultrasound equipment are provided with the information at the time of the actual clinical examination. Since the indices have attracted the interest of regulatory agencies, it is anticipated that on-screen display will become increasingly important in the future.
How Does Ultrasound Work?
Published in John McCafferty, James M Forsyth, Point of Care Ultrasound Made Easy, 2020
Although ultrasound has an excellent safety record, as the ultrasound wave travels through the body, some of its energy will be deposited within the tissues through which it is travelling. Two indices have been introduced and are shown on all ultrasound scanners to provide the user with information about the potential effects which may result from the use of ultrasound. The Thermal Index (TI) provides an indication of the relative potential for a temperature rise in tissue. Three types of thermal indices may be shown: TIS (thermal index soft tissue) when insonating soft tissue; TIB (thermal index bone) when insonating near bone at focal position; and TIC (thermal index cranial) when the transducer is scanning close to bone. The Mechanical Index (MI) provides an indication of the potential of the ultrasound beam to produce a bioeffect from a non-thermal (mechanical) effect.
FUS-Mediated Image-Guided Neuromodulation of the Brain
Published in Yu Chen, Babak Kateb, Neurophotonics and Brain Mapping, 2017
Seung-Schik Yoo, Wonhye Lee, Ferenc A. Jolesz
A summary of safety concerns and its remedies in the context of using low-intensity FUS for neuromodulation are listed in Table 23.1. The dosimetry of exposure to the ultrasound is governed by international standards and national regulations (IEC standard 60601 part 1 and part 2). For example, the acoustic intensity level of 3 W/cm2 is set as the limit for therapeutic equipment by the IEC 60601, part 2 standard (Duck 2007). For the ultrasound imager, the upper limit of the mechanical index (MI) is 1.9 according to the U.S. Food and Drug Administration (FDA) safety guideline (Duck 2007). Most of the previously reported ultrasound-mediated brain neuromodulation studies were performed within these guidelines.
Production of acoustic radiation force using ultrasound: methods and applications
Published in Expert Review of Medical Devices, 2018
There are safety issues related to the use of ARF in humans. The Food and Drug Administration (FDA) regulates the acoustic output of diagnostic ultrasound instruments in the United States, and the IEC 60601–2-37 provides international guidance for safety requirements for ultrasonic medical diagnostic and monitoring equipment [180]. The main bioeffects of ultrasound are thermal and mechanical. With intense, long duration pulses, there is a risk of heating the tissue either at the focal region or at the probe-skin interface, especially if the duty cycle of the ARF push pulses is high. The FDA places limits on the spatial-peak temporal average intensity (Ispta,0.3), which has to be under 720 mW/cm2 for most diagnostic imaging applications that are not related to fetal or ophthalmologic imaging, where the limits are lower. The subscript 0.3 denotes that the pressure fields are derated by 0.3 dB/cm/MHz to conservatively account for attenuation experienced when propagating through soft tissues. Additionally, to prevent thermal damage for diagnostic uses, the Thermal Index must be lower than 6.0, which indicates that during the pulse sequence or scanning sequence, the temperature increase must be lower than 6.0 °C. Additionally, there are limits related to mechanical effects that are meant to prevent the occurrence of cavitation, or the creation of bubbles in the tissue. If the bubbles collapse at a high rate, they can produce high temperature and pressure, which can damage cells. The Mechanical Index (MI) is a predictor of the occurrence of cavitation, and the FDA sets the MI0.3 limit at 1.9. The MI is calculated as
Thermal ablation of hepatocellular carcinoma in patients with abnormal coagulation function
Published in International Journal of Hyperthermia, 2018
Qiannan Huang, Erjiao Xu, Lei Tan, Qingjing Zeng, Rongqin Zheng, Kai Li
Radiofrequency ablation (RFA) was conducted using the cool-tip (Valleylab Corp, USA). Microwave ablation (MWA) was conducted using the Kangyou MWA system (Nanjing, China). The Mylab Twice (Esaote, Italy) equipment with an abdominal probe CA541 (1–8 MHz) was used for ultrasound examination. Contrast enhanced ultrasoundgraphy (CEUS) was performed using the real-time contrast-enhanced imaging technique with a mechanical index less than 0.05. SonoVue (Bracco, Italy) was used as the ultrasound contrast agent, which was infused through a peripheral vein at a dose of 2.4 ml and washed with 5 ml sterile saline.