Note to Physicians and Sonographers on Potential Underestimation of Acoustic Safety Indexes for Diagnostic Array Transducers.

Two scientists from the U.S. Food and Drug Administration comment on limitations of acoustic safety indexes that can arise from spatial averaging effects of hydrophones that are used to measure acoustic output.

Challenges and regulatory considerations in the acoustic measurement of high-frequency (>20 MHz) ultrasound.

This article examines the challenges associated with making acoustic output measurements at high ultrasound frequencies (>20 MHz) in the context of regulatory considerations contained in the US Food and Drug Administration industry guidance document for diagnostic ultrasound devices. Error sources in the acoustic measurement, including hydrophone calibration and spatial averaging, nonlinear distortion, and mechanical alignment, are evaluated, and the limitations of currently available acoustic measurement instruments are discussed. An uncertainty analysis of acoustic intensity and power measurements is presented, and an example uncertainty calculation is done on a hypothetical 30-MHz high-frequency ultrasound system.

Effects of gas pockets on high-intensity focused ultrasound field.

The paper describes experimental and numerical studies of the effects of gas pockets on a high-intensity focused ultrasound (HIFU) field. Air bubbles ranging from 0.8 to 2.

An acoustic backscatter-based method for localization of lesions induced by high-intensity focused ultrasound.

Ultrasound B-mode visualization of lesions produced in soft tissues using high-intensity focused ultrasound (HIFU) has been shown to be challenging when there is no cavitation activity and, therefore, no hyperechogenecity in the focal region. We investigated a method for the visualization and localization of HIFU-induced lesions after HIFU delivery was complete based on the change in backscattered radio-frequency (RF) signals. A HIFU transducer was used with focal dimension of 8 mm by 2 mm working at 5 MHz.

Detection and localization of peripheral vascular bleeding using Doppler ultrasound.

Background: Hemorrhage from wounds in the extremities is the leading cause of preventable death on the battlefield. To successfully treat these injuries, the exact source of bleeding must be localized.

Objective: The purpose of this study was to determine the feasibility of using Doppler ultrasound to precisely detect and localize peripheral vascular bleeding.

A targeting method based on acoustic backscatter for treatment planning in tissue ablation using focused ultrasound.

High-intensity focused ultrasound (HIFU) is a therapeutic modality that can produce coagulative necrosis in biological tissue, noninvasively. This technique requires the determination of the focus of a HIFU transducer before treatment. We investigated a method to localize the focus based on the change in radio-frequency (RF) signal at HIFU intensity levels below the threshold for tissue damage.

Real-time 3D image-guided HIFU therapy.

Real-time three-dimensional ultrasound imaging (4D US) was utilized to monitor the treatment site during high-intensity focused ultrasound (HIFU) treatment. To obtain real-time monitoring during HIFU sonication, a 4D US imaging system and HIFU were synchronized and interference on the US image adjusted so that the region of interest was visible during treatment. The system was tested using tissue mimicking phantom gels and chicken breast tissue.

A localization method of lesions induced by High Intensity Focused Ultrasound based on acoustic backscatter change.

High Intensity Focused Ultrasound (HIFU) has been investigated as a therapeutic modality for many medical applications. We investigated a noninvasive technique for the localization of HIFU-induced lesions based on the change in backscattered radio frequency (RF) signals. HIFU was applied to chicken breast tissue and we compared lesion locations obtained from RF data with our processing method, from the dissected tissues after exposure, and from B-mode images if exposures had resulted in hyperecho.

A rapid three-dimensional high intensity focused ultrasound beam plotting.

The goal of this study was to develop a rapid three-dimensional High Intensity Focused Ultrasound (HIFU) beam plotting system for visualizing the acoustic energy distribution, achieved using a three-dimensional positioning system and data acquisition hardware. Beam plots of a 1.1MHz HIFU transducer were performed to evaluate the capability of the proposed system.

Prevention of post-focal thermal damage by formation of bubbles at the focus during high intensity focused ultrasound therapy.

Safety concerns exist for potential thermal damage at tissue-air or tissue-bone interfaces located in the post-focal region during high intensity focused ultrasound (HIFU) treatments. We tested the feasibility of reducing thermal energy deposited at the post-focal tissue-air interfaces by producing bubbles (due to acoustic cavitation and/or boiling) at the HIFU focus. HIFU (in-situ intensities of 460-3500 W/cm2, frequencies of 3.

Stability of alteplase in presence of cavitation.

Several experimental studies have demonstrated that ultrasound (US) can accelerate enzymatic fibrinolysis and this effect is further enhanced in the presence of ultrasound contrast agents (UCA). Although UCA have been shown to be safe when administered to ischemic stroke patients, safety information of these agents in the thrombolysis setting is limited. Therefore, in this study we investigated potential adverse effects of acoustic cavitation generated by UCA on alteplase (t-PA), the drug used for treatment of ischemic stroke patients.

Effects of high-intensity focused ultrasound on nerve conduction.

The effects of various exposures (intensity, duration) of high-intensity focused ultrasound (HIFU) on sciatic nerve conduction were investigated in vivo in rats. The objective was to identify HIFU exposures that produce biological effects ranging from partial to complete conduction block, indicating potential use of HIFU as an alternative to current clinical methods of inducing nerve conduction block. In the study, 26 nerves were exposed and treated with 5-s applications of 5.

Color and pulsed Doppler sonography for arterial bleeding detection.

Objective: Hemorrhage resulting from penetrating injuries in the extremities is the leading cause of preventable death in the modern battlefield. Development of methods for detection and localization of vascular bleeding is needed that could be applied emergently without special training outside the hospital setting. Our objective was to assess whether Doppler sonography can provide quantitative parameters that characterize the bleeding site in the extremities.

Hemorrhage control using high intensity focused ultrasound.

Hemorrhage control is a high priority task in advanced trauma care, because hemorrhagic shock can result in less than a minute in cases of severe injuries. Hemorrhage was found to be solely responsible for 40-50% of traumatic civilian and battlefield deaths in recent years. The majority of these deaths were due to abdominal and pelvic injuries with hidden and inaccessible bleeding of solid organs such as liver, spleen, and kidneys, as well as major blood vessels.

Hemostasis and sealing of air leaks in the lung using high-intensity focused ultrasound.

Background: Operative management of parenchymal lung injury can be complicated by persistent hemorrhage and air leak, which might require resection. Techniques that preserve parenchyma are associated with improved survival. High-intensity focused ultrasound (HIFU) has been demonstrated as a useful method for hemostasis in experimental solid organ injuries.

Resection of abdominal solid organs using high-intensity focused ultrasound.

Our objective was to evaluate high-intensity focused ultrasound (HIFU) for minimizing blood loss during surgery by hemodynamically isolating large portions of solid organs before their resection. A high-power HIFU device (in situ intensity of 9000 W/cm(2), frequency of 3.3 MHz) was used to produce a wall of cautery for sealing of blood vessels along the resection line in surgically exposed solid organs (liver lobes, spleen and kidneys) of eight adult pigs.

Pulsatile flow phantom for ultrasound image-guided HIFU treatment of vascular injuries.

A pulsatile flow phantom was developed for studies of ultrasound image-guided high intensity focused ultrasound (HIFU) application in transcutaneous hemostasis of injured blood vessels. The flow phantom consisted of a pulsatile pump system with instrumented excised porcine carotid artery, which was imbedded in a transparent agarose gel to model structural configuration of in vivo tissues. Heparinized porcine blood was circulated through the phantom.

Image-guided acoustic hemostasis for hemorrhage in the posterior liver.

We investigated the use of ultrasound image-guided high intensity focused ultrasound (HIFU) to stop bleeding from injuries in the posterior liver. A HIFU transducer with focal length of 3.5 cm and frequency of 3.

Biological and physical mechanisms of HIFU-induced hyperecho in ultrasound images.

Guidance and monitoring of high intensity focused ultrasound (HIFU) therapy, using ultrasound imaging, has primarily utilized formation of a hyperechoic region at the HIFU focus. We investigated biologic and physical mechanisms of a hyperecho, as well as safety of this phenomenon, using thermal, acoustic and light microscopy observations. Single, short-duration HIFU pulses (30-60 ms) were able to produce a hyperechoic region at the HIFU focus, 2 cm deep in a rabbit thigh muscle.

Image-guided high-intensity focused ultrasound for conduction block of peripheral nerves.

The objective of our work has been to investigate the use of ultrasound image-guided high-intensity focused ultrasound (HIFU) to non-invasively produce conduction block in rabbit sciatic nerves in vivo, a technique that could become a treatment of spasticity and pain. The work reported here involved the investigation of the duration of such conduction blocks after HIFU treatment and whether they resulted in axon degeneration. The right sciatic nerves of 12 rabbits were treated, under guidance of ultrasound imaging, with repeated 5-s applications of 3.

Microbubble-enhanced hemorrhage control using high intensity focused ultrasound.

Our objective was to investigate whether hemorrhage control can be achieved faster when high-intensity focused ultrasound (HIFU) is applied in the presence of ultrasound contrast agents (UCA) as compared to HIFU only application. Incisions (3 cm long and 0.5 cm deep) were produced in the livers of anesthetized rabbits.

Detection of bleeding in injured femoral arteries with contrast-enhanced sonography.

Objective: The purpose of this study was to investigate the feasibility of detecting acute arterial bleeding by means of contrast-enhanced sonography.

Methods: Puncture injury was produced transcutaneously with an 18-gauge needle in 26 femoral arteries (13 in the control group and 13 in the contrast-enhanced group) of rabbits. A sonographic contrast agent (Optison; Mallinckrodt Inc, St Louis, MO) was administered intravenously at a dose of 0.

Ultrasonic interrogation of tissue vibrations in arterial and organ injuries: preliminary in vivo results.

Soft tissues surrounding vascular injuries are known to vibrate at audible and palpable frequencies, producing bruits and thrills. We report the results of a feasibility study where Doppler ultrasound (US) was used to quantitatively estimate the tissue vibrations after induced trauma in an animal model. A software-programmable US system was used to acquire quadrature-demodulated ensembles of received US echoes bypassing clutter filtering and other conventional Doppler processing stages.

Annular phased-array high-intensity focused ultrasound device for image-guided therapy of uterine fibroids.

An ultrasound (US), image-guided high-intensity focused ultrasound (HIFU) device was developed for noninvasive ablation of uterine fibroids. The HIFU device was an annular phased array, with a focal depth range of 30-60 mm, a natural focus of 50 mm, and a resonant frequency of 3 MHz. The in-house control software was developed to operate the HIFU electronics drive system for inducing tissue coagulation at different distances from the array.

Gel phantom for use in high-intensity focused ultrasound dosimetry.

An optically transparent phantom was developed for use in high-intensity focused ultrasound (US), or HIFU, dosimetry studies. The phantom is composed of polyacrylamide hydrogel, embedded with bovine serum albumin (BSA) that becomes optically opaque when denatured. Acoustic and optical properties of the phantom were characterized as a function of BSA concentration and temperature.