Ultrasonic imaging: safety considerations

Sound the Alarm: The Sonographer Shortage Is Echoing Across Healthcare

OBJECTIVES

The growth in ultrasound usage necessitates concurrent growth in the number of sonographers. Despite the increasing importance of ultrasound, there is a shortage of sonographers in the United States that has never been specifically quantified. This study examines recent trends in the number of ultrasound exams, sonography graduates, open sonographer positions, and wages.

METHODS

This retrospective study uses public databases and surveys including the Medical Expenditure Panel Survey (MEPS), Bureau of Labor Statistics (BLS), Integrated Postsecondary Education Data System (IPEDS), and Zippia, a human resources platform to determine metrics. These metrics include the number of ultrasound exams conducted in the United States (excluding inpatient setting), number of sonographers and sonographer wages, sonography graduates, and open sonographer positions.

RESULTS

Ultrasound exams in the United States from 2011 to 2021 increased from 38.6 million to 59.8 million (+55.1%,) while the number of sonographers (2011-2021) increased from 54,760 to 78,640 (+43.6%). There was a significant difference between supply and demand of sonographers with the number of sonography graduates (2011-2021) increasing from 4,386 to 5,393 (+23.0%) while the number of open sonographer positions (2012-2021) increased from 18,462 to 25,162 (+36.3%).

CONCLUSIONS

From 2011 to 2021, the increase in the number of ultrasound exams has significantly outpaced the increase in the number of sonographers. Furthermore, the increase in demand for sonographers has grown significantly faster than the supply, leading to a shortage and consequent strain on the healthcare system. To address the shortage, the number of sonography school openings should be increased, and the attendant challenges addressed.

Compact meta-differentiator for achieving isotropically high-contrast ultrasonic imaging

Ultrasonic imaging is crucial in the fields of biomedical engineering for its deep penetration capabilities and non-ionizing nature. However, traditional techniques heavily rely on impedance differences within objects, resulting in poor contrast when imaging acoustically transparent targets. Here, we propose a compact spatial differentiator for underwater isotropic edge-enhanced imaging, which enhances the imaging contrast without the need for contrast agents or external physical fields. This design incorporates an amplitude meta-grating for linear transmission along the radial direction, combined with a phase meta-grating that utilizes focus and spiral phases with a first-order topological charge. Through theoretical analysis, numerical simulations, and experimental validation, we substantiate the effectiveness of our technique in distinguishing amplitude objects with isotropic edge enhancements. Importantly, this method also enables the accurate detection of both phase objects and artificial biological models. This breakthrough creates new opportunities for applications in medical diagnosis and nondestructive testing.

Consensus-based ethical best practices for performing educational point-of-care ultrasonography in the emergency department

Objectives

There is no standardized protocol for performing educational point-of-care ultrasonography (POCUS) that addresses patient-centered ethical issues such as obtaining informed consent. This study sought to define principles for ethical application of educational POCUS and develop consensus-based best practice guidance.

Methods

A questionnaire was developed by a trained ethicist after literature review with the help of a medical librarian. A diverse panel including experts in medical education, law, and bioethics; medical trainees; and individuals with no medical background was convened. The panel voted on their level of agreement with ethical principles and degree of appropriateness of behaviors in three rounds of a modified Delphi process. A high level of agreement was defined as 80% or greater consensus.

Results

Panelists voted on 38 total items: 15 related to the patient consent and selection process, eight related to practices while performing educational POCUS, and 15 scenarios involving POCUS application. A high level of agreement was achieved for 13 items related to patient consent and selection, eight items related to performance practices, and 10 scenarios of POCUS application.

Conclusions

Based on expert consensus, ethical best practices include obtaining informed consent before performing educational POCUS, allowing patients to decline educational POCUS, informing patients the examination is not intended to be a part of their medical evaluation and is not billed, using appropriate draping techniques, maintaining a professional environment, and disclosing incidental findings in coordination with the primary team caring for the patient. These practices could be implemented at institutions to encourage ethical use of educational POCUS when training physicians, fellows, residents, and medical students.

Exploring Different Ultrasonic Parameters and Treatment Conditions to Optimize In Vitro Sonodynamic Therapeutic Effects in Cancer Cells

The effects of ultrasonic parameters and treatment conditions on the in vitro cellular experiments of sonodynamic therapy (SDT) have not been fully studied. Exploring the factors that affect the efficacy of SDT can provide a reference for screening effective sonosensitizers in vitro. The aim of this work is to investigate the factors that affected the SDT effects in cancer cells. Cancer cells in culture plates were exposed to ultrasound and sonosensitizers. The intracellular drug concentration was measured by using flow cytometry and the cell viability was determined by MTT assay. The SDT effects of cancer cells treated with different ultrasonic parameters under the same sonosensitizer concentration were different. The ultrasonic parameters, intracellular drug concentration, drug treatment time, cell amount, and cell status could affect the sonodynamic therapeutic effects. It is necessary to select appropriate ultrasound conditions and optimize the cellular status to make the results of the in vitro cellular experiments more reliable.

Ultrasound Mediated Polymerization for Cell Delivery, Drug Delivery, and 3D Printing

Safe and accurate in situ delivery of biocompatible materials is a fundamental requirement for many biomedical applications. These include sustained and local drug release, implantation of acellular biocompatible scaffolds, and transplantation of cells and engineered tissues for functional restoration of damaged tissues and organs. The common practice today includes highly invasive operations with major risks of surgical complications including adjacent tissue damage, infections, and long healing periods. In this work, a novel non-invasive delivery method is presented for scaffold, cells, and drug delivery deep into the body to target inner tissues. This technology is based on acousto-sensitive materials which are polymerized by ultrasound induction through an external transducer in a rapid and local fashion without additional photoinitiators or precursors. The applicability of this technology is demonstrated for viable and functional cell delivery, for drug delivery with sustained release profiles, and for 3D printing. Moreover, the mechanical properties of the delivered scaffold can be tuned to the desired target tissue as well as controlling the drug release profile. This promising technology may shift the paradigm for local and non-invasive material delivery approach in many clinical applications as well as a new printing method - "acousto-printing" for 3D printing and in situ bioprinting.

Ultrasound robotics for precision therapy

In recent years, the application of microrobots in precision therapy has gained significant attention. The small size and maneuverability of these micromachines enable them to potentially access regions that are difficult to reach using traditional methods; thus, reducing off-target toxicities and maximizing treatment effectiveness. Specifically, acoustic actuation has emerged as a promising method to exert control. By harnessing the power of acoustic energy, these small machines potentially navigate the body, assemble at the desired sites, and deliver therapies with enhanced precision and effectiveness. Amidst the enthusiasm surrounding these miniature agents, their translation to clinical environments has proven difficult. The primary objectives of this review are threefold: firstly, to offer an overview of the fundamental acoustic principles employed in the field of microrobots; secondly, to assess their current applications in medical therapies, encompassing tissue targeting, drug delivery or even cell infiltration; and lastly, to delve into the continuous efforts aimed at integrating acoustic microrobots into in vivo applications.

Comparative analysis of energy transfer mechanisms for neural implants

As neural implant technologies advance rapidly, a nuanced understanding of their powering mechanisms becomes indispensable, especially given the long-term biocompatibility risks like oxidative stress and inflammation, which can be aggravated by recurrent surgeries, including battery replacements. This review delves into a comprehensive analysis, starting with biocompatibility considerations for both energy storage units and transfer methods. The review focuses on four main mechanisms for powering neural implants: Electromagnetic, Acoustic, Optical, and Direct Connection to the Body. Among these, Electromagnetic Methods include techniques such as Near-Field Communication (RF). Acoustic methods using high-frequency ultrasound offer advantages in power transmission efficiency and multi-node interrogation capabilities. Optical methods, although still in early development, show promising energy transmission efficiencies using Near-Infrared (NIR) light while avoiding electromagnetic interference. Direct connections, while efficient, pose substantial safety risks, including infection and micromotion disturbances within neural tissue. The review employs key metrics such as specific absorption rate (SAR) and energy transfer efficiency for a nuanced evaluation of these methods. It also discusses recent innovations like the Sectored-Multi Ring Ultrasonic Transducer (S-MRUT), Stentrode, and Neural Dust. Ultimately, this review aims to help researchers, clinicians, and engineers better understand the challenges of and potentially create new solutions for powering neural implants.

Brain injury mobile diagnostic system: Applications in civilian medical service and on the battlefield-General concept and medical aspects

To present the concept of a portable ultrasound tomography device for diagnosing traumatic and vascular brain lesions. The device consisting of multiple transcranial ultrasound probes placed on the surface of the head, specifically but not exclusively in natural acoustic windows. An integral part of the mobile diagnostic system (MDS) is a decision support system based on artificial intelligence algorithms utilizing information from: head images, laboratory data, and assessment of the patient's clinical condition. The MDS can significantly reduce the time from stroke onset to rtPA therapy in civilian medical services and support therapeutic and evacuation strategies in instances of brain and skull trauma on the battlefield.

Liability, risks, and recommendations for ultrasound use in the diagnosis of obstetrics diseases

This literature review will summarize the liability issues, risks, and ultrasound recommendations for diagnosing obstetrics diseases. One liability issue is related to misdiagnosis or failure to detect abnormalities during an ultrasound examination. Ultrasound images can be subjective interpretations, and errors may occur due to factors such as operator skill, equipment limitations, or fetal positioning. Another liability concern is related to the potential adverse effects of ultrasound exposure on both the mother and fetus. While extensive research has shown that diagnostic ultrasound is generally safe when used appropriately, there are still uncertainties regarding long-term effects. Some studies suggest a possible association between prolonged or excessive exposure to ultrasound waves and adverse outcomes such as low birth weight, developmental delays, or hearing impairment. Additionally, obtaining informed consent from patients is crucial in mitigating liability risks. Patients should be informed about the purpose of the ultrasound examination, its benefits, limitations, potential risks (even if minimal), and any alternative diagnostic options available. This ensures that patients know the procedure and can make informed decisions about their healthcare. Proper documentation helps establish a clear record of the care provided and can serve as evidence in any legal disputes.

A systematic review of ultrasound-mediated drug delivery to the eye and critical insights to facilitate a timely path to the clinic

Ultrasound has long been identified as a promising, non-invasive modality for improving ocular drug delivery across a range of indications. Yet, with 20 years of learnings behind us, clinical translation remains limited. To help address this, and in accordance with PRISMA guidelines, the various mechanisms of ultrasound-mediated ocular drug delivery have been appraised, ranging from first principles to emergent applications spanning both ex vivo and in vivo models. The heterogeneity of study methods precluded meta-analysis, however an extensive characterisation of the included studies allowed for semi-quantitative and qualitative assessments. Methods: In this review, we reflected on study quality of reporting, and risk of bias (RoB) using the latest Animal Research: Reporting of In Vivo Experiments (ARRIVE 2.0) guidelines, alongside the Systematic Review Centre for Laboratory animal Experimentation (SYRCLE) RoB tools. Literature studies from 2002 to 2022 were initially characterised according to methods of ultrasound application, ultrasound parameters applied, animal models employed, as well as safety and efficacy assessments. This exercise contributed to developing a comprehensive understanding of the current state of play within ultrasound-mediated ocular drug delivery. The results were then synthesised and processed into a guide to aid future study design, with the goal of improving the reliability of data, and to support efficient and timely translation to the clinic. Results: Key attributes identified as hindering translation included: poor reporting quality and high RoB, skewed use of animals unrepresentative of the human eye, and the over reliance of reductionist safety assessments. Ex vivo modelling studies were often unable to have comprehensive safety assessments performed on them, which are imperative to determining treatment safety, and represent a pre-requisite for clinical translation. Conclusion: With the use of our synthesised guide, and a thorough understanding of the underlying physicochemical interactions between ultrasound and ocular biology provided herein, this review offers a firm foundation on which future studies should ideally be built, such that ultrasound-mediated ocular drug delivery can be translated from concept to the coalface where it can provide immense clinical benefit.

Non-Contact Monitoring of Fetal Movement Using Abdominal Video Recording

Fetal movement (FM) is an important indicator of fetal health. However, the current methods of FM detection are unsuitable for ambulatory or long-term observation. This paper proposes a non-contact method for monitoring FM. We recorded abdominal videos from pregnant women and then detected the maternal abdominal region within each frame. FM signals were acquired by optical flow color-coding, ensemble empirical mode decomposition, energy ratio, and correlation analysis. FM spikes, indicating the occurrence of FMs, were recognized using the differential threshold method. FM parameters including number, interval, duration, and percentage were calculated, and good agreement was found with the manual labeling performed by the professionals, achieving true detection rate, positive predictive value, sensitivity, accuracy, and F1_score of 95.75%, 95.26%, 95.75%, 91.40%, and 95.50%, respectively. The changes in FM parameters with gestational week were consistent with pregnancy progress. In general, this study provides a novel contactless FM monitoring technology for use at home.

Lung Ultrasound in the Evaluation of Lung Disease Severity in Children with Clinically Stable Cystic Fibrosis: A Prospective Cross-Sectional Study

With the increasing longevity of cystic fibrosis (CF), there is a growing need to minimise exposure to ionising radiation in patients who undergo regular imaging tests while monitoring the course of the lung disease. This study aimed to define the role of lung ultrasounds (LUS) in the evaluation of lung disease severity in children with clinically stable CF. LUS was performed on 131 patients aged 5 weeks to 18 years (study group) and in 32 healthy children of an equivalent age range (control group). Additionally, an interobserver study was performed on 38 patients from the study group. In CF patients, the following ultrasound signs were identified: I-lines; Z-lines; single, numerous and confluent B-lines; Am-lines; small and major consolidations; pleural line abnormalities and small amounts of pleural fluid. The obtained results were evaluated against an original ultrasound score. LUS results were correlated with the results of chest X-ray (CXR) [very high], pulmonary function tests (PFTs) [high] and microbiological status [significant]. The interobserver study showed very good agreement between investigators. We conclude that LUS is a useful test in the evaluation of CF lung disease severity compared to routinely used methods. With appropriate standardisation, LUS is highly reproducible.

Sonoporation of the Round Window Membrane on a Sheep Model: A Safety Study

Sonoporation using microbubble-assisted ultrasound increases the permeability of a biological barrier to therapeutic molecules. Application of this method to the round window membrane could improve the delivery of therapeutics to the inner ear. The aim of this study was to assess the safety of sonoporation of the round window membrane in a sheep model. To achieve this objective, we assessed auditory function and cochlear heating, and analysed the metabolomics profiles of perilymph collected after sonoporation, comparing them with those of the control ear in the same animal. Six normal-hearing ewes were studied, with one sonoporation ear and one control ear for each. A mastoidectomy was performed on both ears. On the sonoporation side, Vevo MicroMarker^® microbubbles (MBs; VisualSonics-Fujifilm, Amsterdam, The Netherlands) at a concentration of 2 × 10⁸ MB/mL were locally injected into the middle ear and exposed to 1.1 MHz sinusoidal ultrasonic waves at 0.3 MPa negative peak pressure with 40% duty cycle and 100 μs interpulse period for 1 min; this was repeated three times with 1 min between applications. The sonoporation protocol did not induce any hearing impairment or toxic overheating compared with the control condition. The metabolomic analysis did not reveal any significant metabolic difference between perilymph samples from the sonoporation and control ears. The results suggest that sonoporation of the round window membrane does not cause damage to the inner ear in a sheep model.

Effectiveness of an educational module in improving knowledge, awareness and perception among pregnant women regarding the safe use of prenatal ultrasound

Background

Lack of public understanding, perception and awareness of the biological effects of prenatal ultrasound has led to the non-medical use of ultrasound. An educational programme is required to enlighten pregnant women and the public regarding prenatal ultrasound safety.

Objective

To evaluate the effectiveness of educational modules (video and brochure) in improving knowledge, awareness and perception (KAP) among pregnant women regarding prenatal ultrasound safety.

Methods

This is a quasi-experimental study with a pre-and post-test design. This study recruited 51 pregnant women as respondents from the Obstetrics and Gynaecology clinic (O&G) of Hospital Canselor Tuanku Muhriz (HCTM). The first phase of the study was conducted by distributing a set of closed-ended questionnaires with multiple choice and Likert scale answers to assess the KAP of pregnant women regarding the safe use of prenatal ultrasound, followed by educational modules where the respondents were allocated into three groups (17 watched a video, 17 received brochure and 17 received combined media). After the intervention, the respondents' KAP were assessed using the same questionnaire.

Results

The Wilcoxon signed rank test showed that educational modules like video, brochure and combined media had a statistically significant increase in post-test scores over the pre-test scores (video: mean rank = 9.00, p < 0.05) (brochure: mean rank = 9.79,p < 0.05) and (combined media: mean rank = 10.17, p > 0.05). The Kruskal Wallis test indicated that educational video was more effective in improving the KAP of pregnant women than the brochure and combined media (mean rank = 34.62, p < 0.05). Among the parameters, the occupation has the strongest positive correlation with the post-test knowledge score in improving the KAP of pregnant women regarding the safe use of prenatal ultrasound.

Conclusion

The educational video is the most effective approach for enhancing pregnant women's KAP. The educational module on the safety of prenatal ultrasound is thought to dispel myths by providing accurate information to audiences from various backgrounds.

Specific-Tuning Band Structure in Hetero-Semiconductor Nanorods to Match with Reduction of Oxygen Molecules for Low-Intensity Yet Highly Effective Sonodynamic/Hole Therapy of Tumors

Sonosensitizers-assisted sonodynamic therapy (SDT) has been emerging as a promising treatment for cancers, and yet few specific regulations of band structure of sonosensitizers have been reported in relation to oxygen in tissues. Herein, by a gradient doping technique to modulate the band structure of hetero-semiconductor nanorods, it is found that the reduction potential of band-edge is very critical to reactive oxygen species (ROS) production under low-intensity ultrasound (US) irradiation and particularly, when aligned with the reduction of oxygen, ROS generation is found to be most significantly enhanced. Withal, US-generated oxidation holes are found to be effective in consuming overexpressed glutathione in tumor lesions, which amplifies cellular oxidative stress and finally induces tumor cell death. Moreover, the intrinsic fluorescence property of semiconductors provides imaging capability to illumine tumor area and guide the SDT process. This study demonstrates that the reduction potential state of sonosensitizers is of crucial importance in ROS generation and the proposed reduction potential-tailored hetero-semiconductor nanorods materialize low-intensity US irradiation yet highly effective SDT and synergetic hole therapy of tumors with imaging guidance and reduced radiation injury.

High shear rate propulsion of acoustic microrobots in complex biological fluids

Untethered microrobots offer a great promise for localized targeted therapy in hard-to-access spaces in our body. Despite recent advancements, most microrobot propulsion capabilities have been limited to homogenous Newtonian fluids. However, the biological fluids present in our body are heterogeneous and have shear rate-dependent rheological properties, which limit the propulsion of microrobots using conventional designs and actuation methods. We propose an acoustically powered microrobotic system, consisting of a three-dimensionally printed 30-micrometer-diameter hollow body with an oscillatory microbubble, to generate high shear rate fluidic flow for propulsion in complex biofluids. The acoustically induced microstreaming flow leads to distinct surface-slipping and puller-type propulsion modes in Newtonian and non-Newtonian fluids, respectively. We demonstrate efficient propulsion of the microrobots in diverse biological fluids, including in vitro navigation through mucus layers on biologically relevant three-dimensional surfaces. The microrobot design and high shear rate propulsion mechanism discussed herein could open new possibilities to deploy microrobots in complex biofluids toward minimally invasive targeted therapy.

Design of a Novel Medical Acoustic Sensor Based on MEMS Bionic Fish Ear Structure

High-performance medical acoustic sensors are essential in medical equipment and diagnosis. Commercially available medical acoustic sensors are capacitive and piezoelectric types. When they are used to detect heart sound signals, there is attenuation and distortion due to the sound transmission between different media. This paper proposes a new bionic acoustic sensor based on the fish ear structure. Through theoretical analysis and finite element simulation, the optimal parameters of the sensitive structure are determined. The sensor is fabricated using microelectromechanical systems (MEMS) technology, and is encapsulated in castor oil, which has an acoustic impedance close to the human body. An electroacoustic test platform is built to test the performance of the sensor. The results showed that the MEMS bionic sensor operated with a bandwidth of 20–2k Hz. Its linearity and frequency responses were better than the electret microphone. In addition, the sensor was tested for heart sound collection application to verify its effectiveness. The proposed sensor can be effectively used in clinical auscultation and has a high SNR.

High resolution ultrasonic neural modulation observed via in vivo two-photon calcium imaging

Neural modulation plays a major role in delineating the circuit mechanisms and serves as the cornerstone of neural interface technologies. Among the various modulation mechanisms, ultrasound enables noninvasive label-free deep access to mammalian brain tissue. To date, most if not all ultrasonic neural modulation implementations are based on ∼1 MHz carrier frequency. The long acoustic wavelength results in a spatially coarse modulation zone, often spanning over multiple function regions. The modulation of one function region is inevitably linked with the modulation of its neighboring regions. Moreover, the lack of in vivo cellular resolution cell-type-specific recording capabilities in most studies prevents the revealing of the genuine cellular response to ultrasound. To significantly increase the spatial resolution, we explored the application of high-frequency ultrasound. To investigate the neuronal response at cellular resolutions, we developed a dual-modality system combining in vivo two-photon calcium imaging and focused ultrasound modulation. The studies show that the ∼30 MHz ultrasound can suppress the neuronal activity in awake mice at 100-μm scale spatial resolutions, paving the way for high-resolution ultrasonic neural modulation. The dual-modality in vivo system validated through this study will serve as a general platform for studying the dynamics of various cell types in response to ultrasound.

The Role of Ultrasound as a Diagnostic and Therapeutic Tool in Experimental Animal Models of Stroke: A Review

Ultrasound is a noninvasive technique that provides real-time imaging with excellent resolution, and several studies demonstrated the potential of ultrasound in acute ischemic stroke monitoring. However, only a few studies were performed using animal models, of which many showed ultrasound to be a safe and effective tool also in therapeutic applications. The full potential of ultrasound application in experimental stroke is yet to be explored to further determine the limitations of this technique and to ensure the accuracy of translational research. This review covers the current status of ultrasound applied to monitoring and treatment in experimental animal models of stroke and examines the safety, limitations, and future perspectives.

Deep impact of superficial skin inking: acoustic analysis of underlying tissue

Abstract Background: Skin tattoos are a common decoration, but profound scientific study whether the presence of a skin tattoo alters the acoustic response from superficial tissue, and therefore from underlying tissue, was previously lacking. Any image aberrations caused by tattoo presence may have been thought negligible, yet empirically found artifacts in brightness-mode images of tattooed skin suggest otherwise. This study investigated the nature of these artifacts theoretically and experimentally in extremely simplified cases of perfectly flat and homogenous layered media and in tattooed pork.Methods: Theory was derived for computing the acoustic response from horizontally and vertically layered media containing a thin inked layer. Experiments were performed in vitro. Artificial and pork skin were tattooed, attached to phantom material, and sonicated with a 13‐6-MHz probe. The speed of sound of these materials was determined, and the perceived refraction angles was measured.Results: The measured speeds of sound of tattooed materials were higher than those of their uninked counterparts. The presence of tattoo ink was found to have increased the linear acoustic attenuation by 1 dB/cm. This value is negligible for typical tattoos of only few millimeters. The perceived critical refraction angles of adjacent materials could be detected, and their corresponding speeds of sound were quantified. These coincided with values derived from theory.Conclusion: The ratio of speeds of sound of adjacent materials was shown to create distinct highlights in brightness-mode images. The artifacts observed in in vitro and in vivo brightness-mode scans were explained from near-vertical transitions between areas of different sound speed. This is the first study correlating so-called critical refraction highlighting with speed-of-sound information. In addition, it was found that phantom material is a room-temperature acoustic alternative for experiments on live human skin. In summary, the presence of superficial tattoos has a small but quantifiable effect on the acoustic response from deeper tissues.

Powering Implantable and Ingestible Electronics

Implantable and ingestible biomedical electronic devices can be useful tools for detecting physiological and pathophysiological signals, and providing treatments that cannot be done externally. However, one major challenge in the development of these devices is the limited lifetime of their power sources. The state-of-the-art of powering technologies for implantable and ingestible electronics is reviewed here. The structure and power requirements of implantable and ingestible biomedical electronics are described to guide the development of powering technologies. These powering technologies include novel batteries that can be used as both power sources and for energy storage, devices that can harvest energy from the human body, and devices that can receive and operate with energy transferred from exogenous sources. Furthermore, potential sources of mechanical, chemical, and electromagnetic energy present around common target locations of implantable and ingestible electronics are thoroughly analyzed; energy harvesting and transfer methods befitting each energy source are also discussed. Developing power sources that are safe, compact, and have high volumetric energy densities is essential for realizing long-term in-body biomedical electronics and for enabling a new era of personalized healthcare.

Modelling Lipid-Coated Microbubbles in Focused Ultrasound Applications at Subresonance Frequencies

We present a computational study of the behaviour of a lipid-coated SonoVue microbubble with initial radius 1 µm ≤ R₀ ≤ 2 µm, excited at frequencies (200-1500 kHz) significantly below the linear resonance frequency and pressure amplitudes of up to 1500 kPa-an excitation regime used in many applications of focused ultrasound. The bubble dynamics are simulated using the Rayleigh-Plesset equation and the Gilmore equation, in conjunction with the Marmottant model for the lipid monolayer coating. Also, a new continuously differentiable variant of the Marmottant model is introduced. Below the onset of inertial cavitation, a linear regime is identified in which the maximum pressure at the bubble wall is linearly proportional to the excitation pressure amplitude and the mechanical index. This linear regime is bounded by the Blake pressure, and, in line with recent in vitro experiments, the onset of inertial cavitation is found to occur at an excitation pressure amplitude of approximately 130-190 kPa, depending on the initial bubble size. In the nonlinear regime the maximum pressure at the bubble wall is found to be readily predicted by the maximum bubble radius, and both the Rayleigh-Plesset and Gilmore equations are shown to predict the onset of sub- and ultraharmonic frequencies of the acoustic emissions compared with in vitro experiments. Neither the surface dilational viscosity of the lipid monolayer nor the compressibility of the liquid has a discernible influence on the quantities studied, but accounting for the lipid coating is critical for accurate prediction of the bubble behaviour. The Gilmore equation is shown to be valid for the bubbles and excitation regime considered, and the Rayleigh-Plesset equation also provides accurate qualitative predictions, even though it is outside its range of validity for many of the cases considered.

Experimental acoustic characterization of an endoskeletal antibubble contrast agent: First results

Purpose

An antibubble is an encapsulated gas bubble with an incompressible inclusion inside the gas phase. Current‐generation ultrasound contrast agents are bubble‐based: they contain encapsulated gas bubbles with no inclusions. The objective of this work is to determine the linear and nonlinear responses of an antibubble contrast agent in comparison to two bubble‐based ultrasound contrast agents, that is, reference bubbles and SonoVueTM.

Methods

Side scatter and attenuation of the three contrast agents were measured, using single‐element ultrasound transducers, operating at 1.0, 2.25, and 3.5 MHz. The scatter measurements were performed at acoustic pressures of 200 and 300 kPa for 1.0 MHz, 300 kPa, and 450 kPa for 2.25 MHz, and 370 and 560 kPa for 3.5 MHz. Attenuation measurements were conducted at pressures of 13, 55, and 50 kPa for 1.0, 2.25, and 3.5 MHz, respectively. In addition, a dynamic contrast‐enhanced ultrasound measurement was performed, imaging the contrast agent flow through a vascular phantom with a commercial diagnostic linear array probe.

Results

Antibubbles generated equivalent or stronger harmonic signal, compared to bubble‐based ultrasound contrast agents. The second harmonic side‐scatter amplitude of the antibubble agent was up to 3 dB greater than that of reference bubble agent and up to 4 dB greater than that of SonoVueTM at the estimated concentration of 8×104 bubbles/mL. For ultrasound with a center transmit frequency of 1.0 MHz, the attenuation coefficient of the antibubble agent was 8.7 dB/cm, whereas the attenuation coefficient of the reference agent was 7.7 and 0.3 dB/cm for SonoVueTM. At 2.25 MHz, the attenuation coefficients were 9.7, 3.0, and 0.6 dB/cm, respectively. For 3.5 MHz, they were 4.4, 1.8, and 1.0 dB/cm, respectively. A dynamic contrast‐enhanced ultrasound recording showed the nonlinear signal of the antibubble agent to be 31% greater than for reference bubbles and 23% lower than SonoVueTM at a high concentration of 2×106 bubbles/mL.

Conclusion

Endoskeletal antibubbles generate comparable or greater higher harmonics than reference bubbles and SonoVueTM. As a result, antibubbles with liquid therapeutic agents inside the gas phase have high potential to become a traceable therapeutic agent.

Audit of the appropriateness of the indication for obstetric sonography in a tertiary facility in Ghana

INTRODUCTION

the use of ultrasound is one of the most vital tools in the management of pregnancies and contributes significantly in improving maternal and child health. Certain indications in pregnancy, guide the obstetrician as to which obstetric scan deems appropriate. The full realization of the benefits of ultrasound depends on whether it is being used appropriately or not, and hence this study aimed at auditing for the appropriate indications for obstetric ultrasound.

METHODS

a review of all request forms for obstetric scan between June 2019 and July 2020 was performed to assess the appropriateness of requests for obstetric ultrasound at the Cape Coast Teaching Hospital. The data obtained was analyzed using SPSS (SPSS Inc. Chicago, IL version 20.0). A Chi-squared test of independence was used to check for statistically significant differences between variables at p ≤ 0.05.

RESULTS

three hundred and fourteen (314) out of the 527 request forms had clinical indications stated. 174 (81.7%) of requests from Cape Coast Teaching Hospital and 39 (18.3%) from other health centers did not indicate patients clinical history/indication on the request forms. Majority 76 (68.5%) of scans in the first trimester were done without indications/history. Only 29 of requests with clinical history were inappropriate.

CONCLUSION

practitioners should be mindful of adequately completing request forms for obstetric investigations since a large number of practitioners do not state the history/indications for the scans. There should be continuous medical education on the importance of appropriate indication for obstetric ultrasound.

Evaluation of the Scan Duration and Mechanical and Thermal Indices Applied for the Diagnostic Ultrasound Examinations

OBJECTIVE

Although epidemiological studies have failed to show the harmful effects of ultrasound in humans, as a form of energy, ultrasound has the potential to cause bio-effects in tissues. Therefore, clinical guidelines have been established for ultrasound technology related to human safety, which include Thermal (TI) and mechanical (MI) indices. The appropriate TI and MI ranges for embryonic examinations are between 0-1.0 and 0-0.4, respectively. The accepted TI and MI ranges are 0-2.0 and 0-1.9, respectively, for general ultrasound examinations. In addition, the scan duration should be kept as low as possible. Therefore, the present study aimed at evaluating the scan duration, TI, and MI as measures of acoustic output during ultrasound studies.

METHODS

A cross-sectional descriptive study was conducted for patients undergoing pregnancy checkups, routine checkups, and initial diagnosis ultrasound examinations. Samples were selected from imaging departments of 4 educational hospitals based on convenience sampling and 321 checklists completed by direct observation of ultrasound examinations.

RESULTS

For pregnancy scans, the mean TI and MI were obtained as 0.32 ± 0.27 and 1.15 ± 0.13, respectively. For non-pregnancy examinations, the mean value of TI and MI were 0.30 ± 0.29 and 1.07 ± 0.35, respectively. Therefore, mean TI for pregnancy and non-pregnancy examinations and mean MI for non-pregnancy studies obtained lower than the permitted values, while the mean MI was higher than the permitted level for first trimester of pregnancy. Also, relatively suitable scan durations were seen in reviewed studies.

CONCLUSION

From this study, it may be concluded that the reported ultrasound scans were safe.

In Vivo Imaging of Biodegradable Implants and Related Tissue Biomarkers

Non-invasive longitudinal imaging of osseointegration of bone implants is essential to ensure a comprehensive, physical and biochemical understanding of the processes related to a successful implant integration and its long-term clinical outcome. This study critically reviews the present imaging techniques that may play a role to assess the initial stability, bone quality and quantity, associated tissue remodelling dependent on implanted material, implantation site (surrounding tissues and placement depth), and biomarkers that may be targeted. An updated list of biodegradable implant materials that have been reported in the literature, from metal, polymer and ceramic categories, is provided with reference to the use of specific imaging modalities (computed tomography, positron emission tomography, ultrasound, photoacoustic and magnetic resonance imaging) suitable for longitudinal and non-invasive imaging in humans. The advantages and disadvantages of the single imaging modality are discussed with a special focus on preclinical imaging for biodegradable implant research. Indeed, the investigation of a new implant commonly requires histological examination, which is invasive and does not allow longitudinal studies, thus requiring a large number of animals for preclinical testing. For this reason, an update of the multimodal and multi-parametric imaging capabilities will be here presented with a specific focus on modern biomaterial research.

Multifocus Thermal Strain Imaging Using a Curved Linear Array Transducer for Identification of Lipids in Deep Tissue

Thermal strain imaging (TSI) is an ultrasound-based imaging technique intended primarily for diseases in which lipid accumulation is the main biomarker. The goal of the research described here was to successfully implement TSI on a single, commercially available curved linear array transducer for heating and imaging of organs at a deeper depth. For an effective temperature rise of the tissue over a large area, which is key to TSI performance, an innovative multifocus beamforming approach was applied. This yielded a heating area from 32 to 96 mm in the axial direction and -7 to +7 mm in the lateral direction. The pressure fields generated from simulation were in agreement with pressure fields measured with the hydrophone. TSI with safe acoustic power identified with high contrast a rubber inclusion and liposuction fat tissue embedded in a gelatin block.

Acousto-optic interaction strengths in optically scattering media using high pressure acoustic pulses

Ultrasound optical tomography (UOT) is a developing medical imaging technique with the potential to noninvasively image tissue oxygenation at depths of several centimeters in human tissue. To accurately model the UOT imaging, it is necessary the calculate the signal produced by the interaction between ultrasound and light in the scattering medium. In this paper we present a rigorous description for modeling this process for ultrasound pulses in the non-linear regime with peak pressures ranging up to the medical safety limit. Simulation results based on the presented model agree well with measurements performed with fully characterized ultrasound pulses. Our results also indicate that the UOT modeling process can be accurately simplified by disregarding the acoustically induced movement of scatterers. Our results suggest that the explored model and its software implementation can be used as a virtual lab to aid future development of pulses and UOT imaging algorithms.

Non-invasive Assessment of Liver Fat in ob/ob Mice Using Ultrasound-Induced Thermal Strain Imaging and Its Correlation with Hepatic Triglyceride Content

Non-alcoholic fatty liver disease is the accumulation of triglycerides in liver. In its malignant form, it can proceed to steatohepatitis, fibrosis, cirrhosis, cancer and ultimately liver impairment, leading to liver transplantation. In a previous study, ultrasound-induced thermal strain imaging (US-TSI) was used to distinguish between excised fatty livers from obese mice and non-fatty livers from control mice. In this study, US-TSI was used to quantify lipid composition of fatty livers in ob/ob mice (n = 28) at various steatosis stages. A strong correlation coefficient was observed (R² = 0.85) between lipid composition measured with US-TSI and hepatic triglyceride content. Hepatic triglyceride content is used to quantify adipose tissue in liver. The ob/ob mice were divided into three groups based on the degree of steatosis that is used in clinics: none, mild and moderate. A non-parametric Kruskal-Wallis test was conducted to determine if US-TSI can potentially differentiate among the steatosis grades in non-alcoholic fatty liver disease.

Safety Review and Perspectives of Transcranial Focused Ultrasound Brain Stimulation

Ultrasound is an important theragnostic modality in modern medicine. Technical advancement of both acoustic focusing and transcranial delivery have enabled administration of ultrasound waves to localized brain areas with few millimeters of spatial specificity and penetration depth sufficient to reach the thalamus. Transcranial focused ultrasound (tFUS) given at a low acoustic intensity has been shown to increase or suppress the excitability of region-specific brain areas. The neuromodulatory effects can outlast the sonication, suggesting the possibility of inducing neural plasticity needed for neurorehabilitation. Increasing numbers of studies have shown the efficacy and excellent safety profile of the technique, yet comparisons among the safety-related parameters have not been compiled. This review aims to provide safety information and perspectives of tFUS brain stimulation. First, the acoustic parameters most relevant to thermal/mechanical tissue damage are discussed along with regulated parameters for existing ultrasound therapies/diagnostic imaging. Subsequently, the parameters used in studies of large animals, non-human primates, and humans are surveyed and summarized in terms of the acoustic intensity and the mechanical index. The pulse-mode operation and the use of low ultrasound frequency for tFUS-mediated brain stimulation warrant the establishment of new safety guidelines/recommendations for the use of the technique among healthy volunteers, with additional cautionary requirements for its clinical translation.

The Gilmore-NASG model to predict single-bubble cavitation in compressible liquids

The Gilmore model is combined with the Noble-Abel-stiffened-gas (NASG) equation of state to yield a simple model to predict the expansion and collapse of spherical bubbles based on real gas thermodynamics. The NASG equation of state resolves the temperature inaccuracy associated with the commonly employed Tait equation of state for liquids and, thus, can provide a consistent description of compressible and thermal effects of the bubble content and the surrounding liquid during cavitation. After a detailed derivation of the proposed Gilmore-NASG model, the differences between the classical Gilmore-Tait model and the proposed model are highlighted with results of single-bubble cavitation related to bubble collapse and driven by an acoustic excitation in frequency and amplitude regimes relevant to sonoluminescence, high-intensity focused ultrasound and shock wave lithotripsy. Especially for rapidly and violently collapsing bubbles, substantial differences in the bubble behaviour can be observed between the proposed Gilmore-NASG model and the classical Gilmore-Tait model. The ability of the Gilmore-NASG model to simultaneously predict reliable pressure and temperature values in gas, vapour and liquid, makes the proposed model particularly attractive for sonochemistry and biomedical applications.

Fetal Movement Counting Using Optical Fibre Sensors

Daily fetal movement counting based on maternal perception is widely deployed to monitor fetal wellbeing. However, the counting performed by the mother is prone to errors for various reasons. There are limited devices on the market that can provide reliable and automatic counting. This paper presents a prototype of a novel fetal movement monitoring device based on fibre Bragg grating sensors. Deformation of the skin caused by a fetal movement can lead to a change of the strain and stress on the optical fibre sensors, therefore can induce distortions to the breathing pattern of the mother. In the study data was gathered by the sensors through strain measurement and was post-processed using independent component analysis (ICA) and high-pass filtering to show the instances of the fetal movements. Information gathered during user trials with the prototype suggests that the system detects significantly higher numbers of fetus movements than that observed based on the mother's perception. Among the various techniques available for fetal movement monitoring, fibre optic sensing provides many advantages including multiplex capability, flexibility and minimal size, making the concept an attractive solution for reliable monitoring of antenatal fetal movements.

Radiation protection in non-ionizing and ionizing body composition assessment procedures

Body composition assessment (BCA) represents a valid instrument to evaluate nutritional status through the quantification of lean and fat tissue, in healthy subjects and sick patients. According to the clinical indication, body composition (BC) can be assessed by different modalities. To better analyze radiation risks for patients involved, BCA procedures can be divided into two main groups: the first based on the use of ionizing radiation (IR), involving dual energy X-ray absorptiometry (DXA) and computed tomography (CT), and others based on non-ionizing radiation (NIR) [magnetic resonance imaging (MRI)]. Ultrasound (US) techniques using mechanical waves represent a separate group. The purpose of our study was to analyze publications about IR and NIR effects in order to make physicians aware about the risks for patients undergoing medical procedures to assess BCA providing to guide them towards choosing the most suitable method. To this end we reported the biological effects of IR and NIR and their associated risks, with a special regard to the excess risk of death from radio-induced cancer. Furthermore, we reported and compared doses obtained from different IR techniques, giving practical indications on the optimization process. We also summarized current recommendations and limits for techniques employing NIR and US. The authors conclude that IR imaging procedures carry relatively small individual risks that are usually justified by the medical need of patients, especially when the optimization principle is applied. As regards NIR imaging procedures, a few studies have been conducted on interactions between electromagnetic fields involved in MR exam and biological tissue. To date, no clear link exists between MRI or associated magnetic and pulsed radio frequency (RF) fields and subsequent health risks, whereas acute effects such as tissue burns and phosphenes are well-known; as regards the DNA damage and the capability of NIR to break chemical bonds, they are not yet robustly demonstrated. MRI is thus considered to be very safe for BCA as well US procedures.

Recent nano-, micro- and macrotechnological applications of ultrasonication in food-based systems

There is a neoteric and rising demand for nutritional and functional foods which behooves food processors to adopt processing techniques with optimal conservation of bioactive components in foods and with minimal pernicious impacts on the environment. Ultrasonication, a mechanochemical technique has proven to be an efficacious panacea to these concerns. In this review, an analytic exploration of recent researches and designs regarding ultrasound methodology and equipment on diverse food systems, technological scales, procedural parameters and outcomes of such experimentations optimally scrutinized. The relative effects of ultrasonication on food formulations, components and attributes such as nanoemulsions, nanocapsules, proteins, micronutrients, sensory and mechanical characteristics are evaluatively delineated. In food systems where ultrasonication was employed, it was found to have a remarkable effect on one or more quality parameters. This review is a supplementation to the pedagogical awareness to scholars on the suitability of ultrasonication for research procedures, and a call to industrial food brands on the adoption of this technique for the development of foods with optimally sustained nutrient profiles.

Strain elastography of palatal tumors in conjunction with intraoral ultrasonography, computed tomography, and magnetic resonance imaging: 2 case reports

Computed tomography (CT) and magnetic resonance imaging (MRI) can be useful for the evaluation of palatal lesions, and strain elastography (performed together with intraoral ultrasonography) is a relatively new sonographic imaging modality. This report describes 2 clinical cases in which strain elastography was used to assess palatal tumors in conjunction with intraoral ultrasonography, CT, and MRI. In the first case, diagnosed as a myoepithelioma, the strain was determined to be 0.000% (strain of normal tissue, 0.556%). In the second case, diagnosed as an adenoid cystic carcinoma, the determined strain was 0.000% (strain of normal tissue, 1.077%). Therefore, we conclude that intraoral strain elastography can be useful for evaluating palatal lesions.

[Safety aspects of ultrasound diagnostics]

Ultrasonography is free of ionizing radiation but during the examination it is accompanied by energy deposition in the tissue. Therefore, users should be familiar with the mechanisms of action and possible risks. Thermal and non-thermal (e.g. cavitation) effects are related to the intensity and sound pressure of ultrasound waves and are therefore also dependent on the ultrasound modality used, e.g., B‑mode, color Doppler and/or pulsed wave (pw) Doppler. With B‑mode ultrasound no dangerous thermal effects are to be expected. In embryos and foetuses as well as febrile patients caution should be exercised. The pw Doppler mode can cause temperature spikes and the risks increase with the duration of use. Ultrasound contrast media are pathogenic for cavitation and should be avoided during the 24 h prior to shock wave lithotripsy. In ultrasound modalities with high local energy deposition, the values for the thermal index (TI) and mechanical index (MI) displayed on the screen should be observed and as with ionizing radiation, the ALARA (as low as reasonably achievable) principle should be adhered to.

Artifactual Lung Ultrasonography: It Is a Matter of Traps, Order, and Disorder

When inspecting the lung with standard ultrasound B-mode imaging, numerous artifacts can be visualized. These artifacts are useful to recognize and evaluate several pathological conditions in Emergency and Intensive Care Medicine. More recently, the interest of the Pulmonologists has turned to the echographic study of the interstitial pathology of the lung. In fact, all lung pathologies which increase the density of the tissue, and do not consolidate the organ, are characterized by the presence of ultrasound artifacts. Many studies of the past have only assessed the number of vertical artifacts (generally known as B-Lines) as a sign of disease severity. However, recent observations suggest that the appearance of the individual artifacts, their variability, and their internal structure, may play a role for a non-invasive characterization of the surface of the lungs, directing the diagnoses and identifying groups of diseases. In this review, we discuss the meaning of lung ultrasound artifacts, and introduce hypothesis on the correlation between their presence and the structural variation of the sub-pleural tissue in light of current knowledge of the acoustic properties of the pleural plane.

Additional benefits of three-dimensional ultrasound for prenatal assessment of twins

Three-dimensional ultrasound (3DUS) may provide additional information for prenatal assessment of twins. It may improve the diagnostic confidence of dating, nuchal translucency (NT) and chorionicity assignment in twin pregnancies. The "virtual 3DUS placentoscopy" can guide selective fetoscopic laser photocoagulation (SFLP) to treat twin-twin transfusion syndrome (TTTS). Volumetric assessment of the dysmorphic acardiac twin with the Virtual Organ Computer-aided Analysis (VOCAL) software is more accurate than the conventional ultrasound measurement. Twin anemia polycythemia (TAP) sequence and selective intrauterine growth restriction (sIUGR) may be clinically monitored with 3DUS placental volume (PV) and power Doppler vascular indices. Congenital anomalies are more common in twins. Evaluation of fetal anomalies with 3DUS could assist perinatal management. The 3DUS power Doppler can provide a better understanding of true and false umbilical cord knots, which are commonly found in monoamniotic (MA) twins. Single demise in monochorionic (MC) twin pregnancies can cause severe neurologic morbidity in the surviving co-twin. Prenatal prediction of brain injury in the surviving co-twin with unremarkable neurosonographic examination is difficult. The 3DUS power Doppler may aid in prenatal detection of subtle abnormal cerebral perfusion. Prenatal assessment of conjoined twins with 3DUS is important if emergency postnatal surgical separation is anticipated. There is no significant additional advantage in using real-time 3DUS to guide prenatal interventions. Assessment of the cervix and pelvic floor during twin pregnancies is enhanced with 3DUS. Due to lack of high-quality studies, routine prenatal 3DUS in twin pregnancies needs to be balanced with risks of excessive ultrasound exposure.

Ultrasound-induced microbubble cavitation via a transcanal or transcranial approach facilitates inner ear drug delivery

Ultrasound-induced microbubble (USMB) cavitation is widely used to promote drug delivery. Our previous study investigated USMB targeting the round window membrane by applying the ultrasound transducer to the tympanic bulla. In the present study, we further extended the use of this technology to enhance drug delivery to the inner ear by introducing the ultrasound transducer into the external auditory canal (EAC) or applying it to the skull. Using a 3-dimensional-printed diffusion apparatus mimicking the pathway for ultrasound passing through and reaching the middle ear cavity in vitro, the models simulating the transcanal and transcranial approach demonstrated 4.8-fold- and 3.7-fold-higher delivery efficiencies, respectively. In an in vivo model of guinea pigs, by filling tympanic bulla with microbubbles and biotin-FITC, USMB applied transcanally and transcranially induced 2.8-fold and 1.5-fold increases in biotin-FITC delivery efficiencies, respectively. In addition, the gentamicin uptake by cochlear and vestibular hair cells and gentamicin-induced hair cell loss were significantly enhanced following transcanal application of USMB. On the 28th day after transcanal USMB, safety assessment showed no significant changes in the hearing thresholds and the integrity of cochlea. These are the first results to our knowledge to demonstrate the feasibility and support the potential clinical application of applying USMB via EAC to facilitate drug delivery into the inner ear.

Advances in Ultrasound Mediated Transdermal Drug Delivery

Low frequency ultrasound-assisted drug delivery has been widely investigated as a non-invasive method to enhance the transdermal penetration of drugs. Using this technique, a brief application of ultrasound is used to permeabilize skin for a prolonged time. In this review, an overview on ultrasound is detailed to help explain the parameters that could be modulated to obtain the desired ultrasound parameters for enhanced transdermal drug delivery. The mechanisms of enhancement and the latest developments in the area of ultrasound-assisted transdermal drug delivery are discussed. Special emphasis is placed on the effects of ultrasound when used in combination with microneedles, electroporation and iontophoresis, and penetration enhancers. Further, this review summarizes the effect of ultrasound on skin integrity and the regulatory requirements for commercialization of the ultrasound based transdermal delivery instruments.

Doppler Ultrasound Technology for Fetal Heart Rate Monitoring: A Review

Fetal well-being is commonly assessed by monitoring the fetal heart rate (fHR). In clinical practice, the de facto standard technology for fHR monitoring is based on the Doppler ultrasound (US). Continuous monitoring of the fHR before and during labor is performed using a US transducer fixed on the maternal abdomen. The continuous fHR monitoring, together with simultaneous monitoring of the uterine activity, is referred to as cardiotocography (CTG). In contrast, for intermittent measurements of the fHR, a handheld Doppler US transducer is typically used. In this article, the technology of Doppler US for continuous fHR monitoring and intermittent fHR measurements is described, with emphasis on fHR monitoring for CTG. Special attention is dedicated to the measurement environment, which includes the clinical setting in which fHR monitoring is commonly performed. In addition, to understand the signal content of acquired Doppler US signals, the anatomy and physiology of the fetal heart and the surrounding maternal abdomen are described. The challenges encountered in these measurements have led to different technological strategies, which are presented and critically discussed, with a focus on the US transducer geometry, Doppler signal processing, and fHR extraction methods.

Ultrastructural Changes Associated With the Enhanced Permeability of the Round Window Membrane Mediated by Ultrasound Microbubbles

The round window membrane (RWM) is the most common entryway for local drug and gene delivery into the inner ear, but its permeability can change the treatment outcome. We previously demonstrated a feasible and highly efficient approach using ultrasound-aided microbubble (USMB) cavitation to enhance the permeability of the RWM. Here, we investigated the safety of USMB exposure and the association between temporal changes in RWM permeability and ultrastructure. Experimental guinea pigs were divided into two treatment groups: a control group receiving round window soaking (RWS) with MBs and treatment (USM) groups undergoing 3 (USM-3) or 5 (USM-5) consecutive USMB exposures (1 min/exposure) at an acoustic intensity of 3 W/cm² and 1 MHz frequency. The trans-RWM delivery efficiency of biotin-fluorescein isothiocyanate conjugates, used as permeability tracers, revealed a greater than 7-fold higher delivery efficiency for the USM groups immediately after 3 or 5 exposures than for the RWS group. After 24 h, the delivery efficiency was 2.4-fold higher for the USM-3 group but was 6.6-fold higher for the USM-5 group (and 3.7-fold higher after 48 h), when compared to the RWS group. Scanning electron microscopy images of the RWM ultrastructure revealed USMB-induced sonoporation effects that could include the formation of heterogeneous pore-like openings with perforation diameters from 100 nm to several micrometers, disruption of the continuity of the outer epithelial surface layer, and loss of microvilli. These ultrastructural features were associated with differential permeability changes that depended on the USMB exposure course. Fourteen days after treatment, the pore-like openings had significantly decreased in number and the epithelial defects were healed either by cell expansion or by repair by newly migrated epithelial cells. The auditory brainstem response recordings of the animals following the 5-exposure USMB treatment indicated no deterioration in the hearing thresholds at a 2-month follow-up and no significant hair cell damage or apoptosis, based on scanning electron microscopy, surface preparations, and TUNEL assays. USMBs therefore appear to be safe and effective for inner ear drug delivery. The mechanism of enhanced permeability may involve a disruption of the continuity of the outer RWM epithelial layer, which controls transmembrane transport of various substances.

Considerations for ultrasound exposure during transcranial MR acoustic radiation force imaging

The aim of this study was to improve the sensitivity of magnetic resonance-acoustic radiation force imaging (MR-ARFI) to minimize pressures required to localize focused ultrasound (FUS) beams, and to establish safe FUS localization parameters for ongoing ultrasound neuromodulation experiments in living non-human primates. We developed an optical tracking method to ensure that the MR-ARFI motion-encoding gradients (MEGs) were aligned with a single-element FUS transducer and that the imaged slice was prescribed at the optically tracked location of the acoustic focus. This method was validated in phantoms, which showed that MR-ARFI-derived displacement sensitivity is maximized when the MR-ARFI MEGs were maximally aligned with the FUS propagation direction. The method was then applied in vivo to acquire displacement images in two healthy macaque monkeys (M fascicularis) which showed the FUS beam within the brain. Temperature images were acquired using MR thermometry to provide an estimate of in vivo brain temperature changes during MR-ARFI, and pressure and thermal simulations of the acoustic pulses were performed using the k-Wave package which showed no significant heating at the focus of the FUS beam. The methods presented here will benefit the multitude of transcranial FUS applications as well as future human applications.

Characterization and modeling of acousto-optic signal strengths in highly scattering media

Ultrasound optical tomography (UOT) is an imaging technique based on the acousto-optic effect that can perform optical imaging with ultrasound resolution inside turbid media, and is thus interesting for biomedical applications, e.g. for assessing tissue blood oxygenation. In this paper, we present near background free measurements of UOT signal strengths using slow light filter signal detection. We carefully analyze each part of our experimental setup and match measured signal strengths with calculations based on diffusion theory. This agreement between experiment and theory allows us to assert the deep tissue imaging potential of ∼ 5  cm for UOT of real human tissues predicted by previous theoretical studies [Biomed. Opt. Express8, 4523 (2017)] with greater confidence, and indicate that future theoretical analysis of optimized UOT systems can be expected to be reliable.

Low-Intensity Ultrasound Induces Thermodynamic Phase Separation of Cell Membranes through a Nucleation-Condensation Process

Membrane fluidity, a broad term adopted to describe the thermodynamic phase state of biological membranes, can be altered by local pressure variations caused by ultrasound exposure. The alterations in lipid spatial configuration and dynamics can modify their interactions with membrane proteins and activate signal transduction pathways, thus regulating several cellular functions. Here fluidity maps of murine fibroblast cells are generated at a sub-micrometric scale during ultrasound stimulation with an intensity and frequency typical of medical applications. Ultrasound induces a phase separation characterized by two-step kinetics leading to a time-dependent decrease in fluidity. First, nucleation of liquid crystallin domains with an average dimension of ∼1 μm occurs. Then, these domains condense into larger clusters with an average dimension of ∼1.5 μm. The induced phase separation could be an important driving force critical for the cellular response connecting the ultrasound-induced mechanical stress and signal transduction.

Recent advances in ultrasound-based transdermal drug delivery

The transdermal transport of pharmaceuticals possesses various advantageous properties over conventional drug administration techniques such as oral delivery and hypodermic injections. However, the stratum corneum persists as the main barrier, which impedes percutaneous transport. The ultrasound-based transdermal delivery of therapeutics is one of the techniques that are being investigated to overcome this obstacle. This review outlines the background information pertaining to sonophoresis and then discusses the individual sections of sonophoretic research. These areas include the sonophoretic application of various drugs, dual-frequency sonophoresis, synergistic combinations of transdermal drug delivery techniques, and the use of nanosized carriers in ultrasound-based transdermal delivery. The various challenges associated with sonophoretic drug delivery and trends of future research are also highlighted.

Safety of Ultrasound Exposure: Knowledge, Attitudes, and Practices of Australasian Sonographers

Introduction:

While perceived as safe, diagnostic ultrasound has the potential to cause biological effects on the body tissues. The aim of this study was to evaluate knowledge, attitudes, and practices of Australasian sonographers on bioeffects and safety of ultrasound scanning.

Methods:

Focus groups were used to develop a questionnaire to explore knowledge, attitudes, and practices of ultrasound safety, which was then distributed to Australasian sonographers. Thematic (focus groups) and descriptive (questionnaires) analyses were undertaken.

Results:

A 37-item questionnaire addressed knowledge, attitudes, and practices of ultrasound safety. In 47 collected responses, sonographers demonstrated good familiarity of thermal index (TI) (79%), mechanical index (MI) (68%), and “as low as reasonably achievable” (ALARA) principle (85%). However, most sonographers could not accurately define TI (13%) and had poor knowledge of safety guidelines relating to TI (19%) and MI (14%). Over 30% were uncertain about their attitudes to ultrasound safety issues. While 52% always and 30% most of the time adhere to ALARA, 37% of sonographers reported never monitoring TI and MI.

Discussion:

While familiar with safety terms, knowledge of safety guidelines was lacking. Many sonographers were uncertain about their attitudes to the safety of scans, and safety practices involving monitoring for bioeffects were not a high priority.