Biomedical Acoustics Research Articles

Capillaries, cancer, and cavitation: An introduction to the Biomedical Acoustics Technical Committee

Biomedical acoustics is a growing field comprised of individuals who study the interaction of sound with biological materials. While ultrasound in medicine is most associated with fetal imaging, researchers and clinicians continue to push the boundaries of ultrasound to improve the diagnosis and treatment of disease. As such, this conference features special sessions on imaging the microvasculature in the brain and beamforming to improve the speed and quality of the ultrasound image. But ultrasound can also be used as a therapeutic due to absorption of the acoustic wave, radiation forces, and cavitation. On the therapy side, special sessions have been organized on: phase-change contrast agents, which can improve imaging contrast or locally deliver medications to cells; sonodynamic therapy, which involves killing cancer cells with ultrasound; sonobiopsy, which uses ultrasound to enhance the release of biomarkers for noninvasive disease diagnosis; and wave propagation in complex media, which helps us to understand our acoustic field for imaging and therapy. BATC has also organized a session on training students in technical writing. Ultrasound is an important diagnostic and treatment modality that continues to advance as researchers and physicians work to improve patient outcomes.

On the elements of an excellent research paper

Journal publications play a key role in the dissemination of research findings in the biomedical acoustics community. However, authors are often unsure of how to write a paper that will be considered as excellent by their peers, because the notion of excellence is arguably subjective and ill-defined. To demystify such an issue, this presentation will discuss four major elements (novelty, significance, rigor, writing quality) that are often found in excellent journal papers in biomedical ultrasound. Since 2022, these four elements have been adopted as the peer review criteria by the flagship ultrasonics journal of the IEEE press. Multi-day writing workshops with interactive, hands-on tutorials have been designed to engage prospective authors on how to plan and prepare journal manuscripts with the four elements of excellence. Reviewer training workshops have also been offered to inform journal reviewers about these evaluation criteria and expectations. Through these initiatives, we aim to establish a quality-driven publishing emphasis within the biomedical acoustics community. Achieving so will have long-term benefits on the reputation and growth of this research field.

Sustainable Solutions in Sound Shielding: Harnessing Metamaterials for Acoustic Cloaking

The development of metamaterials promises to enable smallscale, worldwide industry-wide acoustic, electromagnetic, mechanical, and solar energy harvesting. Engineered structures surpass natural material limitations, offering capabilities unattainable in traditional counterparts. This paper explores metamaterials' manipulation of acoustic, electromagnetic, mechanical, and solar energy. Mechanical metamaterials convert strain into electrical energy, applicable from interstellar travel to terrestrial infrastructure. Precision-configured acoustic metamaterials efficiently harness dispersed acoustic energy, improving renewable energy methodologies. Integration into photovoltaic cells showcases metamaterials' solar potential, with innovative designs enhancing solar energy conversion efficiency. “Metamaterials” is a word used to describe artificial structures whose properties are based on the aggregate expression of individual components. Acoustic metamaterials are the term used for such constructions intended for the manipulation of acoustic waves. Controlled wave propagation is made possible by acoustic metamaterials, which is frequently not possible with bulk materials created chemically. This indicates that the wave propagation in acoustic metamaterials is directed and produces desired acoustic effects, independent of the mass-density properties of the material. The distinct properties of acoustic metamaterials have paved the way for the creation of practical solutions for a variety of uses, such as passive destructive interference, acoustic cloaking, sound focusing, low-frequency sound insulation, and biomedical acoustics. The kind of sound modification determines the general properties of an acoustic metamaterial. The properties of several of the most promising acoustic metamaterials from passive to active are introduced in this work. In order to achieve a sustainable future, it is necessary to combine environmentally friendly technologies with renewable energy sources for their final application. This is demonstrated by highlighting both the fundamental concepts and the physical models that were assessed.

Reconfigurable and Phase‐Engineered Acoustic Metasurfaces for Broadband Wavefront Manipulation

AbstractA novel type of phase‐engineered acoustic metasurfaces with reconfigurable properties is reported, enabling the flexible broadband manipulation of reflected wavefronts. The participants of the metasurface are elements conceived to possess even‐distributed reflected phases covering 2π span with linearity and small acoustic energy loss. The reconfigurable property of the metasurface is implemented by rearranging the fixed meta‐elements based on the phase profile, which is related to the characteristic of a specific wavefront shape. The metasurface's capability is successfully demonstrated to achieve acoustic focusing and bending within the frequency range of 2300–2800 Hz, showcasing its feasibility and adaptability. To enhance its practical applications, porous materials are incorporated, leveraging the robustness of phase differences among the meta‐elements to achieve high acoustic energy cancellation. Effective sound attenuation occurs within the frequency range of 1300–3100 Hz, even under wide‐angle incidences ranging from −80° to 80°. The work paves the way for further research on reconfigurable acoustic metasurfaces in broad frequency regions and exerts favorable implications for generally applicable structures applied in multi‐fields including biomedical acoustics, noise control, and so on.

Lessons learned from mentoring and being mentored in a large environment

The Focused Ultrasound Lab at Sunnybrook Research Institute has over 60 regular members and trains an additional 30 + summer students each summer. Drawing on the speaker’s experience, as well as trainee data, this talk will focus on approaches to effective mentoring in a large environment. The role of mentor teams within biomedical acoustics and in other related fields will be discussed.

Value of multidisciplinary peer mentoring

Biomedical acoustics is a multidisciplinary field. As such, both the scientific field and its members have the potential to benefit from the interactions and cross-fertilization of different subfields. Peer mentoring groups (PMGs) can promote multidisciplinary interaction. A PMG involves the intentional, structured, and consistent interaction of individuals at similar career stages. The horizontal organization of a PMG can promote a safe and supportive environment, enabling greater knowledge sharing. PMG knowledge sharing is bidirectional, providing benefits to all participants and an opportunity to leverage diversity, which yields outcomes. In one example from our institution, a research-active group of junior faculty from different academic divisions within a department of internal medicine met biweekly to review, on a rotating basis, active grant applications, critiques of rejected proposals, and career development challenges. Another example was an interdepartmental graduate program where doctoral students studying a range of fields (e.g., infectious diseases, cancer, metabolism, and cardiovascular disease) engaged in a journal club and a seminar series. In both settings, participants had the opportunity to benefit from the recognition of thematic and methodological overlap in their otherwise disparate studies, which promoted best practices in research. In summary, PMGs provide value to both participants and the field.

Jack of all trades: Challenges and opportunities for mentoring in interdisciplinary research

Biomedical acoustics spans a particularly broad range of disciplines from neuroscience to quantum physics and everything in between. While this diversity is exciting and constantly stimulating, it can pose considerable challenges for students and mentors in finding the appropriate balance between breadth and depth. The aim of this talk is to share the author’s experience of designing graduate and undergraduate courses in biomedical acoustics and particularly of supervision and team building for graduate and post-doctoral researchers from different disciplines. Key topics will include the importance of co-supervision, promoting understanding and implementation of the scientific method; encouraging curiosity driven experiments; vital lessons from science communication; and finally the surprising insights provided by training to teach dance.

Helmholtz-Rayleigh Interdisciplinary Silver Medal in Biomedical Acoustics and Physical Acoustics 2023: Vera A. Khokhlova

The Silver Medal is presented to individuals, without age limitation, for contributions to the advancement of science, engineering, or human welfare through the application of acoustic principles, or through research accomplishment in acoustics.

Mentoring from the other side of the fence: Student perspectives on good advising

As a fourth-year graduate student and ASA Student Council representative, I have had access to the opinions of students and gained insight on what they expect from their mentors and advisors. In this talk, I hope to demystify the student perspective by discussing the themes that have emerged from both Blackstock Mentor Award applications and a mentoring survey sent to Biomedical Acoustics students. One question drives the analysis: What kind of mentor/mentee relationship leads to the most successful outcomes and how is that success measured by students?

The Use of Machine Learning Algorithms in the Classification of Sound

This study is a systematic review of literature on the classification of sounds in three domains - Bioacoustics, Biomedical acoustics, and Ecoacoustics. Specifically, 68 conferences and journal articles published between 2010 and 2019 were reviewed. The findings indicated that Support Vector Machines, Convolutional Neural Networks, Artificial Neural Networks, and statistical models were predominantly used in sound classification across the three domains. Also, the majority of studies that investigated medical acoustics focused on respiratory sounds analysis. Thus, it is suggested that studies in Biomedical acoustics should pay attention to the classification of other internal body organs to enhance diagnosis of a variety of medical conditions. With regard to Ecoacoustics, studies on extreme events such as tornadoes and earthquakes for early detection and warning systems were lacking. The review also revealed that marine and animal sound classification was dominant in Bioacoustics studies.

Babies, bubbles, and brain disease: An introduction to the Biomedical Acoustics Technical Committee

For most folks, ultrasound in medicine is associated with fetal imaging, and it remains among the most widely available and frequently used imaging modalities in the clinic. Recent advances have expanded the capacity of ultrasound imaging to include the ability to quantify mechanical properties of tissue (elastography), microvascular structure (super resolution imaging), perfusion (contrast imaging), and molecular expression such as oxygenation (photo-acoustic imaging). Effective diagnostic information is now possible for targets traditionally avoided by ultrasound imaging, such as lung for COVID-19 diagnoses. Ultrasound energy can also be harnessed for therapeutic purposes. Focused sources enable us to ablate malignancies through thermal or mechanical-based mechanisms. A strong tumor immune response has been observed for histotripsy, a bubble-based ablation method, potentiating a means to treat multi-focal disease. Ultrasound-mediated bubble activity enhances drug delivery to improve treatment for thrombo occlusive disease (e.g., heart attack, stroke, venous thrombosis), cancer, and tissue regeneration. Improved drug delivery is also possible in the brain via ultrasound-mediated opening of the blood brain barrier. Separate from drug delivery, ultrasound can induce neuromodulation for the treatment of essential tremor, neuropathic pain, and Parkinson’s disease. Diagnostic and therapeutic ultrasound continues to advance the field of medicine, and are integral for improving the outcomes for debilitating diseases.

Transformation acoustics for beamforming in anisotropic media

Acoustic wave propagation in anisotropic media like tissue and other biomaterials is important for biomedical acoustics, as ultrasound is commonly used as a technique for non-invasive surgeries and diagnostic imaging purposes. These ultrasound applications require beamformed signals to target specific regions of the body. However, the anisotropic properties of the body (e.g., muscle fibers) distort the beamformed wavefronts, detrimental to the performance of ultrasound therapies and imaging. Here, we propose and experimentally demonstrate a unique transformation acoustic technique that corrects the anisotropic distortive effects to beamform an arbitrarily desired propagation pattern. The experimental measurements demonstrate the effectiveness of this transformation acoustic correction for arbitrary focusing and selfbending beams. Our work provides an important method to suppress undesired anisotropic effects on beamformed waves, to improve upon the precision and effectiveness of medical treatments and diagnostics facilitated by noninvasive ultrasound therapies and imaging.

Acoustic holograms for directing arbitrary cavitation patterns

Cavitation is an important phenomenon in biomedical acoustics. It can produce both desired outcomes (i.e., local therapeutic effects in vivo) and undesired outcomes (i.e., tissue damage), and it is, thus, important to both understand and direct cavitation fields. Through the use of three-dimensional-printed acoustic lenses and cavitation-sensitive acoustic phantoms, we demonstrate the generation of arbitrary shape two-dimensional (2D) microbubble cavitation fields. In this study, we demonstrate shaping a 1 MHz acoustic beam as the character “7” on a target plane that contains a higher mechanical index than the cavitation threshold for encapsulated microbubbles in a gelatin phantom. The lens pattern is first designed by calculating the phase map of the desired field using an angular spectrum approach. After lens implementation, acoustic pulsing through the lens generated the target acoustic field in a phantom and produced a cavitation map following the intended 2D pattern. The cavitation pattern was similar (with the structural similarity of 0.476) to the acoustic pressure map of the excitation beam.

Limitations on nonlinear fractional calculus models used in biomedical acoustics

Fractional calculus models used for biomedical ultrasound are associated with attenuation proportional to ω y, where y is typically in the range 1 < y < 2. To determine whether the attenuation and accompanying dispersion are sufficient to stabilize shock formation, the models are formulated as a Burgers equation with the traditional loss term replaced by a fractional derivative of order y. For y < 1 the resulting equation predicts unphysical solutions beyond the shock-formation distance. The second example pertains to nonlinear Lucassen interface waves, a model equation for which has been proposed to describe mechanical perturbations that accompany the transmission of nerve impulses. Linear Lucassen waves are defined by a second-order space derivative and a fractional time derivative of order 3/2, which falls between order 2 in the wave equation and order 1 in the diffusion equation. The resulting attenuation is proportional to ω3/4, and the corresponding nonlinear “fractional diffusive waves,” while strongly attenuated on the scale of a wavelength, may be lacking essential physics beyond the predicted shock-formation distance. Calculations are presented that determine wave amplitudes and propagation distances for which these two fractional calculus models may be of questionable physical significance due to nonlinearity. [B.E.S. is supported by the ARL:UT McKinney Fellowship in Acoustics.]

Recent Advances in Acoustic Metamaterials for Simultaneous Sound Attenuation and Air Ventilation Performances

In the past two decades, acoustic metamaterials have garnered much attention owing to their unique functional characteristics, which are difficult to find in naturally available materials. The acoustic metamaterials have demonstrated excellent acoustical characteristics that paved a new pathway for researchers to develop effective solutions for a wide variety of multifunctional applications, such as low-frequency sound attenuation, sound wave manipulation, energy harvesting, acoustic focusing, acoustic cloaking, biomedical acoustics, and topological acoustics. This review provides an update on the acoustic metamaterials’ recent progress for simultaneous sound attenuation and air ventilation performances. Several variants of acoustic metamaterials, such as locally resonant structures, space-coiling, holey and labyrinthine metamaterials, and Fano resonant materials, are discussed briefly. Finally, the current challenges and future outlook in this emerging field are discussed as well.

Biomedical Acoustics: Breaking old barriers in science and medicine

The Technical Committee on Biomedical Acoustics (BATC) is one of the most diverse groups in the Acoustical Society of America. BATC is comprised of scientists and engineers who study a wide range of biomedical applications using ultrasound from imaging fetuses to ablating fibroids and treating brain disorders. Diagnostic ultrasound has expanded to include exciting new techniques such as shear wave elastography and opto-acoustic imaging. Therapeutic ultrasound applications include physiotherapy, lithotripsy, as well as the treatment of tumors via thermal ablation, i.e., HITU, or mechanical ablation, i.e., histotripsy. The most recent developments in therapeutic ultrasound involve neuromodulation and transcranial magnetic resonance guided focused ultrasound for the treatment of various brain disorders, including essential tremor, neuropathic pain, and Parkinson’s disease. The ability to temporarily open the blood-brain barrier using focused ultrasound has been demonstrated in animals and, more recently, in humans. Opening of the blood-brain barrier could allow the transmission of drugs to treat brain diseases. Diagnostic and therapeutic ultrasound applications continue to advance the field of medicine and are integral to the advancement of both diagnosis and treatment of debilitating diseases.

Non-Hermitian complimentary acoustic metamaterials for imaging through skull

Complimentary metamaterials are designed to facilitate full acoustic transmission through highly mismatched impedance barriers. Applied to biomedical acoustics, complimentary metamaterials theoretically enable unidirectional acoustic transmission through the skull to realize noninvasive brain imaging and facilitate neural ultrasound therapies. Previously designed complimentary acoustic metamaterials relied on the realization of negative material parameters opposite to that of the skull to cancel the impedance mismatch effect. However, much of the incident acoustic energy is dissipated due to the skull’s internal porosity, preventing full energy transmission. To resolve this issue, we propose to counteract the skull’s acoustic attenuating effects with a non-Hermitian complimentary metamaterial (NHCMM) having an active gain circuit to achieve high acoustic transmission at high frequencies. In addition to the full wave simulations showing near perfect transmission from either side of the skull, the NHCMM preserves imaging information for objects inside the skull, and enhances the focused acoustic energy used for focused ultrasound therapies. By facilitating two-way acoustic transmission through the skull with NHCMMs, we lay the foundation for noninvasive brain imaging and treatment for neural disorders.

Biomedical acoustics research at the Image-Guided Ultrasound Therapeutics Laboratories

The Image-guided Ultrasound Therapeutic Laboratories (IgUTL) are located at the University of Cincinnati in the Heart, Lung, and Vascular Institute, a key component of efforts to align the UC College of Medicine and UC Health research, education, and clinical programs. These laboratories, directed by Christy K. Holland, comprise graduate and undergraduate students, postdoctoral fellows, physician-scientists, and clinical and scientific collaborators in fields including cardiology, neurosurgery, neurology, radiology, and emergency medicine. Holland’s research focuses on biomedical ultrasound including sonothrombolysis, ultrasound-mediated drug and bioactive gas delivery, development of echogenic liposomes, early detection of cardiovascular diseases, and ultrasound-image guided tissue ablation. Imaging algorithms incorporate both passive and active cavitation detection. The Biomedical Acoustics Laboratory within IgUTL, directed by T. Douglas Mast, investigates ultrasound imaging for therapy guidance, including echo decorrelation imaging for monitoring liver cancer ablation and real-time tracking of tongue motion for biofeedback in speech therapy. The Biomedical Ultrasonics and Cavitation Laboratory within IgUTL, directed by Kevin J. Haworth, employs ultrasound-mediated gas scavenging for image-guided treatment of cardiovascular disease, especially reperfusion injury. [Work supported by NIH Grants R01 NS047603, R01 HL135092, R01 HL133334, R01 CA158439, R01 DC017301, and K25 HL133452.]

Biomedical acoustics: From diagnostic imaging to treating brain disorders

The Technical Committee on Biomedical Acoustics (BATC) is one of the most diverse groups in the Acoustical Society of America. BATC is comprised of scientists and engineers who study a wide range of biomedical applications using ultrasound from imaging fetuses to ablating fibroids and treating brain disorders. Diagnostic ultrasound has expanded to include exciting new techniques such as shear wave elastography and opto-acoustic imaging. Therapeutic ultrasound applications include physiotherapy, lithotripsy, as well as the treatment of tumors via thermal ablation, i.e., HITU, or mechanical ablation, i.e., histotripsy. The most recent developments in therapeutic ultrasound involve neuromodulation and transcranial magnetic resonance guided focused ultrasound for the treatment of various brain disorders, including essential tremor, neuropathic pain, and Parkinson’s disease. The ability to temporarily open the blood-brain barrier using focused ultrasound has been demonstrated in animals and, more recently, in humans. Opening of the blood-brain barrier could allow the transmission of drugs to treat brain diseases. Diagnostic and therapeutic ultrasound applications continue to advance the field of medicine and are integral to the advancement of both diagnosis and treatment of debilitating diseases.

Summary of "Biomedical Acoustics and Physical Acoustics: Shock Waves and Ultrasound for Calculus Fragmentation".

This paper summarizes the special session, "Shock Waves and Ultrasound for Calculus Fragmentation," that took place during the 176th Meeting of the Acoustical Society of America and 2018 Acoustics Week in Canada. The sessions were cosponsored by the Biomedical Acoustics and Physical Acoustics Technical Committees and consisted of ten talks by industry and academic researchers from institutions in the United States, France, and the Russian Federation. The sessions described basic and applied acoustic research to manage urinary stones.