–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
The Challenge of Treating the Brain
Focused Ultrasound (FUS) is a revolutionary, incision-free technology that promises to treat brain disorders, such as tumors and Parkinson’s disease. It works by concentrating high-frequency sound waves to a precise point deep within the brain, much like a magnifying glass focuses sunlight. However, this promising therapy faces a major obstacle: the human skull. The skull is a thick, bony barrier that scrambles, reflects, and weakens these high-frequency waves. This makes it incredibly difficult for doctors to monitor the treatment in real-time and confirm that the energy is actually reaching the intended target. This uncertainty limits the safety and effectiveness of FUS brain therapies.
Figure 1: a – Conceptual illustration of the technique. A transmitter (bottom) sends high-frequency (1 MHz) therapeutic ultrasound waves through the skull. Where these waves interact at the focus, they generate a 50kHz low frequency “parametric Array” signal that easily passes through the skull to a receiver (top). The HASPA framework uses this detected signal to map the therapy. b- The reconstructed (first order) 1 MHz high-frequency and 100 kHz low frequency parametric field using HASPA framework with 3,6, and 9 dB contours.
The skull is a thick, bony barrier that scrambles, reflects, and weakens these high-frequency waves. This makes it incredibly difficult for doctors to monitor the treatment in real-time and confirm that the energy is actually reaching the intended target. This uncertainty limits the safety and effectiveness of FUS brain therapies.d
An Acoustic “Trick” to Overcome the Barrier
Researchers at Georgia Tech and Emory University have developed a new computational framework called HASPA (Heterogeneous Angular Spectrum Parametric Array) that exploits a nonlinear acoustic “trick” known as the “parametric array effect.” When two high-frequency ultrasound beams around 1 MHz beams used for therapy meet at the target inside the brain, they interact nonlinearly and mix. This interaction generates a brand-new sound wave at a much lower difference frequency (around 50-100 kHz).
Think of it this way: High-frequency sounds, like a faint whistle, are easily blocked by a thick wall (the skull). However, low-frequency sounds, like the thumping bass from a neighbor’s stereo, travel through walls easily. In this new approach, the therapeutic “whistles” create a localized “bass” beat exactly where the treatment is happening. This low-frequency signal acts as a messenger, traveling cleanly back out through the skull to be detected by external sensors.
Decoding the Message: The HASPA Framework
The challenge is translating this low-frequency message back into a high-resolution picture of the high-frequency treatment zone inside the brain.
To achieve this, the team developed a novel computational framework called HASPA (Heterogeneous Angular Spectrum Parametric Array) and an associated inverse algorithm (iHASPA).
iHASPA analyzes the low-frequency signal measured outside the skull and mathematically reconstructs a map of the original therapy beams deep inside the brain. Crucially, the framework accounts for the complex ways sound travels through the specific properties of the patient’s skull and brain tissue, correcting for distortions.
Impact and Future
By leveraging this nonlinear acoustic effect, the HASPA framework allows us to “see” through the skull using sound. This new technique enables real-time, non-invasive monitoring of ultrasound beams inside the brain, paving the way for safer, more precise, and more effective focused ultrasound therapies for debilitating neurological disorders.
Instagram: @itsdranddr
University of Oxford – Botnar Research Centre, Old Rd, Oxford, Oxfordshire, OX3 7LD, United Kingdom
Complete author list:
[Veerle A. Brans*], Anna P. Constantinou*, Matthew J. Kibble, Valeria Nele, Daniel Reumann, Luca Bau, Sebastien J. P. Callens, James P. K. Armstrong, Nicolas Newell, Constantin Coussios, Molly M. Stevens, Michael D. Gray
* These authors contributed equally to this work
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Back pain affects over 600 million people worldwide and is the leading cause of disability. Most back pain is linked to the breakdown of the intervertebral disc, which is the soft, elastic cushion between the bones of the spine that absorbs shocks and keeps us moving comfortably (Figure 1.a). When these discs wear down with age or injury, bones rub together, causing pain.
Figure 1: a) The main parts of a spinal disc: the tough outer ring (annulus fibrosus), the soft, jellylike centre (nucleus pulposus), and the thin cartilage endplates that separate each disc from the bones above and below. b) How our injectable material works: a liquid is injected into the damaged disc and, when exposed to focused ultrasound, it gently warms and solidifies into a soft gel that restores the disc’s function. Adapted from Brans et al. (2025). Advanced Healthcare Materials. [accepted].
Current treatments are limited: physiotherapy manages symptoms but rarely fixes the problem, while surgery is invasive, costly, and not always successful. Scientists are therefore exploring minimally invasive materials that can be injected as liquids and then solidify (‘gel’) inside the body, restoring cushioning to damaged discs. The challenge is how to control where and when this solidification happens.
For this, we propose to use ultrasound – sound waves beyond human hearing – not just for imaging but for therapy. Focused ultrasound can safely heat deep tissues, much like a magnifying glass focuses light to start a fire. Our team at the University of Oxford and Imperial College London developed an injectable liquid implant that solidifies into a gel when warmed to just over 41°C, a temperature reached locally and non-invasively using ultrasound (Figure 1.b). The material consists of three components: 1) a polysaccharide (sugar) solution, 2) glass spheres to accelerate heating of the material, and 3) lipid vesicles, tiny fluid-filled spheres that release calcium when heated. This released calcium links the sugar molecules into a network, turning the liquid into a gel (Figure 2.b).
To test this, we designed treatment algorithms that precisely control heating while also ‘listening’ to the behaviour of tiny bubbles inside the liquid (Figure 2.a). These bubbles form and move in response to the changing pressure of the ultrasound waves, a process known as cavitation. You can imagine it like opening a bottle of sparkling water: bubbles suddenly appear and grow as the pressure drops, and then collapse.
Figure 2: Testing ultrasound-triggered gel formation. (a) Custom setup for heating and ‘listening’ to the material with focused sound waves. (b) Heating curve and photo of the soft gel formed after ultrasound exposure. (c) Testing the approach in cow spinal segments held in a custom rig. (d) Treated discs regained some biomechanical function, with the gel well integrated into the damaged centre after testing. Adapted from Brans et al. (2025). Advanced Healthcare Materials. [accepted].
In our material, this bubble activity generates sound that changes as the liquid turns into a gel: starting off loud then fading as the material stiffens and the bubbles can no longer move freely (compared to a liquid control, see audiofiles). By tracking these sound changes, we can monitor gelation and thus the treatment’s success in real time.
In our most recent experiments using cow spines (which are anatomically similar to human), we successfully injected the liquid material into degenerated disc tissue and used focused ultrasound to trigger gelation at the correct location (Figure 2.c). Mechanical testing showed that the treatment partially restored the disc’s natural cushioning ability (Figure 2.d), and the material stayed in place without leaking and blended well with the surrounding tissue.
These early results show real promise for using sound-activated gels to repair worn spinal discs, with ongoing improvements in the material and ultrasound technique aiming to make the treatment even more effective in the future, helping millions stand tall again.
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Many pregnancy complications begin with subtle problems in the placenta, the organ that supplies oxygen and nutrients to the baby. Can sound waves reveal these hidden problems before they lead to serious health risks? Our research shows that they can: a simple ultrasound scan may help identify placental problems much earlier than today’s clinical methods.
When the placenta fails to provide adequate support, a condition known as placental insufficiency, pregnancies are at higher risk for preeclampsia in the mother, and growth restriction and oxygen deprivation (hypoxia) in the baby. Because these conditions often show no early symptoms, clinicians need a safe, accessible way to assess placental health during routine prenatal care.
To address this need, researchers at UNC Charlotte and the University of British Columbia are studying a technique called quantitative ultrasound (QUS). QUS analyzes the raw sound echoes returning from the placenta during an ultrasound scan. These echoes contain detailed information about tissue structure. When the placenta begins to show signs of insufficiency, its acoustic “signature” changes. QUS can detect these subtle changes that are not visible on a regular ultrasound image. Video 1 shows the raw signals (right) corresponding to an in utero placental image (left) acquired during a third-trimester ultrasound scan. These raw signals contain the acoustic information that QUS analyzes to detect early changes in placental health that may not be visible on a standard ultrasound image.
Video 1. Ultrasound data collected from a 3rd trimester placenta, along with the raw sound-wave signal (RF signal) that QUS analyzes.
To test whether these acoustic signatures reflect real structural differences, we first applied QUS on placentas collected after delivery. Using QUS, which measures how placental tissue absorbs and weakens sound, scatters the echoes, and what are the average sizes of the tissue structures, we found clear differences between healthy and diseased placentas. When these measurements were entered into a simple prediction model, the tool correctly distinguished healthy and diseased placentas with high accuracy showing that QUS can capture structural changes linked to placenta-mediated diseases: preeclampsia and small-for-gestational-age.
Encouraged by these findings, we evaluated QUS during pregnancy, conducted within the Wellcome Leap In Utero Consortium, an international effort to understand and prevent stillbirth. In this in utero study, we scanned pregnant participants in the USA, Canada, UK and Uganda, and analyzed the acoustic patterns of their placentas. QUS measurements were able to identify pregnancies in which babies later experienced oxygen-related distress and were especially accurate when these complications were linked to placental abnormalities confirmed after birth. Figure 2 shows how raw (RF) signals are transformed into a color-coded QUS map, making subtle differences in placental tissue easier to see and compare. These findings suggest that QUS could help clinicians recognize early signs of risk and monitor pregnancies more closely.
Figure 1: Raw sound waves collected during the scan are transformed into a color-coded quantitative ultrasound (QUS) map that highlights acoustic differences within the placenta
Because QUS uses the same sound waves and equipment already found in clinics, it can be integrated into handheld or portable ultrasound devices, making it practical for hospitals, local clinics, and resource-poor settings, where advanced imaging is not available. This flexibility gives QUS the potential to support more equitable prenatal care worldwide. As we continue refining the technology, our goal is to develop a fast, affordable tool that detects placental insufficiency early enough to improve pregnancy outcomes everywhere, including communities with limited access to specialized medical care.
Instagram: @baglamist
University of Cincinnati, Cincinnati, OH, 45224, United States
Popular version of 2aBAa7 – Measure for measure: Diffraction correction for consistent quantification of bubble-related acoustic emissions
Presented at the 188th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0037529
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Microscopic bubbles, when caused to vibrate by ultrasound waves, can be powerful enough to break through the body’s natural barriers and even to destroy tissue. Growth, resonance, and violent collapse of these microbubbles, called acoustic cavitation, is enabling new medical therapies such as drug delivery through the skin, opening of the blood-brain barrier, and destruction of tumors. However, the biomedical effects of cavitation are still challenging to understand and control. A special session at the 188th meeting of the Acoustical Society of America, titled “Double, Double, Toil and Trouble – Towards a Cavitation Dose,” is bringing together researchers working on methods to consistently and accurately measure these bubble effects.
For more than 30 years, scientists have measured bubble activity by listening with electronic sensors, called passive cavitation detection. The detected sounds can resemble sustained musical tones, from continuously vibrating bubbles, or applause-like noise, from groups of collapsing bubbles. However, results are challenging to compare between different measurement configurations and therapeutic applications. Researchers at the University of Cincinnati are proposing a method for reliably characterizing the activity of cavitating bubbles by quantifying their radiated sound.
A passive cavitation detector (left) listens for sound waves radiated by a collection of cavitating bubbles (blue dots) within a region of interest (blue rectangle).
The Cincinnati researchers are trying to improve measurements of bubble activity by precisely accounting for the spatial sensitivity patterns of passive cavitation detectors. The result is a measure of cavitation dose, equal to the total sound power radiated from bubbles per unit area or volume of the treated tissue. The hope this approach will enable better prediction and monitoring of medical therapies based on acoustic cavitation.
Figure 1: In an experiment simulating drug delivery through the skin (left), a treatment source projects an ultrasound beam onto animal skin. A passive cavitation detector (PCD) listens for sound radiated by bubbles at the skin surface, while the skin’s permeability is measured from its electrical resistance. Measured bubble activity is quantified using the sensitivity pattern of the PCD within the treated region (highlighted blue circle).
The researchers reported results from two experiments testing their methods for characterizing cavitation. In experiments testing ultrasound methods for drug delivery through the skin (Figure 1), they found that total power of subharmonic acoustic emissions (like musical tones indicating sustained vibrations of resonating bubbles) per unit skin surface area consistently increased when the skin became more permeable, quantifying the role of bubble activity in drug delivery. In a second experiment (Figure 2), the researchers quantified bubble activity during heating of animal liver tissue by ultrasound, simulating cancer therapies called thermal ablation. They found that increased bubble activity could indicate both faster tissue heating near the treatment source and reduced heating further from the source.
Figure 2: An ultrasound (US) array sonicates animal liver tissue with a high-intensity ultrasound beam, causing tissue heating (thermal ablation) as used for liver tumor treatments. Increased bubble activity was found to reduce the depth of treatment, while sometimes also increasing the area of ablated tissue near the tissue surface.
This approach to measuring bubble activity could help to establish standard cavitation doses for many different ultrasound therapy methods. Quantitative measurements of bubble activity could help confirm treatment success, such as drug delivery through the skin, or to guide thermal treatments by optimizing bubble activity to heat tumors more efficiently. Standard measures of cavitation dose should also help scientists more rapidly develop new medical therapies based on ultrasound-activated microbubbles.
Additional Authors: John M Cormack , Zhiyu Sheng, Yu-hsuan Chao,1 Allison Bean, Ryan Nussbaum, Jiantao Pu, Ajay D. Wasan, and Kang Kim
Popular version of 2aBAb5 – Three-dimensional vibration-controlled transient elastography in human subjects with myofascial trigger pain points Presented at the 188th ASA Meeting Read the abstract at https://doi.org/10.1121/10.0037535
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Almost everyone experiences back pain at some point in their lives. For many, this pain becomes long-lasting and difficult to manage. One possible cause of chronic back pain is myofascial trigger points. These are small, sensitive knots or tight spots in muscles that not only hurt when pressed but can also spread pain to other areas. Although physicians know these trigger points exist, they are very difficult to detect with current available medical imaging tools. This makes diagnosis and treatment more challenging.
In this research, we are developing a new ultrasound-based method to find these hidden painful spots more accurately. We tested this method on 32 volunteers,16 who had chronic low back pain and known trigger points, and 16 healthy individuals without pain. Our approach uses a small vibrating device placed on the lower back skin. This device produces vibration inside the lower back tissue so that the vibration wave propagates through the skin and muscles of the subject. The propagation speed of this wave called shear wave speed is directly related to stiffness of the tissues. We used an advanced type of three-dimensional ultrasound probe to capture how these waves traveled inside the muscles in three different directions.
Figure 1: experiment setup
By measuring the speed of the waves moving through the muscles, we could assess their stiffness knowing high speed indicates stiffer tissue. Our early results showed that muscles with trigger points had higher wave speeds, meaning they were stiffer compared to muscles without pain points. This finding is important because increased muscle stiffness could be a sign of the presence of painful trigger points.
Video 1: Black and white image showing different layers of lower back tissue using 3D ultrasound. Colorful waves indicating corresponding shear wave propagation through the lower back tissue.
If future studies confirm these findings, this technique could provide physicians with a valuable new tool for diagnosing chronic back pain related to myofascial trigger points. Unlike current methods that mostly rely on physical examination and patient reports, this method could offer objective and visual evidence of muscle problems. This might help guide treatment decisions and track patient progress more accurately.
By improving the way we see and measure muscle stiffness, this research could lead to better care for the many people experiencing chronic low back pain.
Internal Medicine, Division of Cardiovascular Health and Disease and Biomedical Engineering, University of Cincinnati, Cincinnati, Ohio, 45267, United States
Kevin Haworth,
Internal Medicine, Division of Cardiovascular Health and Disease, Biomedical Engineering, and Pediatrics
University of Cincinnati
Cincinnati, OH 45267 USA
Popular version of 2aBAa5 – Bubble, bubble, sonic trouble: Cavitation dose and therapeutic close
Presented at the 188th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0037527
–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–
Imagine doctors activating tiny, drug-delivering bubbles in the body via a computer — almost like playing a video game — to treat life-threatening conditions. This futuristic approach is becoming a reality, thanks to advances in ultrasound technology and biomedical acoustics.
Cavitation is the formation and movement of tiny gas bubbles when ultrasound waves pass through the body. While cavitation might sound like a side effect from ultrasound, scientists have found a way to harness effervescence to improve medication delivery.
Doctors can use cavitation to help medications reach their targets faster and more effectively. One example is tissue plasminogen activator (tPA), a drug used to dissolve blood clots. When paired with cavitation, tPA can penetrate more deeply into clots. That makes it particularly useful in treating serious conditions, including blood clots in the leg known as deep vein thrombosis and pulmonary embolism, a potentially life-threatening blockage in the lungs.
The challenge lies in finding the right amount of cavitation. Too little bubble activity may have little effect, while too much could damage the surrounding blood vessel. So, medical researchers are working to define a safe and effective “cavitation dose” — the ideal amount of bubble activity to enhance treatment, much like a doctor prescribes a certain dose of medicine for a patient to take.
To help strike this balance, scientists are using a new imaging tool to visualize cavitation as it happens. First, a catheter with tiny built-in ultrasound sources is inserted into a blood vessel to generate cavitation. Then, an ultrasound transducer — similar to one used in fetal imaging — is specially programmed to capture images of cavitation around the treatment area. This view helps doctors understand where bubbles are and how they’re vibrating, so they can adjust the treatment in real time.
The bubbles themselves are made of octafluoropropane (OFP) — a safe, colorless gas often used in diagnostic ultrasound imaging of the heart and liver. Thanks to a technique called passive cavitation imaging (PCI), researchers can now track cavitation without interfering with the treatment itself.
Leading this innovative work are Kevin Haworth, PhD, and Christy Holland, PhD, both from the University of Cincinnati College of Medicine. Haworth is principal investigator of the Biomedical Ultrasonics and Cavitation Laboratory, while Holland directs the Image-Guided Ultrasound Therapeutic Laboratories, as well as the Center for Cardiovascular Research. By visualizing and guiding these tiny bubbles, doctors may soon be able to deliver treatments with greater precision — helping patients recover faster and more safely than ever before.
Figure 1: a) The main parts of a spinal disc: the tough outer ring (annulus fibrosus), the soft, jellylike centre (nucleus pulposus), and the thin cartilage endplates that separate each disc from the bones above and below. b) How our injectable material works: a liquid is injected into the damaged disc and, when exposed to focused ultrasound, it gently warms and solidifies into a soft gel that restores the disc’s function. Adapted from Brans et al. (2025). Advanced Healthcare Materials. [accepted].
Figure 2: Testing ultrasound-triggered gel formation. (a) Custom setup for heating and ‘listening’ to the material with focused sound waves. (b) Heating curve and photo of the soft gel formed after ultrasound exposure. (c) Testing the approach in cow spinal segments held in a custom rig. (d) Treated discs regained some biomechanical function, with the gel well integrated into the damaged centre after testing. Adapted from Brans et al. (2025). Advanced Healthcare Materials. [accepted].
A passive cavitation detector (left) listens for sound waves radiated by a collection of cavitating bubbles (blue dots) within a region of interest (blue rectangle).
Figure 1: In an experiment simulating drug delivery through the skin (left), a treatment source projects an ultrasound beam onto animal skin. A passive cavitation detector (PCD) listens for sound radiated by bubbles at the skin surface, while the skin’s permeability is measured from its electrical resistance. Measured bubble activity is quantified using the sensitivity pattern of the PCD within the treated region (highlighted blue circle).
Figure 2: An ultrasound (US) array sonicates animal liver tissue with a high-intensity ultrasound beam, causing tissue heating (thermal ablation) as used for liver tumor treatments. Increased bubble activity was found to reduce the depth of treatment, while sometimes also increasing the area of ablated tissue near the tissue surface.
