Measuring the sounds of microbubbles for ultrasound therapy

T. Douglas mast – doug.mast@uc.edu

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://eppro01.ativ.me/appinfo.php?page=Session&project=ASAICA25&id=3868554

–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.

Tiny bubbles, big impact: Breaking up blood clots

Christy Holland – hollanck@ucmail.uc.edu

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://eppro01.ativ.me//web/index.php?page=Session&project=ASAICA25&id=3867184

–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.

Walk to the Beat: How Your Playlist Can Shape Your Emotional Balance

Man Hei LAW – mhlawaa@connect.ust.hk

Computer Science and Engineering, The Hong Kong University of Science and Technology, Hong Kong, -, -, Hong Kong

Andrew HORNER
Computer Science and Engineering
Hong Kong University of Science and Technology
Hong Kong

Popular version of 1aCA2 – Exploring the Therapeutic Effects of Emotion Equalization App During Daily Walking Activities
Presented at the 187th ASA Meeting
Read the abstract at https://doi.org/10.1121/10.0034927

–The research described in this Acoustics Lay Language Paper may not have yet been peer reviewed–

During our daily tasks, we spend a lot of time getting things done. When walking, some people may find it boring and feel like time drags on. On the other hand, some see it as a chance to think and plan ahead. Our researchers believe that we can use this short period of time to help people rebalance their emotions. This way, individuals can feel refreshed and energized as they walk to their next destination.

Our idea is to provide each participant with a specific music playlist to listen to while walking. The playlists consisted of Uplifting, Relaxing, Angry, and Sad music, each lasting for 15 minutes. While our listeners were walking, they were using our Emotion Equalization App (Figures 1a to 1d) for accessing the playlist and collect all users’ data.

Figures 1a to 1d: The interface of the Emotion Equalization App

The key data we focused on was assessing the changes in emotions. To understand the listeners’ emotions, we used the Self-Assessment Manikin scale (SAM), a visual tool that helps depict emotions based on internal energy levels and mood positivity (refer to Figure 2). After the tests, we analyzed at how their emotions changed before and after listening to the music.

Figure 2: The Self-Assessment Manikin scale, showing energy levels at the top and mood positivity at the bottom [1]

The study found that the type of music influenced how far participants walked. Those listening to Uplifting music walked the farthest, followed by Angry, Relaxing, and Sad music. It was as expected that the music’s energy could affect the participants’ physical energy.

So, if music can affect physical energy, can it also have a positive effect on emotions? Can negative music help in mood regulation? An unexpected finding was that Angry music was found to be the most effective therapeutic music for walking. Surprisingly, listening to Angry music while walking not only elevated internal energy levels but also promoted positive feelings. On the other hand, Uplifting and Sad music only elicited positive emotions in listeners. However, Relaxing music during walking did not contribute to increased internal energy levels or positive feelings. This result breaks the impression on the therapeutic use of music while engaging in walking activities. Angry music has a negative vibe, but our study proved it to be beneficial in helping individuals relieve stress while walking, ultimately enhancing internal energy and mood.

If you’re having a tough day, consider listening to an Angry music playlist while taking a walk. It can help in balancing your emotions and uplifting your mood for your next activity.

[1] A. Mehrabian and J. A. Russell, An approach to environmental psychology. in An approach to environmental psychology. Cambridge, MA, US: The MIT Press, 1974, pp. xii, 266.