Aarushi Bhargava is an assistant professor of biomedical engineering whose research brings a mechanics perspective to ultrasound therapy. Bhargava leads the SonIMate Mechanics group, which focuses on developing noninvasive therapy, targeted drug delivery methods, and understanding the mechanics of ultrasound interaction with synthetic and biological soft materials. Bhargava, a mechanical engineer by training, also studies how to pair ultrasound with medical robots and how to use ultrasound as a therapy for a variety of injuries and diseases.
In this Q&A, Bhargava discusses how ultrasound works and talks about some of its emerging medical applications.
Q: What is ultrasound?
Ultrasound is, at its core, just sound, but at a frequency far too high for human ears to detect. Just like the sound of a voice or a musical instrument, ultrasound travels as waves of pressure moving through a medium, whether that’s air, water or the human body. Those waves carry energy with them as they go.
Most people have encountered ultrasound in a clinic or hospital, where it’s used to create images of the inside of the body. The way it works is that a handheld device called a transducer sends out pulses of these high-frequency sound waves into the body. Within the body, the waves pass through different types of tissue — muscle, fat, fluid or bone — and each one interacts with the waves differently.
Think of it like shining a flashlight through different materials. A thin curtain lets most of the light through, while a brick wall reflects almost all of it back. Sound waves behave similarly. Soft tissues like fluid or blood let waves pass through fairly easily, while denser structures like organs or bone reflect much more of the wave back toward the transducer. The transducer picks up those returning echoes, and a computer translates the timing and strength of each echo into a picture. Areas that reflected a lot of the wave show up brightly such as organ or tumor, while areas that absorbed or transmitted it appear darker, such as blood or a fluid-filled cyst.
Q: What’s the difference between how ultrasound is used for imaging and for therapy?
Ultrasound waves for imaging emit straight, parallel, unfocused waves known as “plane” waves. These waves travel into the body at a very low intensity, so they don’t cause injury. They illuminate a large area because of their unfocused nature.
For medical therapy, we focus high-intensity waves on a very small spot. Imagine using a magnifying glass to concentrate the sun’s energy into a point where it can burn material like leaves or paper. We’re applying the same principle with therapeutic ultrasound and applying so much energy that we can actually alter a tissue.
For therapy, we’re altering the tissue in one of two ways. One is by heating it up to the point that it burns the tissue and causes tissue death. Sometimes that heating can be just above body temperature if we’re using mild heat to relieve pain. But if we heat the tissue to 104 to 105.8 degrees Fahrenheit, when our body temperature is 98.6 degrees Fahrenheit, the tissue starts slowly burning up. We can, for example, use that temperature to destroy a tumor area.
The other way we alter tissue is by causing cavitation. Cavitation often happens on ship turbine blades, where pressure fluctuations cause bubbles to form, collapse and generate shock waves that damage the blades’ surface. Cavitation is a big challenge in the Navy and shipping industries, but we can harness this property for therapeutic uses. By altering the ultrasound’s properties, we can use those bubbles to cause damage to specific tissue. With this technique, we can actually fragment a tumor and treat it.
Heating methods are becoming a little outdated, because we have seen that even though we want to concentrate heat in a small spot, over a longer duration, the heat begins to spread over a larger area. So cavitation has become a better alternative and has received FDA approval for use, for example, on liver tumors.
Q: How are you learning that ultrasound is effective in treating cancers in fibrotic, or scarred, tissue with ultrasound therapy?
The currently established cavitation technique works well in many cases, but it runs into limitations when a tumor is surrounded by a lot of hardened or scarred tissue. This condition, called fibrosis, is common in high-grade breast cancer, pancreatic cancer and pulmonary fibrosis in the lungs. In these cases, the physical properties of the scarred tissue make it much harder for cavitation to do its job effectively.
My research is focused on understanding why fibrotic tissue resists standard cavitation treatment, and on finding new ways to use ultrasound’s mechanical properties to work around that resistance. Rather than simply trying to destroy the tissue outright, I’m exploring whether more nuanced mechanical interventions could make the tumor environment more receptive to treatment: whether that means responding better to the body’s own immune response, or allowing existing therapies like chemotherapy to work more effectively.
The broader goal is to expand the range of patients and cancer types that ultrasound therapy can realistically help, particularly those with more advanced or treatment-resistant disease.
Q: What are the challenges and opportunities in using ultrasound as a medical therapy?
The challenges are many because it’s an emerging technology. Because it’s not established like chemotherapy or radiology, it has not been standardized that well, and there’s a lot of work still needed to make that happen. Because this is a personalized medical therapy, we need to define key metrics that do not give different responses if you go from patient to patient.
We also need to develop standardization methods and proper metrics to gauge the efficacy of treatment and make it more applicable to different types of tumor stages. Though it’s been clinically approved, only a subsection of the population can be treated for more advanced cancer stages. Cases in one subset might not produce results you see in another. So there is still work to be done, but we will continue pushing to overcome them.
Top photo caption: Assistant Professor of Biomedical Engineering Aarushi Bhargava, right, talks to graduate student researchers in her lab. Photo: Joel Hallberg