The Future of Laryngeal Imaging: Michael Johns, Brian Applegate and the Promise of Brillouin Spectroscopy

Dr. Michael Johns, MD, wasn’t planning to become a physician. He grew up in Baltimore and majored in economics at the University of Virginia, sure he would one day attend business school, but, in fact, he found he had a far greater proclivity toward the biomedical sciences. Johns ultimately followed in his otolaryngologist father’s footsteps, attending medical school at Johns Hopkins University and completing a fellowship in laryngology at the University of Michigan, fascinated by the incredible athleticism of the human voice. He would then go on to found the Emory Voice Center with Speech Pathologist Dr. Edie Hapner, PhD, in Atlanta, GA, which was among the first interdisciplinary voice centers in the United States.

Conversely, Dr. Brian Applegate would follow a very different path. He grew up in Ohio, earning his PhD in physical chemistry from The Ohio State University and later continuing his training in biomedical engineering at Duke University under the guidance of Professor Joe Izatt, with a fellowship focused on creating molecular imaging approaches for Optical Coherence Tomography (OCT). He then joined the faculty of Texas A&M University, advancing to the rank of Associate Professor of Biomedical Engineering, where he would continue to develop new imaging technologies, including using OCT to look at the deeper structures of the ear.

In 2015, Dr. Johns was recruited to the University of Southern California to form the USC Voice Center and bring his interdisciplinary model of care to Southern California, and by the time Dr. Applegate joined the faculty several years later, Dr. Johns was still grappling with one of the more significant obstacles in laryngeal imaging. The core diagnostic technique that clinicians employ, a laryngeal videostroboscopy, uses an endoscope to take a video recording of the larynx in action, with strobe lights making the vocal folds appear to move in slow motion and thus enabling doctors to see how well the vocal folds are vibrating. However, one of the significant limitations of using a laryngeal videostroboscopy is that it really only allows doctors to look at the surface of the vocal folds and make inferences about vocal fold problems occurring below the surface, and because the imaging resolution from tools like CT and MRI scans are not refined enough for voice disorders, the only way to confirm vocal fold problems in tissues beneath the surface is through more invasive procedures like surgery.

When Dr. Johns and Dr. Applegate began speaking about the issue, they hypothesized that perhaps they could use a technique known as Brillouin microscopy to measure certain mechanical properties of the vocal folds without having to resort to surgery. Brillouin microscopy takes advantage of a physical phenomenon known as Brillouin light scattering, in which the elastic vibrational waves of solid materials can cause light (measured in photons) to scatter in different ways as a result of interacting with those solid materials. This pattern of scattering can, in turn, be used to measure the viscoelasticity of a given solid material, and thus, maybe Brillouin microscopy could be utilized to determine the viscoelastic qualities of the vocal folds.

Applegate had previous experience working with Brillouin microscopy in conjunction with his Texas A&M colleague Dr. Vladislav V. Yakovlev, a biomedical engineer with a focus on biomedical imaging and optics, and he and Johns were excited at the prospect of applying this technique as a potential diagnostic tool for the larynx. Over the past one and a half years, Johns and Applegate worked remotely with scientists and engineers at Texas A&M to try to prove the validity of their hypothesis, and last month, Johns, Applegate, and Yakovlev, among others, published their research in the article “Porcine vocal fold elasticity evaluation using Brillouin spectroscopy” in the Journal of Biomedical Optics. They discussed how they had used a porcine (pig) model to demonstrate the feasibility of Brillouin spectroscopy for vocal fold imaging that, with more extensive research, could provide a noninvasive way to make an objective assessment of vocal fold mucosal pliability. In practical terms, at some point in the future, Brillouin spectroscopy may be able to be used in lieu of surgery to diagnose certain voice use-related trauma in professionals such as vocalists, teachers, and call-center agents; age-related changes to vocal fold tissues; vocal fold scarring from surgery and cancer treatment; and to allow for earlier detection of cancerous growths.

Johns notes that one of the key ways that USC Caruso’s Department of Otolaryngology–Head and Neck Surgery (OHNS) encourages collaboration among its faculty is through its strength in breaking down silos between different disciplines and departments. For example, OHNS Department Chair Dr. John S. Oghalai, MD, knew Applegate from their time in Houston together (with Applegate having been at Texas A&M University and Oghalai having been at Baylor College of Medicine), and he recruited Applegate to USC with a primary appointment in USC Caruso’s Department of Otolaryngology–Head and Neck Surgery and a courtesy appointment in USC’s Viterbi School of Engineering. Otolaryngology oftentimes has a predominantly clinical focus, but having someone with biomedical engineering expertise in the department has unlocked new research and educational opportunities, giving clinicians like Johns more of an opportunity to get involved with groundbreaking research and engineers like Applegate more of an opportunity to find novel ways to translate research into practical tools that will be useful in a clinical setting. Applegate mentioned that with his joint appointment in Otolaryngology, his clinician colleagues feel comfortable emailing him with engineering questions that can then transform into a catalyst for important research.

The value of the collaboration between Dr. Johns and Dr. Applegate creates not only clinical and research opportunities but educational opportunities as well. As Johns so aptly explains: “Education is one of the core pillars of our tripartite mission in academia…and so we’ve had a myriad of trainees engage in [research]. They’ve been able to learn more about the scholarship and they’ve been able to learn more about the science, and that positions them to be future contributors in their careers.”