Advancements in healthcare and technology have significantly increased the average human lifespan. However, with longer life comes a higher prevalence of age-related disorders that affect overall well-being. One such condition is hearing loss in older adults, which can severely impact communication, social interactions, and daily functioning.
Hearing relies on the cochlea, a spiral-shaped organ in the inner ear that converts sound waves into neural signals. Any structural or functional impairment of the cochlea can lead to hearing loss, making its precise visualization essential for understanding and diagnosing auditory disorders. Conventional imaging techniques often struggle to capture the intricate details of this delicate structure, necessitating the development of more advanced imaging approaches.
To investigate the potential of terahertz (THz) imaging for visualizing cochlear structures, researchers led by Associate Professor Kazunori Serita from Waseda University, along with Professors Takeshi Fujita and Akinobu Kakigi from Kobe University, and Professor Masayoshi Tonouchi and Luwei Zheng from Osaka University, used a micrometer-sized THz point source to visualize the internal structure of the mouse cochlea. The study, published in Optica on 27 March, 2025, explores THz imaging as a non-invasive, high-resolution technique for biological tissue analysis. “By leveraging THz waves, we can achieve deeper tissue penetration while preserving structural clarity,” explains Serita.
To achieve high-resolution THz imaging, a micrometer-sized THz point source was generated using a femtosecond laser at a wavelength of 1.5 μm, which irradiated a GaAs substrate. The cochlea was placed directly on the substrate to facilitate near-field imaging. The system captured 2D THz time-domain images over a broad timescale, allowing structural visualization at varying depths. By applying the time-of-flight principle, the time scale of each THz image was converted into a depth scale. Furthermore, k-means clustering, an unsupervised machine-learning technique, was used to extract structural features and enable 3D reconstruction of the cochlea, resulting in a 3D point cloud and surface mesh model.
The study successfully demonstrated the first THz imaging of the internal structure of the mouse cochlea. The imaging technique provided clear structural information at varying depths, enabling the visualization of intricate cochlear features. The 3D reconstruction process yielded high-quality spatial representations of the cochlea, enhancing the understanding of its internal architecture. These results highlight the potential of THz imaging as a viable alternative to conventional methods for inner ear diagnostics.
The findings of this study open the door to significant advancements in medical imaging. The proposed THz imaging technique could be developed into miniaturized devices, such as THz endoscopes and otoscopes, enabling non-invasive, in vivo imaging for cochlear diagnostics, dermatology, and early cancer detection. "The integration of THz technology with existing medical devices, such as endoscopes, holds great potential for revolutionizing the way diseases are diagnosed, particularly in oncology and pathology," says Serita. Additionally, "THz technology could significantly enhance the speed and accuracy of pathological diagnoses, reducing the time between testing and results, and ultimately improving patient outcomes," he adds.
By demonstrating the potential of THz imaging for visualizing the cochlea through near-field imaging and 3D reconstruction, this study explores its possible applications in biomedical diagnostics. With its non-invasive, high-resolution capabilities, THz technology may offer a useful approach for medical imaging and analysis.
***
Reference
DOI: 10.1364/OPTICA.543436
Authors: Luwei Zheng¹, Haidong Chen¹, Takeshi Fujita², Akinobu Kakigi², Nicole Allen¹˒³, Hironaru Murakami¹, Masayoshi Tonouchi¹˒⁴, Kazunori Serita¹˒⁵
Affiliations
¹Institute of Laser Engineering, Osaka University
²Department of Otolaryngology-Head and Neck Surgery, Kobe University, Graduate School of Medicine
³Department of Biomedical Engineering, Georgia Institute of Technology
⁴Research Institute for Interdisciplinary Science, Okayama University
⁵Graduate School of Information, Production, and Systems, Waseda University
About Waseda University
Located in the heart of Tokyo, Waseda University is a leading private research university that has long been dedicated to academic excellence, innovative research, and civic engagement at both the local and global levels since 1882. The University has produced many changemakers in its history, including nine prime ministers and many leaders in business, science and technology, literature, sports, and film. Waseda has strong collaborations with overseas research institutions and is committed to advancing cutting-edge research and developing leaders who can contribute to the resolution of complex, global social issues. The University has set a target of achieving a zero-carbon campus by 2032, in line with the Sustainable Development Goals (SDGs) adopted by the United Nations in 2015.
To learn more about Waseda University, visit https://www.waseda.jp/top/en
About Associate Professor Kazunori Serita from Waseda University
Dr. Kazunori Serita is an Associate Professor at the Graduate School of Information, Production, and Systems, Waseda University, Japan. He earned his Doctor of Engineering degree from the Institute of Laser Engineering, Osaka University. With over a decade of research experience, Dr. Serita has authored 83 research works, accumulating 699 citations. His research interests encompass terahertz technology, nonlinear optics, electromagnetic field analysis, and metamaterials. Notably, he has contributed to the development of ultrasensitive terahertz microfluidic chips and reflective terahertz point source meta-sensors for high-sensitivity bio-sensing applications.
END
