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 Opticaon 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.