Hearing impairment is generally caused by disorders within the cochlea of the inner ear. Effective treatment of hearing loss requires a clear view of the cochlea’s internal structures, which are difficult to assess noninvasively. To perform nondestructive detection of the cochlea’s internal structure with sufficient spatial resolution, researchers at Waseda University, working with colleagues at Kobe University and Osaka University, developed a terahertz imaging technique to visualize the cochlea through near-field imaging and 3D reconstruction. The imaging technique provided clear structural information at varying depths, enabling the researchers to visualize intricate cochlear features. The 3D reconstruction process yielded high-quality spatial representations of the cochlea, enhancing the researchers’ understanding of the cochlea’s internal architecture. The terahertz imaging technique could be integrated into miniaturized devices, enabling noninvasive, in vivo imaging for cochlear diagnostics, dermatology, and early cancer detection. One of the challenges facing the researchers was the diffraction limit of terahertz waves. The cochlea is a small organ, on the order of millimeters, and the observation of its internal structure requires a spatial resolution on the order of micrometers. In conventional terahertz instruments, the spatial resolution of terahertz imaging is limited to the millimeter level. Terahertz imaging enables noninvasive, high-resolution visualization of cochlear structures, facilitating the early detection of hearing disorders. Courtesy of Waseda University/Kazunori Serita. To achieve high-resolution terahertz imaging, the researchers generated a micrometer-sized terahertz point source with a femtosecond laser at a wavelength of 1.5 μm. They used the femtosecond laser to irradiate a gallium arsenide (GaAs) substrate and placed a mouse cochlear sample directly on the substrate to enable near-field imaging. Using a terahertz near-field point source microscope with micrometer-level spatial resolution, they performed nondestructive terahertz imaging of the mouse cochlea, visualizing its internal structure. “By leveraging terahertz waves, we can achieve deeper tissue penetration while preserving structural clarity,” professor Kazunori Serita, who led the research, said. The researchers applied the time-of-flight principle to convert the time scale of each terahertz image into a depth scale. They used k-means clustering, an unsupervised machine learning algorithm, to extract 3D structural information from scanned 2D time-domain images. With this information, they reconstructed the 3D internal structure of the mouse cochlea, creating a 3D point cloud and surface mesh model. The researchers implemented 3D terahertz time-of-flight imaging and 3D image reconstruction with high reliability and accuracy. The results demonstrate the potential of 2D and 3D terahertz imaging for high-resolution, nondestructive analysis of inner-ear structures, and highlight the value of advanced terahertz imaging for biological studies. The new “The integration of terahertz technology with existing medical devices, such as endoscopes, holds great potential for revolutionizing the way diseases are diagnosed, particularly in oncology and pathology,” Serita said. With its noninvasive, high-resolution capabilities, terahertz technology could offer a useful approach for medical imaging and analysis. “Terahertz technology could significantly enhance the speed and accuracy of pathological diagnoses, reducing the time between testing and results, and ultimately improving patient outcomes,” Serita said. The research was published in Optica (www.doi.org/10.1364/OPTICA.543436).