Scientists have made a major leap in ear imaging by using terahertz radiation to see inside the cochlea – an impossibly tiny, spiral-shaped organ crucial for hearing – without damaging it. This breakthrough could one day allow doctors to detect hearing problems and inner ear diseases with non-invasive tools, something current imaging tech can’t do.
The team created a microscopic terahertz light source that penetrates bone and tissue, giving a 3D view of cochlear structures in unprecedented detail. They’ve already tested it on mouse samples, and with further development, it could be used through the ear canal to catch hearing loss early and even detect cancers.
Breakthrough in Cochlear Imaging with Terahertz Technology
For the first time, scientists have demonstrated that terahertz imaging can reveal the internal structure of the mouse cochlea with micron-level precision. This non-invasive approach could lead to new ways of diagnosing hearing loss and other conditions affecting the inner ear.
“Hearing relies on the cochlea, a spiral-shaped organ in the inner ear that converts sound waves into neural signals,” said research team leader Kazunori Serita from Waseda University in Japan. “Although conventional imaging methods often struggle to visualize this organ’s fine details, our 3D terahertz near-field imaging technique allows us to see small structures inside the cochlea without any damage.”
Why Terahertz Waves Are Perfect for Biology
Terahertz radiation lies between microwaves and mid-infrared light on the electromagnetic spectrum. It’s especially suited for biological imaging because it’s low-energy, non-damaging to tissue, scatters less than visible or near-infrared light, and can penetrate bone. It’s also sensitive to subtle changes in hydration and cell structure.
In a study published today (March 27) in Optica, the journal of the Optica Publishing Group, a team of researchers from multiple institutions describes how their imaging technique captures high-resolution data that can be used to create detailed 3D reconstructions of the inner ear.
“With further development, this technique could lead to a new diagnostic method for ear diseases that have been difficult to diagnose until now,” said Serita. “It has the potential to enable on-site diagnosis of conditions like sensorineural hearing loss and other ear disorders. It might also be useful for early detection of hearing impairments, allowing earlier treatment and better outcomes.”
The images acquired using 3D terahertz near-field imaging were used to create 3D reconstructions, allowing visualization of part of the cochlear duct, the spiral structure inside the cochlea. Credit: Kazunori Serita, Waseda University
Inspired by Medical Challenges
Serita was inspired to develop the technique after learning about cochlear measurement challenges from coauthor Takeshi Fujita from the Department of Otolaryngology-Head and Neck Surgery at Kobe University. “That got me thinking — maybe terahertz imaging could help solve these issues,” said Serita. “We decided to collaborate and explore this idea together. The big question was whether we could visualize the tiny internal structures of the cochlea without causing any damage.”
Terahertz imaging is typically performed by focusing terahertz waves using a lens made for these wavelengths. However, these lenses are typically limited to focal sizes measuring a few millimeters — too large to image the tiny structures of the cochlea. In the new work, the researchers eliminated the need for a focal lens by using a nonlinear optical crystal to create terahertz light emitting from a very small region within the crystal. Because this terahertz point source had a beam diameter of just 20 microns, the researchers could measure much smaller samples with terahertz waves.
“Until now, there was no way to observe the internal structure of the cochlea non-destructively with high resolution,” said Serita. “A key innovation in our work was the use of a nonlinear optical crystal to generate terahertz waves from 1560-nm near-infrared light. This was crucial for our imaging technique.”
The non-invasive method could eventually enable new ways of diagnosing hearing loss and other ear-related conditions. The video shows a 3D terahertz imaging scan. Credit: Kazunori Serita, Waseda University
Confirming Terahertz Penetration and Precision
To test their new approach, the researchers first needed to confirm that the terahertz waves were reaching the inside of the cochlea. They did this by using the terahertz imaging setup to conduct experiments using two different extracted and dried mouse cochlear samples — one with an empty interior and another filled with a metal material that reflects terahertz waves. They observed clear differences between the two samples, confirming that the terahertz waves were penetrating the inside of the cochlea.
The researchers then showed that internal structural information could be easily observed and extracted from 2D terahertz time-domain images using an unsupervised learning algorithm. The team also used the setup to successfully carry out 3D terahertz time-of-flight imaging and 3D reconstruction, allowing visualization of part of the cochlear duct, the spiral structure inside the cochlea.
Toward Real-World Use: Miniaturizing the System
Next, the researchers plan to demonstrate the technique’s feasibility on cochleae in a more realistic biological environment. Since the cochlea is located deep inside the ear and filled with lymphatic fluid, they will first need to miniaturize the system so it can be inserted through the ear canal. They are also developing a stronger terahertz source to reach deeper structures.
The researchers say that once the terahertz imaging technology is miniaturized, it could be incorporated into endoscopes and otoscopes, enabling non-invasive in vivo imaging for cochlear diagnostics and early cancer detection in various organs.
Reference: “Three-dimensional terahertz near-field imaging evaluation of cochlea” by L. Zheng, H. Chen, T. Fujita, A. Kakigi, N. Allen, H. Murakami, M. Tonouchi, K. Serita, 27 March 2025, Optica.
DOI: 10.1364/OPTICA.543436
