Researchers show that subwavelength terahertz imaging works with methods that accelerate imaging speed.
Researchers have developed a new terahertz imaging approach that, for the first time, can acquire micron–scale resolution images while retaining computational approaches designed to speed up image acquisition. This combination could allow terahertz imaging to be useful for detecting early–stage skin cancer without requiring a tissue biopsy from the patient.

Terahertz wavelengths fall between microwaves and infrared light on the electromagnetic spectrum. Light in this region is ideal for biological applications because, unlike x–rays, it doesn’t carry enough energy to harm tissue. Other research has shown that skin cancer cells absorb terahertz light more strongly than healthy cells, demonstrating that terahertz imaging can be useful for distinguishing between cancerous and healthy tissue.

“Skin cancer can already be detected using terahertz light, but because of the low resolution of current imaging approaches, the cancer can only be seen after it has grown quite large,” said the research team’s leader, Rayko Stantchev of the University of Exeter, UK. “Ideally, we want to detect the cancer early, when it is still small. We hope that high–resolution terahertz images, combined with the ability to take an image quickly, could eventually lead to a device that could detect cancer in the doctor’s office.”

In the journal Optica for high impact research, the researchers showed that their near–field approach to terahertz imaging can achieve a spatial resolution of about nine microns and was compatible with compressed sensing and adaptive imaging algorithms that allow three times faster image acquisition than conventional technologies.

In addition to its practical benefits for medical imaging, the research also represents a new way of accomplishing high resolution terahertz imaging. In conventional imaging, spatial resolution is limited by the diffraction limit, which is determined by the wavelength of light used.

Although most imaging techniques detect scattered light at some distance from the object being imaged, the researchers overcame the diffraction limit by using a unique setup to measure close, or near–field, interactions of terahertz waves with the object being imaged. Their approach produced a resolution about 1/45 of the wavelength used for imaging.

“This is the first experimental demonstration, for any spectral region, showing that compressed sensing and adaptive imaging can be performed at resolutions much smaller than the wavelength of light used for imaging,” said Stantchev. “Showing that this is physically possible will allow engineers and scientists to start to think about the full potential of this approach.”