Mid-Infrared Imaging Made Practical for Medicine by Danish Researchers

Researchers have developed a unique high-resolution imaging method that can capture mid-infrared spectral images of fast events or dynamic processes that take place on the order of milliseconds. This spectral range is used for many applications because it can reveal the detailed chemical composition of a sample.

“It could be used to look for the chemical signatures of cancer and other diseases in ways that would increase the accuracy and speed of diagnoses.”

Caption: Researchers developed a new system that uses frequency conversion to shift an entire mid-IR image into the near-infrared wavelength range while preserving the spatial information. The system can be used to look for the chemical specific signatures of cancer and other diseases.

Credit: Peter Tidemand-Lichtenberg, DTU Fotonik

“Although mid-infrared spectroscopy is recognized as a powerful tool for chemical analysis, its applicability has been hampered by a lack of affordable light sources and sensitive detectors,” said Tidemand-Lichtenberg. “To overcome this barrier, we used an approach that translates information from the mid-infrared region, where the chemical signatures are most distinct, to the near-infrared, where today’s camera technology is most mature and sensitive.”

Practical mid-infrared spectroscopy

The researchers drew on a process known as nonlinear frequency conversion in which energy is added to a photon to change its wavelength, and hence its color. Although frequency conversion, or upconversion, is often used to change the wavelength of a laser’s output, the researchers from DTU Fotonik developed a detection system that could shift an entire mid-IR image into the near-infrared wavelength range while preserving all the spatial information.

The system incorporates a new mid-infrared light source developed by collaborators from The Institute of Photonic Sciences (ICFO). This single-wavelength light source can be tuned to different wavelengths and it also uses frequency conversion to generate the mid-infrared light. In fact, the researchers used the same pulsed near-infrared laser for two things: to generate the tunable mid-IR light and to achieve the image upconversion.

“This approach yields high peak power pulses in perfect synchronism, eliminating the need for sophisticated temporal control of the pulses, leading to images.

Caption: The system incorporates a single-wavelength light source that uses frequency conversion to generate mid-infrared light and can be tuned to different wavelengths. The researchers used the same pulsed near-infrared laser to generate the tunable mid-IR light and to achieve the image conversion. They demonstrated the system by imaging a gas flow and distinguishing cancerous and normal samples of esophageal tissue

The researchers demonstrated the imaging speed of their new mid-infrared upconversion spectroscopy approach by tuning the illumination laser to match the peak absorption of a gas flow and acquiring a video with 40 images per second. in which the system was used to evaluate cancerous and healthy esophageal tissue samples. They found that morphology and spectral classification using their system matched well with the standard stained histopathology images. 

“Our upconversion imaging approach is generic and constitutes a major simplification in realizing video-frame-rate, mid-infrared monochromatic imaging,

Study in journal Optica: Video-rate, mid-infrared hyperspectral upconversion imaging

Via: The Optical Society