Optical coherence tomography is a non-invasive optical imaging technique that has been widely used in various fields due to its high resolution and imaging speed. The image contrast is based on the sample’s internal reflectivity profile and, thus, the technique is non-invasive and label-free. Unfortunately, when imaging opaque media such as biological tissue, the imaging performance and penetration depth quickly degrade as an effect of multiple light scattering. Scattering of light as a deterministic process, though, and the scattered field can be manipulated by shaping the optical wavefront incident to the sample considering the linear relationship between the incident field and the scattered optical field.
Up to now, various methods to enhance the signal-to-noise ratio and imaging depth in spectral domain optical coherence tomography have been proposed based on wavefront shaping. These techniques typically require single-pass wavefront manipulation, i.e. shaping of the field incident to the sample only.
Recently, German scientists at University of Hanover: Jonas Kanngiesser, Dr. Maik Rahlves and Dr. Bernhard Roth proposed a compact setup for wavefront manipulation in spectral-domain optical coherence tomography. The idea was to keep the reference beam static while at the same time employing an SLM for wavefront manipulation of the incident field to the sample. Using a phase-only device enabled relative phase shifting at the interferometer arms at the same time and, thus, allowed complex signal acquisition. Their work is currently published in the research journals, Optics Letters and Scientific Reports.
The authors utilized phase shifting by the SLM to reduce the number of imaging artifacts while at the same time increasing the signal-to-noise ratio to enhance the device performances. Consequently, they analyzed the impact of a combination of wavefront shaping and complex optical coherence tomography signal acquisition to further enhance the imaging performance in strongly scattering media.
The authors observed a locally enhanced optical coherence tomography signal acquired from the scattering sample and also an increased signal-to-noise ratio attributed to the combination of phase-shifting with optical wavefront shaping. This further resulted in an increase in the penetration depths as compared to conventional optical coherence tomography systems.
In summary, the German research team successfully demonstrated an iterative wavefront correction for complex spectral-domain optical coherence tomography. Even though it requires long optimization time, the results provide enough evidence that the presented technique surpasses the conventional optical coherence tomography techniques in terms of enhanced performance and thus will advance future imaging in strongly scattered media such as the biological tissues.
Kanngiesser, J., Rahlves, M., & Roth, B. (2019). Iterative wavefront correction for complex spectral domain optical coherence tomography. Optics Letters, 44(6), 1347.Go To Optics Letters
Kanngiesser, J., Rahlves, M., & Roth, B. (2019) Double interferometer design for independent wavefront manipulation in spectral domain optical coherence tomography. Scientific Reports 9, 14651Go To Scientific Reports