Holographic optical coherence tomography (OCT) for functional retina imaging

• Applicant: Professor Dr. Gereon Hüttmann
• Subject Area: Medical Physics, Biomedical Technology
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 392443200

Holography allows to record and evaluate phase and amplitude of a light wave field. Holographic optical coherence tomography (OCT) provides additionally depth-resolved measurements of phase and amplitude in scattering volumes. Using the phase information a purely numerical compensation of defocus and other imaging errors, as well as high-precision interferometric measurements of changes within scattering tissues become possible. Full-field swept-source OCT, which uses high-speed cameras to parallelize OCT imaging, provides phase-locked imaging of human retina. Local and global motion limits the accuracy with which changes in phase can be determined. In the first funding period, motion correction and new algorithms significantly improved the phase evaluation. It was possible to visualize for more than 8 seconds morphological changes in the outer segments of photoreceptor cells and in the inner plexiform layer after an optical stimulation. For the first time in humans, the functional relationship between photoreceptors and ganglion cells in the innermost neuronal layer was imaged. By combining holographic OCT with Doppler measurements, it was possible to simultaneously measure arterial blood flow and pulsation-induced mechanical changes of arteries and retinal tissue in image fields of 5 mm x 14 mm with a time resolution of more than 180 Hz. In the second funding period, these studies will be continued with increased resolution and improved contrast by suppression of multiple scattered light, which strongly affects imaging especially below the retinal pigment epithelium. The function of individual groups of neuronal cells will be selectively imaged; single-cell imaging will be enabled by improving aberration correction and by minute-long volume averaging for improving SNR. The goal is comprehensive functional imaging of all neuronal layers from photoreceptors to ganglion cells. To determine biomechanical parameters of the retina, deformations due to pulsatile vessels will be correlated with local blood flow. The possibility of cell-specific or metabolic contrast due to spontaneous local movement of cells or cell organelles will be investigated. Holographic OCT offers unique opportunities for phase-sensitive imaging in vivo. The research project lays the foundation for comprehensive functional retinal imaging, which will provide a better understanding of physiological processes and may open new avenues for clinical diagnostics.

• DFG Programme: Research Grants