Instituto de Óptica “Daza de Valdés”

Thesis defense of Ryan McAuley, Ph.D. student of Judith Birkenfeld.


Madrid / January 8, 2024

Congratulations to Ryan McAuley who did an excellent job successfully defending his PhD thesis on ‘Probing sub-resolution tissue structural and mechanical properties with optical coherence tomography’ (Supervisors: Prof. Martin Leahy, University of Galway, Dr. Judith S. Birkenfeld, IO-CSIC; Thesis defense/Chair: Prof. Miriam Byrne, University of Galway,  External examiner: Dr. Sabine Kling, ETH Zurich, Internal Examiner: Prof. Patricia Scully, University of Galway).

In his thesis, Dr. McAuley assessed sub-resolution signals related to the static and dynamic, structural and mechanical properties of tissue using vibrometric, nanosensitive, and synthetic Fourier domain extensions of OCT. The thesis includes a fruitful collaboration between the Visual Optics and Biophotonics Laboratory of IO-CSIC, and Prof. Leahy’s research group (TOMI) at the University of Galway, Ireland, based on the European H2020 Imcustomeye project. We wish Dr. McAuley all the best in his new position as a postdoctoral researcher in the research group of Prof. N. Uribe-Patarroyo at the Wellman Center for Photomedicine/Harvard Medical School.
Here is a summary of his thesis:

The structural and mechanical properties of biological tissues are intimately coupled with adequate organ function and tissue health. Optical coherence tomography (OCT) is extensively used in the study of human tissues, such as the cornea, skin and tympanic membrane, owing to its impressive resolution and depth range. However, diseases often manifest as tissue alterations below the resolution limit, and therefore, conventional intensity-based OCT is of limited use for early-stage detection or diagnosis. The aim of this work is to harness the subresolution signals from OCT to understand, detect and diagnose tissues. Vibrometric, nanosensitive and synthetic Fourier domain extensions of OCT were used to access subresolution signals related to the static and dynamic, structural and mechanical properties of tissue. Demonstration examples include corneal tissue, skin and stem cell spheroids.

The vibrational resonance frequency modes of six corneal phantoms and two ex vivo rabbit corneas were successfully measured with the co-axial, acoustic optical coherence vibrometry probe. The resonance frequencies of the corneal phantoms showed sensitivity to the thickness, Young’s modulus and intraocular pressure of the phantoms. The resonance frequencies of the ex vivo rabbit corneas were observed to increase with increased intraocular pressure.

Ryan McAuley thesis defense

The mean spatial period of mesenchymal stem cell pellets undergoing chondrogenic differentiation, measured with nanosensitive OCT, increased between days 1 and 4 and subsequently decreased between day 4 and 21. There was a net decrease in the mean spatial periodicity of the chondrogenic mesenchymal stem cell pellets of all three donors over the 21-day period of differentiation, in contrast to undifferentiated cells.

Synthetic Fourier domain OCT intensity images of reference samples resolved the harmonic refractive index variations within small regions of the samples. Conventional and synthetic Fourier domain OCT greyscale images of a tilted glass slide were compared, and an improvement of the visibility of the slide and tilt were observed. Images of different regions of human skin tissue were imaged, and a difference of the structural spatial periodicity profiles within smaller regions was observed. A comparison between a nanosensitive OCT image and synthetic Fourier domain OCT colour maps of a potato slice showed that the spatial resolution of the synthetic Fourier domain OCT colour map was approximately 10 times superior. The research detailed in this thesis demonstrates that the raw OCT interference signal manifests rich sub-resolution details which can be extracted for discovery and diagnosis of diseases and their mechanisms.

Communication IO-CSIC

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