elastoOCT

Publications

C. Correia et al., "Time-dependent elastic numerical model for Optical Coherence Elastography of the murine retina," 2023 IEEE 7th Portuguese Meeting on Bioengineering (ENBENG), Porto, Portugal, 2023, pp. 207-210, doi: 10.1109/ENBENG58165.2023.10175350.
Batista, A.; Serranho, P.; Santos, M.J.; Correia, C.; Domingues, J.P.; Loureiro, C.; Cardoso, J.; Barbeiro, S.; Morgado, M.; Bernardes, R. Phase-Resolved Optical Coherence Elastography: An Insight into Tissue Displacement Estimation. Sensors 2023, 23, 3974. DOI: 10.3390/s23083974
Serranho, P.; Barbeiro, S.; Henriques, R.; Batista, A.; Santos, M.; Correia, C.; Domingues, J.; Loureiro, C.; Cardoso, J.; Bernardes, R. and Morgado, M. On the Numerical Solution of the Inverse Elastography Problem for Time-harmonic Excitation. Proceedings of the 2nd International Conference on Image Processing and Vision Engineering, ISBN 978-989-758-563-0, ISSN 2795-4943, pages 259-264. DOI: 10.5220/0011125900003209
Batista, A.; Correia, C.; Barbeiro, S.; Cardoso, J.; Domingues, J.; Henriques, R.; Loureiro, C.; Santos, M.; Serranho, P.; Bernardes, R. and Morgado, M. Swept-source Phase-Stabilized Optical Coherence Tomography Setup for Elastography. Proceedings of the 2nd International Conference on Image Processing and Vision Engineering, ISBN 978-989-758-563-0, ISSN 2795-4943, pages 269-274. DOI: 10.5220/0011126500003209
Barbeiro S., Serranho P. (2020) The Method of Fundamental Solutions for the Direct Elastography Problem in the Human Retina. In: Alves C., Karageorghis A., Leitão V., Valtchev S. (eds) Advances in Trefftz Methods and Their Applications. SEMA SIMAI Springer Series, vol 23. Springer, Cham. https://doi.org/10.1007/978-3-030-52804-1_5.
António Araújo, Pedro Serranho, On the use of quasi-equidistant source points over the sphere surface for the method of fundamental solutions, Journal of Computational and Applied Mathematics, 359, 2019, 55-68, https://doi.org/10.1016/j.cam.2019.03.019.

Theses

Ana Rita Bernardo, Optical coherence elastography in dermatology, Master Thesis in Biomedical Engineering, University of Coimbra, September 2022.
Rafael Oliveira Henriques, Mathematical model to reconstruct the mechanical properties of an elastic medium, Master Thesis in Mathematics, University of Coimbra, July 2020.
Melania Buonocunto, Microstrain measurements in soft tissue phantoms through swept-source optical coherence tomography, Master Thesis in Biomedical Engineering, Università degli Studi di Napoli Federico II, Naples, April 2020.
Francesca Tartaglia, Evaluation of phase stability of a swept-source optical coherence tomography system, Master Thesis in Biomedical Engineering, Università degli Studi di Napoli Federico II, Naples, May 2020.

To develop an Optical Coherence Elastography technique for imaging in vivo the mechanical properties of the retina of animal models.

Funding: FCT - Project PTDC/EMD-EMD/32162/2017: 240 k€01/10/2018 - 30/09/2022

Assessment of phase stability of the developed Swept-Source OCT system.

Background

There is a pressing need for techniques with enough sensitivity to detect early signs of neurodegeneration and define biomarkers of neurodegenerative diseases. The recent failure of clinical trials on Alzheimer’s disease shows that it is very difficult to have successful therapies in the late stages of the disease, which are characterized by massive neuronal loss. This justifies the importance of detecting neurodegenerative diseases in their asymptomatic phase.

The traditional modalities of brain imaging, Magnetic Resonance Imaging (MRI) and Computerized Tomography, rely on volumetric changes and lack sensitivity for detecting the subtle alterations that precede clinical symptoms. As the mechanical properties of soft tissue vary over a much greater range than other physical properties, elastography techniques are inherently very sensitive. Magnetic Resonance Elastography (MRE), an imaging modality that measures the stiffness of tissues by imaging through MRI the displacements induced by mechanical waves, demonstrated that inflammation, toxic demyelination and transitory ischemic damage affect directly the brain mechanical properties. These findings support the idea that imaging the mechanical properties can detect changes in the brain's microstructure before volumetric changes or neuronal losses become detectable.

Although MRE offers the prospect of detecting neurodegeneration in its asymptomatic phase, its use as a biomarker will always be hampered by its high-cost making impracticable its application to longitudinal studies or for screening populations. For these purposes, low-cost and easy access are mandatory.

The retina is the visible part of the central nervous system and has been explored for signs of neurodegeneration. Previous research at our research center (CIBIT) showed that it is possible to develop neurodegeneration biomarkers based on data from Optical Coherence Tomography (OCT) images of retinas without any visible structural alteration. These results came from Alzheimer's, multiple sclerosis and Parkinson's patients. More recently, it were obtained biomarkers for Alzheimer's disease (AD) using data from OCT in vivo images of the retina of the triple-transgenic mouse model of AD (3xTg-AD).

From the rationale of brain MRE and our results on OCT neurodegeneration biomarkers, we believe that it is possible to detect early signs of degeneration by measuring the mechanical properties of the retina with an OCT-based elastography technique. Since OCT is a relatively low cost, easy to operate, widespread imaging technique, it has the conditions to be used for screening purposes.

Therefore, in this project we propose to develop an Optical Coherence Elastography technique for imaging in vivo the mechanical properties of the retina of animal models. The technique will combine ultrasound excitation with OCT imaging. The instrumentation will be based on an existing Swept-Source OCT system, entirely developed by us, ensuring full control over data acquisition and processing.

Team

Research Centers:

CIBIT - Coimbra Institute for Biomedical Imaging and Translational Research

CMUC - Centre for Mathemathics of the University of Coimbra

LIBPhys - Laboratory for Instrumentation, Biomedical Engineering and Radiation Physics

CEMMPRE - Centre for Mechanical Engineering, Materials and Processes

Results

We used the method of fundamental solutions (MFS) to to numerically simulate the propagation of an acoustic time-harmonic wave through layered acoustic media and the propagation of the generated elastic wave within the medium of interest (the human retina), in a model with the acoustic and elastic properties of the human eye.

We also considered a finite element approach to model the elastic propagation of waves. This numerical method served as a forward solver for the inverse problem, which consists of determining the set of parameters that characterize the medium’s mechanical properties knowing the displacement field for a given excitation. In practice, it is intended to infer the parameters that characterize the mechanical properties so that the difference between simulated displacements obtained by the forward solver with those parameters and the data is minimized.

The previously developed Optical Coherence Tomography (OCT) system was modified to perform OCE measurements. The system was upgraded to achieve the phase stability demanded by a displacement resolution of tens of nanometer, by developing an optically generated timing reference, based on a fiber Bragg grating, for initiating sampling at a fixed reference wavelength.

The M-acquisition mode was implemented on the system.

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