Multimodal optical imaging combining optical coherence tomography and Brillouin microscopy

Yogeshwari S. Ambekar1, Manmohan Singh1, Alexzander W. Schill1, Jitao Zhang2, Christian

Zevallos1, Behzad Khajavi1, Salavat R. Aglyamov3, Giuliano Scarcelli2, and Kirill V. Larin1,4

1Department of Biomedical Engineering, University of Houston, Houston, TX, USA2Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA

3Department of Mechanical Engineering, University of Houston, Houston, TX, USA4Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA

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SARATOV ANNUAL MEETING 2021

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Global Impact

• Neural tube defect: second most common structural birth defect in humans

• 500,000 pregnancies affected per year worldwide

[1] Botto LD et al., Neural tube defects. N Engl J Med. (1999)

Why Neural Tube Biomechanics?

• Mechanical forces regulate neurulation through

the process of mechanotransduction [2].

• Important to understand the interplay between

forces and tissue stiffness during development

[3,4].

• Disturbance in these complex processes lead to

developmental defects [5].

• Remains poorly understood because of sub-

optimal measurement techniques.

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[2] McShane, Suzanne G., et al. Developmental biology (2015) [3] Campàs O Semin Cell Dev Biol. (2016) [4] Sugimura K, et al. Development. (2016) [5] Blom HJ, et al. Nat Rev Neurosci. (2006)

Current Methods

4 [6] Coleman, Beverly G et al., Fetal diagnosis and therapy (2015)[7] Cortazar, A. Zugazaga, et al. Insights into imaging (2013)

Ultrasound Imaging Magnetic Resonance Imaging

Current Methods

5[8] Wang, Shang, et al. Biomedical optics express (2017)

Current Methods

6 [9] Raghunathan R. et al., Journal of biomedical optics (2018)[10] Zhang J. et al., Birth Defects (2019)

Methods

7 [11] G. Scarcelli, and S. H. Yun, Opt Express (2011)[12] M. Nikolic, and G. Scarcelli, Biomed Opt Express (2019)

Optical Coherence Tomography Brillouin Microscopy

Non-invasive, high resolution. Non-invasive, high resolution.

Swept source laser: ∼8 mW incident power. Single mode 660 nm laser: ~ 35 mW incident power.

Central Wavelength: 1310 nm. Two stage VIPA spectrometer (30 GHz FSR) [13,14].

Scan range of ∼105 nm. Camera exposure time was 0.2s.

Scan rate of ∼50 kHz.Spectrometer calibration with standard materials: water,

acetone and methanol.

Achromatic doublet: 0.25 NA, axial resolution: ∼11 μm in air. Achromatic doublet: 0.25 NA, lateral resolution of 3.8 µm

and axial resolution of 50 µm.

* Structural data, no biomechanics * No structural data, only biomechanics

* To overcome the limitations, we combined OCT+Brillouin

Schematic of Combined Brillouin OCT

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C: collimator, VA: variable attenuator, RM: reference mirror, PC: polarization controller, FC: fiber coupler, BPD: balanced photo detector, PBS: polarized beam splitter, λ/4: quarter wave plate, DM: dichroic mirror, GS: galvo scanning mirrors, VIPA: virtual image phase array

spectrometer, ADC: analog to digital convertor, DAC: digital to analog convertor, DAQ: data acquisition, Br: Brillouin.

Software of Combined Brillouin OCT

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6.05

6.1

6.15

6.2

6.25

6.3

Neural tube cross-section

Sample Preparation

Neural Tube Study:

• Timed matings of CD-1 mice were set up overnight and the mice were checked for a vaginal plug every

morning.

• The morning when a plug was found was considered as embryonic day (E) 0.5.

• Pregnant mice at the desired gestational stage (E 8.5, E 9.5) are euthanized by CO2 inhalation followed by

cervical dislocation.

• The embryos were taken out of the mother mice and dissected out and kept in a culture media at a

controlled temperature.

• After dissection, the embryos were transferred to an incubator at 37°C and 5% CO2 .

• Once the embryos were stabilized, we acquired combined Brillouin+OCT images.

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Results

(a)

(c) (d)

(b)

OCT Brillouin

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• In this study, we demonstrated that the co-aligned and synchronized Brillouin-OCT system can simultaneously map structural and biomechanical properties completely noninvasively.

• The Brillouin-OCT system could map the layer-by-layer distribution of biomechanical properties of the neural tube in mouse embryos with OCT guidance at various developmental stages. The nuclear layer was stiffer compared to the plexiform layer.

• The biomechanical properties at GD 8.5 of mouse embryo are different than the GD 9.5. At GD 9.5, the neuroepithelial layer was stiffer compared to the mesoderm and ectoderm layer.

• Future work involves assessing the changes in the neural tube stiffness due to various neural tube defects in murine models.

Conclusion & Future Work

Acknowledgements

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• Dr. Kirill Larin

• Dr. Salavat Aglyamov

• Dr. Alexander Schill

• Dr. Manmohan Singh

• Dr. Raksha Raghunathan

• Dr. Maryam Hatami

• Dr. Behzad Khajavi

• Dr. José Fernando

This work is supported, in part, by NIH grants R01EY022362 (KL) and R01EY030448 (RP).

Special Thanks to the Biomedical Optics Laboratory and our collaborators

• Achuth Nair

• Justin Rippy

• Harshdeep Singh Chawla

• Christian Delgado-Zevallos

• Hongqiu Zhang

• Jessica Gutierrez

• Mobarak Karim

• Sajede Saeidi

• Dr. Giuliano Scarcelli

• Dr. Jitao Zhang

• Dr. Richard Finnell

• Dr. Carlo Donato Carvalho