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Daniel Feiler, Amanda I Noonan, Justis P Ehlers, Sunil K Srivastava, Andrew Rollins, Yuankai K Tao; Characterization of optical properties of semitransparent materials for the development of novel intraoperative OCT-compatible ophthalmic surgical instruments. Invest. Ophthalmol. Vis. Sci. 2014;55(13):1630.
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© ARVO (1962-2015); The Authors (2016-present)
Microscope-integrated optical coherence tomography (MIOCT) enables real-time visualization of changes in retinal and corneal tissue microstructure during ophthalmic surgical maneuvers. However, traditional metallic surgical instruments obscure OCT light, cast shadows over regions-of-interest, and cause specular reflection artifacts. In this study, we characterize several semitransparent materials using OCT to identify substrates most suitable for the development of novel OCT-compatible surgical instruments to optimize visualization of the instrument tip and underlying tissue.
Six semitransparent materials were imaged using a Bioptigen SDOIS system (830±30 nm, 50 kHz line-rate). The materials were translated at 1 micron increments over a 1.5 mm range relative to a fixed focal plane, and B-scans were acquired at each position. Intensity changes resulting from fall-off and defocus were corrected in post-processing using experimentally measured values. Each B-scan was then averaged to remove speckle noise, and the resulting scattering profile was fit to a Beer’s law model using least-squares minimization to calculate the attenuation coefficient. The scattering density was calculated by measuring the percentage, by volume, of scatterers with intensities two standard deviations above the OCT noise floor.
The measured optical properties of the six semitransparent materials showed comparable attenuation coefficients (Fig. 1), with values ranging from 2.16-3.31 mm-1. The materials showed dramatically different scattering densities, ranging from 0.13-23.2% by volume, which can be clearly distinguished on OCT cross-sections.
Measurement of optical properties allows quantification of material properties best suited for the development of OCT-compatible instruments. The attenuation coefficients show that all of the materials measured are semitransparent over the OCT spectrum used, which will be advantageous in creating surgical tools that do not obscure the underlying tissues during surgical manipulation. Additionally, each material had unique scattering densities, which can potentially be used to optimize instrument visualization with intraoperative OCT.
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