Experimental and numerical investigation of wavelength and resolution dependency of dynamic optical coherence tomography signals

TL;DR

This study investigates how DOCT readouts LIV and OCDS depend on probe wavelength and system resolution, using both experimental measurements on tumor spheroids and numerical simulations. The experimental results reveal strong wavelength dependence but negligible resolution effects, while simulations show wavelength sensitivity for diffusion and random-ballistic motions and reveal subtle resolution influences. The work employs a DSM-based scatterer model and a fast DOCT signal simulation framework to dissect how motion type and system specs shape DOCT signals, with implications for interpreting DOCT images and for motion-parameter estimation. Overall, the findings highlight that DOCT is governed by both tissue dynamics and OCT hardware, suggesting avenues for motion-type classification and quantitative parameter estimation in future work.

Abstract

The wavelength and system-resolution dependencies of dynamic optical coherence tomography (DOCT) are investigated experimentally and numerically. Experimental investigations demonstrate significant wavelength dependency for the DOCT values but no resolution dependency. Numerical simulations were performed using diffusion, random-ballistic motion, and mono-directional flow-based motion models. Diffusion and random-ballistic motion-based simulations show significant wavelength dependency. Additionally, small but certain resolution dependency was revealed by these simulations. Mono-directional flow simulations did not show wavelength dependency, but did demonstrate resolution dependency. The DOCT value is sensitive to both tissue dynamics and the OCT system specification. These effects should be considered when interpreting DOCT images.

Figures (9)

• Figure 1: Boundaries of eight en face blocks. The en face field is split into eight blocks, and each block repeated raster-scanned for 32 times. The consistency of the OCT phase is not high enough around the block boundaries, and thus the B-scans adjacent to the boundaries were not used in the analyses.
• Figure 2: Wavelength dependency of LIV. (a) LIV images of spheroids acquired with short (840-nm) and long (1310-nm) OCT systems. Both the lateral and axial resolutions of 840-om OCT were computationally reduced to match those of 1310-nm OCT. (b) Mean LIV value of whole spheroid volume. The dots indicate the means of mean LIV and whiskers indicate the standard deviations among the four spheroids. The shorter wavelength gave significantly higher LIV with statistical significance (p < 0.001, as indicated by ***).
• Figure 3: Wavelength dependency of OCDS. (a) OCDS images of spheroids acquired with short (840-nm) and long (1310-nm) OCT systems. Both the lateral and axial resolutions of 840-om OCT were computationally reduced to match those of 1310-nm OCT. (b) The mean OCDS value of whole spheroid volume. The dots indicate the means of the mean OCDS and the whiskers indicate the standard deviations among the four spheroids. The shorter wavelength gave significantly lower OCDS with statistical significance (p < 0.001, indicated by ***).
• Figure 4: Axial-resolution dependency of LIV and OCDS. (a, b) LIV and OCDS images of a representative tumor spheroid at four different axial resolutions. All images were generated from an identical sequence of complex OCT image obtained from 840-nm OCT but with the computational-resolution modification. (c, d) Means of (c) mean LIV and (d) mean OCDS. Each of the mean LIV and OCDS were computed from the entire volume of each spheroid, and the means and the standard deviations of the four spheroids were plotted. Both LIV and OCDS showed no significant axial-resolution dependency.
• Figure 5: Lateral-resolution dependency of LIV and OCDS. (a, b) LIV and OCDS images of a representative tumor spheroid at four different lateral resolutions. All images were obtained from high-resolution 840-nm OCT but with the computational-resolution modification. (c, d) Means of (c) mean LIV and (d) OCDS. Each mean LIV and OCDS was computed from the entire volume of each spheroid, and the means and the standard deviations of the four spheroids were plotted. Both LIV and OCDS showed no significant lateral-resolution dependency.