Analysis and reduction of noise-induced depolarization in catheter based polarization sensitive optical coherence tomography

Abstract

In catheter based polarization sensitive optical coherence tomography (PS-OCT), a optical fiber with a rapid rotation in the catheter can cause low signal-to-noise ratio (SNR), polarization state instability, phase change of PS-OCT signals and then heavy noise-induced depolarization, which has a strong impact on the phase retardation measurement of the sample. In this paper, we analyze the noise-induced depolarization and find that the effect of depolarization can be reduced by polar decomposition after incoherent averaging in the Mueller matrix averaging (MMA) method. Namely, MMA can reduce impact of noise on phase retardation mapping. We present a Monte Carlo method based on PS-OCT to numerically describe noise-induced depolarization effect and contrast phase retardation imaging results by MMA and Jones matrix averaging (JMA) methods. The peak signal to noise ratio (PSNR) of simulated images processed by MMA is higher than about 8.9 dB than that processed by JMA. We also implement experiments of multiple biological tissues using the catheter based PS-OCT system. From the simulation and experimental results, we find the polarization contrasts processed by the MMA are better than those by JMA, especially at areas with high depolarization, because the MMA can reduce effect of noise-induced depolarization on the phase retardation measurement.

Estimation of Medium Depolarization Index with Noise Immunity in Catheter-Based PS-OCT toward Vascular Plaques Detection

“…25,34 We use SMM and MMA methods to demodulate the simulation data to obtain the spatial PS-OCT image. 25,28,34 ROR are selected as 2560 pixels on the top area, and reference points for SMM and MMA are selected as a horizontal 1-pixel-width line with 512 pixels on the simulating tissue surface. 25 We calculate EMDI, DI, and DOPU based on simulation images under different g and SNR values, and then these results contrast by setting true DI and DOPU shown in Figure 2(a) shows that DOPU, DI, and EMDI for a nondepolarized simulation material with g = 1 among additive noise from SNR = 0 to 15.…”

“…After the simulation, the photon is sent and received. To achieve a typical PS-OCT device noise model from practical application, ,, we generate additive zero-mean complex Gaussian white noises on signals of wavenumber domain according to average signal intensity of one image and setting SNR. ,,, …”

“…For each simulation, two different SOPs of simulated lights are successively launched into the simulating tissue, and their output signals are collected by H and V channels, respectively. So the noises would appear not only on the intensity but also all 4 elements of Jones and 16 entries of Mueller matrices. , We use SMM and MMA methods to demodulate the simulation data to obtain the spatial PS-OCT image. ,, ROR are selected as 2560 pixels on the top area, and reference points for SMM and MMA are selected as a horizontal 1-pixel-width line with 512 pixels on the simulating tissue surface . We calculate EMDI, DI, and DOPU based on simulation images under different g and SNR values, and then these results contrast by setting true DI and DOPU shown in Figure .…”

“…Several methods are created and widely used to quantify depolarization in PS-OCT, including depolarization index (DI), differential depolarization index (DDI), degree of polarization uniformity (DOPU), ,, entropy, − and characteristic depolarization coefficient based on Lu–Chipman matrix decomposition. ,, However, PS-OCT has some limitation in quantifying depolarization for now. The most worthy of attention is that noises can induce depolarization because noise generates a random change of polarization states. ,, Especially in catheter-based PS-OCT, the rapid rotation of optical fibers in the catheter probe induces a low signal-to-noise ratio (SNR), polarization state instability, and phase change of PS-OCT signals, thus generating serious noise-induced depolarization . Therefore, the depolarization measurement in PS-OCT cannot accurately represent the medium depolarization.…”

“…However, to achieve proper depolarization quantification by DI, a prerequisite is that the Mueller matrix should collect the depolarization effectively. In terms of recording depolarization by a Mueller matrix from PS-OCT, we previously proposed a similar Mueller matrix (SMM) for polarization determination and Mueller matrix incoherent averaging method (MMA) in the catheter-based PS-OCT. , In SMM, the DI can be calculated from a depolarization matrix, which is decoupled from birefringence and diattenuation matrices by Lu–Chipman decomposition. However, traditional DI cannot separate medium depolarization and noise-induced depolarization.…”