Evaluation of a polarization-enhanced laparoscopy prototype for improved intra-operative visualization of peritoneal metastases

Abstract

Despite careful staging, the accuracy for preoperative detection of small distant metastases remains poor, creating a clinical need for enhanced operative staging to detect occult peritoneal metastases. This study evaluates a polarization-enhanced laparoscopy (PEL) prototype and assesses its potential for label-free contrast enhancement of peritoneal metastases. This is a first-in-human feasibility study, including 10 adult patients who underwent standard staging laparoscopy (SSL) for gastrointestinal malignancy along with PEL. Image frames of all detectable peritoneal lesions underwent analysis. Using Monte Carlo simulations, contrast enhancement based on the color dependence of PEL (mPEL) was assessed. The prototype performed safely, yet with limitations in illumination, fogging of the distal window, and image co-registration. Sixty-five lesions (56 presumed benign and 9 presumed malignant) from 3 patients represented the study sample. While most lesions were visible under human examination of both SSL and PEL videos, more lesions were apparent using SSL. However, this was likely due to reduced illumination under PEL. When controlling for such effects through direct comparisons of integrated (WLL) vs differential (PEL) polarization laparoscopy images, we found that PEL imaging yielded an over twofold Weber contrast enhancement over WLL. Further, enhancements in the discrimination between malignant and benign lesions were achieved by exploiting the PEL color contrast to enhance sensitivity to tissue scattering, influenced primarily by collagen. In conclusion, PEL appears safe and easy to integrate into the operating room. When controlling for the degree of illumination, image analysis suggested a potential for mPEL to provide improved visualization of metastases.

Figure 1

Representative SSL, WLL, PEL, and mPEL images of biopsy confirmed benign lesions and parietal peritoneal metastasis. SSL, WLL, and PEL images are shown as RGB images, while the mPEL images are displayed in pseudocolor (jet map).

Figure 2

Monte Carlo simulations of WLL, PEL, and mPEL for a range of scattering powers encountered in peritoneal tissue (shaded region represents range of values for different scatterer and hemoglobin concentrations; note that scattering power is a unitless parameter).

Figure 3

Mean ROI intensity (A) and Weber contrast (B) for all 65 study lesions in gray channel under each imaging modality. Statistical significance was determined by one-way ANOVA with Tukey's HSD post-hoc tests. ** denotes p-value < 0.001.

Figure 4

Box plots of (A) mean intensities and (B) Weber contrast of presumed-benign (n = 56) compared to presumed-malignant (n = 9) lesions in different imaging modalities. * denotes p-value < 0.05. ** denotes p-value < 0.001.

Figure 5

2D variance of collagen fibers of (A) malignant and (B) benign lesions. Box plot of volume fraction (C) and mean directional variance of fibers (D) for malignant and benign lesions. ** denotes p-value < 0.001.

Figure 6

PEL device with proximal optical assembly and distal cap components highlighted in more details.

Figure 7

Flow chart of image pre-processing methods (A) and computing modified PEL using Monte Carlo-based regression analysis (B).