Surgical polarimetric endoscopy for the detection of laryngeal cancer

The standard-of-care for the detection of laryngeal pathologies involves distinguishing suspicious lesions from surrounding healthy tissue via contrasts in colour and texture captured by white-light endoscopy. However, the technique is insufficiently sensitive and thus leads to unsatisfactory rates of false negatives. Here we show that laryngeal lesions can be better detected in real time by taking advantage of differences in the light-polarization properties of cancer and healthy tissues. By measuring differences in polarized-light retardance and depolarization, the technique, which we named ‘surgical polarimetric endoscopy’ (SPE), generates about one-order-of-magnitude greater contrast than white-light endoscopy, and hence allows for the better discrimination of cancerous lesions, as we show with patients diagnosed with squamous cell carcinoma. Polarimetric imaging of excised and stained slices of laryngeal tissue indicated that changes in the retardance of polarized light can be largely attributed to architectural features of the tissue. We also assessed SPE to aid routine transoral laser surgery for the removal of a cancerous lesion, indicating that SPE can complement white-light endoscopy for the detection of laryngeal cancer.


Statistics
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Software and code
Policy information about availability of computer code Data collection SPE data were collected using a LabVIEW2017 program.
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Data
Policy information about availability of data All manuscripts must include a data availability statement. This statement should provide the following information, where applicable: -Accession codes, unique identifiers, or web links for publicly available datasets -A list of figures that have associated raw data -A description of any restrictions on data availability The data supporting the results in this study are available within the paper and its Supplementary Information. Source data for the figures are provided with this paper. The raw images involving human participants are protected owing to data-privacy requirements, and can be made available for research purposes on reasonable request from the corresponding authors, provided that approval is obtained after an institutional review procedure at Imperial College London and London North West University Healthcare NHS Trust. The response from the authors will usually be within four weeks.

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Life sciences study design
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Sample size
We did not conduct a formal power analysis to determine the sample size, owing to the absence of a priori mean and standard deviation polarimetric values for the larynx and thereby the effect size. We aimed to collect as many samples as was reasonably possible given the experimental constraints. A post-hoc analysis has been informally conducted based on the mean and standard deviation obtained in this study using the G*Power 3.1 software [Faul,F.,et. al. Behav. Res. Methods,41.], and given two-sided Mann-Whitney test, α=0.01 and power=0.99, the sample size was estimated to be 34 and 21 for the evaluation of retardance and depolarization respectively. The sample sizes in this study are therefore sufficient according to this analysis.
Data exclusions No data were excluded. Underexposed regions (that is, caused by blood on the tissue surface) and overexposed regions (that is, with strong specular reflection) in the SPE images were marked (rendered green with transparency) in display to avoid misleading viewers. These regions were invalid and not used in data analysis, as clearly stated in the paper. The criteria for underexposure and overexposure were preestablished upon the greyscale of polarization-insensitive-intensity reference image, and are clearly stated in Methods.

Replication
The patient requiring laryngectomy was consecutively imaged 28 times under the retardance mode and 34 times under the depolarization mode. Each time the larynx was imaged from a different view and working distance, owing to the motion of the tissue and the endoscope. The polarimetric properties of the normal and tumorous tissue and their polarimetric contrast remained consistent, and are included in the Supplementary videos. The findings from the first patient were reproduced in the second patient, who was consecutively imaged 30 times under the retardance mode and 71 times under the depolarization mode, respectively. The consistent polarimetric properties are included in the Supplementary videos. The results obtained in vivo also agreed with those obtained ex vivo as well as during histology and polarizationmicroscopy validation.
Randomization Randomization was not required, because all the samples underwent both polarimetric imaging (the method being evaluated) and white-light imaging (the control method), and were compared with pathology (the gold-standard), thereby eliminating potential bias when comparing the two methods in this observational study. This is consistent with other medical-imaging technology evaluation and validation studies, according to [P. Valk,J. Nucl. Med. 41,7; and, E. Lalumera & S. Fanti, Topoi 38, 2.].