Abstract

A pixel-by-pixel tissue classification framework using multiple contrasts obtained by Jones matrix optical coherence tomography (JM-OCT) is demonstrated. The JM-OCT is an extension of OCT that provides OCT, OCT angiography, birefringence tomography, degree-of-polarization uniformity tomography, and attenuation coefficient tomography, simultaneously. The classification framework consists of feature engineering, k-means clustering that generates a training dataset, training of a tissue classifier using the generated training dataset, and tissue classification by the trained classifier. The feature engineering process generates synthetic features from the primary optical contrasts obtained by JM-OCT. The tissue classification is performed in the feature space of the engineered features. We applied this framework to the in vivo analysis of optic nerve heads of posterior eyes. This classified each JM-OCT pixel into prelamina, lamina cribrosa (lamina beam), and retrolamina tissues. The lamina beam segmentation results were further utilized for birefringence and attenuation coefficient analysis of lamina beam.

Highlights

  • Optic nerve head (ONH) morphology and its biomechanics are of interest in the ophthalmic community because this knowledge is important in monitoring the progression of myopia and glaucoma [1, 2]

  • The tissue classification framework discussed in the previous section is a general framework and it could be customized to several types of Jones matrix optical coherence tomography (JM-Optical coherence tomography (OCT)) images, such as anterior eye [29, 30], posterior eye [11, 41, 42], heart [43], and skin [44]

  • In the tissue label and meta-label images, the boundary of lamina cribrosa and retrolamina tissues is relatively poorly delineated, whereas the junction between the prelamina tissue and lamina cribrosa shows relatively sharp appearance. This agrees with histological knowledge, that is, lamina-cribrosa-to-retrolamina transition is moderate, whereas that between the prelamina and lamina cribrosa is sharp [47]

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Summary

Introduction

Optic nerve head (ONH) morphology and its biomechanics are of interest in the ophthalmic community because this knowledge is important in monitoring the progression of myopia and glaucoma [1, 2]. This birefringence-biomechanics relation has been observed in several tissues including skin [14], sclera [15,16,17] and lamina cribrosa [18,19,20] It is indirect, JM-OCT may provide us with relevant biomechanical information in vivo [14,15,16,17]. We develop a framework for tissue classification by exploiting multiple contrasts of JM-OCT This method involves pixel-wise tissue classification, unlike the conventional boundary delineation technique for tissue segmentation [31, 32]. The training dataset for supervised tissue (pixel) classifier is generated using an unsupervised method This combination enables tissue classification using multi-contrast JM-OCT data. The quantitative analyses of lamina beam birefringence and attenuation coefficient are demonstrated by using the segmentation result of lamina beam

Theory and methods
JM-OCT system
The tissue classification framework
Feature engineering
Semi-automatic generation of training dataset
Supervised classification
ONH analysis
Measurement protocol and the subjects
Tissue segmentations
Comparison with manual segmentation
Effect of correlation between the test and training datasets
Long-term robustness of the classifier
Lamina beam birefringence and attenuation coefficient analysis
Rationality of XOR feature
Potential clinical applications
Potential usage of other machine learning algorithms
Processing time
Limitations of the present method
Conclusion
Full Text
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