Refractive Index-Correlated Pseudocoloring for Adaptive Color Fusion in Holotomographic Cytology

Area of Science:

• Biomedical Imaging
• Optical Microscopy
• Cytopathology

Background:

• Conventional bright-field (BF) cytology of thyroid fine-needle aspiration biopsy (FNAB) faces challenges with staining variability and poor subcellular contrast.
• Limited visualization of subcellular structures hinders accurate diagnosis in thyroid FNAB.

Purpose of the Study:

• To introduce a refractive index-correlated pseudocoloring (RICP) framework for enhanced subcellular visualization in thyroid FNAB.
• To integrate quantitative refractive index (RI) maps with BF images for improved diagnostic interpretability.

Main Methods:

• A digital micromirror device (DMD)-based holotomography (HT) system with RGB LED illumination was used for sequential acquisition of RI tomograms and BF images.
• The RICP algorithm adaptively embeds RI-derived structural information into BF images, preserving the original appearance.
• Papanicolaou (PAP)-stained thyroid samples were analyzed using the RICP framework.

Main Results:

• RICP effectively highlighted subcellular features like nucleoli, lipid droplets, and nuclear irregularities in both benign and malignant thyroid clusters.
• Hue-saturation analysis revealed distinct differences between benign and malignant cell clusters.
• Image-fusion metrics and delentropy analysis confirmed systematic changes in structural image content post-fusion, indicating enhanced information.

Conclusions:

• RICP offers a perceptually grounded approach for correlative multimodal visualization in cytology.
• This framework bridges conventional color cytology with quantitative optical imaging, improving diagnostic capabilities.
• The study demonstrates RICP's potential to overcome limitations of traditional BF cytology for thyroid FNAB analysis.