Grad Seminar: Label-free optical microscopy: Photon Absorption Remote Sensing (PARS) for histopathological imaging of tissues
Presenter
Ben Ecclestone, PhD candidate in Systems Design Engineering
Abstract
Emerging label-free microscopy methods offer promising new avenues to view cells and tissues in their native environment while minimizing external influences. This is an exciting departure from gold standard chemical staining methods for visualizing microscopic cellular and tissue structures. Chemical labelling can unavoidably interfere with specimens’ physical and biochemical integrity. As a result, samples are effectively consumed by staining with only a single stain set normally applied to each sample. This limitation is impactful in applications such as clinical oncology and medical histopathology.
This seminar explores new methods for label-free histopathology. The goal of this research is to develop a label-free analog to chemical hematoxylin and eosin (H&E) staining, which is the gold standard contrast used in clinical diagnostics. Developments cover three main accomplishments: (1) developing label-free microscopy methods for H&E-like imaging, (2) exploring the biomolecular specificity of developed methods to validate the label-free H&E-like contrast, and (3) producing a label-free microscopy architecture capable of meeting the imaging requirements necessary for clinical adoption.
Presented research resulted in the development of a new optical absorption microscopy modality, Photon Absorption Remote Sensing (PARS). This comprehensive technique provides biomolecule-specific visualizations characterizing the dominant photophysical effects caused when photons are absorbed by a biomolecule, which may offer unique views into biomolecules’ excited state dynamics. By specifically probing specimens’ response to the absorption of deep ultraviolet light, PARS was shown to provide label-free contrast directly reminiscent of gold standard chemical H&E staining methods. In combination with deep learning-based image-to-image transforms, PARS was shown to produce emulated H&E images indistinguishable from chemically stained representations. This PARS-based H&E-like contrast was validated through established statistical methods. In addition, PARS emulated H&E-like visualizations were validated against chemical H&E staining through a clinical concordance study. Finally, a novel PARS architecture is presented which achieved pragmatic imaging performance nearing the requirements for clinical diagnostic settings. This microscope features a hybrid opto-mechanical scanning architecture which allows for high-speed MHz rate imaging (more than an order of magnitude faster than earlier PARS embodiments).
In total, the findings presented across this thesis encompass the development of a new variation of microscopy technique (PARS). This method provides unique views into the absorption and scattering characteristics of specimens opening a new avenue of label-free contrast. For the presented histopathology application, PARS can provide powerful H&E-like images which may circumvent key challenges of chemical staining. In clinical histopathology, this method could enhance the diagnostic utility of tissue specimens directly improving patient outcomes. Beyond histopathology, the principles of PARS may be directly applicable to a wide range of imaging applications spanning material science, biological research, and clinical diagnostics.