Here we explore the use of Photoacoustic Remote Sensing (PARS™) microscopy, a recently developed non-contact photoacoustic imaging modality, for visualizing subcellular structures label-free in tissues. Operating in an all-optical reflection-mode architecture PARS captures optical absorption contrast within bulk tissue samples. Presented here, by visualizing endogenous optical absorption of DNA and cytochromes, cellular morphology is captured with contrast analogous to the industry standard hematoxylin and eosin (H&E) staining. Subcellular features are recovered from human and murine, brain and gastrointestinal tissues. This work represents a significant step towards the development of a real-time microscopy system for label-free histopathological assessment of tissues in-situ.
Histopathology remains the gold standard for assessing tissue microanatomy. Presently, specimens are examined with bright-field microscopes that require thin stained sections of tissue specimens. However, this requires extensive tissue processing and long turnaround times. Frozen sectioning is commonly used during surgery to assess margin status. However, this method can be unreliable as the slides can be difficult to interpret. Employing photoacoustic remote sensing (PARS), we emulate H and E micrographs by visualizing nuclear and cytoplasm contrast directly. These contrasts are visualized in a variety of human tissue samples and fresh thick unprocessed tissue specimens.
Nonmelanoma skin cancers (NSMC) are among the most common malignancies in the US today. Mohs micrograph surgery (MMS) is the gold standard for most NSMC. However, MMS is time-consuming as it employs frozen section analysis (FSA) for intraoperative assessment. Each FSA can require up to 60 minutes per excision. Using photoacoustic remote sensing (PARS™) we demonstrate first results of imaging tissue morphology on human skin with a non-contact reflection-mode method, enabling rapid label-free pathological assessment. These images are validated against toluidine blue stained sections. The authors believe the proposed method represents a vital step towards an in-situ assessment of NSMC.
To assess cancer resection margins, post-operative histological diagnosis using hematoxylin and eosin (H&E) stained slides remains the gold standard due to the lack of effective intra-operative approaches. Wait times may be up to two weeks and subsequent treatments may be necessary. Therefore, we are motivated to introduce Chromophore Selective Multi-Wavelength Photoacoustic Remote Sensing, an all-optical, non-contact, reflection-mode, label-free approach to produce H&E-like images of human tissue. This work is a step towards in-situ imaging, rapid clinical assessment of tissue, and may permit future developments as a live intraoperative surgical microscope.
Surgery remains the primary method of care for multiple types of solid cancer. The goal of surgical oncology is to remove all tumorous tissue from the body. Frozen sectioning is commonly used during surgery to assess margin status. However, this method can be unreliable as the slides can be difficult to interpret. Using a recently reported imaging modality, Photoacoustic Remote Sensing (PARS), we present the first in human non-contact histology-like imaging in reflection mode. Cellular morphology alongside blood vessels are imaged in the human breast, gastrointestinal, and skin tissues. These images then compared with conventional hematoxylin and eosin-stained samples.
A multi-wavelength imaging technique based on the principle of stimulated Raman scattering (SRS) can be applied to photoacoustic (PA) techniques to produce label-free image contrast in wavelength-dependent targets in biological tissue. Current studies had limited approaches to optimizing the pulse energy of generated peaks. A comprehensive study of various parameters that affect the pulse energy of generated SRS peaks from a 532nm pulsed laser is presented; including fiber polarization, cut-off wavelength, length of fiber, pulse width, pulse repetition rate, and input power. Optimal conditions for designing a multi-wavelength laser source to image wavelength-dependent biological tissues with possible biomedical diagnostics and experimental applications are presented.
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