Pump–Probe Microscopic Imaging of Jurassic-Aged Eumelanin

Deb

Wilson

et al. 2015

Biomed. Opt. Express

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Metastatic melanoma is associated with a poor prognosis, but no method reliably predicts which melanomas of a given stage will ultimately metastasize and which will not. While sentinel lymph node biopsy (SLNB) has emerged as the most powerful predictor of metastatic disease, the majority of people dying from metastatic melanoma still have a negative SLNB. Here we analyze pump-probe microscopy images of thin biopsy slides of primary melanomas to assess their metastatic potential. Pumpprobe microscopy reveals detailed chemical information of melanin with subcellular spatial resolution. Quantification of the molecular signatures without reference standards is achieved using a geometrical representation of principal component analysis. Melanin structure is analyzed in unison with the chemical information by applying principles of mathematical morphology. Results show that melanin in metastatic primary lesions has lower chemical diversity than non-metastatic primary lesions, and contains two distinct phenotypes that are indicative of aggressive disease. Further, the mathematical morphology analysis reveals melanin in metastatic primary lesions has a distinct "dusty" quality. Finally, a statistical analysis shows that the combination of the chemical information with spatial structures predicts metastatic potential with much better sensitivity than SLNB and high specificity, suggesting pump-probe microscopy can be an important tool to help predict the metastatic potential of melanomas.

Section: Introductionmentioning

confidence: 99%

Pump-probe imaging of pigmented cutaneous melanoma primary lesions gives insight into metastatic potential

Deb

Wilson

et al. 2015

Biomed. Opt. Express

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“…Figures 1 and 2(a) shows a schematic representation of various pump-probe signals. Our work to date71415 has lead to a hypothetical physical model for the resulting dynamics in melanin that treats the interactions as a spectral hole burning phenomenon in competition with excited state absorption. This model builds upon the idea that the broad absorption profile of melanin comes from a sum of an ensemble of underlying chromophores with overlapping absorption bands16.…”

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confidence: 99%

Dual-wavelength pump-probe microscopy analysis of melanin composition

Thompson

Wilson

et al. 2016

Sci Rep

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Pump-probe microscopy is an emerging technique that provides detailed chemical information of absorbers with sub-micrometer spatial resolution. Recent work has shown that the pump-probe signals from melanin in human skin cancers correlate well with clinical concern, but it has been difficult to infer the molecular origins of these differences. Here we develop a mathematical framework to describe the pump-probe dynamics of melanin in human pigmented tissue samples, which treats the ensemble of individual chromophores that make up melanin as Gaussian absorbers with bandwidth related via Frenkel excitons. Thus, observed signals result from an interplay between the spectral bandwidths of the individual underlying chromophores and spectral proximity of the pump and probe wavelengths. The model is tested using a dual-wavelength pump-probe approach and a novel signal processing method based on gnomonic projections. Results show signals can be described by a single linear transition path with different rates of progress for different individual pump-probe wavelength pairs. Moreover, the combined dual-wavelength data shows a nonlinear transition that supports our mathematical framework and the excitonic model to describe the optical properties of melanin. The novel gnomonic projection analysis can also be an attractive generic tool for analyzing mixing paths in biomolecular and analytical chemistry.

“…An interesting and important feature of melanin is its high stability-for example, eulemanin from 160 million year old fossils produces the same pump-probe decay as modern eumelanin [3]. This means that retrospective studies of decades-old patient samples, where diagnosis can be correlated with patient outcome, as possible with fixed tissue samples, whereas most genetic or immunohistochemical markers would be degraded and unusable.…”

mentioning

confidence: 99%

Enhancing Pigmented or Transparent Tissue Imaging with Laser Pulse Shaping

Warren

Fischer

Frontiers in Optics 2015

et al. 2015

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Enhanced control over femtosecond lasers (pulse shaping or pulse train modulation) improves contrast in tissue imaging. Pump-probe applications to melanoma diagnosis and cross phase modulation measurement in transparent tissues will be presented.Molecular imaging-the use of chemical signatures to image function instead of merely structure-promises to enable a new generation of clinical modalities that can revolutionize both diagnosis and treatment. In optics, our lab developed femtosecond pulse shaping two decades ago; today we know that the "killer application" is to access intrinsic nonlinear signatures that were not previously observable in tissue, such as excited state absorption, ground state depletion, and cross phase modulation. [1]. These methods permit high resolution imaging in scattering media, without any requirement that the imaging target generate fluorescence or other conventional light signatures.Our principal focus has been to improve biological imaging [2]; for example, we have uniquely identified a variety of biological targets and differentiated between eumelanin and pheomelanin in pigmented skin lesions to improve melanoma diagnosis. An interesting and important feature of melanin is its high stability-for example, eulemanin from 160 million year old fossils produces the same pump-probe decay as modern eumelanin [3]. This means that retrospective studies of decades-old patient samples, where diagnosis can be correlated with patient outcome, as possible with fixed tissue samples, whereas most genetic or immunohistochemical markers would be degraded and unusable. Here we use this approach by correlating eumelanin imaging with sentinel node biopsy to evaluate tumor aggressiveness, which could revolutionize melanoma diagnosis by improving the pathology "gold standard." We show that the approach could alsoimprove diagnosis both of ocular and vulvar melanoma, where simple incision (the "when in doubt, cut it out" approach) is less attractive in questionable cases.We have also shown that cross phase modulation, the nonlinear equivalent of phase contrast imaging, extends detection of transparent species even in scattering tissue [4,5]. The sources of contrast is typically the optical Kerr effect, which can differ by orders of magnitude in different transparent materials, and this contrast correlates with structural features. Traditionally, such effects are measured by their associated beam lensing, using methods such as the Z-scan, but this is not possible in the presence of any significant scattering. In contrast, femtosecond pulse shaping approaches permit robust measurement in an imaging geometry.