Medical imaging is advancing rapidly through the development of novel laser sources and non-linear imaging methodologies. These developments are boosting deep tissue imaging allowing researchers to study diseases deep in the body enabling early diagnosis and better treatment. To help with the testing and optimization of these imaging systems and to aid in this process of deep tissue imaging, it's important to have robust, stable and reproducible standards and phantoms. Herein we present the design and fabrication of robust, multi-layered, hydrogel-based standards. The hydrogel used is a double network hydrogel consisting of two interpenetrating networks agarose and polyacrylamide. Thin layers of tough double network hydrogels are stacked to form multilayered depth standards having modality specific signaling markers embedded in between. Standard design and assembly ensured long term stability and easy transport. These proved useful in-depth imaging studies, utilizing multiple imaging modalities, including one photon fluorescence (1PEF), two photon fluorescence (2PEF), coherent anti-Stokes Raman imaging (CARS) and second harmonic generation imaging (SHG).
SignificanceSkin color affects light penetration leading to differences in its absorption and scattering properties. COVID-19 highlighted the importance of understanding of the interaction of light with different skin types, e.g., pulse oximetry (PO) unreliably determined oxygen saturation levels in people from Black and ethnic minority backgrounds. Furthermore, with increased use of other medical wearables using light to provide disease information and photodynamic therapies to treat skin cancers, a thorough understanding of the effect skin color has on light is important for reducing healthcare disparities.AimThe aim of this work is to perform a thorough review on the effect of skin color on optical properties and the implication of variation on optical medical technologies.ApproachPublished in vivo optical coefficients associated with different skin colors were collated and their effects on optical penetration depth and transport mean free path (TMFP) assessed.ResultsVariation among reported values is significant. We show that absorption coefficients for dark skin are ∼6% to 74% greater than for light skin in the 400 to 1000 nm spectrum. Beyond 600 nm, the TMFP for light skin is greater than for dark skin. Maximum transmission for all skin types was beyond 940 nm in this spectrum. There are significant losses of light with increasing skin depth; in this spectrum, depending upon Fitzpatrick skin type (FST), on average 14% to 18% of light is lost by a depth of 0.1 mm compared with 90% to 97% of the remaining light being lost by a depth of 1.93 mm.ConclusionsCurrent published data suggest that at wavelengths beyond 940 nm light transmission is greatest for all FSTs. Data beyond 1000 nm are minimal and further study is required. It is possible that the amount of light transmitted through skin for all skin colors will converge with increasing wavelength enabling optical medical technologies to become independent of skin color.
SignificanceRapid advances in medical imaging technology, particularly the development of optical systems with non-linear imaging modalities, are boosting deep tissue imaging. The development of reliable standards and phantoms is critical for validation and optimization of these cutting-edge imaging techniques.AimWe aim to design and fabricate flexible, multi-layered hydrogel-based optical standards and evaluate advanced optical imaging techniques at depth.ApproachStandards were made using a robust double-network hydrogel matrix consisting of agarose and polyacrylamide. The materials generated ranged from single layers to more complex constructs consisting of up to seven layers, with modality-specific markers embedded between the layers.ResultsThese standards proved useful in the determination of the axial scaling factor for light microscopy and allowed for depth evaluation for different imaging modalities (conventional one-photon excitation fluorescence imaging, two-photon excitation fluorescence imaging, second harmonic generation imaging, and coherent anti-Stokes Raman scattering) achieving actual depths of 1550, 1550, 1240, and 1240 μm, respectively. Once fabricated, the phantoms were found to be stable for many months.ConclusionsThe ability to image at depth, the phantom’s robustness and flexible layered structure, and the ready incorporation of “optical markers” make these ideal depth standards for the validation of a variety of imaging modalities.
This paper presents a widefield label-free plasmonic method for imaging electrical activity of pancreatic beta cells. MIN6 insulinoma cells were grown on gold surfaces modified with poly-L-lysine to promote adhesion. The results presented show synchronised electrical signals upon extracellular exposure to 10mM glucose solution. Spatiotemporal patterns of electrical activity are recorded with a sampling frequency of 100Hz and the microscopic technique offers a signal-to-noise ratio that enables measurements from an area as small as 1µm2.
KEYWORDS: Tissues, Tissue optics, Stereoscopy, Scattering, Phonons, Organisms, Optical fibers, New and emerging technologies, Light scattering, In vivo imaging
In order to realise the clinical potential of Brillouin scattering-based techniques, it is critical to develop an endoscopic probe for measuring elasticity in future in-vivo environments. We have developed a phonon probe which actively injects high amplitude GHz strain pulses into specimens and have demonstrated proof of concept this technique can be used for high resolution 3D imaging. In this talk we show that this new technology is highly applicable to the 3D elasticity imaging of biological tissue from the single-cell scale to multi-cellular organisms and provides a future pathway for the clinical application of in-vivo Brillouin spectroscopy of tissue.
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