high-speed-continuous-wave-stimulated-brillouin-scattering

High-speed Continuous-wave Stimulated Brillouin Scattering Spectrometer for Material Analysis

Recent years have witnessed a significant increase in the use of spontaneous Brillouin spectrometers for non-contact analysis of soft matter, such as ...

Ben-Gurion University of the Negev

Photoplethysmography is a well-established technique for the noninvasive measurement of blood pulsation. However, photoplethysmographic devices typically need to be in contact with the surface of the tissue and provide data from a single contact point. Extensions of conventional photoplethysmography to measurements over a wide field-of-view exist, but require advanced signal processing due to the low signal-to-noise-ratio of the photoplethysmograms. Here, we present a noncontact method based on temporal sampling of time-integrated speckle using a camera-phone for noninvasive, widefield measurements of physiological parameters across the human fingertip including blood pulsation and resting heart-rate frequency. The results show that precise estimation of these parameters with high spatial resolution is enabled by measuring the local temporal variation of speckle patterns of backscattered light from subcutaneous skin, thereby opening up the possibility for accurate high resolution blood pulsation imaging on a camera-phone. Camera-phone laser speckle imager along with measured relative blood perfusion maps of a fingertip showing skin perfusion response to a pulse pressure applied to the upper arm. The figure is for illustration only; the imager was stabilized on a stand throughout the experiments.

Laser speckle spatiotemporal variance analysis for noninvasive widefield measurements of blood pulsation and pulse rate on a camera-phone.

Laser speckle contrast analysis (LASCA) is an established optical technique for accurate widefield visualization of relative blood perfusion when no or minimal scattering from static tissue elements is present, as demonstrated, for example, in LASCA imaging of the exposed cortex. However, when LASCA is applied to diagnosis of burn wounds, light is backscattered from both moving blood and static burn scatterers, and thus the spatial speckle contrast includes both perfusion and nonperfusion components and cannot be straightforwardly associated to blood flow. We extract from speckle contrast images of burn wounds the nonperfusion (static) component and discover that it conveys useful information on the ratio of static-to-dynamic scattering composition of the wound, enabling identification of burns of different depth in a porcine model in vivo within the first 48 h postburn. Our findings suggest that relative changes in the static-to-dynamic scattering composition of burns can dominate relative changes in blood flow for burns of different severity. Unlike conventional LASCA systems that employ scientific or industrial-grade cameras, our LASCA system is realized here using a camera phone, showing the potential to enable LASCA-based burn diagnosis with a simple imager.

Static laser speckle contrast analysis for noninvasive burn diagnosis using a camera-phone imager.

We demonstrate the effectiveness of stimulated Brillouin scattering for background-free Brillouin spectroscopy in scattering media within the biological spectral window. Using two nearly counter-propagating continuous-wave diode laser beams at 780 nm, we acquired transmission stimulated Brillouin point spectra in 10 mm and 500 μm thick Intralipid tissue phantoms with ∼100  μm and ∼16  μm diameter focal points, respectively. Stimulated gain spectra with high signal-to-noise ratio (8.7-30.7 dB) and frequency accuracy (6-72 MHz) were obtained at 20  MHz/10  ms and 20  MHz/100  ms through 0.24-3.36 mean-free paths of tissue phantoms. Our results suggest that stimulated Brillouin gain can be useful for imaging of Brillouin resonances in submillimeter-thick scattering samples.

Article	Year
Laser speckle spatiotemporal variance analysis for noninvasive widefield measurements of blood pulsation and pulse rate on a camera-phone. Journal of biophotonics\| PubMed ID: 25908015	2015
Static laser speckle contrast analysis for noninvasive burn diagnosis using a camera-phone imager. Journal of biomedical optics\| PubMed ID: 26271055	2015
Background-free Brillouin spectroscopy in scattering media at 780 nm via stimulated Brillouin scattering. Optics letters\| PubMed ID: 26974082	2016

Itay Remer

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