Abstract
.Frequency-domain photon migration (FDPM) uses modulated laser light to measure the bulk optical properties of turbid media and is increasingly applied for noninvasive functional medical imaging in the near-infrared. Although semiconductor edge-emitting laser diodes have been traditionally used as miniature light sources for this application, we show that vertical-cavity surface-emitting lasers (VCSELs) exhibit output power and modulation performance characteristics suitable for FDPM measurements of tissue optical properties at modulation frequencies exceeding 1 GHz. We also show that an array of multiple VCSEL devices can be coherently modulated at frequencies suitable for FDPM and can improve optical power. In addition, their small size and simple packaging make them an attractive choice as components in wearable sensors and clinical FDPM-based optical spectroscopy systems. We demonstrate the benefits of VCSEL technology by fabricating and testing a unique, compact VCSEL-based optical probe with an integrated avalanche photodiode. We demonstrate sensitivity of the VCSEL-based probe to subcutaneous tissue hemodynamics that was induced during an arterial cuff occlusion of the upper arm in a human subject.
Highlights
The frequency-domain photon migration (FDPM) technique, sometimes referred to as frequency-domain near-infrared spectroscopy, is used to measure the optical near-infrared (NIR) absorption and scattering properties of turbid media and is under investigation for noninvasive medical imaging.[1,2] On living tissue, FDPM can provide quantitative functional biophysical information such as the deep tissue (1 to 2 cm) concentrations of chromophores and the size and density of cellular and subcellular components
vertical-cavity surface-emitting lasers (VCSELs) are semiconductor laser light sources that are widely used for applications in telecommunications and sensing
Since laser light in VCSELs is emitted normal to the semiconductor wafer, they can be tested on the wafer without additional die cleaving or dicing
Summary
The frequency-domain photon migration (FDPM) technique, sometimes referred to as frequency-domain near-infrared spectroscopy, is used to measure the optical near-infrared (NIR) absorption and scattering properties of turbid media and is under investigation for noninvasive medical imaging.[1,2] On living tissue, FDPM can provide quantitative functional biophysical information such as the deep tissue (1 to 2 cm) concentrations of chromophores (e.g., hemoglobin, water, and lipid) and the size and density of cellular and subcellular components. Intended for telecommunications applications, VCSELs are intensity-modulated at the frequencies relevant for optical property recovery. Their small size, simple packaging, and low power consumption make them attractive for use in wearable devices and could enable new applications of quantitative diffuse optical spectroscopy. For the first time, to our knowledge, frequency-domain diffuse optical spectroscopy measurements of a human subject using a direct-contact VCSEL-based integrated optical probe
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