Penetration depth of photons in biological tissues from hyperspectral imaging in shortwave infrared in transmission and reflection geometries

Abstract

Measurement of photon penetration in biological tissues is a central theme in optical imaging. A great number of endogenous tissue factors such as absorption, scattering, and anisotropy affect the path of photons in tissue, making it difficult to predict the penetration depth at different wavelengths. Traditional studies evaluating photon penetration at different wavelengths are focused on tissue spectroscopy that does not take into account the heterogeneity within the sample. This is especially critical in shortwave infrared where the individual vibration-based absorption properties of the tissue molecules are affected by nearby tissue components. We have explored the depth penetration in biological tissues from 900 to 1650 nm using Monte–Carlo simulation and a hyperspectral imaging system with Michelson spatial contrast as a metric of light penetration. Chromatic aberration-free hyperspectral images in transmission and reflection geometries were collected with a spectral resolution of 5.27 nm and a total acquisition time of 3 min. Relatively short recording time minimized artifacts from sample drying. Results from both transmission and reflection geometries consistently revealed that the highest spatial contrast in the wavelength range for deep tissue lies within 1300 to 1375 nm; however, in heavily pigmented tissue such as the liver, the range 1550 to 1600 nm is also prominent.

Impact of Lanthanide Nanomaterials on Photonic Devices and Smart Applications

“…Penetration depth relates to how deep light or any electromagnetic radiation can penetrate into a material. It is defined as the depth at which the intensity of the radiation inside the material falls to a fraction 1/e (about 37%) of its original value at (or more properly, just beneath) the surface . The remaining 37% of the light will continue to be absorbed in a manner that is less fully understood.…”

Shortwave infrared fluorescence imaging with the clinically approved near-infrared dye indocyanine green

“…Low levels of background tissue autofluorescence in the SWIR increase imaging sensitivity to a target fluorophore, and the unique tissue absorption and scattering properties increase contrast of structures at greater penetration depths compared with fluorescence imaging in the NIR (13,(16)(17)(18)(19)(20)(21). However, the adoption of SWIR fluorescence imaging into clinical settings has been prevented by the limited availability of SWIR detection technology and the perceived need for FDA-approved fluorophores with peak emission in the SWIR spectral region.…”

Optical fluorescence imaging with shortwave infrared light emitter nanomaterials for in vivo cell tracking in regenerative medicine

“…Their results demonstrated that biological imaging in the SWIR region by wavelengths of 1300 to 1375 nm offers the optimal depth of photon penetration and consequently greater transparency of turbid biological media. In spite of these measurements, they were not able to determine the contrast in longer wavelengths beyond 1650 nm due to the lack of highly sensitive camera . In another study by Sordillo et al, total attenuation length of different tissues in the SWIR windows showed higher lengths of tissue transmittance of SWIR light in the sample, in comparison with NIR I light.…”

“…The use of visible region of electromagnetic spectrum in the range of 400‐650 nm is suitable to get image from accessible or superficial tissues such as colon and skin, but not for structures locating in the deeper parts of the body such as nucleus or stem of the brain due to the scattering and absorption by tissue components …”

“…Deeper penetration of photon is necessary for appropriate spatial and temporal resolution at the cellular level that is an essential prerequisite for more advances in the cell‐based therapies. Further advances in optical imaging using the SWIR region of spectra rely on development of powerful laser sources, sensitive camera and suitable SWIR emitter fluorophores . Until 2014, development of in vivo optical imaging in SWIR region had been prevented mainly due to the lack of high sensitive, low‐cost, high quantum yield detectors (cameras) and SWIR emitter fluorophores together with advanced laser source.…”