Exploring the effect of laser excitation wavelength on signal recovery with deep tissue transmission Raman spectroscopy

Abstract

The aim of this research was to find the optimal Raman excitation wavelength to attain the largest possible sensitivity in deep Raman spectroscopy of breast tissue. This involved careful consideration of factors such as tissue absorption, scattering, fluorescence and instrument response function. The study examined the tissue absorption profile combined with Raman scattering and detection sensitivity at seven different, laser excitation wavelengths in the near infrared region of the spectrum. Several key scenarios in regards to the sample position within the tissue were examined. The highest Raman band visibility over the background ratio in respect to biological tissue provides the necessary information for determining the optimum laser excitation wavelength for deep tissue analysis using transmission Raman spectroscopy, including detection of breast calcifications. For thick tissues with a mix of protein and fat, such as breast tissue, 790-810 nm is concluded to be the optimum excitation wavelength for deep Raman measurements.

High sensitivity non‐invasive detection of calcifications deep inside biological tissue using Transmission Raman Spectroscopy

“…In the first stage of development a range of experiments have been performed at multiple laser wavelengths to measure the deep Raman signal to noise ratio in tissue and to assess the best choice of excitation wavelength. The experimental findings identified the spectral domain between 790 nm and 810 nm as the best choice for Raman excitation wavelength [43]. As a consequence the new TRS prototype presented here was equipped with the laser excitation wavelength of 808 nm.…”

“…During the development stages, in our previous work, we have taken a systematic approach to finding the optimum set of parameters that will improve the detection sensitivity of HAP and CO inside biological tissue [43]. In the first stage of development a range of experiments have been performed at multiple laser wavelengths to measure the deep Raman signal to noise ratio in tissue and to assess the best choice of excitation wavelength.…”

Adaptive band target entropy minimization: Optimization for the decomposition of spatially offset Raman spectra of bone

“…As the photons of Raman scattered light, which originate from inside the bone volume need to pass through the overlaying soft tissue to reach the detector, photons of different energy are absorbed to different extents. A recent work by Stone and co‐workers has explored the effects of laser excitation wavelength on signal recovery as related to transmission Raman spectroscopy focussing particularly on the effects of tissue absorption . It is clear from the work of Stone et al that the absorption coefficient of soft tissue dramatically increases at the amide I band position at our excitation wavelength.…”

Development of deep subsurface Raman spectroscopy for medical diagnosis and disease monitoring

“…The technique can be considered a special case of SORS, where the laser beam and the Raman collection zone are separated to the extreme, being on the opposite sides of sample (see Fig. 16 The study included tissue absorption and fluorescence effects. Unlike SORS it is not able to provide the signatures of individual layers within the sample, instead it provides volumetric information on the entire volume of the sample.…”