Quantitative spatial mapping of tissue water and lipid content using spatial frequency domain imaging in the 900- to 1000-nm wavelength region

. Significance Light emitting diodes (LEDs) are commonly utilized for tissue spectroscopy due to their small size, low cost, and simplicity. However, LEDs are often approximated as single-wavelength devices despite having relatively broad spectral bandwidths. When paired with photodiodes, the wavelength information of detected light cannot be resolved. This can result in errors during chromophore concentration calculations. These errors are particularly apparent when analyzing water and fat in the 900 to 1000 nm window where the spectral bandwidth of LEDs can encompass much of the analysis region, resulting in intense crosstalk. Aim We utilize and present a spectral correction (SC) algorithm to correct for the spectral bandwidth of LEDs. We show the efficacy using a narrowband technique of spectrally broad and overlapping LEDs. Approach Narrowband diffuse reflectance spectroscopy (nb-DRS), a technique capable of quantifying the hydration ratio ( ) of turbid media, was utilized. nb-DRS typically requires a broadband light source and spectrometer. We reduce the hardware to just five LEDs and a photodiode detector, relying on SC to compensate for spectral crosstalk. The effectiveness of our SC approach was tested in simulations as well as in an emulsion phantom and limited selection of human tissue. Results In simulations, we show that calculated errors increased with the spectral bandwidth of LEDs but could be corrected using SC. Likewise, in emulsions, we found an average error of 8.7% (maximum error 14%) if SC was not used. By contrast, applying SC reduced the average error to 2.2% (maximum error of 6.4%). We show that despite utilizing multiple, spectrally broad, and overlapping LEDs, SC was still able to restore the performance of our narrowband method, making it comparable to a much larger full broadband system.

Section: Introductionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Spectral correction of light emitting diodes enables accurate hydration ratio calculation using narrowband diffuse reflectance spectroscopy

Lam

Kim

et al. 2023

“… 10 , 11 Near infrared (NIR) spectroscopy and imaging allow water content assessment in deeper layers (dermis and hypodermis). 3 , 12 , 13 For instance, in heart failure patients, peripheral edema was analyzed with short-wave NIR imaging. 2 Cutaneous edema induced by histamine application was studied with diffuse reflectance spectroscopy (DRS), 9 , 14 Raman fiber probe, 9 and multispectral NIR imaging.…”

Section: Introductionmentioning

confidence: 99%

“…Confocal Raman and THz spectroscopy are mainly applied for studying the skin’s upper (epidermis) layer 10 , 11 . Near infrared (NIR) spectroscopy and imaging allow water content assessment in deeper layers (dermis and hypodermis) 3 , 12 , 13 . For instance, in heart failure patients, peripheral edema was analyzed with short-wave NIR imaging 2 .…”

Section: Introductionmentioning

confidence: 99%

Monitoring the skin structure during edema in vivo with spatially resolved diffuse reflectance spectroscopy

Davydov,

Budylin,

Baev

et al. 2023

. Significance Edema occurs in the course of various skin diseases. It manifests itself in changes in water concentrations in skin layers: dermis and hypodermis and their thicknesses. In medicine and cosmetology, objective tools are required to assess the skin’s physiological parameters. The dynamics of edema and the skin of healthy volunteers were studied using spatially resolved diffuse reflectance spectroscopy (DRS) in conjunction with ultrasound (US). Aim In this work, we have developed a method based on DRS with a spatial resolution (SR DRS), allowing us to simultaneously assess water content in the dermis, dermal thickness, and hypodermal thickness. Approach An experimental investigation of histamine included edema using SR DRS under the control of US was conducted. An approach for skin parameter determination was studied and confirmed using Monte-Carlo simulation of diffuse reflectance spectra for a three-layered system with the varying dermis and hypodermis parameters. Results It was shown that an interfiber distance of 1 mm yields a minimal relative error of water content determination in the dermis equal to 9.3%. The lowest error of hypodermal thickness estimation was achieved with the interfiber distance of 10 mm. Dermal thickness for a group of volunteers (7 participants, 21 measurement sites) was determined using SR DRS technique with an 8.3% error using machine learning approaches, taking measurements at multiple interfiber distances into account. Hypodermis thickness was determined with root mean squared error of 0.56 mm for the same group. Conclusions This study demonstrates that measurement of the skin diffuse reflectance response at multiple distances makes it possible to determine the main parameters of the skin and will serve as the basis for the development and verification of an approach that works in a wide range of skin structure parameters.

“…While often utilized to quantify hemoglobin, NIR technologies have also been used to measure water and lipid in vivo , ex vivo , and in vitro , typically using wavelengths in the 900 to 1000 nm range. 1 – 7 The accurate quantification of tissue water and lipid is of interest, as this capability could enable a wide range of clinical, point-of-care, and consumer applications including volume status monitoring for end-stage kidney disease and heart failure patients, tissue hydration monitoring for athletes, body composition assessment during weight loss, cancer treatment monitoring, and others. 8 With respect to clinical applications, kidney disease patients undergoing dialysis treatment experience fluid accumulation and require fluid removal, making frequent water volume assessment a desirable capability.…”

Section: Introductionmentioning

confidence: 99%

Shortwave infrared diffuse optical wearable probe for quantification of water and lipid content in emulsion phantoms using deep learning

Spink,

Pilvar,

Wei

et al. 2023

The shortwave infrared (SWIR, ∼900 to 2000 nm) holds promise for label-free measurements of water and lipid content in thick tissue, owed to the chromophore-specific absorption features and low scattering in this range. In vivo water and lipid estimations have potential applications including the monitoring of hydration, volume status, edema, body composition, weight loss, and cancer. To the best of our knowledge, there are currently no point-of-care or wearable devices available that exploit the SWIR wavelength range, limiting clinical and at-home translation of this technology.Aim: To design and fabricate a diffuse optical wearable SWIR probe for water and lipid quantification in tissue.Approach: Simulations were first performed to confirm the theoretical advantage of SWIR wavelengths over near infrared (NIR). The probe was then fabricated, consisting of light emitting diodes at three wavelengths (980, 1200, 1300 nm) and four source-detector (S-D) separations (7, 10, 13, 16 mm). In vitro validation was then performed on emulsion phantoms containing varying concentrations of water, lipid, and deuterium oxide (D 2 O). A deep neural network was developed as the inverse model for quantity estimation.Results: Simulations indicated that SWIR wavelengths could reduce theoretical water and lipid extraction errors from ∼6% to ∼1% when compared to NIR wavelengths. The SWIR probe had good signal-to-noise ratio (>32 dB up to 10 mm S-D) and low drift (<1.1% up to 10 mm S-D). Quantification error in emulsion phantoms was 2.1 AE 1.1% for water and −1.2 AE 1.5% for lipid. Water estimation during a D 2 O dilution experiment had an error of 3.1 AE 3.7%.Conclusions: This diffuse optical SWIR probe was able to quantify water and lipid contents in vitro with good accuracy, opening the door to human investigations.