Optical properties of pig skin epidermis and dermis estimated with double integrating spheres measurements

A preliminary study on the utilisation of near infrared spectroscopy to predict age and in vivo human metabolism

The objective of this study was to evaluate the ability of a portable near infrared (NIR) instrument to analyse different tissues in healthy individuals in vivo and relate the spectral data with age, resting metabolic rate (RMR), respiratory quotient (RQ), body fat (BF) and body mass index (BMI). A NIR (950-1600 nm) instrument was used to collect the spectra of different tissues and partial least squares (PLS) regression was used to relate the NIR with RMR, RQ, BF and BMI. Results shown that non-destructive techniques such as those based in vibrational spectroscopy have potential to be used as tools to better categorise and understand the complex inter-individual differences that determine interactions between physiology and nutrition.

Design and Analysis of a Continuous and Non-Invasive Multi-Wavelength Optical Sensor for Measurement of Dermal Water Content

Dermal water content is an important biophysical parameter in preserving skin integrity and preventing skin damage. Traditional electrical-based and open-chamber evaporimeters have several well-known limitations. In particular, such devices are costly, sizeable, and only provide arbitrary outputs. They also do not permit continuous and non-invasive monitoring of dermal water content, which can be beneficial for various consumer, clinical, and cosmetic purposes. We report here on the design and development of a digital multi-wavelength optical sensor that performs continuous and non-invasive measurement of dermal water content. In silico investigation on porcine skin was carried out using the Monte Carlo modeling strategy to evaluate the feasibility and characterize the sensor. Subsequently, an in vitro experiment was carried out to evaluate the performance of the sensor and benchmark its accuracy against a high-end, broad band spectrophotometer. Reference measurements were made against gravimetric analysis. The results demonstrate that the developed sensor can deliver accurate, continuous, and non-invasive measurement of skin hydration through measurement of dermal water content. Remarkably, the novel design of the sensor exceeded the performance of the high-end spectrophotometer due to the important denoising effects of temporal averaging. The authors believe, in addition to wellbeing and skin health monitoring, the designed sensor can particularly facilitate disease management in patients presenting diabetes mellitus, hypothyroidism, malnutrition, and atopic dermatitis.

Effect of CPPU on bulk optical properties of kiwifruit during storage in near-infrared range

BACKGROUND

Investigating the effect of N-(2-chloro-4-pyridyl)-N'-phenylurea (CPPU) on the bulk optical properties of postharvest kiwifruit is helpful in understanding the mechanism of identification of CPPU-treated kiwifruit using spectroscopy and to develop effective optical sensing techniques. In this study, the absorption coefficient μ_a and reduced scattering coefficient μ s ' of flesh and skin of kiwifruit treated with CPPU solutions at CPPU concentration levels (CCLs) of 0, 5, 10 and 15 mg L^-1 were measured by using a single integrating sphere setup over the range 950-1650 nm during 12 weeks' storage.

RESULTS

Generally, at the same storage period, there was no significant difference (P ≤ 0.05) on flesh's μ_a among the kiwifruit treated with different CCLs at absorption peaks of 970, 1190, and 1390 nm. The average flesh's μ s ' of kiwifruit treated with higher CCLs at 1190 nm were larger than those treated with lower CCLs, and there was a significant difference (P ≤ 0.05) between the kiwifruit treated with 0, 5 and 15 mg L^-1 CPPU solutions except for week 6. Contrasted with the μ_a and μ s ' of kiwifruit flesh, the μ_a and μ s ' of skin had bigger standard deviations and larger fluctuations with storage time. Additionally, the CPPU-treated kiwifruit had higher moisture content, lower firmness, and larger cells than CPPU-untreated kiwifruit.

CONCLUSIONS

This study indicates that the μ s ' of flesh has potential in identifying kiwifruit treated with different CCLs during storage. © 2020 Society of Chemical Industry.

Short-wave infrared light imaging measures tissue moisture and distinguishes superficial from deep burns

Existing clinical approaches and tools to measure burn tissue destruction are limited resulting in misdiagnosis of injury depth in over 40% of cases. Thus, our objective in this study was to characterize the ability of short-wave infrared (SWIR) imaging to detect moisture levels as a surrogate for tissue viability with resolution to differentiate between burns of various depths. To accomplish our aim, we constructed an imaging system consisting of a broad-band Tungsten light source; 1,200-, 1,650-, 1,940-, and 2,250-nm wavelength filters; and a specialized SWIR camera. We initially used agar slabs to provide a baseline spectrum for SWIR light imaging and demonstrated the differential absorbance at the multiple wavelengths, with 1,940 nm being the highest absorbed wavelength. These spectral bands were then demonstrated to detect levels of moisture in inorganic and in vivo mice models. The multiwavelength SWIR imaging approach was used to diagnose depth of burns using an in vivo porcine burn model. Healthy and injured skin regions were imaged 72 hours after short (20 seconds) and long (60 seconds) burn application, and biopsies were extracted from those regions for histologic analysis. Burn depth analysis based on collagen coagulation histology confirmed the formation of superficial and deep burns. SWIR multispectral reflectance imaging showed enhanced intensity levels in long burned regions, which correlated with histology and distinguished between superficial and deep burns. This SWIR imaging method represents a novel, real-time method to objectively distinguishing superficial from deep burns.

Topical and intradermal delivery of PpIX precursors for photodynamic therapy with intense pulsed light on porcine skin model

In order to purposely decrease the time of the photodynamic therapy (PDT) sessions, this study evaluated the effects of PDT using topical and intradermal delivery of two protoporphyrin (PpIX) precursors with intense pulsed light (IPL) as irradiation source. This study was performed on porcine skin model, using an IPL commercial device (Intense Pulse Light, HKS801). IPL effect on different administration methods of two PpIX precursors (ALA and MAL) was investigated: a topical cream application and an intradermal application using a needle-free, high-pressure injection system. Fluorescence investigation showed that PpIX distribution by needle-free injection was more homogeneous than that by cream, suggesting that a shorter drug-light interval in PDT protocols is possible. The damage induced by IPL-PDT assessed by histological analysis mostly shows modifications in collagens fibers and inflammation signals, both expected for PDT. This study suggested an alternative protocol for the PDT treatment, possibility half of the incubation time and with just 3 min of irradiation, making the IPL-PDT, even more, promising for the clinical treatment.

Design of a portable phantom device to simulate tissue oxygenation and blood perfusion

We propose a portable phantom system for calibration and validation of medical optical devices in a clinical setting. The phantom system comprises a perfusion module and an exchangeable tissue-simulating phantom that simulates tissue oxygenation and blood perfusion. The perfusion module consists of a peristaltic pump, two liquid storage units, and two pressure suppressors. The tissue-simulating phantom is fabricated by a three-dimensional (3D) printing process with microchannels embedded to simulate blood vessels. Optical scattering and absorption properties of biologic tissue are simulated by mixing graphite powder and titanium dioxide powder with clear photoreactive resin at specific ratios. Tissue oxygen saturation (StO₂) and blood perfusion are simulated by circulating the mixture of blood and intralipid at different oxygenation levels and flow rates. A house-made multimodal imaging system that combines multispectral imaging and laser speckle imaging are used for non-invasive detection of phantom oxygenation and perfusion, and the measurements are compared with those of a commercial Moor device as well as numerical simulation. By acquiring multimodal imaging data from one phantom and applying the calibration factors in different settings, we demonstrate the technical feasibility to calibrate optical devices for consistent measurements. By simulating retina tissue vasculature and acquiring functional images at different tissue oxygenation and blood perfusion levels, we demonstrate the clinical potential to simulate tissue anomalies. Our experiments imply the clinical potential of a portable, low-cost, and traceable phantom standard to calibrate and validate medical optical devices for improved performance.

The Use of Directional Reflectance Measurement for in vivo Assessment of Protective Properties of Cosmetics in the Infrared Radiation Range

Photoprotection of skin is now focused on UV radiation. The aim of this study was to evaluate in vivo cosmetic products in terms of protection against infrared radiation (IR) and propose a methodology for conducting such measurements. The directional reflectance (DR) of 12 UV filters, six care creams and two preparations containing fumed silica applied on the forearm of 36 volunteers was examined in six spectral bands for two angles of incidence. SOC-410 Directional Hemispherical Reflectometer was used to measure DR. There is very little change in DR for all spectral bands for both incident angles for both UV filters, care creams and preparations containing fumed silica. For example, for 15% of fumed silica in glycerin for the spectral band of 0.9-1.1 μm and the incident angle of 20°, skin DR prior to application was 0.543; 5 min after application was 0.533 and 30 min after application was 0.559. Both UV filters, care creams and fumed silica do not protect skin against IR. The proposed method of in vivo measurements is superior to in vitro studies which have been conducted so far because it takes into account both the refractive index at the tissue/air interface and the absorption of IR by adipose tissue.

Short wavelength infrared optical windows for evaluation of benign and malignant tissues

There are three short wavelength infrared (SWIR) optical windows outside the conventionally used first near-infrared (NIR) window (650 to 950 nm). They occur in the 1000- to 2500-nm range and may be considered second, third, and fourth NIR windows. The second (1100 to 1350 nm) and third windows (1600 to 1870 nm) are now being explored through label-free linear and multiphoton imaging. The fourth window (2100 to 2350 nm) has been mostly ignored because of water absorption and the absence of sensitive detectors and ultrafast lasers. With the advent of new technology, use of window IV is now possible. Absorption and scattering properties of light through breast and prostate cancer, bone, lipids, and intralipid solutions at these windows were investigated. We found that breast and prostate cancer and bone have longer total attenuation lengths at NIR windows III and IV, whereas fatty tissues and intralipid have longest lengths at windows II and III. Since collagen is the major chromophore at 2100 and 2350 nm, window IV could be especially valuable in evaluating cancers and boney tissues, whereas windows II and III may be more useful for tissues with high lipid content. SWIR windows may be utilized as additional optical tools for the evaluation of collagen in tissues.

Optical properties of porcine dermis in the mid-infrared absorption band of glucose

Mid-infrared absorption and scattering properties of porcine dermis are quantified using quantum cascade laser-based goniometry.

Near-infrared bulk optical properties of goat wound tissue and human serum: consequences for an implantable optical glucose sensor

Near-infrared (NIR) spectroscopy offers a promising technological platform for continuous glucose monitoring in the human body. Moreover, these measurements could be performed in vivo with an implantable single-chip based optical sensor. However, a thin tissue layer may grow in the optical path of the sensor. As most biological tissues are highly scattering, they only allow a small fraction of the collimated light to pass, significantly reducing the light throughput. To quantify the effect of a thin tissue layer in the optical path, the bulk optical properties of serum and tissue samples grown on implanted dummy sensors were characterized using double integrating sphere and unscattered transmittance measurements. The estimated bulk optical properties were then used to calculate the light attenuation through a thin tissue layer. The combination band of glucose was found to be the better option, relative to the first overtone band, as the absorptivity of glucose molecules is higher, while the reduction in unscattered transmittance due to tissue growth is less. Additionally, as the wound tissue was found to be highly scattering, the unscattered transmittance of the tissue layer is expected to be very low. Therefore, a sensor configuration which measures the diffuse transmittance and/or reflectance instead was recommended. (a) Dummy sensor; (b) explanted dummy sensor in tissue lump; (c) removal of dummy sensor from tissue lump; and (d) 900 µm slices of tissue lump.

Robust metamodel-based inverse estimation of bulk optical properties of turbid media from spatially resolved diffuse reflectance measurements

Estimation of the bulk optical properties of turbid samples from spatially resolved reflectance measurements remains challenging, as the relation between the bulk optical properties and the acquired spatially resolved reflectance profiles is influenced by wavelength-dependent properties of the measurement system. The resulting measurement noise is apparent in the estimation of the bulk optical properties. In this study, a constrained inverse metamodeling approach is proposed to overcome these problems. First, a metamodel has been trained on a set of intralipid phantoms covering a wide range of optical properties to link the acquired spatially resolved reflectance profiles to the respective combinations of bulk optical properties (absorption coefficient and reduced scattering coefficient). In this metamodel, the wavelength (500 - 1700 nm) is considered as a third input parameter for the model to account for the wavelength dependent effects introduced by the measurement system. Secondly, a smoothness constraint on the reduced scattering coefficient spectra was implemented in the iterative inverse estimation procedure to robustify it against measurement noise and increase the reliability of the obtained bulk absorption and reduced scattering coefficient spectra. As the estimated values in some regions may be more reliable than others, the difference between simulated and measured values as a function of the evaluated absorption and scattering coefficients was combined in a 2D cost function. This cost function was used as a weight in the fitting procedure to find the parameters of the µ(s)' function giving the lowest cost over all the wavelengths together. In accordance with previous research, an exponential function was considered to represent the µ(s)' spectra of intralipid phantoms. The fitting procedure also provides an absorption coefficient spectrum which is in accordance with the measurements and the estimated parameters of the exponential function. This robust inverse estimation algorithm was validated on an independent set of intralipid® phantoms and its performance was also compared to that of a classical single-wavelength inverse estimation algorithm. While its performance in estimating µ(a) was comparable (R2 of 0.844 vs. 0.862), it resulted in a large improvement in the estimation of µ(s)' (R2 of 0.987 vs. 0.681). The change in performance is more apparent in the improvement of RMSE of µ(s)', which decreases from 10.36 cm(-1) to 2.10 cm(-1). The SRS profiles change more sensitively as a function of µ(a). As a result, there is a large range of µ(s)' and a small range of µa resulting in a good fit between measurement and simulation. The robust inverse estimator incorporates information over the different wavelengths, to increase the accuracy of µ(s)'estimations and robustify the estimation process.

Review of short-wave infrared spectroscopy and imaging methods for biological tissue characterization

We present a review of short-wave infrared (SWIR, defined here as ∼1000 to 2000 nm) spectroscopy and imaging techniques for biological tissue optical property characterization. Studies indicate notable SWIR absorption features of tissue constituents including water (near 1150, 1450, and 1900 nm), lipids (near 1040, 1200, 1400, and 1700 nm), and collagen (near 1200 and 1500 nm) that are much more prominent than corresponding features observed in the visible and near-infrared (VIS-NIR, defined here as ∼400 to 1000 nm). Furthermore, the wavelength dependence of the scattering coefficient has been observed to follow a power-law decay from the VIS-NIR to the SWIR region. Thus, the magnitude of tissue scattering is lower at SWIR wavelengths than that observed at VIS or NIR wavelengths, potentially enabling increased penetration depth of incident light at SWIR wavelengths that are not highly absorbed by the aforementioned chromophores. These aspects of SWIR suggest that the tissue spectroscopy and imaging in this range of wavelengths have the potential to provide enhanced sensitivity (relative to VIS-NIR measurements) to chromophores such as water and lipids, thereby helping to characterize changes in the concentrations of these chromophores due to conditions such as atherosclerotic plaque, breast cancer, and burns.

Flexible tool for simulating the bulk optical properties of polydisperse spherical particles in an absorbing host: experimental validation

In this study, a flexible tool to simulate the bulk optical properties of polydisperse spherical particles in an absorbing host medium is described. The generalized Mie solution for Maxwell's equations is consulted to simulate the optical properties for a spherical particle in an absorbing host, while polydispersity of the particle systems is supported by discretization of the provided particle size distributions. The number of intervals is optimized automatically in an efficient iterative procedure. The developed tool is validated by simulating the bulk optical properties for two aqueous nanoparticle systems and an oil-in-water emulsion in the visible and near-infrared wavelength range, taking into account the representative particle sizes and refractive indices. The simulated bulk optical properties matched closely (R2 ≥ 0.899) with those obtained by reference measurements.

Quantitative short-wave infrared multispectral imaging of in vivo tissue optical properties

Extending the wavelength range of spatial frequency domain imaging (SFDI) into the short-wave infrared (SWIR) has the potential to provide enhanced sensitivity to chromophores such as water and lipids that have prominent absorption features in the SWIR region. Here, we present, for the first time, a method combining SFDI with unstructured (zero spatial frequency) illumination to extract tissue absorption and scattering properties over a wavelength range (850 to 1800 nm) largely unexplored by previous tissue optics techniques. To obtain images over this wavelength range, we employ a SWIR camera in conjunction with an SFDI system. We use SFDI to obtain in vivo tissue reduced scattering coefficients at the wavelengths from 850 to 1050 nm, and then use unstructured wide-field illumination and an extrapolated power-law fit to this scattering spectrum to extract the absorption spectrum from 850 to 1800 nm. Our proof-of-principle experiment in a rat burn model illustrates that the combination of multispectral SWIR imaging, SFDI, and unstructured illumination can characterize in vivo changes in skin optical properties over a greatly expanded wavelength range. In the rat burn experiment, these changes (relative to normal, unburned skin) included increased absorption and increased scattering amplitude and slope, consistent with changes that we previously reported in the near-infrared using SFDI.