Evaluation of light scattering and absorption properties of in vivo rat liver using a single-reflectance fiber probe during preischemia, ischemia-reperfusion, and postmortem

Characterization of the Optical and Thermal Properties of Cardiac Tissue as a Function of Temperature

In this work, we devised the first characterization of the optical and thermal properties of ex vivo cardiac tissue as a function of different selected temperatures, ranging from room temperature to hyperthermic and ablative temperatures. The broadband (i.e., from 650 nm to 1100 nm) estimation of the optical properties, i.e., absorption coefficient (μa) and reduced scattering coefficient $({\mu ^{\prime}}_s)$, was performed by means of time-domain diffuse optics. Besides, the measurement of the thermal properties was based on the transient hot-wire technique, employing a dual-needle probe to estimate the tissue thermal conductivity (k), thermal diffusivity (α), and volumetric heat capacity (Cv). Increasing the tissue temperature led to variations in the spectral characteristics of μa (e.g., the redshift of the 780 nm peak, the rise of a new peak at 840 nm, and the formation of a valley at 900 nm). Moreover, an increase in the values of ${\mu ^{\prime}}_s$ was assessed as tissue temperature raised (e.g., for 800 nm, at 25 °C ${\mu ^{\prime}}_s = 9.8{\text{ c}}{{\text{m}}^{{\text{ - 1}}}}$, while at 77 °C ${\mu ^{\prime}}_s = 29.1{\text{ c}}{{\text{m}}^{{\text{ - 1}}}}$). Concerning the thermal properties characterization, k was almost constant in the selected temperature interval. Conversely, α and Cv were subjected to an increase and a decrease with temperature, respectively; thus, they registered values of 0.190 mm2/s and 3.03 MJ/(m3•K) at the maximum investigated temperature (79 °C), accordingly.Clinical Relevance- The experimentally obtained optical and thermal properties of cardiac tissue are useful to improve the accuracy of simulation-based tools for thermal therapy planning. Furthermore, the measured properties can serve as a reference for the realization of tissue-mimicking phantoms for medical training and testing of medical instruments.

Estimation of porcine pancreas optical properties in the 600-1100 nm wavelength range for light-based therapies

This work reports the optical properties of porcine pancreatic tissue in the broad wavelength range of 600–1100 nm. Absorption and reduced scattering coefficients (µ_a and µ_s′) of the ex vivo pancreas were obtained by means of Time-domain Diffuse Optical Spectroscopy. We have investigated different experimental conditions—including compression, repositioning, spatial sampling, temporal stability—the effect of the freezing procedure (fresh vs frozen-thawed pancreas), and finally inter-sample variability. Good repeatability under different experimental conditions was obtained (median coefficient of variation less than 8% and ~ 16% for µ_a and µ_s′, respectively). Freezing–thawing the samples caused an irreversible threefold reduction of µ_s′ and no effect on µ_a. The absorption and reduced scattering spectra averaged over different samples were in the range of 0.12–0.74 cm⁻¹ and 12–21 cm⁻¹ with an inter-sample variation of ~ 10% and ~ 40% for µ_a and µ_s′, respectively. The calculated effective transport coefficient (µ_eff) for fresh pancreatic tissue shows that regions between 800–900 nm and 1050–1100 nm are similar and offer the lowest tissue attenuation in the considered range (i.e., µ_eff ranging from 2.4 to 2.7 cm⁻¹). These data, describing specific light-pancreas interactions in the therapeutic optical window for the first time, provide pivotal information for planning of light-based thermotherapies (e.g., laser ablation) and instruction of light transport models for biophotonic applications involving this organ.

Non-alcoholic Fatty Liver Disease and Steatohepatitis: Risk Factors and Pathophysiology

Non-alcoholic fatty liver disease (NAFLD) and its progressive subtype non-alcoholic steatohepatitis (NASH) are the most prevalent liver diseases, often leading to hepatocellular carcinoma (HCC). This review aims to describe the present knowledge of the risk factors responsible for the development of NAFLD and NASH. I performed a literature review identifying studies focusing on the complex pathogenic pathway and risk factors of NAFLD and steatohepatitis. The relationship between NAFLD and metabolic syndrome is well established and widely recognized. Obesity, dyslipidemia, type 2 diabetes, hypertension, and insulin resistance are the most common risk factors associated with NAFLD. Among the components of metabolic syndrome, current evidence strongly suggests obesity and type 2 diabetes as risk factors of NASH and HCC. However, other elements, namely gender divergences, ethnicity, genetic factors, participation of innate immune system, oxidative stress, apoptotic pathways, and adipocytokines, take a leading role in the onset and promotion of NAFLD. Pathophysiological mechanisms that are responsible for NAFLD development and subsequent progression to NASH are insulin resistance and hyperinsulinemia, oxidative stress, hepatic stellate cell (HSC) activation, cytokine/adipokine signaling pathways, and genetic and environmental factors. Major pathophysiological findings of NAFLD are dysfunction of adipose tissue through the enhanced flow of free fatty acids (FFAs) and release of adipokines, and altered gut microbiome that generate proinflammatory signals and cause NASH progression. Understanding the pathophysiology and risk factors of NAFLD and NASH; this review could provide insight into the development of therapeutic strategies and useful diagnostic tools.

In vivo diffuse reflectance spectroscopic analysis of fatty liver with inflammation in mice

Background

Nonalcoholic steatohepatitis is a progressive liver disease that can lead to cirrhosis, hepatocellular carcinoma, and hepatic failure. Thus, the diagnosis of nonalcoholic steatohepatitis, especially discrimination from nonalcoholic fatty liver, is crucial, but reliable methods other than invasive biopsy have not been established yet. In this study, we investigated the usefulness of diffuse reflectance spectroscopy, which does not require tissue collection, to evaluate the pathological states of fatty liver with inflammation.

Materials and Methods

We performed in vivo optical fiber-based diffuse reflectance spectroscopy in both the near-infrared and visible spectral regions for livers in STAM mice, which typically show steatosis at 6 weeks, steatohepatitis at 8 weeks, and fibrosis at 12 weeks of age. After diffuse reflectance spectroscopy, all of the liver tissues were histologically analyzed and scored on the basis of the rodent nonalcoholic fatty liver disease scoring system. We examined correlations between the diffuse reflectance spectra and scores associated with steatosis and inflammation.

Results and Conclusion

The results showed that the second derivative values of reflectance at 1204 nm, the lipid absorption peak in the near-infrared region, were strongly correlated with steatosis scores (r = 0.9172, P < .0001, n = 20) and that the differences of the first derivative values of reflectance in the visible region (570 nm − 550 nm) that reflect hemoglobin deoxygenation were significantly correlated with inflammation scores (r = 0.5260, P = .0172, n = 20). These results suggest that our diffuse reflectance spectroscopy method is useful for diagnosis of the states of steatosis with inflammation in livers and hence nonalcoholic steatohepatitis.

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Optical reflectance signals are used to diagnose nonalcoholic steatohepatitis in mice.

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The near-infrared reflectance signals are strongly correlated with steatosis scores.

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The visible reflectance signals are significantly correlated with inflammation scores.

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Nonalcoholic steatohepatitis can be noninvasively detected by reflectance signals.

Molecular Imaging of Infarcted Heart by Biofunctionalized Gold Nanoshells

The unique combination of physical and optical properties of silica (core)/gold (shell) nanoparticles (gold nanoshells) makes them especially suitable for biomedicine. Gold nanoshells are used from high-resolution in vivo imaging to in vivo photothermal tumor treatment. Furthermore, their large scattering cross-section in the second biological window (1000-1700 nm) makes them also especially adequate for molecular optical coherence tomography (OCT). In this work, it is demonstrated that, after suitable functionalization, gold nanoshells in combination with clinical OCT systems are capable of imaging damage in the myocardium following an infarct. Since both inflammation and apoptosis are two of the main mechanisms underlying myocardial damage after ischemia, such damage imaging is achieved by endowing gold nanoshells with selective affinity for the inflammatory marker intercellular adhesion molecule 1 (ICAM-1), and the apoptotic marker phosphatidylserine. The results here presented constitute a first step toward a fast, safe, and accurate diagnosis of damaged tissue within infarcted hearts at the molecular level by means of the highly sensitive OCT interferometric technique.

Noninvasive evaluation of hemodynamics and light scattering property during two-stage mouse cutaneous carcinogenesis based on multispectral diffuse reflectance images at isosbestic wavelengths of hemoglobin

We investigate a multispectral imaging method to evaluate spatiotemporal changes in both cutaneous hemoglobin concentration and light scattering parameter in mouse skin through diffuse reflectance spectroscopy using the reflectance images acquired at isosbestic wavelengths of hemoglobin (420, 450, 500, and 585 nm). In the proposed approach, Monte Carlo simulation-based empirical formulas are introduced to extract the scattering power b representing the wavelength dependence of light scattering spectrum of skin tissue, as well as the total hemoglobin concentration Cth in dermal vasculatures. The use of isosbestic wavelengths of hemoglobin enables the values of Cth and b to be estimated independently of the oxygenation of hemoglobin. Experiments using in vivo mice two-stage chemical carcinogenesis model are performed to confirm the feasibility of the proposed method for evaluating the changes in cutaneous vasculatures and tissue morphology during tumor initiation, promotion, and progression processes. The experimental results reveal that the changes in scattering power b of back skin are significantly reduced and followed by the increase in total hemoglobin concentration Cth in the carcinogenesis mice group, which indicates morphological changes in skin tissue such as edema and cell swelling caused by tumor promotion and successive angiogenesis along with tumor progression. The results suggest that the potential of the present method to detect cutaneous carcinogenesis in an early stage and monitor physiological changes during promotion and progression process of nonmelanoma tumors.

In vivo imaging of hepatic hemodynamics and light scattering property during ischemia-reperfusion in rats based on spectrocolorimetry

A red-green-blue camera-based imaging method is proposed for estimating spatial maps of concentrations of oxyhemoglobin (CHbO), deoxyhemoglobin (CHbR), total hemoglobin (CHbT), tissue oxygen saturation (StO2), and scattering power (b) in liver tissue. Hemodynamic responses to hepatic ischemia-reperfusion of in vivo rat liver tissues induced by portal triad occlusion were evaluated. Upon portal triad occlusion, this method yielded images of decreased CHbO, CHbT, StO2, and b, and increased CHbR followed by a progressive increase in CHbO and StO2 during reperfusion. Time courses of the changes in CHbO, CHbR, CHbT, and StO2 over different regions of interest (ROIs) revealed that ischemia results in an abrupt significant (P<0.05) reduction in CHbO, CHbT, and StO2 with a simultaneous increase in CHbR compared to the baseline level, indicative of the hemodynamic responses during hepatic ischemia-reperfusion. Upon reperfusion, there was a gradual increase in CHbO and StO2, and decrease in CHbR. The change in average scattering power b implies the presence of morphological alterations in the cellular and subcellular structures induced by ischemia or anoxia. This study shows the potential of monitoring spatiotemporal changes in hemodynamic parameters and morphological changes in studies of hepatic pathophysiology.