Effect of optical clearing agents on optical coherence tomography images of cervical epithelium

Correlation between light absorbance and skin color using fabricated skin phantoms with different colors

The objective of this study is to investigate the need for detailed classification of skin colors through the quantification of skin color and light absorbance differences. Skin color is one of the most important factors in dermatological laser treatments. Dermatological laser treatments are currently performed based on the experience and judgment of the doctor with the Fitzpatrick scale. However, the Fitzpatrick scale and the doctor's experience were not quantified assessment methods for skin color classification and laser parameters selection. Improper selection of laser irradiating parameters can lead to undesirable tissue effects and treatment outcomes. We analyzed the correlations between absorbance and quantified colors using skin phantoms to identify that using the Fitzpatrick scale in dermatological treatments have limitations. Absorbance differences for different skin colors are measured at 532 nm with a custom-built system for radiant power measurements using skin phantoms fabricated with nine different colors. Some correlations between the color and absorbance agree with the Fitzpatrick scale. Generally, absorbance for the bright colored phantoms is lower than that for the darker colored phantoms. However, some phantoms fabricated with bright colors exceptionally have higher absorbance than those with darker colors. This means that for conventional standards, the Fitzpatrick scale may not always be accurate at 532-nm lights. Through these experiments, we demonstrate the need for a reliable classification standard for skin colors based on quantification of the skin colors and absorbance differences for each skin color as an alternative to the Fitzpatrick scale, which has limitations at certain wavelengths.

Spectroscopic imaging with spectral domain visible light optical coherence microscopy in Alzheimer's disease brain samples

A visible light spectral domain optical coherence microscopy system was developed. A high axial resolution of 0.88 μm in tissue was achieved using a broad visible light spectrum (425 - 685 nm). Healthy human brain tissue was imaged to quantify the difference between white (WM) and grey matter (GM) in intensity and attenuation. The high axial resolution enables the investigation of amyloid-beta plaques of various sizes in human brain tissue and animal models of Alzheimer's disease (AD). By performing a spectroscopic analysis of the OCM data, differences in the characteristics for WM, GM, and neuritic amyloid-beta plaques were found. To gain additional contrast, Congo red stained AD brain tissue was investigated. A first effort was made to investigate optically cleared mouse brain tissue to increase the penetration depth and visualize hyperscattering structures in deeper cortical regions.

Noninvasively Imaging Subcutaneous Tumor Xenograft by a Handheld Raman Detector, with the Assistance of an Optical Clearing Agent

A handheld Raman detector with operational convenience, high portability, and rapid acquisition rate has been applied in clinics for diagnostic purposes. However, the inherent weakness of Raman scattering and strong scattering of the turbid tissue restricts its utilization to superficial locations. To extend the applications of a handheld Raman detector to deep tissues, a gold nanostar-based surface-enhanced Raman scattering (SERS) nanoprobe with robust colloidal stability, a fingerprint-like spectrum, and extremely high sensitivity (5.0 fM) was developed. With the assistance of FPT, a multicomponent optical clearing agent (OCA) efficiently suppressing light scattering from the turbid dermal tissues, the handheld Raman detector noninvasively visualized the subcutaneous tumor xenograft with a high target-to-background ratio after intravenous injection of the gold nanostar-based SERS nanoprobe. To the best of our knowledge, this work is the first example to introduce the optical clearing technique in assisting SERS imaging in vivo. The combination of optical clearing technology and SERS is a promising strategy for the extension of the clinical applications of the handheld Raman detector from superficial tissues to subcutaneous or even deeper lesions that are usually "concealed" by the turbid dermal tissue.

Optical clearing for luminal organ imaging with ultrahigh-resolution optical coherence tomography

The imaging depth of optical coherence tomography (OCT) in highly scattering biological tissues (such as luminal organs) is limited, particularly for OCT operating at shorter wavelength regions (such as around 800 nm). For the first time, the optical clearing effect of the mixture of liquid paraffin and glycerol on luminal organs was explored with ultrahigh-resolution spectral domain OCT at 800 nm. Ex vivo studies were performed on pig esophagus and bronchus, and guinea pig esophagus with different volume ratios of the mixture. We found that the mixture of 40% liquid paraffin had the best optical clearing effect on esophageal tissues with a short effective time of ∼ 10 min, which means the clearing effect occurs about 10 min after the application of the clearing agent. In contrast, no obvious optical clearing effect was identified on bronchus tissues.

Backscattering intensity measurements in optical coherence tomography as a method to identify parathyroid glands

BACKGROUND AND OBJECTIVE

Previous studies have shown that the use of optical coherence tomography (OCT) permits the differentiation between parathyroid tissue, thyroid tissue, lymph nodes and adipose tissue. We investigated the backscattering intensity profiles of OCT images in order to determine whether significant differences between these tissue types exist.

METHODS

Mean backscattering intensity profiles were obtained from OCT images of parathyroid glands, thyroid tissue, lymph nodes and adipose tissue. The profiles were analyzed employing Fisher's Linear Discriminant Analysis (LDA). The results were cross validated employing improved parameter estimation techniques.

RESULTS

Mean backscattering intensity profiles from 300 OCT images of 34 patients undergoing thyroid or parathyroid surgery were analyzed. The overall rate of correct classifications was 96.15%. The cross validation employing improved parameter estimation techniques yielded results identical to those derived from Fisher's LDA.

CONCLUSION

Besides the individual assessment of OCT images by interpreting morphological criteria, backscattering intensity measurements can reliably distinguish between different tissue entities.