Fluorescence excitation photography of epidermal cellular proliferation

Autofluorescence Excitation Imaging of Nonmelanoma Skin Cancer for Margin Assessment Before Mohs Micrographic Surgery: A Pilot Study

BACKGROUND

Autofluorescence photography can detect specific light-tissue interactions and record important pathophysiological changes associated with nonmelanoma skin cancer (NMSC), which has been ascribed to the fluorescence of an aromatic amino acid, tryptophan.

OBJECTIVE

To assess the impact of a novel, autofluorescence imaging (AFI) device on margin control for NMSCs before Mohs micrographic surgery (MMS) in an effort to decrease overall operating time.

METHODS

Before the initial stage of MMS, NMSCs were measured with a 2-mm margin as standard of care (normal margin). The tumor was then imaged with the AFI device. A 2-mm margin was drawn around the fluorescent area captured by the AFI device and was referred to as the camera margin. The tumor was excised based on the normal margin and evaluated on frozen histological section.

RESULTS

Imaging based on the AFI device resulted in appropriate recommendations for margin control in 8 of 11 tumors. Four of these tumors did not fluoresce and demonstrated a lack of tumor residuum on stage I specimen, as anticipated. There were no side effects from the AFI device.

CONCLUSION

This is an initial pilot study that supports the use of a novel, noninvasive imaging device to help with margin assessment before MMS. On optimization, this device has potential to extend applicability to surgical excisions for tumors that do not fulfill criteria for MMS.

Tryptophan intrinsic fluorescence from wound healing correlates with re-epithelialization in a rabbit model

BACKGROUND

Wound healing monitoring and timely decision-making are critical for wound classification. Tryptophan (Tr) intrinsic fluorescence, detected at 295/340 nm, provides a noninvasive approach for wound assessment. Our previous work demonstrated that this autofluorescence is associated with keratinocytes in a highly proliferative state in vitro.

OBJECTIVE

We investigated the correlation between Tr fluorescence and key wound healing parameters, including re-epithelialization, fibrosis, neovascularization, and acute and chronic inflammation, using a rabbit model.

METHODS

Seven rabbits underwent wound healing assessment over a 15-day period. We employed histological analysis from central and marginal biopsies, and UV fluorescence imaging captured by a monochromatic near-UV sensitive camera equipped with a passband optical filter (340 nm/12 nm). Excitation was achieved using a 295 nm LEDs ring lamp. Normalized fluorescence values were correlated with histological measurements using Pearson correlation.

RESULTS

The UV fluorescence strongly exhibited a strong correlation with re-epithelization (r = 0.8) at the wound edge, with peak intensity observed between the sixth and ninth days. Notably, wound-healing dynamics differed between the wound center and edge, primarily attributed to variations in re-epithelialization, neovascularization, and chronic inflammation.

CONCLUSION

Our findings highlight the presence of autofluorescence at 295/340 nm during wound healing, demonstrating a robust association with re-epithelialization. This excitation/emission signal holds promise as a valuable noninvasive strategy for monitoring wound closure, re-epithelialization, and other biological processes where Tr plays a pivotal role.

Method for measuring the extinction coefficient of fluorescing media within the emission band

We propose and test a method for determining a fluorescent medium's absorption or extinction index while it is fluorescing. The method uses an optical arrangement that records changes in fluorescence intensity at a fixed viewing angle as a function of the angle of incidence of an excitation light beam. We tested the proposed method on polymeric films doped with Rhodamine 6G (R6G). We found a strong anisotropy in the fluorescence emission and, thus, limited the method to TE-polarized excitation light. The method proposed is model dependent, and we provide a simplified model for its use in this work. We report the extinction index of the fluorescing samples at a selected wavelength within the emission band of the fluorophore R6G. We found that the extinction index at the emission wavelengths in our samples is appreciably larger than the extinction index at the excitation wavelength, which is the opposite of what one might expect from measuring the absorption spectrum of the medium with a spectrofluorometer. The proposed method could be applied to fluorescent media with additional absorption other than by the fluorophore.

Noninvasive Assessment of Mycotic Nail Tissue Using an Ultraviolet Fluorescence Excitation Imaging System

BACKGROUND AND OBJECTIVES

Mycological diagnosis of onychomycosis is based on direct microscopy using external fluorophores to visualize fungal tissue in nail samples and agar culture. Ultraviolet fluorescence excitation imaging (u-FEI) has shown potential in monitoring biological processes by exploiting variations in autofluorescence. This study aimed at assessing the potential of a handheld u-FEI system as a practical screening tool for fungal nail infections.

STUDY DESIGN/MATERIALS AND METHODS

Ninety samples from 29 patients with microscopy-confirmed fungal infection and 10 control samples from healthy participants were collected (n = 100). Using a prototype u-FEI system (single bandpass 25 mm filter with a central pass wavelength of 340 nm and a bandwidth of 12 nm, 295 nm excitation flash, resolution of 640 × 480), images of all samples were acquired under standardized conditions. Average and maximum fluorescence intensity image values in arbitrary units (AU) of manually delineated regions of interests were quantitated and statistically assessed for significant differences between healthy and mycotic samples.

RESULTS

UV-images clearly depicted all 100 nail samples, with a visibly stronger signal in infected samples. Statistically significant differences (P < 0.05) in signal intensity between mycotic samples and healthy controls were observed for maximum and average fluorescence values. Mean fluorescence values of onychomycotic samples showed 23.9% higher maximum (mycotic: 34.9 AU [standard deviation [SD] 4.7]; healthy: 28.2 AU [SD 1.9]) and 10.2% higher average (mycotic: 27.6 AU [SD 2.0]; healthy: 25.0 AU [SD 0.7]) signal intensity values. Receiver operating characteristic curves demonstrated excellent discriminatory ability (area under the curve > 0.9). Analysis of fluorescence measurements of the reference standard demonstrated very low variation (coefficient of variation = 0.62%) CONCLUSION: Quantitation of u-FEI intensities enables differentiation between healthy and mycotic nail samples, constituting a potential point-of-care tool for cost-effective screening for onychomycosis at a primary care level. Lasers Surg. Med. © 2020 Wiley Periodicals LLC.

Variations in the endogenous fluorescence of rabbit corneas after mechanical property alterations

Keratoconus is an eye disease in which the cornea progressively deforms due to loss of cornea mechanical rigidity, and thus causes deterioration of visual acuity. Techniques to characterize the mechanical characteristics of the cornea are important to better monitor changes and response to treatments. To investigate the feasibility of using the endogenous fluorescence of cornea for monitoring alterations of its mechanical rigidity, linear tensiometry was used to quantitate stiffness and Young's modulus (YM) after treatments that increase cornea stiffness (collagen photocross-linking) or decrease stiffness (enzymatic digestion). The endogenous ultraviolet fluorescence of cornea was also measured before and after these treatments. The fluorescence excitation/emission spectral ranges were 280 to 430/390 to 520 nm, respectively. A correlation analysis was carried out to identify fluorescence excitation/emission pairs whose intensity changes correlated with the stiffness. A positive correlation was found between variations in fluorescence intensity of the 415-/485-nm excitation/emission pair and YM of photocross-linked corneas. After treatment of corneas with pepsin, the YM decreased as the fluorescence intensity at 290-/390-nm wavelengths decreased. For weakening of corneas with collagenase, only qualitative changes in the fluorescence spectrum were observed. Changes in the concentration of native or newly created fluorescent molecular species contain information that may be directly or indirectly related to the mechanical structure of the cornea.

Protoporphyrin IX fluorescence as potential indicator of psoriasis severity and progression

BACKGROUND AND OBJECTIVES

In psoriatic lesions, fluorescence diagnosis with blue light can detect protoporphyrin IX accumulation, especially after topical 5-aminolaevulinic acid (ALA) application. However, variable fluorescence distributions, interpersonal variations and long incubation time limit its wide application in clinic. This study is aimed to identify a consistent and convenient method to facilitate diagnosis and evaluation of psoriatic lesions.

METHODS

104 psoriatic lesions from 30 patients were evaluated. Single lesion PSI scoring and fluorescence by macrospectrofluorometry were recorded on each lesion before and after treatment with narrow-band UVB.

RESULTS

Punctate red fluorescence, emitted mainly by protoporphyrin IX, is observed in some psoriatic lesions. According to psoriasis severity index, fluorescence-positive lesions are more severe than lesions without fluorescence. We found a significant positive correlation between psoriasis severity and fluorescence intensity from protoporphyrin IX.

CONCLUSIONS

Protoporphyrin IX-induced red fluorescence can be used as a novel and convenient approach for psoriasis diagnosis and progression evaluation.

UV fluorescence excitation imaging of healing of wounds in skin: Evaluation of wound closure in organ culture model

BACKGROUND AND OBJECTIVE

Molecules native to tissue that fluoresce upon light excitation can serve as reporters of cellular activity and protein structure. In skin, the fluorescence ascribed to tryptophan is a marker of cellular proliferation, whereas the fluorescence ascribed to cross-links of collagen is a structural marker. In this work, we introduce and demonstrate a simple but robust optical method to image the functional process of epithelialization and the exposed dermal collagen in wound healing of human skin in an organ culture model.

MATERIALS AND METHODS

Non-closing non-grafted, partial closing non-grafted, and grafted wounds were created in ex vivo human skin and kept in culture. A wide-field UV fluorescence excitation imaging system was used to visualize epithelialization of the exposed dermis and quantitate wound area, closure, and gap. Histology (H&E staining) was also used to evaluate epithelialization.

RESULTS

The endogenous fluorescence excitation of cross-links of collagen at 335 nm clearly shows the dermis missing epithelium, while the endogenous fluorescence excitation of tryptophan at 295 nm shows keratinocytes in higher proliferating state. The size of the non-closing wound was 11.4 ± 1.8 mm and remained constant during the observation period, while the partial-close wound reached 65.5 ± 4.9% closure by day 16. Evaluations of wound gaps using fluorescence excitation images and histology images are in agreement.

CONCLUSIONS

We have established a fluorescence imaging method for studying epithelialization processes, evaluating keratinocyte proliferation, and quantitating closure during wound healing of skin in an organ culture model: the dermal fluorescence of pepsin-digestible collagen cross-links can be used to quantitate wound size, closure extents, and gaps; and, the epidermal fluorescence ascribed to tryptophan can be used to monitor and quantitate functional states of epithelialization. UV fluorescence excitation imaging has the potential to become a valuable tool for research, diagnostic and educational purposes on evaluating the healing of wounds. Lasers Surg. Med. 48:678-685, 2016. © 2016 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Evaluation of cell and matrix mechanics using fluorescence excitation spectroscopy: Feasibility study in collagen gels containing fibroblasts

BACKGROUND AND OBJECTIVE

Collagen gels containing cells are commonly used in tissue engineering, wound healing, and cancer research to investigate the interplay between cells and the extracellular matrix (ECM), as changes in the density and stiffness of the microenvironment are known to play a role in many diseases or pathological conditions. In these gels, the stiffness is regularly determined using destructive methods, such as indentation and tensile tests. Certain molecules native to cells and the ECM display fluorescence upon irradiation with ultraviolet light. The objective of the present study was to investigate the feasibility of using the endogenous, or innate, fluorescence of collagen gels containing fibroblasts as an optical marker to evaluate changes in the mechanical properties of the ECM.

MATERIALS AND METHODS

Human foreskin fibroblasts cells at concentrations of 50,000 and 100,000 cells/ml were cultured in three-dimensional gels of type I collagen for 16 days. Fibroblast cells remodeled the ECM, contracting and increasing the stiffness of the gel. During this remodeling process, changes in mechanical properties and fluorescence were measured with an indentation test and a spectrofluorometer, respectively. Force and displacement measurements from the indentation test were used to calculate the elastic modulus of the gel. Maps of fluorescence intensity, at excitation/emission of 240-520/290-530 nm, were used to identify the wavelengths of interest.

RESULTS

Fluorescence excitation/emission maps exhibited two distinct excitation/emission bands whose intensities increased as the fibroblasts remodeled and increased the stiffness of the ECM: The 290/340 nm band ascribed to tryptophan and the 330/390 nm band ascribed to cross-links of collagen (pepsin-digestible cross-links). A Spearman correlation analysis, between the elastic modulus of the gel containing fibroblasts and the fluorescence of cross-links of collagen, resulted in R = 0.95 (P < 0.05) and R = 0.77 (P = 0.12) for 50,000 and 100,000 cells/ml, respectively.

CONCLUSIONS

The endogenous fluorescence intensity ascribed to pepsin-digestible cross-links of collagen may serve as an optical marker to evaluate changes in the mechanical properties of the ECM; this is relevant to collagenous tissues for which pathological states are related to mechanical alterations, such as keratoconus in cornea and osteoarthritis in articular cartilage.