Depth Penetration of Light into Skin as a Function of Wavelength from 200 to 1000 nm.

An increase in the use of light-based technology and medical devices has created a demand for informative and accessible data showing the depth that light penetrates into skin and how this varies with wavelength. These data would be particularly beneficial in many areas of medical research and would support the use and development of disease-targeted light-based therapies for specific skin diseases, based on increased understanding of wavelength-dependency of cutaneous penetration effects. We have used Monte Carlo radiative transport (MCRT) to simulate light propagation through a multi-layered skin model for the wavelength range of 200-1000 nm. We further adapted the simulation to compare the effect of direct and diffuse light sources, varying incident angles and stratum corneum thickness. The lateral spread of light in skin was also investigated. As anticipated, we found that the penetration depth of light into skin varies with wavelength in accordance with the optical properties of skin. Penetration depth of ultraviolet radiation was also increased when the stratum corneum was thinner. These observations enhance understanding of the wavelength-dependency and characteristics of light penetration of skin, which has potential for clinical impact regarding optimizing light-based diagnostic and therapeutic approaches for skin disease.

Development of a Predictive Monte Carlo Radiative Transfer Model for Ablative Fractional Skin Lasers.

It is possible to enhance topical drug delivery by pretreatment of the skin with ablative fractional lasers (AFLs). However, the parameters to use for a given AFL to achieve the desired depth of ablation or the desired therapeutic or cosmetic outcome are hard to predict. This leaves open the real possibility of overapplication or underapplication of laser energy to the skin. In this study, we developed a numerical model consisting of a Monte Carlo radiative transfer (MCRT) code coupled to a heat transfer and tissue damage algorithm. The simulation is designed to predict the depth effects of AFL on the skin, verified with in vitro experiments in porcine skin via optical coherence tomography (OCT) imaging. Ex vivo porcine skin is irradiated with increasing energies (50-400 mJ/pixel) from a CO2 AFL. The depth of microscopic treatment zones is measured and compared with our numerical model. The data from the OCT images and MCRT model complement each other well. Nonablative thermal effects on surrounding tissue are also discussed. This model, therefore, provides an initial step toward a predictive determination of the effects of AFL on the skin. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC.

A novel light source with tuneable uniformity of light distribution for artificial daylight photodynamic therapy.

OBJECTIVES: Implementation of daylight photodynamic therapy (dPDT) is somewhat limited by variable weather conditions. Light sources have been employed to provide artificial dPDT indoors, with low irradiances and comparable treatment times to dPDT. Uniform light distribution across the target area is desirable in effective treatment planning, particularly for large areas. A novel light source is developed with tuneable direction of light emission in order to meet this challenge. METHODS: Wavelength composition of the novel light source is controlled such that the protoporphyrin-IX (PpIX) weighted spectra of both the light source and daylight match. The uniformity of the light distribution is characterised on a flat surface, a model head and a model leg. For context, a typical conventional PDT light source is also characterised. Additionally, the wavelength uniformity across the treatment site is characterised. RESULTS: The PpIX-weighted spectrum of the novel light source matches the PpIX-weighted daylight spectrum, with irradiance values within the bounds for effective dPDT. By tuning the direction of light emission, improvements are seen in the uniformity across large anatomical surfaces. Wavelength uniformity is discussed. CONCLUSIONS: We have developed a light source that addresses the challenges in uniform, multiwavelength light distribution for large area artificial dPDT across curved anatomical surfaces.

A quantitative study of in vivo protoporphyrin IX fluorescence build up during occlusive treatment phases.

BACKGROUND: Topical photodynamic therapy (PDT) is a non-invasive light based therapy used to treat non-melanoma skin cancer (NMSC) and dysplasia. During PDT, the light sensitive molecule protoporphyrin IX (PpIX) is activated, resulting in the production of singlet oxygen, which subsequently leads to cell death. PpIX is metabolised from a topically applied pro-drug and the strong fluorescence signal associated with PpIX can be utilised as an indicator of the amount of PpIX present within the tumour tissue. In this work we measure the build up PpIX during the occlusive treatment phase and investigate how the PpIX production rate is affected by different lesion and patient characteristics. METHODS: Fluorescence measurements were used to investigate the build up of PpIX within the tumour tissue during the 3h long occlusive treatment prior to irradiation. The study included in vivo measurements of 38 lesions from 38 individual patients. Actinic keratosis (AK) and basal cell carcinoma (BCC) were the lesion types included in this study. The resulting data from the study was analysed using generalised linear mixed effects models. RESULTS: It was found that the surface fluorescence signal linearly increased with occlusive treatment time. The predictive models suggest that there is a significant difference in PpIX production between lesion location, however no significant difference is demonstrated between different lesion types, gender and skin type. CONCLUSIONS: The study extends and supports previous knowledge of PpIX production during the occlusive treatment phase.

Suppression of amplitude-to-phase noise conversion in balanced optical-microwave phase detectors.

We demonstrate an amplitude-to-phase (AM-PM) conversion coefficient for a balanced optical-microwave phase detector (BOM-PD) of 0.001 rad, corresponding to AM-PM induced phase noise 60 dB below the single-sideband relative intensity noise of the laser. This enables us to generate 8 GHz microwave signals from a commercial Er-fibre comb with a single-sideband residual phase noise of -131 dBc Hz(-1) at 1 Hz offset frequency and -148 dBc Hz(-1) at 1 kHz offset frequency.

Modelling fluorescence in clinical photodynamic therapy.

Understanding the interactions of non-ionizing radiation with living organisms has been the focus of much research over recent decades. The complex nature of these interactions warrants development of theoretical and experimental studies to gain an insight into predicting and monitoring the success of photodynamic therapy (PDT) protocols. There is a major impetus towards evidence-based recommendations for patient diagnosis, treatment and management. Knowledge of the biophysical aspects of PDT is important for improving dosimetry protocols. Fluorescence in clinical PDT may be used to detect and diagnose pre-malignant and malignant conditions, while photobleaching can monitor changes in fluorescence during treatment. Combining empirical fluorescence photobleaching clinical data with computational modelling enables clinical PDT dosimetry protocols to be investigated with a view to optimising treatment regimes. We will discuss how Monte Carlo radiation transfer (MCRT) modelling has been intercalated in the field of fluorescence detection and PDT. In this paper we highlight important aspects of basic research in PDT by reporting on the current utilisation of fluorescence in clinical PDT from both a clinical and theoretical perspective. Understanding and knowledge of light propagation in biological tissue from these perspectives should have a positive impact on treatment planning.

Wavelength-orthogonal photolysis of neurotransmitters in vitro.

Irradiation of a mixture of 4-methoxyphenacyl-caged (S)-glutamate and 4,5-dimethoxy-2-nitrobenzyl-caged γ-amino butyric acid (GABA) on neurons, at ~260 nm, evokes selective photorelease of (S)-glutamate (Glu) whereas photolysis at 405 nm causes selective photorelease of GABA.

Monte Carlo modeling of in vivo protoporphyrin IX fluorescence and singlet oxygen production during photodynamic therapy for patients presenting with superficial basal cell carcinomas.

We present protoporphyrin IX (PpIX) fluorescence measurements acquired from patients presenting with superficial basal cell carcinoma during photodynamic therapy (PDT) treatment, facilitating in vivo photobleaching to be monitored. Monte Carlo (MC) simulations, taking into account photobleaching, are performed on a three-dimensional cube grid, which represents the treatment geometry. Consequently, it is possible to determine the spatial and temporal changes to the origin of collected fluorescence and generated singlet oxygen. From our clinical results, an in vivo photobleaching dose constant, ß of 5-aminolaevulinic acid-induced PpIX fluorescence is found to be 14 ± 1 J/cm(2). Results from our MC simulations suggest that an increase from our typical administered treatment light dose of 75-150 J/cm(2) could increase the effective PDT treatment initially achieved at a depth of 2.7-3.3 mm in the tumor, respectively. Moreover, this increase reduces the surface PpIX fluorescence from 0.00012 to 0.000003 of the maximum value recorded before treatment. The recommendation of administrating a larger light dose, which advocates an increase in the treatment time after surface PpIX fluorescence has diminished, remains valid for different sets of optical properties and therefore should have a beneficial outcome on the total treatment effect.

A quantitative comparison of 5-aminolaevulinic acid- and methyl aminolevulinate-induced fluorescence, photobleaching and pain during photodynamic therapy.

The characteristics of protoporphyrin IX (PPIX) fluorescence in superficial basal cell carcinoma (sBCC) and carcinoma in situ (Bowen's Disease, BD) following application of 5-aminolaevulinic acid (5-ALA) and its methyl ester (methyl aminolevulinate [MAL]) before, during and after photodynamic therapy (PDT) were investigated in 40 patients. Photosensitizer prodrug penetration can limit PDT efficacy and understanding the characteristics of PPIX fluorescence through fluorescence spectroscopy, may improve knowledge of photosensitizer delivery. Fluorescence intensity was assessed quantitatively, and the rate of photobleaching was determined by fitting an exponential decay. As a secondary end-point, PDT-induced pain was also measured continuously during treatment using a novel hand-held device, known as a pain logger. In vivo PPIX fluorescence was shown to decrease during irradiation, allowing the in vivo photobleaching of PPIX to be monitored. No significant difference was found between ALA- or MAL-induced PPIX fluorescence in lesions of sBCC and BD (P>0.05), indicating no detectable difference in PPIX kinetics for the two prodrugs as assessed by these measures. Pain, as assessed by the logger device, showed high interindividual variability and pain levels tended to be higher initially, decreasing during treatment. No difference was seen in pain experienced during ALA-or MAL-PDT (P>0.05).

Synthesis, photolysis studies and in vitro photorelease of caged TRPV1 agonists and antagonists.

The synthesis of a range of caged TRPV1 agonists and antagonists is reported. The photolysis characteristics of these compounds, when irradiated with a 355 nm laser, have been studied and in all cases the desired compound was produced. Photolysis of a caged TRPV1 agonist in cultured trigeminal neurons produced responses that were consistent with the activation of TRPV1 receptors.

Caged AG10: new tools for spatially predefined mitochondrial uncoupling.

The study of mitochondria and mitochondrial Ca2+ signalling in localised regions is hampered by the lack of tools that can uncouple the mitochondrial membrane potential (DeltaPsi(m)) in a spatially predefined manner. Although there are a number of existing mitochondrial uncouplers, these compounds are necessarily membrane permeant and therefore exert their actions in a spatially unselective manner. Herein, we report the synthesis of the first caged (photolabile protected) mitochondrial uncouplers, based on the tyrphostin AG10. We have analysed the laser photolysis of these compounds, using (1)H NMR and HPLC, and demonstrate that the major product of caged AG10 photolysis is AG10. It is shown that photolysis within single smooth muscle cells causes a collapse of DeltaPsi(m) consistent with photorelease of AG10. Furthermore, the effect of the photoreleased AG10 is localised to a subcellular region proximal to the site of photolysis, demonstrating for the first time spatially predefined mitochondrial uncoupling.

In vitro photo-release of a TRPV1 agonist.

Intracellular photolysis of a novel 'caged' capsaicin analogue results in in vitro activation of the capsaicin receptor TRPV1.