{'fraction_non_alphanumeric': 0.021948608137044967, 'fraction_numerical': 0.004817987152034261, 'mean_word_length': 5.467128027681661, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Simulations of time-resolved fluorescence in multilayered biological tissues: applications to clinical data modeling

We present a computational code capable of simulating time-resolved fluorescence emission from multi-layered biological tissues, and apply this code to model tissue fluorescence emission data acquired in vivo during clinical endoscopy. The code for multi-layered media is based on a Monte Carlo model we developed previously to simulate time-resolved fluorescence propagation in a semi-infinite turbid medium. Here, the code is applied to simulate data acquired from measurements on tissues in the lower gastrointestinal tract. Clinical data were obtained in vivo during endoscopy using a portable time-resolved fluorescence spectrometer employing a single fiber-optic probe for excitation and detection. Tissue was modeled as a two-layered medium consisting of a mucosal layer of finite thickness above a sub-mucosal layer. The emitted fluorescence was considered as arising from mucosal epithelial cells, due to the presence of nicotinamide dinucleotide as the constituent fluorophore (lifetime τ = 1.5 ns), and from sub-mucosal structural proteins (collagen, lifetime τ = 5.2 ns). Simulations modeled changes in tissue pathology as a function of independently changing the mucosal layer thickness, the fluorophore absorption coefficients and the fluorescence quantum yields. It was observed that the emanating fluorescence from the mucosal layer changes by ~50-60% with these changes resulting in appreciable differences of ~2 ns in the average lifetimes. These simulations indicate that it may be possible to quantify the fluorescence observed from tissue based on both biochemical and histological criteria. The simulations may also be used to provide a useful method for designing and testing the efficacies of different fiber-probe geometries.