Foot ulceration remains a serious health concern for diabetic patients and has a major impact on the cost of diabetes treatment. Early detection and preventive care, such as offloading or improved hygiene, can greatly reduce the risk of further complications. We aim to assess the use of hyperspectral tissue oximetry in predicting the risk of diabetic foot ulcer formation. Tissue oximetry measurements are performed during several visits with hyperspectral imaging of the feet in type 1 and 2 diabetes mellitus subjects that are at risk for foot ulceration. The data are retrospectively analyzed at 21 sites that ulcerated during the course of our study and an ulceration prediction index is developed. Then, an image processing algorithm based on this index is implemented. This algorithm is able to predict tissue at risk of ulceration with a sensitivity and specificity of 95 and 80%, respectively, for images taken, on average, 58 days before tissue damage is apparent to the naked eye. Receiver operating characteristic analysis is also performed to give a range of sensitivity/specificity values resulting in a Q-value of 89%.
Foot ulceration is a debilitating comorbidity of diabetes that may result in loss of mobility and amputation. Optical
detection of cutaneous tissue changes due to inflammation and necrosis at the preulcer site could constitute a preventative
strategy. A commercial hyperspectral oximetry system was used to measure tissue oxygenation on the feet of diabetic
patients. A previously developed predictive index was used to differentiate preulcer tissue from surrounding healthy tissue
with a sensitivity of 92% and specificity of 80%. To improve prediction accuracy, an optical skin model was developed
treating skin as a two-layer medium and explicitly accounting for (i) melanin content and thickness of the epidermis,
(ii) blood content and hemoglobin saturation of the dermis, and (iii) tissue scattering in both layers. Using this forward
model, an iterative inverse method was used to determine the skin properties from hyperspectral images of preulcerative
areas. The use of this information in lowering the false positive rate was discussed.
A noncontact optical detection system is developed for the in vivo identification and localization of high-grade cervical intraepithelial neoplasia (CIN 2,3). Diagnostic scans of the entire human cervix are performed following acetic acid application employing three integrated optical measurements: laser-induced fluorescence spectroscopy, white light diffuse reflectance spectroscopy, and video imaging. Full cervical scans comprising 499 interrogation locations at 1-mm spatial resolution are completed in 12 s. Diffuse reflectance and fluorescence spectra with signal-to-noise ratios of better than 100-to-1 are collected between 360 and 720 nm in increments of 1 nm, with an inherent spectral resolution of 8 nm. Glare reduction and optical vignetting are handled with a novel illumination scheme and subsequent spectral arbitration algorithms. The system is designed and found to be well below acceptable safe optical exposure levels. Typical reproducibility across multiple systems is approximately 5%, providing reliable and accurate detection of in vivo cervical neoplasia in normal clinical use.
KEYWORDS: Tissues, Monte Carlo methods, Luminescence, Time resolved spectroscopy, Absorption, Quantum efficiency, Collagen, Colon, Pathology, In vivo imaging
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.
Fluorescence emission and diffuse reflectance spectra of freshly excised cervical tissue were studied with two specially designed contact probes. The objective of the study was to reach a better understanding of the relationship between spectroscopic measurements and cervical tissue morphology. Tissue samples from loop electro-surgical excision and hysterectomy specimens were measured within 20 to 90 minutes of excision. Emission spectra with 337 nm excitation, and reflectance spectra were collected at wavelengths between 370 and 720 nm from different tissue sites. Hematoxylin-eosin stained slides of the measured zones were obtained and compared to the spectra.
In one experiment, a contact probe with a central illumination fiber and two concentric rings of detection fibers (radii 0.1 and 1 mm), was placed in contact with the epithelium and used to measure spectra from ectocervix and endocervix. The influence of 5% acetic acid on fluorescence and reflectance spectra was also investigated. In another experiment, a single 100-micron fiber probe was placed perpendicular to a cut edge of tissue and scanned to measure spectra in depth. Depth scans were made over various areas of the cervix
The detection of cervical intraepithelial neoplasia (CIN) in human uterine cervix is possible through the use of fluorescence and reflectance spectroscopy. Fluorescence and reflectance spectra were recorded from the cervix of over 200 patients. Classification performance for distinguishing high-grade CIN (CIN II and III) from normal squamous, normal columnar and metaplastic tissues is 84%. On average, the intensity of fluorescence for CIN II/III lesions is two-fold less than non-CIN II/III tissue. However, variability in the spectra, associated with specific patient, tissue and instrumental parameters, is also noted and tends to blur the distinction between tissue groups. In particular, the intensity of fluorescence was found to increase with patient's age. The magnitude of age-dependence was evaluated using spectra from two of the largest tissue groups: metaplasia (1089 sites in 90 patients) and normal squamous mucosa (763 sites in 56 patients). The metaplasia class shows a stronger age dependence compared to normal squamous tissue: 7.5%/yr versus 2.6%/yr at 390 nm and 2.8%/yr versus 0.9%/yr at 460 nm, representing a two-fold increase in the intensity of fluorescence over 30 years. Hence, the accuracy of tissue classification algorithms may be improved with proper corrections to the spectra for these variables prior to classification.
Fiber optic probes used to deliver and collect light for biomedical fluorescence spectroscopy applications have varied widely in design. Critical design parameters include fiber diameter, tissue fiber-tip spacing, and illumination- collection fiber separation distance. While device design has been shown to influence spectral distributions, previous studies have not thoroughly addressed how probe geometry affects the spatial origin of detected fluorescence or how probe design might be customized for specific tissue sites or applications. We have developed a Monte Carlo model of laser-induced fluorescence and investigated the effect of design parameters on light propagation using gastrointestinal tissue optical properties. The distribution of emission locations for detected fluorescence were calculated. Initial results indicated that average fluorescence emission depth and total signal intensity are highly dependent on fiber size and tissue-fiber spacing. The implications of these results for optimization of probes used in the detection of neoplasia are discussed.
Photobleaching of 5-aminolevulinic acid (ALA) -induced protoporphyrin IX (PpIX) and benzoporphyrin derivative-monoacid ring A (BPD-MA) was investigated using an orthotopic rat bladder tumor model. For both photosensitizers used, the photobleaching rate constant was not fluence- rate-dependent under conditions that photodynamic response was fluence rate-dependent. These data suggest that photobleaching pathways may be independent of the photochemical paths involved in tissue destruction. The fluorescence spectrum was followed during irradiation by using laser-induced fluorescence method and a build-up of photoproducts of PpIX was observed whereas no fluorescence of photoproducts was obtained in the case of BPD-MA.
Oxygen dependent phototoxicity was investigated in vivo in an orthotopic rat bladder tumor model. Two photosensitizers, benzoporphyrin derivative monoacid ring A and 5-aminolevulinic acid-induced protoporphyrin IX were studied. For a given cumulative light dose of 30 J/cm2, enhanced tumor destruction was obtained for both photosensitizers by either using a low fluence rate or fractionated light delivery mode. These observations may be attributed to rapid local oxygen consumption during photochemical reactions.
The ability of laser-induced fluorescence (LIF) to detect flat dysplasia has not been carefully studied. A multiexcitation wavelength LIF system was used to develop an algorithm to detect chemically-induced dysplasia in the rat urinary bladder.
Laser-induced fluorescence has been used to measure tissue levels of chloroaluminum phthalocyanine tetrasulfonate versus time in order to determine its pharmacokinetics. A hamster cheek pouch carcinoma model was used in vivo. The data have been modeled using a four compartment pharmacokinetic model, yielding rate constants which describe the transport. A minimum of 13 rate constants was needed to achieve acceptable fits to the tumor and normal tissue as well as plasma data. The model gives insight into the role of binding and unbinding processes that are not otherwise evident.
The present study uses photodynamic therapy (PDT) for the treatment of IH in the rat carotid artery model. PDT is a relatively new cancer treatment technique which utilizes light-activated photosensitizers (PS) to produce injury to targeted cells. PS have no cytotoxic effects unless they are activated by the appropriate wavelength of light. Upon absorption of a photon, the activated PS can either by directly cytotoxic or give rise to cytotoxic oxygen species, commonly singlet oxygen, via energy transfer to the ground state molecular oxygen. Singlet oxygen then becomes the mediator of cellular injury by affecting cellular membranes and subcellular organelles.
Although lasers have traditionally been used in medicine as therapeutic devices,
there has been considerable interest in using them as diagnostic tools.
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