On the Feasibility of Skin Water Content Imaging Adjuvant to Tissue Oximetry.

Oxygen supply to tissues can be seriously impacted during wound healing. In particular, edema can increase the distance between capillaries, thus decreasing oxygen supply to cells. Thus, the detection of edema, preferably at the preclinical stage, is of great importance. However, there is no reference standard for a cross-sectional, objective measurement of edema. Multispectral imaging can be such adjuvant technology to elucidate the impact of edema on oxygen transport to tissues. The purpose of the current study is to assess the feasibility of multispectral imaging for visualization of water content in surface tissues. METHODS: The skin (hand and forearm) of healthy volunteers was imaged using the Multi-Spectral Imaging Device (MSID). MSID is a multispectral imaging system for visualization of tissue chromophores in surface tissues. It uses a 12-bit scientific-grade NIR-enhanced monochrome camera and ten wavelength light source (600-1000 nm range) to visualize the distribution of oxy- and deoxyhemoglobins, methemoglobin, water, and melanin. The imaging distance is 30 cm and the field of view: 7 × 7 cm. RESULTS: Water content was extracted using various subsets of two and three wavelengths. To mimic the use of a consumer-grade camera, four least significant bits for each pixel value of a 12-bit image were discarded during preprocessing. Eight-bit results were compared with 12-bit results. CONCLUSIONS: Rough numerical calculations and initial experiments show feasibility of water content imaging in the skin using 970 nm band illumination and 12- and 8-bit cameras.

Optimization of Band Selection in Multispectral and Narrow-Band Imaging: An Analytical Approach.

Hyperspectral imaging is a promising clinical imaging modality with multiple applications in wound care, dermatology, and ophthalmology. However, with current technologies, hyperspectral imagers are relatively large and expensive devices, mainly affordable only by hospitals. Multispectral imaging can be a cost-effective alternative for hyperspectral imaging and is capable of bringing diagnostics to primary health care. Multispectral imaging uses known features of tissue chromophores to simplify imaging device design. However, to maintain design simple and cost-effective the number of illumination bands should be minimal. Thus, proper band selection is very important. The goal of the current study is to develop an analytical model for the optimization of band selection for multispectral and narrow-band imaging techniques (e.g., narrow-band microscopy). METHODS: The contrast ratio has been proposed for quantification of image quality of subsurface inhomogeneities in the skin. Based on the two-flux Kubelka-Munk model, we developed an analytical approach which links the contrast ratio with optical tissue parameters. RESULTS: We obtained an explicit analytical solution for the dependence of maximal contrast ratio on optical tissue parameters. Then, we linked the minimally observable contrast ratio (cmin) with the bit depth of the camera, d: cmin = 1/(2d-1). Based on this analysis we were able to derive an explicit expression, which links camera properties with the minimally detectable changes in optical tissue parameters (both scattering and absorption). CONCLUSIONS: The proposed analytical model can be used for rapid assessment and optimization of multispectral and narrow band imaging techniques and for estimation of the accuracy of imaging techniques. The developed model confirms the utility of the contrast ratio for tissue imaging.

Methemoglobin: A New Way to Distinguish Burn Depth.

In this work, we present a model of dynamics of methemoglobin (MetHb) in burn injuries and show that measuring levels of MetHb can distinguish thickness in burn injuries. METHODS: The model of dynamics of MetHb levels in blood of subjects with burn injuries has been developed based on the vascular morphology of the skin. The model contains burn-specific and non-specific components. RESULTS: The model predicts three distinct outcomes: (a) superficial burn, where the superficial plexus is mainly intact, (b) partial thickness burn, where the superficial plexus lies within the zone of coagulation, but the deep plexus is mainly intact, and (c) full depth burn, where the deep plexus lies in the zone of coagulation. The use of MetHb as a marker of burn injury has not just anatomical, but also physiological justification. The model is in qualitative agreement with a clinical study and an animal model (Yorkshire swine), which used Near Infrared Spectroscopy to assess MetHb levels in burns. CONCLUSIONS: MetHb level in burn injuries is a physiological variable that can be used to classify burn injuries.

Mathematical Model of an Innate Immune Response to Cutaneous Wound in the Presence of Local Hypoxia.

We developed a 2D multi-agent stochastic model of interaction between cellular debris, bacteria and neutrophils in the surface cutaneous wound with local hypoxia. Bacteria, which grow logistically with a maximum carrying capacity, and debris are phagocytosed by neutrophils with probability determined by the partial pressure of oxygen in the tissue, pO 2 = 4-400 mmHg, according to the Michaelis-Menten equation with K m = 40 mmHg. The influx of new neutrophils depends linearly (k = 0.05-0.2) on the amount of (a) platelets and (b) neutrophils, which are in contact with bacteria or debris. Each activated neutrophil can accomplish a certain amount of phagocytosis, n max = 5-20, during its lifespan, T = 1-5 days. The universe of outcomes consists of (a) bacteria clearance (high k and n max ), (b) infection is not cleared by neutrophils (low k and nmax), and (c) intermittent (quasiperiodic) bursts of inflammation. In the absence of infection, phagocytosis stops within 48 h. We found that pO 2 alone did not change the type of outcome, but affects the number of recruited neutrophils and inflammation duration (in the absence of infection by up to 10 and 5 %, respectively).

Diffuse reflectance spectroscopy in Barrett's esophagus: developing a large field-of-view screening method discriminating dysplasia from metaplasia.

We evaluated diffuse reflectance spectroscopy implemented as a small field-of-view technique for discrimination of dysplasia from metaplasia in Barrett's esophagus as an adjuvant to autofluorescence endoscopy. Using linear discriminant analysis on 2579 spectra measured in 54 patients identified an optimum a 4-wavelength classifier (at 485, 513, 598 and 629 nm). Sensitivity and specificity for a test data set were 0.67 and 0.85, respectively. Spectroscopic results show that this technique could be implemented in wide-field imaging mode to improve the accuracy of existing endoscopy techniques for finding early pre-malignant lesions in Barrett's esophagus. Results show that the discrimination occurs likely due to redistribution of blood content in the tissue sensed by the optical probing with the wavelength-dependent sampling depth.