Visualization of cutaneous hemoglobin oxygenation and skin hydration using near-infrared spectroscopic imaging

The visualization of skin hemodynamics and tissue water content has important implications in a number of areas of dermatology, plastic surgery, and clinical skin evaluation. The aim of this study was to develop instrumentation and techniques for infrared spectroscopic imaging, and to evaluate whether they can be used to make objective assessments of skin health, perhaps even before clinical signs are evident.

A liquid-crystal tunable filter was mounted on the front of the objective lens of an infrared-sensitive charge-coupled device digital camera. Sets of narrow-band images of skin were acquired in vivo at wavelength intervals of 10 nm from 650 to 1050 nm, under computer control. The data processing techniques used to extract interpretable clinical information from the raw image sets included normalization, ratios, and multivariate analysis.

To highlight the capabilities of these techniques, results are presented of two studies that generated spectroscopic images. One examined a volunteer's forearm subjected to short interruptions of blood flow, and the other followed changes in a skin flap elevated on a rat model. The data sets were processed in different ways to determine several skin and blood parameters, in particular hemoglobin oxygen saturation, blood volume, and skin hydration. Variations in these parameters were followed non-invasively as a function of time and location to study the skin's response to blood flow changes, and to predict the viability of the skin.

Near-infrared reflectance spectroscopic imaging is demonstrated to be a powerful augmentation to the standard clinical assessment of skin.