Hyperspectral technology (first developed by Dept of Defense) provides a method to generate a “gradient map” of a region of interest based on local chemical composition (Figure 1). Hyper-spectral technology (HT) has been used in satellite investigation of suspected chemical weapons production areas, geological features, and agricultural field conditions. At the micro level, HT also has been applied to the study of physiologic and pathologic changes in living human tissue to provide information as to the health or disease of tissue that is otherwise unavailable.
In medicine, spectroscopy is used to monitor metabolic status in a variety of tissues; consider the spectroscopic methods used in pulse oximeters which utilize the different absorption bands oxy- & deoxy-Hb to estimate arterial oxygen saturation. No other method however provides information towards the spatial distribution or heterogeneity of the data. Such spatial information is achieved by HT, where the multi- dimensional (spatial & spectral) data is represented in what is called a “hypercube” (see example in Figure 2). The spectrum of reflected light is acquired for each pixel in a quadrant and each such spectrum is subjected to standard analysis. From this we create a map of the tissue based on the chemistry of the region of interest.
Tissues have optical signatures or chromophores that reflect their chemical characteristics. The two major chromophores of physiological relevance are oxyhemoglobin (OxyHb) and deoxyhemoglobin (DeoxyHb). When measured by HT, these chromophores delineate local oxygen delivery and extraction within the tissue microvasculature. With ischemia, such as in cases of limb ischemia or shock, the spatial composition of OxyHb and DeoxyHb varies across the skin, presenting a mottled appearance. This explains the inherent variability and unreliability seen in tissue oximetry when measured at a single site. Understandably, tissue undergoing wound healing also presents varying oxygenation status, depending on where the measurement is taken relative to the wound. This makes point measurements poor indicators of the wound healing process. HT enables the efficient collection of data from over a million points, producing a 2-dimensional map of the state of tissue oxygenation, essential to assess “oxygen anatomy”.
Oxygen anatomy mapping of tissue has been used by clinicians in evaluating pathogenic conditions of localized microcirculation, irritant-induced inflammation, ischemia-reperfusion injury, optical detection of cancer, and peripheral arterial disease.
Hyperspectral Technology Cutaneous Oxygenation Monitoring (HTcOM):
Combining HT with quantitative oxygen anatomy is HTcOM.
Published studies have been done by clinicians regarding:
- Published studies on HTcOM demonstrated HTcOM predicts wound healing in diabetic foot ulcers from images collected at a single patient measurement.
- Published studies on HTcOM demonstrated HTcOM accurately predicts viability and survival of tissue deprived of adequate perfusion and can differentiate ischemic tissue from normal tissue.
- Published studies on HTcOM demonstrated HTcOM has been used to reveal otherwise unobservable pathophysiology.
HTcOM delivers a map of hemoglobin oxygenation status with 100 micron resolution. Hemoglobin oxygenation maps provide information to the physician about oxygen delivery to and oxygen extraction from tissue in an anatomically relevant fashion. The combination of spectral and spatial information provided by HTcOM offers otherwise unavailable information about local tissue physiology and metabolism that may be useful in the assessment of local wounds or adequacy of regional blood flow superimposed on the systemic microvascular status.