Hyperspectral Technology
Hyperspectral technology (HT) provides a method
to generate a “gradient map” of a region of interest
based on local chemical composition (Figure 1). Hyper-spectral
technology 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.
Figure 1: Hyperspectral Technology Concept
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- and deoxy-Hb to estimate tissue 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 and 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. |
Figure 2: Hypercube
|
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 is a compelling application
of HT that includes pathologic conditions of localized microcirculation,
irritant-induced inflammation, ischemia-reperfusion injury, optical
detection of cancer, and peripheral arterial disease.
Combining HT with quantitative oxygen anatomy is HTcOM, with
medical applications developed over the past 10 years by HyperMed,
Inc.
- HTcOM predicts wound healing in diabetic foot ulcers from
images collected at a single patient measurement.
- 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 can be useful in the assessment of local wounds or adequacy
of regional blood flow superimposed on the systemic microvascular
status. |
