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can be evaluated. With a proper temperature scale, measurements
taken at different times or places can be compared. Without a ther-
mometer, it would be impossible to measure the temperature of a hu-
man with respect to a fixed scale of reference. Remember, the human
test of temperature is relative to the detector. A cold hand will indicate
a warm body surface that a warm hand will indicate as cold.
Numerous techniques and devices are employed in the measurement
of temperature. Many of these techniques, such as the use of glass
mercury thermometers or electronic display devices using thermo-
couples or thermistors, are generally understood and as a result well
accepted in clinical medical practice. All three of the devices have one
very important characteristic: they measure their own temperature, not
the temperature of the object being measured, except in an indirect
way. In order to make an accurate temperature determination using
one of these measurement techniques, it is necessary for the device to
have intimate contact with the subject for sufficient time to raise the
temperature of the thermometer to the same, or close to the same,
temperature as that of the subject. Thermal contact thermometers re-
quire too much time to equilibrate, are sensitive to variations in contact
pressure resulting in changes in the thermal resistance between the
skin and the temperature detector, and tend to have too great a varia-
tion from reading to reading. If these devices are not properly located,
properly attached, or left in place for enough time to equilibrate, they all
will give incorrect readings.
The infrared method is fundamentally different from the other methods
in that there is no temperature device to heat. Like an eye, the infrared
instrument simply looks at the heat radiation naturally emitted from the
body surface. Since there is nothing to heat, the measurement can be
made very fast, orders of magnitude faster than the probe devices.
Historically, most of the published clinical data on body surface tem-
perature measurements are based on the use of infrared thermogra-
phy. Infrared thermography has long been recognized as a reliable,
highly technical diagnostic tool, and refers to the process of recording
and interpreting variations in temperature of the surface of the skin in
color or shades of gray. The clinical information is contained in the
relative temperature profiles. The technique is effective, but the equip-
ment is complex and expensive.
Decades ago, the common image of a computer was that of an enor-
mous, very expensive piece of equipment, something requiring an en-
vironmentally controlled room and complex installation. Today’s com-
puters have been reduced to hand held units. Infrared thermography
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