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FEATURE
ARTICLE
Thermal Imaging
Fu Chit Yaw, Eddie Tan Khay Ming, Yang Kwang Wei
During the SARS epidemic, thermal imaging camera has become almost a household name. Just how does it work and how reliable is
it? The authors explain, and provide some suggestions for improvement.
Thermal infrared (IR) imaging is commonly used for
night vision. During the recent SARS epidemic, thermal
imaging cameras were used for fast and non-contact measurement
of a person’s temperature to determining if the
person has a fever [1]. In many medical cases, temperature
rise or abnormal distribution of temperature may
appear as one of the first symptoms. Therefore, thermal
imaging is also a useful complementary clinical tool to aid
in the diagnosis of other medical condition, most notably
breast cancer (see Ref. 2 for more details).
Let’s first explore how thermal imaging works [3]:
Figure 1: Image courtesy of Infrared, Inc.
1. The focused light is scanned by a phased array of
infrared-detector elements. The detector elements
create a very detailed temperature pattern called a
thermograph. It only takes about one-thirtieth of
a second for the detector array to obtain the temperature
information to make the thermograph.
This information is obtained from several thousand
points in the field of view of the detector array.
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2. The thermograph created by the detector elements
is translated into electric impulses.
3. The impulses are sent to a signal-processing unit,
a circuit board with a dedicated chip that translates
the information from the elements into data for the
display.
4. The signal-processing unit sends the information
to the display, where it appears as various colors depending
on the intensity of the infrared emission.
The combination of all the impulses from all of the
elements creates the image.
A thermograph of a human face, taken by one of the authors
(Joel Yang) is shown in Fig. 2 [4].
Figure 2: A thermograph of a human face take by a commercial
IR camera [courtesy Photonitech Pte Ltd., Singapore]