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Page 2 of 12 Hallock. Plast Aesthet Res 2019;6:29 I http://dx.doi.org/10.20517/2347-9264.2019.029

Conclusion: Smartphone thermography is an inexpensive and expeditious means for identification of “hot spots” that
correlate with perforators that would suffice to insure perfusion to a free perforator flap. However, since perforator
caliber and course cannot be determined, this should be considered to be only a complementary adjunct for conventional
methods. Nevertheless, its simplicity will overall improve the safer design, harvest, and subsequent monitoring of free
flaps.

Keywords: Smartphone, thermography, thermal image camera, perforator free flap, microvascular tissue transfer, monitor

INTRODUCTION
Thermal imaging is in reality not an esoteric principle of physics that should be feared, as multiple roles are
already commonplace as this is the basis for night vision utilized by the military, or in civilian life a means to
detect heat loss sources from construction sites or something as prevalent in the hospital setting as preexisting
[1]
[2]
deep-tissue pressure injuries . It is amazing that more than 30 years ago, Theuvenet et al. actually applied
this concept for assessment of perforator arteries of fasciocutaneous and musculocutaneous flaps! How this
is possible is the intriguing aspect, and requires some understanding of human biophysiology, particularly
as regards our homeostatic mechanisms for maintaining body temperature equilibrium.

Many factors actively influence skin temperature; however, assuming all else is constant, the principal
[3,4]
mechanism for heat dissipation is via radiative heat loss from the skin to the environment . The medium
used to transport heat throughout the body is blood circulation, thus a good correlation exists between
[3]
the given skin temperature and the quality of its skin perfusion . From a basic physics standpoint, what is
perceived as heat loss by the body is really infrared radiation whose wavelength falls within the non-visible
[5]
range (700-1 mm) within the electromagnetic spectrum . The quantity of infrared radiation that is emitted
will be manifested by increments in alterations of the skin temperature observed, and this is directly
[5,6]
correlated to variations in the cutaneous blood flow .

A thermal imaging camera will be essential for the desired analysis of the given cutaneous infrared
emission, and more importantly variations in flap perfusion. Muntean et al. correctly pointed out that
[7]
professional cameras are superior in their ability to do this, as these can pick-up temperature differences
[8]
of as little as 0.04 °C that can be modulated by the cardiac rhythm itself ! Such diminutive variations will
allow detection of skin “hot spots”, where greater heat is being emitted and most likely via a dominant
perforator, as well as the degree of thermal extension into the surrounding vascular network so served,
which today we might call the perforasome of that perforator [3-6,8-10] . Unfortunately, the widespread
acquisition of this technology has been hampered by the extreme cost of these cameras.

Fortunately, however, technology has moved on, as today everyone has a smartphone. Incredibly
inexpensive miniature thermal imaging cameras [FLIR ONE Pro (FLIR Systems, Inc., Willsonville,
Oregon), FLIR.com/FLIRONE/Start] are available for ~ 1/100th the cost of a professional camera, or just
a few hundred dollars. This may be plugged into any type of smartphone. Using an app provided by the
vendor, rapid real time thermogram still images or videos can be digitally merged with the visible light
[11]
camera photograph from the smartphone . Although the smartphone provides a lower resolution image
and narrower temperature detection range than the more expensive professional cameras [10,11] , Pereira
[12]
insisted that, for applications such as for perforator flaps, the accuracy thus far has proven to be enough.

Because of the lesser sensitivity of the smartphone thermal imaging camera, an initial thermal stress or
“cold challenge” not required by the professional cameras will be more informative. This is why dynamic
infrared thermography (DIRT) is a preferred adjunct [3-5,13,14] . DIRT is simplest done preoperatively using
Muntean’s method of spraying the proposed flap donor site with isopropyl alcohol followed by accelerated