Important to the laser based diagnosis of burn depth is an adequate understanding of the optical properties
of thermally coagulated blood. Although the optical properties of photocoagulated blood have been studied in
some detail, they are inadequate at completely characterizing the optical properties associated with the thermally
coagulated blood of burn injuries. Using a photoacoustic method involving the addition of an absorber to
thermally coagulated blood, we obtained data that will be used to derive a spectrum for the optical absorption
coefficient, a, of thermally coagulated blood within the wavelength range from 580 to 700 nm. Before implementing
this method, the stability of photoacoustic measurements within the diffusion theory realm was tested
on two weakly absorbing, highly scattering Intralipid solutions. In addition, the absorber, Chlorazol Black, was
tested for resistance to change caused by photobleaching and heating.
Early and accurate determination of burn depth is crucial to monitoring the burn wound and aiding in the
precise excision of necrotic tissue. A simplified model of a partial-thickness burn wound can be described as a
layer of necrotic dermal tissue, containing thermally coagulated blood, atop a layer of inflamed dermal tissue
characterized by the presence of viable (non-coagulated) blood. Using photoacoustic methods it is possible
to discriminate between coagulated and non-coagulated blood and, therefore, discriminate between the two
layer types. However, the effectiveness of such a photoacoustic method is limited by the thickness of the upper
coagulated layer. Sufficient laser energy must be deposited into both layers to create detectable and characteristic
signals from those layers. To determine the maximum thickness of the coagulated layer, at which the underlying
non-coagulated layer was still able to generate detectable acoustic waves, we performed a Monte Carlo simulation
on a human burn wound model with varying depths of the coagulated layer. The depths of the coagulated layer
ranged from 100 to 1,100 &mgr;m, in 100 &mgr;m increments. Our analysis concluded that burn depth measurements can
be achieved up to a burn depth of 900 &mgr;m with an incident radiant exposure of 0.255 J/cm2 at 543nm and 0.1275
J/cm2 at 633 nm.
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