Bloodless human dermis as a function of wavelength
A sample of human dermis was obtained from the abdomen at autopsy.
The epidermis was manually separated following mild thermal
treatment (two minute exposure in a 55 C water bath).
The dermal sample was soaked in saline prior to measurement
to remove residual blood. One 2 x 2 centimeter sample was cut
with a dermatome. The sample was sandwiched between glass microscope
slides and the tissue thickness (360 m) was determined with
micrometer.
A spectrophotometer (Beckman UV 5270) was used for measurements
of reflection and transmission. The sample was placed at the
entry port of the integrating sphere for measurements of total
transmission. Collimated light directly struck the sample, and
all light passing through the sample was collected by the integrating
sphere. Diffuse reflection was measured by placing the sample
in the exit port of the sphere. Specularly reflected light from
the sample travelled back along the incident beam path and was
not collected by the integrating sphere. For calibration purposes,
zero and 98% reflection were obtained by measuring the reflectance
with the sample removed and with a BaSO4 plate repectively.
Collimated transmission measurements were made by removing the
integrating sphere assembly and placing the sample in the path
of the beam. Collimated light struck the sample, but only light
propagating co-linear with the incident beam was detected. The
measurements of reflection and transmission as a function of
wavelength are presented in Figure 6.6.
The iteration algorithm was used to convert these measurements
to optical properties. These properties are shown in Figures
6.7. Both absorption and scattering coefficients decrease with
increasing wavelength. This indicates that longer wavelengths
of light penetrate deeper into a tissue. The anisotropy increases
with wavelength indicating that light scattering increases in
the forward direction.
Figure 6.6:
Total transmission, collimated transmission, and
diffuse reflection from a 360m sample of bloodless human
dermis. Transmission increase with wavelength and reflection
decreases with wavelength.
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Figure 6.7:
Optical properties of bloodless human dermis as a
function of wavelength.
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![\includegraphics [scale=0.907]{fig66.eps}](img569.gif)
![\includegraphics [scale=0.907]{fig67.eps}](img570.gif)