Tissue preparation
Skin 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) which avoids thermal
denaturation of dermal collagen. The dermal sample was frozen.
The dermis was cut two different ways: (1) with a cold dermatome
to yield dermal sections 200-400 microns in thickness and (2)
with a freezing microtome to obtain 20 micron thick samples from
6 millimeter diameter punch biopsies. Both the dermatome and
the freezing microtome made cuts parallel to the surface of the
dermis. Dermatome specimens from five subjects were studied
with nine measurements at different sites on each specimen.
To obtain different very thin sample thicknesses, several 20
micron sections were stacked to obtain 40, 60, 80, and 100 micron
samples. Freezing microtome specimens from four subjects were
studied: twenty-six 20 micron samples, nine 40 micron samples,
four 60 micron samples, four 80 micron samples, and ten 100 micron
samples. All samples were soaked in saline prior to measurements
to ensure standardized 85% hydrated dermis. All samples were
sandwiched between glass microscope slides.
Tissue samples were placed in the center of the tank with the
front surface oriented perpendicular to the incident beam. Before
each experiment the total beam power was measured. The detector
was aligned so that 0
corresponded to an on-axis measurement.
An initial on-axis measurement was made. The detector was moved
in 1.8
steps clockwise around the sample until it reached
the on-axis (co-linear) position again. It was found that for
all samples the reproducibility of an entire scan was excellent
if the sample was not moved between scans. When the beam was
moved to a different location on the sample there was often a
substantial change in the measured distribution. This was especially
true of thin tissue sections or thick sections that were not
uniform in thickness. Nine scans were made on each sample to
assess this variability.
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