Biomedical Engineering Reference
In-Depth Information
HAP, COHAP and COD were measured through slabs of varying thick-
ness from 2 to 10.2 mm of normal chicken breast tissue, and chicken breast
with chicken skin on the surface. Chicken breast and skin tissue were used in
the model due to their spectrally homogenous nature. Normal fresh chicken
breast was obtained and a small section cut varying thicknesses between 2 and
10.2 mm (2.0, 3.1, 5.0, 5.9, 8.7, 10.2 mm) with other dimensions approximately
20
20 mm. A small section of skin tissue was also cut (to 1.1 mm thick).
The samples were stored in a refrigerator and warmed to room temperature
before use.
The SORS experimental setup is described in detail elsewhere [111]
(Fig. 3.3, Chap. 3 shows a schematic). In brief, 60 mW of laser light at 827 nm
was incident on the sample surface into a 0.6 mm spot. The spectra collected
from the outer ring of fibres of the SORS fibre probe [111], i.e. at 3 mm spatial
offset, were used throughout the data analysis for this study. All spectra were
background subtracted and pre-processed with a seven-point Savitzky-Golay
smooth. At each depth measured, the calcification spectra were recovered by
obtaining the difference between the spectra obtained from the slab of tissue
over a calcification standard and the spectrum from the slab of tissue without.
Discrimination between spectra of different calcification types with SORS at
8.7 mm depth was demonstrated to be trivial leading to the possibility of per-
forming this study with lower calcification concentrations or through another
few millimetres of tissue [112].
×
Reverse SORS
Further recent advances by both Matousek [113] and Morris [114] have demon-
strated significant advantages to using SORS in the reverse configuration,
whereby the illumination is made in a ring offset from the central collection
point. Flexible depth selection can be achieved with adjustable spatial offsets
using an axicon lens. Furthermore, significantly greater powers of illumination
can be used safely. For example, with a central spot illumination, 60 mW in a
0.6 mm spot (as we have used) gives a power density of 18 mWmm
−
2
, whereas
illumination into a 200
m thick ring at 8 mm spatial offset at similar power
density would require 1 W of laser power. It can be seen from this that pro-
vided the tissue can manage to dissipate any total heat buildup, then signals
can be significantly increased in this configuration. This illumination could
theoretically rise to 2 W into a 15 mm offset ring and 3 W into a 22 mm offset
ring.
μ
13.5 Transmission Raman Spectroscopy (TransRaman)
for Deep Probing of Calcifications
In the transmission Raman approach, the laser beam is incident upon one side
of the probed object and the Raman light is collected from the opposite side.
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