Infrared and Raman Spectroscopy and Imaging of Breast Cancer - Vibrational Spectroscopy for Tissue Analysis - page 132

Spectroscopic analysis

Infrared spectra were obtained using a Digilab rapid-scan FTIR spectrom-
eter Excalibur FTS 3000 with the UMA-600 infrared microscope equipped
with a liquid nitrogen-cooled MCTA detector and a mercury cadmium tel-
luride (MCT) focal plane array detector. The samples were mounted on glass
slides and collected using infrared reflectance techniques. A gold mirror was
used as a background. Spectra were collected at 8 cm −1 resolution, averaging
256 scans. A variety of techniques, such as imaging and mosaic images, were
employed for samples with areas varying from 350 × 350 µm to a maximum
area of 1.4 × 1.4 mm. The collection time for a single image was 5 minutes
with 256 scans. For the larger image at 64 scans, the mosaic was collected in
17 minutes.
The infrared spectra exhibited signs of specular reflectance, which were
indicated by restrahlen bands in the spectral region 2000-900 cm −1 . The spec-
tra were converted to percentage reflectance and the Kramers-Krönig correc-
tion applied to correct for specular reflectance.
A spectral region is defined and the shift of the centre of gravity of this peak
relative to a baseline can be imaged. In the image presented in Figure 5.17,
the red region of the image illustrates the greatest shift and the blue region
shows the minimum shift. The image in Figure 5.17 was collected using a
64 × 64 MCT focal plane array and was collected at 8 cm −1 resolution. This
technique was used for imaging all the biological tissue provided.
Strong absorption bands in the region of 1700 to 1600 cm −1 arising from C=O
vibrations of the amide groups of polypeptide chain, tend to be among the
strongest and the intensity of the carbonyl band makes the detection of this

PCA map

120
108
96
84
72
60
48
36
24
12

12 24 36 48 60 72 84 96 108 120

Figure 5.17 (See colour insert.)
Red region of the image illustrates the area that gives rise to greatest shift and the blue region
shows the minimum shift in the IR spectrum.