Infrared and Raman Spectroscopy and Imaging of Breast Cancer - Vibrational Spectroscopy for Tissue Analysis - page 137

Each sample has an infrared image consisting of 64 × 64 = 4096 spectra over
the wavelength range 900-4000 cm −1 . The spectra were originally recorded
in absorbance mode, that is,

A = −log10( R )

where R is the reflectance relative to a gold background. This transforma-
tion may not be correct for specular reflectance spectra; therefore, transform
these back to reflectance mode. One transformation that can be useful is the
Kramers-Krönig transform (KKT). This calculates the imaginary part of the
refractive index, which can be compared more easily to absorbance spectra.
Spectra of the three grades of IDC samples are presented in Figure 5.19,
measured in three ways. The reflectance and reflectance-KKT spectra were
obtained by choosing a sample of the appropriate type and taking the aver-
age of all its spectra. A number of points of comparison can be made:

• There are differences between the three grades of cancer in the ATR
spectra and these differences are reproducible. The full dataset from
that paper would probably be amenable to quite a straightforward
statistical classification analysis, and would be large enough to pro-
vide reasonable validation.

Re ectance-KKT

G3
G2

G1

Reectance

G3

G2

G1

ATR

G3

G2

G1

1000 1500 2000 2500

Wavenumber/cm -1

3000 3500 4000

Figure 5.19 (See colour insert.)
Spectra of three grades of IDC samples.