  Optical coherence tomography (OCT) uses low-coherence reflectometry to obtain
cross-sectional images of inhomogeneous media, such as biological tissue. OCT
is particularly useful in the biomedical ea, since the imaging can be performed
non-invasively, and in a relatively short time. As such, OCT is not only used
in research, but has proven to be effective in clinical practice, with the
fields of its application continuing to grow. In OCT, essentially, the
reflectance of each cross-section along the depth direction is obtained with
high spatial resolution ($\bm {\sim10\,\mu}$m), revealing the structure of the
sample. We have developed a system that combines OCT with thermal fluctuation
measurements, which extracts physical properties, such as the viscoelastic
characteristics, of each cross-section in the depth direction. We demonstrate
the efficacy of this system using various samples. Furthermore, the noise is
reduced to below shot-noise levels using averaged correlations, making it
possible to extract spectral information otherwise unobtainable. The
measurement system can in principle lead to tissue characterization and
pathological diagnosis.
