Phase-Sensitive Optical Coherence Microscopy (OCM) - Biomedical Optical Phase Microscopy and Nanoscopy - page 260

Together they achieved a three-dimensional (3D) resolution of 3 m. The

OCM system included a spectrometer, consisting of a transmissive grating and two-line CMOS
detector. The light source used is a bandpass-filtered ultrafast Ti:sapphire laser, with 160 nm
bandwidth and central wavelength of 800 nm. The line acquisition rate was 167 kHz.

μ m 3 3 μ m 3 3 μ

13.4.2 Determining Elastic Properties of Skin

The mechanical properties of the skin are an important tissue parameter used in the study of
skin pathophysiology. Most skin pathologies result in changes to their elastic properties and/or
thickness. Therefore, the evaluation of the elastic properties of skin tissues is important for the
early diagnosis and the treatment of many skin diseases. One such use of this parameter is in
the detection of skin cancer, which has a different stiffness than the surrounding healthy skin.

The method described in Ref. [16] combines the use of an impulse-stimulated surface wave
with a phase-sensitive OCM system to evaluate the mechanical properties of skin. In this
study, an inexpensive homemade shaker was used to generate physical impulse stimulations,
which produced surface waves. The shaker head needs to be in contact with the sample
surface in order to generate the surface waves. The Young's modulus can be deduced from
measuring the behavior of these waves using the phase OCM system. Measurements were
performed in tissue-mimicking phantoms and human skin in vivo. Phantoms were made out
of different concentrations of agar solution and with different layer thickness to simulate
similar elastic properties of skin. Dispersion phase-velocity curves were calculated to obtain
the elastic properties from layers with different mechanical properties.

The shaker applied a tissue displacement of approximately 100 nm in the axial direction
and produced frequencies of approximately 10 kHz.

The phase OCM imaging system was based on a Michelson interferometer and used a
superluminescent diode with 1310 nm central wavelength and 46 nm bandwidth. It provided
an axial resolution of approximately 15 mm in air and 10 mm within the skin (assuming the
refractive index (RI) is approximately 1.4). The focal length of the objective lens was
approximately 50 mm and provided a transverse resolution of approximately 18 mm. The
interference pattern recorded with a spectrometer with a maximum acquisition rate of
approximately 47 kHz.

For the measurements, seven single and double-layer agar agar phantoms were used to

simulate soft tissues. In addition, in vivo experiments were carried out on five healthy
human volunteers with an age span between 25 and 45 years old. Measurements were
obtained from two skin sites, the forearm and the palm.

Phase and amplitude measurements results from an agar sample are shown in Figure 13.6 .
To determine the system noise, data were collected from the phase surface with no sample