Air-jet based optical coherence elastography of brain tumor tissue: stiffness evaluation by structural histological analysis

The long-term aim of this project is to establish optical coherence elastography for tumor delineation in the field of
neurosurgery. Because of the challenging highly viscoelastic properties of brain tissue, we developed a new Air-Jet based
excitation source. With pulse duration of up to 700 ms and real time force measurement, this novel system allows the
sample to reach a semi-steady state. In parallel with a 3.2 MHz Swept-Source Optical Coherence Tomography system over
800 line scans are acquired over the whole sample excitation process. The phase data is extracted, unwrapped and the
displacement per pixel is calculated. This system enables the measurement of mechanical properties like stiffness and
Young’s modulus, similar to the standard indentation measurement. As well as viscoelastic properties i.e. relaxation times,
in non-contact. The first processing step is to split the excitation progression into three main time ranges: the high dynamic,
the steady state, and the viscoelastic range. In each range typical features of the displacement curve are extracted for every
pixel in the B-scan. For those features, various mechanical parameters are calculated mainly, the stiffness and Young’s
modulus and stored as feature matrices. The results are processed, visualized and overlaid with either the OCT intensity
image or the histological sections. Strain stress curves are generated for some selected positions in the B-scan leading to a
specific viscoelastic hysteresis. The feature matrices will be utilized as a fingerprint for each tissue, and are the first step
for an AI based classification of the tissue.