Recent studies have shown potential for using polarisation sensitive optical coherence tomography (PS-OCT) to study cartilage morphology, and to be potentially used as an in vivo, non-invasive tool for detecting osteoarthritic changes. However, there has been relatively limited ability of this method to quantify the subtle changes that occur in the early stages of cartilage degeneration. An established mechanical indenting technique that has previously been used to examine the microstructural response of articular cartilage was employed to fix the bovine samples in an indented state. The samples were subject to creep loading with a constant compressive stress of 4.5 MPa and, when imaged using PS-OCT, enabled birefringent banding patterns to be observed. The magnitude of the birefringence was quantified using the birefringence coefficient (BRC) and statistical analysis revealed that PS-OCT is able to detect and quantify significant changes between healthy and early osteoarthritic cartilage (p < 0.001). This presents a novel utilization of PS-OCT for future development as an in vivo assessment tool.

We investigate changes in optical coherence tomography (OCT) images in response to evoked neural activity in the sciatic nerve of rats in vitro. M-scans were obtained on peripheral nerves of rats using a swept source polarisation sensitive OCT system, while a nerve cuff acquired electrical neural recordings. From a total of 10 subjects: three had no stimulation (controls), three had paw stimulation, and four had nerve stimulation. Changes in the OCT signal intensity, phase retardation, phase, and frequency spectra were calculated for each subject and reference samples of a mirror and microspheres in solution. Observed changes in intensity in three paw stimulation and two nerve stimulation subjects and changes in frequency spectra amplitude in two paw stimulation subjects were above the reference noise level and were temporally consistent with osmotic swelling from ion currents during neural activity. Light scattering changes produced by osmotic swelling, which have previously been characterised in squid and crab nerves, are also thought to occur in myelinated fibres on a scale which is detectable using OCT. Imaging neural activity in myelinated tissue using OCT creates new possibilities for functional imaging in the peripheral and central nervous systems.

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