Thermally induced birefringence changes in cartilage using polarization sensitive optical coherence tomography

Thermodynamic induced changes in birefringence of nasal septal cartilage following Nd:YAG laser irradiation were investigated using a polarization-sensitive optical coherence tomography (PSOCT) system. Birefringence in cartilage is due to the asymmetrical collagen fibril structure and may change if the underlying structure is disrupted due to local heat generation by absorption of laser radiation. A PSOCT instrument and an infrared imaging radiometer were used to record, respectively, depth-resolved images of the Stokes parameters of light backscattered from ex vivo porcine nasal septal cartilage and radiometric temperature changes following laser irradiation. PSOCT images of cartilage were recorded before (control), during, and after laser irradiation. From the measured Stokes parameters (I, Q, U, and V), an estimate of the relative phase retardation between two orthogonal polarizations was computed to determine birefringence in cartilage. Stokes parameter images of light backscattered from cartilage show significant changes due to laser irradiation. From our experiments we differentiate dehydration and thermal denaturation effects and observe the birefringence changes only in the dehydration effect. Therefore, a dynamic measurement of birefringence changes in cartilage using PSOCT as a feedback control methodology to monitor thermal denaturation is problematic in non-ablative surgical procedures such as laser assisted cartilage reshaping.