Tuesday, July 1, 2014

Publication: Accurate Quantification of Tissue Birefringence

Microstructures support the mechanical property of a tissue. And hence, investigating tissue microstructure has been a great interest both in the biomechanical research and for investigation of diseases associated with biomechanics, such as glaucoma. However, there was no way for in vivo quantification of tissue biomechanics. One promising approach, as we believe, is quantifying tissue birefringence for quantifying biomechanics. This approach is based on the fact that both the tissue biomechanics and birefringence are based on the same aspect of the tissue, i.e., microstructure. Our group has been working for polarization sensitive optical coherence tomography (PS-OCT) for the quantification of the biomechanics through quantitative measurement of tissue birefringence.

Since its innovation in 1997, PS-OCT was nice to qualitatively visualize the tissue birefringence. However, its quantification ability was low. It was mainly because its non-linear and complex effects of measurement noise into the birefringence values to be measured. To be honest, the raw birefringence value measured by PS-OCT has not been reliable at all.

Our colleagues Deepa Kasaragod recently developed a mathematical framework to accurately estimate the tissue birefringence from the raw birefringence values measured by PS-OCT. She first numerically characterized the relationship between the measurement noise and measured birefringence values. And then, she designed a mathematical frame work, by using a Bayesian rule together with the numerically obtained property, to obtain a “maximum likelihood estimation” of the tissue birefringence.

Both numerical and experimental validations proved that this framework has high ability to quantitate the birefringence. This method was recently published in Optics Express (full citation is shown below). In this paper, some in vivo human eye results including a pathologic case (anterior eye of trabeculectomy bleb) are presented.

Currently, a clinical study with this method is ongoing. I believe we can present impressive clinical results soon. The details of the technology are now available on the following paper.

Full length article (open access)
D. Kasaragod, S. Makita, S. Fukuda, S. Beheregaray, T. Oshika, and Y. Yasuno, Optics Express 22, 16472-16492 (2014), http://dx.doi.org/10.1364/OE.22.016472

Joschi, Yoshiaki Yasuno