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
Our colleague Kazuhiro Kurokawa reported in vivo imaging of choriocapillaris by using Doppler optical coherence tomography (Doppler OCT) equipped with adaptive optics (AO) retinal scanner. Doppler OCT have been long time utilized for the investigation of retinal vasculature. Despite of its high ability for the visualization of vasculature, it was not possible to visualize choriocapillaris mainly because of its very small dimensions. We overcame this issue by using a custom made AO retinal scanner.
The details are presented in our recent paper in Optics Express.
>> Full length article (open access)
Citation: K. Kurokawa, K. Sasaki, S. Makita, Y.-J. Hong, and Y. Yasuno, "Three-dimensional retinal and choroidal capillary imaging by power Doppler optical coherence angiography with adaptive optics," Opt. Express 20, 22796-22812 (2012).
Our colleague Masahiro Yamanari recently reported a new method for noninvasive assessment of scleral biomechanics. The biomechanics of sclera is supported by its micro-structure that is mainly formed by collagen fibers. Since the collagen fibers is known to have strong form birefringence, we may be able to assess the biomechanics by measuring the birefringence. Yamanari demonstrated significant correlation between the scleral mechanical stiffness and its birefringence which was measured by a polarization sensitive optical coherence tomography.
You can find more details in our article on PLoS ONE.
Our colleague Masahiro Miura from Tokyo Medical University recently reported our first trial of quantification of choroidal blood flow. He utilized a custom made Doppler optical coherence tomography with a probe beam at 1.0-um band. The Doppler signal at the choroid was further processed with a structural structural information of the vessel. Finally an absolute velocities of choroidal blood flow in in vivo human eyes were presented.
The details are presented in a recent issue of Investigative Ophthalmology and Visual Science.
Citation: M. Miura, S. Makita, T. Iwasaki, Y. Yasuno, "An approach to measure blood flow in single choroidal vessel using Doppler optical coherence tomography," Invest. Ophthalmol. Vis. Sci.53, 7137-7141 (2012).
Yasuno recently released a short instruction article of a step-by-step method to write a scientific paper. This article was originally written to teach his students the way of scientific writing. In this instruction, he discusses a purpose of scientific writing and a detailed way to construct a logic of the paper.
The instruction is distributed under a Creative Commons Attribution No Derivatives 3.0 License (CC BY-ND 3.0), and hence you can freely read it, use it for your teaching, and also can distributed. Although you don't need to obtain any permission to use/re-distribute this document, any criticism and positive feedback are also welcome.
Non-invasive and three-dimensional angiography of choroid with several blood-velocity range is available now. Our colleague Franck Jaillon recently published the details of this methodology in Optics Express. In this paper he demonstrated non-invasive visualization of fine vasculature of the choroid of normal eyes. This technology is based on Doppler optical coherence tomography, and hence it is totally noninvasive and three-dimensional. The Doppler detection is performed with our original dual beam scan Doppler scheme, which provides extremely high Doppler sensitivity. In addition, this system uses a 1-um probe beam, it provides deep penetration into the choroid.
The details are described in the following paper.
>> Full length article on Journal web-site (open access)
Citation: F. Jaillon, S. Makita, Y. Yasuno, "Variable velocity range imaging of the choroid with dual-beam optical coherence angiography," Opt. Express20, 385-396 (2012).