Methodology development and evaluation of optical properties characterisation of small size tissue samples

Abstract

Optical imaging modalities are non-ionizing methods with significant potential for noninvasive, portable, and cost-effective medical diagnostics and treatments. The design of critical parameters of an optical imaging system depends on a thorough understanding of optical properties of the biological tissue within the purposed application. Integrating sphere technique combined with inverse adding doubling algorithm has been widely used for determination of biological tissue ex vivo. It has been studied for tissues typically with a large sample size (approx. 20 x 20 mm) and over a spectral range of 400 nm to 1100 nm. The aim of this study is to develop a methodology for calculating optical absorption µ a and reduced scattering µ ′ s of small size (approx. 6 x 8 mm) biological tissues from reflectance and transmittance measurements at a wide spectral range of 400 to 1800 nm. We developed a small sample adaptor kit to allow integrating sphere measurements of samples with small sizes using a commercial device. Dual beam single integrating sphere technique was used to the total transmittance (T total ) and total reflectance (R total ) measurements of samples, and inverse adding doubling (IAD) was used to convert the measurements T total and R total to optical properties. We proposed a two-tier IAD algorithm to mitigate the profound cross-talk effect in reduced scattering using IAD. We evaluated the two-tier IAD with both simulated data by Monte Carlo Simulation and data obtained from phantom experiments. We also investigated the accuracy the proposed work flow of using small sample kit and condensed incident light beam. We found that the small sample measurements despite with condense beam size led to overestimated absorption coefficient across the whole wavelength range while the spectrum shape well preserved. Our proposed method of a two-tier IAD and small sample kit could be a useful and reliable tool to characterise optical properties of biological tissue ex vivo particularly when only small size samples are available.

Development of a platform for broadband, spectra-fitted, tissue optical phantoms

“…To address this, we utilized the two-stage IAD process as proposed by Xie et al for all of our measurements. 31,32 The first stage of this process is to run IAD as previously described. The second stage takes the resulting reduced scattering coefficient and fits it to a Mie-Rayleigh power law equation.…”