Comparison of time- and angular-domain scatter rejection in mesoscopic optical projection tomography: a simulation study

Abstract

Optical imaging offers exquisite sensitivity and resolution for assessing biological tissue in microscopy applications; however, for samples that are greater than a few hundred microns in thickness (such as whole tissue biopsies), spatial resolution is substantially limited by the effects of light scattering. To improve resolution, time-and angular-domain methods have been developed to reject detection of highly scattered light. This work utilizes a modified version of a commonly used Monte Carlo light propagation software package (MCML) to present the first comparison of time-and angular-domain improvements in spatial resolution with respect to varying sample thickness and optical properties (absorption and scattering). Specific comparisons were made at various tissue thicknesses (1-6 mm) assuming either typical (average) soft tissue scattering properties, μ s ' = 10 cm −1 , or low scattering properties, μ s ' = 3.4 cm −1 , as measured in lymph nodes.

Angular restriction fluorescence optical projection tomography to localize micrometastases in lymph nodes

“…Fat, which had intermediate scattering properties, therefore showed improvements between that of lymph nodes and muscle. These findings support the conclusions of the previous simulation study 26 in that angle restriction is an appropriate scatter rejection method specifically for lymph node applications because of its mesoscopic size and low scattering optical properties. While the resolution is obviously not sufficient to localize the 200-μm inclusions from these single projections, based on the aforementioned simulation, 27 it is expected that, upon tomography and reconstruction, they would be detected and localized with ease.…”

“…Specifically, for objects with the size and optical properties of lymph nodes, it has been demonstrated, in absorption-based OPT simulation study, that angular restriction with a numerical aperture (NA) = 0.005 is sufficient to detect and localize 0.2mm-diameter objects. 26 While small NA is common in standard OPT to maximize depth of field, the level required for scatter rejection as demonstrated in the aforementioned study is an order of magnitude lower than what is typically used. Using the time-resolved lymph node transmittance optical property measurements and OPT system optimization (e.g., NA and associated optical components) with Monte Carlo simulation in the work done by Sinha et al, 26 study was conducted where it was demonstrated that up to 100% detectability and 95% localization of 0.2-mm micrometastases in 10-mm-diameter nodes could be achieved with FBP reconstruction.…”

“…26 While small NA is common in standard OPT to maximize depth of field, the level required for scatter rejection as demonstrated in the aforementioned study is an order of magnitude lower than what is typically used. Using the time-resolved lymph node transmittance optical property measurements and OPT system optimization (e.g., NA and associated optical components) with Monte Carlo simulation in the work done by Sinha et al, 26 study was conducted where it was demonstrated that up to 100% detectability and 95% localization of 0.2-mm micrometastases in 10-mm-diameter nodes could be achieved with FBP reconstruction. 27 These predictions were generated from a system configuration with expanded beam illumination, no time restriction, a detection NA ¼ 0.005, and clinically feasible levels of fluorescence contrast (100 nM); therefore, verifying the potential for implementation of a simple, low-cost, and relatively quick system with the ability to detect and localize the smallest clinically significant metastases.…”

“…at 780 nm26 ). Reported values for piglet muscle are μ s ¼ 239 cm −1 , g ¼ 0.732, μ 0 s ¼ 62.1 cm −1 and μ s ¼ 179 cm −1 , g ¼ 0.858, μ 0 s ¼ 24.7 cm −1 measured at 630 and 632.8 nm, respectively.…”

Challenges and advances in optical 3D mesoscale imaging

“…As well as allowing comparison between instruments and enabling the standardisation of best practice, 112 phantoms facilitate the assessment of novel or more complex experimental setups by allowing a robust assessment of any effects on image quality and quantification (for example, multiple animal scanning in preclinical studies) 113 . Consequently, reconstruction algorithms used for OPT are also discussed that include scattering 106,114,115 …”