Gaussian Light Model in Brightfield Optical Projection Tomography

Olli Koskela,Toni Montonen,Sampsa Pursiainen,Edite Figueiras,Birhanu Belay,Jari Hyttinen

doi:10.1038/s41598-019-50469-6

Abstract

This study focuses on improving the reconstruction process of the brightfield optical projection tomography (OPT). OPT is often described as the optical equivalent of X-ray computed tomography, but based on visible light. The detection optics used to collect light in OPT focus on a certain distance and induce blurring in those features out of focus. However, the conventionally used inverse Radon transform assumes an absolute focus throughout the propagation axis. In this study, we model the focusing properties of the detection by coupling Gaussian beam model (GBM) with the Radon transform. The GBM enables the construction of a projection operator that includes modeling of the blurring caused by the light beam. We also introduce the concept of a stretched GBM (SGBM) in which the Gaussian beam is scaled in order to avoid the modeling errors related to the determination of the focal plane. Furthermore, a thresholding approach is used to compress memory usage. We tested the GBM and SGBM approaches using simulated and experimental data in mono- and multifocal modes. When compared with the traditionally used filtered backprojection algorithm, the iteratively computed reconstructions, including the Gaussian models GBM and SGBM, provided smoother images with higher contrast.

Highlights

The imaging of samples in the mesoscopic size range of few millimeters to a centimeter is important for understanding the processes of a biological system, such as embroyos, organs or organoids of a small animal
With respect to relative error measure (REM), filtered backprojection (FBP) was found to perform generally better than Gaussian beam model (GBM)
The results indicate, that the choice of cS seems to be stable as the difference between K5, K10 and K20 was quite small in simulations in terms of relative error measure (REM) and total variation error (TVE)

Summary

Introduction

The imaging of samples in the mesoscopic size range of few millimeters to a centimeter is important for understanding the processes of a biological system, such as embroyos, organs or organoids of a small animal. The X-rays that penetrate the sample are considered to be straight lines but, in contrast, the focusing objectives in the OPT detection path shape the light beam to a Gaussian bell-shaped intensity profile[23,24,25]. The Gaussian shape has a certain focal distance, and in the projection images, blurring is induced into particles depending on their distance from the focus. This blurring is further seen in a decrease of radial resolution in the reconstructions. Decreasing the effects of the Gaussian beam shape have been studied using image post-processing[2,27,28], Fourier beam propagation with regularized inversion[29], and multifocal acquisition[19,30,31,32]. Multifocal acquisition is considered and compared with the results of the GBM

Methods

Results

Discussion

Conclusion