Tomographic reconstruction with non-uniform optical transfer functions (OTF) and an additive SMART approach

Abstract

A new approach to the weighting function, which describes particle imaging in the reconstruction process of tomographic PIV, is introduced. Instead of assuming a spatially homogeneous mapping function of a voxel to the images, a variable optical transfer function (OTF) is applied. By this method, the effects of optical distortions, introduced during the recording process, can be reduced considerably. The most common distortions of particle imaging are blurring due to a small depth of field and astigmatisms due to imaging optics. The effect of both of these distortions on reconstruction and correlation quality is investigated via simulated data. In both cases, a strong influence on relevant parameters can be seen. Reconstructions using a spatially varying OTF, calibrated to the imaging conditions, show a significant improvement in reconstruction quality, correlation quality and accuracy of the particle peak position. First results on experimental data show a reduction in ghost intensity compared to other approaches. Spatially varying particle imaging is present in nearly all experimental setups to a certain degree. Therefore, the proposed method should yield better results in nearly all applications of tomographic PIV.