Towards optical CT scanning of radiochromic 3D dosimeters in mismatched refractive index solutions

Abstract

The clinical utility of the PRESAGE® solid dosimeter is inhibited by the need for viscous, oil-based refractive index matching liquids during optical CT scan readout. Practically, it would be advantageous to work with lower viscosity, water-soluble matching fluids. The use of non-matching refractive index results in non-uniformly sampled, incomplete CT data, making standard CT filtered backprojection reconstruction infeasible. However, with iterative CT reconstruction, incomplete and non-uniformly sampled data can be used to reconstruct good quality images. Here we present a method to measure the path of primary rays through a dosimeter scanned with intentionally mismatched fluids. We present preliminary results from an experiment that mimics PRESAGE®-like refractive effects in a low viscosity surrounding liquid, using a scanning-laser CT scanner with a large area detector. We show that a uniformly attenuating object can be reconstructed to 3% accuracy within the central 80-85% of the sample in this case.