Quantitative and qualitative optimisation of dosimetry in computed tomography explorations of the temporal bone using two iterative reconstruction algorithms

Abstract

Purpose: Iterative reconstruction (IR) has recently demonstrated its ability to reduce the dose of X-rays used in the exploration of several anatomical regions. However, there is no study involving a qualitative and quantitative comparison of the various IRs available for exploring the temporal bone. The aim of this study is to analyse two IR algorithms (ASiR®, statistical iterative reconstruction and SAFIRE®, model based iterative reconstruction). Methods: Using a Catphan® phantom, we studied the quantitative relationship of the contrast on noise/CDTIvol/IR. We verified the absence of a reduction in spatial resolution during the use of IRs by measuring MTF50%. Based on these data we acquired a series of images on an anthropomorphic phantom with an authentic human temporal bone for each level of iteration; the purpose of this was to evaluate them qualitatively. The CDTIvol of temporal bone IRs was adjusted based on the measurements taken with the Catphan phantom in order to acquire images with a constant CNR. Results: The resulting measurements demonstrated a reduction in noise without a loss of spatial resolution in the two manufacturers' systems. The quantitative study by four radiologists allowed us to optimise CDTIvol and the level of iteration. This optimisation made it possible to reduce the dose in the two manufacturers' systems, and the most effective of these algorithms enabled a reduction in CDTIvol of 64.6% during explorations of the temporal bone. Conclusion: The two analysed iterative reconstruction algorithms responded well to the objectives of dose reduction in the exploration of the temporal bone.