Impact of iodinated contrast medium on dual-layer dual-energy ct ability to characterise calcium urinary calculi: A phantom study

INTRODUCTION: Dual-layer detector-based spectral CT (DL DECT) analysis is shown to reliably determine the chemical composition of urinary calculi, differentiating between uric and non-uric acid calculi in phantom studies. The aim of this study is to investigate the influence of iodinated contrast on the ability of DL DECT to correctly characterise calcium urinary calculi as not containing uric acid. METHODS: Three calcium phosphate urinary calculi of varying size were suspended in solutions composed of different ratios of gelatine, water and iodinated contrast media exhibiting specific iodine-induced attenuation and placed in the centre of a body equivalent phantom. DL DECT scans were acquired with conventional and virtual non-contrast imaging data sets reconstructed. Mean attenuation and iodine concentration within the gelatine mixture and mean attenuation and atomic number of each calculus was recorded. Statistical analysis was performed using a linear regression mixed effects model. RESULTS: A ten unit increase in density (HU) of the gelatine surrounding the urinary calculi resulted in an increase in the effective Z of the urinary calculi of 0.04 units (95% CI 0.03-0.04, p < 0.00). At none of the concentrations of surrounding contrast media was uric acid incorrectly measured in any of the calculi. Iodine subtraction and iodine concentration measurements became biased above 500 HU. CONCLUSION: Despite the effective Z values for the calculi becoming less accurate as the density of surrounding iodine increased, all calculi were visualised on vNC imaging, and all calculi were correctly categorised as non-uric acid. IMPLICATION OF PRACTISE: This study demonstrates the usefulness of DL DECT spectral analysis specifically for imaging of the urinary system. Helping to inform and guide radiographers' selection of spectral CT data reconstruction tools in clinical practice.