Impact of iodine concentration and scan parameters on image quality, contrast enhancement and radiation dose in thoracic CT

Abstract

<jats:title>Abstract</jats:title> <jats:sec> <jats:title>Background</jats:title> <jats:p>We investigated the impact of varying contrast medium (CM) densities and x-ray tube potentials on contrast enhancement (CE), image quality and radiation dose in thoracic computed tomography (CT) using two different scanning techniques.</jats:p> </jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Seven plastic tubes containing seven different CM densities ranging from of 0 to 600?HU were positioned inside a commercial chest phantom with padding, representing three different patient sizes. Helical scans of the phantom in single-source mode were obtained with varying tube potentials from 70 to 140?kVp. A constant volume CT dose index (CTDIvol) depending on phantom size and automatic dose modulation was tested. CE (HU) and image quality (contrast-to-noise ratio, CNR) were measured for all combinations of CM density and tube potential. A reference threshold of CE and kVp was defined as = 200?HU and 120?kVp.</jats:p> </jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>For the medium-sized phantom, with a specific CE of 100–600?HU, the diagnostic CE (200 HU) at 70?kVp was ~ 90% higher than at 120?kVp, for both scan techniques (<jats:italic>p</jats:italic> &lt; 0.001). Changes in CM density/specific HU together with lower kVp resulted in significantly higher CE and CNR (<jats:italic>p</jats:italic> &lt; 0.001). When changing only the kVp, no statistically significant differences were observed in CE or CNR (<jats:italic>p</jats:italic> = 0.094), using both dose modulation and constant CTDIvol.</jats:p> </jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>For thoracic CT, diagnostic CE (= 200?HU) and maintained CNR were achieved by using lower CM density in combination with lower tube potential (&lt; 120?kVp), independently of phantom size.</jats:p> </jats:sec>