Comparisons of Water-Equivalent Diameter Measured on Images of Abdominal Routine Computed Tomography with and without A Contrast Agent

Abstract

The size-specific dose estimate (SSDE) is a metric for an estimation of patient dose in computed tomography (CT). The SSDE strongly depends on the       water-equivalent diameter (D_W). In abdominal CT examinations, a contrast agent is sometimes used to more clearly visualize tissue lesions. The Hounsfield unit (HU) of CT images with and without the use of a contrast agent at specific areas is slightly different and it may affect the D_W value. This study aimed to compare the D_W values calculated from axial CT images in patients who had undergone routine abdominal scans both with and without the use of a contrast agent. Axial images of 144 patients with a weight range of 3.5 kg to 90 kg who had undergone routine abdominal scans both with and without the use of a contrast agent using a Siemens Sensation 64 CT scanner were retrospectively collected. The D_W values were automatically calculated using the Matlab-based IndoseCT (version 15a) software. The results show the percentage difference between D_W,contrast and D_{W,non-contrast} is below 2 %.As a result, the mean SSDE_contrast is 1.5 % smaller than SSDE_non-contrast. Due to the effect of a contrast agent on the D_W and SSDE values is below 2 %, the axial images of CT abdomen without the use of a contrast agent can be used as the accurate estimation of D_W and SSDE for images with the use of a contrast agent.