Effect of Contrast Agent Administration on Size-Specific Dose Estimates (SSDE) Calculations based on Water Equivalent Diameter in CT Head Examinations

Abstract

Size-specific dose estimate (SSDE) is dose metrics of computed tomography, to calculate SSDE we first calculate the patient's body size. In CT head examination, the head size is better to use water-equivalent diameter (Dw), because Dw considers tissue attenuation. CT Head examination with contrast agent increased patient attenuation and increased Dw. In this study, we observed the effect of contrast agent on the Dw value on the axial image of patients with CT head examination. A total of 96 patients underwent a CT Head examination with a contrast agent in the two CT scan modalities. 46 patients underwent CT Head examination with contrast agent using CT Scanner Toshiba Alexion 16 and 50 patients underwent CT Head examination with contrast agent using CT Scanner GE Medical System Optima CT660. Dw value is calculated automatically using IndoseCT version 20b. We compared the Dw pre-contrast and Dw post-contrast values with the two independent sample t-test statistical analysis. To consider the effect of changing Dw values on SSDE we normalized dose coefficient (NDC). We did not find a significant difference between Dw pre-contrast and Dw post-contrast. The P-value statistical analysis results for the CT Scanner Toshiba Alexion 16 and the CT Scanner GE Medical System Optima CT660 were 0.65 and 0.45. The NDC change in this study was below 20%. On CT Head examination, the Dw and SSDE pre-contrast values can be used to estimate the Dw and SSDE post-contrast values.