Introduction: Ionizing radiation is extensively used in medicine and its contribution to both diagnosis and therapy is undisputable. The number of computed tomographic (CT) studies performed is rapidly increasing. Because CT scans involve much higher doses of radiation than plain films, there is a marked increase of radiation exposure in the general population. Epidemiologic studies shown an association between radiation exposure and increased risk of developing cancers. A patient who underwent a triphasic CT scan of the abdomen receives an average effective dose of 10. 3 mSv. In Slovenia, the average annual background radiation dose is about 2. 64 mSv, which means that a patient receives almost four times the annual radiation dose after a three-phase CT scan of the abdomen.Purpose: The purpose of this study is to compare attenuation measurements (Hounsfield units, HU) of virtual unenhanced images (VNC) with those of conventional non contrast images (NC) of abdominal tissues and to assess potential reduction in radiation dose. Methods: The study involved patients who underwent three-phase abdominal imaging at the University Clinic Golnik. Study was performed on a Somatom Drive CT scanner (Siemens Healthineers, Erlangen, Germany) using a modified protocol: the native phase and the arterial phase were acquired using conventional single-spectral imaging (helical imaging). The venous phase was acquired using dual energy imaging, where post-processing allows us to subtract iodine from a series of venous images. The images were analysed by placing a region of interest (ROI) of the same size in the same position in both the NS and VNC images. HU values were measured on liver, spleen, right kidney, left kidney, right adrenal, left adrenal, aorta, subcutaneous adipose tissue and muscle. Results: An important criterion for clinical use of VNC images is that they are comparable to non contrast images. 918 ROIs were analysed. The high accuracy of HU between NC images and VNC images was demonstrated for all tissues except subcutaneous adipose tissue. The average difference between NC and VNC image was less than 10 HU for all tissues except subcutaneous adipose tissue. Discussion and conclusion: The radiation dose could be reduced by 25.1 % by avoiding native phase and using the VNC algorithm to acquire the native images. VNC images could be alternative to NS in the future, but further research is needed. It is necessary to assess the quality of reconstructed VNC images and their diagnostic value in characterising lesions of malignant and benign origin (adenomas, cysts, metastases, bleeding).
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