Comparative study of radiation dose and image noise between single-source fast kilo voltage peak switching technique and conventional mode on abdominal CT

Objective To investigate the radiation dose and image noise of abdominal CT with spectral imaging and conventional scan mode. Methods This was a retrospective study.The first part of this study was a phantom study.A standard quality assessment phantom was scanned with gemstone spectral imaging mode and conventional helical mode using 120 k Vp with different m As.A regression function for the m As between conventional scan mode and spectral imaging mode was obtained.According to the regression function,the m As on 120 k Vp corresponding to different gemstone spectral imaging protocol were calculated.The second part of this study was a clinical study.Twenty-two patients who underwent contrast enhanced abdominal CT scanning were included.The pre-contrast CT was scanned by a conventional mode with automatic exposure control technique.According to the m As of pre-contrast scan,corresponding spectral imaging parameters were selected for the portal venous phase of post-contrast scan.Five sets of images with 5 mm slice thickness were reconstructed,with 65 keV monochromatic image for spectral imaging and FBP,20%, 40% and 60% ASIR image for conventional imaging respectively.Image noise was measured on hepatic parenchyma and urinary bladder for each set of image.Radiation dose and image noise were compared between CT spectral imaging and conventional imaging with paired t-test. Results No significant differences were found for the CTDIvol[ (13.8±4.8) mGy versus (14.0±7.0) mGy] and DLP[ (691.1±274.2) mGy·cm versus (678.8±385.0) mGy·cm] between CT spectral imaging and conventional imaging.Monochromatic image (65 keV) by spectral imaging[ (7.6±1.4) HU for hepatic parenchyma and (9.1±1.3) HU for urinary bladder] had equal image noise with 40% ASIR[hepatic parenchyma: (7.8±0.7) HU]and 20% ASIR[urinary bladder: (9.2±1.2) HU]and lower image noise than FBP image[ (10.4±1.0) HU for hepatic parenchyma and (10.5±1.3) HU for urinary bladder]by conventional imaging. Conclusions The radiation dose of CT spectral imaging and conventional CT scan is equivalent with spectral imaging parameters appropriately selected.Monochromatic image (65 keV) by CT spectral imaging has lower image noise than FBP image,and same image noise with 40% ASIR (hepatic parenchyma) and 20% ASIR (urinary bladder) by conventional imaging. Key words: Tomography,X-ray computed; Radiation Dosage; Comparative study