Comparison between conventional pre-contrast and virtual non-contrast images from IQon spectral CT

Abstract

Dual-layer CT is a dual-energy CT is technology that uses the dual layer detector to generate two different tube voltage image.  The image raw data can be reconstructed many image types, such as virtual mono-energetic image, virtual non-contrast image, etc. This study aimed to evaluate the difference in the CT number between the pre-contrast CT image or True non-contrast (TNC) and Virtual non-contrast (VNC) of the brain. The retrospective data of 35 patients who underwent CT brain without and with contrast media were collected from Philips IQon Spectral CT at Advanced Diagnostic Imaging Center. CT number values of white matter (WM) and gray matter (GM) of TNC and VNC CT images were measured at both left and right hemispheres of the frontal lobe, parietal lobe, temporal lobe, occipital lobe, and pons (WM) & cerebellum (GM) and compared with T-test (two-tailed) with the level of confidence p-value 0.05. The patient’s average and standard deviation were 65.6±7.8 years, and CTDI_vol ranged from 45.5 to 58.3 mGy. The study found that the average CT numbers at all measured positions in TNC and VNC images were 27.1±1.3 and 27.1±1.8 HU for white matter, and 34.0±1.6 and 28.9±2.6 HU for gray matter, respectively. CT numbers of white matter was no significant difference (p=0.05) and gray matter was differ significant (<0.05). Conclusions, the image contrast of white and gray matter in VNC images is inferior to TNC images. It is concluded that using the VNC image of the brain instead of the TNC image had to be particularly cautions, especially in the case of white and gray matter diagnoses. However, it may be used in the followed-up case to reduce the patient’s dose.