Comparing Arterial- and Venous-Phase Acquisition for Optimization of Virtual Noncontrast Images From Dual-Energy Computed Tomography Angiography

Abstract

BackgroundFollow-up with computed tomographic angiography is recommended after endovascular aneurysm repair, exposing patients to significant levels of radiation and iodine contrast medium. Dual-energy computed tomography allows virtual noncontrast (VNC) images to be reconstructed from contrast-enhanced images using a software algorithm. If the VNC images are a good-enough approximation of true noncontrast (TNC) images, a reduction in radiation dose can be ensured through omitting a TNC scan.PurposeTo compare image quality of VNC images reconstructed from arterial phase and venous phase dual-energy computed tomographic angiography to TNC images and to assess which one is more suitable to replace TNC images.MethodsSixty-three consecutive patients were examined using a dual-energy computed tomography as elective follow-up after endovascular aneurysm repair. The examination protocol included 1 unenhanced and 2 contrast-enhanced scans (80 kV/Sn140 kV) of the aorta. Virtual noncontrast data sets were reconstructed from the arterial (A-VNC) and venous (V-VNC) phase scans, respectively. Mean attenuation and image noise were measured for TNC, A-VNC, and V-VNC images within regions of interest at 2 levels in the aorta, the liver, retroperitoneal fat, and psoas muscle. Subjective image quality was assessed on a 4-point scale by 2 blinded readers.ResultsThe differences between A-VNC and TNC, and between A-VNC and V-VNC, were substantial aorta at the level of diaphragm and aorta at the level of renal arteries. The difference between V-VNC and TNC was, on the other hand, very small and not statistically significant for the renal artery aorta. For liver, fat, and muscle tissue, there were significant differences between both A-VNC and V-VNC compared with TNC, but findings were similar between A-VNC and V-VNC.ConclusionsVirtual noncontrast images based on venous-phase scans appear to be a more accurate representation of TNC scans than VNC images based on arterial-phase scans.

Virtual Noncontrast Abdominal Imaging with Photon-counting Detector CT

“…We found inferior subjective image quality of VNC compared with TNC images. This is in line with the findings of Lehti et al (36), who reported higher subjective image quality of TNC compared with VNC images acquired with EID CT. Overall, in our study, the subjective image quality, image noise, and noise texture of VNC images reconstructed from arterial and portal venous phase CT were still rated as "good" by both readers.…”

Virtual Non-Contrast Reconstructions of Photon-Counting Detector CT Angiography Datasets as Substitutes for True Non-Contrast Acquisitions in Patients after EVAR—Performance of a Novel Calcium-Preserving Reconstruction Algorithm

“…Based on dual-energy information, the iodine-containing contrast material can be quantified and subtracted, resulting in a 'virtual non-contrast' (VNC) series. In theory, these could be used as a substitute for a prior 'true non-contrast' (TNC) acquisition [1,7]; in practice, however, studies reported diverging results [8][9][10][11][12][13][14]. Therefore, initial non-contrast scans are still widely performed in this clinical context [3].…”

Comparison between Conventional Unenhanced and Virtual Unenhanced Imaging of Hepatopancreaticobiliary System with Third-Generation Dual-Source Dual-Energy CT—An Observational Study

“…However, in a study done by Lehti et al, they have concluded that PVU images are superior than AVU images and better approximate noncontrast unenhanced (NCU) images. 21 The possible reasons could be that their study was done in second-generation, dual-source CT and they have started their arterial phase acquisition earlier compared with our scans. Complete separation of iodine signal is possible in third-generation, dual-source CT because of its advanced hardware and software applications.…”