Optimized Bolus Threshold for Dual-Energy CT Angiography with Monoenergetic Images: A Randomized Clinical Trial

Abstract

C T angiography (CTA) has been widely used for a broad range of indications: evaluation of aortic vascular anatomy and disease condition (1), therapy planning for endovascular aortic aneurysm repair and transcatheter aortic valve implantation (2,3), and follow-up after endovascular aortic aneurysm repair (4). Surveillance imaging with CTA after endovascular aortic aneurysm repair is routinely recommended in detecting potential complications such as endoleak (5). Patients undergoing endovascular aortic aneurysm repair often have associated medical comorbidities including varying degrees of renal dysfunction. Intravenous iodinated contrast agent administration for CTA often poses the risk for contrast agent-associated acute renal injury, which is related to the iodine load (6,7).Virtual monochromatic images (VMIs) generated from a dual-energy CT (DECT) acquisition have been reported to enable lower iodine load in several studies (8-10). VMIs at lower energy levels show increased CT numbers because of approximation of the energy level closer to the k-edge of iodine at 33 keV (11). DECT angiography (DECTA) with reduced iodine dose (24 g) provided up to 185% higher CT attenuation and 25% higher contrast-to-noise ratio at low-energy VMIs compared with conventional single-energy CTA (SECTA) at 120 kVp by using a standard iodine dose (33.3 g) ( 9). Studies investigating DECTA commonly use a threshold of 100 HU for triggering scanning with the bolus-tracking technique (9,12-14), a threshold adapted from traditional single-energy CT Background: The bolus-tracking technique from single-energy CT has been applied to dual-energy CT (DECT) without optimization or validation. Further optimization is imperative because of a paucity of literature and differences in the attenuation profile of virtual monoenergetic images (VMIs).Purpose: To determine the optimal trigger threshold with bolus-tracking technique for DECT angiography (DECTA) in a phantom study and assess the feasibility of an optimized threshold for bolus-tracking technique in DECTA at 40 keV with a 50% reduced iodine dose in human participants. Materials and Methods:A phantom study with rapid kilovoltage-switching DECT was performed to determine the optimal threshold for each kiloelectron-volt VMI. In a prospective study, consecutive participants who underwent whole-body CT angiography (CTA) from August 2018 to July 2019 were randomized into three groups: single-energy CTA (SECTA) with standard iodine dose (600 mg of iodine per kilogram), DECTA with 50% reduced iodine dose (300 mg of iodine per kilogram) by using a conventional threshold, and DECTA with 300 mg of iodine per kilogram by using an optimized threshold. A trigger threshold of 100 HU at 120 kVp was used as a reference for comparison. Injected iodine doses and aortic CT numbers were compared among the three groups using Kruskal-Wallis test.Results: Ninety-six participants (mean age 6 standard deviation, 72 years 6 9; 80 men) were evaluated (32 participants in each group). The optimized threshold for VMIs at ...

Virtual Monoenergetic Imaging of Lower Extremities Using Dual-Energy CT Angiography in Patients with Diabetes Mellitus

“…Through the post-processing of raw data obtained from high-and low-energy radiation beams, low-keV VMI images (40-75 keV) close to the iodine K-edge (33.17 keV) improve image contrast and iodine signal. In this context, studies have demonstrated that the VMI+ reconstruction algorithm provides the best image contrast with the least possible image noise in low-keV reconstructions, potentially leading to a reduction in contrast medium dose [10][11][12][13].…”