Computed Tomography Angiography of the Aorta—Optimization of Automatic Tube Voltage Selection Settings to Reduce Radiation Dose or Contrast Medium in a Prospective Randomized Trial

Abstract

Objectives: The aim of this study was to compare the image quality of low-kV protocols with optimized automatic tube voltage selection (ATVS) settings to reduce either radiation dose or contrast medium (CM) with that of a reference protocol for computed tomography angiography (CTA) of the thoracoabdominal aorta. Materials and Methods: In this institutional review board-approved, singlecenter, prospective randomized controlled trial, 126 patients receiving CTA of the aorta were allocated to one of three computed tomography protocols: (A) reference protocol at 120 kVp and standard weight-adapted CM dose; (B) protocol at 90 kVp, reduced radiation and standard CM dose; and (C) protocol at 90 kVp, standard radiation and reduced CM dose. All three protocols were performed on a third-generation dual-source computed tomography scanner using the semimode of the ATVS system. The image-task-dependent optimization settings of the ATVS (slider level) were adjusted to level 11 (high-contrast task) for protocols A and B and level 3 (low-contrast task) for protocol C. Radiation dose parameters were assessed. The contrast-to-noise ratios (CNRs) of protocols B and C were tested for noninferiority compared with A. Subjective image quality was assessed using a 5-point Likert scale. Results: Size-specific dose estimate was 34.3% lower for protocol B compared with A (P < 0.0001). Contrast medium was 20.2% lower for protocol C compared with A (P < 0.0001). Mean CNR in B and C was noninferior to protocol A (CNR of 30.2 ± 7, 33.4 ± 6.7, and 30.5 ± 8.9 for protocols A, B, and C, respectively). There was no significant difference in overall subjective image quality among protocols (4.09 ± 0.21, 4.03 ± 0.19, and 4.08 ± 0.17 for protocols A, B, and C, respectively; P = 0.4). Conclusions: The slider settings of an ATVS system can be adjusted to optimize either radiation dose or CM at noninferior image quality in low-kV CTA of the aorta. This optimization could be used to extend future ATVS algorithms to take clinical risk factors like kidney function of individual patients into account.

Individualized Scan Protocols in Abdominal Computed Tomography

“…25,26 Reducing both parameters at the same time will decrease CNR and may lead to insufficient image quality. 13 However, in the current study, CNR was comparable between groups by adapting both radiation and CM dose, as intended in the study design.…”

“…Information regarding the CM injection protocol (eg, CM volume) is not taken into account despite playing a role in ATVS methodology. [11][12][13] Automated tube current modulation and ATVS together optimize radiation dose by adjusting tube current and tube voltage based on the clinical question and patient characteristics. By incorporating the CM injection protocol into these algorithms, protocols can be further adapted to individual requirements, such as for patients with reduced kidney function or young age or to specific disease management regimes and active surveillance.…”

“…The ATVS techniques are intended for contrast-enhanced CT scans, because they exploit the strong increase of iodine attenuation at lower tube voltage. Depending on patient body shape and imaging task, ATVS proposes the tube voltage that provides a desired contrast-tonoise ratio (CNR) at lowest radiation dose [11][12][13] -typically the lowest tube voltage with sufficient tube current reserves for the planned examination. The extent of radiation dose reduction at lower kV can be controlled by the user, for example, by applying different slider settings.…”

Optimization of Computed Tomography Angiography Protocols for Follow-Up Type B Aortic Dissection Patients by Using 3D Printed Model

“…For patients with aortic dissection, follow-up CT is mandatory and continues for many years [8,11,26]. Various dose-reduction strategies continue to develop with the advancement of CT imaging technology, striving to reduce the risk of patients being exposed to excessive radiation while maintaining image quality including low kVp, use of IR algorithms, tube current modulation, high-pitch protocol, and use of dual energy CT [10,15,25]. Low-dose CTA using low kVp and high-pitch protocols has been proven to achieve diagnostic image quality compared to the standard aortic CTA protocol while significantly reducing radiation dose [10,13,27].…”

“…Finding a balance between image quality and radiation risk has always been a challenging issue in achieving optimal scanning protocols. A number of studies describe different strategies to lower the radiation dose including the use of iterative reconstruction (IR) for reducing image noise, use of low tube kilovoltage peak (kVp), and use of high-pitch protocols with fast speed CT scanners [13][14][15]. Despite these studies providing promising results, research is still limited with regard to the reduction of radiation dose for aortic dissection patients who require repeat scanning for many years.…”