Dual-Layer Spectral CTA for TAVI Planning Using a Split-Phase Protocol and Low-keV Virtual Monoenergetic Images: Improved Image Quality in Comparison with Single-Phase Conventional CTA.

Abstract

Purpose: Adaptation of computed tomography protocols for transcatheter aortic valve implantation (TAVI) planning is required when a first-generation dual-layer spectral CT scanner (DLCT) is used. The purpose of this study was to evaluate the objective image quality of aortic CT angiography (CTA) for TAVI planning using a split-phase technique with reconstruction of 40 keV virtual monoenergetic images (40 keV-VMI) obtained with a DLCT scanner. CT angiography obtained with a single-phase protocol of a conventional single-detector CT (SLCT) was used for comparison.

Materials and methods: 75 CTA scans from DLCT were retrospectively compared to 75 CTA scans from SLCT. For DLCT, spiral CTA without ECG-synchronization was performed immediately after a retrospectively ECG-gated acquisition covering the heart and aortic arch. For SLCT, spiral CTA with retrospective ECG-gating was performed to capture the heart and the access route simultaneously in one scan. Objective image quality was compared at different levels of the arterial access route.

Results: 40 keV virtual monoenergetic images of DLCT showed a significantly higher mean vessel attenuation, SNR, and CNR at all levels of the arterial access route. With 40 keV-VMI of DLCT, the overall mean aortic attenuation of all six measured regions was 589.6 ± 243 HU compared to 492.7 ± 209 HU of SLCT (p < 0.01). A similar trend could be observed for SNR (23.6 ± 18 vs. 18.6 ± 9; p < 0.01) and CNR (21.1 ± 18 vs. 16.4 ± 8; p < 0.01). No deterioration was observed for vascular noise (27.8 ± 9 HU vs. 28.1 ± 8 HU; p = 0.599).

Conclusion: Using a DLCT scanner with a split-phase protocol and 40 keV-VMI for TAVI planning, higher objective image quality can be obtained compared to a single-phase protocol of a conventional CT scanner.

Key points: · Adaption of TAVI planning CT protocols may be required when using a first-generation dual-layer CT scanner.. · Reconstruction of virtual monoenergetic images at 40 keV improves image quality.. · With a split-phase protocol, the radiation dose is lower compared to a single-phase ECG-gated CT acquisition..

Citation format: · Mangold D, Salatzki J, Riffel J et al. Dual-Layer Spectral CTA for TAVI Planning Using a Split-Phase Protocol and Low-keV Virtual Monoenergetic Images: Improved Image Quality in Comparison with Single-Phase Conventional CTA. Fortschr Röntgenstr 2022; 194: 652 - 659.