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

Zusammenfassung

Ziel Die Anpassung der CT-Protokolle zur TAVI-Planung (Transkatheter-Aortenklappen-Implantation) ist erforderlich, wenn ein Dual-Layer Spektral-CT (DLCT) der ersten Generation verwendet wird. Ziel dieser Studie war es, die objektive Bildqualität der CT-Angiografie (CTA), die mit einem DLCT angefertigt wurden, zu bewerten. Untersucht wurden diesbezüglich virtuell monoenergetische Bilder bei 40 keV (40 keV-VMI) eines Zwei-Phasen-Protokolls. Zum Vergleich dienten CTA, die mit dem einphasigen Protokoll eines konventionellen CTs (SLCT) angefertigt wurden.

Material und Methoden 75 CTAs des DLCT wurden retrospektiv mit 75 CTAs eines konventionellen CTs verglichen. Mit dem DLCT wurde die CTA ohne EKG-Synchronisation unmittelbar nach einer retrospektiv EKG-gegateten Aufnahme des Herzens und des Aortenbogens durchgeführt. Mit dem SLCT wurde eine einphasige CTA durchgeführt, welche sowohl das Herz als auch die Zugangsgefäße in einem retrospektiv EKG-synchronisierten Scan erfasste. Die objektive Bildqualität wurde auf verschiedenen Ebenen des arteriellen Zugangsweges verglichen.

Ergebnisse Die virtuell monoenergetischen Bilder des DLCT bei 40 keV zeigten eine signifikant höhere absolute CT-Zahl, SNR und CNR auf allen Ebenen des arteriellen Zugangswegs. Bei den 40 keV-VMI der DLCT betrug das durchschnittliche aortale Gefäßsignal aller 6 gemessenen Regionen 589,6 ± 243 HU im Vergleich zu 492,7 ± 209 HU des SLCT (p < 0,01). Ein ähnlicher Trend konnte für SNR (23,6 ± 18 vs. 18,6 ± 9; p < 0,01) und CNR (21,1 ± 18 vs. 16,4 ± 8; p < 0,01) beobachtet werden. Für das Signalrauschen wurden keine signifikanten Unterschiede beobachtet (27,8 ± 9 HU vs. 28,1 ± 8 HU; p = 0,599).

Schlussfolgerung Bei der TAVI-Planung kann unter Verwendung eines DLCT mit einem Zwei-Phasen-Protokoll und 40 keV-VMI eine höhere objektive Bildqualität im Vergleich zu einem einphasigen Protokoll eines konventionellen CT-Scanners erzielt werden.

Kernaussagen: 

• Bei Verwendung eines Dual-Layer-CT der ersten Generation kann eine Anpassung der CT-Protokolle zur TAVI-Planung erforderlich sein.

• Die Rekonstruktion virtuell-monoenergetischer Bilder bei 40 keV verbessert die Bildqualität.

• Bei einem Zwei-Phasen-Protokoll ist die Strahlendosis geringer im Vergleich zu einer einphasigen EKG-gegateten CT-Akquisition.

Key words

transcatheter aortic valve implantation (TAVI) - transcatheter aortic valve replacement (TAVR) - dual-energy CT - spectral detector CT - aortography - virtual monoenergetic imaging

Publication History

Received: 03 August 2021

Accepted: 18 November 2021

Article published online:
28 December 2021

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