256-MSCT Image Acquisition with Sequential Axial Scans: Evaluation of Image Quality and Resolution in a Phantom Study

Abstract

Purpose: Evaluation of image quality and resolution of varying sequential axial scan protocols utilizing two resolution phantoms with a 256-MSCT scanner.

Materials and Methods: Sequential axial scans were performed on a z-axis and an axial-plane resolution phantom with varying acquisition and reconstruction parameters. Two independent observers evaluated the image quality and resolution, and analyzed quantitative image quality parameters and radiation doses.

Results: The best image quality and resolution were achieved with an activated z-flying focal spot (zFFS) and overlapping reconstruction. With an activated zFFS, image degradation was significantly minimized in marginal or overlapping zones of the beam, but the maximum effective detector width was reduced to 82 % and 75 %, respectively depending on the field of view. With a deactivated zFFS, the effective detector width was not restricted, but the image quality decreased and the artifacts increased as the collimation increased.

Conclusion: For sequential axial CT data acquisition with multi-planar image reformation, the zFFS technique is crucial to achieve the best image quality and resolution. Major advantages are minimized image degradation and increased spatial resolution along the z-axis, but the zFFS reduces the maximum effective detector width.

Zusammenfassung

Ziel: Evaluation der Bildqualität und -auflösung von unterschiedlichen sequentiellen axialen Scanprotokollen in einer Phantomstudie an einem 256-MSCT.

Material und Methoden: Die sequenziellen axialen Scans erfolgten an einem z-Achsen- und einem Axialebenen-Auflösungsphantom mit unterschiedlichen Scan- und Rekonstruktionseinstellungen. Die Bildqualität und die -auflösung wurden durch zwei unabhängige Beobachter beurteilt. Außerdem wurden quantitative Bildqualitätsparameter und die applizierte Strahlendosis analysiert.

Ergebnisse: Die beste Bildqualität und -auflösung wurden mit aktiviertem z-Achsen-Spingfokus (zFFS) und einer überlappenden Bildrekonstruktion erzielt. Durch Aktivierung des zFFS wurden Qualitätsverluste insbesondere in den Randbereichen bzw. in den Überlappungszonen des Kegelstrahls signifikant minimiert. Jedoch wurde dabei die effektive Detektorbreite in Abhängigkeit vom Sichtfeld auf 82 bzw. 75 % reduziert. Bei deaktiviertem zFFS konnte zwar die maximale effektive Detektorbreite ausgeschöpft werden, aber die Qualitätsverluste stiegen mit der Wahl zunehmend breiterer Kollimationseinstellungen an.

Schlussfolgerung: Für die sequenzielle axiale CT-Datenakquisition mit multiplanarer Bildreformatierung trägt die zFFS-Technik entscheidend zu einer optimalen Bildqualität und -auflösung bei. Wesentliche Vorzüge sind minimierte Qualitätsverluste und eine höhere räumliche Auflösung entlang der z-Achse, nachteilig ist eine reduzierte maximale effektive Detektorbreite.

Key words

256-MSCT - step and shoot - axial image acquisition - image quality and resolution - phantom - artifacts

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