Upgrade to Iterative Image Reconstruction (IR) in Abdominal MDCT Imaging: A Clinical Study for Detailed Parameter Optimization Beyond Vendor Recommendations Using the Adaptive Statistical Iterative Reconstruction Environment (ASIR)

Abstract

Purpose: To compare the image quality of dose-reduced 64-row abdominal CT reconstructed at different levels of adaptive statistical iterative reconstruction (ASIR) to full-dose baseline examinations reconstructed with filtered back-projection (FBP) in a clinical setting and upgrade situation.

Materials and Methods: Abdominal baseline examinations (noise index NI = 29; LightSpeed VCT XT, GE) were intra-individually compared to follow-up studies on a CT with an ASIR option (NI = 43; Discovery HD750, GE), n = 42. Standard-kernel images were calculated with ASIR blendings of 0 – 100 % in slice and volume mode, respectively. Three experienced radiologists compared the image quality of these 567 sets to their corresponding full-dose baseline examination (– 2: diagnostically inferior, – 1: inferior, 0: equal, + 1: superior, + 2: diagnostically superior). Furthermore, a phantom was scanned. Statistical analysis used the Wilcoxon – the Mann-Whitney U-test and the intra-class correlation (ICC).

Results: The mean CTDIvol decreased from 19.7 ± 5.5 to 12.2 ± 4.7 mGy (p < 0.001). The ICC was 0.861. The total image quality of the dose-reduced ASIR studies was comparable to the baseline at ASIR 50 % in slice (p = 0.18) and ASIR 50 – 100 % in volume mode (p > 0.10). Volume mode performed 73 % slower than slice mode (p < 0.01).

Conclusion: After the system upgrade, the vendor recommendation of ASIR 50 % in slice mode allowed for a dose reduction of 38 % in abdominal CT with comparable image quality and time expenditure. However, there is still further dose reduction potential for more complex reconstruction settings.

Zusammenfassung

Ziel: Zielsetzung dieser klinischen Studie war im Rahmen eines System-Upgrades ein Vergleich der Bildqualität dosisreduzierter abdomineller 64-Zeilen-CTs, die mit unterschiedlichem Einfluss von adaptiver statistischer iterativer Rekonstruktion (ASIR) rekonstruiert wurden, mit Voll-Dosis-Voruntersuchungen, welche mittels gefilterter Rückprojektion (FBP) rekonstruiert wurden.

Material und Methoden: Abdominelle Baseline-Untersuchungen (Rauschindex NI = 29; LightSpeed VCT XT, GE) wurden intraindividuell mit Follow-up-Untersuchungen eines CT mit ASIR-Option verglichen (NI = 43; Discovery HD750, GE), n = 42. Im Standard-Kernel wurden Bilder mit 0 – 100 % ASIR-Einfluss sowohl im Slice- als auch im Volumen-Modus berechnet. Drei erfahrene Radiologen verglichen die Bildqualität dieser 567 Serien mit der jeweiligen Voll-Dosis-Baseline (– 2: diagnostisch schlechter, – 1: schlechter, 0: gleich, + 1: besser, + 2: diagnostisch besser). Zudem wurde ein Phantom gescannt. Zur statistischen Analyse wurden der Wilcoxon-, der Mann-Whitney-U-Test verwendet und die Intra-Class-Correlation (ICC) errechnet.

Ergebnisse: Der mittlere CTDIvol verringerte sich von 19,7 ± 5,5 auf 12,2 ± 4,7 mGy (p < 0,001). ICC war 0,861. Die mittlere Bildqualität der etwa um 40 % dosis-reduzierten ASIR Studien war für ASIR 50 % im Slice- (p = 0,18) und für ASIR 50 – 100 % im Volumen-Modus mit der Baseline vergleichbar (jeweils p > 0,10). Der Volumen-Modus war hierbei 73 % langsamer als der Slice-Modus (p < 0,01).

Schlussfolgerung: Nach dem Upgrade wurde mit der Herstellerempfehlung von ASIR 50 % im Slice-Modus eine Dosiseinsparung von 38 % bei gleichbleibender Bildqualität und konstantem Zeitaufwand erreicht. Darüber hinaus besteht für komplexere Bildrekonstruktionssettings ein weiteres Potenzial zur Dosiseinsparung.

Key words

abdomen - iterative reconstruction - dose reduction - ASIR - computed tomography

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