Impact of Hybrid Iterative Reconstruction on Agatston Coronary Artery Calcium Scores in Comparison to Filtered Back Projection in Native Cardiac CT

Abstract

Purpose: To investigate whether the effects of hybrid iterative reconstruction (HIR) on coronary artery calcium (CAC) measurements using the Agatston score lead to changes in assignment of patients to cardiovascular risk groups compared to filtered back projection (FBP).

Materials and Methods: 68 patients (mean age 61.5 years; 48 male; 20 female) underwent prospectively ECG-gated, non-enhanced, cardiac 256-MSCT for coronary calcium scoring. Scanning parameters were as follows: Tube voltage, 120 kV; Mean tube current time-product 63.67 mAs (50 – 150 mAs); collimation, 2 × 128 × 0.625 mm. Images were reconstructed with FBP and with HIR at all levels (L1 to L7). Two independent readers measured Agatston scores of all reconstructions and assigned patients to cardiovascular risk groups. Scores of HIR and FBP reconstructions were correlated (Spearman). Interobserver agreement and variability was assessed with ĸ-statistics and Bland-Altmann-Plots.

Results: Agatston scores of HIR reconstructions were closely correlated with FBP reconstructions (L1, R = 0.9996; L2, R = 0.9995; L3, R = 0.9991; L4, R = 0.986; L5, R = 0.9986; L6, R = 0.9987; and L7, R = 0.9986). In comparison to FBP, HIR led to reduced Agatston scores between 97 % (L1) and 87.4 % (L7) of the FBP values. Using HIR iterations L1 – L3, all patients were assigned to identical risk groups as after FPB reconstruction. In 5.4 % of patients the risk group after HIR with the maximum iteration level was different from the group after FBP reconstruction.

Conclusion: There was an excellent correlation of Agatston scores after HIR and FBP with identical risk group assignment at levels 1 - 3 for all patients. Hence it appears that the application of HIR in routine calcium scoring does not entail any disadvantages. Thus, future studies are needed to demonstrate whether HIR is a reliable method for reducing radiation dose in coronary calcium scoring.

Key Points:

• Agatston-Scores showed excellent correlation between HIR and FBP.

• The higher the HIR Level, the more Agatston scores deviated to lower values.

• No change in risk group assignment using Level 1 – 3.

• Change in risk group assignment when using HIR compared to FBP in 1.5 % (Level 4), 5.4 % (Level 5 – 7).

Citation Format:

• Obmann VC, Klink T, Heverhagen JT et al. Impact of Hybrid Iterative Reconstruction on Agatston Coronary Artery Calcium Scores in Comparison to Filtered Back Projection in Native Cardiac CT. Fortschr Röntgenstr 2015; 187: 372 – 379

Zusammenfassung

Ziel: Ziel dieser Studie war es zu prüfen, ob die Erfassung des Agatston-Scores durch hybride iterative Rekonstruktion (HIR) gegenüber der gefilterten Rückprojektion (FBP) zu einer Änderung der kardiovaskulären Risikogruppe führt.

Material und Methoden: 68 Patienten (mittleres Alter 61,5 Jahre; 48 Männer, 20 Frauen) erhielten eine prospektiv EKG-getriggerte native 256-MSCT des Herzens zum Kalziumscoring. Die Scanparameter waren wie folgt: Röhrenspannung 120 kV, Röhrenstromzeitprodukt im Mittel 63,67 mAs (50 – 150 mAs); Kollimation 2 × 128 × 0,625 mm. Die Rohdaten wurden mittels FBP und HIR in allen Iterationsstufen (L1 – L7) rekonstruiert. Zwei unabhängige Beobachter erfassten die Agatston-Scores der HIR- und FBP-Rekonstruktion und nahmen eine Einteilung in kardiovaskuläre Risikogruppen vor. Die Resultate wurden zwischen HIR und FBP korreliert (Spearman). Die Übereinstimmung und Variabilität zwischen den beiden Beobachtern wurde mittels ĸ-Statistik und Bland-Altmann-Plots bestimmt.

Ergebnisse: Die Agatston-Scores der HIR korrelierten gut bis exzellent mit den FBP-Rekonstruktionen (L1: R = 0,9996, L2: R = 0,9995, L3: R = 0,9991, L4: R = 0,9986, L5: R = 0,9986, L6: R = 0,9987 und L7: R = 0,9986). Im Vergleich zu FBP führte die HIR zu niedrigeren Agatston-Scores zwischen 97 % (L1) und 87,4 % (L7). Bei niedrigen Iterationsstufen (L1 – L3) wurden alle Patienten in identische Risikogruppen eingeteilt wie bei FBP. Nur bei Verwendung der höchsten HIR-Stufen änderte sich die Gruppe bei 5,4 % der Patienten gegenüber FBP.

Schlussfolgerung: Aufgrund der exzellenten Korrelation der Agatston-Scores nach FBP- und HIR-Rekonstruktion und den identischen kardiovaskuläre Risikokategorien zwischen FBP- und HIR-Level 1 – 3 bei allen Patienten, scheint der Einsatz der iterativen Rekonstruktion unter diesen Bedingungen bei Kalziumscoring nicht von Nachteil zu sein. Weitere Studien müssen zeigen, ob sich die HIR auch als zuverlässige Methode zur Dosisreduktion bei Kalziumscoring eignet.

Key words

cardiac - image manipulation/reconstruction - CT-quantitative - treatment effects - arteriosclerosis - calcifications/calculi

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