Bestimmung des koronaren Kalzium-Scores mittels 64-Zeilen-CT - Variabilität der Scores und Einfluss des Rekonstruktionszeitpunktes

Zusammenfassung

Ziel: Evaluation der Variabilität des koronaren Kalzium-Scores in Abhängigkeit des Rekonstruktionszeitpunktes mittels 64-Zeilen-CT. Material und Methoden: Bei 30 Patienten (18 männlich, 12 weiblich, mittleres Alter 57 ± 9 Jahre) mit einer mittleren Herzrate von 66 ± 10 Schlägen/Minute wurde der koronare Kalzium-Score mittels 64-Zeilen-CT (Somatom Sensation 64, Siemens Medical Solutions, Erlangen) und eines standardisierten Untersuchungsprotokolls bestimmt. Orale β-Blocker wurden bei 12 Patienten mit einer Herzfrequenz > 70 Schlägen/Minute appliziert. Die Bildrekonstruktion erfolgte in 10 %-Schritten von 10 - 100 % des RR-Intervalls im EKG. Für jede dieser Bildrekonstruktionen berechneten zwei erfahrene, geblindete Untersucher den Agatston-Score (AS), den Kalzium-Massen-Score (MS) und den Kalzium-Volumen-Score (VS). Die Ergebnisse wurden mit entsprechenden Studien aus der 16-Zeilen-CT verglichen. Ergebnisse: Die Mittelwerte und mittleren Variationskoeffizienten für alle Patienten waren wie folgt: AS, 397 ± 829, 109 % MS, 88 ± 225, 154 % VS, 335 ± 669, 100 %. Bezüglich des Rekonstruktionsintervalls waren die mittleren Variationskoeffizienten wie folgt: 107 % (AS), 97 % (VS), 116 % (MS). Für keinen Score konnte ein spezifisches Rekonstruktionsintervall identifiziert werden, welches eine statistisch signifikant geringere Variabilität aufwies. Die Interobserver-Übereinstimmung war hoch (K = 0,98). 10/30 Patienten (pts) konnten mit statistischer Signifikanz (p < 0,05) mehr als einer Risikogruppe (RG) zugeordnet werden: 6 pts = 2 RG; 3 pts = 3 RG; 1 pts = 4 RG. Bei 5/30 Patienten wurde ein Score von null in zumindest einem Rekonstruktionsintervall gefunden, jedoch konnte mittels weiterer Bildrekonstruktionen Kalzium nachgewiesen werden. Die Anzahl von Patienten, die mehreren Risikogruppen zugeordnet werden konnten, war signifikant geringer im Vergleich zu publizierten Daten für die 16-Zeilen-CT (p < 0,05). Schlussfolgerung: Die Bestimmung der koronaren Kalzium-Scores mittels 64-Zeilen-CT weist, wie bereits für die 16-Zeilen-CT beschrieben, eine hohe Variabilität in Abhängigkeit des Rekonstruktionszeitpunktes auf. Unsere Ergebnisse zeigen im Vergleich zu früheren Studien, dass mit CT-Geräten dieser Herstellergeneration der Einfluss der Score-Schwankungen auf die Risikostratifizierung reduziert werden kann.

Abstract

Purpose: To evaluate the variability of coronary calcium scores depending on the image reconstruction interval using a 64-slice CT scanner. Materials and Methods: 30 patients (18 male, 12 female; mean age 57 ± 9 yrs; mean heart rate 66 ± 10 bpm) underwent coronary calcium scoring using a 64-slice CT scanner (Somatom Sensation 64, Siemens Medical Solutions, Erlangen) and a standardized scanning protocol. Oral β-blockers were administered to 12 patients with a baseline heart rate > 70 bpm. Images were reconstructed in 10 % increments from 10 - 100 % of the RR interval. Two blinded experienced observers independently calculated Agatston (AS), calcium mass (MS) and volume scores (VS) for every reconstructed image series. The results were compared to similar studies for 16-slice CT scanners. Results: The mean values and mean coefficients of variation among all patients were as follows: AS, 397 ± 829, 109 % MS, 88 ± 225, 154 % VS, 335 ± 669, 100 %. Regarding the reconstruction intervals, the mean coefficients of variation were as follows: 107 % (AS), 97 % (VS), 116 % (MS). No specific image reconstruction interval with statistically significant lower variability for each score could be identified. High inter-observer agreement was achieved (K = 0.98). With statistical significance (p < 0.05) 10/30 patients (pts) were able to be allocated to more than one risk group (RG): 6 pts = 2 RG; 3 pts = 3 RG; 1 pts = 4 RG. The scores for 5/30 patients were zero for at least one reconstruction interval, but further reconstructions revealed calcifications. The number of patients assignable to different risk groups was significantly lower compared to published data using a 16-slice scanner (p < 0.05). Conclusion: Coronary calcium scores determined using a 64-slice scanner display a wide range of variability depending on the image reconstruction interval as already described for 16-slice CT scanners. However, compared to previous studies, our data indicate that this vendor’s generation of scanners reduces the influence of score variations on the risk stratification.

Key words

cardiac imaging - computed tomography - coronary calcium - calcium scoring

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