Anatomical accuracy of abdominal lesion localization

Summary

Software-based image registration can improve the diagnostic value of imaging procedures and is an alternative to hybrid scanners. The aim of this study was to evaluate the anatomical accuracy of automatic rigid image registration of independently acquired datasets of positron emission tomography with ¹⁸F-deoxyglucose and abdominal magnetic resonance imaging. Patients, methods: Analyses were performed on 28 abdominal lesions from 20 patients. The PET data were obtained using a stand-alone PET camera in 14 cases and a hybrid PET/CT scanner in 9 cases. The abdominal T1- and T2-weighted MRI scans were acquired on 1.5 T MRI scanners. The mean time interval between MRI and PET was 7.3 days (0–28 days). Automatic rigid registration was carried out using a self-developed registration tool integrated into commercial available software (InSpace for Siemens Syngo). Distances between the centres of gravity of 28 manually delineated neoplastic lesions represented in PET and MRI were measured in X-, Y-, and Z-direction. The intra- (intraclass correlation 0.94) and inter- (intraclass correlation 0.86) observer repeatability were high. Results: The average distance in all MRI sequences was 5.2 ± 7.6 mm in X-direction, 4.0 ± 3.7 mm in Y-direction and 6.1 ± 5.1 mm in Z-direction. There was a significantly higher misalignment in Z-direction (p < 0.05). The misalignment was not significantly different for the registration of T1- and T2- weighted sequences (p = 0.7). Conclusion: The misalignment between FDG-PET and abdominal MRI registered using an automated rigid registration tool was comparable to data reported for software-based fusion between PET and CT. Although this imprecision may not affect diagnostic accuracy, it is not sufficient to allow for pixel-wise integration of MRI and PET information.

Zusammenfassung

Retrospektive Bildregistrierung kann die diagnostische Genauigkeit erhöhen und in einigen Anwendungsbereichen eine Alternative zu Hybridgeräten sein. Ziel der Studie war es, die anatomische Genauigkeit einer retrospektiven, automatisierten und starren Registrierung zwischen unabhängig akquirierten Aufnahmen der ¹⁸F-Deoxyglukose-Positronenemissions-tomographie und abdomineller Magnetresonanztomographie zu ermitteln. Patienten, Methoden: Die Analyse wurde an 28 abdominellen Läsionen von 20 Patienten durchgeführt. Bei 14 Patienten wurden Datensätze mit einer dedizierten PET-Kamera, bei 9 Patienten mit einem hybriden PET/CT aufgenommen. Unabhängig davon wurden T1- und T2-gewichtete MRT-Aufnahmen des Abdomens an 1,5-T-MR-Tomographen akquiriert. Die mittlere Zeit zwischen den beiden Aufnahmen betrug 7,3 Tage (0–28 Tage). Die automatisierte und starre Registrierung wurde mit einem selbst entwickelten Registrierungstool, integriert in eine kommerzielle Plattform (InSpace für Siemens Syngo) durchgeführt. Die Distanzen zwischen den Schwerpunkten der 28, manuell markierten, neoplastischen Läsionen im PET und MRT wurden bei hoher Wiederhol- (Intra-Klassen-Korrelation 0,94) und Vergleichspräzision (Intra-Klassen Korrelation 0,86) in X-, Y-, und Z-Richtung vermessen. Ergebnisse: Die mittlere Schwerpunktdistanz für alle MRT-Sequenzen betrug 5,2 ± 7,6 mm in X-Richtung, 4,0 ± 3,7 mm in Y-Richtung und 6,1 ± 5,1 mm in Z-Richtung. Verschiebungen in Z-Richtung waren signifikant größer (p < 0,05). Es gab keine signifikant unterschiedlichen Abstände für die Registrierung der T1- und T2-gewichteten Sequenzen (p = 0,7). Schlussfolgerung: Die Ungenauigkeit der automatischen und starren Bildregistrierung zwischen FDG-PET und abdomineller MRT ist mit denjenigen für die retrospektive Registrierung zwischen PET und CT publizierten Daten vergleichbar. Obwohl diese Ungenauigkeit die diagnostische Zuverlässigkeit wohl nicht einschränkt, ist sie für eine pixelweise Verrechnung der Datensätze nicht ausreichend.

Keywords

PET - FDG - MRI. image registration - image fusion

Schlüsselwörter

PET - FDG - MRI. Bildregistrierung - Bildfusion

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