Anatomical accuracy of lesion localization

A. Nömayr; W. Römer; T. Hothorn; A. Pfahlberg; J. Hornegger; W. Bautz; T. Kuwert

doi:10.1055/s-0038-1625102

Nuklearmedizin - NuclearMedicine, Table of Contents

Nuklearmedizin 2005; 44(04): 149-155
DOI: 10.1055/s-0038-1625102

Original Articles

Schattauer GmbH

Anatomical accuracy of lesion localization

Retrospective interactive rigid image registration between ¹⁸F-FDG-PET and X-ray CTGenauigkeit der Lokalisierungmaligner Herde mittels retrospektiver, interaktiver starrer Bildfusion von FDG-PET und CT

Authors

A. Nömayr

¹Clinic of Nuclear Medicine
W. Römer

¹Clinic of Nuclear Medicine
T. Hothorn

²Department of Medical Informatics, Biometry and Epidemiology
A. Pfahlberg

²Department of Medical Informatics, Biometry and Epidemiology
J. Hornegger

³Department of Computer Science, Chair for Pattern Recognition
W. Bautz

⁴Institute of Diagnostic Radiology, University of Erlangen/Nürnberg, Erlangen, Germany
T. Kuwert

¹Clinic of Nuclear Medicine

Abstract

Summary

The aim of this study was to evaluate the anatomical accuracy and reproducibility of retrospective interactive rigid image registration (RIR) between routinely archived X-ray computer tomography (CT) and positron emission tomography performed with ¹⁸F-deoxyglucose (FDG-PET) in oncological patients. Methods: Two observers registered PET and CT data obtained in 37 patients using a commercially available image fusion tool. RIR was performed separately for the thorax and the abdomen using physiological FDG uptake in several organs as a reference. One observer performed the procedure twice (O1a and O1b), another person once (O2). For 94 malignant lesions, clearly visible in CT and PET, the signed and absolute distances between their representation on PET and CT were measured in X-, Y-, and Z-direction with reference to a coordinate system centered in the CT representation of each lesion (X-, Y-, Z-distances). Results: The mean differences of the signed and absolute distances between O1a, O1b, and O2 did not exceed 3 mm in any dimension. The absolute X-, Y-, and Z-distances ranged between 0.57 ± 0.58 cm for O1a (X-direction) and 1.12 ± 1.28 cm for O2 (Z-direction). When averaging the absolute distances measured by O1a, O1b, and O2, the percentage of lesions misregistered by less than 1.5 cm was 91 % for the X-, 88 % for the Y-, and 77 % for the Z-direction. The larger error of fusion determined for the remaining lesions was caused by non-rigid body transformations due to differences in breathing, arm position, or bowel movements between the two examinations. Mixed effects analysis of the signed and absolute X-, Y-, and Z-distances disclosed a significantly greater misalignment in the thorax than in the abdomen as well as axially than transaxially. Conclusion: The anatomical inaccuracy of RIR can be expected to be <1.5 cm for the majority of neoplastic foci. Errors of alignment are bigger in the thorax and in Z-direction, due to non-rigid body transformations caused, e.g., by breathing.

Zusammenfassung

Ziel: Evaluierung der anatomischen Genauigkeit und Reproduzierbarkeit der Lokalisierung von malignen Herden mittels der retrospektiven, interaktiven, starren Bildfusion von FDG-PET und CT. Methodik: Bei 37 onkologischen Patienten wurden innerhalb von 30 Tagen eine Ganzkörper- FDG-PET und ein Spiral-CT gemäß klinischen Standardprotokollen aufgenommen. Zwei Untersucher fusionierten unabhängig voneinander PET und CT. Die Fusion erfolgte für Thorax und Abdomen getrennt. Hauptorientierungsmarken waren Zwerchfell, Leber, Harnblase, Mediastinum und Lungengrenzen. 94 PET- und CT-positive maligne Läsionen wurden evaluiert. Die Abweichung zwischen der Darstellung in PET und CT wurde in den 3 Ebenen ermittelt. Wir bestimmten den absoluten Betrag der Abweichung sowie die vektorielle Richtung in der X-, Y- und Z-Achse durch das Setzen eines Vorzeichen. Ergebnisse: Die absoluten Werte für die Fehlregistrierung der Läsionen reichten von 0,57 cm ± 0,58 (X-Richtung) bis 1,12 cm ± 1,28 (Z-Richtung). Die Ergebnisse beider Untersucher unterschieden sich um maximal 3 mm in allen Ebenen für die vektorielle oder absolute Fehlregistrierung der Läsion im fusionierten Bild. Die Inter- und Intraobservervariabilität war niedrig und statistisch nicht signifikant. Eine Fehlregistrierung von weniger als 1,5 cm wurde bei 91% (X-Richtung), 88% (Y-Richtung) und 77% (Z-Richtung) der Läsionen erreicht. Größere Abweichungen wurden v. a. durch unterschiedliche Atemlage und Armposition in PET und CT oder durch Peristaltik-bedingte Lageveränderungen von Magen und Darm zwischen den Untersuchungen verursacht. Die statistische Analyse ergab eine signifikant höhere Fehlregistrierung im Thorax als im Abdomen sowie eine höhere Abweichung in Z-Richtung (kranio-kaudal) als in der X/Y-Ebene. Schlussfolgerung: Der Registrierungsfehler bei der retrospektiven, interaktiven Fusion von PET- und CT beträgt bei den meisten neoplastischen Läsionen <1,5 cm. Bedingt durch die Atmung ist der Registrierungsfehler im Thorax größer als abdominell sowie ausgeprägter in Z-Richtung als in der axialen Bildebene.

Keywords

PET - CT - image registration - image fusion - FDG

Schlüsselwörter

PET - CT - Bildregistrierung - Bildfusion - FDG

Full Text

References

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