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Nonrigid Versus Rigid Registration of Thoracic ¹⁸F-FDG PET and CT in Patients with Lung Cancer: An Intraindividual Comparison of Different Breathing Maneuvers

¹ Department of Nuclear Medicine, Saarland University Medical Center, Homburg/Saar, Germany; ² Department of Radio-Oncology, University Hospital Freiburg, Freiburg, Germany; and ³ Department of Radio-Oncology, Saarland University Medical Center, Homburg/Saar, Germany

Correspondence: For correspondence or reprints contact: Aleksandar Grgic, Department of Nuclear Medicine, Saarland University Medical Center, Kirrbergerstrasse 1, Gebäude 50, 66421 Homburg/Saar, Germany. E-mail: aleksandar.grgic{at}uks.eu

In lung cancer, ¹⁸F-FDG PET, CT, and ¹⁸F-FDG PET/CT are used for noninvasive staging and therapy planning. Even with improved image registration techniques—especially in the modern hybrid PET/CT scanners—inaccuracies in the fusion process may occur, leading to errors in image interpretation. The aim of this study was to investigate by an intraindividual analysis whether, in comparison with a rigid algorithm, a nonrigid registration algorithm improves the quality of fusion between ¹⁸F-FDG PET and CT. Methods: Sixteen patients with histologically proven non–small cell lung cancer underwent a thoracic ¹⁸F-FDG PET acquisition in radiotherapy treatment position and 3 CT acquisitions (expiration, inspiration, and mid breath-hold) on the same day. All scans were registered with rigid and nonrigid procedures, resulting in 6 fused datasets: rigid inspiration, rigid expiration, rigid mid breath-hold, nonrigid inspiration, nonrigid expiration, and nonrigid mid breath-hold. The quality of alignment was assessed by 3 experienced readers at 8 anatomic landmarks: lung apices, aortic arch, heart, spine, sternum, carina, diaphragm, and tumor using an alignment score ranging from 1 (no alignment) to 5 (exact alignment). Results: Nonrigid PET/CT showed better alignment than rigid PET/CT (3.5 ± 0.7 vs. 3.3 ± 0.7, P < 0.001). Regarding the breathing maneuver, no difference between nonrigid mid breath-hold and rigid mid breath-hold was observed. In contrast, the alignment quality significantly improved from rigid expiration to nonrigid expiration (3.4 ± 0.7 vs. 3.6 ± 0.7, P < 0.001) and from rigid inspiration to nonrigid inspiration (3.1 ± 0.7 vs. 3.3 ± 0.7, P < 0.001). With regard to individual landmarks, an improvement in fusion quality through the use of nonrigid registration was obvious at the lung apices, carina, and aortic arch. Conclusion: The alignment quality of thoracic ¹⁸F-FDG PET/CT exhibits a marked dependence on the breathing maneuver performed during the CT acquisition, as demonstrated in an intraindividual comparison. Nonrigid registration is a significant improvement over rigid registration if the CT is performed during full inspiration or full expiration. The best fusion results are obtained with the CT performed at mid breath-hold using rigid registration, without an improvement using nonrigid algorithms.

Key Words: non–small cell lung carcinoma (NSCLC) • spiral computed tomography • positron emission tomography • image registration • computer-assisted image analysis

COPYRIGHT © 2009 by the Society of Nuclear Medicine, Inc.

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