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Whole-Body ¹⁸F-FDG PET/CT in the Presence of Truncation Artifacts

¹ Department of Nuclear Medicine; University Hospital Essen, Essen, Germany; ² Institute of Diagnostic and Interventional Radiology and Neuroradiology; University Hospital Essen, Essen, Germany; and ³ Department of Nuclear Medicine; Technical University Munich, Munich. Germany

Correspondence: For correspondence contact: Thomas Beyer, PhD, Department of Nuclear Medicine, University Hospital Essen, Hufelandstrasse 55, D 45122 Essen, Germany. E-mail: thomas.beyer{at}uni-essen.de

We investigated the effect of CT truncation in whole-body (WB) PET/CT imaging of large patients, and we evaluated the efficacy of an extended field-of-view (eFOV) correction technique. Methods: Two uniform phantoms simulating a "torso" and an "arms-up" setup were filled with ¹⁸F-FDG/water. A third, nonuniform "body phantom was prepared with hot and cold lesions. All 3 phantoms were positioned in the center of the PET/CT gantry with 10% of their volume extending beyond the maximum CT FOV. An eFOV algorithm was used to estimate complete CT projections from nonlinear extrapolation of the truncated projections. CT-based attenuation correction (CT AC) of the phantom data was performed using CT images reconstructed from truncated and extended projections. For clinical validation, we processed truncated datasets from 10 PET/CT patients with and without eFOV correction. Results: When using truncated CT images for CT AC, PET tracer distribution was suppressed outside the transverse CT FOV in phantom and patient studies. PET activity concentration in the truncated regions was only 10%–32% of the true value but increased to 84%–100% when using the extended CT images for CT AC. At the same time, the contour of phantoms and patients was recovered to the anatomically correct shape from the uncorrected emission images, and the apparent distortion of lesions near the maximum CT FOV was reduced. Conclusion: Truncation artifacts in WB PET/CT led to visual and quantitative distortions of the CT and attenuation-corrected PET images in the area of truncation. These artifacts can be corrected to improve the accuracy of PET/CT for diagnosis and therapy response evaluation.

Key Words: combined PET/CT • truncation effects • image quality • image artifacts

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