Thomas Beyer, Presenter: Nothing to Disclose

Otto Sembritzki, Abstract Co-Author: Nothing to Disclose

Maria-Jose Martinez, Abstract Co-Author: Nothing to Disclose

Fiona Roberts, Abstract Co-Author: Nothing to Disclose

Sibylle Ziegler, Abstract Co-Author: Nothing to Disclose

Marcus Seemann, Abstract Co-Author: Nothing to Disclose

Hilmar Kuehl MD, Abstract Co-Author: Nothing to Disclose

Andreas Bockisch MD, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

When scanning large patients, or patients with their arms down truncation artifacts may arise from the limited transverse field-of-view (FOV) of the CT. In combined PET/CT these artifacts may propagate through CT-based attenuation correction (CT-AC) into the corrected PET images. We evaluate the magnitude of truncation artifacts in whole-body (WB) PET/CT, and test the efficacy of a recovery procedure for truncated CT data prior to CT-AC for clinical PET/CT.

A 20cm cylinder was centered in the FOV of a WB-PET/CT (2-row CT) with 2 10cm bottles simulating the ‘arms’ placed first next to the cylinder inside the CT-FOV and then 22cm off-center to simulate truncation. The plastic phantom was filled with 7kBq/mL FDG in water. 3D-PET/CT imaging involved the use of the CT images for CT-AC and the visual and quantitative evaluation of the CT and corrected PET. 10 WB-studies with CT truncation artifacts (large patients, or arms down) were chosen from both, a 2- and 16-row WB-PET/CT system. Truncated CT images were corrected using an algorithm that extends the truncated projections by means of a profile-fitting algorithm (Schaller, RSNA 2002). Both, the truncated and extended CT images were used for CT-AC, and the corrected PET images were assessed qualitatively and quantitatively.

Quantitative accuracy of the tracer recovery in the main cylinder was unaffected by CT truncation, which was 10% of all attenuating pixels. When using the truncated CT for CT-AC the outline of the truncated arms was recovered. The activity concentration in the truncated portion was underestimated by up to 40% in comparison to the non-truncated portion of the arms. None of the patients exhibited disease that would have been missed on the corrected PET images due to truncation artifacts. Using the extended CT attenuation maps for CT-AC the tracer distribution was recovered in 20/20.

CT-truncation in PET/CT imaging leads to masking effects of the corrected tracer distribution for standard CT-AC. This bias is corrected by employing extended CT transmission maps from a projection-based correction technique that is available routinely for 16-row PET/CT and that was implemented for a 2-row PET/CT.

Beyer, T, Sembritzki, O, Martinez, M, Roberts, F, Ziegler, S, Seemann, M, Kuehl, H, Bockisch, A, et al, , PET/CT Imaging in the Presence of Truncation Artifacts from Scanning Large Patients beyond the Transverse CT Field-of-View.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4414119.html