Coronal (above) and axial (below) F18-FDG PET images
View main image(pt) in a separate image viewer
View second image(pt). Axial CT in soft tissue (upper left) and lung windows (upper right); fused PET-CT (lower left) and F18-FDG PET (lower right) images.
View third image(pt). Attenuated-corrected and non-attenuation corrected PET images.
View fourth image(xr). PA and lateral chest radiographs performed the same day as the PET examination.
Full history/Diagnosis is available below
Chest radiograph (not shown, obtained same day as PET examination): Demonstrates retained barium in the proximal third of the esophagus or false lumen.
Conventional PET scanners generate an attenuation map by obtaining transmission images with the patient positioned between a rotating germanium source and the camera detectors. With current dual modality PET/CT scanners, the CT data substitutes for the PET transmission data. CT acquisition not only is more rapid but also generates less image noise compared with the PET transmission scan. Thus, total scan duration is reduced, and with image fusion, anatomic localization is markedly improved.
Because of differences in photon energy during the acquisition of CT data (40-140 keV) compared with PET data (511 keV), the CT attenuation data must be transformed into linear attenuation coefficients at 511 keV. Current attenuation maps have a maximum threshold of approximately 300 Hounsfield units. Difficulties arise when very dense objects (e.g. metal, barium, dental amalgam) are encountered because attenuation of 40-140 keV photons is greater than with 511 keV photons. This results in an over-estimation of attenuation and corrected images appear to demonstrate increased activity.
A follow up CT chest examination 3 months later demonstrated interval enlargement of the pulmonary nodule from 1.8 x 1.4 cm to 2.3 x 1.9 cm likely representing pulmonary metastatic disease.
View followup image(gs). Barium swallow examination performed 2 days prior to PET imaging examination. This demonstrates a fistula between the esophagus and the retropharyngeal soft tissues.
2. One potential solution to this problem is to raise the maximum threshold when deriving the attenuation map so that when differences in attenuation of very dense objects are encountered, it is properly included in the correction.
Bujenovic, S. et al. "Artifactual 2-Deoxy-2(F18)Fluoro-D-Glucose Localization Surrounding Metallic Objects in a PET/CT Scanner Using CT-Based Attenuation Correction." Molecular Imaging and Biology. Vol. 5. No. 1. 20-22, 2003.
Seigel, B. “Interpreting Oncologic FDG PET Images.” PET Imaging for the Radiologist. CD-ROM. ACR Publications. September 2002.
References and General Discussion of PET Tumor Imaging Studies (Anatomic field:Lung, Mediastinum, and Pleura, Category:Other(Artifact))
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