Artifacts on FDG PET/CT




Abstract


All imaging modalities may be compromised by artifacts that obscure malignancy or mimic malignancy. FDG PET/CT may be compromised by a multitude of artifacts, primarily associated with technical performance of PET/CT scanners and unexpected biodistribution of FDG. A few of the more common artifacts on FDG PET/CT are discussed in this chapter, including motion, attenuation correction, partial volume effects, suboptimal FDG biodistribution, and blooming artifacts.




Keywords

FDG, PET/CT, artifacts, motion, attenuation correction, partial volume effects, blooming artifact

 


All imaging modalities may be compromised by artifacts which obscure malignancy or mimic malignancy. 18F-fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) may be compromised by a multitude of artifacts, primarily associated with technical performance of PET/CT scanners and unexpected biodistribution of FDG. A few of the more common artifacts on FDG PET/CT are discussed here.




Motion


Patient motion during acquisition of PET/CT images may introduce multiple artifacts which need to be recognized. The PET/CT scanner is composed of separate PET and CT imaging elements. Thus, although we refer to PET/CT images, it is important to remember that separate PET and CT images are obtained and then fused together. Under idealized conditions we expect there to be perfect alignment of the PET and CT images; however, this is virtually never the case. Motion of the patient between acquisition of the CT images and the PET images will result in misregistration of the combined PET/CT images, which may obscure an otherwise appreciable malignancy. This is common in the head and neck, if the head is not immobilized. This will also produce incorrect attenuation correction maps from the CT images and lead to incorrect calculation of standardized uptake values (SUVs).


Even if voluntary muscular motion of the head/neck and extremities is perfectly controlled for, involuntary motion will invariably affect PET/CT images. Motion of the diaphragm will cause misregistration between CT and PET images in the lower lungs and upper abdomen, sometimes quite significantly. This could result in artifactual placement of liver lesions over the lung on PET ( Fig. 23.1 ), or vice versa. Incorrect localization of photons and suboptimal attenuation correction maps from diaphragmatic motion will artifactually lower SUVs for lesions near the diaphragm. In the extreme, this problem may cause lesions in the lower lungs or upper abdomen to artifactually disappear from PET images ( Fig. 23.2 ). Careful evaluation of the CT images near the diaphragm is important to prevent these errors.




FIG. 23.1


Diaphragmatic Motion Causing Mislocalization of a Liver Metastasis on to the Lung.

(A) FDG maximum intensity projection (MIP) in a patient with metastatic paraganglioma demonstrates substantial abnormal FDG avidity overlying the midline abdomen (arrow) and an abnormal focus overlying the lower right chest (arrowhead) . (B) Axial PET, CT, and fused FDG PET/CT images demonstrate the focus overlying the chest localizes to the right lung; however, no lung abnormalities are apparent of CT (arrowheads) . (C) Axial PET, CT, and fused FDG PET/CT images over the upper abdomen demonstrate the primary malignancy (arrows) and the liver metastasis on CT (arrowhead), which is mislocalized onto the lung on the PET images.



FIG. 23.2


Diaphragmatic Motion Contributing to “Disappearing” Liver Metastases.

(A) FDG maximum intensity projection (MIP) in a patient with primary esophageal cancer demonstrates the FDG-avid primary esophageal malignancy (arrow) and abnormal FDG foci overlying the liver (arrowhead) . (B) Axial CT and fused FDG PET/CT images demonstrate the primary esophageal malignancy (arrow) and FDG-avid liver metastases (arrowheads) . (C) FDG MIP in the same patient on a repeat baseline FDG PET/CT performed for requirements of a clinical trial. No therapy in the interim. The primary esophageal malignancy (arrow) in unchanged, but metastases in the superior portion of the liver have disappeared (arrowhead) . Note the flattening of the superior surface of the liver near the arrowhead, which is a clue to the problem on PET. (D) Axial CT and fused FDG PET/CT images also demonstrate the primary esophageal malignancy is unchanged (arrow) but the superior liver metastases have disappeared. Motion at the diaphragm between CT and PET images, and the arms-down positioning, has contributed to obscuring the metastases that should be seen on the superior aspect of the liver.

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Jun 18, 2019 | Posted by in GENERAL RADIOLOGY | Comments Off on Artifacts on FDG PET/CT

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