Focal F-18 fluoro-deoxy-glucose accumulation in the lung parenchyma in the absence of CT abnormality in PET/CT

Division of Nuclear Medicine, Department of Radiology, Mayo Clinic, Rochester, MN, USA.
Journal of Computer Assisted Tomography (Impact Factor: 1.41). 01/2007; 31(5):800-5. DOI: 10.1097/RCT.0b013e3180340376
Source: PubMed

ABSTRACT To demonstrate 3 cases of artifactual focal F-18 fluoro-deoxy-glucose accumulation in the lung parenchyma in the absence of any computed tomographic (CT) abnormality.
Three patients were examined: a 30-year-old man who had a positron emission tomography (PET)/computed tomography for restaging a biopsy-proven recurrence of head and neck cancer, a 68-year-old woman who was referred for initial staging of esophageal carcinoma, and a 57-year-old man who had a PET/computed tomography for initial staging of melanoma. In each case, there was intense focal activity in the lung parenchyma with no corresponding CT abnormality. Each patient was further evaluated with a repeat PET scan in days 1 and 3 in the first 2 cases and with a delayed repeat acquisition in the third case. Patients were followed for 24, 10, and 1 month, respectively.
In the first 2 cases, the abnormal focal activity in the lungs had resolved in the repeat study. In the third case, the focus of increased activity in the lung had moved more peripherally in the delayed acquisition. Clinical follow-up was negative for disease in the corresponding pulmonary parenchymal sites.
The finding of significant focal accumulation of fluoro-deoxy-glucose in the lung parenchyma in the absence of corresponding CT abnormality was artifactual. This was likely due to injection technique and the creation of particulate embolus. Positron emission tomography/Computed tomographic readers should be aware of this type of artifact to avoid misinterpretation.

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    • "The technical aspects that can determine an underestimation of the true 18 F-FDG activity, especially in nodules smaller than 1 cm, are: the respiratory motion because of the displacement caused by shallow breathing, particularly in nodules located in the periphery and in the base of the lungs; the partial volume effect because nodules smaller than the resolution of the PET scanners (ranging from 6 to 10 mm in clinical applications) are not, or only faintly visualized [8,16,17]. Likewise, 18 F-FDG PET specificity for characterizing pulmonary nodules as probably malignant can be compromised by ‘metabolic’ causes and ‘technical’ aspects, which lead to false-positive results. "
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