PET/CT in the Thorax: Pitfalls

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Key points

  • In PET/CT, the use of CT for attenuation correction of PET data has introduced artifacts that can lead to misinterpretation.

  • Knowledge of the variants in physiologic uptake of [18F]-fluoro-2-deoxy-d-glucose is useful in avoiding misinterpretation in PET/CT.

  • Potential pitfalls in interpretation of PET/CT include malignancies that are PET negative and benign conditions that are PET positive.

Technical artifacts

In integrated PET/CT, the data sets of PET and CT are matched, resulting in more accurate localization of regions of increased FDG uptake and more accurate staging compared with visual correlation of PET and CT images acquired separately.4 Integrated PET/CT uses CT values for attenuation correction of the 511-keV positron annihilation photons of FDG. This correction has introduced artifacts that can result in quantitative errors in SUV measurements and misinterpretation.3 These artifacts

Physiologic FDG uptake

FDG is a glucose analog that is transported into both normal and malignant cells.12 Consequently, FDG uptake is not tumor-specific and can be seen in active tissues with high glucose metabolism. High physiologic uptake of FDG typically occurs in the brain, kidneys, and urinary tract. Low degree of physiologic uptake of FDG is seen in the thorax, including the heart, great vessels, esophagus, thymus, and bone marrow. Variations in physiologic uptake of FDG in striated muscle and brown fat can

PET negative malignancy

The role of PET/CT in the evaluation of solitary pulmonary nodules is well-known, with a sensitivity of 97% and a specificity of 78% for the detection of malignancy.19 Metabolism of glucose is typically increased in malignancy and an SUV cutoff of 2.5 has been used to differentiate benign from malignant nodules.1 In terms of patient management decision analysis, FDG-PET evaluation of solitary pulmonary nodules must be considered alongside such clinical risk factors as patient age, smoking

Infection and Inflammation

The major causes of false-positive results in PET/CT of the thorax are infectious and inflammatory etiologies (Fig. 5). Increased FDG uptake in infectious and inflammatory conditions has been reported to be due to increased glycolysis in leukocytes, lymphocytes, and macrophages.23 False-positive lesions have been reported to include pneumonia, caseating granulomas, sarcoidosis, amyloidosis, talc pleurodesis, rounded atelectasis, pleural fibrosis, atherosclerosis, and pulmonary embolism.24

In

Summary

Integrated PET/CT is increasingly being used to evaluate oncologic patients, and applications include tumor detection and characterization, differentiation of benign from malignant lesions, and staging of malignant lesions.

Accurate interpretation of PET/CT requires knowledge of the normal physiologic distribution of FDG, artifacts due to the use of CT for attenuation correction of the PET scan, and potential pitfalls due to malignancies that are PET-negative and benign conditions that are

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