28. Accuracy of Qualitative and Semiquantitative Analysis of 18FDG Positron Emission Tomography Scans in the Evaluation of Primary and Metastatic Lesions

Background: ¹⁸FDG PET scans are often interpreted on the basis of visual estimation of regional tracer uptake. Whether semiquantitative analysis may help clinicians in the recognition of neoplastic masses still remains debated.

Materials and Methods: 134 patients with 144 dubious lesions on CT scans (89 pulmonary, 16 hepatic, 39 soft tissue) were studied by means of PET and ¹⁸(F)fluorodeoxyglucose. PET images were qualitatively interpreted by the consensus of two nuclear physicians. Standardized uptake value (SUV) and SUV lean were quantified in both normal and suspicious tissues. SUVs results in the lesion were also expressed as normalized values for the normal mean value in each organ (SUVs/org) and for the overall mean value in normal tissues (SUVs/norm).

Results: All patients underwent cytological and/or hystological evaluation of the lesions: 53/144 (37%) were recognized as negative while 91/144 (63%) as positive for primary or metastatic disease. Qualitative analysis resulted in 75% specificity and 93% sensitivity. SUVs, SUVs lean, SUVs/org and SUVs/norm resulted significantly (p < 0.001) higher in positive than in negative lesions by cytology/histology. ROC curves analysis provided optimal cut-off values of 2.5, 0.8, 2.5 and 3, for SUVs, SUVs lean, SUVs/org and SUVs/norm, respectively. Using these cut-offs, specificity and sensitivity resulted 90 and 94%, 83 and 97%, 88 and 93%, 94 and 93%, respectively.

Conclusion: Our data suggest that, in patients with CT scan suspicious lesions, visual analysis of PET scans is affected by a high number of false negative results. Semiquantitative assessment of regional metabolic activity has an incremental value and should be used in PET scan interpretation of dubious lesions.