Diagnostic values of 18F-FDG PET / CT Diagnostic values of PET / CT for recurrent, metastatic thyroid cancer In this study, the diagnostic values of PET / CT were as follow: sensitivity 92.9%, specificity 75%, positive predictive value 92.9%, negative predictive value 75%, fale positive rate 25%, false negative rate 7.1% and accuracy 89% (Table 3.31).