*3.8. Discriminatory Power between Benign and Malignant Lymph Nodes*

The parametric PET parameters MR-FDGmean, Patlak Kimean, and DV-FDGmean provided excellent discriminatory power between LNM and benign LN. The AUC of the static PET parameter SUVmean (AUC 0.993) was slightly, but not significantly, higher than parametric PET parameters, as detailed in the ROC (Figure 7) and Table 4. SUVmean showed the highest sensitivity and specificity within all PET parameters at an optimal cut-off value of SUV 2.6.

For parametric PET, MR-FDGmean revealed the highest AUC of 0.987 followed by Patlak Kimean and DV-FDGmean with non-significantly lower AUC of 0.958 and 0.948, respectively. Semiautomatic diameter measurements also reached excellent AUC with 0.969 for the short-axis and 0.947 for the long-axis diameter, as shown in Figure 7 and Table 4. The calculation of the tumor-to-liver or tumor-to-metastases ratios did not improve AUC for either Patlak Kimean, MR-FDGmean, DV-FDGmean, or SUVmean.


**Table 4.** AUC values of mediastinal lymph nodes (n = 65, prevalence: 18.5%).

Significant results are highlighted in bold.

**Figure 7.** ROC analyses of CT morphologic, static as well as parametric, PET data to differentiate between malignant and benign lymph nodes. CT = Computer Tomography; DV-FDG = Distribution Volume of FDG; FDG = Fluorodeoxyglucose; Ki = Influx Rate Constant; MR = Metabolic Rate; NSCLC = Non Small Cell Lung Cancer; SUV = Standardized Uptake Value; SCLC = Small Cell Lung Cancer.
