Comparison of visual and ROI-based brain tumour grading using F-18-FDG PET: ROC analyses

Several studies have suggested that the use of simple visual interpretation criteria for the investigation of brain tumours by positron emission tomog raphy with fluorine-18 fluorodeoxyglucose (FDG-PET) might be similarly or e ven more accurate than quantitative or semi-quantitative approaches. We inv estigated this hypothesis by comparing the accuracy of FDG-PET brain tumour grading using a proposed six-step visual grading scale (VGS; applied by th ree independent observers unaware of the clinical history and the results o f histopathology) and three different region of interest (ROI) ratios (maxi mal tumour uptake compared with contralateral tissue [Tu/Tis], grey matter [Tu/GM] and white matter [Tu/WM]). The patient population comprised 47 pati ents suffering from 17 benign (7 gliomas of grade II, 10 non-gliomatous tum ours) and 30 malignant (23 gliomas of grade III-IV, 7 non-gliomatous tumour s) tumours. The VGS results were highly correlated with the different ROI r atios (R=0.91 for Tu/GM, R=0.82 for Tu/WM, and R=0.79 for Tu/Tis), and high inter-observer agreement was achieved (kappa =0.63, 0.76 and 0.81 for the three observers). The mean ROI ratios and VGS readings of gliomatous and no n-gliomatous lesions were not significantly different. For all measures, hi gh-grade lesions showed significantly higher FDG uptake than low-grade lesi ons (P<0.005 to P<0.0001, depending on the measure used). Nominal logistic regressions and receiver operating characteristic (ROC) analyses were used to calculate cut-off values to differentiate low- from high-grade lesions. The predicted (by ROC) diagnostic sensitivity/specificity of the different tests (cut-off ratios shown in parentheses) were: Tu/GM: 0.87/0.85 (0.7), T u/WM: 0.93/0.80 (1.3), Tu/Tis: 0.80/0.80 (0.8) and VGS: 0.84/0.95 (uptake < GM, but <much greater than> WM). The VGS yielded the highest Az (+/-SE) va lue (i.e. area under the ROC curve as a measure of predicted accuracy), 0.9 7+/-0.03, which showed a strong tendency towards being significantly greate r than the Az of Tu/Tis (0.88+/- 0.06; P=0.06). Tu/GM (0.92+/-0.04) and Tu/ WM (0.91+/- 0.05) reached intermediate Az values (not significantly differe nt from any other value). We conclude that the VGS represents a measure at least as accurate as the Tu/GM and Tu/WM ratios. The Tu/Tis ratio is less v alid owing to the high dependence on the location of the lesion. Depending on the investigator's experience and the structure of the lesions, the easi ly used VGS might be the most favourable grading criterion.