Figure 4a. (a) Scatterplot of Cho/Cr values obtained at an echo time of 136 msec for Warthin tumors, pleomorphic adenomas, an oncocytoma, and malignant tumors. A Cho/Cr ratio greater than 2.4 (dotted line) completely separates benign SGTs from cancers. In discriminating between Warthin tumors and pleomorphic adenomas, a Cho/Cr ratio of 4.5 or greater (dashed line) would give a sensitivity of 71.4% and a specificity of 84.6%. (b) Receiver operating characteristic curve (dashed line) of Cho/Cr values obtained at an echo time of 136 msec for use in differentiating Warthin tumor from pleomorphic adenoma. The area under the curve is 0.86 ± 0.09.