A Whole-Tumor Histogram Analysis of Apparent Diffusion Coefficient Maps for Differentiating Thymic Carcinoma from Lymphoma

OBJECTIVE: To assess the performance of a whole-tumor histogram analysis of apparent diffusion coefficient (ADC) maps in differentiating thymic carcinoma from lymphoma, and compare it with that of a commonly used hot-spot region-of-interest (ROI)-based ADC measurement. MATERIALS AND METHODS: Diffusion weighted imaging data of 15 patients with thymic carcinoma and 13 patients with lymphoma were retrospectively collected and processed with a mono-exponential model. ADC measurements were performed by using a histogram-based and hot-spot-ROI-based approach. In the histogram-based approach, the following parameters were generated: mean ADC (ADC(mean)), median ADC (ADC(median)), 10th and 90th percentile of ADC (ADC(10) and ADC(90)), kurtosis, and skewness. The difference in ADCs between thymic carcinoma and lymphoma was compared using a t test. Receiver operating characteristic analyses were conducted to determine and compare the differentiating performance of ADCs. RESULTS: Lymphoma demonstrated significantly lower ADC(mean), ADC(median), ADC(10), ADC(90), and hot-spot-ROI-based mean ADC than those found in thymic carcinoma (all p values < 0.05). There were no differences found in the kurtosis (p = 0.412) and skewness (p = 0.273). The ADC(10) demonstrated optimal differentiating performance (cut-off value, 0.403 × 10(−3) mm(2)/s; area under the receiver operating characteristic curve [AUC], 0.977; sensitivity, 92.3%; specificity, 93.3%), followed by the ADC(mean), ADC(median), ADC(90), and hot-spot-ROI-based mean ADC. The AUC of ADC(10) was significantly higher than that of the hot spot ROI based ADC (0.977 vs. 0.797, p = 0.036). CONCLUSION: Compared with the commonly used hot spot ROI based ADC measurement, a histogram analysis of ADC maps can improve the differentiating performance between thymic carcinoma and lymphoma.