Quantitative Histogram Analysis of T2-Weighted and Diffusion-Weighted Magnetic Resonance Images for Prediction of Malignant Thymic Epithelial Tumors

Abstract

Purpose: To assess the value of histogram analysis for differentiating a high-risk thymic epithelial tumor (TET) from a low-risk TET using T2-weighted images and the apparent diffusion coefficient (ADC).Methods: Forty-nine patients with histopathologically proven TET after thymectomy were enrolled in this study and retrospectively classified as having low-risk TET (low-risk thymoma) or high-risk TET (high-risk thymoma or thymic carcinoma). Twelve parameters were obtained from the quantitative histogram analysis. The histogram parameters were compared using the Mann-Whitney U test. Diagnostic efficacy was estimated by receiver-operating characteristic curve analysis.Results: Twenty-five patients were classified as having low-risk TET and 24 as having high-risk TET. The mean ADC value showed diagnostic efficacy for differentiating high-risk TET from low-risk TET, with an area under the curve of 0.7, and was better than when using conventional methods alone. Conclusion:The ADC-based histogram analysis could help to differentiate between high-risk and low-risk TETs.

Utility of non-contrast-enhanced magnetic resonance imaging in predicting preoperative clinical stage and prognosis in patients with thymic epithelial tumor

“…Of the 32 cases in this study in which ADC values were obtained, there was no significant difference in ADC values between stage I-II and stage III-IV tumors. In contrast to our results, several previous studies have found a significant difference in ADC values of TETs between Masaoka-Koga or Masaoka stage I-II and stage III-IV but differ as to whether the ADC values of stage III-IV tumors are significantly higher [ 23 ] or significantly lower [ 24 – 26 ] as compared to stage I-II tumors. Variability in results of these studies may relate to the differences in the placement of the ROI or volume of interest (VOI).…”

“…Inoue et al similarly reported significant differences in heterogeneous signal intensity on T1- and T2-weighted images and intratumor low-signal foci on T2-weighted image which may reflect tumor degeneration seen in histologically high-grade TETs, especially thymic carcinoma [ 11 ]. Morikawa et al reported that although the T2 minimum value on histogram analysis did not show significant differences in differentiating histological classification, the T2 minimum values were significantly lower in Masaoka-Koga stage III-IV than stage I-II [ 23 ]. Similar to previous reports [ 2 , 11 ], there was a significant correlation between the TNM classification and the WHO histological classification in the present study.…”

“…Variability in results of these studies may relate to the differences in the placement of the ROI or volume of interest (VOI). Since Morikawa et al included not only the solid component but also the hemorrhagic, cystic, and necrotic components within the VOIs to assess the ADC values, it is likely that the ADC maximum value would be higher for stage III-IV tumors than for stage I-II tumors [ 23 ]. Therefore, evaluation of ADC values requires careful consideration because the results may differ depending on the way placing the ROI or VOI.…”