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. 2018 Mar-Apr;19(2):358-365.
doi: 10.3348/kjr.2018.19.2.358. Epub 2018 Feb 22.

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

Wei Zhang  1 , Yue Zhou  2 , Xiao-Quan Xu  1 , Ling-Yan Kong  1 , Hai Xu  1 , Tong-Fu Yu  1 , Hai-Bin Shi  1 , Qing Feng  3
Affiliations

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

Wei Zhang et al. Korean J Radiol. 2018 Mar-Apr.

Abstract

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 (ADCmean), median ADC (ADCmedian), 10th and 90th percentile of ADC (ADC10 and ADC90), 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 ADCmean, ADCmedian, ADC10, ADC90, 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 ADC10 demonstrated optimal differentiating performance (cut-off value, 0.403 × 10-3 mm2/s; area under the receiver operating characteristic curve [AUC], 0.977; sensitivity, 92.3%; specificity, 93.3%), followed by the ADCmean, ADCmedian, ADC90, and hot-spot-ROI-based mean ADC. The AUC of ADC10 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.

Keywords: Apparent diffusion coefficient; Diffusion weighted imaging; Histogram analysis; Lymphoma; Mediastinal mass; Thymic carcinoma.

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Figures

Fig. 1
Fig. 1. Schematic diagram of placements of ROIs.
In terms of hot spot ROI based mean ADC measurements, slice on which tumor showed biggest diameter was chosen. Three circular ROIs were drawn on tumor's area which demonstrated mostly increased signal intensity on diffusion weighted image (b1000 map) (A). In terms of histogram analysis, ROIs were manually drawn on each slice that encompassed much of tumor area (B). ADC = apparent diffusion coefficient, ROI = region of interest
Fig. 2
Fig. 2. Box plots show comparison of histogram-based and hot-spot-ROI-based ADC measurements between thymic carcinoma and lymphoma.
Fig. 3
Fig. 3. Images of 39-year-old man with diffuse large B cell lymphoma.
Axial T1-weighted image (A) shows mass in anterior mediastinal region. After ROI was placed (B), pixel-by-pixel colored ADC map (C) was generated and embedded in axial diffusion-weighted imaging. Histogram analysis of whole lesion shows lower cumulative ADC value but higher relative frequency (D). ADCmedian and ADC10 were 0.502 and 0.146 × 10−3 mm2/s, respectively. Typical histopathologic appearance on hematoxylin-eosin stain (E, × 10) and CD20 positive on immunohistochemistry (F, × 10) confirmed diagnosis of lymphoma.
Fig. 4
Fig. 4. Images of 42-year-old man with thymic squamous cell carcinoma.
Axial T1-weighted image shows mass in anterior mediastinal region (A). After ROI was placed (B), pixel-by-pixel colored ADC map (C) was generated and embedded in axial diffusion-weighted imaging. Compared with lymphoma, histogram analysis of whole lesion showed higher cumulative ADC value but lower relative frequency (D). ADCmedian and ADC10 were 0.895 and 0.395 × 10−3 mm2/s, respectively. Typical histopathologic appearance on hematoxylin-eosin stain (E, × 10) and P63 positive on immunohistochemistry (F, × 10) confirmed diagnosis of squamous cell carcinoma.
Fig. 5
Fig. 5. Receiver operating characteristic curves of histogram-based and hot-spot-ROI-based ADC measurements for differentiating thymic carcinoma from lymphoma.
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