Abstract Background Diffusion weighted imaging (DWI) has been used to evaluate parotid gland tumors. Warthin’s tumors (WTs) have very high diffusion-derived vessel ‘density’ (DDVD) and low ADC, while pleomorphic adenomas (PAs) have moderately high DDVD and very high apparent diffusion coefficient (ADC). These two most common benign tumors (BTs) can be largely separated by a combination of ADC and DDVD. However, most of the MTs (malignant tumors) had moderately high DDVD and low ADC, the differentiation between BT and MT remains challenging. Slow diffusion coefficient (SDC) is a novel metric being proposed to measure in vivo tissue slow diffusion. In its basic form, SDC is derived from a high b -value DWI image and a higher b -value DWI image. This study tested the application of SDC to evaluate parotid gland tumors. Methods Twenty-four PAs, 16 WTs, and 14 MTs had DWI at 3T. ADC was calculated with b = 0 and 800 s/mm 2 images. SDC was calculated with b = 600 and 800 s/mm 2 images. DDVD was calculated with b = 0 and 20 mm 2 /s images. The ratio of a tumor diffusion metric measure to a contra-lateral tumor-free parotid gland tissue diffusion metric measure was obtained, resulting in ADCr, SDCr, and DDVDr. Pearson test was used for correlation analysis. A receiver operating characteristic curve analysis and the area under the ROC curve (AUROC) were used to assess the diagnostic performance. Results Parotid gland tumors had a higher SDC than normal parotid gland tissue with SDCr > 1. SDCr was on average PAs (median: 3.075) > MTs (2.755) > WTs (2.250). Separation of BT against MT by ADCr alone, by a combination of ADCr and SDCr, and by a combination of ADCr, SDCr, and DDVDr had AUROC of 0.7393, 0.8018, 0.8054, respectively. The probability of a tumor being MT is given by: ln(p/1-p) = 0.7006*SDCr-3.198*ADCr + 1.417; or ln(p/1-p)=-0.2225*DDVDr-3.41ADCr + 0.7603*SDCr + 2.103. SDCr was positively correlated with ADCr with a Pearson r of 0.624, while SDCr was not apparently correlated with DDVDr. Conclusion This study tested the principle of applying four b -values DWI to generate three diffusion metrics, namely, ADC, SDC, and DDVD, to evaluate parotid gland tumors. A combination of these three diffusion metrics may offer clinically useful separation of MT from BT. Clinical trial number Not applicable.
Yao et al. (Mon,) studied this question.