MRI Assessment of Chylous and Nonchylous Effusions: Use of Multipoint Dixon Fat Quantification.

Background Diagnosis of chylous effusions normally requires invasive paracentesis. Purpose To assess whether MRI with multipoint Dixon fat quantification allows for noninvasive differentiation of chylous and nonchylous ascites and pleural effusions. Materials and Methods Phantom, ex vivo, and in vivo MRI examinations were performed by using a commercially available multipoint Dixon pulse sequence with a 1.5-T MRI system. Fat fraction values were measured with a region of interest-based approach on reconstructed maps. For phantom evaluation, eight titrated fatty fluid solutions (nonhuman samples) with varying triglyceride content (145-19 000 mg/dL [1.64-214.7 mmol/L]) were examined. For ex vivo evaluation, 15 chylous and five nonchylous study participant fluid samples were examined. In a prospective study performed from June 2016 to February 2018, 29 study participants with known chylous (n = 17) and nonchylous (n = 12) effusions were evaluated with MRI. All clinical samples underwent laboratory testing for triglyceride level, total protein level, white blood cells, and red blood cells. Laboratory values were correlated with fat fraction values; the optimal fat fraction threshold was determined to differentiate chylous and nonchylous fluids. Results Phantom analysis showed that fat fraction values correlated with triglyceride content (r = 0.99, P < .001). In ex vivo studies, multipoint Dixon-derived fat fraction was higher in chylous versus nonchylous fluids (mean, 2.5% ± 1.2 [standard deviation] vs 0.8% ± 0.2; P = .001). Fat fraction was correlated with triglyceride content (r = 0.96, P < .001). For in vivo studies, fat fraction was greater for chylous versus nonchylous fluids (mean, 6.2% ± 4.3 vs 0.6% ± 0.6; P < .001). In vivo fat fraction was correlated with triglyceride content (r = 0.96, P < .001). Use of a fat fraction cutoff value greater than 1.8% yielded a sensitivity of 14 of 17 (82% [95% confidence interval (CI): 57%, 97%]) and a specificity of 12 of 12 (100% [95% CI: 74%, 100%]) for differentiation of chylous and nonchylous effusions. Conclusion MRI can help identify chylous versus nonchylous ascites and pleural effusions through use of multipoint Dixon fat quantification. © RSNA, 2020 Online supplemental material is available for this article.