Contrast Agent Free MRI of the Thoracic Duct: Cream Improves Feasibility

Objectives: The anatomical complex lymphatic system is difficult to image. Conventional lymphangiography, which involves invasive procedures and patient discomfort, is used for this purpose. Recently, MR lymphography based on heavily T2-weighted magnetic resonance cholangiopancreatography (MRCP) sequences appears to be a useful noninvasive technique to visualize the lymphatic system (Arrivé et al and Dori et al). As fat-free diet is recommended to reduce the lymphatic flow in patients having a chylothorax, a fat meal might improve feasibility of the lymphatic vessels. Chen et al (Clin Physiol Funct Imaging 2016) hypothesized that a high-fat meal improves visualization of the TD in nonenhanced MR lymphography. In this study, we wanted to develop an optimal sequence for MRI of the lymphatic vessels and prove the hypothesis of Chen et al.

Methods: We examined 15 healthy volunteers (18.9–32.4 years) on a 3.0T unit (MAGNETOM Prisma^Fit system (Siemens Healthineers). A 3D turbo spin echo (TSE) sequence was applied using respiratory gating with isotropic voxel size 0.6 × 0.6 × 0.6 mm³, TR 2,400 ms, TE 692 ms, FoV 460 mm, and acquisition time (11:56–23:28 min). First examination was conducted after an overnight fast, second examination 3 hours after a drink of 200 mL cream (fat content 64 g) and a solid meal. Before the MRI examination, volunteers drank a glass of pineapple juice which is the clinical standard when using MRCP approach. Pineapple contains manganese, which reduces undesired signals from the stomach.

Results: The TD was divided for evaluation into four parts (abdominal, distal half of the thoracic part, proximal half of the thoracic part, and cervical part). Two radiologists and one pediatric cardiologist with special experience in MRI evaluated the visibility with a score according to Chen et al (0 = poor, 1 = good, and 2 = excellent). The score of the whole TD improved after a fat meal (mean ± SD: 4.5 ± 1.7 vs. 5.9 ± 1.8, p = 0.007) tested by sign test was statistically significant. Rater reliability was assessed using the intraclass correlation coefficient according to Shrout and Fleiss.

Conclusion: We could show in 15 healthy volunteers that a fat meal with cream improves feasibility of the TD, which confirms the findings of Chen et al. This noninvasive and gentle method might be useful to examine the thoracic lymphatic vessels in patients, for example, with Fontan circulation to visualize pathologies. It shows a single image, for visualization of leaks dynamic lymphangiography is of advantage.