Mediastinal and Pleural MR Imaging: Practical Approach for Daily Practice.

Radiologists in any practice setting should be prepared to use thoracic magnetic resonance (MR) imaging for noncardiac and nonangiographic applications. This begins with understanding the sequence building blocks that can be used to design effective thoracic MR imaging protocols. In most instances, the sequences used in thoracic MR imaging are adapted from protocols used elsewhere in the body. Some modifications, including the addition of electrocardiographic gating or respiratory triggering, may be necessary for certain applications. Once protocols are in place, recognition of clinical scenarios in which thoracic MR imaging can provide value beyond other imaging modalities is essential. MR imaging is particularly beneficial in evaluating for benign features in indeterminate lesions. In lesions that are suspected to be composed of fluid, including mediastinal cysts and lesions composed of dilated lymphatics, MR imaging can confirm the presence of fluid and absence of suspicious enhancement. It can also be used to evaluate for intravoxel lipid, a finding seen in benign residual thymic tissue and thymic hyperplasia. Because of its excellent contrast resolution and potential for subtraction images, MR imaging can interrogate local treatment sites for the development of recurrent tumor on a background of post-treatment changes. In addition to characterization of lesions, thoracic MR imaging can be useful in surgical and treatment planning. By identifying nodular sites of enhancement or areas of diffusion restriction within cystic or necrotic lesions, MR imaging can be used to direct sites for biopsy. MR imaging can help evaluate for local tumor invasion with the application of "real-time" cine sequences to determine whether a lesion is adherent to an adjacent structure or surface. Finally, MR imaging is the modality of choice for imaging potential tumor thrombus. By understanding the role of MR imaging in these clinical scenarios, radiologists can increase the use of thoracic MR imaging for the benefit of improved decision making in the care of patients. ©RSNA, 2018.