ARRS 2022 Abstracts

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E2008. Fat Suppression MRI Techniques and Their Application for Evaluation of Fat-Containing Mediastinal and Pulmonary Lesions
Authors
  1. bruno Hochhegger; University of Florida
  2. Jeanne B Ackman; Harvard University
  3. Tan-Lucien H Mohammed; University of Florida
  4. Pratik P. Patel; University of Florida
  5. Nupur Verma; University of Florida
  6. Ryan Schwertner; University of Florida
Background
CT can be helpful in the detection and diagnosis of fat-containing mediastinal and pulmonary lesions, including thymic hyperplasia, dermoid cysts, pulmonary hamartomas, and lipoid pneumonia, but CT can only do so if the lesions contain macroscopic fat. Because CT cannot demonstrate microscopic fat (intravoxel fat and water), it fails to identify and diagnose microscopic fat-containing lesions. MRI, employing spectral and chemical shift MR fat suppression techniques, can identify both macroscopic and microscopic fat, with resultant enhanced capability to diagnose these intrathoracic lesions noninvasively.

Educational Goals / Teaching Points
This paper aims to review the MRI findings of fat-containing lesions of the mediastinum and lung and describe the fat suppression techniques utilized in their assessment.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Our paper will discuss MR fat suppression techniques and clinical applications. MR fat suppression can be achieved by two primary means and for two different purposes: (1) spectral fat suppression or "fat saturation" to identify the presence of macroscopic fat, and (2) fat suppression by chemical shift gradient-echo imaging for identification of microscopic fat. On MRI, macroscopic fat within a lesion appears hyperintense on T1- and T2-weighted fast spin-echo images and in-phase T1-weighted images. When spectral fat suppression is utilized, the macroscopic fat signal is suppressed – an occurrence often referred to as "fat-saturation." Spectral fat suppression can also be employed to enhance the soft tissue contrast of non-macroscopic fat-containing tissues, highlighting the T2-hyperintensity of non-fatty lesions and the enhancement of lesions on post-contrast T1-weighted imaging. When in- and opposed-phase chemical shift MRI is employed, areas within a lesion containing intravoxel fat and water, so-called "microscopic fat," that are imperceptible by CT are suppressed on opposed-phase imaging.

Conclusion
In summary, MRI is a valuable tool for the evaluation of fat-containing thoracic lesions. In particular, MRI helps detect CT-occult fat, thereby refining the differential diagnosis and adding diagnostic specificity, without ionizing radiation exposure. Fundamental knowledge about MRI techniques, findings, and pathology can help radiologists and other healthcare providers with non-invasive diagnosis and clinical management of fat-containing intrathoracic lesions.