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Background
MRI is the primary imaging modality used to assess the soft tissue structures around the ankle joint including the ligaments, tendons, and articular cartilage. 2D fast spin echo/turbo spin echo (FSE/TSE) sequences are routinely used for ankle joint imaging. Although the 2D sequences provide a good signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) with in-plane resolution, there are some limitations to their use, owing to the thick slices, interslice gaps leading to partial volume artifacts, limited fluid contrast, and the need to acquire separate images in different orthogonal planes. 3D MR imaging can overcome these limitations and recent advances have led to technical improvements that enable its widespread clinical use in acceptable time periods of 3 - 4 minutes. Recent advances have enabled the acquisition of thin continuous slices with isotropic voxels allowing multiplanar reconstructions. This exhibit reviews the technical developments in the domain 3D MRI, compares imaging with 3D versus 2D sequences, and demonstrates the use-case scenarios and benefits of 3D MRI in evaluating various ankle and foot pathologies.

Educational Goals / Teaching Points
Discuss MRI protocol and technical specifications of the 3D MRI protocol with a comparison to 2D MRI protocol. Case scenarios of different tissue structures in and around ankle joint outlining the utility of 3D isotropic MRI and related structure-specific reconstructions. Illustrate pathology of ankle tendons, ligaments, and hyaline cartilage with fine-detailed demonstration, such as split tears of tendons, measurement of tendon gap along their long axes, depiction of bilaminar and multilaminar anatomy of ankle ligaments and tears of individual portions, spring ligament pathology, and accurate grading of hyaline cartilage damage. 3D depiction of nerves with effective arterial signal suppression on 3D MRI with demonstration of nerve anatomy, nerve injuries and other lesions.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Ankle ligaments: lateral collateral ligaments, the medial collateral ligaments, and the distal tibiofibular syndesmosis. Lisfranc ligament and other midfoot ligaments. Tendons: tendinopathy to complete tears. Hyaline cartilage of the ankle joint: Flexor digitorum brevis (flexor hallucis brevis for the first MTP joint) tendon, intermetatarsal ligament, suspensory or accessory ligaments, and plantar fascia. Peripheral nerves: acute trauma, chronic microtrauma, or pressure injury due to entrapment syndromes (like tarsal tunnel syndromes) or other pathologies like nerve sheath tumors, systemic neuropathies or metabolic conditions (diabetic neuropathy).

Conclusion
In conclusion, this exhibit will demonstrate how high-resolution 2D and 3D isotropic MRI can produce excellent quality imaging with fine-detailed assessment of ankle ligaments, tendons, articular cartilage, and nerves. The reader can use this information to enhance their diagnostic confidence and accuracy for ankle derangement diagnosis.