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Background
Intravascular ultrasound (IVUS) provides critical information on intravascular morphology and aids as a diagnostic, preprocedural, and intraprocedural guide. In the current exhibit, we describe the various applications of IVUS including venous interventions such as stent venoplasty, Inferior vena cava (IVC) filter placement, and May-Thurner syndrome, and aortic interventions such as fenestration of aortic dissection, endovascular aortic aneurysmal repair, and assessment of invasive tumor involving the aortic wall. Our exhibit targets practicing radiologists and radiology residents.

Educational Goals / Teaching Points
Review the various diagnostic and therapeutic applications of IVUS, imaging description of the IVUS-guided interventions, limitations, and future directions of IVUS.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
IVUS provides information on the morphology and size of the target vessel for stent placement in addition to visualization of small branches of the target vessels which may interfere with the proper stent fitting. The long-term stent patency rate was reported to be 62 - 100% in IVUS guided and 69 - 83% in non-IVUS-guided procedures. During the transjugular intrahepatic portosystemic shunt technique, the IVUS facilitates the direct real-time visualization of the portal and hepatic vein puncture sites, thereby increasing the technical success rate, particularly in portal vein thrombosis and Budd-Chiari syndrome. In patients with May-Thurner syndrome (MTS), IVUS determines the acuity of the lesion, visualizes the degree of vessel compression, and detects the venous “spurs.” The technical success rate of IVUS-guided stenting in MTS and acute vessel occlusion is 100%, while in chronic occlusion, it is 90%. It plays a crucial role in patients who require IVC filter placement and have contraindications or limitations to routine angiographic techniques. Studies reported that IVUs guided IVC filter placement has a success rate of 96.3%. To relieve the distal vessel ischemia secondary to aortic dissection, balloon catheter-guided fenestration of the intimal flap is performed with the guidance of IVUS and x-ray fluoroscopy. IVUS demonstrates the hypoechogenic vessel wall which is 90% sensitive and 95% specific to the tumor invasion into the aortic wall.

Conclusion
IVUS aids in the proper evaluation of vascular conditions in real-time. Specifically, in situations where contrast cannot be used or have concerns about ionizing radiation, IVUS plays a crucial role. Hence, an insight into its various applications in clinical practice is imperative to improve the quality of care to the patients.