Magnetic Resonance Imaging of Pulmonary Embolism: Diagnostic accuracy of contrast-enhanced 3D MRA, contrast- enhanced low flip angle 3D gradient echo and noncontrast steady-state free precession sequences

Introduction: Acute pulmonary thromboembolic disease is a significant cause of morbidity and mortality, with estimated yearly incidence of 650,000 cases in the USA. Pulmonary computed tomography angiography (CTA) is the current gold standard for PE diagnosis. However CTA has limitations regarding the use of iodinated contrast and relatively high ionizing radiation burdens, a consideration given that many PE studies are performed in young adult females. Magnetic resonance angiography (MRA) has a potential role for PE diagnosis, shown in multiple studies. However, alternative MRA-like methods that further improve diagnostic accuracy and simplify the acquisition techniques remains an area of clinically important development. Conventional MRA requires precise bolus timing acquisition, which may be hampered by a symptomatic PE patient. Non-bolus timed and motioninsensitive alternatives would provide improved clinical robustness of MRA-like methods. Another MRA limitation is that it provides a lumen-only imaging; mural PE filling defects will lack conspicuity as these appear as dark signal against the dark adjacent lung. MRA-like alternatives that produce enhancing signal from the vessel wall, provide high contrast without need for bolus timing, and/or provide motion-insensitivity to respiration include low flip angle (FA) 3D gradient echo (3D GRE), or steady state free precession (SSFP) sequences.