Transesophageal Magnetic Resonance Imaging of Thoracic Aorta

Introduction Current standard techniques for imaging the thoracic aorta include CT, standard body-coil MRI, transesophageal echocardiography (TEE), and contrast aortography. Each of these techniques suffers some limitation in its ability to allow detailed mapping of the aortic wall and its anatomic and functional lesions. Body-coil MRI and CT lack adequate resolution of the aortic wall for precise characterization of aortic atheromata, and are not able to provide aortic wall tissue tagging information. TEE allows real time imaging, but suffers from both an inability to image clearly the quadrant of the aortic wall which is directly against the esophagus, and from an inability to register images to a fixed frame of reference. Contrast aortography is lumenography; the tissues which make up the aorta are not seen directly. Figure 1. Transesophageal MR images showing thoracic aorta. Arrow indicates position of antenna. Imaging parameters (A-C): ECG-gated, segmented k-space, SPGR with HOT pulses [3] at 10cm FOV, 256 x 140 matrix, flip=15°. (A) Short axis 7mm slice obtained during a single 27 second breath-hold, 4NEX, TR/TE 7.7/2.2ms. (B) and (C) are tagged tranverse and longitudinal slices allowing direct visualization of aortic wall strain in response to pulsatile blood flow (B: 7mm thick, 10s breath-hold, 2NEX, TR/TE 7.7/2.2ms; C: 3mm thick, 28s Previously a loopless catheter antenna has been used for in vivo intravascular imaging of rabbit aortae [1]. To address the need for a less invasive method of aortic imaging we exploited the fact that the esophagus and the aorta are directly juxtaposed throughout the length of the descending thoracic aorta. Our goal was to design and animal-test a device which, in principle, could be passed down the esophagus of a non-sedated human patient and provide information not obtainable by other non-invasive methods. breath-hold, 6NEX, TR/TE 8.7/2.6ms.)