It bears mentioning that the CMR magnet is generally not in close proximity to the emergency room or intensive care units. As a precaution, unstable patients have not been routinely imaged by CMR; however, careful screening of patients permits reasonably safe, accurate and relatively fast, high-quality images to be obtained in certain circumstances. For the intubated and paralyzed patient, paradoxically, CMR performs better, because it is much easier to manage breath-holding by manual control, permitting high-quality imaging in the patient who may otherwise have been uncomfortable. In our facility, we conduct a discussion with the patient when possible, to explain the details of the study to be performed, the breath-hold instructions to be followed, and the plan for contrast administration. All of this helps to reassure and relax the patient. Nonetheless, evaluation of the patient by the imaging clinician is important in cases of a patient in extremis. By evaluating each patient prescan, when believed to be in an emergent situation, we have been successful in imaging many patients who might not have been considered candidates for CMR, turning down only the rare patient who is severely hypotensive, coding, or actively infarcting. This adds a small element of a time penalty, but the benefit to the patient to have the optimal examination performed is far more beneficial than the added morbidity and mortality of other more invasive and, potentially less accurate, techniques.

Once in the scanner, a rapid series of non-breath-hold double axial inversion recovery (IR) images are first obtained, which quickly provide a large amount of information, allowing a preliminary working diagnoses to be formed. If breath-hold images are required, they are then conducted. A series of parasagittal and coronal SSFP images of the aorta serves as the major imaging strategy, providing a large amount of important clinical information relating to structure, flow direction and characteristics, lumen patency, and localization of pathology. Oftentimes, in the setting of aortic dissection, the ability to detect and characterize intrinsic intimal flap fenestrations helps to dictate the need for subsequent interventional protection of mesenteric, renal, and runoff vessels. Specifically, if a Type aortic III dissection is present (see Tables 10-1 and 10-2 for classifications), surgical correction of the
ascending and arch aorta may be performed followed by balloon correction of aortic intimal flap fenestrations if they are not detected. In our laboratory, the evaluation of aortic pathology is not complete until the associated valvular and ventricular anatomy and physiology are defined. This entails evaluation of the aortic valve, sinus of Valsalva, and sinotubular junction, to detect the presence of aortic regurgitation. If present, the mechanism of valvular dysfunction is described, aiding in considerations for composite graft implantation. The extent, direction, and magnitude of the aortic regurgitation can be semiquantitatively assessed, and can be quantified by phase velocity mapping. SSFP images of the ventricle can be obtained to assess the impact of aortic regurgitation, left and right ventricular function, the presence of left ventricular hypertrophy, regional wall motion abnormalities, and left ventricle (LV) size. The presence of a pericardial effusion is an ominous sign, and should alert the interpreter that the dissection plane has extended through the pericardium. Generally, this means that there is occult dissection extending into the proximal ascending aorta. Given the large field of view (FOV) that CMR provides, the presence of a pleural effusion, especially a left pleural effusion, suggests that there has been extravasation of blood beyond the aortic wall and this is a major adverse cardiovascular prognostic sign.