Computed tomography (CT) and magnetic resonance imaging (MRI) are the most commonly used imaging examinations to evaluate thoracic aortic diseases because of their high spatial and temporal resolutions, large fields of view, and multiplanar imaging reconstruction capabilities. CT and MRI play an important role not only in the diagnosis of thoracic aortic disease but also in the preoperative assessment and followup after treatment. In this review, the CT and MRI appearances of various acquired thoracic aortic conditions are described and illustrated. 1. Introduction Computed tomography (CT) and magnetic resonance imaging (MRI) are the commonly used imaging examinations for evaluating a variety of acquired aortic lesions including aneurysm, dissection, ulcer, intramural hematoma, traumatic injury, and aortitis. Both CT and MRI have excellent spatial and temporal resolutions, wide fields of view, and multiplanar imaging capabilities [1]. Multidetector-row CT (MDCT) of the aorta is more commonly used than MRI because of the rapid scan times and wider availability. CT is usually performed with electrocardiographic (ECG) gating in order to avoid motion artifacts in the ascending aorta that might produce a false appearance of dissection or result in inaccurate measurements [2]. Since ECG gating is associated with significant increase in radiation dose, various dose reduction techniques such as prospective ECG triggering, ECG-based tube current modulation, automatic exposure control, lower peak kilovoltage (kVp), and iterative reconstruction algorithms are used [3–6]. CT requires the use of potentially nephrotoxic iodinated contrast agents, which should be avoided in patients with renal dysfunction. Serum creatinine and GFR should be obtained in patients receiving intravenous contrast. If the GFR is >45？mL/min, contrast can be administered without any preparation. If the GFR is between 30 and 44？mL/min, contrast can be administered with pre- and postprocedural hydration. If GFR is less than 30？mL/min, contrast should not be administered. If the patient is on dialysis, contrast can be administered regardless of GFR. MRI does not involve the use of radiation or nephrotoxic iodinated contrast media. Three-dimensional contrast-enhanced magnetic resonance angiogram (3D CE-MRA) acquired after administration of gadolinium can be reconstructed in multiple planes enabling evaluation of complex vascular abnormalities. These examinations are typically acquired without ECG gating, which can lead to blurring of the aortic root and proximal ascending aorta. However,
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