الفهرس 
AcknowledgementOnly 14 pages are availabe for public view
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Abstract
The diagnosis of vascular rings is easily accessible with MRI. In double aortic arch, axial and coronal views show the encirclement of the esophagus and trachea by the double arches and the caliber of both arteries. In cases of right aortic arch and aberrant right subclavian artery, the vascular course and origin are shown. The location and severity of compression varies with the configuration of the lesion. By using cine MRI, evaluation of the amount of constriction the ring exerts on the esophagus and trachea is determined.
The MR diagnosis of cervical aortic arch shows the arch cranial to its usual position.
In transposition of the great vessels, axial, sagittal and coronal planes demonstrate the normal relationship of the ventricles, the abnormal, parallel relationship of the aortic and pulmonary arteries and the caliber of each artery. Also, the presence and severity of any associated anomalies can be determined.
In patients with patent ductus arteriosus, MR images can clearly depict the connection, showing the course of the ductus from the proximal descending aorta to the left pulmonary artery.
The diagnosis of aortic arch obstructive lesions using MRI is a standard procedure nowadays; the MR images show the site of the coarcatation and the jet flow giving an idea about the severity of the stenosis, and the presence of collaterals. All these information allows the surgeon to plane a proper corrective surgical procedure.
The advantages of MRI over CT can be summarized in the fact that MRI does not require the use of an iodinated contrast medium and, obviously, the use of non-ionizing radiation.
The advantages that MRI has as compared to Transesophageal Echocardiography (TEE) are the wider field of view, greater topographical detail, and especially its non-invasiveness.
TEE is less efficient than MRI in the study of the ascending aorta and the arch of the aorta and requires a highly skilled operator to follow the tortuous coursing of the vessel, as often happens. Moreover, TEE is a semi-invasive technique that is usually not well tolerated by the patient.
Catheter angiography has been the traditional imaging modality in more difficult cases of aortic arch anomalies. This technique also has its limitations, including ionizing radiation, potential reactions to contrast media and more important, the limited amount of contrast (based on the patient weight) that can be used in evaluation of complex disease. Because of this, repeated angiography is often required to delineate the entire extent of the anomaly.
However, MRI has its limitations; it is less available and takes a relatively long examination time. Sedation is usually needed for children and some adults. MRI is contraindicated in patients with pacemakers. MR images are vulnerable to patient’s motion and arrhythmia that disturb the ECG gating. Metal objects in the chest wall, coils, stents and surgically placed prostheses all produce artifacts especially in GRE studies that could decrease diagnostic capacity of MRI.
In addition, velocity mapping necessitates special gradient systems to measure the high velocities across stenotic lesions; these systems are not present in most of the available MRI machines and are expensive softwares.
The relatively modest use of MRI compared to these other techniques is mainly due to its scarce diffusion and, consequently, the reduced familiarity of clinicians to its use.
In conclusion, MR imaging and MR angiography, suggest that MR imaging will play an increasingly important role in the evaluation of aortic arch anomalies and their consequences, since it provides a non invasive mean of evaluation, allowing the demonstration of the morphologic and functional abnormalities necessary for planning case management.