The scanning delay was determined with the use of a bolus tracking technique. Imaging data was acquired after an intravenous injection of 1.5-2 ml/kg iodinated contrast agent (Iodixanol, 320 mgI/ml Visipaque, GE Healthcare) at a rate of 3-4 ml/sec. A tube current of 100 mAs was used for patients weighing between 45 and 54 kg and a tube current of 120 mAs was used for patients weighing more than 54 kg. A tube current of 75 mAs was used for patients weighing between 35 and 44 kg. A tube current of 45 mAs was used for patients weighing between 25 and 34 kg. A tube current of 30 mAs was used for patients weighing between 15 and 24 kg. A tube current of 25 mAs was used for patients weighing less than 15 kg. A tube voltage of 80 kV was used for patients weighing less than 50 kg and 100 kV was used for patients weighing more than 50 kg.
In pediatric patients, a body weight-based low-dose protocol (80-100 kV, 25-120 mA) was used to further reduce radiation exposure. Imaging parameters were as follows: tube voltage, 100-120 kV tube current, 140-300 mA, collimation, 16 × 1.25 mm slice thickness, 1.25 mm increment 0.6 mm table feed, 27.5 mm/sec rotation time, 0.5 sec. In adult patients, automatic tube current dose modulation was used. Patients were examined while in the supine position and all images were acquired during a single breath hold, extending from the base of the neck to the diaphragm. Multidetector CT angiography examinations were performed with a 16-row MDCT (LightSpeed Ultra, GE Healthcare, Milwaukee, WI). Although MR angiography may show vascular anomalies, the technique does not provide sufficient information regarding the esophagus and trachea. However, the method is time-consuming and may require the need for prolonged sedation in pediatric patients. Magnetic resonance (MR) angiography is an alternative non-invasive tool without the need for contrast material or radiation exposure. Disadvantages of the use of MDCT angiography, especially in pediatric patients, are the necessity to use iodinated contrast medium as well as an increase in patient radiation exposure.
The advantage of the use of MDCT angiography is that the modality is a noninvasive technique that enables evaluation of vascular anomalies and the status of tracheal or esophageal compression in the same study ( 2, 3). Multidetector computed tomography (MDCT) angiography has recently become a principal diagnostic method for the assessment of thoracic aortic abnormalities. A congenital anomaly of the aortic arch is usually an incidental radiological finding in asymptomatic patients, except when the anomaly constitutes a vascular ring that is formed when the abnormally patterned arch vessels completely encircle the trachea and esophagus ( 1). Congenital anomalies of the aortic arch are uncommon and may be associated with other congenital cardiovascular diseases.
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