The precise technique and scan parameters may depend on the specific CT machine and the type of study. Overall, the risk of adverse events from CT scan is likely much lower than the expected benefit for the great majority of patients. Iodinated contrast agents are also known nephrotoxic agents, and it should be noted that unlike other imaging modalities such as MRI or echocardiography, CT cannot assess or quantify normal or abnormal blood flow and pattern. However, CT imaging utilizes potentially carcinogenic ionizing radiation and often requires iodinated contrast agents that on occasion evoke anaphylactoid reactions (about 0.6–0.7/100 adult patients). The speed, ease, access, and lack of sedation requirements make CT a reasonable imaging choice in both the adult and pediatric populations. Improvements in advanced post-processing methods utilizing maximum and minimum intensity projections, as well as three-dimensional models with surface and volume rendering methods, allow CT to play an important role in imaging aortic arch pathology. Using these techniques, CT is capable of generating detailed anatomic images in a matter of seconds with isotropic submillimeter resolution that can be used to reconstruct images in any two-dimensional plane. The advent of ECG gating, multiple detectors and spiral imaging, and radiation dose reduction methods has recently revolutionized computed tomography (CT) imaging. Rarely, aortic arch anomalies may also be diagnosed in utero through fetal echocardiography. Although at experienced centers echocardiography can be utilized to accurately diagnose vascular rings, local expertise may limit its role to the diagnosis of associated cardiac abnormalities. However, it is challenging to visualize the entirety of the thoracic aorta, and patient habitus, operator skill, and available sonographic windows may limit the final images. Echocardiography has the benefit of not utilizing ionizing radiation and the relative ease at which it can be performed at the bedside. Along with CXR, echocardiography has been used as a first-line imaging modality to examine pediatric patients for suspected aortic arch anomalies. Lateral CXR may suggest a vascular anomaly when there is obscuration of the retrotracheal lucency (an area commonly known as Raider’s triangle). Similarly, in infants and small children, a deviated trachea may serve an indirect sign of compression by an aortic arch opposite the side of deviation. Evaluation of the position of the aortic knob and para-aortic stripe provides information as to whether the arch is left or right sided, as does the position of the descending aorta. Although limited in its ability to provide detailed anatomic information regarding the aorta and its associated vessels, there are several direct and indirect findings on chest radiography (CXR) that may raise the suspicion for an aortic arch anomaly.
0 Comments
Leave a Reply. |