Pediatric Cardiothoracic Computed Tomographic Angiography

Costs and Benefits

Although echocardiography is generally the first-line imaging modality in evaluation of structural congenital cardiovascular disease, pediatric CTA offers several advantages over echocardiography and other imaging modalities.

The primary advantage of CTA is speed. With newer technology, such as wide detector multidetector computed tomography (MDCT) (e.g., 320 detector array single rotation acquisition) or dual-source MDCT ( Fig. 66.1 ), an examination of the entire chest of an infant can be completed in less than 1 second. With echocardiography, magnetic resonance (MR) vascular imaging, or angiography, imaging times typically exceed 20 minutes and may last 1 to 2 hours. Its rapid examination time means that CTA is frequently performed without sedation, an important consideration given the potential risks posed by anesthesia to the developing brains of very young children, as well as the frequently tenuous conditions of critical care patients undergoing imaging evaluation.

CTA is particularly useful in evaluation of extracardiac vascular structures and may be used for preoperative evaluation of pulmonary arteries, pulmonary veins, and/or aortic arch and other systemic arteries (such as aortopulmonary collaterals) in children with known congenital heart disease or for investigation of postoperative complications. Computed tomography (CT) provides the best global assessment of the lungs and airways ( e-Fig. 66.2 and Fig. 66.3 ). Congenital cardiovascular disorders may cause tracheal compression or deviation (e.g., from vascular rings or pulmonary slings) with resulting obstructive effects or air trapping at the parenchymal level. In addition, CT can suggest or demonstrate associated primary abnormalities of the respiratory system, such as pulmonary hypoplasia or tracheomalacia.

The excellent spatial and temporal resolutions of CTA allow for high-quality off-line multiplanar and three-dimensional (3D) volumetric reconstructions and printed models, a major benefit over both echocardiography and direct angiography. The technical quality is also more consistent with CT compared with echocardiography, a more operator-dependent examination, and compared with magnetic resonance imaging (MRI), where parameter and sequence selection may result in variable study quality. In addition, many of the contraindications of MRI (e.g., pacemakers, internal support apparatus, and some surgical devices) are not contraindications to CTA and produce less image artifact than with MR angiography. The cost of CT is comparable with that of Doppler echocardiography, in general is less than that of MR, and is much less than that of conventional angiography.

CTA has some disadvantages. Similar to catheter angiography, CTA involves the use of ionizing radiation, which is not an issue with MRI or echocardiography. CT radiation doses can vary greatly depending on examination parameters and can be managed with utilization of dose optimization techniques. In general, CTA should be performed with a radiation dose similar to or lower than that of a routine chest CT. CTA dose estimates in young children can be less than 1.0 mSv. When using electrocardiographic (ECG) synchronization, prospective triggering and smaller volume scanning substantially lower radiation dose when compared with retrospective gating. With rare exceptions, properly performed pediatric CTA results in a lower radiation dose than conventional diagnostic angiographic evaluation. ECG-synchronized CTA may involve a greater radiation dosage than limited diagnostic conventional angiography or a nongated CTA. Intravenous (IV) contrast material is required for CTA but also is required for conventional angiography and for MR angiography. The risk of major adverse effects (e.g., airway spasm and cardiovascular collapse) from iodinated IV contrast material is extremely low in children. In addition, there is no long-term deposition of components of iodinated contrast media as with gadolinium-based contrast agents. Unlike with echocardiography, MRI, and conventional angiography, pediatric thoracic CTA typically is used for morphologic assessment. Although cardiac function and other hemodynamic information can be obtained from CTA, this requires retrospective cardiac gating with a potential radiation dose penalty and thus is reserved for select circumstances.

Various factors must be taken into consideration in choosing an appropriate imaging algorithm. Individual expertise is a strong consideration, as is the availability of the desired modality. Personnel must be able to perform these examinations, and imaging experts, such as radiologists, may have preferences. In general, echocardiography should be the first examination considered, followed by MRI or CT. Performing CTA on an MDCT system that is less than 64 slice is problematic, and image quality (both contrast enhancement and multiplanar reformations) is more limited. A CT study that can be performed relatively quickly may be preferred over waiting several days for an MR evaluation.

Technique

Box 66.1 shows the steps taken to perform a pediatric CTA study (see e-Fig. 66.2 ).