Pediatric Cardiothoracic Computed Tomographic Angiography

Chapter 66


Pediatric Cardiothoracic Computed Tomographic Angiography



Remarkable advances have occurred in noninvasive imaging evaluation of pediatric cardiothoracic vascular disorders. One such technologic advancement is multidetector array computed tomography (MDCT). MDCT, using the computed tomography angiographic (CTA) technique, has become a primary imaging consideration for structural cardiovascular evaluation beginning as early as the newborn period.1–5 Attention to technique is fundamental for pediatric CTA.68 Without optimal or at least sufficient technical performance, diagnostic capabilities may be limited. This technical aspect (in addition to the diagnostic interpretation and communication of results) is the responsibility of the imaging expert. Therefore the objective of this chapter is to provide technical guidelines for performing pediatric thoracic CTA. The clinical examples provided illustrate these technical considerations.



Costs and Benefits


Pediatric CTA offers several advantages over other contemporary imaging modalities, including echocardiography, magnetic resonance imaging (MRI), and conventional cardiac catheterization and angiography. First, computed tomography (CT) provides the best global assessment of the lungs and airways, as well as other regional structures, in both congenital9 and acquired vascular disorders (e-Figs. 66-1 and 66-2).





Congenital cardiovascular disorders may affect the respiratory system by causing tracheal compression or deviation (e.g., from vascular rings or pulmonary slings) with resulting obstructive effects on the lungs, or by causing air trapping at the parenchymal level, such as diffuse hypoinflation or mosaicism as a result of cardiogenic pulmonary edema. In addition, CT can suggest or demonstrate associated primary abnormalities of the respiratory system, such as pulmonary hypoplasia or tracheomalacia. Although conventional angiography could supply information on the lungs and airway, it is focused primarily on the evaluation of the vascular intraluminal anatomy. In addition, sedation is needed less frequently in younger children for CT than for magnetic resonance (MR) vascular imaging, echocardiography, or conventional angiography.


With newer technology, such as volume MDCT (e.g., 320 detector array single rotation acquisition)10 or dual-source MDCT (Fig. 66-3),11 a complete examination of the entire chest of an infant can be completed in less than 1 second. With echocardiography, MR vascular imaging, or angiography, imaging times typically exceed 20 minutes and may occur over hours. A reduced examination time means that CT is better tolerated by infants, children, and patients in the intensive care unit who may have a limited ability to hold still or require the examination to be performed quickly for other reasons. The technical quality, including display, also is more consistent with CT compared with echocardiography, which is a more operator-dependent examination, and compared with MR evaluation, where operators select parameters and sequences that may give a different study quality from one examination to the next. CT also allows better patient monitoring than does MRI. In addition, many of the contraindications of MRI (e.g., pacemakers, internal support apparatus, and some surgical devices) are not contraindications with CTA and produce less image artifact than with MR angiography. Unlike with conventional angiography, the multiplanar and three-dimensional capabilities of CTA provide for off-line review of information in virtually any plane. For conventional angiography, this feature is limited to the planes selected during a particular sequence, and for echocardiography, the examination planes or views recorded are the only information available for off-line evaluation. The cost of CT is comparable with that of Doppler echocardiography, in general is less than that of MR, and is much less than conventional angiography.



CTA has some disadvantages. CTA involves the use of radiation, which is an issue with angiocardiography but not with MRI or echocardiography. CT radiation dosages depend on the technique used. In general, CTA can be performed with a dosage similar to or lower than that of a routine chest CT. CTA dose estimates in young children can be less than 1.0 mSv.12,13 With gated technology, employing prospective gating and newer volume scanning, doses also can be substantially lower than with older CT technology and retrospective gating.1316 With rare exceptions, properly performed pediatric CTA results in a lower radiation dose than conventional diagnostic angiographic evaluation. Electrocardiographic-gated CTA usually involves 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 small in children.17,18 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.19 CT for cardiovascular evaluation also is not portable.


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 modality desired. Personnel must be able to perform these examinations, and imaging experts, such as radiologists, may have preferences. Performing CTA on an MDCT device that offers less than 16 slice (e.g., a 4- and 8-slice MDCT device) is problematic, and image quality (both contrast enhancement and multiplanar reformations) is more limited. A CT scan that can be performed within the same day or relative quickly may be preferred compared with waiting several days for an MR evaluation. In general, echocardiography should be the first examination considered, with MR being second, unless contraindications are present.



Technique


Box 66-1 shows the steps taken in performing a pediatric CTA (see e-Fig. 66-2).68



Box 66-1


Steps in Performing Pediatric Computed Tomography Angiography


The subject is an otherwise healthy, 4-week-old, 4.0-kg male infant with congenital stridor. Findings of an echocardiogram suggest the presence of a vascular ring (see Fig. 66-6).




Performing the Computed Tomography Angiogram



1. Intravenous contrast material



2. Select scan parameters: 16-detector row



3. Scan interpretation


Dec 20, 2015 | Posted by in PEDIATRIC IMAGING | Comments Off on Pediatric Cardiothoracic Computed Tomographic Angiography
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