Multidetector Computed Tomography of the Aorta
For many years, invasive angiography was considered the gold standard for the assessment of aortic abnormalities. However, the complexities and complications inherent to invasive imaging have meant that more recently non-invasive techniques such as echoca
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Alistair C. Lindsay, Arjun Nair, and Michael B. Rubens
25.1 Technical Considerations The CT angiography (CTA) technique chosen to image the thoracic aorta should always be tailored to the diagnostic information being sought and is dependent on a number of clinical, technical and patient-based factors (Table 25.1). The main technical considerations in CT protocol selection are discussed below, and situation-specific protocols are described in Table 25.2 and discussed in later sections on different aortic pathologies.
25.1.1 Scanner Technology and ECG Synchronisation The introduction of multidetector row CT (MDCT) systems in the late 1990s afforded the opportunity for considerably greater acquisition speeds, longitudinal (z) axis coverage and spatial and temporal resolution, all of which improved further as the number of detector rows with each successive generation of CT scanner increased [1–4]. These improvements over helical single-slice CT are parA. C. Lindsay Department of Cardiology, Royal Brompton Hospital, London, UK A. Nair · M. B. Rubens (*) Department of Radiology, Royal Brompton Hospital, London, UK e-mail: [email protected]
Table 25.1 Factors that influence the choice of CT scanning technique Patient factors Body mass index Heart rate Heart rhythm (beat-to-beat variability) Excessive respiratory motion Scan factors Number of detector rows Number of X-ray tubes (single- vs. dual-source) CT gantry speed CT reconstruction technique (e.g. statistical iterative reconstruction) Intravenous iodinated contrast: volume, phase, timing of injection, scan initiation (bolus tracking or test bolus) Clinical factors (see also Table 25.2) Suspected diagnosis (e.g. aortic dissection versus acute coronary syndrome) Acute versus stable presentations Pre-operative workup (e.g. aortic root replacement versus trascatheter aortic valve implantation)
ticularly advantageous to aortic imaging; the entire thoracoabdominal aorta can now be scanned in as little as 10 s with a 128-detector row scanner [5]. Narrow detector collimation provides the option of thinner sections (for high-resolution detail) or thicker sections (for quick review and with less noise) from a single acquisition while simultaneously generating an isotropic volumetric dataset [1]. In this way, accurate depiction of multiple facets of aortic pathology (e.g. intimal tears, fenestrations and side-branch involvement in aortic dissection) can be complemented by smooth
© Springer-Verlag GmbH Austria, part of Springer Nature 2019 O. H. Stanger et al. (eds.), Surgical Management of Aortic Pathology, https://doi.org/10.1007/978-3-7091-4874-7_25
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A. C. Lindsay et al.
386 Table 25.2 Suggested protocols for common aortic CT indications Clinical indication Acute aortic syndromes
Acquisition Non-contrast, top of arch to groin Gated thoracic aorta post-contrast (“step-and- shoot” prospective gating if available) If extension of dissection above arch/ below heart: angiogram from base of skull to lesser trochantera
Pre-operative evaluation: aortic r
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