• CT angiography (CTA) is a rapid (takes ∼ 5 min), readily available, and non-invasive imaging method used to assess extra- and intracranial arteries
  • it is based on the spatial reconstruction of the image from a series of axial scans after iodinated contrast agent administration  
  • examination usually starts at the level of the aortic arch (or better, LAA) and extends up to the vertex
  • approx. 50-60 ml of contrast agent is needed
  • source images (SI) are essential for the evaluation
  • reconstruction images (MIP – maximum intensity projection) may be helpful in certain circumstances
  • adjust the window width (WW) and window level (WL) parameters to assess heavily calcified stenoses  CT angiography (CTA) source images. A - standard image settings (W300/L30) B - adjusted window width and level (W730/ L310)
    • the ideal parameters vary in different scanners
CT angiography

CTA reconstruction (MIP)

Stenosis and occlusion assessment

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Carotid stenosis evaluation

Stenosis of the left carotid artery on CTA

Left interal carotid artery (ICA) stenosis on CTA

Evaluation of atherosclerotic plaques characteristics

  • CTA is a helpful tool for diagnosing extracranial stenoses
  • it shows not only the grade of stenosis but it yields information about carotid plaque characteristics (which can also be assessed by ultrasound or MRI → see here)
  • each plaque can be characterized by the following:
    • size (length and width)
    • shape (circular, semicircular, eccentric)
    • surface (smooth, rough, exulcerated)
    • density (hypodense, isodense, hyperdense)
    • homogeneity (homogeneous x heterogeneous)
    • presence of calcifications and thrombi (ILT)
  • presence of intraluminal thrombi (ILT) increases the likelihood of symptomatic stenosis
  • smooth or heavily calcified plaques are associated with a low risk of CV event [Eesa, 2010]
  • in the presence of extensive calcifications, CTA outperforms the ultrasound, which must rely on the Doppler examination (B mode and color mode are usually inconclusive)  A significant left ICA stenosis, caused by heterogeneous plaque with significant calcifications, that limit the ultrasound evaluation Hemodynamically significant stenosis (Doppler examination)
Smooth, irregular and exulcerated plaque on CTA
Homogenous and heterogenous plaque
Hypodense, isodense and hyperdense plaque on CTA

Stenosis diameter measurement (NASCET and ECST)

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ICA stenosis 58% according to NASCET (1-2.44.01/5.77 x 100)
ICA stenosis 71% according to NASCET (1-1.45/5.03 x 100)

Stenosis area measurement on source images

  • apart from the diameter, CTA source images allow measuring the area of stenosis as well
    • in the NASCET/ECST equation, exact area instead of diameter can be used [Saba, 2009]
    • below is an approximate correlation between diameter and area measurements
  • however, all major CEA trials were based on diameter measurement

Assessment of collateral circulation on CTA

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CTA “perfusion”

  • besides the evaluation of stenosis/occlusion, CTA source images can also be used for a rough assessment of perfusion deficit (especially if CTP is not part of the standard examination protocol or is not available) [Coutts, 2004]
  • the contrast agent fills the capillaries in the normally perfused tissue but is absent in the ischemic area, which will appear hypodense
  • many studies have shown that CTA “perfusion” improves the prediction of final infarct volume and clinical outcome
  • for optimal display, adjust the window parameters
Early CT signs of ischemia on NCCT (A,B) and hypoperfusion on CT angiography source images ("CTA perfusion") (C,D)

Cardiac CTA

  • CTA can be used for the detection of left atrial thrombus
    • both high sensitivity and specificity were reported in comparison with TEE  (Hur, 2009)
    • LAA thrombus is a potential radiological marker of AF   (Senadeera, 2020)
  • the examination might rule out major pulmonary embolism (PE) as well
  • the protocol would entail imaging from the level of the left atrium up to the vertex
LAA thrombus in a patient with atrial fibrillation
Thrombus in the left atrium appendage (LAA)
Pulmonary embolism on CTA

CTA and the brain death diagnosis

→ see here

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CT angiography (CTA)
link: https://www.stroke-manual.com/ct-angiography-cta/