Computed Tomographic Angiography

The development of multi-detector CT scanners has greatly improved the practicality of CTA. Multislice scanners (e.g., 8 channels, 16 channels), collecting several channels of data simultaneously, provide a speed advantage over older single-slice helical and incremental models.

With the commonly available 16-channels scanners, it is possible to scan the entire body very rapidly (in less than 30 seconds).  With this speed, the images are usually not degraded by motion or breathing (it can be completed in a single breath-hold). The major limitation of the technique remains the undesired (particularly in children) radiation exposure, although the absorbed dose using CTA has proven to be less than that for conventional arteriography. Contrast doses ranging from 1-3 ml/kg are used for pediatric CT and CTA, with a dose of 2 ml/kg used most frequently (300 mg iodine/ml, total dose not to exceed 5 ml/kg). 

         

Large venous malformation of the chest wall on the right in a young male patient. These CTA images are processed in different window settings to see various soft tissue components. First image clearly demonstrates no arterial inflow into this malformation. There are small phleboliths and obvious inhomogeneous soft tissue prominence. 2nd image demonstrates contrast enhancement pattern of this low-flow vascular malformation.  

 

 

Image quality is similar to or better than conventional arteriograms. The post-processing options that are most beneficial with respect to evaluating pediatric vascular anomalies are multiplanar reformation (MPR), curved planar reformation (CPR), volume rendering (VR), and maximum intensity projection (MIP).A number of different projection angles may be used to view the anatomy of interest from different perspectives or to rotate it around an axis.  With this technique, images similar those achieved with conventional angiography are generated.  Even blood vessels that do not lie in a single plane can be demonstrated in their entirety.

CTA is particularly helpful to evaluate high-flow anomalies (e.g., Arteriovenous malformation - AVM, arteriovenous fistula - AVF) including some hemangiomas. On the other hand, the technique has a limited value to evaluate the low-flow malformations such as venous malformations or lymphatic malformations. 

 

       

CT angiography of high-flow vascular anomalies (vascular birthmarks). 1st and 2nd images show an extensive arteriovenous malformation (AVM) in the left knee in different widow settings. 3rd image is a different patient who was diagnosed with Parkes-Weber syndrome (PWS). 

 
   

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