Streak artifact

Fig. 3 Transaxial slices reconstructed with filtered back projection (top row) and iterative reconstruction (bottom row). Negative reconstructed values have been set to zero for the filtered back projection reconstruction. The streak artifacts and count defects caused by focal activity deposition in the central airways are clearly evident on the reconstructions with filtered back projection. The iterative reconstruction provides artifact free images.

Finally, attention must be paid to avoiding interpretation pitfalls such as streak artifact (Fig. 3.9), patient tilt (Fig. 3.2b), and stroke mimics - such as multiple sclerosis - that can present with similar signs and symptoms (Fig. 3.10). 

Fig. 3.9 (a) NCCT with heavy streak artifact (arrows) due to the presence of a metallic foreign body seen in (b)... 

Saline chaser Less contrast medium Decreased streak artifact at origin of great vessels Greater absolute difference in attenuation Requires potentially expensive specialized dual head CT power injectors... 

Fig. 4.10 Limited evaluation of the vertebral artery due to streak artifact and poor choice of scan delay. In this example, there is a left C7 transverse process fracture through the foramen transversaiium. Fortunately, the ipsilateral vertebral artery, although poorly opacified, does not enter the foramen at this...

Fig. 4.18 Dense contrast results in streak artifact in the right innominate vein and accounts for apparent nonopacification of the right common carotid artery (RCCA). On an axial image superior to the apparent obstruction, there is uniform enhancement...

Contrast resolution characterizes a C-arm CT systems capacity to resolve soft tissue differences. For good low-contrast imaging results, it is advantageous to acquire a high number of views, because this reduces streak artifacts. To further reduce noise in appUcations such as head scans, an additional option may be to increase system dose. 

C-arm CT images may not only suffer from motion artifacts, but also from streak artifacts caused by any dense objects, such as the catheter or high concentrations of contrast media. Ideally, the system is set up as in conventional CT with an automated two-syringe contrast injector that injects either diluted contrast media or at slow flow rates at a predefined time point ahead of the acquisition followed by a saline chaser bolus. This delay time between the contrast injection and the acquisition is essentially necessary to order to enhance the liver parenchyma and flush the arteries with saline. 

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