Acute CT Brain
Brain CT quality and artifacts

Key points

  • Check for medical artifact
  • Common artifacts which affect image quality include movement, beam-hardening and scatter
  • Do not view only a single slice in isolation of others in the image 'stack'
  • Check if post-contrast images have been performed

CT brain image quality depends on the quality of the CT scanner, the skills of the radiographer, and the cooperation of the patient. There are common artifacts that should be taken in to consideration when viewing CT brain images. Some of these artifacts are unavoidable.

Medical artifacts

As with assessment of any radiological investigation, the presence of medical artifacts should be noted.

Medical artifact - CT brain

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Medical artifact

  • This scan shows an intraventricular shunt in situ used for treatment of hydrocephalus
  • The ventricles are very large

Movement artifact

Agitated patients may move during the acquisition of CT images. It may be difficult to exclude pathology if there is movement artifact and selected images may need to be repeated.

Movement artifact - CT brain

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Movement artifact

  • The image on the left shows the result of movement during scanning
  • The degraded image was repeated and no pathology was shown

Beam-hardening and scatter artifact

CT images of the brain often show dark or bright streaks. These are most commonly seen as lines running between two dense parts of the skull, such as the prominences of the inner table of the skull, or between the petrous bones.

These artifacts are partly due to scattering of the X-ray beam and partly due to alteration of the average power of the X-ray beam as it passes through relatively dense structures.

Beam-hardening and scatter artifact - CT brain

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Beam-hardening and scatter artifact - CT brain

  • White stripes are seen along the lines between the thickest part of the skull

Beam-hardening and scatter artifact - CT brain

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Beam-hardening and scatter artifact

  • The brain stem is a common place to see beam-hardening artifact
  • Streaks of low density are visible in the pons passing between the thick and dense petrous bones

Clinical significance

  • The density of bones of the skull base often limits CT image quality of brain stem structures
  • If there is specific clinical concern regarding the possibility of brain stem pathology then MRI should be considered

Single slice v image stack

It is important to view CTs of the brain as a stack of images, and not to assess a single slice in isolation of those above or below it.

Single slice caution - CT brain

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Single slice caution

  • This single image shows an isolated focus of high density which could be mistaken for blood
  • The image below this slice (roll over image) shows the area of high density is part of the petrous bone

Contrast enhancement

Administration of intravenous contrast material may provide additional information regarding pathological processes seen on CT brain images. Usually a non-contrast CT is performed first and if there is an abnormality that is thought to represent a solid or cystic mass lesion then, assuming there are no contraindications, intravenous contrast may be given and the scan repeated.

Contrast enhancement - CT brain

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Contrast enhancement

  • This CT shows a large irregular area of low density which is distorting surrounding structures (mass effect)
  • The roll over image demonstrates 'ring enhancement'
  • Contrast enhancement indicates that the edge of this lesion has a high vascular supply
  • The central part does not enhance as it is necrotic tissue with no vascular supply
  • In this case the lesion is a glioma - a primary malignant brain tumour