Prior to interpreting a CT scan it is essential that the patient's details are checked.
The date and time of the imaging should also be checked to ensure the most recent examination is being viewed.
Acute CT Brain
Patient and image information
Key points
- Check the patient and image information
- Look at old images and reports if available
- View the brain and bone window images
- Modify windowing to show intracranial haemorrhage more clearly
Patient and image information
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Patient and image information
- Always check the name, date of birth, ID number
- The date AND time must be checked
Previous images and reports
Reviewing old images is an important principle of radiology. Often the previous images will provide information which is as clinically important as the current images.
Even more importantly, the reports of any relevant previous imaging examination should be read.
Previous images
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Previous images
- This elderly patient - who presented with acute confusion - has a large area of low density in the right frontal lobe seen on the current CT
- Review of a previous CT revealed that the abnormality in the brain was not new, but related to an infarct which occurred 5 months earlier
- The current CT appearances were not the cause of the acute confusion (urinary tract infection in this case)
CT windowing
A CT scan provides a 3-dimensional map based on variations of density of anatomical structures. This CT data can be presented in different ways to view structures within specific ranges of density. 'Brain windows' are used to view a range of densities close to the average density of the soft tissues of the brain. 'Bone windows' are used to emphasise a narrow range of densities close to the density of bone.
When viewing a CT scan of the brain, both the brain window images and the bone window images must be viewed routinely.
Brain v bone CT windows
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Brain v bone CT windows
- The roll over images show the 'bone window' images at the same level as the 'brain windows'
- The brain window images provide limited detail of bone structures
- The bone window images provide no useful detail of brain structure
Modified CT window settings
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Modified CT window settings
- The image on the left shows the original brain window settings
- In the context of suspected intracranial haemorrhage it is often helpful to adjust the window settings manually
- The image on the right - which uses a modified window setting - shows the large subdural haematoma more clearly
Orthogonal plane images
CT images are acquired in the axial plane, in line with the base of the skull base. This helps reduce artifact caused by the dense structures of the skull base bones.
Most modern viewing software facilitates assessment of reconstructed CT images in planes other than the axial plane.
Orthogonal CT images
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Orthogonal CT images
- Axial images with corresponding coronal and sagittal plane images are shown using brain windows