Brain

Published on 01/04/2015 by admin

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Last modified 01/04/2015

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Chapter 13 Brain

Methods of imaging the brain

Imaging the brain’s structure and examining its physiology, both in the acute and elective setting, is now the domain of multiplanar, computer-assisted imaging. The imaging modalities in use today include the following:

COMPUTED TOMOGRAPHY OF THE BRAIN

Magnetic Resonance Imaging of the Brain

Technique

IMAGING OF INTRACRANIAL HAEMORRHAGE

Imaging of suspected intracranial haemorrhage is one of the most common requests of clinicians, usually in the emergency setting. Follow-up of haematomas and formulating a differential diagnosis can sometimes be quite challenging. In the acute setting CT and the neurophysiological information available as a result of multidetector technology is often the first and only modality used to assess these patients. MRI is more often used in situations where the initial workup has been negative and a more sensitive modality is required.

COMPUTED TOMOGRAPHY

A conventional study consists of 3-mm sections through the brainstem and posterior fossa, and 7-mm sections through the cerebrum. This is the basic multi-detector CT protocol for brain imaging. This is done without contrast to avoid diagnostic difficulty in deciding whether a parenchymal lesion is due to enhancement or blood. Acute blood is typically hyperdense on CT. An exhaustive differential diagnosis for bleeding in different compartments of the brain can be sourced elsewhere but in general bleeding can be extra-axial (i.e. epidural, subdural, subarachnoid, intraventricular) or intra-axial. Intra-axial bleeding can be due to head trauma, ruptured aneurysms or arteriovenous malformations, bleeding tumours (either primary disease or secondaries), hypertensive haemorrhages (cortical or striatal) or haemorrhagic transformation of venous or arterial infarcts. In the assessment of subarachnoid haemorrhage and ischaemic stroke CTA is becoming increasingly used as the screening modality for deciding further intervention. Neurosurgeons are increasingly using CTA alone as the modality for planning microsurgical clipping, especially in the cases where a haematoma exerting mass effect needs to be evacuated immediately adjacent to a freshly ruptured intracranial aneurysm. In ischaemic stroke CTA can localize an acute embolus and CT perfusion imaging can demonstrate the ischaemic core (irreversibly damaged brain) by calculating the relative cerebral blood volume and the ischaemic penumbra (recoverable brain parenchyma) by evaluating the relative cerebral blood flow (rCBF).