Flashcards in CNS Imaging Deck (21):
What are plain films useful for in terms of the CNS?
Only occasionally used to look at the skull (but mostly CT now)
Previously used for pneumoencephalography
What is catheter angiography?
A flexible catheter is inserted through the aorta and travels through the vessels of the neck and head, where contrast is injected in order to visualise the cerebral vessels
When is ultrasound a relevant technique for CNS imaging?
In neonates (can image through fontanelles)
What is Doppler ultrasound used for when imaging the CNS?
Used in adults to measure flow in the MCAs
What is the appearance of grey and white matter in a T1-weighted MRI?
Grey matter appears grey
White matter appears white
What is Blood Oxygen Level Dependent (BOLD) imaging and when is it used clinically?
Imaging which measures local regulation of blood supply over a small area (a specific action is performed and the area responsible for regulating that action increases its oxygen delivery by vasodilating local vessels)
Used when resecting a tumour and attempting to avoid/predict effects of resection
What types of nuclear medicines are available for brain imaging and when are these used?
Single positron emission computer tomography (SPECT) and positron emission tomography (PET)
Used to assess the metabolic function of the brain with labelled glucose e.g. in epilepsy (to determine site of seizure), AD (hypometabolism in areas of neurodegeneration before macroscopic changes appear)
What is the basis of tractography and when is it used?
Movement of water is limited by axons
Brain can be divided into voxels and the dominant direction of the movement of water can be mapped to determine the trajectory of fibres
Used to image the white matter tracts e.g. to determine where to enter for tumour resection (avoid disrupting tracts)
What is the drawback of using CT to image the cortex?
Grey and white matter have similar densities on CT and require a narrow window to be able to distinguish them; this produces a relatively "noisy" image
What are T1 weighted images useful for?
Provide the best differentiation between grey and white matter
Able to identify areas of cortical thickening as seen in migrational disorders e.g. grey matter heterotopia, focal cortical dysplasia
What are T2 weighted images useful for?
Outlining areas of abnormal physiology
"Water sensitive" and can detect areas of abnormal water content due to abnormal metabolism of normal cells (e.g. inflammation leading to oedema) or abnormal cells (e.g. tumours, cortical dysplasia)
What 2 structures make up the lentiform nucleus?
Caudate nucleus and globus pallidus
What are the basal ganglia?
Deep grey matter structures of the brain
Includes caudate nucleus, globus pallidus and putamen (+/- thalamus, subthalamic nuclei, substantia nigra, claustrum)
What is the clinical relevance of the basal ganglia in terms of their metabolic requirements?
More metabolically active and therefore more susceptible to injury (i.e. anoxia occurs here first)
List 4 imaging methods/modalities that can be used to image intracranial arteries
Digital subtraction angiography (DSA)
CT angiography (CTA)
MR angiography (MRA)
What are watershed strokes and what usually causes them?
Strokes occuring in the area between vascular territories
Typically due to hypoperfusion, often superimposed on a stenosis
List 3 imaging methods/modalities that can be used to image intracranial veins and dural sinuses
Digital subtraction angiography (DSA)
CT venography (CTV)
MR venography (MRV)
Where does the superior anastomotic vein of Trolard run between?
Middle cerebral vein and inferior sagittal sinus
Where does the inferior anastomotic vein of Labbe run between?
Middle cerebral vein and transverse sinus
How is inferior petrosal sinus sampling performed and why?
Catheters enter either side of the pituitary gland to supply a corticotrophin analogue; the inferior petrosal sinus (where the pituitary drains) is then sampled for ACTH and this is compared to serum levels
Used in suspected pituitary microadenoma