Imaging of the CNS Flashcards
Methods used
X-rays: mainly used for imaging the spine, in 2 planes, especially for the dens/axis.
US: used in infants through the fontanels. Can also be used through the temporal bone with doppler imaging to estimate cerebral flow and flow velocity.
CT: for bones, calcifications, and CSF. Can distinguish white from gray matter. Fresh hemorrhage - hyperdense
CTA: for the cerebral vessels, occlusions, aneurysms. It is not used for routine imaging, only when an intervention will be done, embolisation, balloon angioplasty or stent implantation.
MRI. Best for the actual CNS tissue. Always must be used when there is suspected Spinal Cord Injury.
SPECT and PET-CT
SPECT for cerebral circulation
FMRI - for functional/activity analysis of brain regions, imaging areas of increased oxygenated blood compared to areas with lower oxygenation levels. higher oxygen content indicates higher blood flow to the region, indicates higher activity.
When is CT used
To investigate hemorrhages
Fresh bleeds - hyperdense
When is DWI used
To detect early stroke
To map fiber tracts
When is MRI used for the brain
For suspected spinal trauma
White matter lesions
Old hemorhages
MR angiography
Acute ischemic stroke phase imaging characteristics
Acute phase 12-24 hours after occlusion
CT will show loss of white/gray differentiation
MRI hyperintense lesion on T2.
Border of the infarct zone will show contrast enhancement
Stroke changes 1-3
Pronounced loss of gray/white differentiation
Hypodense lesion in general on CT.
Peri-lesion edema and increased contrast
Stroke changes 4-7 days
Marked hypodensity, continued contrast at the border
Stroke changes 1-8 weeks
The effects persist, it gets even more hypodense down to the level as CSF.
Eventual depletion of the contrast enhancement.
Cystic degeneration and possible calcification at the infarct border.
What is the hypderdense MCA sign
Focal/unilateral increased density of the MCA during an ischemic stroke, showing the thromus occluding the lumen.
It is the earliest visible sign of an MCA infarct.
What imaging is used to identify a sinus venous thrombosis, how does it appear
CT. Shows hyperdense thrombus, and loss of enhancement in the thrombotic vein segment
What can alter the hyperdense signal of hemorrhage on CT?
Low hematocrit levels/anemia
How do CNS tumors usually appear on CT
They are not restricted to a vascular supply domain, and have a perilesion hypodense region.
How do CNS tumors appear on MRI
T1 images they are usually hypOintense
Have a high signal intensity on T2.
How do contrast materials affect CNS tumors
They normally do NOT cross the blood brain barrier, and remain intravascular in healthy CNS tissue.
SO, if contrast enhancement or retention of a lesion is observerd, then there is BBB damage.
What imaging method is used to best detect brain neoplasms?
MRI.
T1 images are usually hypointense lesions
T2, hyperintense to normal parenchyma.
