Neuro Radiology Flashcards
Advantages of CT over MRI
- Fast
- Widely available
- Portable at some institutions
- Opportunity for multiplanar reformating (axial, saggital)
- Inexpensive
On CT, gray matter appears ___ relative to white matter.
On CT, gray matter appears brighter relative to white matter.
Because it is more dense!
Uses of head CT
- In trauma
- To rule in or out intracranial hemorrhage
- Rule in or out bone fracture
- To identify calcifications
- Serial evaluation of inpatients
- CT angiography may be performed to assess for thrombotic or thromboembolic stroke or for aneurysm
Limitations of CT
- Radiation exposure
- Relatively insensitive for ischemic stroke in first 6 hours
- Evaluation of posterior fossa is limited on CT due to artifacts in this area
Advantages of MRI over CT
- No radiation (much safer for pediatrics!)
- Multiplanar capability
- Exquisite detail of brain anatomy
- Superior for evaluation of the brain parenchyma
Uses of head MRI
- Best for acute infarction with diffusion-weighted imaging
- Best for visualizing brain tumors and differentiating them from cysts
- Useful in subacute to chronic hemorrhage
- Better than CT for evaluating the posterior fossa and brainstem
- MR angiogram can be used to assess vascular anatomy
Limitations of MRI
- Claustrophobia
- Takes a long time
- Patient motion causes artifacts
- Bone lesions not visualized well
- Metal may be a safety hazard
- Much more expensive than CT
Fundamentally, a CT scan is basically. . .
. . . a fancy X-ray that uses digitalized information and reconstruction instead of direct analog imaging
Phases of a CT
- Scanning phase
- Reconstruction phase
- Digital-to-analog conversion phase
Fundamentally, an MRI scan is basically. . .
. . . a big nuclear magnetic resonance chamber that uses a strong magnetic field to create differences in the rotational states of protons. Radio-frequency light is then fired at these protons and data is acquired from the light absorbed vs bounced back, and based on the exact frequency of the light used.
On T1-weighted MRI. . .
. . . the fat appears bright and the fluid appears dark
On T2-weighted MRI. . .
. . . the fluid appears bright
Most brain lesions are ___ on T1-weighted imaging and ___ on T2-weighted imaging.
Most brain lesions are dark on T1-weighted imaging and bright on T2-weighted imaging.
For both cases, this is because edema is ubiquitous in these lesions, and edema is essentially just an increased density of fluid.
Fluid-attenuated inversion recovery (FLAIR) imaging
A T2 weighted sequence MRI with suppression of water signal from the CSF.
Helps to see more subtle anatomical abnormalities. Appears more similar to a T1.
___ is best in the evaluation of acute ischemic stroke
Diffusion-weighted MRI is best in the evaluation of acute ischemic stroke
