Brain Imaging Flashcards
What disorders/diseases can a CT scan detect?
Infarction, tumor, calcification, hemorrhage, and bone trauma
A hypodense region on a CT indicates what? What does a hyperdense region on CT indicate?
Hypodense: edema or infarction
Hyperdense: calcification or hemorrhage
What are the advantages and disadvantages of using CT?
Advantages: faster and less expensive than other imaging; often easy to use for initial screening; provides the patient with flexibility
Disadvantages: ionizing radiation used, lower resolution, less contrast between soft tissue structures
How would a tumor appear on CT?
Swelling (hypodensity) with a visible anatomical distortion
What is the basic mechanism by which MRI works?
Protons within hydrogen atoms each have a spin producing their own magnetic fields; when applied to an external force the protons align with the external magnetic force. Then add a short pulse of radiofrequency which causes increase in energy. Record the time it takes for the proton to decay, and is then transposed to a gray scale to make an image
How can a clinician accentuate the tissue of interest while using an MRI?
Vary the timing of the radiofrequency pulse
What types of disorders can be detected with MRI?
Tumors, demyelination diseases (like MS), stroke, degenerative disease
What does MRS (mass resonance spectroscopy) allow us to see in the brain? We can look at NAA, Choline, Creatinine, and Lactate concentration with MRS, what does each indicate?
Chemical structure of the brain.
NAA - located in cell bodies and dendrites: considered a neuronal marker.
Choline - cell membrane synthesis and degradation; marker for demyelination
Creatinine - glial marker
Lactate - found following ischemic events
What are the advantages and disadvantages of using MRI?
Advantages: high spatial resolution, no radiation, good contrast between soft tissue structures (between gray/white/CSF), provides functional/chemical imaging
Disadvantages: time consuming for the patient, claustrophobic, can’t put in patients with ferromagnetic or electronic devices (pins/stents/pacemakers)
What is MRS particularly useful in diagnosing? What marker is used?
Multiple Sclerosis– use choline to detect demyelyination
What imaging method allows us to visualize white matter tracts within the brain?
Diffusion weighted imaging and Diffusion tensor imaging
What does diffusion weighted imaging/ diffusion tensor imaging measure?
The rate at which water moves freely
A diffusion weighted imaging/diffusion tensor image that shows a high degree of aniostropy indicates what? What does a low degree of aniostropy indicate?
High degree of aniostropy: indicates that more water is diffusing longitudinally than perpendicularly; normal- restricted by axons/myelin
Low degree of aniostropy: indicates that the water is flowing equally in longitudinal and perpendicular directions; pathological-unrestricted
What imaging method allows us to get images while the patient is performing cognitive tasks?
fMRI (functional MRI)
What imaging method uses BOLD (blood oxygen level dependency) ? How is the image formed from BOLD?
fMRI
Compare baseline to experimental with cognitive function; increasing neural activity increases the blood flow to the area
