Imaging Flashcards
What are benefits and features of T1 weighted MRI of the brain?
Good for anatomy, fluid has a dark signal intensity, white matter is brighter than gray matter
What are benefits and features of T2 weighted MRI of the brain?
Good for pathology, fluid has a bright signal intensity, gray matter is brighter than white matter, and Gas, calcium, ferromagnetic particles, and flow show up dark
What is the benefit of using T2 weighted FLAIR sequences?
Good for looking for cerebral edema (CSF appears dark, but edema will show up white)
What is diffusion weighted imaging (DWI) on MRI used for?
To look for cell death (areas of cell death appear whiter due to cellular edema and diffusion restriction) - it is the most sensitive imaging modality for detection of acute ischemia (can detect within 15-30 minutes of the insult)
At what point does Acute ischemic stroke become conspicuous on CT?
6-8 hours
What is the best screening tool for brain aneurysms?
MR angiogram
How is cavernous sinus thrombosis diagnosed?
MRI (with gadolinium and MR venography), or can also be diagnosed with CT angiography and CT venography
Why does myelin show up white on T1 weighted MRI?
Because fat shows up bright
How do the time to echo (TE) and time to repetition (TR) differ on T1 and T2 weighted MRIs?
T1: short TE and TR
T2: long TE and TR
(TE is the time interval that signal intensity is measured following radiofrequency (RF) pulses. TR is the time between RF pulses)
What does contrast enhancement indicate?
A breakdown in the BBB (may be due to areas of inflammation, infection, or tumor)
What areas of the brain is MRI especially useful for imaging over CT?
The posterior fossa and the craniocervical junction due to artifact from surrounding bone on CT
How does the nephrotoxicity of CT iodinated contrast agents compare with gadolinium for MRI?
Iodinated agents are more nephrotoxic
What is the imaging modality of choice for acute intracranial bleed?
CT without contrast
How does MR angiography compare with conventional angiography?
MRA uses blood flow as a contrast agent, whereas angiography uses contrast dye. MRA is also less invasive and can be performed more quickly and less expensively, but it is less sensitive and specific
Where is hypometabolism seen on FDG-PET scans of patients with Alzheimer’s?
The temporal and parietal lobes
