Neuroimaging

Question 1

contraindication for MRI?

Answer 1

ferromagnetic implants, cochlear implants, metallic cardiac valves, non-MRI compatible aneurysm clips, pacemakers. gadolinium c/i in pregnancy

Question 2

severe side effect of gadolinium?

Answer 2

systemic nephrogenic fibrosis (caution in patients with renal disease)

Question 3

advantages of T1 MRI over T2? Advantages of T2?

Answer 3

T1: optimal for demonstrating anatomy, higher resolution.
T2: more sensitive to inflammatory, ischemic, or neoplastic alterations in tissue

Question 4

Fat suppression v FLAIR?

Answer 4

Fat suppression (example, short tau inversion recovery or STIR) is used w/ T1 MRI to decrease confounding bright fat signal; especially useful in the orbit.

FLAIR is used w/ T2 images to decrease bright water signal (i.e. CSF); ideal for periventricular white matter

Question 5

Relative signal intensity of water (CSF/vitreous), fat, white matter, gray matter, and air in

1. T1
2. T2
3. SITR
4. FLAIR

Answer 5

1. T1: fat>white>gray>water>air
2. T2: water>gray>white>fat
3. SITR: water = gray>white>fat>air
4. FLAIR: fat>grey>white>water>air

Question 6

What is diffusion-weighted imaging, and how can this study detect chronicity of certain diseases?

Answer 6

DWI is sensitive to recent alterations in vascular perfusion and detects detects cerebral ischemia within minutes (opposed to hours with conventional MRI) and persists for 3 weeks (thus serving as a time marker for acute and subacute ischemic events). Abnormal signal is bright.

Question 7

What if functional MRI and how does it work?

Answer 7

Imaging modality that depends on change in regional blood flow to detect areas of higher metabolic activity; allows visualization in the cortical areas involved with specific tasks (reading, writing, moving a finger)