2 - Neuroimaging

Question 1

Patient characteristics to consider with neuro-imaging.

Answer 1

1. Age, weight, allergies, renal function, metallic devices such as pacemaker, claustrophobia

Question 2

CT

Answer 2

1. Orbit good for CT because fat provides excellent contrast to globe and surrounding elements
2. Soft tissue enhanced by IV Contrast
3. Need GFR > 60 for IVC

Question 3

MRI

Answer 3

1. Open MRI machines lower strength and lower quality
2. MRI sensitive to changes in water content of soft tissue
3. Gadolinium alters MRI signal that may be crucial in identifying inflammatory, infectious or neoplastic lesions
   
   1. Gadolinium may cause nephrogenic systemic fibrosis characterized by widespread soft-tissue collagen deposition that results in skin thickening and muscle contracture

Question 4

T1

Answer 4

1. CSF is dark on T1-weighted imaging
2. Gad is very bright on T1-weighted images. Gad enhanced images are especially useful in looking at vascular structures (Gad enhanced bright signal in blood vessels) and breakdown in the blood-brain barrier [e.g., tumors, abscesses, inflammation (herpes simplex encephalitis, multiple sclerosis, etc.)].
3. Very intense bright FAT on T1 may obscure subtle signal abnormalities — STIR used.
4. May also see STIR + Gad images

Question 5

STIR

Answer 5

1. Fat suppression technique used to obtain T1 images without confounding fat bright fat signal
2. Useful for MRI of orbit to eliminate high intensity T1 fat signal

Question 6

T2

Answer 6

1. CSF is bright on T2-weighted imaging. World War II (Water is White on T2)
2. FLAIR
   
   1. The FLAIR sequence provides T2-weighted image without high bright CSF signal. By doing so, abnormalities remain bright but normal CSF fluid is attenuated and made dark. This sequence is very sensitive to pathology and makes the differentiation between CSF and an abnormality much easier — useful for detecting periventricular white matter lesions in a demyelinating process.
3. FLAIR — gray matter lighter than T1

Question 7

DWI

Answer 7

1. Water molecules diffuse relatively freely in the extracellular space; their movement is significantly restricted in the intracellular space. Spontaneous movements, referred to as diffusion, rapidly become restricted in ischemic brain tissue. During ischemia, the sodium - potassium pump shuts down and sodium accumulates intracellularly. Water then shifts from the extracellular to the intracellular space due to the osmotic gradient. As water movement becomes restricted intracellularly, this results in an extremely bright signal on DWI. Thus, DWI is an extremely sensitive method for detecting acute stroke — within hours to 3 weeks.

Question 8

Catheter Angiography

Answer 8

1. Gold standard for intracerebral vascular imaging
2. Uses iodinated radiodense contrast dye

Question 9

MRA

Answer 9

1. Does not used contrast unless gadolinium added
2. Look at medium and large arteries
3. Less invasive than catheter angiography
4. Does NOT depict small vessels like catheter angiography
5. No radiation
6. May overestimate stenosis

Question 10

CTA

Answer 10

1. Uses Contrast and radiation
2. Same contraindications as CT
3. Less invasive than catheter angiography

Question 11

Orbital Doppler US

Answer 11

1. Useful for CCF to assess retrograde venous flow within SOV

Question 12

Imaging Choice Based on Clinical Scenario

Answer 12