Neuroimaging

Question 1

How does CT work

Answer 1

• xrays emitted in a beam and detected on the opposite side
• creates 2d slices that can be visualized into 3D by scrolling through
• Bone/calc = bright white
• Air = black
• Soft tissue = grayscale (Hornsfield)

Question 2

What is CT the most sensitive/specific for

Answer 2

SAH, SDH, EDH, abscesses, masses

Question 3

What are some limitations of CT

Answer 3

poor differentiation of soft tissue (Can miss inflammatory changes and ischemia)

Question 4

How does contrast work in CT

Answer 4

• iodine contrast media blocks passage of xrays
• helps distinguish enhanced tissues from background
• timing of contrast admin determines what lights up
• renally excreted

Question 5

What does CT contrast help highlight

Answer 5

vascular and inflamed tissues (also malignancy, abscess)
- typically not as good as MRI if it is available

Question 6

How to interpret a CT

Answer 6

• identify pt
• identify plane (axial and soft tissue is good to start with)
• scroll superior to inferior
• blood, cisterns, brain, ventricles, bones (blood can be very bad)

Question 7

Where is the blood

Answer 7

epidural

Question 8

where is the blood

Answer 8

subdural

Question 9

where is the blood

Answer 9

intracerebral

Question 10

Where is the blood

Answer 10

intraventricular

Question 11

where is the blood

Answer 11

subarachnoid (cisterns/circle of willis)

Question 12

What to check when evaluating cisterns on CT

Answer 12

are they open and do they have blood in them

Question 13

What to look for when evaluating the brain parenchyma on CT

Answer 13

• symmetry
• grey-white differentiation
• shift
• hyper/hypodensity

Question 14

What to look for when evaluating the ventricles on CT

Answer 14

should be open, symmetrical, without blood

Question 15

What to look for when evaluating bone on CT

Answer 15

• switch software to bone window
• look for fractures, step-offs, gaps (compare to other side)

Question 16

What is CTA head/neck

Answer 16

CT angiography of head and neck vessels to assess for vascular cut-offs/occlusions, or high risk stenoses

Question 17

What are the indications for CTA head/neck

Answer 17

• TIA
• vertebral/carotid artery dissection
• dense/cortical strokes (large vessel occlusion)
• aneurysm detection and operative planning

Question 18

Describe brain MRI mechanism of action

Answer 18

best for viewing soft tissue
- harnesses natural tendency of hydrogen ions to align in magnetic field (alignment and relaxation)
- different tissues realign at different intensities
- T1, T2, FLAIR, STIR, DWI, ADC

Question 19

Describe the difference between T1 and T2 view

Answer 19

T1 highlights tissue (fat) and T2 highlights mostly water

Question 20

Describe FLAIR

Answer 20

Fluid attenuated inversion recovery
- nullifies signal from CSF
- helps find subtle problems near CSF rich areas, pre-infarct edema, demyelinated MS lesions

Question 21

Describe STIR

Answer 21

• nullifies signal from tissue
• good for finding subtle problems in fat-rich areas, fracture, osteomyelitis

Question 22

Describe DWI and ADC

Answer 22

(Diffusion weighted imaging, apparent diffusion coefficient)
Helpful for identifying stroke within minutes of happening
- combines T2 and water enhancement
- ADC is a superimposed sequence to control quality (DWI can appear too bright)

Question 23

What contrast is used in MRI

Answer 23

Gadolinium: a rare earth metal that interacts with H+ ions in a magnetic/pulsing field
- contraindicated in pregnancy
- need renal panel (predisposition to nephrogenic systemic fibrosis)
**- enhances arteries and vascularly abnormal tissues (tumors, abscess)

Question 24

What is the likely diagnosis in this MRI with contrast

Answer 24

Tumor: lit up because it is vascularized

If it was an abscess it would be dark because it wouldn’t be vascularized

Question 25

Describe the indication of MRA head/neck

Answer 25

Uses inversion recovery sequences and "time of flight" sequences to differentiate fast moving blood from static surrounding tissues - gadolinium not required **- can identify vascular cut offs, aneurysms, arteriovenous malformation, arterial dissection** (CTA more sensitive for neck vessel dissection)

Question 26

What is the diagnosis

Answer 26

right MCA aneurysm

Question 27

Describe the method of interpreting MRI

Answer 27

- verify pt - start with T2 for background anatomy and pathology - scroll top to bottom - look for asymmetry, abnormal signals - T2 then FLAIR then DWI/ADC - compare with previous images if possible

Question 28

Describe how PET scans work

Answer 28

Identifying and tracking tumors and relative blood flow - variable uptake of radiolabeled substances to metabolically active tissue, which lights up brighter - injected substance is radioactive

Question 29

Describe fluoroscopic angiography (cerebral angiogram)

Answer 29

procedure performed by neuro interventional radiologist - catheter inserted and directed to target vessel with iodinated contrast dye - catheter can direct thrombolytics/suction thrombectomy, or aneurysm coiling

Question 30

What is the diagnosis

Answer 30

Right MCA stroke

Question 31

what is the diagnosis

Answer 31

subarachnoid hemorrhage

Question 32

what is the diagnosis

Answer 32

brain abscess (with periabscess edema)

Question 33

what is the diagnosis

Answer 33

brain tumor

Question 34

what is the diagnosis

Answer 34

subdural hematoma

Question 35

what is the diagnosis

Answer 35

epidural hematoma

Question 36

what is the diagnosis

Answer 36

multiple sclerosis

Question 37

what is the diagnosis

Answer 37

cerebellar stroke