Imaging

Question 1

What is CT?

Answer 1

• use ionizing radiation
• based on tissue attentuation (density) - grey scale diff tissues. Hyperdense = BRIGHTER
• Multidetector CTs: allow reconstruction, faster, physiology b/c look at multiple slices
• Contrast-enhanced CTs (CT myelography): better visualiztion of targeted tissue

Question 2

Adv and Disadv of CT?

Answer 2

Adv:

• fast
• available
• can scan multiple parts of body
• reconstruction
• allows rapid diagnosis
• good for bony details

Disdv:

• radiation
• contrast agent > renal dysfnc

Question 3

2 types of CT windowing

Answer 3

1. Soft tissue algorith: kernal
   - standard for head
   - good for soft tissu
   - poor for bones
2. Bone window “kernal”
   - good for bones

Question 4

Uses of CT

Answer 4

• fractures (bone/calcifications = white)
• acute trauma: acute blood = white
• acute hemorrhage
• acute stroke

Question 5

What is MRI?

Answer 5

• magnetic resonance, proton directions
• differentite by pulse length, f, type
• T1: spin-lattic relaxation time (longitudinal). fluid = DARK
• T2: spin-spin relacation time (horizontal). fluid = BRIGHT

Question 6

What is contrast enhanced MRI?

Answer 6

• use gadolinium in T1 weighted
• if brain tissue is bright = leaking of blood brain barrier
• fat-suppressed since fat is also bright on T1

Question 7

What is bright on T1-weighted MRI?

Answer 7

• fat
• melanin
• Ca
• high protein
• subacute blood (Met-hb)

Question 8

What is bright on T2weighted MRI?

Answer 8

• most pathologies
• normal CSF
• EXCEPT:
• old blood (hemosiderin), Ca, air = dark on T2

Question 9

What is FLAIR? When is it used?

Answer 9

• Fluid attenuation inversion recovery MRI
• nulls CSF signal
• lesion = BRIGHT
• used for MS, white matter lesions
• good for lesions close to brain-CSF (ex: near ventricles)

Question 10

What is DWI? When is it used?

Answer 10

• Diffusion-weighted imaging using MRI
• calculates restricted movement (stroke = BRIGHT)to differentite cytotoxic vs vsogenic edema. based on NaK pump activity.
  ex: stroke: NaK pumps fail, water enter cells, see swelling - BRIGHT
• apparent diffusion coefficient map use mathematical summation of images to overcome artifacts > INFARCT on ADC = DARK
• used for acute stroke
• fast
• BUT can be used in first 7-10 days of stroke (afterwards, DWI - no longer bright; ADC - stroke is bright)

-good for ischemic strokes, BBB breakdown, inflmation, tumour

Question 11

What is GRE nd SWI? when are they used

Answer 11

• gradient echo and susceptibility-weighted imaging in MRI
• micro-hemorrhages, chronic hemorrhages
• make BRIGHTER more obvious but resultant is larger than true lesion

Question 12

Adv and disadv of MRI?

Answer 12

Adv:

• good for subacute to chronic setting
• small strokes, lacunar strokes
• no radiation
• good detail

Disdv:

• long
• not good for acute/unstable
• not as available
• contraindicated with pacemakers
• claustrophobia

Question 13

How can we image vessels?

Answer 13

1. ultrasound
2. CT angiography
3. MRi angiography

Question 14

What is doppler ultrasound? Use?

Adv and Disadv

Answer 14

-use sound energy
-blood: hypoechoic (dark)
-tissue: hyperechoic (bright)
-flow analysis to determine STENOSIS
Use: neck region (ICA, VA)

Adv:

• available
• stroke: subacute, chronic in neck

Disadv:

• long
• Not good to penetrate bones

Question 15

What is CT angiography? Use?

Adv and Disadv

Answer 15

• MDCT
• IV contrast
• quick scan: seconds
• reconstruction

Question 16

What is MR angiography? Use?

Adv and Disadv

Answer 16

• MRI with/ without contrast
• good resoluation
• no radiation
• fast: minutes
• same disadv as normal MRI

Question 17

Catheter Angiography? Use?

Answer 17

-minimally invasive
-enter via femoraal, radial, or brachial As to brain
-inject contrast
-use Xrays
Use: endovscular tx for arterial disease