Imaging Flashcards
What is CT?
- 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
Adv and Disadv of CT?
Adv:
- fast
- available
- can scan multiple parts of body
- reconstruction
- allows rapid diagnosis
- good for bony details
Disdv:
- radiation
- contrast agent > renal dysfnc
2 types of CT windowing
- Soft tissue algorith: kernal
- standard for head
- good for soft tissu
- poor for bones - Bone window “kernal”
- good for bones
Uses of CT
- fractures (bone/calcifications = white)
- acute trauma: acute blood = white
- acute hemorrhage
- acute stroke
What is MRI?
- 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
What is contrast enhanced MRI?
- use gadolinium in T1 weighted
- if brain tissue is bright = leaking of blood brain barrier
- fat-suppressed since fat is also bright on T1
What is bright on T1-weighted MRI?
- fat
- melanin
- Ca
- high protein
- subacute blood (Met-hb)
What is bright on T2weighted MRI?
- most pathologies
- normal CSF
- EXCEPT:
- old blood (hemosiderin), Ca, air = dark on T2
What is FLAIR? When is it used?
- 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)
What is DWI? When is it used?
- 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
What is GRE nd SWI? when are they used
- gradient echo and susceptibility-weighted imaging in MRI
- micro-hemorrhages, chronic hemorrhages
- make BRIGHTER more obvious but resultant is larger than true lesion
Adv and disadv of MRI?
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
How can we image vessels?
- ultrasound
- CT angiography
- MRi angiography
What is doppler ultrasound? Use?
Adv and Disadv
-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
What is CT angiography? Use?
Adv and Disadv
- MDCT
- IV contrast
- quick scan: seconds
- reconstruction
What is MR angiography? Use?
Adv and Disadv
- MRI with/ without contrast
- good resoluation
- no radiation
- fast: minutes
- same disadv as normal MRI
Catheter Angiography? Use?
-minimally invasive
-enter via femoraal, radial, or brachial As to brain
-inject contrast
-use Xrays
Use: endovscular tx for arterial disease
