Neuroimaging Flashcards
what uses of brain imaging are there
locating cysts and tumours
oedema, haemorrhage
identify stroke effects
some show structure, function, or both
what factors should you consider when choosing neuroimaging
availability
cost
practicality
side effects
what does ct stand for
computerised tomography
how does ct work
uses x-ray and a computer
advantages and disadv of ct
adv:
fast (0.3 seconds to image, up to 64 slices per rotation/ second)
widely available
disadv:
ionising radiation- damage nucleus and bone
what is radiation measured in
Sievert (Sv)
therefore can calculate radiation risk
what is radiation risk factor
total lifetime risk of radiation-induced fatal cancer for the general population
0.05% per mSv
what is good about photon-counting ct
reduce radiation
better resolution
safer
what planes can ct be used
what is the view
only in axial plane, oblique
can be reconstructed- supraorbitomeatal plane
it is caudal
what is the scale of ct
grey scale- white to black
bone - white +1000
air- black -1000
generated by ABSORPTION
poor differentiation for soft tissues
what is MRI reliant on
hydrogen atoms- they have a single proton in its atom
they are found in abundance in the body
how does mri work
uses a combo of magnetic field and radio waves to produce images
Rf pulse (radio frequency) used in MRI is non-ionising, may cause heating effect
why can’t you scan eyes only in MRI
because of the heating effect, dangerous
what does the Rf pulse do in MRI
applied to hydrogen nuclei of patient, which flips them to a higher energy state
nuclei return to their resting state when Rf off
receiver measures time and energy until nuclei return to original orientation
what planes can mri do
saggital
coronal- LOOKING AT FACE OF PT
axial- FOOT OF THE BED
oblique
ANY PLANE
What three properties of tissues affect contrast
T1 time (t1 recovery)
T2 time (t2 decay)
Proton density (pd)
what is a pulse sequence
series of RF and magnetic field applications to create contrast
what is t-1 weighted image good for
anatomy and contrast
- water is dark, grey matter is dark grey, white matter is off-white, fat is white
number 1 priority for radiologist is anatomy
what is t2 wighted image good for
identifying pathology, inflammtion and oedema
MORE SENSTIVE TO WATER
water is white, white matter is darker than grey matter
WW2 Water is White of t2 images
what is magnetic resonance angiography
make vessels visible
with or without contrast agent
can over-exaggerate stenoses
when to not use contrast agent
if allergies
kidney disease might be hard to eliminate the contrast
which angiographies do not require contrast agent
inflow angiography
phase-contrast angiogprahy
what are contrast agents
liquid injected into vessels to make them visible
plus oedema
what happens in a healthy person vs person w tumour when contrast agent is added
healthy- light up vessels
tumour- BBB damaged so contrast seep through , highlight oedema
what do positive contrast agents do, give an example
produce increase in signal intensity
gadolinium BUT may build up in the body
what do negative contrast agents do
produce a decrease in signal intensity in affected tissue
contain iron oxide
what is diffusion weighted imaging DWI dependant on
diffusion of water molecules
it is the standard when you suspect stroke, early detection of ischaemia, infarct, stroke, differentiation of brain tumours and intracranial infections
how do DWI work with regards to water molecules
if there is a disruption to the blood flow, brain cells run out of atp therefore na/k pump stops functioning and interstitial fluid rushes in and cell swells
then interstitial space narrows, so water molecules have difficulty diffusing
lower diffusion, brighter the image (increased signal intensity).– infarct black
what is the apparent diffusion coefficient ADC
measure of the magnitude of diffusion of water molecules within tissue
determine age of infarct
it is the OPPOSITE of DWI
what is tractography
makes white matter tracts, axons visible
see if pathways are going through tumour or tumour is invading tract
what is fMRI
obtain info on function and structure by visualising cortical activity
DETECTS SUBTLE ALTERATION IN BLOOD FLOOW/OXYGENATION IN RESPONSE TO STIMULI/ ACTIONS
there are limitations
what are the disadv of mri
cant use for everyone:
-pacemakers, cochlear implants, non-mri compatible heart valves, stents
-foreign bodies (shrapnel)
-claustrophobia
less available as ct, more expensive, need better facilities
v good for soft tissues
what is SPECT and PET
intravenous contrast agents
show metabolic and biochem function by measuring radiotracer uptakes (glucose) by the tissues- cancer, infection, coronary artery disease, brain disorder
PET offers better spatial resolution, higher diagnostic accuracy, lower patient dosimetry than SPECT but EXPENSIVE
What is the system for interpreting scans
ABC’S
What are the ABCs
A- adequacy, alignment, artefact
B- bones, blood, brain
C- CSF-filled spaces (cisterns and ventricles)
S- subcutaneous and surfaces, symmetry
can you see bones on mri
not directly as need h+ ions, no water in bone
shows other structures around bones, so creates a silhouette
what does a subdural heamatoma look like
crescentric
semi-lunar
blood collection between dura and arachnoid matter
tear in bridging veins
alcoholics and elderly are prone
what does an epidural hematoma look like
lens shape
blood between dura and skull
tearing of MIDDLE MENINGEAL ARTERY
adolescents and young adults affected (trauma)
what doe s a subarachnoid hemorrhage look luke
blood in circle of willis, cisterns, fissures
rupture of BERRY ANEURYSM
polycystic kidney disease is a risk factor
what does intracerebral hemorrhage look like
blood in parenchyma and ventricles
hypertensive vasculopathy
territory of PENETRATOR ARTERIES
pay more attention to bones or soft tissue in ct scans
BONES
