Imaging and neurophysiology Flashcards
What are the strengths of ultrasound imaging?
- cheap and quick
- non-ionizing and no neurologicla risk
- no contrast injection needed
what are the limitations of ultrasound imaging?
- limited coverage (cannot image the brain)
- operator dependent
what can ultrasound be used for?
routine tool for patients with TIA/stroke
- can use doppler and contrast techniques to measure velocity
relationship between vessel width and velocity?
- tighter the blood vessels the increase in velocity (higher risk of clot formation)
what are the strengths of CT scan?
- relatively quick
- no neurological risks even though uses ionising radiation
- excellent coverage (aortic arch to cerebral vertex)
- can look at the brain, blood vessels and perfusion
what are the limitations of CT scanning?
- IV contrast injection required (risk of contrast reactions)
- can get anaphalactoid reactions
what are CTs useful for?
1st line investigation for acute stroke
what can CT perfusion image show?
CBV (cerebral blood volume)
TTP (time to peak perfusion)
CBF (cerberal blood flow)
why is TTP (time to peak) important information in CT perfusion?
- in early stroke the brain uses collateral circulation and can increase blood flow through micro channels so can get increased blood volume so could look like normal perfusion but TTP can show damage
what are the strengths of MR scanning?
- relatively quick
- no ionizing radiation and no neurological risks
- excellent coverage
- can image the vessel (plaque characterisation and dissection)
- tissue perfusion and viability
what are the limitations of MR scanning?
- IV contrast injection required sometimes
- requires good patient cooperation
- cannot use with all patients ie. pacemakers
what is thrombosis?
occurs when blood clots veins or arteries
why is viability imaging important?
- even though there may be an area of low perfusion, only part of this area may be non-viable brain (ischaemic pendumbra)
strengths of catheter anigography (DSA)?
- exquisite anatomical detail
- most dynamic information
- can combine with neurointerventional procedures
limitations of catheter angiography (DSA)?
- requires day case administration and post-procedure observations)
- uses ionizing radiation and risk of neurological complications
what is SPECT used for?
- functional NM imaging to evaluate regional cerebral perfusion (not uptake)
-tracer distribution related to regional blood flow
what is a nerve conduction study (sensory)?
-electrical stimulation makes the outside of the nerve negative and therefore inside positive (triggers AP)
- measure size of repsonse (number of axons recording from) and speed (myelin)
what is nerve conduction study (motor)?
- electrical stimulation induces AP
- AP reaches NMJ causing ACh release
- ACh activates AChRs on muscle and causes muscle to contract
- measure size of response and speed
what are the general rules of nerve conduction studies?
- small amplitude means axon loss
- slow speed means demyelination
whats an EMG?
- use needle to pick up electrical activity from muscles
- record activity of individual motor units
what do big motor units indicate on EMG?
- nerve, root or motor neuron pathology
- surviving motor untis compensate so motor units are bigger
what do small motor units indicate?
- muscle pathology
what is carpal tunnel syndrome?
- pressure on median nerve in wrist
- causes tingling, numbness and pain in hand and fingers
how to spot carpal tunnel syndrome on EMG?
- look for responses that are small or slow
Myasthenia gravis and EMG?
- in MG neuromuscular transmission is dodgy (the time between muscle fibres next to each other contracting is not the same)
- loss of synchrony makes patient weak
- absence of one of potentials is called blocking
what is an EEG?
- primarily done for patients with seizures
- electrodes placed in specific locations of the scalp
what is used to investigate spinal cord and optic nerves?
- evoked potentials
somatosensory evoked potentials?
- look at integrity of dorsal columns
- stimulate peripheral nerves and record a response form somatosensory cortex using scalp electrodes
Main use of somatosensory evoked potentials?
- MS (demyelinating slows impulses so response recorded from scalp is delayed)
- IOM (if cord is compressed in spinal cord surgery the response gets smaller and then is lost)
main use of visual evoked potentials?
MS (demyelination of otpic nerves)
whats transcranial magnetic stimulation?
- place magnets over motor cortex and record from a contralateral muscle
- brief magnetic pulse induces electric current that excites cells in motor cortex and these fire down motor pathway
Uses of transcranial magnetic stimulation?
MND and MS
- therapeutically used to treat severe depression
