Imaging and neurophysiology

Question 1

What are the strengths of ultrasound imaging?

Answer 1

• cheap and quick
• non-ionizing and no neurologicla risk
• no contrast injection needed

Question 2

what are the limitations of ultrasound imaging?

Answer 2

• limited coverage (cannot image the brain)
• operator dependent

Question 3

what can ultrasound be used for?

Answer 3

routine tool for patients with TIA/stroke
- can use doppler and contrast techniques to measure velocity

Question 4

relationship between vessel width and velocity?

Answer 4

• tighter the blood vessels the increase in velocity (higher risk of clot formation)

Question 5

what are the strengths of CT scan?

Answer 5

• 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

Question 6

what are the limitations of CT scanning?

Answer 6

• IV contrast injection required (risk of contrast reactions)
• can get anaphalactoid reactions

Question 7

what are CTs useful for?

Answer 7

1st line investigation for acute stroke

Question 8

what can CT perfusion image show?

Answer 8

CBV (cerebral blood volume)
TTP (time to peak perfusion)
CBF (cerberal blood flow)

Question 9

why is TTP (time to peak) important information in CT perfusion?

Answer 9

• 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

Question 10

what are the strengths of MR scanning?

Answer 10

• relatively quick
• no ionizing radiation and no neurological risks
• excellent coverage
• can image the vessel (plaque characterisation and dissection)
• tissue perfusion and viability

Question 11

what are the limitations of MR scanning?

Answer 11

• IV contrast injection required sometimes
• requires good patient cooperation
• cannot use with all patients ie. pacemakers

Question 12

what is thrombosis?

Answer 12

occurs when blood clots veins or arteries

Question 13

why is viability imaging important?

Answer 13

• even though there may be an area of low perfusion, only part of this area may be non-viable brain (ischaemic pendumbra)

Question 14

strengths of catheter anigography (DSA)?

Answer 14

• exquisite anatomical detail
• most dynamic information
• can combine with neurointerventional procedures

Question 15

limitations of catheter angiography (DSA)?

Answer 15

• requires day case administration and post-procedure observations)
• uses ionizing radiation and risk of neurological complications

Question 16

what is SPECT used for?

Answer 16

• functional NM imaging to evaluate regional cerebral perfusion (not uptake)
  -tracer distribution related to regional blood flow

Question 17

what is a nerve conduction study (sensory)?

Answer 17

-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)

Question 18

what is nerve conduction study (motor)?

Answer 18

• 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

Question 19

what are the general rules of nerve conduction studies?

Answer 19

• small amplitude means axon loss
• slow speed means demyelination

Question 20

whats an EMG?

Answer 20

• use needle to pick up electrical activity from muscles
• record activity of individual motor units

Question 21

what do big motor units indicate on EMG?

Answer 21

• nerve, root or motor neuron pathology
• surviving motor untis compensate so motor units are bigger

Question 22

what do small motor units indicate?

Answer 22

• muscle pathology

Question 23

what is carpal tunnel syndrome?

Answer 23

• pressure on median nerve in wrist
• causes tingling, numbness and pain in hand and fingers

Question 24

how to spot carpal tunnel syndrome on EMG?

Answer 24

• look for responses that are small or slow

Question 25

Myasthenia gravis and EMG?

Answer 25

• 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

Question 26

what is an EEG?

Answer 26

• primarily done for patients with seizures
• electrodes placed in specific locations of the scalp

Question 27

what is used to investigate spinal cord and optic nerves?

Answer 27

• evoked potentials

Question 28

somatosensory evoked potentials?

Answer 28

• look at integrity of dorsal columns
• stimulate peripheral nerves and record a response form somatosensory cortex using scalp electrodes

Question 29

Main use of somatosensory evoked potentials?

Answer 29

• 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)

Question 30

main use of visual evoked potentials?

Answer 30

MS (demyelination of otpic nerves)

Question 31

whats transcranial magnetic stimulation?

Answer 31

• 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

Question 32

Uses of transcranial magnetic stimulation?

Answer 32

MND and MS
- therapeutically used to treat severe depression