Chapter 21 - Transcranial doppler

Question 1

Limitations to using transcranial doppler

Answer 1

1) recent eye surgery 2) hyperostosis of the temporal bone 3) user error

Question 2

Type of doppler for the transcranial doppler

Answer 2

2MHz pulsed Doppler with spectral analysis

Question 3

Acoustic windows for transcranial doppler

Answer 3

1) Transtemporal approach 2) Transorbital approach 3) Transforamenal approach (suboccipital) 4) Submandibular approach (under jaw)

Question 4

Transtemporal approach description

Answer 4

1) Anterior to ear 2) superior to zygomatic arch (thinnest portion of skull 3) three areas: anterior, middle, posterior The more posterior of the probe placement, the more anterior the angulation of doppler beam

Question 5

Transorbital approach description

Answer 5

Over closed eyelid

Question 6

Transforamenal approach description

Answer 6

1) concave area of upper neck/back of head 2) at foramen magnum

Question 7

Submandibular approach description

Answer 7

Under jawline to provide velocity for calculating extracranial-to-intracranial ratio

Question 8

TAMV stands for

Answer 8

Time-averaged mean flow velocity

Question 9

Guidelines for identifying the intracranial arteries

Answer 9

Question 10

Factors that affect intracranial blood flow

Answer 10

1) Blood pressure
2) heart rate
3) arterial CO2
4) fever
5) other metabolic demands
6) age
7) hematocrit

Question 11

Crossover collateralization

Answer 11

1) reversal of flow in ACA
2) ipsiilateral to ICA disease
3) flow rate > 150% of contralateral MCA

Question 12

External to internal collateralization

Answer 12

1) Flow reversal in ophthalmic artery
2) ipsilateral to proximal stenosis/occlusion
3) attributed to flow from ECA
4) confirm by compressing other ECA branches

Question 13

Posterior-to-anterior collateralization

Answer 13

1) shunted blood from vertebrobasilar via ipsilateral PCA and PCOM to supply anterior circulation
2) PCA velocity > 125% of MCA

Question 14

Anterior-to-posterior collateralization

Answer 14

1) occlusion of subclavian/innominate
2) flow direction in precommunicating segments of PCA reverses

Question 15

Signs of vessel occlusion on transcranial doppler

Answer 15

1) absence of doppler arterial signal
2) low systolic and diastolic velocity just proximal to occlusion
3) dampened qualities distal to suspected occlusion
4) increased velocity in adjacent vessels due to collateral effects
5) multiple noncontiguous collaterals with varying velocities

Question 16

Lindegaard ratio

Answer 16

hemispheric ratio

Index to differentiate between high velocities (vasospasm) and hyperdynamic flow

TAMV of MCA divided by TAMV of ipsilateral distal extracranial ICA

Question 17

Causes of hyperdynamic flow

Answer 17

1) low hematocrit
2) volume expansion
3) increased blood pressure

Question 18

Normal TAMV and hemispheric ratio

Answer 18

TAMV < 120 cm/s

Ratio < 3

Question 19

TAMV for Sickle Cell disease normal and abnormal values

Answer 19

Normal < 170 cm/s = annual follow up

Conditional: 171-199 cm/s = q3-6 months follow up

Critical: > 200 cm/s = chronic blood transfusion to reduce hemoglobin S needed

Question 20

Right to left heart shunt detection with TCD

Answer 20

1) Contrast agent (agitated saline) injected into arm vein
2) detect microbubbles in MCA
3) patient does valsalva

Question 21

Diagnosis of PFO with TCD

Answer 21

International consensus scale: A single HITS (high intensity transient signal

OR

Spencer scale: Grade 0-5

Question 22

Four characteristic stages to signal cerebral circulatory arrest

Answer 22

1) increase pulsatility with end diastole reaching zero
2) oscillating flow (reverberatory flow) = forward and reverse flow are equal
3) narrow, reduced-velocity systolic spikes
4) no flow signal