TCD (14)

what is TCD?

transcranial doppler

• non invasive, non ionizing, inexpensive, ultrasound method used to examone the blood circulation within brain

what can TCD detect for?

• intracranial stenoses and occlusion

• assess collateral circulation

• eval intracranial arteriovenous malf

• detect emboli

• brain death

• subclavian steal assessment

• classify strokes

risk factors for TCD

hypertension

diabetes

cardiac disease

hereditary

smoking

oral contraceptives

what transducer is used for TCD imaging?

2MHz cardiac probe

what are the three windows used in TCD?

transtemporal

transorbital

transforamenal (suboccipital)

what vessels are scanned in transtemporal window?

MCA

ACA

• ACoA

PCA

• PCoA

what is the depth and direction of the MCA?

3-6cm

towards transducer/above baseline → RED

what is the depth and direction of the PCA?

5-7cm

towards transducer/above baseline → RED

what is the depth and direction of the ACA?

6-8cm

away from transducer/below baseline → BLUE

what if there is a blue vessel seen below 3cm?

might be collaterals

what is the landmark in the transtemporal window?

cerebral peduncles

what do the arrow and arrowheads represent?

arrow : midbrain

arrowheads : sphenoid bone

what vessels are scanned in the suboccipital view/transforamenal?

distal vertebral artery

basilar artery

** in asterick is the foramen magnum

what is the direction and depth of vertebral artery in suboccipital view?

depth : 6-9cm

direction : away from transducer/below baseline → BLUE

what is the direction and depth of basilar artery in suboccipital view?

depth : 8-12cm

direction : away from transducer/below baseline → BLUE

what vessels are scanned in transorbital view?

opthalmic artery

carotid siphon

what is the direction and depth of opthalmic artery in transorbital view?

depth : 4-6cm

direction : towards transducer/ above baseline → RED

what is the direction and depth of carotid siphon in transorbital view?

depth : 6-8cm

direction : bidirectional

when doing a transorbital, mechanical index should not exceed

.23MI (AIUM)

compare normal velocity relationships between MCA, ACA, PCA, VA, BA, Carotid siphon, OA

MCA > ACA > PCA ~ Carotid siphon & VA & BA > OA

Qs what are common pitfalls in TCD scanning?

lack of knowledge

lack of sight

• depth

• spatial anatomy

• phsiology

poor acoustic windows

operator dependent with large learning curve

how can we differentiate between PCA and MCA?

measure velocities

MCA > ACA > PCA

what are common pitfalls regarding collaterals?

• posterior to anterior collateral through posterior communicating artery

• external carotid to internal carotid thorugh reversed opthalmic artery

• crossover collateralization through ACA

why would TCD be used/applied?

emboli monitoring

• carotid endartectomy, stenting

• cardiopulm bypass surgery

detection of cardiac shunts

• confirmed when HITS (high intensity transient signal) detected in MCA

brain death

• used to correlate with other diagnostic tests

• brain death is clinical diagnosis, TCD is a confirmatory test

sickle cell disease

• early detection of abnormal MCA velocities

what are the causes of intracranial stenosis?

atherosclerosis

thrombus

dissection

vasculitis

vasospasm

extrinsic vessel compression

how is the MCA affected when there is occlusion?

lack of signal

how is the ACA/PCA affected when there is occlusion?

velocities are unreliable

• collaterals can cause reversed, increased or absent flow

what is a vasospam and what is it associated with?

pathologic response due to irritation of cerebral arteries by blood breakdown products

• associated with subarachnoid hemorrhage

results in structural wall changes and lumenal narrowing

20% of population and women are more likely to have poor

temporal windows

embolic events are characterized by

an audible chirp and simultaneous visual HIT on screen

Qs explain crossover collateralization through the anterior communicating artery

when blood from unaffected side flows across ACA to supply compromised side