Intracranial Arteries Flashcards
What are two different modalities of transcranial doppler?
Duplex and continuous wave
Transcranial doppler assess cerebral hemodynamics by measuring what?
The blood flow velocities in the basal vessels in the circle of willis.
What must be known in the extracranial vessels before performing transcranial doppler?
Status
Traditional Transcranial doppler method uses range-gated pulsed wave (PW) doppler to penetrate what?
Windows or openings through the cranium and assess intracranial blood flow
What type of probe is used for PW doppler with spectral analyzer?
Non imaging 2-2.5 MHz
Why is it effective to use non-imaging 2-2.5 MHz probes for traditional transcranial doppler?
- Excellent signal to noise ratio, which means a lower bandwidth
- Variable focusing depth
- Transmit power up to 100 W/cm/sec
- Adjustable gate depth
What is the main benefit of traditional transcranial doppler?
It is more portable than TCI
What is the most common pitfall of traditional transcranial doppler?
Misidentification of vessels
Vessel identification with TCD is aided by knowing what following parameters?
- Depth of insonation
- Flow velocity
- Direction of beam angle
- Response to carotid compression
- Direction of flow
- Probe position (windows used)
- Traceability of vessels
TCI/ TCCD adds _________________ as a guide and permits ___________________ of the ____________.
- Imaging and uses color flow
- Accurate placement
- Sample flow
TCI/ TCCD uses what type of frequencies?
1.8-2.5 MHz
What type of footprint does TCI/TCCA use? What happens?
Larger footprint and decreased doppler sensitivity
For TCI and TCCD what type of doppler is preferred? why?
Power doppler due to the increased sensitivity and angle independence
What is some of the capabilities and applications of Transcranial Doppler? (10 things)
- Serial monitoring of MCA and other vessels for vasospasm (caused by subarachnoid).
- Monitor vasospastic effect of sickle cell anemia (Children)
- Detecting Intracranial stenosis and occlusions
- Adjunct to extracranial carotid duplex exam
- Assess Collateral circulation
- Functional reserve testing
- Confirm brain death
- Intraoperative monitoring
- Detect right to left cardiac shunts, PFO (using ultrasound contrast and watch for MES)
- Evaluate intracranial aneurysm and AV malformation
What are some limitations of Transcranial Doppler?
- Recent eye surgery may eliminate transorbital approach
- No window, or bone may be too thick (5-10%)
- Inaccurate identification of vessels with TCD
- Patient compliance
- Technical expertise
What is TCD most frequently used for?
Serial monitoring of MCA and other vessels for vasospasm
What is the internal carotid artery divided into?
- Cervical ICA
- Petrous ICA
- Cavernous ICA
Where is the cervical ICA located?
Carotid bifurcation to the carotid canal of the petrous portion of the temporal bones
Where does the petrous ICA runs?
Runs through the petrous portion of the temporal bone
What are the portions of the cavernous ICA?
- Paraseller portion (proximal segment)
- Genu poriton (the bend)
- Supraclinoid portion (distal portion)
Label the images
What is the first major branch of the ICA?
Ophthalmic artery
What does the ophthalmic artery arise from?
The cavernous portion of the ICA
What bifurcates from the terminus of the ICA
Middle cerebral artery and anterior cerebral artery
What is the size of the circle of willis?
Varies in size
How many different variations of the Circle of Willis?
At least 9 congenital variations
The most common variations of the Circle of Willis involve what/
The communicating arteries
What is the diameter of the Circle of Willis diameter at the base of the brain?
3 cm
In the Circle of Willis, MCA carries how much of flow?
80% of flow
In the Circle of Willis, velocities are higher where?
In anterior circulation (ICA distribution)
In the Circle of Willis, Velocities from highest to lowest are what?
- MCA
- ACA
- PCA
- BA
- VERTS
The velocities in the Circle of Willis decreases with what?
Age
Label the image
What does this image demonstrate?
Circle of Willis
What are these an example of?
Circle of Willis
How much of the population have an intact and functioning circle?
50%
How much of the population have a classic configuration?
18-25%
The Middle cerebral artery courses how and towards what?
It courses laterally towards the temporal bone with several branches
The middle cerebral artery carries how much flow to cerebral hemispheres?
75-80% of flow
What is the MCA larger than?
ACA
Where is the M1 segment of the MCA located?
From MCA origin to first branch
Where is the M2 Segment located?
From MCA distal to first branch
What is the velocity of the MCA?
<90 cm/sec, typically 55cm/sec +/- 12 cm/sec
Label the images
What does this demonstrate?
The normal MCA
Note the
- Towards flow
- Depth of 3-6
- Mean velocity of 55 cm/s +/-12cm/s
What does this image demonstrate?
MCA/ACA bifurcation
Notice the Bidrectional” flow
What is the spectral waveform of the MCA/ACA bifurcation?
Bidirectional
What are the segments of the ACA?
A1 and A2
Where does the A1 segment course towards?
A1 Courses medially towards the midbrain
Where does the A2 segment course towards?
Anteriorly to supply the anterior segments of the brain
What does the ACA (anterior cerebral artery) give rise to?
Anterior communicating arteries, which run between the two ACA
What does image demonstrate? why?
ACA
- The flow is away from the probe
- Depth is 6-8 cm
- Mean velocity s 50cm/s +/-11
What does the Posterior Cerebral Artery (PCA) perfuse?
The posterior hemisphere
Wheat does the PCA wrap around?
The cerebral peduncles
What are the segments of the PCA?
P1 Segment
P2 Segment
Where is the P1 segment located?
Origin to the posterior communicating arteries (PCoA).
What does the P1 Segment connect?
The anterior circulation and is a route for collateralization
Where is the P2 segment?
Distal to the PCoA
What does this image demonstrate?
PCA
What does this image demonstrate?
PCA, Note the:
- P1 Flow is towards
- Depth is at 6-7 cm
- P2 flow away
- Mean velocity 40cm/s +/- 10cm/s
Label the image?
What does the vertebral arteries arise from?
Subclavian arteries
Where does the vertebral arteries course between?
The transverse processes of the spine
Where does the Vertebral arteries enter the skull?
Foramen magnum