Intracranial Arteries Flashcards
1
Q
What are two different modalities of transcranial doppler?
A
Duplex and continuous wave
2
Q
Transcranial doppler assess cerebral hemodynamics by measuring what?
A
The blood flow velocities in the basal vessels in the circle of willis.
3
Q
What must be known in the extracranial vessels before performing transcranial doppler?
A
Status
4
Q
Traditional Transcranial doppler method uses range-gated pulsed wave (PW) doppler to penetrate what?
A
Windows or openings through the cranium and assess intracranial blood flow
5
Q
What type of probe is used for PW doppler with spectral analyzer?
A
Non imaging 2-2.5 MHz
6
Q
Why is it effective to use non-imaging 2-2.5 MHz probes for traditional transcranial doppler?
A
- Excellent signal to noise ratio, which means a lower bandwidth
- Variable focusing depth
- Transmit power up to 100 W/cm/sec
- Adjustable gate depth
7
Q
What is the main benefit of traditional transcranial doppler?
A
It is more portable than TCI
8
Q
What is the most common pitfall of traditional transcranial doppler?
A
Misidentification of vessels
9
Q
Vessel identification with TCD is aided by knowing what following parameters?
A
- Depth of insonation
- Flow velocity
- Direction of beam angle
- Response to carotid compression
- Direction of flow
- Probe position (windows used)
- Traceability of vessels
10
Q
TCI/ TCCD adds _________________ as a guide and permits ___________________ of the ____________.
A
- Imaging and uses color flow
- Accurate placement
- Sample flow
11
Q
TCI/ TCCD uses what type of frequencies?
A
1.8-2.5 MHz
12
Q
What type of footprint does TCI/TCCA use? What happens?
A
Larger footprint and decreased doppler sensitivity
13
Q
For TCI and TCCD what type of doppler is preferred? why?
A
Power doppler due to the increased sensitivity and angle independence
14
Q
What is some of the capabilities and applications of Transcranial Doppler? (10 things)
A
- 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
15
Q
What are some limitations of Transcranial Doppler?
A
- 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
16
Q
What is TCD most frequently used for?
A
Serial monitoring of MCA and other vessels for vasospasm
17
Q
What is the internal carotid artery divided into?
A
- Cervical ICA
- Petrous ICA
- Cavernous ICA
18
Q
Where is the cervical ICA located?
A
Carotid bifurcation to the carotid canal of the petrous portion of the temporal bones
19
Q
Where does the petrous ICA runs?
A
Runs through the petrous portion of the temporal bone
20
Q
What are the portions of the cavernous ICA?
A
- Paraseller portion (proximal segment)
- Genu poriton (the bend)
- Supraclinoid portion (distal portion)
21
Q
Label the images
A
22
Q
What is the first major branch of the ICA?
A
Ophthalmic artery
23
Q
What does the ophthalmic artery arise from?
A
The cavernous portion of the ICA
24
Q
What bifurcates from the terminus of the ICA
A
Middle cerebral artery and anterior cerebral artery
25
What is the size of the circle of willis?
Varies in size
26
How many different variations of the Circle of Willis?
At least 9 congenital variations
27
The most common variations of the Circle of Willis involve what/
The communicating arteries
28
What is the diameter of the Circle of Willis diameter at the base of the brain?
3 cm
29
In the Circle of Willis, MCA carries how much of flow?
80% of flow
30
In the Circle of Willis, velocities are higher where?
In anterior circulation (ICA distribution)
31
In the Circle of Willis, Velocities from highest to lowest are what?
1. MCA
2. ACA
3. PCA
4. BA
5. VERTS
32
The velocities in the Circle of Willis decreases with what?
Age
33
Label the image
34
What does this image demonstrate?
Circle of Willis
35
What are these an example of?
Circle of Willis
36
How much of the population have an intact and functioning circle?
50%
37
How much of the population have a classic configuration?
18-25%
38
The Middle cerebral artery courses how and towards what?
It courses laterally towards the temporal bone with several branches
39
The middle cerebral artery carries how much flow to cerebral hemispheres?
75-80% of flow
40
What is the MCA larger than?
ACA
41
Where is the M1 segment of the MCA located?
From MCA origin to first branch
42
Where is the M2 Segment located?
From MCA distal to first branch
43
What is the velocity of the MCA?
<90 cm/sec, typically 55cm/sec +/- 12 cm/sec
44
Label the images
45
What does this demonstrate?
The normal MCA
Note the
1. Towards flow
2. Depth of 3-6
3. Mean velocity of 55 cm/s +/-12cm/s
46
What does this image demonstrate?
MCA/ACA bifurcation
*Notice the Bidrectional" flow*
47
What is the spectral waveform of the MCA/ACA bifurcation?
Bidirectional
48
What are the segments of the ACA?
A1 and A2
49
Where does the A1 segment course towards?
A1 Courses medially towards the midbrain
50
Where does the A2 segment course towards?
Anteriorly to supply the anterior segments of the brain
51
What does the ACA (anterior cerebral artery) give rise to?
Anterior communicating arteries, which run between the two ACA
52
What does image demonstrate? why?
ACA
1. The flow is away from the probe
2. Depth is 6-8 cm
3. Mean velocity s 50cm/s +/-11
53
What does the Posterior Cerebral Artery (PCA) perfuse?
The posterior hemisphere
54
Wheat does the PCA wrap around?
The cerebral peduncles
55
What are the segments of the PCA?
P1 Segment
P2 Segment
56
Where is the P1 segment located?
Origin to the posterior communicating arteries (PCoA).
57
What does the P1 Segment connect?
The anterior circulation and is a route for collateralization
58
Where is the P2 segment?
Distal to the PCoA
59
What does this image demonstrate?
PCA
60
What does this image demonstrate?
PCA, Note the:
1. P1 Flow is towards
2. Depth is at 6-7 cm
3. P2 flow away
4. Mean velocity 40cm/s +/- 10cm/s
61
Label the image?
62
What does the vertebral arteries arise from?
Subclavian arteries
63
Where does the vertebral arteries course between?
The transverse processes of the spine
64
Where does the Vertebral arteries enter the skull?
Foramen magnum
65
What does the intracranial branches of the vertebral include?
1. Anterior spinal artery
2. Posterior inferior cerebellar artery
66
What is the basilar artery formed by?
The two intracranial vertebral arteries
67
How long is the basilar artery?
3 cm long
68
What does the basilar artery bifurcate into?
Two posterior cerebral arteries (PCA)
69
Label the image
70
There are four different approaches or windows to allow insonation of the arteries. What are they?
1. Transtemporal
2. Transorbital
3. Transforaminal/suboccipital
4. Submandibular (uncommon)
71
What are the assumed angle for TCD/TCI?
0 degrees
72
What kind of imaging is TCI (TCCD)?
Non invasive imaging of the intracranial vessels
73
What does TCI (TCCD) determine in terms of flow?
1. Whether there is flow in a vessel
2. Rea time flow of the arteries
74
How do we identify vessels with TCD?
1. Probe position and beam angle
2. Depth of vessel
3. Flow direction
4. Traceability of vessel
5. Mean velocity value
75
What is time-averaged MEAN velocity used for?
Flow volume calculation
76
In terms of time averaged mean velocity, when the mean velocity calculation is displayed you'll see what?
A line running through the middle of the waveforms
77
What is time averaged PEAK velocity used in?
TCD and TCI (Not peak systolic velocity)
78
Although time averaged peak velocity is referred to as the mean velocity, it is actually what?
The mean of the peak velocities over time
79
In terms of time averaged PEAK velocity, Velocity measurement traces will course how? What does this mean?
1. It will course over the top of the spectral waveforms
2. All TCD velocity values are mean velocities
80
"Mean" velocity is a mean of the peak velocities over time, sometimes referred to as what?
TAMX (time averaged max)
81
Label the image in what it means?
82
What is the most promising window?
Transtemporal window
83
Where is the transtemporal window?
Over temporal bone superior to the zygomatic arch
84
In the transtemporal window, what does the anterior angulation (6 degrees) interrogate?
1. The MCA
2. Portion of the carotid siphon (ICA)
3. ACA
4. ACCA
85
In terms of the transtemporal window, what does the Posterior angulation (5 degrees) Interrogate?
1. PCA
2. Basilar
3. PCCA
86
Label the images for the transtemporal window?
1. Posterior
2. Middle
3. Anterior
87
Label the image
88
What is the transorbital window probe situated?
Medially on closed eyelid
89
What should we do with power when we scan the eye?
Power should be reduced to prevent damage to they eye and scanning time should be limited
90
Label the image
91
What is the transforamenal window also known as?
Sub-occipital
92
What does this image demonstrate?
Transforamenal window
93
Label the image
94
What is the submandibular window's extradural segments?
The distal ICA and Carotid siphon
95
What is the depths used for the submandibular window? Velocity? And flow direction?
80mm, 30 cm/s, retrograde
96
In terms of ICA obstruction, what does the anterior and posterior communicating arteries do?
Allow for cross filling and collateralization
97
Patients without a functioning Circle of Willis may suffer more significant what?
Neurologic ischemia
98
What happens during intracerebral aneurysms?
Weakening of the structural proteins within the media
99
In terms of intracerebral aneurysms, Large aneurysms can constrict surrounding arterial flow and have the risk of what?
1. Rupture
2. Subsequent SAH (subarachnoid hemorrhage)
3. Cerebral infarct
100
ACoA (ACCA) is the most common site for what?
Intracranial aneurysms, especially when associated with SAH
101
Even though the ACoA is the most common site for intracranial aneurysms, what are also common sites/
PCoA and MCA bifurcation
102
What do sonographers do for patients with potential intracranial stenosis/ Occlusive disease?
Evaluate acute stroke patients for intracranial high grade stenosis or occlusion
103
In terms of intracranial stenosis/ Occlusive disease what signs do we see with stenosis in the large basal arteries?
Large basal arteries would show
1. Increased velocity
2. Increased spectral broadening
3. Co-vibration phenomenon
104
What are some pitfalls for TCD and intracranial stenosis/ occlusive diseases, specifically a stenosis?
Changes can be due to collateral flow or vessels supplying AVM's
105
In terms of occlusive disease, what should we see with TCD?
1. Absence of arterial signal at expected depth
2. Patent communicators
3. Altered flow in communicating vessels
106
In terms of scanning for Occlusive disease, what are some pitfalls?
Inadequate temporal window causing non-visualization, displacement of vessel from its normal position by a tumor
107
In terms of a extracranial stenosis/ occlusion, what are some clinical applications?
1. Assess effects of extracranial disease on intracranial circulation
2. Critical extracranial stenoses cause significant changes intracranially
3. Potential for collateralization via Circle of Willis
4. Patency of Circle of Willis can be tested with compression or oscillation maneuvers
5. **Compressions**
6. **Oscillations**
7. Already increased velocities in collaterals are accentuated during contralateral CCA compressions
108
In terms of Extracranial stenosis/ Occlusion, what does compressions do?
Applications of slow pressure to CCA for 2-4 cardiac cycle with slow release noting changes to flow direction and velocity
109
In terms of extracranial stenosis/ occlusions, what does oscillations do?
Short rapid incomplete compressions. Note Transmitted oscillation
110
In terms of collateralization pathways in the vertebrobasilar, abnormalities are due to what?
Subclavian steals (which are uncommon)
111
In terms of collateralization pathways in the vertebrobasilar, basilar artery flow may be reduced or show what if both vertebras are diseased?
"to and fro" pattern if both vertebral arteries are diseased
112
In terms of collateralization pathways in the vertebrobasilar do we see reversed flow?
Rarely
113
In terms of collateralization pathways in the vertebrobasilar, Subclavian steals are what kind of conditions?
Benign conditions
114
Label the image
115
Label the image
116
Label the image
117
What happens when there is AV malformations? 5
1. Arteries supplying AVM have increased systolic and diastolic flow velocities
2. Adjacent arteries have decreased flow
3. Reduced pulsatility
4. Velocities can be as high as 280 cm/sec
5. Little response to CO2 stimualtion
118
What is the clinical applications of intraoperative monitoring?
1. Monitoring of blood flow during endarterectomies and bypass surgery
2. Detects rapid alterations in flow which alert the surgeon to possible complications and therefore alter operative technique
3. MCA is monitored giving information about cerebral perfusion
119
In terms of intraoperative monitoring, If the MCA velocity is >10cm/sec what does this indicate?
Adequate collateral flow during clamping of the carotid artery, which means a shunt is usually not needed for surgery
120
What is the most frequent clinical application of transcranial doppler?
Vasospasm
121
Spasms of cerebral arteries is a complication of what?
Subarachnoid hemorrhage
122
Subarachnoid hemorrhage occurs between what?
The arachnoid and pia matter layers of the cerebrum
123
Mild vasospasms can be asymptomatic but severe spasms do what?
Reduces cerebral perfusion and symptomatic ischemic deficit can result
124
What are some symptoms of vasospasms?
1. Confusion
2. Decreased levels of consciousness
3. Stroke
125
Vasospasms can occur on which side of hemorrhage?
Ipsilateral or contralateral to the side of the hemorrhage or occur bilaterally, and may involve any of the major intracranial arteries
126
What may vasospasms lead to?
Significant mortality and morbidity
127
In terms of clinical applications of TCD for Vasospasms, vasospasms usually occurs when?
4-14 days post hemorrhage but TCD is useful in detecting flow changes before the clinical onset. This allows prophylactic treatment to be stated
128
In terms of clinical applications of TCD for Vasospasms, MCA velocity indicates what?
1. >120 cm/sec indicates reaction to a documented hemorrhage
2. Increase of >20 cm/sec per day indicative or poor prognosis
3. MCA velocity >200 cm/sec is associated with critical reduction in cerebral blood flow. Ischemic neurologic deficits highly probable
129
In terms of clinical applications of TCD for Vasospasms, TCD monitoring of known vasospasm to the patient in ICU allows for what?
Adjustments to treatment and information regarding cerebral flow
130
In terms of clinical applications of TCD for Vasospasms, What is a alternate method of diagnosis? What is a pitfall?
Angiography, but follow-up monitor is difficult with such an invasive procedure on an unstable patient
131
What does these images demonstrate?
Severe spasms in the RT MCA and the effect on the LT MCA
132
Determination of brain death is based on what things?
1. Clinical status
2. EEG results
3. Angiographic demonstrations of absent intracranial circulation
133
In terms of clinical applications of TCD for brain death, TCD monitoring demonstrates what?
Cerebral circulatory arrest
134
In terms of clinical applications of TCD for brain death, Spectral signals progressing towards brain death show what?
a decrease in diastolic flow, eventually reaching zero
135
In terms of clinical applications of TCD for brain death, Just prior to brain death the spectral signals show what?
Reversed flow with a to and fro motion that is detected easily on a TCD spectral tracing
136
In terms of clinical applications of TCD for brain death, Systolic velocity decreases to what?
To the end result of no flow to the brain
137
What is the functional reserve testing or vasomotor reactivity test?
Patient breaths different air concentrations through a mask
138
What does the functional reserve testing or vasomotor reactivity test do?
Evaluates the reserve mechanism of cerebral vasculature in the presence of carotid occlusive disease using CO2 as a stimulus
139
During Functional reserve testing or vasomotor reactivity test, what is monitored?
The MCA is monitored during change CO2 concentrations
140
In terms of clinical applications of TCD for functional reserve testing or vasomotor reactivity testing, the peripheral vascular bed should do what?
Dilate in response to hypoxia (lack of oxygen) and flow in the MCA should increase
141
In terms of clinical applications of TCD for functional reserve testing or vasomotor reactivity testing, If there is no change in the change with CO2 stimulus this indicates what?
That the peripheral beds are already maximally dilated therefore exhausting the vasomotor reserve
142
In terms of clinical applications of TCD for functional reserve testing or vasomotor reactivity testing, Rather than administering CO2 the patient can do what? What is a pitfall?
1. Hold their breath for 30 seconds to achieve the same response.
2. This may be difficult in elderly patients or those with compromising lung disease
143
What is sickle cell anemia?
Genetic defect of hemoglobin synthesis, occurring almost exclusively in people of African descent as well as Europeans and Asians
144
Sickle shaped RBC's do what?
They clump together
145
Patients with sickle cell anemia have an increased risk for what?
Stroke
146
In terms of sickle cell anemia, how many children will have sickle cell anemia?
2-20%
147
In terms of sickle cell anemia, TCD is used to monitor these patients by doing what?
Screening MCA velocities
148
In terms of sickle cell anemia, velocities of >200 cm/s indicates risk of what?
Stroke and these patients should receive transfusions which is the treatment
149
What is emboli?
Particulate matter which can arise from the carotid system plaque, heart tumors or thrombus
150
Air emboli can occur when?
During operative procedures
151
Air or particulate emboli can be monitored when?
During or after operative procedures
152
Emboli detection symbols are known as what ?
1. Micro-embolic signals (MES)
2. High intensity transient signals (HITS)
153
>50 HITS over a 10 minute period is considered what?
Serious and increases the patient's risk of stroke
154
What is the criteria for emboli detection?
1. Duration usually <300 msec
2. Unidirectional signal within the doppler velocity spectrum
3. Signal is accompanied by a "snap" or "chirp" on the audible output
155
What is this an example of?
1. MCA with spectral doppler and audio spectrum
2. Example of MES
156
What is an example of a patent foramen ovale?
Abnormal right to left blood shunt in the heart that bypasses the pulmonary artery and lungs
157
Patent foramen ovale have the potential for what?
Venous thromboemboli ending up in the peripheral arterial system or in the cerebral vasculature
158
What modalities can be used to detect a patent foramen ovale?
TCD and has a high sensitivity and specificity when compared to TEE the gold standard
159
In terms of patent foramen ovale testing, micro air bubbles (agitated saline) are injected into what?
A superficial vein in the arm during bilateral monitoring of the MCA flow
160
When the testing is done, if the foramen ovale is closed where does the bubbles go?
To the lungs
161
When testing is done, If the foramen ovale is open, the bubbles will cause what?
HITS in the MCA after a few seconds
