What is the circle of Willis?
It is a network of vessels that distributes flow to all regions of the RT ad LT hemispheres of the brain.
What is the most important source of cerebral blood supply and collateral circulation?
Circle of Willis
Where is the circle of Willis?
It is located at the base of the brain.
How many people have a complete Circle of Willis?
Only 20% of the population.
What is the criteria for vessel identification?
- Depth of SV
- Direction of flow
- Traceability
- Transducer angulation
- Spatial relationship of waveform spectra
What are the characterisitics of transcranial doppler?
- Non-invasive
- Painless
- Inexpensive
- Provides instantaneous and continuous
- Cerebral blood flow information
- Can be used in any hopsital enviroment
- Safe
What are the pitfalls and trouble spots of TCD?
- Variations and incomplete circle of willis
- Absent or small temporal windows
- Not identifying/finding best temporal window
- Improper doppler settings.
What should you set the equipment prior to an exam?
- Wipe down the transducer and cable
- Label vessel, adjust depth, power and direction of flow, before applying transducer on patient.
How should you position the patient pior to an exam?
- Exam can be preformed with the patient in a supine or sitting position
- DO NOT reposition a patient with EDV w/o nursing assistance
What window can the MCA be seen in?
Transtemporal window
What is the M1 segment depth range?
40-60mm
What is the M2 segment depth range?
30-40mm
What is the flow direction of the MCA?
Towards the transducer
How should you sample the MCA?
In 2mm increments
Can the MCA change direction?
No, it will never change direction.
Where can the MCA/ACA bifurcation?
In the transtemporal window
What is the depth range of the MCA/ACA bifurcation?
60-70 mm
What is the flow pattern in the MCA/ACA bifurcation?
Bidirectional
What is the flow direction in the ACA?
Away from the transducer
What window can the ACA be seen in?
Transtemporal window
What is the segment depth of the ACA?
60-80 mm
What is the normal flow direction of the ACA?
Away from the transducer
When can the ACA flow direction change?
It can change direction with the presence of disease
Where can the PCA be seen?
It can be seen in the transtemporal window
What is the PCA’s segment depth range?
60-70 mm
What is the flow direction of the PCA?
Bidirectional
What is the flow direction of P1?
Towards the transducer
What is the flow direction of P2?
Away from the transducer
When can the PCA flow direction change?
It can change direction with the presence of disease
Where can you see the VA?
Transforamenal (suboccipital) window
What is the segment depth range of the VA?
60-80 mm
What is the flow direction of the VA?
Away from the transducer
When can the VA flow direction change?
It can change direction with the presence of disease such as subclavian steal.
What is formed by the two vertebrals?
The basilar artery
Where does the vertebral arteries enter through?
Foramen Lacerum
Where is the BA seen?
Transforamenal (suboccipital) window
What is the BA segment depth range?
80-100 mm
What is the flow direction of the BA?
Away from the transducer
What is the first branch of the ICA?
OA
Where can the OA be seen?
Transorbital window
What is the segment depth range of the OA?
40-60mm
What is the flow direction of the OA?
Towards the transducer
When can the OA change direction?
Presence of disease.
What is the only high resistance cerebral artery?
OA
Where can the CS be seen?
Transforamenal (suboccpital) window
What is the segment depth range of the CS?
60-80mm
What is the flow direction of the CS?
Bidrectional from transducer because of tortuosity
Where can the ICA be seen?
Submandibular window
What is the segment depth range of the ICA?
40-70mm
What is the flow direction of the ICA?
Away from the transducer
What is used to calculate the lindegaard ratio?
ICA
