How has TCD evolved?
It has evolved as a diagnostic, monitoring, and therapeutic tool.
What is the only diagnostic tool that can provide real time information about cerebral hemodynamics and can detect embolization to the cerebral vessels.
TCD
What is TCD?
It is a noninvasive, cost-effective, and beside tool for obtaining information regrading the collateral flow across various branches of the circle of Willis in patients with cerebrovascular disorders.
What are some advanced applications of TCD?
Helps in the detection of:
- Right-to-left shunts
- Vasomotor reactivity
- Diagnosis
- Monitoring of vasospasm in subarchnoid hemorrhage
- Supplementary test for confirmation of brain death
Who is Rune Aaslid?
Introduced the transcranial doppler for detecting blood flow in the basal intracerebral arteries.
It was a single gate spectral TCD.
Who is Mark Moehring?
He invented the transcranial power-motion Doppler (PMD) with 33 sampling gates.
What are the advantages that PMD or M-mode Doppler had?
It had the advantage of simultaneously displaying the intensity and direction of intracranial blood flow with over 6 cm or more of intracranial space.
Simplified the examination technique
What was TCD intially introduced for?
Detecting the vasospasm following a subarachnoid hemorrhage.
What is the TCD now used/known for?
TCD has emerged as a noninvasive and cost effective tool for evaulating cerebral arterial patency, detecting stenosis, collateral flow patterns, and embolization.
TCD is known to ______ the rates of arterial recanalization.
Enhance
What is the only diagnostic tool available that provides real-time information about the cerebral hemodynamics over extended periods of monitoring, as well as detects embolization to cerebral vessels?
TCD
What can be done in the setting of an acute ischemic stroke?
A combination of TCD and cervical duplex US can evaluate the cerebral hemodynamics consequences of an extracranial carotid stenosis and help in identifying the lesion amendable for interventional therapy
How does TCD compare to CTA?
TCD demonstrated 79% sensitivity and 94% specificity in detecting intracranial stenosis.
What are TCD findings complementary to?
They are complementary to CTA in:
- Detecting real time embolization
- Various collateral flow patterns due to prox. stenosis
- Detecting alternating flow signals in the posterior circulation→suggestve of the steal phenomenon.
What does alternating flow in the posteror circulation suggest?
It is suggestive of the steal phenomenon.
What are some of the important and established applications of TCD?
- Detection of right-to-left shunt
- Cerebral vasomotor reactivity
- Monitoring flow velocities for stroke prevention in sickle cell dis.
- Supplementary diagnostic test for the confirmation of brain death
Continuous TCD monitoring during systemic thrombolysis is known to do what?
Enhance the rates of clot dissolution in acute ischemic stroke.
Current diagnostic ultrasound systems are based on what?
Pulse-echo technique.
What is the difference between the transmitted and the refected sound frequencies called?
Doppler shift.
What does the doppler shift enable?
It enables the detection of tissue motion and blood flow.
The complex signals resulting from the reflections of moving RBC are broken into indivual velocities by a method called_______.
Fast Fourier Transform
What is the angle of insonation in TCD?
0°
What is the biggest hurdle in order to obtain acoustic information from the intracranial space is what?
The skull bone.
How much does the skull bone attenuate?
About 90% of the ultrasound wave.
What is doppler sonography?
It is obtaining information regarding tissue motion and blood flow velcoties only, without structural imaging.
When tissue imaging is combined with flow velocities, the process is called________.
Duplex sonography.
What does TCCD stand for?
Transcradial color-coded doppler.
What time of tranducer is used for TCCD?
a 2MHz Phased-array transducer is used
What are the pro’s and con’s to TCCD?
PRO: Provides parenchymal imaging with a structural flow map of cerebal vessles
CONS: Fewer successful examinations can be done, especially with elderly with insufficent temporal acoustic bone windows.
What are con’s of the single gate TCD developed by Rune Aaslid?
- Could only obtain informaation from a small volume of intrancranial space.
- this limitation led to difficulaties in evaluating the information gathered from multiple points.
- Made it “operator-dependent”
- this limitation led to difficulaties in evaluating the information gathered from multiple points.
How did Moehring’s PMD revolutionize the application of TCD?
Systems simultaneously displayed flow intensity and direction, over 6 cm or more of intracranial space.
Made possible by using 33 overlapping sample gates
What does the circle of Willis provide?
It provides an important communication between the anterior and posterior circulatory systems.
Where does the ICA enter the cranial cavity?
Through the foramen lacerum.
It divides into the anterior and middle cerebral arteries,
The ACA are connected to eachother by what?
Anterior communicating artery.
Posteriorly, the right and left vertebrals join to form the _______
Basilar artery
Where does the basilar artery run?
It runs along the ventral surface of the pons and terminates by dividing into the right and left posterior cerebral arteries.
The ICA on either side if connected with the PCA’s by the_________.
Posterior communicating arteries.
What is the circle of Willis?
It is a natural collateral conduit through which blood gets diverted in case of proximal vessel occlusion.
In some areas on the skull, the bones are relatively thinner and permit sufficient penetration of ultrasound….what are these areas called?
Acoustic windows.
What are the 4 common acoustic windows?
- Temporal
- Orbital
- Suboccipital
- Submandibular
What flow velocities can be obtained through the transtemporal window?
- MCA
- ACA
- PCA
- PCOM
What can be insonated throught the transorbital window?
- Opthamalic artery
- ICA
What can be insonated in the in the suboccipital window?
- VA
- BA
Where can the BA be insonated?
The subocciptal and transforaminal
The submandibular approach approach is emplyed to evaluate the what?
The distal ICA in order to evaulate vasospasm in patients with subarachnoid hemorrhage.
How are intracranial arteries indentified?
Depth, direction of blood flow, and the Doppler spectra.
What does a red color signal indicate?
Flow towards the probe.
Red signal between 40 and 65 mm represents the flow in the ______
Ipsilateral MCA
What does blue signal indicates what?
Flow away from the probe.
What does a blue signal between 65 and 80 mm represents?
It represents the flow from the ipsilateral ACA
In favorable patients, a red signal may be noted beyond ______ which represents_______.
- 80 mm
- Represents flow in the contralateral A1 ACA
The power output is reduced to_____ when the transorbital acoustic window is employed.
10%
Flow signals at a depth of less than 60 mm, with a high resistance pattern and towards the probe represents what?
Opthamalic artery
In order to obtain the ICA siphon, how should you move?
Sample volume has to be moved beyond a 60 mm depth.
How is flow in the ICA Siphon?
The flow signals may be directed towards or away form the probe since its a curved artery
How does the sample volume compare to the diameter of the intracranial arteries?
The SV is usually large in reference to the diameter of the intracranial arteries
What does a normal spectral waveform look like?
It shows a sharp systolic upstroke and stepwise deceleration with positive end-diastolic.
What is the PSV?
This is the first peak on the TCD waveform from each cardiac cycle.
A rapid upstroke represents the absence of a severe stentoic lesion between the insonated intracranial arterial segments.
What is the EDV?
EDV lies between 20 and 50% of the PSV values, indicating a low resistance intracranial arterial flow pattern.
How is the MFV calculated?
It is claculated as EDV plus 1/3 of the difference between PSV and EDV.
Who should have the highest MFV?
The MCA should have the highest MFV among all major intracranial arteries.
the spectrum is commonly seen where?
distal steno-occlusive lesion,
