1. Diagnostic Medical Sonography Program
Lecture 20: Transcranial Doppler (TCD)
Holdorf

2. Transcranial Doppler (TCD)
Capabilities:
Detect intracranial stenosis, occlusions, and assess collateral circulation
Evaluate onset, severity, and time course of vasoconstriction from subarachnoid hemorrhage
Evaluate intracranial arteriovenous malformations
Assess patients with suspected brain death

3. Limitations Recent eye surgery may eliminate trans-orbital approach
Adequate penetration of temporal bone
Inaccurate vessel identification with non-imaging technique

4. Patient Positioning Physical principles
Patient supine and avoids speaking during examination
Physical principles
Same as pulsed Doppler

5. Important Points 2 MHz pulsed Doppler used with spectrum analysis
Zero angle of insonation is assumed
Three acoustic windows used:
Trans-temporal
Trans-orbital
Trans-foraminal / sub-occipital

6. Important Points Accurate vessel identification requires:
Depth of sample volume
Velocity of the blood flow
Direction of blood flow
Relationship of flow patterns to one another
Time averaged maximum velocity (TAMV) or mean velocity used

8. Technique
Unilateral trans-temporal approach of MCA, ACA, PCA and Terminal ICA
Ipsilateral trans-orbital approach to evaluate ophthalmic artery and carotid siphon
Preceding two steps completed contra laterally
Trans-foraminal / sub-occipital approach used to evaluate the intracranial vertebra land basilar arteries
Inappropriate Doppler angle usually negates ability to insonate posterior communicating (Pcom) arteries. However, flow direction is normally from anterior to posterior.

10. Interpretation Based on flow characteristics: Direction Velocity
Turbulence
Pulsatility
Systolic upstroke

11. Collateral Pathways
Cross-over: antegrade flow in anterior cerebral artery (ACA) from cross-over collateralization, e. g., flow from contralateral ACA via anterior communicating artery
External-to-internal: Retrograde flow in ophthalmic artery (OA)
Posterior-to-anterior: Increased flow in posterior cerebral artery (PCA), reversing direction of flow in the Pcom artery.

12. Factors that may alter intracranial blood flow, e. g
Factors that may alter intracranial blood flow, e.g., age, sex, hematocrit, blood gases, metabolism
Occlusion:
Most accurate in ICA or MCA
Criterial similar to those used in other vessels
Vasospasm
Most accurate in MCA
Serial recordings necessary
Mean velocities > 120 cm/sec. Severe vasospasm = > 200 cm/sec

13. Arteriovenous malformations
Increased systolic and diastolic flow velocities
Very low pulsatility indices
Reduced flow in adjacent arteries

14. Intraoperative monitoring
Capabilities: Identification of flow abnormalities may warrant change in surgical technique, e. g., carotid endarterectomy or coronary artery bypass grafting
Technique
Headset utilized for continuous monitoring
Not working in sterile field
Interpretation
Significant decrease in MCA flow velocities during cross-clamping of vessels may indicate need for shunting
Audible signals related to micro-emboli may alter surgical technique

15. Additional Notes: Lecture 20 Transcranial Doppler (TCD)
TCD does not image.

16. Collaterals: MCA: if the ipsilateral ICA is occluded
Antegrade flow in the ACA means ipsilateral ICA is occluded.
The monster chart
ACA- Direction is supposed to be Retrograde-away from the probe
PCA-Direction is supposed to be Antegrade- towards the probe
Ophthalmic artery- Direction is supposed to be antegrade- towards the probe
ICA at the siphon-retrograde and antegrade flow patterns.
Vertebral artery- retrograde
Basilar Artery- retrograde
DEPTH is an important question; usually asked only for the ID of the MCA mm

17. Collateral pathways are important!!!
But, can be confusing.
At this point, you need to know what the expected flow directions are (antegrade-toward the probe or retrograde-away from the probe). Ex. if the MCA demonstrates retrograde flow, you know that something is not right and that there is collateral flow occurring, and that this is due to save parts of the brain that may otherwise not receive blood.

18. Homework Textbook: Chapter 21: Transcranial Doppler SDMS Assignments
Pages 239 – 248
SDMS Assignments