Transcranial Doppler (TCD)

Anterior Circulation of the Circle of Willis

Carotid siphon - parasellar, genu, and supraclinoid segments

ICA branches - ophthalmic & posterior communicating

MCA

Anterior cerebral - pre & post-communicating

Anterior communitating

Posterior Circulation of the Circle of Willis

Vertebral

Basilar

Posterior Cerebral - pre & post-communicating

Vertebrobasilar Circulation of the Circle of Willis

Vertebral - posterior inferior cerebellar

Basilar - anterior inferior cerebellar & superior cerebellar

Common Anatomical Variants in Cranial Vessels

Hypoplasia of posterior communicating A

Hypoplasia of pre-communicating posterior cerebral A

Hypoplasia &/or Duplication of anterior communicating A

Hypoplasia of pre-communicating anterior cerebral A

Collateral Flow Patterns of Cranial Vessels

ECA to ICA via reversed ophthalmic A

Crossover collateral via anterior communicating A

Posterior-to-anterior collateral via posterior communicating A

Disadvantages to TCD

Extracranial status

CO2 status

Intracranial pressure

Limited windows

Blind spots

Pilot error (6 month learning curve)

TCD Indications

Vasospasm - trauma or aneurysm

Vertebral basilar insufficiency

Intraoperative monitoring

Intracranial pressure

Brain death

PFO - right to left shunts

Sickle Cell

Sub arachnoid hemorrhage - head trauma, aneurysms, AVM

TCD Risk Factors

Diabetes

Hypertension

High cholesterol

Tobacco abuse

Cardiac disease or hx of heart attack

Claudication

Stroke or TIA

Previous vascular procedures - stents or bypass

TCD Relevant Patient History

Face, leg, or arm numbness, tingling, weakness

Problems speaking/understanding speech

Vision problems - blindness or double vision

Gait disturbance or leg weakness

Vertigo or fainting

Severe headaches

Equipment for Non-Imaging TDC

Dedicated non-imaging System

1-2 MHz transducer

Equipment for TDC Duplex Imaging

Ultrasound system

1-5 MHz sector transducer

Equipment for TCD Monitoring

How to Identify Vessels on TDC

Scanning window/approach

Sample volume depth

Bloodflow direction - antegrade/retrograde

Spatial anatomical relationship to other vessels

Flow velocity

TCD Velocity Measurements

Time average peak velocity (TAPV)

Mean of the max velocity

Transtemporal TCD

Over temporal bone

Frontal, middle, anterior, and posterior windows

Transtemporal TCD Bony Structures

Sphenoid

Petrous ridge

Anterior clinoid process

Transorbital TCD

Through orbital place, optic canal, and superior orbital fissure

Acoustic Output for Transorbital TCD

MI < 0.23

Transforaminal/Sub-Occipital TCD

Through foramen magnum

Submandibular TCD

Under jaw angled cephalad

*images ICA

Atlas Loop TCD

Behind ear between mastoid & sternocleidomastoid muscle

1.25 cm below mastoid process

Terminal Internal Carotid A (tICA)

Temporal window

60 - 70 mm depth

Bidirectional flow (red or blue)

39 +/- 9 cm/sec

Middle Cerebral A (MCA)

Temporal window

30 - 60 mm depth

Flow towards tx (red)

55 +/- 12 cm/sec

Anterior Cerebral A (ACA)

Temporal window

60-75 mm depth

Flow away from tx (blue)

50 +/- 11 cm/sec

Posterior Cerebral A (PCA)

Temporal window

60 - 80 mm depth

Pre-communicating: flow towards tx (red)

Post-communicating: flow away from tx (blue)

39 +/- 10 cm/sec

Ophthalmic A

Orbital window

35 - 55 mm depth

Flow towards tx (red)

21 +/- 5 cm/sec

Carotid Siphon

Orbital window

60 - 80 mm depth

41 +/- 11 cm/sec

Parasellar Segment of Carotid Siphon Flow

Towards tx (red)

Genu Segment of Carotid Siphon Flow

Bidirectional (red or blue)

Supraclinoid Segment of Carotid Siphon Flow

Away from tx (blue)

Vertebral A

Transforaminal/sub-occipital window

60-90 mm depth

Flow away from tx (blue)

38 +/- 10 cm/sec

Basilar artery

Transforaminal/sub-occipital window

70-120 mm depth

Flow away from tx (blue)

41 +/- 10 cm/sec

Intracranial/Extracranial Stenosis

Most commonly caused by cardiac disease & atherosclerosis

Matches stenotic flow profile - pre-stenotic high resistance with post-stenotic turbulence & drop in velocity

Intracranial/Extracranial Occlusion

Most commonly caused by embolism

Flow returns to normal within 6 hours - good prognosis

Flow remains decreased after 12 hours - poor recovery

Vasospasm

Transient narrowing of cerebral arteries - mainly at skull base

Commonly due to subarachnoid hemorrhage (SAH)

Can lead to stroke - delayed cerebral ischemia (DCI)

Progression of Vasospasm

Begins 3-4 days after SAH

Peaks 6-8 days after

Resolves in 2-4 weeks

Sviri Ratio

Used for posterior circulation vasospasm

Average of bilateral vertebral A velocities ÷ highest basilar A mean velocity

Severe MCA/ICA Vasospasm Velocity

> 200 cm/s

Lindegaard Ratio

Used for anterior circulation

Differentiates increased flow volume (hyperemia) from vasospasm

MCA mean velocity ÷ submandibular ICA mean velocity

Severe MCA/ICA Vasospasm Ratio

> 6

Detecting PFO Via TCD

Agitated saline with micorbbubles area seen as "hits" or microembolic signals (MES) during/after injection if a PFO is present

Perform valsalva if needed

Low-Grade Shunt

1-10 hits

Medium-Grade Shunt

> 10 hits without curtain effect

High-Grade Shunt

Curtain effect

Vasomotor Reserve

Brain's ability to dilate/constrict vessels in response to CO2 changes (holding breath) to maintain stable blood flow

Reduced with stenosis, small artery disease, concussion

Functional Testing via TCD

Assessment of cerebral ischemia with high grate stenosis/occlusion

Assess vasomotor reserve

Cerebral Circulatory Arrest (CCA)

Brain death - ECG criteria must also be met

Early - low diastolic flow

Final stage - persistent oscillating high resistance waveforms with no diastolic flow

Advantages of TCD for CCA Diagnosis

Portable

Non-invasive

Repeatable

Does not require contrast

Not affected by drugs that suppress the CNS

Disadvantages of TCD for CCA Diagnosis

Need experienced operators

Inadequate acoustic windows in up to 20% of the time

False negatives in anoxic patients

False positives

Patient's with sickle cell anemia are prone to...

MCA & ACA strokes

MCA Mean Velocity in Sickle Cell Anemia Patients on TCD

> 200 cm/sec

MCA Mean Velocity in Sickle Cell Anemia Patients with Stoke on TCD

190-250 cm/sec