TRANSCRANIAL DOPPLER ULTRASOUND

INTRODUCTION TO TCD

Nicolet Vascular, Inc.

A Division of

VIASYS HEALTHCARE

WHAT IS TCD?

• TCD (Transcranial Doppler) is a

non-invasive assessment of cerebral blood flow in the basal cerebral arteries

• Utilizes low frequency Doppler ultrasound

WHAT IS TCD?

• Uses 2 MHz pulsed Doppler ultrasound

• Passes through cranial “windows”

• Provides information regarding velocity and direction of cerebral blood flow

Middle Cerebral Artery

BLOOD FLOW VELOCITY

• Changes in flow velocity occur when:

• There is a change in vessel caliber• There is a change in volume flow

TRANSCRANIAL DOPPLER

• Non-invasive• Painless• Inexpensive• Can provide instantaneous and continuous

cerebral blood flow information • Can be used in any hospital environment• Safe

DEVELOPMENT OF TCD

• 1982 Dr. Rune Aaslid– First publication Transtemporal Approach

• 1984 Dr. Merrill Spencer– First publication Transorbital Approach

• 1986 Dr. M. Von Reutern– First publication Suboccipital Approach

• 1983 First commercial TCD unit (EME)

TCD APPLICATIONS

• Accepted applications *(AAN):

– Detect intracranial stenosis– Follow the time course of vasospasm– Confirm the diagnosis of brain death– Assist in the detection an management

of AVMs

*American Academy of Neurology

TCD APPLICATIONS

• Other reported uses:– Assess of collateral pathways– Assess autoregulation and vasomotor

reactivity– ICU monitoring (effects of ICP)– Surgical monitoring (CEA, CABG)– Detection of emboli (HITS)– Aid in classification of strokes

TCD APPLICATIONS

• Other reported uses:– Subclavian steal assessment– Assess mechanical compression of the

vertebral arteries– Evaluate Sickle Cell patients– Evaluate patients with carotid

dissections

TCD APPLICATIONS

• Assess the effects of pharmacological interventions

• Research applications

• Surgical monitoring

INTRAOPERATIVE MONITORING APPLICATIONS

• Carotid Endarterectomy

• Carotid Stenting

• Coronary Artery Bypass Surgery

• Cardiac Valve Surgery

• Abdominal Aortic Aneurysm

• Liver Transplants

• Orthopedic Surgery

TCD MONITORING

• Patent Foramen Ovale evaluation

• Implantable cardioverter defibrillator testing

• Any procedure where knowledge of the state of blood flow to the brain is of critical importance

TRANSCRANIAL DOPPLER

EXAMINATION TECHNIQUE

TCD - APPROACHES

• Transtemporal

• Transorbital

• Suboccipital (Transforaminal)

• Submandibular

TRANSCRANIAL DOPPLER ACCESS ROUTES

TRANSTEMPORAL APPROACH

• Middle Cerebral Artery MCA• Anterior Cerebral Artery ACA• Terminal Internal Carotid Artery T-ICA• Posterior Cerebral Artery PCA• Communicating Arteries

– Anterior Communicating Artery

ACoA– Posterior Communicating Artery PCoA

CRITERIA FOR VESSEL IDENTIFICATION

• Depth of the sample volume

• Direction of flow

• Traceability of the vessel

• Transducer angulation

• Spatial relationship of spectra

• Response to carotid or vertebral oscillations or compressions

TRANSTEMPORAL WINDOWS

Frontal

AW

PW

MW

AW

MW

PW

FW

Middle Cerebral Artery

MCA / ACA

Anterior Cerebral Artery

Posterior Cerebral Artery – P1

TRANSORBITAL APPROACH

• Ophthalmic Artery OA

• Internal Carotid Artery Siphon

– Parasellar

– Genu

– Supraclinoid

Ophthalmic Artery

Carotid Siphon - Genu

SUBOCCIPITAL APPROACH

• Vertebral Artery VA

• Basilar Artery BA

Vertebral Artery

Basilar Artery

NORMAL VELOCITY RELATIONSHIPS

MCA > ACA > PCAPCA ~ VA and BA

PRIMARY DIAGNOSTIC FEATURES

• Changes in velocity

• Changes in pulsatility

• Changes in systolic upstroke

• Changes in flow direction

• Side to side differences

• Embolic phenomena (HITS)

TRANSCRANIAL DOPPLER

COLLATERAL CIRCULATION

Effects of Extracranial Carotid Stenosis / Occlusion

• Factors affecting cerebral blood flow:

– Degree of proximal stenosis– Size and extent of collateral channels

EFFECTS OF CAROTID STENOSIS

• Mild to Moderate Stenosis (< +/- 75%)

– TCD exam: Essentially normal

• Severe Stenosis (> +/- 75%)

– TCD exam: Abnormal– Changes in Doppler spectral waveform shape– Changes in flow patterns (Collateral)

WAVEFORM CHANGES

• Decreased velocity

• Delayed systolic upstroke

• Decreased pulsatility

DOPPLER WAVEFORM CHANGES

Normal MCA

Abnormal MCA

COLLATERAL SOURCES

• Collateral detectable by TCD include:

– Circle of Willis, including the vertebrobasilar system

– ECA to ICA collateral via the ophthalmic artery

COLLATERAL SOURCES

• Collateral not detectable by TCD include:

– Branches of the ECA connecting to branches of the vertebral artery

– Leptomeningeal anastomoses

INTRACRANIAL STENOSIS

• Focal elevated velocities above adjacent segments

• Side to side differences exceeding normal variation (usually > 15% or 30 cm/sec between right and left MCA)

• Downstream effects: – Turbulence– Delayed systolic upstroke– Decreased velocity

TCD WAVEFORMS WITH INTRACRANIAL STENOSIS

INTRACRANIAL STENOSISCauses

• Atherosclerosis

• Intraluminal thromboembolism

• Arterial dissection

• Moyamoya disease

• Vasculitis

• Vasospasm

• Extrinsic vessel compression

TRANSCRANIAL DOPPLER

EMBOLI DETECTION(HITS)

EMBOLIC EVENTS

• Foreign solids and / or gaseous materials within the blood stream

• Reflect sound waves more intensely than surrounding red blood cells

• Characterized by an audible “chirp” and simultaneous visual “HIT” on the screen

TCD - EMBOLI DETECTION

• Can detect the presence of embolic signals caused by the presence of a variety of materials, both gaseous and solid

• Cannot determine the size of an embolus

• Cannot determine the composition of an embolus

• Can detect particles as small as 50 microns

EMBOLI RECOGNITION International Consensus Committee

• Short < 0.1 second, 3-60 dB transients

• Unidirectional in spectra

• Occur randomly in cardiac cycles

• Change frequency within spectrum

• Audible sound: chirps, clicks, plunks

• Solid vs. air emboli distinguished by circumstance (solid designated when there is no invasion of vasculature)

EMBOLI DETECTION

• Carotid artery stenosis

• Arterial dissection

• Post endarterectomy

• Heart valve replacement

• Patent foramen ovale

• Atrial fibrillation

• Significant CHF

• Endocarditis

• Acute MI

MCA Microembolic Signal (MES)

Transcranial Doppler

Paradoxical Stroke

and

PFO Evaluation

Ischemic Stroke

• Represents the third greatest cause of death in the western word

• Is the greatest cause of functional incapacity

• Origin is undetermined in 40% of cases according to conventional etiological criteria

Sacco R.L.,et al, Infarcts of undetermined cause: the

NINCDS Stroke Data Bank. Ann. Neurol. 1989:25:382-390

Cryptogenic Stroke

• Stroke of unknown etiology

• Suspicion of paradoxical brain emboli arising from the venous circulation

• Emboli from the venous system can pass to the arterial circulation through

a PFO (Patent foramen ovale)

Paradoxical Brain Emboli (PBE)

• Emboli whose source is not from an identifiable source in the arterial system

• Also referred to as venous-to-arterial emboli

Positive TCD Bubble Test“Shower” Type HITS with Valsalva Maneuver

R MCA

L MCA

TRANSCRANIAL DOPPLER

Cerebral Circulatory Arrest

TCD - BRAIN DEATH

• Brain death is a clinical diagnosis

• TCD is a confirmatory test

• TCD can detect cerebral circulatory arrest

Transcranial Doppler

• Can aid in timing of other necessary tests

• Helpful in following potential organ donors

• Useful when patients are being treated with barbiturates which affect EEG

CEREBRAL CIRCULATORY ARRESTTCD Evaluation

• Bilateral study including posterior circulation

• Oscillating flow pattern persists over time (20 – 30 minutes minimum)

CEREBRAL CIRCULATORY ARREST