Transcranial Doppler TCD

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Transcranial Doppler (TCD)
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TCD What is it?

• The noninvasive assessment of the intracranial
  cerebral vasculature
• Distal Internal Carotid Artery
• Middle Cerebral Artery
• Anterior Cerebral Artery
• Posterior Cerebral Artery
• Vertebral Artery
• Basilar Artery
• Posterior Anterior Communicating Arteries

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Techniques

• TCD
• Transcranial Doppler
• A blind free hand, non-imaging technique
• TCI or TCCS
• Transcranial Imaging
• Transcranial Color-Coded Duplex Sonography

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General Prerequisites

• Status of the extracranial arteries has to be
  known
• The patient needs to rest comfortably to avoid
  major fluctuations in pCO2 and movement artifacts

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General Considerations

• Accessibility of the ultrasonic windows within
  the skull that can be penetrated with the
  ultrasonic beam are often limited
• Arteries at the base of the skull vary greatly in
  respect to size, course, development site of
  access
• The power measured behind the skull is rarely
  gt35 of the transmitted power, i.e., the bone of
  the skull absorbs the major portion of the power

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TCD TCCS Devices

• To achieve acceptable signal-to-noise ratio
  systems utilize Dopplers with
• Lower bandwidth
• Larger less-defined sample volume
• TCD systems
• 2 MHz pulsed-wave Doppler
• TCCS systems
• 1.8 3.6 MHz phased array sector transducer

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Devices - continued

• Instrument requirements
• Transmitting powers between 10 and 100 mW/cm2
• Adjustable Doppler gate width
• PRF up to 20 kHz
• Focusing of the US beam at a depth of 40-60 mm
• Online display of
• Time-averaged velocity (TAMV)
• Peak systolic velocity (PSV)
• Equipment for continuous monitoring

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Ultrasonic Windows

• Four main windows
• Transtemporal
• Transorbital
• Suboccipital
• Transforamenal
• Submandibular

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The Vessels
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Windows

• Transtemporal
• 3 positions
• Assess the
• MCA
• M1 M2 segments
• ACA
• A1 segment
• Carotid Siphon
• C1 segment
• AComA
• PCA
• P1 P2 segments
• Basilar artery
• Top
• PComA

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Transtemporal Window
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Transorbital Window

• Reduce the system power
• Generally to 50
• Components of the anterior cerebral circulation
• Ophthalmic artery
• 45-50 mm
• Flow is towards the signal
• Carotid siphon
• C3 segment 60-65 mm
• Flow is towards the signal
• C2 segment 70-75 mm
• Flow is away from the signal
• C4 segment 65-80 mm
• Flow is towards the signal

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Transorbital Window
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Suboccipital Window (Transforamenal)

• Utilized for the evaluation of the vertebral and
  basilar arteries throughout their lengths
• Probe placement is midline between the foramen
  magnum and the spinous process of the first rib
• The Doppler beam is aimed at the bridge of the
  nose
• Sample volume depth
• Vertebral arteries 40-95 mm
• Aim right and left for the vertebral arteries
• Flow is away from the signal
• Basilar artery 70-115 mm
• Flow is away from the signal

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Suboccipital Window (Transforamenal)
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Submandibular Window

• Distal segments of the extradural internal
  carotid artery (C5 C6 segments)
• Useful for the detection of
• ICA dissection
• Chronic ICA occlusion
• Velocities for calculating a Lindegaard ratio

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Submandibular Window
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Diagnostic Approach Basic TCD

• Start with transtemporal window
• Identify the middle cerebral artery (MCA)
• Locate at a depth of 45-50 mm trace laterally
  to 35 mm medially to 65-70 mm at the MCA/ACA
  bifurcation
• At the MCA/ACA bifurcation a slight tilt
  anteriorly caudally will generally yield the
  terminal portion of the ICA (C1 segment)
• Trace to the A1 segment of the ACA
• Angle the beam posteriorly to evaluate the P1
  segment of the PCA trace to the basilar artery
  then into the contralateral PCAs P1 segment

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Criteria for Vessel Identification

• Depth in millimeters from the probe face
• Direction toward or away from the transducer
  signal
• Velocity mean flow velocity in the vessel being
  interrogated
• Probe position temporal, suboccipital, etc

• Direction angling anterior, posterior, cephalad,
  etc.
• Spatial Relationship location of the current
  signal in relationship to the previous signals
  obtained
• Traceability of the vessel(s)

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Diagnostic Approach Basic TCD

• Additional information may be obtained and
  evaluated after completion of the evaluation from
  the transtemporal window
• General rule of thumb for velocities
• MCA gt ACA gt PCA VA
• Know Table 12-1, pgs. 232 233

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Transtemporal Approach

• Vessel Depth-mm Velocity-cm/s
  Direction
• MCA 30-60 (50) 43-67 (55)
• MCA/ACA 55-65 /-
• ACA(A1) 60-75 (65) 39-61 (50)
  -
• PCA(P1) 60-75 (70) 29-49 (39)
  
• TICA 55-65 30-48 (39)
  

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Suboccipital (Transforamenal) Approach

• Vessel Depth-mm Velocity-cm/s
  Direction
• VA 60-90 (70) 28-48 (38) -
• BA 80-120 (95) 31-51 (41) -

Submandibular Approach
Vessel Depth-mm Velocity-cm/s
Direction ICA 35-80 (50) 31-39 (30)
-
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Transorbital Approach

• Vessel Depth-mm Velocity-cm/s
  Direction
• OA 40-60 (45) 16-26 (21)
• Siphon 55-80
• Supraclinoid 30-52 (41) -
• Genu /-
• Parasellar 33-61 (47)

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IndicationsRefer to Table 12-8, pg. 246

• Detect intracranial stenosis occlusions in the
  major basal arteries
• Evaluation of intracranial hemodynamic effects in
  the presence of extracranial occlusive disease
• Monitoring of intracranial vessel recanalization
  in acute stroke
• Monitoring of intracranial cerebral hemodynamics
• After subarachnoid hemorrhage
• In patients with increased ICP
• During/after extracranial revascularization
  procedures
• Carotid endarterectomy
• Balloon angioplasty
• Before/during neuroradiologic interventions
• Balloon occlusion
• Coiling of AVM
• During open heart surgery
• Evolution of brain death
• Detection quantification of right-to-left shunt
• Patent foramen ovale

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Indications

• Functional tests
• Stimulation of intracranial arterioles with CO2
  or other vasoactive drugs
• Language lateralization before neurosurgery
• External stimulation of visual cortex
• Compression tests to assess collateralizing
  capability
• NEW
• Brain perfusion imaging
• Ultrasound-assisted thrombolysis

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Diagnostic Criteria Stenosis

• Increased flow velocity generally focal
• Disturbed flow
• Turbulence spectral broadening
• Covibration phenomena
• Vibration of the vessel wall surrounding soft
  tissue
• Drop in post-stenotic velocity
• Changes in post-stenotic waveform morphology
• Prolonged systolic upstroke
• Decreased pulsatility

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Diagnostic Criteria StenosisZwiebel, 5th Ed.,
pg 236

• Mean velocity 100 cm/s
• Comparison of PSV with contralateral vessel PSV
• ?PSV gt30 - suspicious
• ?PSV gt50 - definite
• Sensitivity - 100
• Specificity - 97.9
• PPV - 88.8
• NPV - 94.9

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MCA Stenosis
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Diagnostic Criteria Occlusion

• Absence of arterial signal at expected depth
• Presence of signals in vessels which communicate
  with the occluded artery
• Altered flow in communicating vessels, indicating
  collateralization

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Pitfalls Diagnostic Accuracy

• Lack of flow signal due to an inadequate temporal
  window
• Misinterpretation of hyperdynamic collateral
  channels or AVM feeders as stenosis
• Displacement of arteries because of a
  space-occupying lesion
• Misinterpretation of physiologic variables in the
  circle of Willis
• Misdiagnosis of vasospasm as stenosis
• Misinterpretation of reactive hyperemia following
  spontaneous recanalization as stenosis

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Pitfalls Diagnostic AccuracyVertebral-Basilar
System

• Normal flow and size of vessels are highly
  variable
• Location and course of the arteries are
  unpredictable
• Difficulty in reliably identifying the junction
  of the vertebral arteries
• Absence of the vertebral artery flow signal on
  one side may not represent disease
• Lack of flow in one vertebral artery distally,
  above the origin of the PICA due to vertebral
  artery hypoplasia
• Occlusion of one vertebral artery or a top of
  the basilar occlusion does not necessarily lead
  to relevant flow abnormalities