TCD examination technique

A single-gate spectral transcranial Doppler (TCD) was introduced by Rune Aaslid in 1982 to non-invasively assess cerebral hemodynamics [1], The four 'windows' for insonation (Figure 2.1) are temporal, orbital, suboccipital and submandibular [2], The transtemporal approach allows velocity measurements in the middle (MCA), anterior (ACA), posterior (PCA) and communicating arteries [1-5]. The transorbital approach is used to insonate the ophthalmic artery (OA) and internal carotid artery (ICA) siphon. The suboccipital approach allows insonation of the terminal vertebral (VA) and basilar (BA) arteries through the foramen magnum. The submandibular approach is used to obtain ICA velocities as it enters the skull.

For a typical diagnostic TCD examination, use a fast 3-5-s sweep speed that allows details of the waveform and spectrum to be seen (Figure 2.2). To shorten the time necessary to find the window and to identify different arterial segments with a single-gate spectral TCD, the examination should begin with the maximum power and gate settings (i.e. power 100%, gate 10-15 mm) for the transtemporal and suboccipital approaches. Although this recommendation seemingly violates the rule of using ultrasound power 'as low as reasonably achievable' (ALARA), it allows the time

Image Not Available suboccipital and submandibular. (Reproduced with permission from Alexandrov AV. Vascular Ultrasound Today 1998; 3:141-60.)

Figure2.1 Windowsfor intracranial vessel location. There are four windows of insonation: temporal, orbital.

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Submandibular Window Tcd Waveform

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Figure 2.2 Pulsed-wave spectral waveform display. Identify flow direction, velocity scale, depth of insonation as well as sweep speed and power settings. Small arrows indicate the cardiac cycle measured to calculate the peak, mean and end-diastolic (ED) flow velocities. PI, pulsatility index (Gosling-King); Rl, resistance index (Pourcellot).

necessary to find windows and to complete the examination to be shortened, thus reducing the overall patient exposure to ultrasound energy. The goals of a 'non-image-guided' single-gate spectral TCD examination are:

1 to follow the course of each major branch of the circle of Willis with spectral display;

2 to identify, optimize and store the highest velocity signals;

3 to obtain TCD spectra at at least two key points per artery (Figure 2.3); and

4 to identify, optimize and store any abnormal or unusual waveforms.

Transtemporal insonation steps (Figure 2.4) Step 1 Set the depth at 50-56 mm (midpoint of the Ml MCA segment was established at approximately 50 mm depth [6]). Place the probe at position 1 (Figure 2.1) above the zygomatic arch and aim it slightly upwards and anterior to the contralateral ear/window. Find any flow signal (window), and avoid too anterior and too posterior angulation. Find a flow signal directed towards the probe which resembles MCA flow. A normal MCA flow is a low-resistance waveform (Figure 2.2) similar to the ICA flow pattern. By decreasing the depth, follow the signal to the distal Ml key-point of insonation without losing the signal. Often, a slight adjustment of the probe angulation is needed. Store distal Ml MCA signal at 45 mm. If bidirectional signals are found, store the highest-velocity signal in each direction (distal Ml-proximal M2 branches).

Figure 2.2 Pulsed-wave spectral waveform display. Identify flow direction, velocity scale, depth of insonation as well as sweep speed and power settings. Small arrows indicate the cardiac cycle measured to calculate the peak, mean and end-diastolic (ED) flow velocities. PI, pulsatility index (Gosling-King); Rl, resistance index (Pourcellot).

OA t

Basilar Artery Doppler
Figure 2.3 Key insonation segments and depths for transcranial Doppler examination.

Step 2 Follow the signals until they disappear at shallow 30-45-mm depths. Store any abnormal signal. Return to the distal Ml MCA signal.

Step3 Follow the Ml MCA stem to its origin at 60-70-mm depths dependent on the size of adult patient skull. Pay attention to the sound and velocity changes since insonation of the terminal ICA is also possible at these depths.

Transcranial Mca

Figure 2.4 Steps for Doppler examination through the transtemporal window. Steps are represented by numbers 1 through 7. Abbreviations: dA1, distal A1 segment of the anterior cerebral artery (flow is directed away from transducer, or displayed below the baseline); dMI, distal Ml middle cerebral artery (towards transducer, above the baseline); pM2, proximal M2 (bidirectional, above and below the baseline); pM1, proximal M1 MCA; tICA, terminal internal carotid artery (both towards the transducer, above the baseline); pA1, proximal A1 anterior cerebral artery (away from transducer, below the baseline); P1, first segment of the posterior cerebral artery (towards transducer, above the baseline); P2, second segment of the posterior cerebral artery (away from transducer, below the baseline).

Figure 2.4 Steps for Doppler examination through the transtemporal window. Steps are represented by numbers 1 through 7. Abbreviations: dA1, distal A1 segment of the anterior cerebral artery (flow is directed away from transducer, or displayed below the baseline); dMI, distal Ml middle cerebral artery (towards transducer, above the baseline); pM2, proximal M2 (bidirectional, above and below the baseline); pM1, proximal M1 MCA; tICA, terminal internal carotid artery (both towards the transducer, above the baseline); pA1, proximal A1 anterior cerebral artery (away from transducer, below the baseline); P1, first segment of the posterior cerebral artery (towards transducer, above the baseline); P2, second segment of the posterior cerebral artery (away from transducer, below the baseline).

Find the ICA bifurcation at approximately 65 mm (range 58-70 mm in adults) and obtain both proximal Ml MCA and proximal A1 ACA signals.

Store a bidirectional signal of the bifurcation (Ml/Al).

Step 4 Follow the A1 ACA signal to 70-75-mm depths. Store the distal A1 ACA signal at 70 mm.

Step 5 Follow the distal A1 ACA signal to the midline depth range (75-80 mm). The A1 ACA signal may disappear, or a bidirectional signal may appear at the midline depth. Store any abnormal signals. Return to bifurcation at 65 mm. Step 6 Find the terminal ICA signal just inferior and sometimes slightly posterior to the bifurcation at 60-65 mm. If the probe is angled inferior and anterior to the ICA bifurcation at 60-70-mm depths, the distal part of the supraclinoid siphon can be found through the temporal window. Store any abnormal signal. Return to the bifurcation at 65 mm. Step 7 Set the depth at 63 mm and slowly turn the transducer posteriorly by 10-30°. Usually there is a flow gap between the ICA bifurcation and the PCA signals. Find PCA signals directed towards (PI) and away (P2) from the probe at a depth range of 55-75 mm.

Store the PCA signals with the highest velocity.

Transorbital insonation steps (Figure 2.5) Step 1 Decrease power to minimum (17 mW) or 10%. Set the depth at 50-52 mm, place the transducer over eyelid and angle it slightly medially. Determine flow pulsatility and direction in the distal ophthalmic artery (OA). Store the distal OA signals at 52 mm. Step2 Increase the depth to 60-64 mm and find the ICA siphon flow signals. The siphon signals are usually located medially in the orbital window.

Store bidirectional signals at 62 mm (C3 or the siphon genu).

If only unidirectional signals are obtainable,

Upper limb of the Siphon

Figure 2.5 Steps 1-2 of Doppler examination through the orbital window. OA, ophthalmic artery; C2, C3, C4, sequential segments of the internal carotid artery.

Upper limb of the Siphon

Figure 2.5 Steps 1-2 of Doppler examination through the orbital window. OA, ophthalmic artery; C2, C3, C4, sequential segments of the internal carotid artery.

Lower Limb Examination Power Grade
Lower limb of the Siphon

Bridge or the nose

Bridge or the nose

Suboccipital Probe Position

Transducer positions Figure 2.6 Steps 1-6 of Doppler examination through the foraminal window. BA, basilar artery; VA, vertebral artery.

Transducer positions Figure 2.6 Steps 1-6 of Doppler examination through the foraminal window. BA, basilar artery; VA, vertebral artery.

store signals directed towards (C4 or the lower limb of the siphon) and away (C2 or the upper limb) from the probe.

Suboccipital insonation steps (Figure 2.6) Step 1 Set the system back to full power.

Place the transducer at midline an inch below the edge of the skull and aim it at the bridge of the nose.

Set the depth at 75 mm (presumed location of both terminal VAs and proximal BA). Identify a flow signal directed away from the probe, i.e. find the window. This signal can be arbitrarily assigned to the terminal vertebral arteries (slightly lateral probe angulation) or the proximal basilar artery (medial and slightly upward angulation). Increasing the depth, follow the flow directed away from the probe. This depth increase presumably focuses the beam on the proximal BA in most adults.

Store the proximal BA signal arbitrarily assigned to a depth of 80 mm. Step 2 Follow the basilar artery to 90 mm (mid-BA segment).

Bidirectional signals may be found at various depths with a low-resistance flow in the cerebellar arteries directed towards the probe.

Store any abnormal signals.

Step 3 Follow the distal BA segment to a depth of 100 + mm until it disappears or is replaced by the anterior circulation signals. Store the highest-velocity signal obtained at the most distal depth of the basilar artery insonation.

Step 4 Follow the stem of the basilar artery backwards while decreasing the depth of insonation to 80 mm and confirm previous findings.

Step 5 Place the probe about an inch laterally to the midline and aim towards the bridge of the nose or slightly towards the contralateral eye. Find the vertebral artery (VA) flow signal directed away from the probe. Follow the course of the terminal VA segment intracranially from 80 mm to 40 mm. Store the VA signals at 60 mm or at the depth of the highest-velocity signal.

Step 6 Place the probe on the contralateral side an inch off the midline position. Repeat the VA examination steps for the contralateral vessel from 80 to 40 mm. Store the VA signals at 60 mm or at the depth of the highest-velocity signal.

Submandibular insonation steps (Figure 2.7)

Step 1 Place the probe laterally under the jaw anterior and medial to the sternocleidomastoid

Transcranial Doppler Windows

Submandibular probe position (lateral view)

Figure 2.7 Steps 1-2 of Doppler examination through the submandibular window.

muscle. Aim the transducer upwards and slightly medially.

Set the depth at 50 mm.

Find a low-resistance flow directed away from the probe.

Step 2 Increase the depth from 50 to 60 mm and decrease to 40 mm.

Store the distal ICA signal at the depth that shows the highest-velocity signal. At a shallow depth, perform the temporal artery tap to differentiate from the external carotid artery flow signals.

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Responses

  • DON GLADNEY
    HOW TO AIM YOUR PROBE TO OBTAIN THE MCA?
    1 year ago
  • ADALGISO
    Where are transtemporal window?
    5 months ago
  • futsum
    Where do u get the terminal ICA on the TCD exam?
    3 months ago
  • Afwerki
    How to get siphon on transcranial dopplers?
    21 days ago
  • PRIMA
    How to insonate aca on tcd?
    6 days ago

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