Transcranial Doppler: An Introduction for Primary Care Physicians

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Figure 1.
TCD probe positions over different acoustic windows of the skull.
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Figure 2.
TCD screen waveform with velocity scale on the left.

Table 1.

Accepted Guidelines for a Normal TCD Study

Artery	Window	Depth (mm)	Direction	Mean Flow Velocity
MCA	Temporal	30 to 60	Toward probe	55 ± 12 cm/s
ACA	Temporal	60 to 85	Away	50 ± 11 cm/s
PCA	Temporal	60 to 70	Bidirectional	40 ± 10 cm/s
TICA	Temporal	55 to 65	Toward	39 ± 09 cm/s
ICA (siphon)	Orbital	60 to 80	Bidirectional	45 ± 15 cm/s
OA	Orbital	40 to 60	Toward	20 ± 10 cm/s
VA	Occipital	60 to 80	Away	38 ± 10 cm/s
BA	Occipital	80 to 110	Away	41 ± 10 cm/s

TCD, transcranial Doppler; MCA, middle cerebral artery; ACA, anterior cerebral artery; PCA, posterior cerebral artery; TICA, terminal internal carotid artery; ICA, internal carotid artery; OA, ophthalmic artery; VR, vertebral artery; BA, basilar artery.

Table 2.

Effects of Different Physiological States on TCD Flow Velocity

Physiologic Factor	Effects
Increase age	Decrease FV
Increase CSF pressure	Decrease FV
Increase central venous pressure	Decrease FV
Increase PaCO₂	Increase FV due to vasodilatation
Increase cardiac output	Decrease FV to maintain normal CBF
Increased blood viscosity	Decrease FV
Anemia	Increase FV
Drugs with vasodilatation properties	Increase FV
Drugs with vasoconstriction properties	Decrease FV

TCD, transcranial Doppler; CSF, cerebrospinal fluid; FV, flow velocity; CBF, cerebral blood flow.