Transcranial Doppler (TCD) ultrasound examination of blood flow
velocity through the brain can be used to detect cerebral arterial
vasospasm, steno-occlusive disease of the cerebral arteries, or the
absence of blood flow (in the determination of brain death).
- ▪ Doppler ultrasound: A technique based on the principles
of sound travel and reflectance in tissues—transmitted
sound waves change their frequency when they come into contact with
moving blood cells and the frequency change is known as the Doppler
- ▪ Blood flow velocity: Measurement of the speed (Figure 21-1)
and direction of blood flow (as distinct from total blood flow).
- ▪ Continuous wave Doppler: Continuous measurement of sound
pitch changes relating to blood flow velocity through vessels, around
obstructions, or through narrowings.
- ▪ Duplex Doppler: Provides a picture of the vessels and information
about the speed and direction of blood flow in the vessels.
- ▪ Color flow Doppler: Velocities are mapped into colors and
overlaid on the image of the blood vessels.
- ▪ Acoustic window: A portion of the skull that permits transmission
and reception of ultrasound through the skull—the temporal,
transorbital, suboccipital, and submandibular windows are typically
Color map of blood flow velocities in an artery of interest.
- ▪ The probe is applied lightly to the skin over the
acoustic window using ultrasound gel to improve contact and sound
wave transmission (Figure 21-2).
- ▪ Indications
- —Evaluation of intracranial vascular disease
- —Monitoring of vasospasm (increased blood flow velocity
through narrowed vessels)
- —Detection of cerebral emboli
- —Evaluation of vertebrobasilar vascular disease
- —Detection of arteriovenous malformations
Doppler probe applied to the skin over the temporal acoustic
Clinical Pearls and Pitfalls
- ▪ Normal cerebral
arterial velocities decrease with age, which is phenomenon related
to decreasing cardiac output.
- ▪ TCD temporal
bone windows are not as good in females as in males.
- ▪ Arterial
velocities increase in anemia, as viscosity decreases.
- ▪ Arterial
velocities are increased in fever.
Katz ML, Alexandrov AV. A Practical Guide to Transcranial Doppler
Examinations. Littleton, CO: Summer Publishing Company; 2003.