Lecture 6: Transcranial Doppler (TCD) & Transcranial Duplex Imaging (TCDI)

TCD

non-imaging ultrasound technique that directly insonates cerebral vessels to measure blood flow velocity

TCDI

Combines ultrasound imaging with Doppler to visualize blood vessels and measure velocities

TCD Equipment

1-2 MHz pulsed wave transducer, spectral analysis, optional M-mode

TCDI Equipment

Duplex ultrasound with a broadband phased-array transducer (1-5 MHz range)

transtemporal

Accesses MCA, ACA, PCA, ICA

Transorbital

Evaluates ophthalmic artery and carotid siphon

Transoccipital

Accesses vertebral and basilar arteries

Submandibular

Evaluates ICA

Stenosis

velocity increase, turbulence, velocity drop

Occlusion

no flow detected

Vasospasm

increased velocity over time

Emboli Detection

HITS on M-mode

Limitations

• Inadequate temporal windows** may prevent successful insonation.

• Recent eye surgery contraindicates the transorbital approach.

• Vessel misidentification (less common in TCDI).

• Patient motion can disrupt the examination.

MCA

transtemporal - towards

ACA

transtemporal - away

t-ICA

transtemporal - bidirectional

PCA

transtemporal

• P1 towards

• P2 away

ophthalmic

transorbital - towards

ICA siphon

transorbital - bidirectional

vertebral

suboccipital - away

basilar

suboccipital - away

ICA

Submandibular - away

primary diagnostic feature

mean velocity

Disturbed or turbulent flow

This is represented in the spectral waveform as high- amplitude, low-velocity signals

Systolic upstroke

This is the initial slope of the peak velocity envelope during the acceleration phase of systole