Functional Imaging of Cerebral Blood Flow Using Transcranial Doppler Ultrasound

To measure cerebral blood flow velocity, or CBFV, begin with a human participant with a secured Doppler ultrasound transducer.

Pre-applied ultrasound gel on the transducer facilitates efficient wave transmission.

The transducer is positioned over the middle cerebral artery, or MCA, which delivers oxygenated blood to the brain.

The transducer emits sound waves reflected by moving blood cells in the MCA. The motion of these cells alters the reflected wave frequency, known as a Doppler shift.

Record these frequencies, generating a CBFV baseline spectrum.

Now, instruct the participant to hold his breath while the recording continues.

During breath-holding, blood CO₂ levels rise, causing MCA dilation and increasing blood flow with a higher Doppler shift. This generates a broader spectral profile, confirming elevated CBFV.

After the breath-hold ends, blood CO₂ levels and MCA diameter normalize, and CBFV returns to baseline.

The Doppler ultrasound measures real-time blood velocity, acting as a functional imaging tool.