Does long-term continuous transcranial Doppler monitoring require a pause for safer use?

Area of Science:

• Neuroscience
• Medical Imaging
• Biophysics

Background:

• Transcranial Doppler sonography (TCD) is a common tool for monitoring cerebral blood flow.
• Potential thermal effects of prolonged TCD insonation on brain tissue have been under-investigated.
• Ultrasound absorption by the skull and brain tissue can lead to temperature increases.

Purpose of the Study:

• To quantify the actual temperature rise in brain tissue during long-term TCD insonation.
• To determine if pauses are necessary for safe, continuous TCD monitoring.
• To establish safety guidelines for extended TCD applications.

Main Methods:

• In vivo animal study using 15 New Zealand White rabbits.
• Thermocouples inserted at the skull-brain interface (SBI) to measure temperature changes.
• TCD applied at maximum output (0.2 W, 2 MHz) for 90 minutes, with a control group.

Main Results:

• Skull-brain interface temperature (SBIT) in the TCD group increased by 3.47°C within 25 minutes, reaching a plateau.
• The estimated maximum safe duration for continuous TCD application was determined to be 33 minutes.
• Significant temperature elevation indicates a thermal risk associated with prolonged TCD use.

Conclusions:

• Cerebral blood flow per brain weight, a key factor in heat dissipation, shows similarities between rabbits and humans.
• Findings suggest that clinical long-term TCD monitoring should incorporate a pause after approximately 30 minutes of insonation.
• Implementing intermittent TCD application is recommended to mitigate the risk of thermal brain damage.