Intracranial temperature elevation from diagnostic ultrasound

Area of Science:

• Medical Physics
• Neuroscience
• Biophysics

Background:

• Central nervous system tissues are vulnerable to physical agents like heat and ultrasound.
• Pulsed spectral Doppler ultrasound can cause significant tissue heating due to high intensities and stationary beams.
• This poses risks to sensitive neural tissues, particularly during fetal cerebral vessel examinations.

Purpose of the Study:

• To assess the risk/benefit ratio of ultrasound use in fetal neurosonography.
• To inform ultrasound users about potential thermally mediated bioeffects.
• To provide conclusions from scientific literature on ultrasound-induced heating in the fetal brain.

Main Methods:

• Literature review of published scientific studies on ultrasound bioeffects.
• Analysis of factors influencing ultrasound-induced intracranial heating.
• Evaluation of the thermal index (TI) as an indicator of heating.

Main Results:

• Ultrasound-induced intracranial heating increases with gestational age and fetal bone development.
• Pulsed spectral Doppler ultrasound can cause biologically significant fetal brain heating, particularly rapid near bone.
• Blood flow has a minimal cooling effect on brain tissue heating with clinical beams.
• The threshold for irreversible damage is a 4°C increase for 5 min; a 1.5°C increase in 120s shows no electrophysiologic response.
• The thermal index (TI) may underestimate intracranial temperature increases under certain conditions.

Conclusions:

• Ultrasound users must carefully assess risks, considering gestational age, bone proximity, and TI limitations.
• Biologically significant heating can occur in the fetal brain, necessitating cautious application of spectral Doppler.
• Further research may be needed to refine safety standards and thermal index calculations for fetal neurosonography.