Angle correction in transcranial Doppler sonography

Area of Science:

• Neurology
• Medical Imaging
• Ultrasound Technology

Background:

• Transcranial Doppler (TCD) sonography traditionally assumes a 0-30 degree angle of insonation for flow velocity estimation.
• This assumption, based on limited anatomical data, may introduce errors due to the Doppler formula's cosine function.
• Advancements in transcranial color duplex sonography (TCD-CS) enable direct assessment of insonation angles and their impact on velocity measurements.

Purpose of the Study:

• To evaluate the accuracy of the assumed 0-30 degree insonation angle in TCD sonography.
• To determine the effect of actual insonation angles on cerebral artery flow velocity measurements.
• To assess the discrepancies between angle-corrected and uncorrected flow velocities in healthy volunteers.

Main Methods:

• Fifteen healthy volunteers underwent bilateral TCD-CS using a unilateral transtemporal approach.
• Velocity measurements were taken from the middle, anterior, and posterior cerebral arteries.
• Flow velocities were recorded with and without angle correction, and compared with conventional Doppler findings.

Main Results:

• The average insonation angle was approximately 30 degrees, but individual angles showed wide variability (0-70 degrees).
• Angle-corrected velocities exceeded uncorrected velocities by over 25% in approximately 25% of the studied vessels.
• In 10.8% of vessels, angle-corrected velocities were more than 50% higher than uncorrected values.

Conclusions:

• The actual angle of insonation in TCD sonography is unpredictable and frequently exceeds the traditionally assumed range.
• Significant underestimation of flow velocities can occur when relying on uncorrected or assumed angles.
• Further research is needed to understand the clinical implications of these angle-dependent velocity variations.