Transcranial Doppler Imaging (TCDI)
TCDI was performed through the temporal window using the GE, Vivid 3,
USA ultrasound machine with a 1-3 MHz phased-array transducer, equipped
with both color and power Doppler capabilities. With the patient lying
in a supine position on the ultrasound table at room temperature (22 ±
2°C), terminal internal carotid artery (t-ICA-C5),
middle cerebral artery (MCA-1), anterior cerebral artery (ACA-1),
posterior cerebral artery (PCA-1), and basilar artery were respectively
insonated. No angle correction was used. An envelope outlining the peak
velocity throughout 3 to 5 cardiac cycles was taken. The envelope of the
waveform was traced electronically or manually, depending on the quality
of the waveform.
The highest cerebral blood flow velocities with an insonation sample
gate diameter of 4-6 mm was recorded. Flow direction, PSV (peak systolic
velocity), EDV (end diastolic velocity), TAMMV (time-averaged mean
maximum velocity), RI (resistivity index), and PI (pulsatility index)
were stored on the ultrasound machine memory and recorded on the scan
template for later analysis. RI was calculated automatically by the
PSV-EDV/PSV formula and PI was calculated from the Doppler trace by
PSV-EDV/MV(mean velocity) formula. The TCDI was performed by one
experienced vascular sonographer (AA), who was blinded to the previous
data at the time of follow-up.