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.