Hemodynamic parameters will include PSV, EDV, RI, and PI from bilateral ACAs and MCAs as obtained by the pulse wave color Doppler. The ACA will be approached through the anterior fontanel on the sagittal plane and its blood flow velocity will be determined at the proximal part. The MCA will be approached under the transverse plane by placing the transducer on the temporal bone below the zygomatic arch. The flow velocity measurements will be obtained by Fourier transform analysis from homogeneous blood flow wave patterns over at least 3 cardiac cycles with good clear signals. Those signals that show complete and similar waveforms in the adjacent cycles and have high magnitudes with visible margin recognized from the background noise will be selected. The RI and PI are the ratio between the different velocities with the formulas: RI = (PSV-EDV) / PSV, PI = (PSV-EDV) / mean velocity. The whole ultrasound examination will take about 10 minutes.