Figure 1: (a) Ultrasound measurement of the radial artery. 13 MHz linear transducer is fixed along radial artery with a special probe holder (MP-PH0001, Aloka Co., Ltd., Tokyo, Japan). (b) Display of CDI. Left: the vessel image and the position of the artery tracking gate. Right: changes in vessel diameter, Doppler flow, and flow velocity as determined by an automated edge-detection device and computer analysis software (e-Tracking system; Aloka Co., Ltd., Tokyo, Japan).