Purpose: Wall shear stress (WSS), a type of friction exerted on the artery wall by flowing blood,is considered a crucial factor in atherosclerotic plaque development. Currently, achieving a reliable WSS mapping of an artery noninvasively by using existing imaging modalities is still challenging. In this study, a WSS mapping based on vector Doppler flow velocity estimation was proposed to measure the dynamic WSS on the human femoral artery. Methods: Because ultrafast ultrasound imaging was used here, flow-enhanced imaging was also performed to observe the moving blood flow condition. The performance of WSS mapping was verified using both straight (8 mm in diameter) and stenosis (70% of stenosis) phantoms under a pulsatile flow condition. A human study was conducted from five healthy volunteers. Results: Experimental results demonstrated that the WSS estimation was close to the standard value that was obtained from maximum velocity estimation in straight phantom experiments. In a stenosis phantom experiment, a low WSS region was observed at a site downstream of an obstruction, which is a high-risk area for plaque formation. Dynamic WSS mapping was accomplished in measurement in the femoral artery bifurcation. In measurements, the time-averaged WSS of the common femoral artery, superficial femoral artery, and deep femoral artery was 0.52± 0.19,0.44 ± 0.21,and 0.29 ± 0.16 Pa,respectively,for the anterior wall and 0.29 ± 0.11, 0.54 ± 0.24, and 0.23 ± 0.10 Pa, respectively, for the posterior wall. Conclusions: All results indicated that WSS mapping has the potential to be a useful tool for vessel duplex scanning in the future. K E Y W O R D Speripheral artery disease,ultrasound blood flow,ultrafast ultrasound imaging,vector doppler velocity, wall shear stress mapping INTRODUCTIONPeripheral artery disease (PAD) refers to a major systemic vascular disease, involving many symptoms that affect noncardiac and nonintracranial arteries. 1 The common causes of PAD are atherosclerosis and inflammatory disorders of the arterial wall, which lead to changes in the structure and function of arteries, especially in the lower limbs. 2 In the end stage of PAD, symptoms progress to ischemic ulcers and gangrene, and amputation is eventually required. 3,4 The femoral artery is one of the most common sites of lower limb atherosclerosis in PAD. 5,6 Several studies have indicated that atherosclerosis not only causes PAD and femoral artery stenosis but is also related to other arterial-affecting diseases, such as cardiovascular disease, 7,8 chronic kidney disease, 9,10 and femoral artery aneurysm. 11 Many studies have suggested that shear stress is a key factor in the development of vascular disease and atherosclerosis. 12 Shear stress is described as friction induced by the different movements of two flowing layers in a fluid. In hemodynamics, wall shear stress (WSS) is expressed as the tangential force exerted on the