Abstract： Objective To explore the optimal protocol of lower-extremity contrast-enhanced MRA (CE-MRA) in the evaluation of diabetic foot.Methods Twenty eight healthy volunteers were scanned by CE-MRA in crus twice with parellel imaging factor (PIF) of 3 or 4.The signal-to-noise ratio (SNR),contrast-to-noise ratio (CNR) and image quality of popliteal artery,posterior tibial artery,anterior tibial artery and peroneal artery were compared.Twenty patients with diabetic foot underwent CE-MRA by both of protocol 1 and 2 in leg,crus and foot.Protocol 1 was the traditional Care-bolus protocol and protocol 2 was the optimized K-space center filling delay-time protocol.The difference of two protocols in venous aliasing and in display of femoral artery,popliteal artery,posterior tibial artery,anterior tibial artery,peroneal artery,dorsalis pedis artery,medial plantar artery and lateral plantar artery were compared.The SNR,CNR of two different PIF sequences were compared by paired t test,and the display of artery of crus was compared by Wilcoxon.The display of vessels and venous aliasing of 2 protocols of diabetic foot patients were compared by Wilcoxon.Results In the images of healthy volunteers with PIF of 3,the SNR were 267±84,174±51,147±42;and the CNR were 232 ±83,139±51,108±39 at popliteal artery,posterior tibial artery and peroneal artery.However,in the images with PIF of 4,the SNR were 239±73,157±53,132±35;and CNR were 206±71,124±50,103±33,respectively.Both the SNR and CNR were higher in the former than in the latter(t values were 2.31 to 4.11,P＜0.05).There was no significant difference in the vessel display between the different PIF volunteers (P＞0.05).In the protocol 1 of patients with diabetic foot,the display of popliteal artery,posterior tibial artery,anterior tibial artery,peroneal artery,dorsalis pedis artery,medial plantar artery and lateral plantar artery,the venous aliasing in crus and foot were 3.40±0.82,2.70±0.80,2.50±1.00,2.20±0.77,2.30±0.92,2.15± 1.04,1.45±0.60,2.20± 1.01,2.20± 1.06.And in the protocol 2,they were 3.85±0.37,3.55± 0.69,3.30±0.92,2.90±0.79,3.30±0.92,3.25±0.79,1.95±1.10,3.70±0.47,3.65±0.49,respectively(P＜0.05).All of these parameters of protocol 2 were superior to protocol 1.Conclusion Using a higher PIF properly,setting the personalized K-space center filling delay-time can contribute to improving the image quality of whole lower-extremity MRA in patients with diabetic foot.