Fresh Blood Imaging using variable TR and variable refocusing flip angle for non-contrast peripheral MR angiography at 3T: a 7-Minute iliac to calf station run-offs scan

Background Non-contrast Fresh Blood Imaging (FBI) scan time can be greatly reduced using variable TR for imaging the peripheral artery without contrast infusion, in which each slice encoding (SE) and the followed echo train are played in a variable TR (vTR) (TR=n*RR) pattern. In vTR FBI, the lower limit of TR depends on the length and timing of data acquisition, and it is also limited by SAR, which is mostly affected by refocusing flip angle, echo train length, and echo spacing. Often in the case of short TR FSE acquisition, SAR can be an issue for the patient with fast heart rate. To reduce SAR so that the shortest TR can be enabled for the slice encodings at the kz edge, variable refocusing flip angle (vFA) is proposed in this work. The optimized vTR FBI sequence with vFA was applied on volunteers to achieve a 7-minutes 3 station run-off scan.