Real-time or near-real-time acquisition plays a key role in providing immediate image guidance for interventional magnetic resonance imaging (iMRI). However, the requirement of accurate needle tip localization has made several accelerating techniques, like Keyhole imaging or sliding window reconstruction, difficult to be applied to iMRI. The purpose of this work was to further explore the possible ways of applying view sharing techniques to iMRI. Inspired by Keyhole imaging, we present an easy-to-implement accelerating strategy called "Alternate update of shifted extended keyholes (AUSEK)". In this method, the keyhole views are not only extended but also shifted towards either high-frequency edge to form two divisions in k-space. The divisions which are mirrored to each other along the center are alternately updated following a reference scan. By using simulations and experiments, we demonstrate that AUSEK could effectively preserve the spatial resolution of the image, especially of the needle, at a temporal acceleration rate of about 2.5. AUSEK was implemented online in an open-configuration low-field MR imaging system.

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Objectives To evaluate the feasibility of foot arteries using flow-spoiled-fresh blood imaging (FS-FBI) and to investigate how the FS-FBI scanning parameters affect the flow sensitivity and impact the depiction of pedal arteries. Methods The study included 46 young healthy volunteers examined by FS-FBI using 1.5T MRI scanner. Additional FS-FBI examination with different flip angles (FA) of the radiofrequency refocusing pulse and echo time (TE) was performed on 36 volunteers. Two radiologists separately analyzed and graded the venous contamination, image quality, displaying rate, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) values of foot arteries. Multi-sample Friedman test and paired two-sided Student's t test were used for statistical analysis (P < 0.05).Results Average image quality and venous contamination score of all arteries was good. The demonstration rate of distal anterior and posterior tibial artery, and lateral plantar artery was 100%. Dorsalis pedis artery, first dorsal metatarsal artery, medial plantar artery, and plantar arch were demonstrated at a rate above 90%. The demonstration rate of medial tarsal artery was 73.9%, whereas arcuate artery was detected with a rate of only 5.4%. Significant differences in image quality, SNR, and CNR of distal arterial area were observed between different FA and TE. Conclusion Non-contrast-enhanced MR angiography of foot using FS-FBI enables clear separation of veins from arteries, and yields reliable depiction of the foot arterial tree in healthy volunteers. Distal arterial branches of foot can be better depicted by appropriate adjustment of the flow-sensitivity parameters.Keywords Non-contrast-enhanced magnetic resonance angiography · Flow spoiled-fresh blood imaging · Foot arteries · Flip angle of the refocusing pulse · Echo time * Dairong Cao Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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