In patients with peripheral arterial disease (PAD), the presence of arterial wall calcifications substantially impacts patient management, e.g. increasing the difficulty of arterial access for percutaneous procedures such as TAVR and decreasing success rates for balloon angioplasty. Unlike CT angiography, MR angiography is insensitive to vascular calcifications, so that critical diagnostic information is lost. PETRA, an ultra-short echo time 3D MRI technique, has shown promise for detecting vascular calcifications [1]. However, it suffers from sensitivity to respiratory motion introducing blurring. Furthermore, it is not known how well lesion volumes determined by MRI correlate with the standard of reference, CT angiography. The primary aims of this study were: (1) to optimize a stack-of-stars 3D pulse sequence to detect peripheral vascular calcifications, and (2) to determine the accuracy for measuring calcification volumes using CT angiography as the standard of reference. In addition, we tested the feasibility of fusing these images with non-enhanced QISS MR angiography in order to allow direct correlation with vascular landmarks.A prototype stack-of-stars 3D FLASH pulse sequence was applied in three patients with PAD who had recently undergone CT angiography. MR imaging was performed in a 3T scanner (MAGNETOM Verio, Siemens Healthcare, Erlangen, Germany). Images were acquired in an oblique coronal plane parallel to the vessels. Chemical shift artifact at fat/water interfaces was minimized by the use of a radial k-space trajectory for in-plane spatial encoding, since this artifact manifests as blurring with radial encoding versus as a dark band with Cartesian encoding. The use of an in-phase echo time (2.46 ms) further minimized artifacts at fat/water interfaces. A flip angle close to the Ernst angle of blood (2.5 degrees) was used so that arterial and venous spins would appear moderately bright, so as to provide adequate contrast with low-signal vascular calcifications on minimum intensity projections. Other parameters were as follows: 660-896 views per partition, TR=4.8ms, 1.0 mm in-plane spatial resolution, 48-64 1.0-mm-thick slices interpolated to 96-128 0.5-mm-thick slices, bandwidth 460Hz/pixel, 2 averages, 7 min 42 s scan time. MR images were compared qualitatively and quantitatively with CT angiography. The volume of vascular calcifications was quantified using in-house software. Calcification volumes were quantified for two segments of the femoral artery: (1) from the femoral artery bifurcation to 5 cm above (segment 1), and (2) from the bifurcation to 5 cm below (segment 2). QISS MRA was also acquired.Peripheral vascular calcifications were well visualized in all 3 subjects. In one of the patients with a unilateral hip prosthesis, only the contralateral leg was evaluated, resulting in a total of 10 segments that were quantitatively analyzed. Figure 1A is a minimum intensity projection image (displayed with inverted contrast) of a stack-of-stars 3D FLASH MRI that shows extensive calcifications along the femoral arteries (arrows). There was excellent morphological correlation with CT angiography (Figure 1B). Quantitative analysis showed excellent correlation (r = 0.884, P<0.001) between MR- and CT-based measures of calcification volume (Figure 2). Fusion of the stack-of-stars 3D FLASH images with QISS MR angiography was successful in all subjects (Figure 3).In this pilot study, peripheral vascular calcifications were accurately depicted using a stack-of-stars 3D FLASH pulse sequence at 3 Tesla. The technique appears to be robust to respiratory motion and flow artifacts. The combination of a radial k-space trajectory for in-plane spatial encoding with an in-phase echo time minimized dark band artifacts at fat/water interfaces that might otherwise obscure calcifications on minimum intensity projection images. There was excellent morphological and quantitative correlation with CT angiography. In addition, fusion with QISS MRA has the potential to be a useful adjunctive tool for planning of percutaneous interventions.