Targeted PET/CT and PET/MRI Imaging of Vascular Inflammation

20 subjects with either carotid bifurcation stenosis of \>50% by ultrasound on at least one side (10 patients) or advanced AAAs (10 patients) and surgical intervention planned will be identified from physicians from the Division of Vascular Surgery at Stanford. Either a PET/CT or a PET/MRI will be performed for each subject: * PET/CT scans will be performed in 3D mode using GE Discovery 600 or GE Discovery 690 scanners (GE Healthcare). * PET/MRI scans will be performed using the novel PET/MRI system at Stanford, including a sensitive PET time-of-flight (TOF) scanner with an advanced 3T MRI scanner. The study patients will receive an intravenous administration of 10mCi of the prescribed radiotracer (18F-FPPRGD2). PET/CT or PET/MRI images will be obtained starting 45-60 minutes after radiotracer administration. For PET/CT, each image acquisition will begin with a non-contrast CT scan obtained from the vertex through the mid-thighs of the subjects. For PET/MRI, non-contrast images of the carotid or aorta will be performed. PET imaging will follow. Patient's vital signs will be monitored during the procedure and a physician will be available if there is need for immediate medical attention. The PET images will be reconstructed with a standard iterative algorithm using GE software release 5.0. After the planned surgery, we will also assess the histopathological correlation between the disease lesions and PET/CT or PET/MRI imaging characteristics.