In this study, the investigator propose to determine the efficiency of a new and more sophisticated imaging prototype, the Spectral Photon Counting Computed Tomography (SPCCT), at characterizing vulnerable plaques and luminal stenosis in Carotid Atherosclerosis patients compared to DECT (Dual Energy CT) and MRI (Magnetic Resonance Imaging) which are used in current practice

Inclusion Criteria:

• Male or female subjects of any ethnic background, aged > 18 years
• Any of the following known or suspected supra-aortic arterial disease based on : Prior stroke; Transient Ischemic Attack; Amaurosis Fugax; Referred for evaluation of any supra-aortic vessel; Follow-up for a stent in a supra-aortic vessel; Prior imaging ultrasounds study showing > ou = 50 % stenosis of a supra-aortic vessel segment (within 60 days before consent)
• Patient undergoing surgery within one month of carotid plaque evaluation
• Willingness and ability to follow directions and complete all study procedures specified in the protocol
• Pre-menopausal women only : Negative urinary pregnancy test on the day of imaging before the administration of study drug
• Patient has accepted to participate to the study and has signed the written consent
• Patient is affiliated to social security

Exclusion Criteria:

• Contraindication to MRI examinations (e.g. inability to hold breath, severe arrhythmias, very low cardiac output, severe claustrophobia, metallic devices not approved for MRI such as defibrillators, pacemaker, heart valve prostheses, cochlear implants, neuro-stimulators, implanted automated injection device, intraocular metallic foreign bodies, neurosurgical and vascular clips);
• Contraindication to the use of iodine and gadolinium containing contrast media (including subjects with suspicion for/or known to have NSF);- History of severe allergic or anaphylactic reaction to any allergen including drugs and contrast agents (as judged by the investigator, taking into account the intensity of the event);
• Estimated Glomerular Filtration Rate (eGFR) value < 30 mL/min/1.73 m2 derived from a serum creatinine result within 1 month before the imaging;
• Any subject on hemodialysis or peritoneal dialysis (Note: If there are multiple creatinine values, the values obtained prior to and closest to the time of the examination should be used);
• Acute renal insufficiency of any intensity, either due to hepato-renal syndrome or occurring in the per-operative liver transplantation period;
• Known subject history of severe cardiovascular disease (e.g. acute myocardial infarction [< 14 days], unstable angina, congestive heart failure New York Heart Association class IV) or known long QT syndrome;
• Suspected clinical instability or unpredictability of the clinical course during the study period (e.g. due to previous surgery);
• Scheduled or potentially expected for the period between the SPCCT or DECT and MRI: Any procedure that may alter the MRI or CT interpretation; Any interventional or surgical procedure involving the supra-aortic vessels.
• Pregnant or nursing (including pumping for storage and feeding); 11. Patient under guardianship, curators or safeguard of justice.

The images will be read without knowing the CT scan used