CT Angiography and MR Angiography of Carotid Arteries

CT angiography (CTA) has revolutionized vascular imaging. Vessels smaller than 1mm in diameter can be visualized with single slice CTA and vessels 2 mm or more in diameter can be diagnostically evaluated. The acquisition of 3D data volumes makes it possible to generate "angiographic" views that facilitate anatomic orientation."nWith the advent of multi slice CTA, near isotropic resolution becomes available for most applications and allows evaluation of even smaller vessels."nMulti slice scanning makes CTA less technically challenging and more robust. It reduces scan time and the vulnerability to motion artifacts, and may be used to substantially decrease the required contrast material volume to as little as 50 ml in selected cases."nThe advantages of CTA over arterial angiography (DSA) include substantially lower invasiveness, less cost, less radiation exposure, and better patient tolerance. Diagnostic advantages include simultaneous visualization of the vessel wall and lumen, and the ability to study vascular anatomy from arbitrary viewing angles using only one data acquisition."nCTA even allows projections (such as Caudocranial) that cannot be obtained with conventional angiographic techniques."nAlthough CTA can replace diagnostic ultrasound with its various Doppler techniques, it may be preferred over CTA in regions that are easily accessible by sonography or when flow information is required. It also holds advantages whenever bedside imaging is to be preferred."nMagnetic resonance angiography (MRA) has become the common place in the last few years. The improvements in pulse sequence design, hardware design, and post processing methods make it possible to acquire data in a short period with excellent vascular visualization in a variety of clinical applications."nContrast -enhanced magnetic resonance angiography (MRA) offers competitive results to CTA, although spatial resolution is often lower than with multi slice CT scanning. The lack of ionizing radiation of MRA is important in young patients, for vascular screening, and for patients requiring repeated follow-up examinations."nIn patients with impaired renal function, contrast-enhanced MRA requires less (and therefore less nephrotoxic) contrast material."nDynamic MRA examinations offer therapeutically relevant additional information in only a relatively small number of cases and flow quantification with MR may again increase the importance for therapeutic decision-making.