In addition, ultrasound is a test that can be performed at the bedside. With improvements in clarity and resolution over the past two decades as well as the ability to perform color flow imaging, ultrasound is typically the first line test to evaluate the blood vessels. Ultrasound can also provide hemodynamic information regarding a lesion through duplex evaluation by evaluating velocities within a stenosis as well as proximal and distal to it.
The major disadvantage of ultrasound is that it is operator dependent, much more than CT or MRI. It is also somewhat patient dependent, as imaging can be less accurate in larger patients. Even with these disadvantages, ultrasound remains a mainstay in the initial evaluation of blood vessels. However, other techniques such as CT and MRI are catching up as noninvasive ways of evaluating the cardiovascular system.
There has been a substantial increase in the use of computed tomographic angiography (CTA) for evaluation of the vascular system in recent years. This increase is partly due to advances in hardware, including spiral and multidetector CT, which can be used for rapid imaging of large scan volumes using thin section collimation. Newer scanners can provide as many as 64 slice views, which increase speed as well as resolution of these studies.
Other advantages of CTA beside speed and resolution include its relative ease to perform. There are fewer pitfalls associated with CT and results typically are very reproducible. In addition, like ultrasound, CTA is noninvasive, only requiring an I.V. in a peripheral vein to inject contrast material. Traditionally, CTA has been very effective in evaluating larger vessels such as the aorta, but is now being used more commonly to evaluate smaller vessels, including the carotid arteries and arteries of the lower extremities.