Ischemic skin lesions are further on the continuum of CLI.These typically occur on the feet and can be initiated by a slight insult to skin integrity. Poor perfusion results in poor healing and subsequent development of ulceration. Ischemic ulcers may progress to frank gangrene. Beware of other lower extremity skin lesions such as diabetic ulcers and venous stasis ulcers in the evaluation of CLI.Diabetic ulcers are due to neuropathy and often result from a pivotal event such as wearing shoes that are too tight or stepping on a sharp object. Venous stasis ulcers classically occur on the lower leg above the medial malleolus.

Duplex ultrasound determines morphology of a lesion and calculates blood ow velocities and turbulence within a vessel (Fig.31.2). Increasing ow velocity indicates a higher degree of stenosis until the narrowing becomes so severe that ow is nearly obstructed. It is particularly useful in monitor­ing patency of bypass grafts. Computed tomography angiog­raphy (CTA) provides a timely assessment and mapping of lower extremity arteries (Fig.31.3). It requires the use of intravenous iodinated contrast, which may be contraindi­cated in patients with renal failure. Additionally, it subjects the patient to ionizing radiation exposure. Magnetic reso­nance angiography (MRA) is highly sensitive for the evalua­tion of luminal stenosis (Fig.31.4). Intravenous gadolinium is typically used. It is possible to obtain MRA without gado­linium, but this requires much longer image acquisition sequences termed time of ight, which some patients may not be able to tolerate. MRA is the most expensive of these imaging studies and may not be as widely available as CTA or ultrasound [13].