Current Imaging Approaches and Challenges in the Assessment of Peripheral Artery Disease

Abstract

In current practice, vessel wall disease in the peripheral arteries is evaluated primarily by imaging the vessel lumen, rather than by imaging the vessel walls themselves, or by imaging the perfusion of the adjacent soft tissues. Bedside diagnostic methods include ankle-brachial index and Doppler ultrasound; however, these are usually considered insufficient for interventional planning. Digital subtraction angiography (DSA) remains the gold standard for evaluating peripheral arterial vessel wall disease because of its high resolution and because it provides the option to intervene at the time of diagnosis; however, even diagnostic-only DSA poses the risks inherent in any invasive procedure and in the uses of ionizing radiation and iodinated contrast. Computed tomography angiography (CTA) is sufficiently sensitive for diagnosis of stenoses requiring intervention and for interventional planning but also risks renal injury due to iodinated contrast and contributes to the stoichiometric risks of ionizing radiation. Magnetic resonance angiography (MRA) without and with contrast is usually at least as sensitive to stenosis as is CTA, without the risks of ionizing radiation or of iodinated contrast. Currently commercially available gadolinium-based contrast agents (GBCAs) pose essentially zero risk. Only one possible case of nephrogenic sclerosing fibrosis (NSF) has been reported since 2008. Gadolinium deposition does occur, but there are no known associated symptoms or long-term sequelae. T2-weighted magnetic resonance imaging can show vessel wall disease, such as cystic adventitial disease (CAD), vessel wall edema in the vasculitides, and soft tissue edema adjacent to the vessels. Non-contrast-enhanced MRA (NE MRA) is currently a challenge due to the commercial nonavailability of the sequences that are most sensitive and with the shortest table time. Also, tortuous, in-plane vessels may not be visualized. Techniques for evaluating microvasculature that are not currently in wide clinical application and are therefore not discussed in detail in this chapter include contrast-enhanced ultrasound, contrast-enhanced MRI perfusion imaging, non-contrast-enhanced blood-oxygen-level-dependent (BOLD) and arterial spin labeling (ASL) MRI, and magnetic resonance spectroscopy with 31-phosphorus.