Which of the following is a non-invasive diagnostic study for peripheral artery disease?

The ankle-brachial index (ABI) is a widely accepted non-invasive diagnostic test specifically used to assess peripheral artery disease (PAD). It measures the ratio of the blood pressure in the patient's ankle to the blood pressure in their arm. A decreased ABI indicates reduced blood flow to the limbs, which suggests the presence of PAD.

ABI is advantageous because it is simple, quick, and does not require any invasive procedures or contrast agents, making it safer and more accessible for a broader range of patients. In contrast, CT angiography and magnetic resonance angiography, while useful for visualizing blood vessels and potentially diagnosing PAD, are invasive in that they require contrast media and more complex preparation and interpretation. Angiography is an invasive procedure that involves catheterization and is not classified as a non-invasive diagnostic study.

This clarity of purpose and approach makes the ABI a cornerstone in the non-invasive evaluation of patients suspected of having peripheral artery disease.