Diagnostic Imaging for Peripheral Arterial Disease: the DIPAD trial.

Peripheral arterial disease (PAD) is the expression of atherosclerosis in the lower limb distal to the aortic bifurcation, which is a major problem in the population of 55 years and older. The first manifestation of symptomatic PAD is usually intermittent claudication. In a minority of patients, the disease progresses to critical limb ischemia, i.e. rest pain and tissue necrosis. If PAD is suspected on the basis of patient history and physical examination, ankle-brachial indices (ABI) are generally measured to document the severity of the disease.
Diagnostic imaging is performed when PAD becomes lifestyle limiting and a revascularization procedure is considered. Non-invasive imaging tests including Duplex ultrasound (DUS), computed tomographic angiography (CTA), and magnetic resonance angiography (MRA) are increasingly used for the initial evaluation of patients with PAD. DUS provides both anatomical and functional information about the arterial system and has been shown to be a reliable modality with fairly good sensitivity and specificity. DUS is, however, operator dependent and does not provide a precise roadmap for planning treatment. Both MRA and CTA are relatively new non-invasive vascular imaging tests used in the diagnostic workup of peripheral arterial disease. Both modalities provide three-dimensional images of the arterial system with high sensitivity and specificity.
Disadvantages of MRA include the higher investment cost for equipment, the small number of cases in whom the image is uninterpretable due to artifacts, and the fact that some patients are claustrofobic or have a contraindication for MR scanning. The main disadvantages of CTA are the use of radiation, the use of potentially nephrotoxic iodinated contrast media, vessel wall calcifications that affect image interpretation, and the time-consuming 3D reconstruction techniques. The question arises which imaging test is preferred in the diagnostic work-up of PAD.
To determine which non-invasive test is preferred as initial imaging test in clinical practise we need to take into account not only the diagnostic accuracy of each test, but also the related effects of diagnostic imaging tests on treatment planning, functional improvement, quality of life, and costs. For this purpose we designed the Diagnostic Imaging of Peripheral Arterial Disease (DIPAD) randomized trial to compare outcomes following DUS, MRA, and CTA as the initial imaging test in the diagnostic workup of patients with peripheral arterial disease. Primary outcomes evaluated were quality of life and costs. Secondary outcomes evaluated were clinical utility and functional patient outcomes.

Is the diagnostic imaging workup of patients with peripheral arterial disease performed initially with MR angiography cost-effective compared to the currently employed workup with duplex ultrasound or CT angiography?

1. Magnetic resonance angiography: requires intravenous contrast material injection and duration of the examination is 30 minutes;

2. Duplex ultrasound: requires no intravenous contrast material injection and duration of the examination is variable;

3. Computed tomographic angiography:requires intravenous contrast material injection and duration of the examination is 10 minutes.