Screening for PAD can be readily obtained by matching patient risk factors with a focused health history and examination. The type and extent of arterial testing should be individualized taking into account clinical presentation (e.g. claudication, dependent rubor, ulceration, gangrene, etc.), prior arterial testing, and a history of arterial intervention. Measurements of ankle-brachial systolic pressure index (ABI) and digit systolic pressures can adequately screen for PAD and is recommended for persons age >65 (age 50 in smokers or diabetics), exertional leg symptoms (claudication), lower extremity or foot wounds (Fig. 24.1) [14]. Toe systolic pressures are especially helpful in diabetics in whom calcified, incompressible tibial vessels produce erroneously high ABIs (>1.3). Atypical presentations of exertional leg pain especially in patients with an abnormal ABI (<0.9) should be considered for exercise treadmill testing in order to exclude nonvascular conditions that may be responsible for lower extremity claudication-like pain. In patient with symptomatic PAD (disabling claudication, gangrene, or rest pain), segmental lower limb pressures measured at one or more levels in combination with Doppler or plethysmographic (pulse volume) waveform analysis does not provide sufficient information to counsel the referring physician on the extent of arterial disease and potential treatment options. In these patients, arterial duplex testing is preferred to characterize disease location, extent, severity, and morphology (atherosclerosis, aneurysm). Protocol guided arterial duplex testing of the aorto-iliac and infrainguinal vessels can also identify other relevant concomitant vascular conditions such as artery entrapment, visceral artery stenosis, abdominal aorta aneurysm development, or venous thrombosis.

Duplex scanning is particularly helpful in stratifying the level of occlusive disease (e.g., aortoiliac, femoropopliteal, popliteal-tibial or multilevel disease segments) [2–4]. Additional clinical applications for arterial duplex scanning include:

The accuracy of duplex scanning is sufficient to permit arterial mapping analogous to contrast arteriography for the aorta and lower extremities in most individuals. Compared to arteriography, the “gold standard” for peripheral arterial imaging, duplex scanning has a diagnostic accuracy of >80% for the detection of a >50% diameter reducing stenosis or occlusion Diagnostic accuracy tends to decrease when multilevel disease is present. However, in the absence of multilevel disease, diagnostic accuracy exceeds 90% for the detection of high-grade stenosis or occlusion involving iliac, femoral, popliteal, or tibial arterial segments. Technological enhancements have enriched the value of color flow Doppler imaging in a manner analogous to CT, MR and DS arteriography. The classification of occlusive lesions is based on the same general principles that apply to the duplex evaluation of other arterial circulatory systems (e.g., cerebrovascular, mesenteric, renal). Although arteriography has for some time been considered the “gold standard”, multiple series have demonstrated a diagnostic accuracy is >80% for the detection of a >50% diameter reducing stenoses or occlusions using duplex scanning (Table 24.2) [1, 2, 4, 7–9]. In the absence of multilevel disease, diagnostic accuracy exceeds 90% for the detection of high-grade stenosis or occlusion involving iliac, femoral, popliteal or tibial vessels. Additionally, several centers have conducted small prospective blinded trials comparing duplex imaging to contrast arteriography for planning infrainguinal reconstructions for atherosclerotic occlusive disease. These studies indicate that duplex imaging is equal to angiography in predicting suitable distal bypass with confidence intervals in the range of 95% [10, 11].

When duplex scanning has been used in the evaluation of symptomatic lower limb atherosclerotic disease , approximately 45% of patients have lesions suitable for treatment with endovascular techniques [9, 13]. Whether a diseased arterial segment is suitable for endovascular intervention often depends on the specific characteristics of the lesion. In the lower limb, duplex findings of category 1 or 2 lesions based on the Society of Cardiovascular and Interventional Radiology guidelines indicate endovascular intervention is a treatment option (Table 24.3) [12]. Technical success rates in excess of 95% can be achieved with clinical results similar to surgical reconstruction. Category 3 lesions (>4 cm length calcified stenosis, multilevel disease, 5–10 cm length chronic occlusions) are also amendable to endovascular procedures. While short term primary patency rates are comparable to surgical bypass grafting, mid and long-term patency rates remain below that of surgical reconstruction [17].

For most examinations 30–45 min should be allotted. The vascular examination room should be kept warm (75–77 °F) to avoid vasoconstriction. The patient should be instructed not to eat within 6 h of examination in order to reduce abdominal gas in the event that aortoiliac imaging is required. A brief history should be obtained noting PAD risk factors: diabetes, hypertension, hyperlipidemia, smoking, obesity, heart disease, and family history. A focused physical exam can be provided according to individual lab protocols. Previous imaging studies should be reviewed in order to improve the testing accuracy. Abdominal imaging begins with a 3.5–5 MHz curvilinear or phased array transducer with the evaluation of the infrarenal aorta at the level of the renal artery origins and moves caudal towards the iliac arteries. As the exam is continued to the inguinal ligament at the level of the femoral artery, the transducer frequency is increased to a 5–10 MHz probe. Multiple scanning windows may be required for complete insonation/imaging of the pelvic and infrainguinal circulation due to imaging limitations such as obesity (vessels >15 cm deep), bowel gas, large limbs, edema, surgical wounds, ulcers, joint contractures, small vessels, and vessel calcification. Aortic diameter is documented as the technologist moves distally evaluating the iliac circulation, followed by the common femoral, deep femoral, superficial femoral, popliteal, and mid to distal tibial vessels. B-mode imaging can be used to measure diameter and document plaque character or stenosis. Color Doppler permits rapid location of sites of turbulence by lumen narrowing, color-map aliasing, color flow jets, and occasionally a tissue bruit. Identification of vessel branching, collateral circulation, aneurismal change, and occlusive disease as well as sampling blood flow patterns are important components of duplex imaging. Because occlusive lesions have a tendency to develop at specific sites, scanning should be focused on these areas especially when proximal-to-distal changes in velocity waveform configuration are recorded (Table 24.4) [6, 7]. In order to adequately grade the severity of stenosis a center-stream Doppler angle-corrected to 60° with pulsed Doppler spectral analysis is carried out proximal to, at the site of maximum flow disturbance, and distal to the site of stenosis. Attention to changes in velocity waveform (pulsatility) and measurement of peak systolic and end-diastolic blood flow velocities are recorded. Identification of luminal narrowing , plaque character , color map aliasing (turbulent flow), color flow jets and tissue bruits should be documented if present (Fig. 24.2). Doppler velocity spectra from the distal tibial and pedal arteries are assessed and should aide in correlating waveform pulsatility and peak systolic velocity with measured ABI (Fig. 24.3). Again, this correlation is especially important if heavily calcified or incompressible vessels are present. An ABI value of >1.3 suggests the presence of noncompliant or calcified vessels. Assessment of pulsed Doppler spectra at all stations of the extremity; common femoral, superficial femoral, popliteal, and tibial vessels; allows for comparison of pulsatility index and acceleration time between arterial segments.