DUAM is commonly performed with a high-frequency linear transducer. Imaging of the adductor canal (and at times entire femoral arterial segment) may need addition of evaluation with low-frequency curved probe in patients with large thighs/deeper arteries. Monophasic flow waveform in the popliteal artery is indicative of severe stenosis(es) or segmental occlusion(s) of the proximal arterial segments. Scanning of these arteries is performed in transverse and/or longitudinal sections to obtain B-mode, color flow, and/or power Doppler images. High persistence, high sensitivity, and low pulse repetition frequency (PRF) scale improve detection of low flow in obstructed arteries.

Endovascular treatment of this segment requires complete mapping as multiple serial significant stenoses or occlusions can be present.

A short protocol can be established if the patient is a candidate for a distal bypass or even a femoropopliteal bypass. The arterial mapping continues from the common femoral to the site of most proximal occlusion or severe stenosis. The site of a proximal anastomosis is then selected within this patent segment. The scanning is resumed at the popliteal artery level. This artery is scanned in its entirety to determine if it is a candidate for the site of the distal anastomosis.

Occlusions are confirmed by lack of color flow or Doppler waveforms performed in very low PRF, high persistence and sensitivity color and Doppler scales. The first stenosis may be graded based on velocity measurements (Fig. 28.2). Doubling or tripling of peak systolic velocity (PSV) at the stenotic site indicates a hemodynamic significant or severe stenosis, usually equated to a 50 or 70% diameter reduction (Fig. 28.3). The hemodynamic energy lost in the first stenosis precludes velocity grading of additional, distal, sequential stenoses. It may be possible to locate such stenoses based on aliasing at low, high sensitive color flow velocity scales. Otherwise, stenoses are perceived based on narrowing of the color flow channel. Branch analysis clarifies sites of collateral flow takeoff prior to severe obstructions and/or collateral flow reentry distal to such obstructions (Fig. 28.4).

In summary, a full-length femoropopliteal imaging protocol is required prior to an endovascular procedure. A modified short protocol from the common femoral down to the first occlusion/severe stenosis site is acceptable to select the location of the proximal anastomosis of a bypass graft. Imaging of the entire popliteal artery is recommended in both instances. Imaging must continue distally in search of a distal anastomotic site. Color flow bleeding beyond stenotic lumen or noncircular lumen requires additional imaging for a complete evaluation.

Imaging of diseased i nfrapopliteal arteries demands appropriate patient preparation. The room and the patient must be warm. Creating conditions for vasodilation of the peripheral arteries helps detection of patent segments. Mapping may actually be easier in patients with inflammatory or infectious conditions due to the degree of vasodilation already present. Detection of patent, small segments is most difficult in extremities with severe rest pain and cold feet. Manual compression maneuvers may elicit blood movement in apparently occluded segments. Performing the scan with the leg dependent may actually help visualization of small arteries dilated by the hydrostatic pressure.

DUAM is performed with high-frequency linear transducers (linear and compact linear). The posterior tibial artery at the ankle is an easy start. Occlusion or patency is determined. If patent, the scan continues until the tibio-peroneal trunk, if anatomically or ultrasonographically possible, or until a reentry branch distal to an occlusion. Edema, large legs, calcifications, and occlusions make imaging difficult. Occlusions are documented by association with the posterior tibial veins (Fig. 28.5). Large and edematous legs may have to be scanned with a low-frequency sector probe.

On occasion color flow imaging of a patent distal posterior tibial artery is followed toward the posterior terminal branch of the peroneal artery (Fig. 28.6). Once the proximal scan of the posterior tibial artery is completed, the scan continues distally through the common plantar artery and its bifurcation. The objectives of the distal scan are to find a potential plantar target for a distal anastomosis and to evaluate the posterior tibial artery runoff in case the distal anastomosis is to be placed at the calf or ankle level. A short protocol may start at the ankle and stop at the most distal location of a stenosis or occlusion that needs to be bypassed. Wasting time imaging occluded or diseased arteries that are going to be bypassed is avoided.

The mapping of the anterior tibial artery follows a similar routine in the anterolateral leg compartment. First, the segment at the ankle level is evaluated. The relation to the tibia and fibula is essential for identification of the anterior tibial artery. The learning of cross-sectional anatomy is extremely valuable. A monophasic waveform indicates proximal severe stenosis or occlusion. The scan toward the popliteal artery can be performed in transverse or longitudinal sections. Although a B-mode scan is potentially feasible, longitudinal color flow or power Doppler imaging is most common and practical. A patent distal anterior tibial artery may be fed via the anterior terminal branch of the peroneal artery. The anterior tibial veins are smaller than the posterior tibial veins. Therefore, identification of potentially occluded segments must rely on other secondary information. For example, the arterial channel may appear irregular in sites where the flow is diverged via short collaterals. Long collaterals may also take over the task to deliver blood to patent distal segments. A sector lower-frequency probe may be needed to image the proximal part of the anterior tibial artery. From a posterior approach, the anterior tibial artery branches deeply from the popliteal artery. A common beginner’s error is to identify a superficial, posterior branch of the popliteal artery as the anterior tibial artery instead of a geniculate branch or an artery toward the gastrocnemius muscle.

Once the proximal scan of the anterior tibial artery is completed, the scan continues distally through the dorsalis pedal artery. It is necessary to pay attention to anatomic variants that include tarsal arteries or unusual endings of the anterior terminal branch of the peroneal artery. The dorsal pedal divides into a deep plantar branch that communicates with the posterior circulation and a more superficial transmetatarsal artery that eventually feeds the digits. The objectives of the distal scan are to find a potential pedal target for a distal anastomosis at the dorsal pedal artery and to evaluate the anterior tibial artery runoff in case the distal anastomosis is to be placed at the calf or ankle level. A short protocol may start at the ankle and stop at the most distal location of a stenosis or occlusion that needs to be bypassed. Wasting time imaging occluded or diseased arteries that are going to be bypassed is avoided.

The peroneal artery is approached first with a high-frequency linear probe at a posterolateral position. Learning cross-sectional anatomy to identify the peroneal vessels in relation to the fibula is recommended. Longitudinal color flow or power Doppler scanning is preferred to transverse or B-mode imaging for practical reasons. If possible, a transverse scan is highly informative about other arteries, veins, and anatomic references. Completion of a peroneal artery scan is less likely than completion of a posterior tibial or anterior tibial artery scan. The problems are encountered in a large, edematous calf. The proximal peroneal artery and the tibio-peroneal trunk are often difficult, and they may have to be studied with a low-frequency curved probe. Branching and collateral networks may create difficulties in identifying a patent peroneal artery. Bypasses have been extended to a branch of the peroneal artery initially identified as the peroneal artery on arteriography. Ultrasound has the advantage of identifying the peroneal veins adjacent to the peroneal artery. The anterior and posterior terminal branches of the peroneal artery may feed the distal posterior tibial and anterior tibial arteries. Therefore, posterior or anterior tibial ABIs may actually represent peroneal pressures. A short protocol may start at the ankle and stop at the most distal location of a stenosis or occlusion that needs to be bypassed. Wasting time imaging occluded or diseased arteries that are going to be bypassed is avoided.

Ultrasound B-mode imaging allows for detailed examination of the arterial walls. A thin, soft, compressible arterial segment can be selected. A rigid, calcified wall can be avoided. Although calcification may be a hindrance for ultrasonic valuation of some stenoses, a great advantage of ultrasound is to identify all calcified segments and redirect the anastomotic site to a soft arterial segment. In the challenging cases, the surgeon may opt for a local endarterectomy and patch over a stenotic site to provide blood flow not only distally but proximally also. Often the bypass graft provides enough pressure to dilate small arteries and collaterals that feed the muscles upstream. A decision has to be made if the arterial wall is thickened. Initially, the tendency is to avoid a thickened wall as a site for a distal anastomosis. Close examination, however, has shown that vascular surgeons have approached thickened arteries and have performed anastomoses in arteries apparently normal by arteriography. Indeed, if needed, an anastomosis may even be performed over a calcified segment [25]. Nevertheless, ultrasound imaging can classify the segments into soft, thickened, or calcified as well as differentiate posterior (more benign) from anterior wall thickening.

Arterial mapping should either start or end with vein mapping , particularly if a distal bypass graft is being considered as treatment [13]. Anastomotic sites may be altered based on length of vein available for the bypass. Saphenous or arm vein mapping is performed with high-frequency transducers. Venous patency and conditions of the vein wall are evaluated. Diameters and length of vein available are measured. Location of the vein may be marked on the skin to facilitate the surgical procedure. Tributaries may be marked if an in situ bypass is being considered. A cephalic vein 2 mm in diameter often dilates to become a 4-mm bypass graft [26]. The arm veins dilate with placement of a tourniquet in the upper arm. Saphenous veins do not dilate as much. A dilation maneuver to determine if vein diameter can increase with temperature or hydrostatic pressure is recommended if the saphenous vein diameter is less than 4 mm. The vein wall must be thin. Thickened walls suggest a previous event of venous thrombosis. Usually these vein segments are avoided. Valve sinuses can be disrupted. The ultrasound imaging shows various structures apparently floating in the vein valve sinus region. The potential for causing graft stenosis or occlusion exists if these segments are implanted.

In summary, veins are mapped in conjunction with the arteries to plan for arterial revascularization. The conditions of the venous wall, vein diameters, and length available are recorded.

Ultrasound or physiologic testing is recommended to follow patients (1) with mild peripheral arterial disease, (2) treated medically, (3) who had an endovascular procedure, or (4) who had open surgery, particularly a bypass graft.

Follow-up of bypass grafts in the postoperative period and at 3, 6, 9, 12, 18, and 24 months and yearly thereafter is recommended. Long protocols include evaluation of the bypass graft and proximal and distal arteries, particularly the bypass runoff arteries. A stenosis can be graded based on the B-mode/color flow imaging or on increased velocities. The scan must continue after one defect is found. The graft or arteries may have additional stenoses. A short protocol can be performed based on the measurements of volumetric blood flow rate in mL/min. If a first ultrasound scan is normal, then flow rate can become a parameter to indicate the need for another complete scan. If flow rate decreases by 20–30% between tests, then a complete scan is indicated. Several details, however, must be followed during flow rate measurement. Only pulsatile flow must be considered. Diastolic flow is variable and adaptable to numerous conditions of vasodilation. It is recommended that measurements be performed in similar conditions of vasodilation as indicated by toe temperatures. Recommended toe temperature for such measurements is 28 °C (26–30 °C). Another indication for a full duplex ultrasound evaluation is if pulsatile flow rate falls below a minimum flow threshold value indicating poor perfusion: <50, 40, and 30 mL/min of pulsatile flow for bypass grafts to the popliteal, tibial, or paramalleolar level, respectively. Low flow states are not caused only by graft or peripheral arterial obstruction. A failing heart is often the cause of a low flow state. A low flow state with unobstructed peripheral conduits is an indicator of a poor heart condition with a high mortality rate within 1 year. The natural history of endovascular procedures has yet to be determined for most of the procedures now performed. Follow-up, therefore, should be more stringent than that for bypass grafts. A full duplex ultrasound evaluation is recommended. Sites of wall thickening, neointimal proliferation, and stenoses are documented with imaging and velocity measurements. Stents have different compliance than arteries apparently causing increases in velocity. Criteria used to classify arteries as normal or stenosed still need to be adapted to stented conduits. In summary, peripheral arterial procedures must be followed routinely and constantly at least for the first 12 months. Detection and treatment of stenoses provide better long-term patency rates than thrombectomy of an occluded bypass or than a secondary vascular reconstruction [27].

Patient follow-up includes testing the contralateral limb besides evaluation of an extremity treated with open or endovascular surgery. Eventually the contralateral limb will demand similar treatment. Patients treated medically are often tested annually in the vascular laboratory. Patients at risk of developing significant peripheral arterial occlusive disease should also be tested routinely. All these patients benefit from a vascular rehabilitation program designed to educate patients on risk factors, peripheral arterial disease, dieting, and exercise habits. Indeed, patient conditioning is suggested prior to surgical treatment to potentially minimize the operative morbidity.

This section deals with the third objective of this chapter. It discusses several philosophies to prepare a team for DUAM as the sole preoperative imaging modality prior to open surgery or endovascular procedures to treat the ischemic leg.