With the newer noncontrast techniques, cardiac arrhythmia can impair image quality, limiting evaluation of the distal tibial and pedal arteries. Although useful tools to improve image quality have been suggested, larger-scale trials are required for evaluation of small-vessel PAD with noncontrast MRA [29,36]. US Duplex Doppler Lower Extremity Duplex US of the extremities can be used to identify the location, degree, and extent of stenosis to the level of the knee [37]. Although duplex US includes images in grayscale or in color or power Doppler, the clinically relevant information derived from duplex studies has been validated from analysis of the velocity of blood flow. The sensitivity and specificity for the diagnosis of stenoses >50% in diameter from the iliac arteries to the popliteal arteries are each approximately 90% to 95% [37-39]. Accuracy of the duplex examination depends on the ability of the technique to visualize the vessel adequately. The use of color improves accuracy [40]. Accuracy is diminished in examinations of the iliac arteries if bowel gas or tortuosity obscures the iliac vessels. Dense calcification can also obscure flow, particularly if flow is slow. Accuracy of duplex US is also decreased in the setting of multiple sequential lesions [41]. Duplex US has been established as a useful surveillance tool for arterial bypass grafts with established criteria for graft stenosis and thresholds for reintervention [42]. However, evidence and standards for duplex US surveillance after endovascular treatment are lacking, although duplex US is commonly used for this indication [42]. In comparison with CE-MRA, duplex US is less accurate for detecting significant stenoses and for preoperative planning [31]. In a randomized controlled trial comparison with CE-MRA, duplex US for the initial imaging workup of patients with PAD increased the need for additional imaging [32]. CTA is more clinically useful than duplex US [21].
Lower Extremity Arterial Claudication Imaging Assessment for Revascularization. With the newer noncontrast techniques, cardiac arrhythmia can impair image quality, limiting evaluation of the distal tibial and pedal arteries. Although useful tools to improve image quality have been suggested, larger-scale trials are required for evaluation of small-vessel PAD with noncontrast MRA [29,36]. US Duplex Doppler Lower Extremity Duplex US of the extremities can be used to identify the location, degree, and extent of stenosis to the level of the knee [37]. Although duplex US includes images in grayscale or in color or power Doppler, the clinically relevant information derived from duplex studies has been validated from analysis of the velocity of blood flow. The sensitivity and specificity for the diagnosis of stenoses >50% in diameter from the iliac arteries to the popliteal arteries are each approximately 90% to 95% [37-39]. Accuracy of the duplex examination depends on the ability of the technique to visualize the vessel adequately. The use of color improves accuracy [40]. Accuracy is diminished in examinations of the iliac arteries if bowel gas or tortuosity obscures the iliac vessels. Dense calcification can also obscure flow, particularly if flow is slow. Accuracy of duplex US is also decreased in the setting of multiple sequential lesions [41]. Duplex US has been established as a useful surveillance tool for arterial bypass grafts with established criteria for graft stenosis and thresholds for reintervention [42]. However, evidence and standards for duplex US surveillance after endovascular treatment are lacking, although duplex US is commonly used for this indication [42]. In comparison with CE-MRA, duplex US is less accurate for detecting significant stenoses and for preoperative planning [31]. In a randomized controlled trial comparison with CE-MRA, duplex US for the initial imaging workup of patients with PAD increased the need for additional imaging [32]. CTA is more clinically useful than duplex US [21].