We compared ultrasonic duplex scanning and angiography for the localization and classification of arterial stenoses and occlusions in 32 patients. The criteria for the detection of a greater than 50% diameter reducing stenosis was an increase in peak systolic velocity of greater than 100%, loss of reverse flow, and spectral broadening. Duplex studies and angiograms were evaluated in a blinded fashion. locations along visualized arteries. The path of the Doppler beam is indicated by a white line on the B mode image, and the region from which velocity data are obtained (the sample volume) is indicated by a cross mark on that line (figure 1). Because this system permits measurement of the angle of incidence of the Doppler beam with the vessel axis, velocity can be calculated by the Doppler equation. All examinations were performed by one of two technologists (M. C. or N. V.). Our technique has been previously described. 1 2 Patients are asked to fast for 12 hr before the examination to decrease interference by abdominal gas. This has allowed us to obtain velocity signals from aortoiliac segments in approximately 90% of patients. Study of the recumbent patient starts at the proximal abdominal aorta, with a 3 MHz transducer for average-sized adults and a 5 MHz transducer for asthenic individuals. The transducer is placed just above the umbilicus to image the aorta and is then moved distally to the inguinal ligament, following the course of the iliac arteries. Examination of the more superficial distal arteries is performed with higher-resolution, 5 or 7.5 MHz, transducers. The popliteal artery is examined with the patient prone and the knee slightly flexed. When time permits we attempt to study all segments in each patient. Occasionally limited examinations directed at specific arterial sites are performed. A single extremity can be studied in less than an hour, whereas a complete study may take 2 hr or more.We prospectively applied classification criteria previously described by Jager et al. 1' 2Each arterial segment is graded into five categories of stenosis: normal, 1% to 19% diameter reduction, 20% to 49% diameter reduction, 50% to 99% diameter reduction, and total occlusion. Typical waveforms for each category are shown in figure 2. Normal arteries have a triphasic signal and minimal spectral broadening. The spectral band is narrow with a clear area below the systolic peak (systolic window
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