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Seeing Is Believing A Clot Is a Clot on a Duplex Scan or Phlebogram

Duplex scanning has ushered in a new era in the diagnosis of deep venous thrombosis. It now poses a challenge to phlebography’s past role as the exclusive standard for proving the presence or absence of thrombi within a vein. Dupler scanning is a second anatomical test, providing immediate evidence of obstruction or patency of a vein. Noninvasive functional tests require confirmation by phlebography because they “diagnose” indirectly, that is, by measuring an abnormality of pressure or volume in the limb, a change in the velocity of blood flow detected by the Doppler examination, or the change in electrical impedance as blood drains out of a limb. The clinician can place equal credence in a clot visualized on a phlebogram or on a duplex scan, both being immediately evident. Similarly, a vein shown to be patent on x-ray film can be demonstrated to be free of obstruction on the scan: the vein wall can be observed being coapted by slight pressure from the probe, prime evidence that the vein does not contain solid matter. The concept of combining Doppler examination with ultrasonic imaging (a modality used for at least a generation to image the abdomen) originated with a group of investigators working under Strandness,’ whose pioneering efforts in scanning the arteries gave impetus to other investigators2 to study the veins of the extremity. The addition of an integrated Doppler capability provides functional information in instances when the clot is difficult to see. The image cursor pinpoints the source of the sound of blood flowing within the vein. Does the phlebogram still have an advantage over the duplex scan? If perfect, the x-ray technique offers more complete evaluation of the venous tree, visualizing areas to which the du-