Duplex sonography of the portal venous system: pitfalls and limitations.

Duplex pulsed-Doppler sonographic examinations of the portal venous systems of 14 patients were reviewed, and the results were compared with the findings of other examinations including endoscopy and angiography. The sonograms of virtually every patient in the sample showed at least one of four pitfalls. The "mirror-image" artifact, in which the Doppler signal contained simultaneous and symmetric elements on both sides of the zero baseline, was identified in 11 patients (79%). The "flip" artifact, in which the Doppler signal would either flip from one side of the zero baseline to the other or would indicate a direction of blood flow opposite to that normally expected, was seen in six patients (43%). In four patients (29%), a Doppler flow signal could not be obtained from small vessels that were identified on standard real-time images. In 10 patients (71%), important vascular channels including bleeding gastroesophageal varices were obscured by bowel gas, ascites, or the patient's body habitus. Duplex sonography may still provide useful information about portal venous hemodynamics. However, it remains a prodigious technical undertaking whose accuracy can be severely hampered by artifacts and inherent technical difficulties.