IN TRADITIONAL clinical-radiologic interactions, the radiologic workup of diagnostic problems is orchestrated by the clinical service. This relationship works satisfactorily in the evaluation of straightforward clinical problems, but commonly breaks down if the workup is complex. This is true in large measure because few areas of medicine have shown greater recent change than has diagnostic radiology. Radiologic techniques unheard of ten years ago, such as computerized axial tomography, ultrasonography, percutaneous biopsy technique, and subselective angiography, are now generally available and regarded as nearly indispensable tools. In addition to remarkable advances in imaging techniques, radiology now offers startling interventionist services such as percutaneous internal biliary drainage, selective embolization procedures, and transcutaneous intraarterial dilation. Even if a referring physician were to make extraordinary effort to review the contemporary radiologic literature pertinent to his specialty, he would still be relatively unfamiliar with the particulars of the radiologic equipment, skills, and biases available to