Noninvasive carotid testing in threatened stroke. 1. Principles and techniques.

The noninvasive tests for evaluation of atherosclerotic disease in the region of the carotid bifurcation are of two types, the physiologically based indirect tests and the hemodynamically or structurally based direct imaging techniques. Limitations of the indirect methods led to development of the latter technologies, but the direct tests, especially imaging techniques, are generally more expensive and have limitations of their own. Duplex scanning, which combines physiologic and anatomic interrogation, should circumvent some shortcomings of the other direct techniques, but the necessary instruments are expensive and the method is technically difficult.