***AMA version (for Physicians)***
First published December 13, 2020
In 1981, the Norwegian physiologist, Rune Aaslid, developed a device that made it possible to apply the transcranial Doppler (TCD) sonographic technique to the human brain. In 1983, Albrecht Harders, a German neurosurgeon, worked out a clinically practicable method that would allow for bedside, atraumatic measurements to be made of the blood flow velocity in the large arteries in the Circle of Willis. This simple test is based on a single-element transducer technology but requires a knowledge of anatomy, physiology, and pathology that transcends any single discipline.