There are at least three ways (that I know of) to assess stenosis in the arteries, provided they are close enough to the skin for the procedure to be accurate. Angiogram has been mentioned, but it doesn't need to be close to the surface. Doppler ultrasound can be done on the carotid arteries, as an example, and other imagery can show narrowing. The Doppler measures speed. If the blood moves through a narrowing, where plaque has built up, it must speed up in order to keep the pressure and volume constant along the entire path of movement. This speeding volume of blood squeezing past a narrowing shows up on Doppler, and the speed change can be calculated, and from there the extent of narrowing.