In humans or animal models?

Augmentation index is a widely studied method.

Pulse Wave Velocity is considered a gold standard.

Ultrasound is also used in some population studies.

A few references below maybe helpful:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2293959/

http://qjmed.oxfordjournals.org/content/95/2/67

http://www.aktn.org.au/publications/documents/PWVTomlinson.pdf

Appanational tonometry and augmentation

European Heart Journal (2006) 27, 2588–2605: "Carotid-femoral PWV is the ‘gold standard’ for arterial stiffness" .... "Central SBP, central PP, and the AIx are dependent on the speed of wave travel, the amplitude of reflected wave, the reflectance point, and the duration and pattern of ventricular ejection, especially with respect to change in heart rate and ventricular  contractility, whereas aortic PWV, which is the speed of wave travel, represents intrinsically arterial stiffness, according to the Bramwell–Hill formula"

PWV - pulse wave velocity, AIx - augmentation index

Statement is from 2006 (you can look for updates), but PWV is still considered as 'gold standard'.

Agree with Heidi Hintsala. PWV may also be measured by oscillometric methods (like a blood pressure cuff) http://www.ncbi.nlm.nih.gov/pubmed/23571229 which make for easy measurement in the clinic.

The aortic augmentation index (AI) and aortic pulse wave velocity (PWV) are known to be indicators of arterial stiffness. However, it is not clear whether aortic AI and PWV reflect aortic stiffness in similar ways.

thanks all for the reply..PWV is the best method for finding arterial stiffness..Based on different methods like PWV,AI etc .many instruments are developed for finding Arterial stiffness..I would like to know which instrument is generally using to find arterial stiffness in hospitals ?