What technique is least effective in detecting significant DVT?

Photoplethysmography (PPG) is a technique that measures changes in blood volume in microvascular tissue, primarily using light absorption. While it can provide some information about venous function and has application in assessing conditions like chronic venous insufficiency, it is generally less sensitive for detecting significant deep vein thrombosis (DVT) compared to other techniques.

In the context of detecting DVT, the other methods listed offer more direct measurements related to venous flow and pressure changes that are critical for identifying occlusion. For instance, air plethysmography measures the change in volume of a limb and can identify abnormalities related to venous drainage. Segmental pressure measurements assess blood pressure in different segments of the limb, providing insights into flow obstructions. Strain gauge plethysmography quantifies changes in limb circumference due to venous filling, which can be indicative of DVT.

Therefore, photoplethysmography is considered the least effective technique for detecting significant DVT because it does not directly measure deep venous flow or occlusions with the same degree of sensitivity and reliability as the other methods.