A balloon catheter is used for dilating tubular members of the body such as dilating stenotic aortic valve leaflets found in the aortic root, and measuring the shape and dimensions of the annulus. The balloon has two larger diameter bulbous regions； one is positioned in the left ventricular outflow tract (LVOT) and the other in the aortic sinus； a smaller diameter waist region is positioned across the aortic annulus. During inflation of the balloon, the balloon waist expands in diameter until it comes into contact with the aortic annulus. The balloon pressure and inflation volume is monitored during inflation so that an inflection point in the dP/dV curve is seen at the point of contact of the waist with the annulus. Radiopaque rings and/or marker bands in the device allow the size and orientation of the elliptical annulus to be calculated.
