A catheter for measuring a fractional flow reserve includes a proximal shaft, a distal shaft coupled to a distal portion of the proximal shaft, and a pressure sensor coupled to the distal shaft. The proximal shaft includes a distal portion configured to extend through a stenosis in a vessel. The distal portion of the proximal shaft includes a radially expanded configuration having a first diameter and a radially collapsed configuration having a second diameter, wherein the first diameter is larger than the second diameter. The distal shaft includes a guidewire lumen configured to receive therein.