A catheter for measuring a fractional flow reserve includes a proximal shaft, a distal shaft coupled to the proximal shaft, a pressure sensor coupled to the distal shaft, and at least one pressure sensor wire operably connected to the pressure sensor. The proximal shaft includes a radially expanded configuration and a radially collapsed configuration, wherein the proximal shaft has a first outer diameter in the radially expanded configuration and a second outer diameter smaller than the first outer diameter in the radially collapsed configuration. The distal shaft defines a guidewire lumen configured to receive a guidewire therein.