A method of removing tissue in a body lumen includes advancing a tissue-removing catheter over a guidewire in the body lumen to position a distal end of the catheter adjacent the tissue and a proximal end portion of the catheter outside of the body lumen. The catheter includes an elongate body, a tissue removing element mounted on a distal end portion of the elongate body, and an inner liner disposed within the elongate body. The inner liner defines a guidewire lumen in which the guidewire is disposed during the advancement of the catheter. The method further includes rotating the elongate body and tissue-removing element of the catheter to remove the tissue. Detecting wear of the inner liner caused by the elongate body contacting the inner liner during use.