A catheter for measuring a flow of blood through a body tissue comprises a light emitter for emitting light into the body tissue and at least one light receiver for receiving light reflected in the body tissue and back to the catheter. The light emitter and the at least one light receiver are arranged in the catheter, wherein the catheter comprises a middle piece and a first and a second connection tube. The middle piece has a distal fastening piece for fastening to the first connection tube and a proximal fastening piece for fastening to the second connection tube, wherein the light emitter and the at least one light receiver are arranged in the middle piece.
