In part, the invention relates to catheters, methods, and blood clearing technologies suitable for use in an optical coherence tomography system. The optical coherence tomography system includes a control system, a probe including a catheter defining a lumen and a rotatable optical fiber located within the lumen, a fluid cartridge holder in communication with the lumen of the probe, a pump to move fluid from the fluid cartridge to the lumen of the probe and a motor configured to rotate and pull the optical fiber through the lumen of a blood vessel. The pump and the motor are controlled by the control system. The catheter can include a wall that bounds the lumen of the probe, which defines a flush port and includes a valve in fluid communication with the flush port, the valve configured to permit fluid from the lumen to pass through the wall.
