Intravascular imaging catheters are provided that include a distal sheath portion having a lumen that is configured to optionally receive a guidewire or an imaging assembly. The distal sheath portion may be configured to have dimensions such that when a guidewire is inserted through the lumen and extends through a distal exit port the distal sheath portion may be employed as a microcatheter. External tissue may be imaged at a location at or near the distal end of the catheter enabling for example the controlled imaging of a total occlusion and the positioning of the distal end (and guidewire) within a true lumen associated with a total occlusion. A structural stop may be provided at or near the distal end of the distal sheath portion to prohibit extension of the imaging assembly out of the distal exit port while permitting the extension of the guidewire through the distal exit port.
