Apparatus and methods for determining a type of a material in a region within a vascular system of a patient and/or a distance to the material are provided. At least one source fiber is provided that supplies light from a light source to a region within a vascular system of a patient. At least one return fiber is provided to receive light reflected from the region within the vascular system. At least one controller is provided to determine at least one property of the region within the vascular system from the reflected light, and to determine a type of a material in the region within the vascular system and/or an indication of a distance to the material. Techniques such as laser ablation may then be performed based on the determined material type and/or distance to remove unwanted buildup, deposits, etc., while avoiding harmful results such as tearing of tissue.