A system includes an optical interferometer, an interference detector, and a controller. The optical interferometer includes a measurement arm, a reference arm, and an optical splitter. The measurement arm has a probe. The arms are coupled to receive light from the optical splitter and to cause light outputted by the arms to interfere. The interference detector is coupled to receive a portion of the interfering light to determine information representative of a location, an orientation, or a velocity of a portion of the patient or animal from the received light. The controller is coupled to receive the information and to adjust data collection on the animal or patient in a manner responsive to a change in a relative location, orientation, or velocity between the probe and the portion of the animal or patient.