1. A method of imaging a subject animal, comprising: treating the animal with an x-ray contrast agent and an optical imaging agent; supporting the animal in an immobilized state; acquiring an x-ray anatomical image of the animal; acquiring an optical, dark-field image of the animal; and registering the x-ray anatomical image and the optical, dark-field image, whereby features of the optical image can be observed in relation to features of the anatomical image.