Medical devices are made visible under ultrasonic or magnetic imaging techniques by adding a series of features on their surfaces. The features are desirably placed at more than one angle to the surface in order to enhance the visibility of the surface. Laser-machining can make a series of depressions or voids that are symmetric with respect to the surface and another series of depressions or voids that are non-symmetric. The pattern of voids is also varied by using more than one size of void, the depth of the voids, and the distribution of voids, i.e. more voids in some areas than others.