1. A mammography compression apparatus comprising: an upper compression assembly comprising a mount comprising parallel, spaced-apart guide elements with a fabric stretched across the guide elements to form a first compression plane, said fabric being permeable to x-rays and to ultrasound; a lower compression assembly comprising an x-ray radiation detector having a surface that forms a second compression plane, said first and second compression planes being adapted to receive a breast therebetween; a mammography apparatus support component to which said upper and lower compression assemblies are attached so that at least said upper compression assembly is movable, relative to said lower compression assembly, in a direction perpendicular to said first and second compression planes in order to compress the breast between the fabric and the surface of the x-ray radiation detector; an ultrasound applicator situated in a space in said upper compression assembly between said guide elements and adjacent to said fabric, said ultrasound applicator being guided and confined in said upper compression assembly by said guide elements so as to be movable on said fabric in at least one direction parallel to said first compression plane, while the breast is compressed by said fabric.