This invention relates to a mammographic tomography test object (hereinafter referred to as a phantom) and more particularly, but not exclusively, to a mammographic tomography test phantom for use in the verification of image reconstruction positions in digital breast tomosynthesis. The phantom includes a body made from an approximately tissue equivalent x-ray attenuating material; an upper spacer located on top of the body, and a lower spacer located below the body, the spacers being made from a substantially non-compressible material; and a plurality of x-ray opaque granules located at predetermined positions within the body.