Abstract: A table top is positioned on a base for supporting a patient between a radiation source and a radiation detector of the computed tomography system. The table top has a supporting surface which is translatable in the longitudinal direction of the computed tomography system. The table top includes a plurality of samples of reference materials which extend uniformly and longitudinally along the underside of the supporting surface. The reference materials are stable and homogeneous throughout their length and have properties which correspond to known radiation attenuation coefficients. Each computed tomography slice will include a slice of each of the samples of reference material. The resulting image will display a cross sectional slice of each samples which can be used to calibrate the system or correlate the images of the patient. The table top may be equipped with a removable portion.