Abstract: In a computer tomography system, a flexible calibration phantom is utilized simultaneously with analysis of a patient to ensure accuracy of imagry and to facilitate interpretation of tomographs created. The flexible calibration phantom is preferably placed directly upon a patient between a radiation source and a radiation detector. It includes two solid and flexible samples of reference materials, each having a substantially uniform density, and a solid and flexible encasement surrounding the samples of reference material. The encasement has a substantially uniform density different than that of each of the samples of reference material, and the combination provides suitable reference points for proper analysis of tomographs obtained.