Change in trabecular bone mineral content is an early indicator of change in metabolic function. CT, with its superior contrast discrimination, is a major tool in the evaluation of trabecular bone in the central skeleton. All CT scanners require a standard of reference to properly perform quantitative tissue analysis. The Model 004 takes into account all known variability factors that can adversely affect the use of CT for bone densitometry. The CIRS anthropomorphic phantom design minimizes beam hardening effects and variances associated with scan field position. The Model 004 is the only CT densitometry system to provide a solid epoxy matrix with true calcium hydroxyapatite references. The system provides extremely stable density references and does not require special extrapolations or complex calculations. The reporting software runs on a PC or Macintosh platform and does not require CT scanner time. The Model 004 system is designed to be used immediately on any whole body CT scanner and does not require special setups or software configurations.