Dual energy x-ray absorptiometry is the current technique used for bone mineral density measurements and recently for soft tissue analysis. The technique of dual energy absorptiometry was investigated as a method of measuring heavy elements induced or found in human body, in particular platinum and iodine, by using two energies, one energy below the k-edge and the other above it. The accuracy of iodine measurement was predicted to be 3.2, which is comparable with other methods. The discrimination between different tissue types was investigated by building a phantom and scanning it at 180 different angles using the Hologic QDR-1000/W system. The raw data files were analysed and tomographically reconstructed to produce 6 different axial images from beams with different energy spectra, produced by a combination of two x-ray voltages and three beam filters. The final part of the thesis concerns a new method to solve the beam hardening problem. A new exponential beam hardening formula was derived first by simulation work and then tested on real phantom. The measured attenuations were combined in a polynomal (quadratic) expression, which was optimised using a least squares program, and separation between different tissue components was successfully carried out on the data from the Hologic system. Measuring the bone density with the new procedure can achieve an r.m.s error of 0.26% over a wide range of body composition, and a maximum error of 1.5%, which represents a significant improvement over previous published work.