The purpose was to obtain reliable measures of fat and muscle tissue areas with CT at a reduced radiation dose level. Repeated CT-scans with four different levels of reduced radiation dose were perfomed on a water phantom and a volunteer at the L4-L5 level. Dose measurements were performed in a phantom and free in air. A histogram model function for fat, muscle and partial volume affected voxels was proposed and used in the analysis of image noise. The result was at most a 25-fold reduction in radiation dose with an image noise of 40 HU but only a minor influence on the tissue area determination [corrected].