A comparative study of CT densitometry of vertebral cancellous bone, abdominal aorta, paravertebral fat and the relative fat volume

Fluctuations are observed in CT densitometry of cancellous bone of the lumbar vertebra in relation to age and sex and also per age/sex group. An investigation was carried out in 119 patients to possibly detect comparable fluctuations in CT measurements of other tissues. The spongiosa of the fourth lumbar vertebra, the abdominal aorta, paravertebral fat and the ratio fat volume/total irradiated volume were compared in the slice plane through the middle of the fourth lumbar vertebra. Calibration was performed using a water phantom. A correlation between the mentioned parameters could not be demonstrated. The relation between Bone Mineral Density (BMD) and age and sex showed the same values as known from the literature, being representative for a normal population. Using the aorta as a reference (which in fact is related to water) a similar curve is found as in Cann and Cann et al. The density of the aorta showed a constant value, varying between 38 and 50 HU with a mean of 45 HU. Extreme values were only found with streak artefacts. It seems useful to use the aorta values as a reference to measure the relative value of vertebral cancellous bone.