Optimal CT settings for bone evaluations.

In CT densitometry the precision, sensitivity and accuracy of the procedure are limited by photon noise, the degree of tissue differentiation and artefacts caused by the finite size of the x-ray beam, hardening of the x-rays and scattered radiation. These artefacts are highly dependent on the CT settings, such as x-ray spectrum and effective energy, intensity of photon flux and collimation of the beam. To monitor the progression of a disease or the efficacy of a therapy, longitudinal studies are necessary; thus the radiation dose per examination should be kept at a minimum. For bone evaluation of the peripheral skeleton it is shown that there is a narrow optimal energy range of 30-40 keV where a dose below 150 mu Sv is sufficient to detect a change of 1% in trabecular bone density at the 0.1 confidence level. Concomitantly accuracy might be better than 1% if adequate beam collimation is applied.