Quantitative computed tomography for spinal density measurement. Factors affecting precision.

Quantitative computed tomography (QCT) was performed in duplicate on 84 patients to test the short-term precision of the technique. Statistical analysis of the data revealed that precision was not a function of spinal density. It appeared to be worse in osteopenic individuals only when expressed as a percentage. Precision was slightly better in male than in female patients. There is a 90% likelihood that a duplicate measurement will fall within 20 CT units of the first determination in female patients and within ten units in male patients.