[X-ray bone densitometry. Study of in vitro and in vivo reproducibility]

We studied the reproducibility in vitro and in vivo of a new bone densitometer (HOLOGIC QDR-1000, software version 4.03) which uses an x-ray source at two different levels of energy. Short and long term coefficient of variation (c.v.) in vitro is less than 0.5%. In vivo c.v. is less than 1% in normal body weight subjects and less than 3% in obese subjects. The ingestion of 500 mg of calcium element did not modify bone mineral density (BMD), while 1000 mg determined an increase of BMD equal to 2.6% and 1.5% in the two subjects examined. The increase of water thickness on a three femoral heads phantom caused a progressive reduction of bone mineral content (BMC) and BMD until 12.1% less than basal value and an increase of c.v. from 0.1% to 1%. The addition of oil to water at different percentages determined a slight increase of both BMC and BMD, till 3.5% with 66% of oil in water, if compared with the values obtained with water alone. The reduction of soft tissue around the bone determined a progressive decrease of BMD reaching 3.4% less than basal value when the reduction was 30%.