A PORTABLE DUAL-ENERGY X-RAY ABSORPTIOMETRY TECHNIQUE FOR THE MEASUREMENT OF BONE-MINERAL IN PRETERM INFANTS

A dual energy x-ray absorptiometry technique has been developed for th e measurement of bone mineral in preterm infants. Two films are taken of the infant's forearm using a standard mobile x-ray set on the ward at two x-ray energies. Included in the field of view is a double step wedge made of aluminum and Perspex. The images are digitized by viewin g them on a light box with a TV camera. The bone mineral content in th e forearm can then be mapped by the measurement of light intensity in matching pixels of the two films and comparison with the intensities i n the step wedge. The bone mineral concentration in the radius, expres sed as bone mineral per unit length (mg/mm), is calculated. The techni que has been tested using phantoms of calcium hydroxylapatite set in a tissue equivalent material and in Perspex. It has been shown that the reproducibility of the technique is approximately 7% and that there i s a systematic underestimate of bone mineral of about 17%. The techniq ue has been shown to be linear up to a bone mineral concentration of 8 mg mm(-1). Longitudinal studies for 14 infants that show an initial 6 -wk period of demineralization after birth with a subsequent mineraliz ation phase are reported.