Osteopenia associated with renal transplantation remains a problem in the cyclosporine era. The loss of vertebral bone in our subjects was due to an imbalance in bone remodeling consistent with a toxic effect of glucocorticoids.

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Several methods are presently available for measuring the mineral content of bone. Those in widespread use include dual-photon absorptiometry and quantitative CT. The feasibilIty of using dual-energy digital chest radiography for determination of the mineral content of posterior ribs on digital chest images was studied by using a prototype unit The resufts showed a significant difference in the mineral density of the posterior ribs of control subjects and those of patients who had osteoporosis (251.1 ± 36 mg Ca2 / cm2 of rib vs 158.8 ± 48 mg Ca2 /cm2, p .01) and a close correlation with values obtained by dual-photon absorptiometry of the lumbar spine (r = .77). The results suggest that this technique Materials and MethodsImages of the chest were obtained in posteroantenor projection with the second-generation Picker scanning-slit dual-energy chest unit (Picker International, Cleveland, OH). The charactenstics of this unit have been described in detail elsewhere [1 -5]. Briefly, an X-ray fan beam is created by a 0.5-mm slit collimator placed between the patient and the focal spot of the Xray tube; the beam is aligned with a 1 .0-mm collimator placed between the patient and the detector array (consisting of 1 024 vertical pixels). The collimators and the detector array are linked mechanically and pivot about the focal spot as the beam scans horizontally across the patient (Fig. 1). A key feature of this device is its linear detector array of 1024 elements. Each element is a low/high atomic sandwich:The first section consists of a low-atomic-number phosphor (optically coupled to a photodiode) that preferentially absorbs the lower-energy photons emerging from the patient; the higher-energy photons penetrate the first section and strike the rear section, which is composed of a high-atomic-number phosphor (also optically coupled to a photodiode) (Fig. 2). In this way, low-and high-energy images are acquired simultaneously. These in turn are summed to obtain a standard digital image (comparable to a conventional radiograph) (Fig. 3) and are processed to obtain soft-tissue (bone cancelled, Fig. 4A) and bone (soft-tissue cancelled, Fig. 4B The posterior ribs were selected as the first site of measurement;they are easily accessible and provide a reproducible location for the parallelogram technique. The efficacy of using the nbs in screening for osteoporosis is suggested by dual-photon absorptiometry studies that have noted a parallel reduction in the mineral content of the ribs and spine in patients who have osteoporosis and in elderly persons [6,7].

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