Photon absorptiometry of bone after successful renal transplantation.

Photon absorptiometric measurements of the right lower femur were carried out at regular intervals of one to three months in 58 recipients of renal transplant. (1) During the first six months after transplant 57% showed a significant and abnormal rate of loss of bone mineral (mean 11.7% per year. +/- 1.1% S.E.M.) while 30 months' after transplantation only 17% showed such a significant loss (p=0.025). (2) Eighteen months after transplantation both male and female recipients of transplants had a significantly lower mean bone mineral index than controls (p less than 0.001). (3) Male patients who developed new post-transplant fractures had a lower mean bone mineral content compared with age and sex-matched controls taken from transplant recipients without such fractures (p less than 0.01). Similarly male patients with post-transplant fractures had a significantly longer mean period on regular haemodialysis (p less than 0.05) compared with patients without such fractures. Regular photon absorptiometric measurements provide an accurate, informative and non-invasive technique for following changes of bone mineral content after successful renal transplantation.     

Photon absorptiometry for non-invasive measurement of bone mineral content

Bone mineral content of the distal radius was determined in 106 patients by single photon absorptiometry using iodine-125 monochromatic source. The technique provided a reliable means to assess the degree of mineral loss in conditions such as osteoporosis, renal osteodystrophy in patients on chronic maintenance dialysis, subjects on long-term steroid therapy, and those with diabetes mellitus. It is more sensitive than conventional radiography and completely noninvasive compared to bone biopsy. It is suggested that photon absorptiometry is a simple, sensitive, and reliable technique for assessment and follow-up of the bone mineral content in a host of disorders associated with bone demineralization.     

Photon absorptiometry of hydrocarbons

Measured and parametrised values of the attenuation coefficients of several hydrocarbons having a hydrogen-to-carbon weight ratio in the range from 0.05 to 0.16 and for photon energies 33, 75, 145, 279 and 662 keV are presented. The values are compared and possible trends and applications discussed.     

Dual-photon Gd-153 absorptiometry of bone

Dual-photon absorptiometry with gadolinium 153 was used to measure the mineral content of lumbar vertebrae in cadavers, excised vertebrae with marrow, and dry, marrow-free vertebrae. The error introduced by the surrounding soft tissue of cadavers was 3%, and the error in determining mineral mass or density in excised vertebrae was about 5%. The correlation coefficient between the results of Gd-153 and corrected iodine 125 (single-photon) absorptiometry on 24 femoral necks was 0.99, and the predictive error was 3.7%. Dual-photon absorptiometry accurately indicates bone mass and bone density and is only slightly affected by either surrounding tissue or fat changes in bone marrow.     

Triple-photon energy absorptiometry in the measurement of bone mineral

The feasibility of determination of bone mineral content using a triple-photon absorptiometric technique is presented. Using three different photon energies it is possible to correct the measured 'bone mineral' value for fat and lean soft tissue. The theoretical basis of the method, as well as the experimental determination of mass attenuation coefficients, is described. It is shown that the results are reproducible within 5 per cent, which means that the method could be of value in the management of metabolic bone diseases.     

Comparison of single- and dual-photon absorptiometry in postmenopausal bone mineral loss

We describe a single photon absorptiometric (SPA) technique, which enables differential estimation of the rates of loss from trabecular and cortical bone. Ten scans are obtained in the forearm: six in an area with about 7% trabecular bone and four scans in the adjacent distal area with a trabecular bone content of 25%. By comparing bone masses of these two sites in 19 postmenopausal and 53 premenopausal women, the postmenopausal trabecular bone loss was estimated to be approximately seven times greater than cortical loss within the first years of cessation of regular vaginal bleeding. On a group basis the bone loss at the distal forearm scan site (by SPA) corresponded closely to the spinal bone loss (by dual-photon absorptiometry). The reproducibility of the two scan sites in the forearm was 1-1.5% (CV%), which makes the method suitable for longitudinal studies. Corrections for variations in fatty tissue covering can be made without deterioration of the reproducibility. The high precision can only be achieved with a good calibration procedure; if calibration is not done the reproducibility error increases two- or threefold.     

Pitfalls of bone mineral density evaluation by dual-photon absorptiometry.

Material absorbing photons aligned with the lumbar vertebrae can create falsely elevated measurements of bone mineral density during dual-photon absorptiometry. Three cases illustrating this phenomenon are presented. Although bone mineral density was overestimated in each case, calculated fracture risk was normal in two cases and greatly increased in the third. Photon-absorbing material can create overestimates of bone mineral density during dual-photon absorptiometry, even when a greatly increased fracture risk is computed.