The effects of physical exercise on the status of bone mineralization for a population of lifetime athletes were investigated. The bone mineral content of the radii of experienced male tennis players was measured. The bone mass of the radius of the playing arm (mean, 1.37 g/cm) was greater than that of the nonplaying arm (mean, 1.23 g/cm) in all but one person. The results were compared with data for a nonathletic (normal) population. The quantity of bone mineral present in the playing arms of the athletic population was greater than that of the dominant arms of nonathletes, which suggests that playing tennis during a lifetime may produce a localized increase in bone mineralization that is greater than that found in nonathletes.

Principal-components analysis is used to obtain a set of parameters for dual-energy radiography that completely describes the attenuation coefficient of any tissue over a given energy range. These parameters are the weighted averages of the densities of the elements present in a substance. Principal-components (PC) parameters are calculated for several soft tissues from measured attenuation coefficients published by Phelps et al. The calculated PC parameters are compared to the more conventional dual-energy representations of the attenuation coefficient: (1) the electron density/effective atomic number (or Compton/photoelectric) representation and (2) the equivalent water/equivalent aluminum thickness representation. The principal-components parameters represent the attenuation coefficients more accurately, and are more stable than the currently used parameters. In addition, these new parameters are sensitive to differences in the chemical composition and density, whereas the previous representations are primarily sensitive to changes in the density. It is concluded that the principal-components method provides a more sensitive and accurate indicator of changes in tissue composition than previous characterizations of the linear attenuation coefficient. The principal-components method provides a means for improving the accuracy of the characterization of tissues in dual-energy computed tomographic imaging and in dual-energy digital radiography.

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Using a method combining the velocity of ultrasound and photon absorptiometry in the human radius in vivo, the authors measured the speed of sound in bone (U) and bone mineral content (BMC). From these measurements and a "simple" bone model, they then computed the bone mineral density, compact bone density, and modulus of elasticity. The accuracy of these parameters and of the bone model is assessed, and normal values for each parameter are given and compared with published values. The authors feel that a combination of U and BMC permits better discrimination between normal and abnormal in patients with osteoporosis or metabolic bone disease than either parameter alone.

The modulus of elasticity was derived by combining the velocity of ultrasound measurements and photon absorption (Norland-Cameron method) in human cortical bone (proximal radius) in vivo. The results compare favorably with published values of the elasticity modulus obtained in vitro. Values obtained for a heterogeneous group of patients with bone and joint complaints differed from those of normal volunteers.