We have carried out measurements of the frequency dependence of ultrasonic attenuation in the range 0.2-1 MHz in in vitro samples of bovine cancellous bone and in vivo 0s calcis heel bones. A comparison of the results allows us to infer that the in vivo measurements are dependent on the bone mineral content of the 0s calcis. The bone mineral content has been determined in this way for three female populations and indicates that the technique allows determination of bone loss and the study of the onset and progress of osteoporosis. The technique has the great advantage of health safety over radiographic and neutron activation analysis. It may also prove to be more sensitive to small changes in bone mineral content. Engineering in Medicine MEP Ltd 1984at UNSW Library on August 5, 2015 eim.sagepub.com Downloaded from

The laser generation d ultrasound in solids is reviewed with particular emphasis on the application of this unique ultrasonic source. Three regimes for the generation of ultrasound in solids using lasers in the visible near infrared wavelength region exist: thermoelastic, plasma and constrained surface source regimes. The mechanism for ultrasonic generation in each of these regimes is given. Recent experimental investigations into laser-generated unrasound are also described, including a description d a different mechanism for the generation of ultrasound in solids using a COn laser. Finally, the many applications of lasergenerated ultrasound are reviewed. These applications range from nondestructive testing to the determination of candle flame parameters. Possible future applications are also outlined.

Main outcome measures-Broad band ultrasonic attenuation (BUA) index, Clifton assessment procedures for the elderly test (for cognisance), and mobility on a six point scale, and fracture of the hip in the subsequent two year period.Results-73 Women fractured their hip during the two years. Their mean age was not significantly different from that of the women who did not have a fracture (85.3 (SD 5.6) v 83-9 (6.3); p=0.07), but their mean BUA index (40.3 (19-3) v 50*9 (22.2) db/MH2), and score for cognisance (median 19 (interquartile range 10-5-27-0) v 24 (17-30)) were significantly lower (both p<0001). These variables had independent associations with fracture of the hip. Women with fractures had a significantly lower score for the psychomotor component of the cognisance test (4.5 (1-8) v 7 (2-10); p<0.0025 and were significantly more mobile (1 (1-3) v 3 (1-6); p<002). Subdividing women according to high, medium, and low scores for BUA index and cognisance testing disclosed a high risk group (118 women) with low BUA index and cognisance score, whose incidence offracture was 12-8%; in the group at lowest risk (136 women) with high BUA index and cognisance score, the incidence of fracture was only 1-5% (relative risk (95% confidence interval -2-0 to 35.5)). Further analysis showed that those most at risk were, additionally, most mobile but that less mobile women with good cognisance had a low incidence of fractures, regardless of the BUA index, (1-2%, high index, v 0 9%, low index).Conclusions-Elderly women most at risk of sustaining hip fractures were those with low BUA index, low cognisance test score, and high mobility.

The generation of acoustic waves in metals by pulsed laser irradiation over a wide range of material conditions has been studied. Capacitance transducers have been used to obtain quantitative measurements of the amplitude of bulk acoustic waveforms where the laser beam was directed onto free metal surfaces in the presence and absence of surface plasmas, and onto modified metal surfaces. The application of acoustic wave propagation theory has allowed theoretical waveforms to be determined. By combining data for thermoelastic and normal force sources, waveforms have been produced that follow closely those measured experimentally.

Quantitative experimental measurements have been made in the study of thermoelastic generation of elastic waves in a metal by unfocused laser radiation. A calibrated wide-band detection system, incorporating a capacitance transducer, has enabled acoustic waveforms to be recorded with a minimum of distortion. From these measurements, a theoretical model has been developed. The transfer function of the metal block has been deconvoluted to give the acoustic source function, which was modeled as a rapidly expanding point volume of material. The thermoelastic source generated longitudinal (L) and (S) waves, but the latter predominated at the epicenter, where, in experiments presented here, both wave amplitudes L and S were proportional to the total absorbed energy in the laser pulse.