Ultrasonic measurement: an evaluation of three heel bone scanners compared with a bench-top system

Three commercial ultrasound bone scanners designed for os calcis measurements (Lunar Achilles, C.U.B.A. "Research" and UBA 575) were compared using the Leeds Ultrasonic Bone Phantoms. The porosity of the phantoms ranged from 50% to 83% with velocities between 1490 and 1621 m s-1 and broadband ultrasound attenuation (BUA) values in the range 46-115 dB MHz-1. The three devices tested were able to discriminate porosity differences of at least 3%, although the values obtained for the propagation parameters varied widely. Velocity differences of up to 38 m s-1 and BUA variations of up to 33 dB MHz-1 were found, although a relationship was identified between the velocity and BUA measurements. In some cases, the variation can be attributed to differences in the measurement technique adopted, although there also seem to be detailed differences in the definition of the parameters themselves. The variation between different devices from the same manufacturer (Lunar) was also studied. Measurements taken from five devices showed variation in velocity values of up to 25 m s-1 (SD 10.8 m s-1) and in BUA values of up to 11 dB MHz-1 (SD 4.3 dB MHz-1). We conclude that the variation both between manufacturers and between nominally identical machines may be of clinical significance. Both users and manufacturers need to consider urgently the introduction of quality standards and consensus definition of terms and techniques. The fact that all machines studied have been superseded commercially does not invalidate these conclusions, since many of the devices tested remain in clinical use and there is no evidence of fundamental change in manufacturers' procedures.