Ultrasonic bone testing apparatus with repeatable positioning and repeatable coupling

An ultrasonic bone testing apparatus has a foot well assembly and a shin guide assembly which are mechanically coupled to secure a foot and lower leg of patient during the measurement process. The shin guide assembly includes a molded form which has a shin restraint section, an instep guide section and a foot restraint section. An instep support guide having sliding blocks is mounted on the molded form. The sliding blocks are inserted into respective channels of respective bridge brackets of the foot well assembly to attach the shin guide assembly to the foot well assembly. The apparatus further includes a transducer drive mechanism for positioning a pair of transducer assemblies. A controller automatically modifies the positioning of the transducer assemblies until ultrasonic coupling is achieved and a receiving transducer receives a signal of a predetermined quality. A coupling pad and acoustical delay line of the transducer assembly provide a waveguide function to collimate an acoustical beam a sufficient distance along a propagation axis to allow wavefronts to evolve onto a more uniform intensity pattern. The elastomer coupling pad has an angled surface which expels air bubbles from a contact area when pressure is applied to the pad.