  We report a method to monitor the setting process of bone-graft substitutes
(calcium sulphate) using ultrasonic backscattering techniques. Analyzing the
backscattered fields using a pulse-echo technique, we show that it is possible
to dynamically describe the acoustic properties of the material which are
linked to its setting state. Several experiments were performed to control the
setting process of calcium sulphate using a 3.5-MHz transducer. The variation
of the apparent integrated backscatter (AIB) with time during the setting
process is analyzed and compared with measurements of the speed of sound (SOS)
and temperature of the sample. The correlation of SOS and AIB allows to clearly
identify two different states of the samples, liquid and solid, in addition to
the transition period. Results show that using backscattering analysis the
setting state of the material can be estimated with a threshold of 15 dB. This
ultrasonic technique is indeed a first step to develop real-time monitoring
systems for time-varying complex media as those present in bone regeneration
for dental implantology applications.
