OMNISENSE 7000S/8000S
Clinical Summary #3
An In-Vitro Investigation of the Dependence on
Sample Thickness of the Speed of Sound Along the
Specimen
C.F. Njeh, D. Hans, C. Wu, E. Kanorovich, M. Sister, T. Fuerst, H.K. Genant
Medical Engineering & Physics 21 (1999) 651-659
The article describes the effect of cortical thickness effect on Speed Of Sound
measurement using Omnisense.
Introduction
Quantitative ultrasound (QUS) has been shown to be a valid technique in the non-destructive
evaluation of the elastic properties of bone tissue in vitro. Since the work of Langton et al. in 1984,
there has been increasing interest in the assessment of bone status in vivo. QUS is particularly
attractive because it is simple, relatively inexpensive, portable, non-invasive and free of ionizing
radiation. As such, QUS has much greater potential for widespread application than standard bone
densitometry approaches.
The Technology
Omnisense generates pulsed acoustic waves at a center frequency of 1.25 MHz
(bandwidth 0.7-1.8 MHz). Four sets of transducers are embodied within the probe.
A pair of transducers acts as transmitters, while the other pair acts as
receivers. When ultrasound waves are incident on a specimen (bone), depending on
the angle of incidence, the waves are reflected, refracted and transmitted. The
refracted wave which propagates along the sample can be measured. The transit
time is defined as the time it takes for the first detectable signal above noise
to arrive at the receiving transducer. According to Snell's Law and the
Principle of Minimal Action, the first signal to arrive always follows a path
which is characterised by the shortest propagation time.
Study Design
The study examined the dependence of SOS measured along the sample by
Sunlight Omnisense™ on the thickness and composition of the bone sample. The
measurements were carried out using Perspex* phantoms and bovine mid and
trochanteric femurs.
Results
SOS was found to depend on the sample thickness (when the thickness is
smaller than the wavelength, approx. 2 mm), shape, and global composition, all
of which define a sample's overall strength. These results concur with the
theoretical predictions.
Conclusion
This study measured the
sensitivity of the Omnisense™ device to sample thickness. Omnisense's proven
sensitivity means that it will also be sensitive to the changes in thickness of
cortical bone that accompany aging and lead to osteoporosis.
*Perspex was used for its
well-known and documented ultrasound properties.
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