Estimation of thickness and speed of sound in cortical bone using multi-focus pulse-echo ultrasound.
IEEE transactions on ultrasonics, ferroelectrics, and frequency control(2020)
Abstract
Most bone loss during the development of osteoporosis occurs in cortical bone at the peripheral skeleton. Decreased cortical thickness (
Ct.Th
) and the prevalence of large pores at the tibia are associated with reduced bone strength at the hip.
Ct.Th
and cortical sound velocity, i.e., a surrogate marker for changes of cortical porosity (
Ct.Po
), are key biomarkers for the identification of patients at high fracture risk. In this study, we have developed a method using a conventional ultrasound array transducer to determine thickness (
Ct.Th
) and the compressional sound velocity propagating in the radial bone direction (
Ct.
$\nu _{11}$
) using a refraction-corrected multifocus imaging approach. The method was validated
in-silico
on porous bone plate models using a 2-D finite-difference time-domain method and
ex vivo
on plate-shaped plastic reference materials and on plate-shaped cortical bovine tibia samples. Plane-wave pulse-echo measurements provided reference values to assess precision and accuracy of our method.
In-silico
results revealed the necessity to account for inclination-dependent transmission losses at the bone surface. Moreover, the dependence of
Ct.
$\nu _{11}$
on both porosity and pore density was observed.
Ct.Th
and
Ct.
$\nu _{11}$
obtained
ex vivo
showed a high correlation
$(R 2>0.99$
) with reference values. The
ex-vivo
accuracy and precision for
Ct.
$\nu _{11}$
were 29.9 m/s and 0.94%, respectively, and those for
Ct.Th
were 0.04 mm and 1.09%, respectively. In conclusion, this numerical and experimental study demonstrates an accurate and precise estimation of
Ct.Th
and
Ct.
$\nu _{11}$
. The developed multifocus technique may have high clinical potential to improve fracture risk prediction using noninvasive and nonionizing conventional ultrasound technology with image guidance.
MoreTranslated text
Key words
Bones,Ultrasonic imaging,Cortical bone,Bovine,Acoustics,Transducers,Thickness measurement
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