Estimation of Thickness and Speed of Sound in Cortical Bone Using Multifocus Pulse-Echo Ultrasound

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.ν 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 inclinationdependent transmission losses at the bone surface. Moreover, the dependence of Ct.ν 11 on both porosity and pore density was observed. Ct.Th and Ct.ν 11 obtained ex vivo showed a high correlation (R2 > 0.99) with reference values. The ex-vivo accuracy and precision for Ct.ν 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.ν 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. Index Terms-Medical beamforming and beam steering, medical signal and image processing, medical tissue characterization, pulse-echo ultrasound. I. INTRODUCTIONO STEOPOROSIS (OP) is one of the most important global health problems of our aging population, which reduces mobility and quality of life, increases mortality,

Bulk Wave Velocities in Cortical Bone Reflect Porosity and Compression Strength

“…Measuring velocities in vivo can be achieved, e.g. with axial transmission (Foiret et al, 2014) or quantitative imaging (Renaud et al, 2018;Nguyen Minh et al, 2020) and can complement US diagnosis of cortical bone fragility.…”

“…Ultrasound (US) methods have been developed as an alternative to DXA to provide a non-ionizing, portable, and affordable diagnostic tool for osteoporosis (Laugier and Haïat, 2011;Raum et al, 2014). Since cortical bone plays an important role in bone resistance (Mayhew et al, 2005;Holzer et al, 2009), and because a large part of bone loss arises from the cortical compartment (Zebaze et al, 2010), several US approaches have been specifically designed to assess cortical bone (Karjalainen et al, 2008;Sai et al, 2010;Minonzio et al, 2019;Renaud et al, 2018;Nguyen Minh et al, 2020;Grimal and Laugier, 2019). These approaches aim at evaluating cortical bone thickness or material properties (e.g., mass density, elasticity, bulk wave velocities), which are dramatically altered with bone pathologies.…”

Decreased Compressional Sound Velocity Is an Indicator for Compromised Bone Stiffness in X-Linked Hypophosphatemic Rickets (XLH)

“…The absolute deviation of individual values from age and gender-matched controls may be a suitable indicator for the severity of the mineralization deficit. However, the individual parameters contributing to the reduction of ν FAS in XLH patients remain subject to further studies, which should also integrate more recent techniques that are able to measure Ct.Th, Ct.Po, and speed of sound independently (24,36,37) as well as second-generation HR-pQCT, which can provide site-matched measurements at central shaft regions. As BDAT and other ultrasound-based quantitative bone imaging modalities use no ionizing radiation, they would be ideal for the treatment monitoring of children and young adults with bone diseases.…”

Estimation of Cortical Bone Microstructure From Ultrasound Backscatter

“…We anticipate that the evaluation of the pore diameter distribution has the potential to establish novel biomarkers that are sensitive to discriminate pathological tissue remodeling from normal age and gender specific alterations prior to the reduction of bone strength. The latter is predominantly predicted by the reduction of cortical thickness [37], which can be measured with the same system [44] or similar multi-channel systems [4] in combination with the compressional sound velocity by means of refraction corrected imaging, or alternatively by means of axial transmission ultrasound [3,15]. Thus, the combined assessment of cortical thickness, sound velocity, and pore size distribution in a mobile, non-ionizing measurement system could have a major impact to prevent osteoporotic fractures.…”