Simultaneous estimation of cortical bone thickness and acoustic wave velocity using a multivariable optimization approach: Bone phantom and in-vitro study

The paper presents a method that allows the thickness of a compact bone layer and longitudinal wave velocity in the bone to be determined simultaneously with the use of reflected waves, with particular emphasis on the case of layers when the propagation time through the layer is shorter than the time duration of the interrogating pulse. The proposed method estimates simultaneously the thickness of the cortical bone layer and acoustic wave velocity by fitting the temporal spectrum of the simulated reflected wave to the spectrum of the reflected wave measured experimentally. For the purpose of echo-simulations the model of "soft tissue - compact bone layer - cancellous bone" was developed. Next, the cost function was defined as the least square error between the measured and simulated temporal spectra. Minimization of the cost function allowed us to determine the values of the parameters of the cortical bone layer which best fitted the measurements. To solve the optimization problem a simulated annealing algorithm was used. The method was tested using acoustic data obtained at the frequency of 0.6 MHz and 1 MHz respectively for a custom designed bone mimicking phantom and a calf femur. For the cortical shell of the calf femur whose thickness varies from 2.1 mm to 2.4 mm and velocity of 2910 m/s, the relative errors of the thickness estimation ranged from 0.4% to 5.5%. The corresponding error of the acoustic wave velocity estimation in the layer was 3.1%. In the case of artificial bone the thickness of the cortical layer was equal to 1.05 and 1.2 mm and acoustic wave velocity was 2900 m/s. These parameters were determined with the errors ranging from 1.9% to 10.8% and from 3.9% to 4.5% respectively.

Multi-frequency axial transmission bone ultrasonometer

The last decade has seen a surge in the development of axial transmission QUS (Quantitative UltraSound) technologies for the assessment of long bones using various modes of acoustic waves. The condition of cortical bones and the development of osteoporosis are determined by numerous mechanical, micro-structural, and geometrical or macro-structural bone properties like hardness, porosity and cortical thickness. Such complex manifestations of osteoporosis require the evaluation of multiple parameters with different sensitivities to the various properties of bone that are affected by the disease. This objective may be achieved by using a multi-frequency ultrasonic examination The ratio of the acoustic wavelength to the cortical thickness can be changed by varying the frequency of the ultrasonic pulse propagating through the long bone that results in the change in composition of the induced wave comprised of a set of numerous modes of guided, longitudinal, and surface acoustic waves. The multi-frequency axial transmission QUS method developed at Artann Laboratories (Trenton, NJ) is implemented in the Bone Ultrasonic Scanner (BUSS). In the current version of the BUSS, a train of ultrasonic pulses with 60, 100, 400, 800, and 1200 kHz frequencies is used. The developed technology was tested on a variety of bone phantoms simulating normal, osteopenic, and osteoporotic bones. The results of this study confirm the feasibility of the multi-frequency approach for the assessment of the processes leading to osteoporosis.

Osteoporosis detection in postmenopausal women using axial transmission multi-frequency bone ultrasonometer: clinical findings

The objective of this study was to evaluate if the Bone UltraSonic Scanner (BUSS) can detect osteoporosis in postmenopausal women. BUSS is an axial transmission multi-frequency ultrasonometer for acquisition of wave propagation profiles along the proximal anterior tibia. We derived 10 diagnostically significant BUSS parameters that were then compared with the DXA spine T-score, which was used in this study as the "gold standard" for the assessment of osteoporosis (T-score<-2.5). BUSS wave parameters were studied in 331 postmenopausal women examined by 9 trained operators at 3 clinical sites with use of 3 devices. The efficiency of each BUSS parameter in osteoporosis detection was assessed using a receiver operating characteristic curve analysis. Area under the curve (AUC) for each of 10 parameters ranged from 58.1% to 70.2%. Using these parameters a linear classifier was derived which provided at its output 83.0% AUC, 87.7% sensitivity and 63.2% specificity to DXA-identified osteoporosis. The results of this study confirm BUSS's capability to detect osteoporosis in postmenopausal women.

Low 25-hydroxyvitamin D levels and low bone density assessed by quantitative ultrasonometry in a cohort of postmenopausal Italian nuns

This study was aimed at evaluating the effect of clothing style on bone mass and fractures in 70 postmenopausal nuns residing in a monastery in Naples. Sixty healthy women matched for age, body mass index, and menopausal status were enrolled as controls. Each participant underwent measurement by quantitative ultrasonometry (QUS) using a DBM Sonic Bone Profiler (IGEA S.p.A., Carpi, Modena, Italy) at proximal phalanges, responded to questionnaires regarding lifestyle, calcium intake, medical history, including clinical fragility fractures, and was submitted to routine biochemical assessment. A significant reduction in ultrasonometric parameters of bone mass was found in nuns compared with controls (p from 0.007 to <0.0001). 25-hydroxyvitamin D (25-OH vit D) levels were reduced by more than 50% in nuns (9.8 ± 4.2 vs 23.5 ± 5.7 nmol/L; p < 0.0001), whereas their estimated daily calcium intake was higher (1.004 ± 0.23 vs 0.721 ± 0.25 g of controls; p = 0.0007). Age at menopause was significantly lower in nuns' group (p = 0.016). Incidence of fractures was higher in nuns (39% vs 10%; p = 0.0029), and the best predictors of fractures were age at menopause (odds ratio [OR]: 1.12; 95% confidence interval [CI]: 1.01-1.30), amplitude-dependent speed of sound T-score (OR: 1.15; 95% CI: 1.03-1.63), and bone transmission time T-score (OR: 1.30; 95% CI: 1.15-1.81). This study documented low 25-OH vit D levels, increased frequency of clinical fractures, and low bone mass detected by QUS in Southern Italian nuns.