Mechanisms of Interaction of Ultrasound With Cancellous Bone: A Review

Abstract

Ultrasound is now a clinically-accepted modality in the management of osteoporosis. The most common commercial clinical devices assess fracture risk from measurements of attenuation and sound speed in cancellous bone. This review discusses fundamental mechanisms underlying the interaction between ultrasound and cancellous bone. Because of its two-phase structure (mineralized trabecular network embedded in soft tissue-marrow), its anisotropy, and its inhomogeneity, cancellous bone is more difficult to characterize than most soft tissues. Experimental data for the dependences of attenuation, sound speed, dispersion, and scattering on ultrasound frequency, bone mineral density, composition, microstructure, and mechanical properties are presented. The relative roles of absorption, scattering, and phase cancellation in determining attenuation measurements in vitro and in vivo are delineated. Common speed of sound metrics, which entail measurements of transit times of pulse leading edges (to avoid multipath interference), are greatly influenced by attenuation, dispersion, and system properties including center frequency and bandwidth. However, a theoretical model has been shown to be effective for correction for these confounding factors in vitro and in vivo. Theoretical and phantom models are presented to elucidate why cancellous bone exhibits negative dispersion, unlike soft tissue, which exhibits positive dispersion. Signal processing methods are presented for separating "fast" and "slow" waves (predicted by poro-elasticity theory and supported in cancellous bone) even when the two waves overlap in time and frequency domains. Models to explain dependences of scattering on frequency and mean trabecular thickness are presented and compared with measurements. Anisotropy, the effect of the fluid filler medium (marrow in vivo or water in vitro), phantoms, computational modeling of ultrasound propagation, acoustic microscopy, and nonlinear properties in cancellous bone are also discussed.

Bone Chemical Composition Assessment with Multi-Wavelength Photoacoustic Analysis

“…where β is the thermal coefficient of volume expansion, c is the SOS of tissue, and C p is the heat capacity at constant pressure; k is a constant accounting for the impulse response of the detection system; η th is the heat conversion efficiency; µ a is optical absorption of bone tissue; F 0 is the light fluence generated by the laser; µ e f f is the effective optical attenuation coefficient in the bone; e −µ e f f (λ)•r is the light attenuation in the bone; α is the ultrasound attenuation coefficient in the bone; e −α•(z 0 −r) is the ultrasound attenuation in the bone. Since both the ultrasound and optical attenuation are large in bone tissue [4,31,32], the PA signal received by the transducer is mostly generated from the bone surface (r = 0). Then, the amplitude of the PA signal received by the transducer could be simplified as…”

The feasibility study of the transmission mode photoacoustic measurement of human calcaneus bone in vivo

“…Although the PA signal from a human calcaneus bone received by the transducer in the transmission mode can contain both compressional wave and shear wave, the contribution from the shear wave is minimal. This is mainly due to the fact that the shear wave attenuation in trabecular bone is very high, at approximately 17 dB/mm at 1 MHz according to a previous study [ 49 ]. Hence, the shear wave propagation in human calcaneus, as shown in Fig.…”

“…In 3D simulations of PA signal generation and propagation, we used the elastic wave model provided by the open-source k-Wave MATLAB toolbox [ 48 ]. The propagation medium was isotropic and homogeneous with different propagation speeds, densities, and coefficients of ultrasound attenuation for water, soft tissue, and bone, respectively, as shown in Table 2 [ [49] , [50] , [51] ]. The three-dimensional grid was made of 200, 200, and 400 points along the x (elevation), y (azimuth), and z (depth) directions, respectively.…”

Polyacrylamide hydrogel phantoms for performance evaluation of multispectral photoacoustic imaging systems

“…This ensures that the phantoms are also suitable for bimodal ultrasound and photoacoustic imaging [ 46 , 47 ]. PAA acoustic properties were characterized using a broadband through-transmission substitution technique [ 48 , 49 ] in a tank containing deionized, degassed water. This technique has been previously validated against time-delay spectrometry measurements [ 50 ].…”