Properties of ultrasonic waves in bovine bone marrow

A Numerical Study on Mechanical Effects of Low-Intensity Pulsed Ultrasound on Trabecular Bone and Osteoblasts

The lack of sufficient mechanical stimulation to the human bone, results in disuse osteoporosis. Low-intensity pulsed ultrasound (LIPUS) promotes fracture healing and the treatment of disuse osteoporosis, but its biomechanical mechanism remains unknown. Simulative research on the mechanical effects of LIPUS on disuse trabecular bone and osteoblasts have been performed. The von Mises stress of disuse trabecular bone and osteoblasts obviously increased under LIPUS irradiation. The average von Mises stress of osteoblasts were two orders of magnitude higher under the irradiation of simulant LIPUS than that without LIPUS irradiation, and the von Mises stress of osteoblasts was positively correlated with the amplitude of sound pressure excitation. The results showed that LIPUS irradiation could obviously improve the mechanical micro-environment of trabecular bone and osteoblasts to alleviate the lack of mechanical stimulation. The results of the research can reveal the biomechanical mechanism of LIPUS in the treatment of disuse osteoporosis to some extent and provide theoretical guidance for clinical treatment of disuse osteoporosis through physical methods.

Patient-specific effects on sonication heating efficiency during magnetic resonance-guided focused ultrasound thalamotomy

PURPOSE

During magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy for refractory tremor, high temperatures must be achieved and sustained for tissue necrosis. We assessed the impact of both patient-specific as well as procedure-related factors on the efficiency of acoustic energy transfer, or heating efficiency (HE).

METHODS

Retrospective analysis of 92 consecutive patients (857 sonications) with essential tremor or tremor-dominant Parkinson's disease treated at a single institution. Temperature elevations at the target were measured for each sonication with MR thermometry. HE of each sonication was defined as the ratio of peak temperature elevation and the delivered energy. HE was analyzed with respect to patient skull features (area, thickness, skull density ratio [SDR]), computed from CT scans, as well as demographic and clinical variables (age, sex, diagnosis, and duration of symptoms).

RESULTS

Across the full range of sonication energies that can be delivered with current devices (up to 36 kJ), average sonication HE was diminished in patients with lower SDR. In individual subjects, there was a progressive loss in HE as sonication energy was titrated up throughout the course of treatment, with a more rapid decline in patients with higher SDR. This energy-dependent loss in HE was not related to procedural factors, namely, the number of previous sonications, or the cumulative energy deposited during previous sonications. In contrast to SDR, neither skull area nor thickness was an independent predictor of average HE or the rate of its decline with increasing energies. In 11% of patients, all of whom with SDR < 0.45, sonication HE fell below the threshold to reach 54°C even with delivery of maximum energy. In contrast, temperatures ≥ 50°C could be obtained in all but one patient.

CONCLUSIONS

SDR is predictive of sonication HE, and determines patient-specific limits on the magnitude of temperature elevation that can be achieved with current devices. These data inform strategies for predictable lesioning in MRgFUS thalamotomy.

Effect of high pressure heating on physical and chemical characteristics of Asian sea bass (Lates calcarifer) backbone

Physical and chemical properties of Asian sea bass (Lates calcarifer) backbone subjected to high pressure heating (autoclaving, 121ºC) for different times (30 min; AT-30; 60 min; AT-60; 90 min; AT-90) were studied. As heating time augmented, the increases in protein, α-amino group and hydroxyproline contents in liquor were attained, while hardness was declined indicating that more organic compounds were leached out from the bone matrix. More pronounced XRD pattern was observed in backbone autoclaved for 90 min as a consequence of nano-hydroxyapatite crystals agglomeration. Extension of high-pressure heating time reduced the organic matters as elucidated by TGA and DTA data. Asian sea bass backbone heated at 121ºC for 90 min using autoclave had the lowered protein and lipid contents but increased ash content with highest calcium (29.65 ± 0.69%), phosphorus (15.80 ± 0.07%) and iron (15.10 ± 0.61 mg/kg) contents, compared to those with shorter heating time. Therefore, pre-heat treatment could reduce the organic compounds and decrease bone hardness for further process, especially for bio-calcium production.

Mechanisms of Interaction of Ultrasound With Cancellous Bone: A Review

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 dependencies 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 poroelasticity theory and supported in cancellous bone) even when the two waves overlap in time and frequency domains. Models to explain dependencies 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.

Influence of cancellous bone microstructure on ultrasonic attenuation: a theoretical prediction

Background

Quantitative ultrasound has been used for the assessment of cancellous bone status. The attenuation mechanisms of cancellous bone, however, have not been well understood, because the microstructure of cancellous bone is significantly inhomogeneous and the interaction between ultrasound and the microstructure of cancellous bone is complex. In this study, a theoretical approach was applied to investigate the influence of the microstructure of cancellous bone on ultrasonic attenuation.

Results

The scattering from a trabecular cylinder was significantly angle dependent. The dependencies of the ultrasonic attenuation on frequency, scatterer size, and porosity were explored from the theoretical calculation. Prediction results showed that the ultrasonic attenuation increased with the increase of frequency and decreased linearly with the increase in porosity, and the broadband ultrasound attenuation decreased with the increase in porosity. All these predicted trends were consistent with published experimental data. In addition, our model successfully explained the principle of broadband ultrasound attenuation measurement (i.e., the attenuation over the frequency range 0.3–0.65 MHz was approximately linearly proportional to frequency) by considering the contributions of scattering and absorption to attenuation.

Conclusion

The proposed theoretical model may be a potentially valuable tool for understanding the interaction of ultrasound with cancellous bone.

Quantifying temperature-dependent T1 changes in cortical bone using ultrashort echo-time MRI

PURPOSE

To demonstrate the feasibility of using ultrashort echo-time MRI to quantify T1 changes in cortical bone due to heating.

METHODS

Variable flip-angle T1 mapping combined with 3D ultrashort echo-time imaging was used to measure T1 in cortical bone. A calibration experiment was performed to detect T1 changes with temperature in ex vivo cortical bone samples from a bovine femur. Ultrasound heating experiments were performed using an interstitial applicator in ex vivo bovine femur specimens, and heat-induced T1 changes were quantified.

RESULTS

The calibration experiment demonstrated that T1 increases with temperature in cortical bone. We observed a linear relationship between temperature and T1 with a linear coefficient between 0.67 and 0.84 ms/°C over a range of 25-70°C. The ultrasound heating experiments showed increased T1 changes in the heated regions, and the relationship between the temperature changes and T1 changes was similar to that of the calibration.

CONCLUSION

We demonstrated a temperature dependence of T1 in ex vivo cortical bone using a variable flip-angle ultrashort echo-time T1 mapping method.

Ultrasonic wave properties of human bone marrow in the femur and tibia

Ultrasonic wave properties of human bone marrow obtained in the femur and tibia were measured using an ultrasound pulse technique. The measured frequency range was 4-10 MHz, and the temperature range was 30 °C-40 °C. The sound velocity was 1410 m/s, and the attenuation coefficient was 4.4 dB/cm at 36 °C (10 MHz). These values decreased with temperature. Site dependence and individual differences in elderly human bone marrow were negligible. The slopes of the attenuation coefficient were estimated by a power law. The values of the exponent n were 2.0 (30 °C-38 °C) and 2.3 (40 °C).

Modeling of femoral neck cortical bone for the numerical simulation of ultrasound propagation

Quantitative ultrasound assessment of the cortical compartment of the femur neck (FN) is investigated with the goal of achieving enhanced fracture risk prediction. Measurements at the FN are influenced by bone size, shape and material properties. The work described here was aimed at determining which FN material properties have a significant impact on ultrasound propagation around 0.5 MHz and assessing the relevancy of different models. A methodology for the modeling of ultrasound propagation in the FN, with a focus on the modeling of bone elastic properties based on scanning acoustic microscopy data, is introduced. It is found that the first-arriving ultrasound signal measured in through-transmission at the FN is not influenced by trabecular bone properties or by the heterogeneities of the cortical bone mineralized matrix. In contrast, the signal is sensitive to variations in cortical porosity, which can, to a certain extent, be accounted for by effective properties calculated with the Mori-Tanaka method.

A deconvolution method for deriving the transit time spectrum for ultrasound propagation through cancellous bone replica models

The acceptance of broadband ultrasound attenuation for the assessment of osteoporosis suffers from a limited understanding of ultrasound wave propagation through cancellous bone. It has recently been proposed that the ultrasound wave propagation can be described by a concept of parallel sonic rays. This concept approximates the detected transmission signal to be the superposition of all sonic rays that travel directly from transmitting to receiving transducer. The transit time of each ray is defined by the proportion of bone and marrow propagated. An ultrasound transit time spectrum describes the proportion of sonic rays having a particular transit time, effectively describing lateral inhomogeneity of transit times over the surface of the receiving ultrasound transducer. The aim of this study was to provide a proof of concept that a transit time spectrum may be derived from digital deconvolution of input and output ultrasound signals. We have applied the active-set method deconvolution algorithm to determine the ultrasound transit time spectra in the three orthogonal directions of four cancellous bone replica samples and have compared experimental data with the prediction from the computer simulation. The agreement between experimental and predicted ultrasound transit time spectrum analyses derived from Bland–Altman analysis ranged from 92% to 99%, thereby supporting the concept of parallel sonic rays for ultrasound propagation in cancellous bone. In addition to further validation of the parallel sonic ray concept, this technique offers the opportunity to consider quantitative characterisation of the material and structural properties of cancellous bone, not previously available utilising ultrasound.

Quantitative ultrasound of cortical bone in the femoral neck predicts femur strength: results of a pilot study

A significant risk of femoral neck (FN) fracture exists for men and women with an areal bone mineral density (aBMD) higher than the osteoporotic range, as measured with dual-energy X-ray absorptiometry (DXA). Separately measuring the cortical and trabecular FN compartments and combining the results would likely be a critical aspect of enhancing the diagnostic capabilities of a new technique. Because the cortical shell determines a large part of FN strength a novel quantitative ultrasound (QUS) technique that probes the FN cortical compartment was implemented. The sensitivity of the method to variations of FN cortical properties and FN strength was tested. Nine femurs (women, mean age 83 years) were subjected to QUS to measure the through transmission time-of-flight (TOF) at the FN and mechanical tests to assess strength. Quantitative computed tomography (QCT) scans were performed to enable analysis of the dependence of TOF on bone parameters. DXA was also performed for reference. An ultrasound wave propagating circumferentially in the cortical shell was measured in all specimens. Its TOF was not influenced by the properties of the trabecular compartment. Averaged TOF for nine FN measurement positions/orientations was significantly correlated to strength (R2  = 0.79) and FN cortical QCT variables: total BMD (R(2)  = 0.54); regional BMD in the inferoanterior (R2  = 0.90) and superoanterior (R2  = 0.57) quadrants; and moment of inertia (R2  = 0.71). The results of this study demonstrate that QUS can perform a targeted measurement of the FN cortical compartment. Because the method involves mechanical guided waves, the QUS variable is related to the geometric and material properties of the cortical shell (cortical thickness, tissue elasticity, and porosity). This work opens the way to a multimodal QUS assessment of the proximal femur, combining our approach targeting the cortical shell with the existing modality sensitive to the trabecular compartment. In vivo feasibility of our approach has to be confirmed with experimental data in patients.