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This study investigated the effects of low-intensity pulsed ultrasound (LIPUS) of different spatial-average-temporal-average intensity (ISATA) ranging from 15-150 mW/cm2 on the treatment of osteoporosis in ovariectomized rats. Healthy 3-mo-old female Sprague-Dawley rats were randomly divided into nine groups (n = 12 per group): sham-ovariectomy (OVX) control group, OVX control group and OVX groups treated with LIPUS at seven different intensities (ISATA: 15, 30, 50, 75, 100, 125 and 150 mW/cm2, respectively). LIPUS was applied to bilateral femurs 12 wk post-OVX for 20 min/d for 6 wk. Micro-computed tomography, biomechanical tests, serum biochemical analysis and grip strength tests were performed to evaluate the therapeutic effects of LIPUS at different intensities. Results revealed that LIPUS intensity yielded strong correlations with bone mineral density and bone microstructure (R2 = 0.57-0.83) and bone mechanical strength (R2 = 0.80-0.97), and that the intensity of 150 mW/cm2, instead of the 30 mW/cm2 widely used in bone fracture healing, was most effective in maintaining bone mass among all the LIPUS signals between 15 and 150 mW/cm2. This suggests that higher ultrasound intensity (i.e., 150 mW/cm2) may be more effective than lower intensity in mitigation of osteopenia and osteoporosis. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the effect of low-intensity ultrasound on articular cartilage and subchondral bone alterations in joints under normal and functional disuse conditions during osteoarthritis (OA) progression. Total of thirty 5-mo-old female Sprague-Dawley rats were randomly assigned to six groups (n = 5/group): age-matched group, OA group, OA + ultrasound (US) group, hindlimb suspension (HLS) group, HLS + OA group and HLS + OA + US group. The surgical anterior cruciate ligament was used to induce OA in the right knee joints. After 2 wk of OA induction, low-intensity ultrasound generated with a 3-MHz transducer with 20% pulse duty cycle and 30 mW/cm2 acoustic intensity was delivered to the right knee joints for 20 min a day, 5 d a week for a total of 6 wk. Then, the right tibias were harvested for micro-computed tomography, histologic and mechanical analysis. Micro-computed tomography results indicated that the thickness and sulfated glycosaminoglycan content of cartilage decreased, but the thickness of the subchondral cortical bone plate and the formation of subchondral trabecular bone increased in the OA group under the normal joint use condition. Furthermore, histologic results revealed that chondrocyte density and arrangement in cartilage corrupted and the underlying subchondral bone increased during OA progression. These changes were accompanied by reductions in mechanical parameters in OA cartilage. However, fewer OA symptoms were observed in the HLS + OA group under the joint disuse condition. The cartilage degeneration and subchondral bone sclerosis were alleviated in the US treatment group, especially under normal joint use condition. In conclusion, low-intensity ultrasound could improve cartilage degeneration and subchondral sclerosis during OA progression. Also, it could provide a promising strategy for future clinical treatment for OA patients. [ABSTRACT FROM AUTHOR]

Abstract The objective was to evaluate the effect of low-intensity pulsed ultrasound (LIPUS)-induced acoustic radiation force on trabecular bone defect repair and healing in a rat tibial model. A uniform surgical defect, 3.5 mm in diameter, was generated in the proximal bilateral tibial region of rats (N = 20). LIPUS was applied to the defects in the left tibia for 20 min every day for 2 wk. Contralateral defects in the right tibia served as a control without active LIPUS treatment. The micro-computed tomography data revealed that LIPUS-treated tibia exhibited higher bone volume/total volume, connectivity density, trabecular number, and bone mineral density and significantly lower trabecular separation. Histomorphometry analysis indicated a similar trend. Mechanical testing data revealed that LIPUS treatment significantly increased bone stiffness relative to that of the control group. Short-term (2-wk) LIPUS therapy initiated trabecular bone repair and regeneration in large trabecular bone defects, whereas cortical bone remained in the initial non-mineralization stage. [ABSTRACT FROM AUTHOR]

Abstract: Mode conversion occurs when the ultrasonic guided waves encounter fractures. The aim of this study was to investigate the feasibility of fracture assessment in long cortical bone using guided-mode conversion. Mode conversion behavior between the fundamental modes S0 and A0 was analyzed. The expressions proposed for modal velocity were used to identify the original and converted modes. Simulations and phantom experiments were performed using 1.0-mm-thick steel plates with a notch width of 0.5 mm and notch depths of 0.2, 0.4, 0.6 and 0.8 mm. Furthermore, in vitro experiments were carried out on nine ovine tibias with 1.0-mm-wide partial transverse gap break and cortical thickness varying from 2.10 to 3.88 mm. The study confirmed that mode conversion gradually becomes observable as fracture depth increases. Energy percentages of the converted modes correlated strongly with fracture depth, as illustrated by the frequency-sweeping experiments on steel phantoms (100–1100 kHz, r 2 = 0.97, p < 0.0069) and the fixed-frequency experiments on nine ovine tibias (250 kHz, r 2 = 0.97, p < 0.0056). The approaches described, including mode excitation, velocity expressions and energy percentage criteria, may also contribute to ultrasonic monitoring of long bone fracture healing. [Copyright &y& Elsevier]

Microgravity (MG) is known to induce bone loss in astronauts during long-duration space mission because of a lack of sufficient mechanical stimulation under MG. It has been demonstrated that mechanical signals are essential for maintaining cell viability and motility, and they possibly serve as a countermeasure to the catabolic effects of MG. The objective of this study was to examine the effects of high-frequency acoustic wave signals on osteoblasts in a simulated microgravity (SMG) environment (created using 1-D clinostat bioreactor) using a modified low-intensity pulsed ultrasound (mLIPUS). Specifically, we evaluated the hypothesis that osteoblasts (human fetal osteoblastic cell line) exposure to mLIPUS for 20 min/d at 30 mW/cm(2) will significantly reduce the detrimental effects of SMG. Effects of SMG with mLIPUS were analyzed using the MTS proliferation assay for proliferation, phalloidin for F-actin staining, Sirius red stain for collagen, and Alizarin red for mineralization. Our data showed that osteoblast exposure to SMG results in significant decreases in proliferation (∼ -38% and ∼ -44% on days 4 and 6, respectively; p < 0.01), collagen content (∼ -22%; p < 0.05) and mineralization (∼ -37%; p < 0.05) and actin stress fibers. In contrast, mLIPUS stimulation in SMG condition significantly increases the rate of proliferation (∼24% by day 6; p < 0.05), collagen content (∼52%; p < 0.05) and matrix mineralization (∼25%; p < 0.001) along with restoring formation of actin stress fibers in the SMG-exposed osteoblasts. These data suggest that the acoustic wave can potentially be used as a countermeasure for disuse osteopenia. [ABSTRACT FROM AUTHOR]

Abstract: Microgravity (MG) is known to induce bone loss in astronauts during long-duration space mission because of a lack of sufficient mechanical stimulation under MG. It has been demonstrated that mechanical signals are essential for maintaining cell viability and motility, and they possibly serve as a countermeasure to the catabolic effects of MG. The objective of this study was to examine the effects of high-frequency acoustic wave signals on osteoblasts in a simulated microgravity (SMG) environment (created using 1-D clinostat bioreactor) using a modified low-intensity pulsed ultrasound (mLIPUS). Specifically, we evaluated the hypothesis that osteoblasts (human fetal osteoblastic cell line) exposure to mLIPUS for 20 min/d at 30 mW/cm2 will significantly reduce the detrimental effects of SMG. Effects of SMG with mLIPUS were analyzed using the MTS proliferation assay for proliferation, phalloidin for F-actin staining, Sirius red stain for collagen, and Alizarin red for mineralization. Our data showed that osteoblast exposure to SMG results in significant decreases in proliferation (∼ −38% and ∼ −44% on days 4 and 6, respectively; p < 0.01), collagen content (∼ −22%; p < 0.05) and mineralization (∼ −37%; p < 0.05) and actin stress fibers. In contrast, mLIPUS stimulation in SMG condition significantly increases the rate of proliferation (∼24% by day 6; p < 0.05), collagen content (∼52%; p < 0.05) and matrix mineralization (∼25%; p < 0.001) along with restoring formation of actin stress fibers in the SMG-exposed osteoblasts. These data suggest that the acoustic wave can potentially be used as a countermeasure for disuse osteopenia. [Copyright &y& Elsevier]

Abstract: This study investigated the efficacy of frequency modulated ultrasound attenuation in the assessment of the trabecular structural properties. Four frequency modulated signals were created to represent four frequency bands centered at 500 kHz, 900 kHz, 1.3 MHz and 1.7 MHz with the bandwidth of 400 kHz. Five 1-cm trabecular cubes were harvested from fresh bovine distal femur. The cubes underwent four steps of demineralization process to expand the sample size to 25 with the greater variations of the structural properties for the better correlation study. Pearson correlation study was performed between the ultrasound attenuation in four frequency bands and the trabecular structural properties. The results showed that correlations of frequency modulated ultrasound attenuation to the trabecular structural properties are dependent on frequency bands. The attenuation in proximal-distal orientation had the highest correlation to BV/TV (R 2  = 0.73, p < 0.001) and trabecular thickness (R 2  = 0.50, p < 0.001) at the frequency band centered at 1.7 MHz. It was equivalent in the four frequency bands in correlation to the trabecular number (average R 2  = 0.80, p < 0.001) and to the trabecular separation (average R 2  = 0.83, p < 0.001). The attenuation in anterio-posterial orientation had the highest correlation to BV/TV (R 2  = 0.80, p < 0.001) and trabecular thickness (R 2  = 0.71, p < 0.001) at the frequency band centered at 1.3 MHz. The attenuation in the first frequency band was the most sensitive to the trabecular number (R 2  = 0.71, p < 0.001) and trabecular separation (R 2  = 0.80, p < 0.001). No significant correlation was observed for the attenuation in medial-lateral orientation across the four frequency bands. [Copyright &y& Elsevier]

Abstract: Phase cancellation in ultrasound due to large receiver size has been proposed as a contributing factor to the inaccuracy of estimating broadband ultrasound attenuation (BUA), which is used to characterize bone quality. Transducers with aperture size ranging from 2 to 5 mm have been used in previous attempts to study the effect of phase cancellation. However, these receivers themselves are susceptible to phase cancellation because aperture size is close to one center wavelength (about 3 mm at 500 KHz in water). This study uses an ultra small receiver (aperture size: 0.2 mm) in conjunction with a newly developed two-dimensional (2-D) synthetic array system to investigate the effects of phase cancellation and receiver aperture size on BUA estimations of bone tissue. In vitro ultrasound measurements were conducted on 54 trabecular bone samples (harvested from sheep femurs) in a confocal configuration with a focused transmitter and synthesized focused receivers of different aperture sizes. Phase sensitive (PS) and phase insensitive (PI) detections were performed. The results show that phase cancellation does have a significant effect on BUA. The normalized BUA (nBUA) with PS is 8.1% higher than PI nBUA while PI BUA is well correlated with PS BUA. Receiver aperture size also influences the BUA reading for both PI and PS detection and smaller receiver aperture tends to result in higher BUA readings. The results also indicate that the receiver aperture size used in the confocal configuration with PI detection should at least equal the aperture of the transmitter to capture most of the energy redistributed by the interference and diffraction from the trabecular bone. [Copyright &y& Elsevier]

The objective was to evaluate the effect of low-intensity pulsed ultrasound (LIPUS)-induced acoustic radiation force on trabecular bone defect repair and healing in a rat tibial model. A uniform surgical defect, 3.5 mm in diameter, was generated in the proximal bilateral tibial region of rats (N = 20). LIPUS was applied to the defects in the left tibia for 20 min every day for 2 wk. Contralateral defects in the right tibia served as a control without active LIPUS treatment. The micro-computed tomography data revealed that LIPUS-treated tibia exhibited higher bone volume/total volume, connectivity density, trabecular number, and bone mineral density and significantly lower trabecular separation. Histomorphometry analysis indicated a similar trend. Mechanical testing data revealed that LIPUS treatment significantly increased bone stiffness relative to that of the control group. Short-term (2-wk) LIPUS therapy initiated trabecular bone repair and regeneration in large trabecular bone defects, whereas cortical bone remained in the initial non-mineralization stage. [ABSTRACT FROM AUTHOR]