The measurement of broadband ultrasonic attenuation in cancellous bone-a review of the science and technology

The measurement of broadband ultrasonic attenuation (BUA) in cancellous bone at the calcaneus was first described in 1984. The assessment of osteoporosis by BUA has recently been recognized by Universities UK, within its EurekaUK book, as being one of the “100 discoveries and developments in UK Universities that have changed the world” over the past 50 years, covering the whole academic spectrum from the arts and humanities to science and technology. Indeed, BUA technique has been clinically validated and is utilized worldwide, with at least seven commercial systems providing calcaneal BUA measurement. However, a fundamental understanding of the dependence of BUA upon the material and structural properties of cancellous bone is still lacking. This review aims to provide a science- and technology-orientated perspective on the application of BUA to the medical disease of osteoporosis.

Attenuation of muscle damage by preconditioning with muscle hyperthermia

This study investigated the hypothesis that muscle damage would be attenuated in muscles subjected to passive hyperthermia 1 day prior to exercise. Fifteen male students performed 24 maximal eccentric actions of the elbow flexors with one arm; the opposite arm performed the same exercise 2-4 weeks later. The elbow flexors of one arm received a microwave diathermy treatment that increased muscle temperature to over 40°C, 16-20 h prior to the exercise. The contralateral arm acted as an untreated control. Maximal voluntary isometric contraction strength (MVC), range of motion (ROM), upper arm circumference, muscle soreness, plasma creatine kinase activity and myoglobin concentration were measured 1 day prior to exercise, immediately before and after exercise, and daily for 4 days following exercise. Changes in the criterion measures were compared between conditions (treatment vs. control) using a two-way repeated measures ANOVA with a significance level of P < 0.05. All measures changed significantly following exercise, but the treatment arm showed a significantly faster recovery of MVC, a smaller change in ROM, and less muscle soreness compared with the control arm. However, the protective effect conferred by the diathermy treatment was significantly less effective compared with that seen in the second bout performed 4-6 weeks after the initial bout by a subgroup of the subjects (n = 11) using the control arm. These results suggest that passive hyperthermia treatment 1 day prior to eccentric exercise-induced muscle damage has a prophylactic effect, but the effect is not as strong as the repeated bout effect. © Springer-Verlag 2006.

A gust-attenuation controller for fixed-wing UAVs during collision avoidance course

This paper presents a nonlinear gust-attenuation controller to stabilize velocities, attitudes and angular rates of a fixed-wing unmanned aerial vehicle (UAV) in the presence of wind gusts. The proposed controller aims to achieve a steady-state flight condition such that the host UAV can avoid airspace collision with other UAVs during the cruise flight. Based on the typical UAV model capturing flight aerodynamics, a nonlinear Hinf controller is developed with rapid response property in consideration of actuator constraints. Simulations are conducted for the Shadow UAV to verify performance of the proposed controller. Comparative studies with the proportional-integral derivative (PID) controllers demonstrate that the proposed controller exhibits great performance improvement in a gusty environment, making it suitable for integration into the design of flight control systems for cruise flight with safety guarantees.

Quantitative evaluation of polymer gel dosimeters by broadband ultrasound attenuation

Ultrasound has been examined previously as an alternative readout method for irradiated polymer gel dosimeters, with authors reporting varying dose response to ultrasound transmission measurements. In this current work we extend previous work to measure the broadband ultrasound attenuation (BUA) response of irradiated PAGAT gel dosimeters, using a novel ultrasound computed tomography system.

Flight validation of a feedforward gust-attenuation controller for an autonomous helicopter

This paper presents a practical scheme to control heave motion for hover and automatic landing of a Rotary-wing Unmanned Aerial Vehicle (RUAV) in the presence of strong horizontal gusts. A heave motion model is constructed for the purpose of capturing dynamic variations of thrust due to horizontal gusts. Through construction of an effective gust estimator, a feedback-feedforward controller is developed which uses available measurements from onboard sensors. The proposed controller dynamically and synchronously compensates for aerodynamic variations of heave motion, enhancing disturbance-attenuation capability of the RUAV. Simulation results justify the reliability and efficiency of the suggested gust estimator. Moreover, flight tests conducted on our Eagle helicopter verify suitability of the proposed control strategy for small RUAVs operating in a gusty environment.

Design of a gust-attenuation controller for landing operations of Unmanned Autonomous Helicopters

This paper presents an innovative and practical approach to controlling heave motion in the presence of acute stochastic atmospheric disturbances during landing operations of an Unmanned Autonomous Helicopter (UAH). A heave motion model of an UAH is constructed for the purpose of capturing dynamic variations of thrust due to horizontal wind gusts. Additionally, through construction of an effective observer to estimate magnitudes of random gusts, a promising and feasible feedback-feedforward PD controller is developed, based on available measurements from onboard equipment. The controller dynamically and synchronously compensates for aerodynamic variations of heave motion resulting from gust influence, to increase the disturbance-attenuation ability of the UAH in a windy environment. Simulation results justify the reliability and efficiency of the suggested gust observer to estimate gust levels when applied to the heave motion model of a small unmanned helicopter, and verify suitability of the recommended control strategy to realistic environmental conditions.

Cyclooxygenase-2-linked attenuation of hypoxia-induced pulmonary hypertension and intravascular thrombosis

Exogenous prostacyclin is effective in reducing pulmonary vascular resistance in some forms of human pulmonary hypertension (PH). To explore whether endogenous prostaglandins played a similar role in pulmonary hypertension, we examined the effect of deleting cyclooxygenase (COX)-gene isoforms in a chronic hypoxia model of PH. Pulmonary hypertension, examined by direct measurement of right ventricular end systolic pressure (RVESP), right ventricular hypertrophy (n = 8), and hematocrit (n = 3), was induced by 3 weeks of hypobarichypoxia in wild-type and COX-knockout (KO) mice. RVESP was increased in wild-type hypoxic mice compared with normoxic controls (24.4 ± 1.4 versus 13.8 ± 1.9 mm Hg; n = 8; p < 0.05). COX-2 KO mice showed a greater increase in RVESP following hypoxia (36.8 ± 2.7 mm Hg; p < 0.05). Urinary thromboxane (TX)B2 excretion increased following hypoxia (44.6 ± 11.1 versus 14.7 ± 1.8 ng/ml; n = 6; p < 0.05), an effect that was exacerbated by COX-2 gene disruption (54.5 ± 10.8 ng/ml; n = 6). In contrast, the increase in 6-keto-prostacyclin1α excretion following hypoxia was reduced by COX-2 gene disruption (29 ± 3 versus 52 ± 4.6 ng/ml; p < 0.01). Tail cut bleed times were lower following hypoxia, and there was evidence of intravascular thrombosis in lung vessels that was exacerbated by disruption of COX-2 and reduced by deletion of COX-1. The TXA2/endoperoxide receptor antagonist ifetroban (50 mg/kg/day) offset the effect of deleting the COX-2 gene, attenuating the hypoxia-induced rise in RVESP and intravascular thrombosis. COX-2 gene deletion exacerbates pulmonary hypertension, enhances sensitivity to TXA2, and induces intravascular thrombosis in response to hypoxia. The data provide evidence that endogenous prostaglandins modulate the pulmonary response to hypoxia. Copyright © 2008 by The American Society for Pharmacology and Experimental Therapeutics.

Dependence of light attenuation and backscattering on collagen concentration and chondrocyte density in agarose scaffolds

Optical coherence tomography (OCT) has been applied for high resolution imaging of articular cartilage. However, the contribution of individual structural elements of cartilage on OCT signal has not been thoroughly studied. We hypothesize that both collagen and chondrocytes, essential structural components of cartilage, act as important light scatterers and that variation in their concentrations can be detected by OCT through changes in backscattering and attenuation. To evaluate this hypothesis, we established a controlled model system using agarose scaffolds embedded with variable collagen concentrations and chondrocyte densities. Using OCT, we measured the backscattering coefficient (µb) and total attenuation coefficient (µt) in these scaffolds. Along our hypothesis, light backscattering and attenuation in agarose were dependent on collagen concentration and chondrocyte density. Significant correlations were found between µt and chondrocyte density (ρ = 0.853, p < 0.001) and between µt and collagen concentration (ρ = 0.694, p < 0.001). µb correlated significantly with chondrocyte density (ρ = 0.504, p < 0.001) but not with collagen concentration (ρ = 0.103, p = 0.422) of the scaffold. Thus, quantitation of light backscattering and, especially, attenuation could be valuable when evaluating the integrity of soft tissues, such as articular cartilage with OCT.

Ultrasound attenuation computed tomography assessment of PAGAT gel dose

Ultrasound has been previously investigated as an alternative readout method for irradiated polymer gel dosimeters, with authors reporting varying dose responses. We extend previous work utilizing a new computed tomography ultrasound scanner comprising of two identical 5 MHz, 128-element linear-array ultrasound transducers, co-axially aligned and submerged in water as a coupling agent, with rotational of the gel dosimeter between the transducers facilitated by a robotic arm. We have investigated the dose-dependence of both ultrasound bulk attenuation and broadband ultrasound attenuation (BUA) for the PAGAT gel dosimeter. The ultrasound bulk attenuation dose sensitivity was found to be 1.46  ±  0.04 dB m −1 Gy −1, being in agreement with previously published results for PAG and MAGIC gels. BUA was also found to be dose dependent and was measured to be 0.024  ±  0.003 dB MHz −1 Gy −1; the advantage of BUA being its insensitivity to frequency-independent attenuation mechanisms including reflection and refraction, thereby minimizing image reconstruction artefacts.