The effect of phase cancellation on estimates of broadband ultrasound attenuation and backscatter coefficient in human calcaneus in vitro

Broadband ultrasound attenuation (BUA) is a clinically proven indicator of osteoporotic fracture risk. BUA measurements are typically performed in through- transmission with single-element phase sensitive (PS) receivers and therefore can be compromised by phase cancellation artifact. Phase-insensitive (PI) receivers suppress phase cancellation artifact. To study the effect of phase cancellation on BUA measurements, through-transmission measurements were performed on 16 human calcaneus samples in vitro using a two-dimensional receiver array that enabled PS and PI BUA estimation. The means plus or minus standard deviations for BUA measurements were 22.1 plusmn 15.8 dB/MHz (PS) and 17.6 plusmn 7.2 dB/MHz (PI), suggesting that, on the average, approximately 20% of PS BUA values in vitro can be attributed to phase cancellation artifact. Therefore, although cortical plates are often regarded as the primary source of phase cancellation artifact, the heterogeneity of cancellous bone in the calcaneal interior may also be a significant source. Backscatter coefficient estimates in human calcaneus that are based on PS attenuation compensation overestimate 1) average magnitude of backscatter coefficient at 500 kHz by a factor of about 1.6 plusmn 0.3 and 2) average exponent (n) of frequency dependence by about 0.34 plusmn 0.12 (where backscatter coefficient is fit to a power law form proportional to frequency to the nth power).     

The dependence of ultrasonic backscatter on trabecular thickness in human calcaneus: theoretical and experimental results

Trabecular thickness within cancellous bone is an important determinant of osteoporotic fracture risk. Noninvasive assessment of trabecular thickness potentially could yield useful diagnostic information. Faran's theory of elastic scattering from a cylindrical object immersed in a fluid has been used to predict the dependence of ultrasonic backscatter on trabecular thickness. The theory predicts that, in the range of morphological and material properties expected for trabecular bone, the backscatter coefficient at 500 kHz should be approximately proportional to trabecular thickness to the power of 2.9. Experimental measurements of backscatter coefficient were performed on 43 human calcaneus samples in vitro. Mean trabecular thicknesses on the 43 samples were assessed using micro computed tomography (CT). A power law fit to the data showed that the backscatter coefficient empirically varied as trabecular thickness to the 2.8 power. The 95% confidence interval for this exponent was 1.7 to 3.9. The square of the correlation coefficient for the linear regression to the log transformed data was 0.40. This suggests that 40% of variations in backscatter may be attributed to variations in trabecular thickness. These results reinforce previous studies that offered validation for the Faran cylinder model for prediction of scattering properties of cancellous bone, and provide added evidence for the potential diagnostic utility of the backscatter measurement.     

评价松质骨状况的一种背散射频谱方法

采用超声背散射信号的质心偏移量来评价松质骨,并对牛胫骨和人体跟骨中背散射信号的质心偏移量与松质骨表观密度的关系,以及人体跟骨松质骨中背散射信号频谱质心位置与年龄的关系进行了分析讨论。分析结果表明,随松质骨表观密度的增大,背散射信号频谱的质心向低频方向移动;随年龄的增大,质心位置越接近于发射超声的中心频率。根据超声背散射信号质心偏移量的大小,可用于评价松质骨健康状况。     

The relationship between ultrasonic backscatter and bone mineral density in human calcaneus

Backscatter and attenuation coefficients were measured from 24 human calcanei in vitro. The logarithm of the backscatter coefficient at 500 kHz showed moderate correlations with bone mineral density (r=0.81, 95% confidence interval: 0.59-0.91) and attenuation (r=0.79, 95% CI: 0.56-0.91). These results suggest that backscatter measurements may be useful in the diagnosis of osteoporosis.     

Mechanisms for attenuation in cancellous-bone-mimicking phantoms

Broadband ultrasound attenuation (BUA) in cancellous bone is useful for prediction of osteoporotic fracture risk, but its causes are not well understood. To investigate attenuation mechanisms, 9 cancellous-bone-mimicking phantoms containing nylon filaments (simulating bone trabeculae) embedded within soft-tissue-mimicking fluid (simulating marrow) were interrogated. The measurements of frequency-dependent attenuation coefficient had 3 separable components: 1) a linear (with frequency) component attributable to absorption in the soft-tissue-mimicking fluid, 2) a quasilinear (with frequency) component, which may include absorption in and longitudinal-shear mode conversion by the nylon filaments, and 3) a nonlinear (with frequency) component, which may be attributable to longitudinal-longitudinal scattering by the nylon filaments. The slope of total linear (with frequency) attenuation coefficient (sum of components #1 and #2) versus frequency was found to increase linearly with volume fraction, consistent with reported measurements on cancellous bone. Backscatter coefficient measurements in the 9 phantoms supported the claim that the nonlinear (with frequency) component of attenuation coefficient (component #3) was closely associated with longitudinal-longitudinal scattering. This work represents the first experimental separation of these 3 components of attenuation in cancellous bone-mimicking phantoms.     

COMPACT BACKSCATTER FIBER OPTIC SYstems FOR SUBMICROSCOPIC PARTICLE SIZING

A compact backscatter fiber optic system, comprising a semiconductor laser diode, a fiber optic probe and a self-contained photomultiplier, is described. Backscatter fiber optic probes provide easy access over a range of scattering angles between 95 and 175 degrees. Accuracy of the portable dynamic light scattering system is assessed through measurements made on a 39 nm polystyrene latex spheres suspension.     

Strong dependence of rain-induced lidar depolarization on the illumination angle: experimental evidence and geometrical-optics interpretation

Backscatter and depolarization lidar measurements from clouds and precipitation are reported as functions of the elevation angle of the pointing lidar direction. We recorded the data by scanning the lidar beam (Nd:YAG) at a constant angular speed of ~3.5 degrees /s while operating at a repetition rate of 10 Hz. We show that in rain there is an evident and at times spectacular dependence on the elevation angle. That dependence appears to be sensitive to raindrop size. We have developed a three-dimensional polarization-dependent ray-tracing algorithm to calculate the backscatter and the depolarization ratio by large nonspherical droplets. We have applied it to raindrop shapes derived from existing static and dynamic (oscillating) models. We show that many of the observed complex backscatter and depolarization features can be interpreted to a good extent by geometrical optics. These results suggest that there is a definite need for more extensive calculations of the scattering phase matrix elements for large deformed raindrops as functions of the direction of illumination. Obvious applications are retrieval of information on the liquid-solid phase of precipitation and on the size and the vibration state of raindrops.     

Ultrasonic characterization of human cancellous bone in vitro using three different apparent backscatter parameters in the frequency range 0.6-15.0 mhz

Ultrasonic techniques based on measurements of apparent backscatter may provide a useful means for diagnosing bone diseases such as osteoporosis. The term "apparent" means that the backscattered signals are not compensated for the frequency-dependent effects of attenuation and diffraction. We performed in vitro apparent backscatter measurements on 23 specimens of human cancellous bone prepared from the left and right femoral heads of seven donors. A mechanical scanning system was used to obtain backscattered signals from each specimen at several sites. Scans were performed using five different ultrasonic transducers with center frequencies of 1, 2.25, 5, 7.5, and 10 MHz. The -6 dB bandwidths of these transducers covered a frequency range of 0.6-15.0 MHz. The backscattered signals were analyzed to determine three ultrasonic parameters: apparent integrated backscatter (AIB), frequency slope of apparent backscatter (FSAB), and time slope of apparent backscatter (TSAB). Linear regression analysis was used to examine the correlation of these ultrasonic parameters with five measured physical characteristics of the specimens: mass density, X-ray bone mineral density, Young's modulus, yield strength, and ultimate strength. A total of 75 such correlations were examined (3 ultrasonic parameters x 5 specimen characteristics x 5 transducers). Good correlations were observed for AIB using the 5 MHz (r = 0.70 - 0.89) and 7.5 MHz (r = 0.75-0.93) transducers; for FSAB using the 2.25 MHz (r = 0.70 - 0.88), 5 MHz (r = 0.79 - 0.94), and 7.5 MHz (r = 0.80 - 0.92) transducers; and for TSAB using the 5 MHz (r = 0.68 - 0.89), 7.5 MHz (r = 0.75 - 0.89), and 10 MHz (r = 0.75 - 0.92) transducers.     

Aerosol and cloud backscatter at 1.06, 1.54, and 0.53 mum by airborne hard-target-calibrated Nd:YAG /methane Raman lidar

A lidar instrument was developed to make simultaneous measurements at three distinct wavelengths in the visible and near infrared at 0.532, 1.064, and 1.54 mum with high cross-sectional calibration accuracy. Aerosol and cloud backscatter cross sections were acquired during November and December 1989 and May and June 1990 by the NASA DC-8 aircraft as part of the Global Backscatter Experiment. The instrument, methodology, and measurement results are described. A Nd:YAG laser produced 1.064- and 0.532-mum energy. The 1.54-mum transmitted pulse was generated by Raman-shifted downconversion of the 1.064-mum pulse through a Raman cell pressured with methane gas. The lidar could be pointed in the nadir or zenith direction from the aircraft. A hard-target-based calibration procedure was used to obtain the ratio of the system calibration between the three wavelengths, and the absolute calibration was referenced to the 0.532-mum lidar molecular backscatter cross section for the clearest scattering regions. From the relative wavelength calibration, the aerosol backscatter cross sections at the longer wavelengths are resolved for values as small as 1% of the molecular cross section. Backscatter measurement accuracies are better than 10(-9) (m sr)(-1) at 1.064 and 1.54 mum. Results from the Pacific Ocean region of the multiwavelength backscatter dependence are presented. Results show extensive structure and variation for the aerosol cross sections. The range of observed aerosol cross section is over 4 orders of magnitude, from less than 10(-9) (m sr)(-1) to greater than 10(-5) (m sr)(-1).     

Lidar aerosol backscatter cross sections in the 2-νm near-infrared wavelength region

Lidar backscatter cross-sectional measurements at 1.064, 0.532, and 1.54 μm were acquired during November 1989 and May-June 1990 around the Pacific region by the NASA DC-8 aircraft as part of the Global Backscatter Experiment. The primary motivation for the Global Backscatter Experiment was the study of lidar backscatter cross sections for the development of a spaceborne wind-sensing lidar. Direct backscatter measurements obtained by the NASA Goddard Space Flight Center visible and infrared lidar are compared with backscatter cross sections calculated from aerosol size distributions obtained by particle counters. Results for one flight with pronounced aerosol layers in the upper troposphere southeast of Japan are presented. Because 2-μm region wavelengths are possible candidates for a spaceborne wind-sensing lidar, the visible and infrared lidar backscatter cross sections at 1.064, 0.532, and 1.54 μm are extrapolated to the 2-μm region. The extrapolated 2-μm cross sections are compared with lidar measurements at 9 μm. A significant range in the ratio of 2-9-μm backscatter cross sections is found, but a large number of points concentrate near ratios of three to ten. A large number of 1.064- and 1.54-μm cross sections were binned to provide an estimate of backscatter for various percentiles for the flight. The ratio of the 50-percentile backscatter values at 1.064 and 1.54 μm suggest a λ(-1.9) to λ(-3.0) wavelength dependence of aerosol backscatter cross section in the near infrared for the observational case.     

Frequency dependence of backscatter coefficient versus scatterervolume fraction

Various groups are using the frequency dependence of backscattering to characterize tissue. In most cases, sparse scatterer concentrations are assumed in relating scattering parameters to tissue properties. This study addresses the relationship between backscatter frequency dependence and scatterer volume fraction. Backscatter coefficients (BSC) in the 2.5 to 9.0 MHz frequency range were measured for agar-gel phantoms containing Sephadex scatterers (mean diameter 42 μm) at volume fractions ranging from 5 to 50%. The BSC increased with scatterer volume fraction at low scatterer concentrations; at higher concentrations, the BSC reached a maximum with concentration and then decreased with yet increasing scatterer concentrations, as has been noted by previous authors. In addition, the volume fraction for the maximum backscatter coefficient varied with frequency, generally being greater at higher frequencies than lower frequencies, and the frequency dependence of the backscatter coefficient was greater for the higher scatterer concentrations than for the lower concentrations. These results are predicted by continuum models, where the spatial autocorrelation function depends on scatterer volume fraction     

Simplified inverse filter tracking algorithm for estimating the mean trabecular bone spacing

Ultrasonic backscatter signals provide useful information relevant to bone tissue characterization. Trabecular bone microstructures have been considered as quasi-periodic tissues with a collection of regular and diffuse scatterers. This paper investigates the potential of a novel technique using a simplified inverse filter tracking (SIFT) algorithm to estimate mean trabecular bone spacing (MTBS) from ultrasonic backscatter signals. In contrast to other frequency-based methods, the SIFT algorithm is a time-based method and utilizes the amplitude and phase information of backscatter echoes, thus retaining the advantages of both the autocorrelation and the cepstral analysis techniques. The SIFT algorithm was applied to backscatter signals from simulations, phantoms, and bovine trabeculae in vitro. The estimated MTBS results were compared with those of the autoregressive (AR) cepstrum and quadratic transformation (QT) . The SIFT estimates are better than the AR cepstrum estimates and are comparable with the QT values. The study demonstrates that the SIFT algorithm has the potential to be a reliable and robust method for the estimation of MTBS in the presence of a small signal-to-noise ratio, a large spacing variation between regular scatterers, and a large scattering strength ratio of diffuse scatterers to regular ones.     

Vertical variability of aerosol backscatter from an airborne-focused continuous-wave CO2 lidar at 9.1-microm wavelength

Atmospheric aerosol backscatter measurements taken with a continuous-wave focused Doppler lidar at 9.1-mum wavelength were obtained over western North America and the Pacific Ocean from 13 to 26 September 1995 as part of a NASA airborne mission. Backscatter variability was measured for ~52 flight hours, covering an equivalent horizontal distance of ~30,000 km in the troposphere. Some quasi-vertical backscatter profiles were also obtained during various ascents and descents at altitudes that ranged from ~0.1 to 12 km. Similarities and differences for aerosol loading over land and ocean were observed. A midtropospheric aerosol backscatter background mode near 3 x 10(-11) to 1 x 10(-10) m(-1) sr(-1) was obtained, which is consistent with those of previous airborne and ground-based data sets.     

Characterization of trabecular bone using the backscattered spectral centroid shift

Ultrasonic attenuation in bone in vivo is generally measured using a through-transmission method at the calcaneus. Although attenuation in calcaneus has been demonstrated to be a useful predictor for osteoporotic fracture risk, measurements at other clinically important sites, such as hip and spine, could potentially contain additional useful diagnostic information. Through-transmission measurements may not be feasible at these sites due to complex bone shapes and the increased amount of intervening soft tissue. Centroid shift from the backscattered signal is an index of attenuation slope and has been used previously to characterize soft tissues. In this paper, centroid shift from signals backscattered from 30 trabecular bone samples in vitro were measured. Attenuation slope also was measured using a through-transmission method. The correlation coefficient between centroid shift and attenuation slope was -0.71. The 95% confidence interval was (-0.86, -0.47). These results suggest that the backscattered spectral centroid shift may contain useful diagnostic information potentially applicable to hip and spine.     

Rotational Raman scattering (Ring effect) in satellite backscatter ultraviolet measurements

A detailed radiative transfer calculation has been carried out to estimate the effects of rotational Raman scattering (RRS) on satellite measurements of backscattered ultraviolet radiation. Raman-scattered light is shifted in frequency from the incident light, which causes filling in of solar Fraunhofer lines in the observed backscattered spectrum (also known as the Ring effect). The magnitude of the rotational Raman scattering filling in is a function of wavelength, solar zenith angle, surface reflectance, surface pressure, and instrument spectral resolution. The filling in predicted by our model is found to be in agreement with observations from the Shuttle Solar Backscatter Ultraviolet Radiometer and the Nimbus-7 Solar Backscatter Ultraviolet Radiometer.     

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.     

Signal processing and calibration of continuous-wave focused CO(2) Doppler lidars for atmospheric backscatter measurement

Two continuous-wave (CW) focused CO(2) Doppler lidars (9.1 and 10.6 μm) were developed for airborne in situ aerosol backscatter measurements. The complex path of reliably calibrating these systems, with different signal processors, for accurate derivation of atmospheric backscatter coefficients is documented. Lidar calibration for absolute backscatter measurement for both lidars is based on range response over the lidar sample volume, not solely at focus. Both lidars were calibrated with a new technique using well-characterized aerosols as radiometric standard targets and related to conventional hard-target calibration. A digital signal processor (DSP), a surface acoustic wave spectrum analyzer, and manually tuned spectrum analyzer signal analyzers were used. The DSP signals were analyzed with an innovative method of correcting for systematic noise fluctuation; the noise statistics exhibit the chi-square distribution predicted by theory. System parametric studies and detailed calibration improved the accuracy of conversion from the measured signal-to-noise ratio to absolute backscatter. The minimum backscatter sensitivity is ~3 × 10(-12) m(-1) sr(-1) at 9.1 μm and ~9 × 10(-12) m(-1) sr(-1) at 10.6 μm. Sample measurements are shown for a flight over the remote Pacific Ocean in 1990 as part of the NASA Global Backscatter Experiment (GLOBE) survey missions, the first time to our knowledge that 9.1-10.6-μm lidar intercomparisons were made. Measurements at 9.1 μm, a potential wavelength for space-based lidar remote-sensing applications, are to our knowledge the first based on the rare isotope (12)C (18)O(2) gas.     

Airborne CO(2) coherent lidar for measurements of atmospheric aerosol and cloud backscatter

An airborne CO(2) coherent lidar has been developed and flown on over 30 flights of the NASA DC-8 research aircraft to obtain aerosol and cloud backscatter and extinction data at a wavelength near 9μm. Designed to operate in either zenith- or nadir-directed modes, the lidar can be used to measure vertical profiles of backscatter throughout the vertical extent of the troposphere and the lower stratosphere. Backscatter measurements in absolute units are obtained through a hard-target calibration methodology. The use of coherent detection results in high sensitivity and narrow field of view, the latter property greatly reducing multiple-scattering effects. Aerosol backscatter profile intercomparisons with other airborne and ground-based CO(2) lidars were conducted during instrument checkout flights over the NASA Ames Research Center before extended depolyment over the Pacific Ocean. Selected results from data taken during the flights over the Pacific Ocean are presented, emphasizing intercom arisons with backscatter profile data obtained at 1.06 μm with a NASA Goddard Space Flight Center Nd:YAG lidar on the same flights.     

Ultrasonic attenuation in human calcaneus from 0.2 to 1.7 MHz

Ultrasonic attenuation has been demonstrated to be a useful measurement in the diagnosis of osteoporosis. Most studies have employed ultrasound in a range of frequencies from about 200 kHz-300 kHz to 600 kHz-1 MHz, and many have assumed a linear dependence of attenuation on frequency. In order to investigate the attenuation properties of human calcaneus at higher frequencies, 16 defatted human calcanea were interrogated in vitro using two matched pairs of transducers with center frequencies of 500 kHz and 2.25 MHz. The linear dependence of attenuation on frequency seems to extend up to at least 1.7 MHz. The correlation between attenuation coefficient and frequency from 400 kHz to 1.7 MHz was r = 0.999 (95% confidence interval, CI, = 0.998-1.00). The measurements suggest that some deviations from linear frequency dependence of attenuation may occur at lower frequencies (below 400 kHz), however.     

Modell zur Analyse des knöchernen Anwachsverhaltens auf bioaktiv beschichteten Implantatoberflächen

Model to analyse the bone on‐growth on bioactive coated implant surfaces Especially on the field of bone regeneration, transient and permanent implants are an important method of therapy in the Orthopaedic Surgery. In this context, bioactive surfaces on metallic implants provide an improved contact to the surrounding bone. The goal of our study was to establish an in‐vitro test system to evaluate the on‐growth of bone‐derived cells on different surface coatings. Therefore, we invented a special kind of clamps made of commercially‐pure (c‐p) titanium and blasted with hydroxyapatite particles followed by electrochemically coating with calcium phosphate (BONIT®‐HA, BONIT®). Definite pieces of human cancellous bone were attached to these clamps, inserted onto tissue culture plates and cultivated in DMEM for ten days. Finally, the contact area between human cancellous bone and the implant surface was analyzed and the spreading of osteoblast‐like cells evaluated by scanning electron microscopy (SEM). A well‐spread morphology of bone cells was observed on the implant surfaces coated with calcium phosphate (CaP). In comparison the clamps without CaP coatings showed only a marginal growth of bone cells on the clamp surface. The presented newly in‐vitro test setup using titanium clamps coated with bioactive layers attached to human cancellous bone represents a well‐functioning model for qualitative evaluation of bone on‐growth.