Matthew T. Huber

Effect of gate choice on backscatter difference measurements of cancellous bone

A variety of ultrasonic techniques have been developed to detect changes in bone caused by osteoporosis. One approach, called the backscatter difference technique, analyzes the power difference between two different portions of a backscatter signal. Analysis gates with a certain delay τd, width τw, and separation τs are used to define portions of the backscatter signal for analysis. The goal of the present study was to investigate how different choices of τd, τw, and τs affect four backscatter difference parameters: the normalized mean of the backscatter difference (nMBD), the normalized slope of the backscatter difference (nSBD), the normalized intercept of the backscatter difference (nIBD), and the normalized backscatter amplitude ratio (nBAR). Backscatter measurements were performed on 54 cube shaped specimens of human cancellous bone. nMBD, nSBD, nIBD, and nBAR were determined for 34 different combinations of τd, τw, and τs for each specimen. nMBD and nBAR demonstrated the strongest correlations with apparent bone density (0.48 ≤ Rs ≤ 0.90). Generally, the correlations were found to improve as τw + τs was increased and as τd was decreased. Among the four backscatter difference parameters, the measured values of nMBD were least sensitive to gate choice (<16%).

Optical detection of mach shock wave cones in water using refracto-vibrometry

Recently, a hydrophone array was used to demonstrate Mach shock wave cone formation in water when 1m diameter steel pile rods for civil structures were driven into the ground by massive impact hammers. These shock wavefronts are of concern for marine mammals and fish. In the current project, Mach shockwave cones were directly imaged using refracto-vibrometry. A Polytec PSV-400 laser Doppler vibrometer was directed through a water tank towards a stationary retroreflective surface. The density variations of acoustic wavefronts which pass through the laser cause variations in the optical path length between the laser and retroreflector. This results in a time-varying modulation of the laser signal returning to the vibrometer, enabling optical detection of the acoustic wavefronts. A 35 mm diameter rod (steel or other metal) immersed in a water tank was repeatedly “impacted” by narrow pulses from a 1 MHz ultrasound transducer. The vibrometer sampled numerous scan points to generate videos of the time evolution...

Characterization of ultrasound attenuation and angular distribution from trabecular bone phantom material using refracto-vibrometry

Ultrasound is being researched and used for diagnosing osteoporosis. Researchers use trabecular bone from humans as a test material, but such bone is bio-hazardous, not uniform, and of limited size. Recently it has been demonstrated that the open-cell polyurethane foam, known as “Sawbones” could be utilized as a substitute for trabecular bone in ultrasound studies. In the current study, rectangular slices of Sawbones trabecular bone phantom material were insonified with a 25 mm diameter 500 kHz ultrasound transducer oriented both normal to the surface and at an angle. Refracto-vibrometry (RV), an interferometric method for optically measuring ultrasound, was compared with conventional transducer measurements of ultrasound transmission through the bone phantom samples. The measurement beam from a Polytec PSV-400 scanning laser Doppler vibrometer was directed through a water tank towards a stationary retroreflective surface. Acoustic wave fronts (density variations) which pass through the ~50µm diameter mea...

Comparison of conventional transducer and refracto-vibrometry measurements of ultrasonic transmission parameters from heel bones

Ultrasonic measurements of the heel bone (calcaneus) are used commonly for osteoporosis screening. Ultrasound pulses that pass through the calcaneus are detected with a receiving transducer. Parameters, such as normalized broadband ultrasound attenuation (nBUA) and speed of sound (SOS) calculated from the wave forms detected by the receiving transducer, are utilized to assess bone health. In the current study, refracto-vibrometry (RV), an interferometric method for optically measuring ultrasound, was compared with conventional transducer measurements of ultrasound transmission in-vitro through a human calcaneus sample. The measurement beam from a Polytec PSV-400 scanning laser Doppler vibrometer was directed through a water tank towards a stationary retroreflective surface. Acoustic wave fronts (density variations) which pass through the ~50μm diameter measurement laser cause variations in the integrated optical path length. The signals detected by the vibrometer at numerous scan points were used to determine the time evolution of ultrasonic wave fronts. Because there is not a physical receiving transducer, the RV measurements do not experience the same frequency response and reflection artifacts of conventional transducers. Parameters such as nBUA and SOS were calculated at multiple RV scan points, and the results were compared to parameters measured using a conventional ultrasound transducer.Ultrasonic measurements of the heel bone (calcaneus) are used commonly for osteoporosis screening. Ultrasound pulses that pass through the calcaneus are detected with a receiving transducer. Parameters, such as normalized broadband ultrasound attenuation (nBUA) and speed of sound (SOS) calculated from the wave forms detected by the receiving transducer, are utilized to assess bone health. In the current study, refracto-vibrometry (RV), an interferometric method for optically measuring ultrasound, was compared with conventional transducer measurements of ultrasound transmission in-vitro through a human calcaneus sample. The measurement beam from a Polytec PSV-400 scanning laser Doppler vibrometer was directed through a water tank towards a stationary retroreflective surface. Acoustic wave fronts (density variations) which pass through the ~50μm diameter measurement laser cause variations in the integrated optical path length. The signals detected by the vibrometer at numerous scan points were used to deter...

Ultrasonic backscatter difference measurements of cancellous bone from the human femur: Relation to bone mineral density and microstructure.

Ultrasonic backscatter techniques are being developed to detect changes in cancellous bone caused by osteoporosis. One technique, called the backscatter difference technique, measures the power difference between two portions of a backscatter signal. The goal of the present study is to investigate how bone mineral density (BMD) and the microstructure of human cancellous bone influence four backscatter difference parameters: the normalized mean of the backscatter difference (nMBD) spectrum, the normalized slope of the backscatter difference spectrum, the normalized intercept of the backscatter difference spectrum, and the normalized backscatter amplitude ratio (nBAR). Ultrasonic measurements were performed with a 3.5 MHz broadband transducer on 54 specimens of human cancellous bone from the proximal femur. Volumetric BMD and the microstructural characteristics of the specimens were measured using x-ray micro-computed tomography. Of the four ultrasonic parameters studied, nMBD and nBAR demonstrated the strongest univariate correlations with density and microstructure. Multivariate analyses indicated that nMBD and nBAR depended on trabecular separation and possibly other microstructural characteristics of the specimens independently of BMD. These findings suggest that nMBD and nBAR may be sensitive to changes in the density and microstructure of bone caused by osteoporosis.

Characterization of a polymer, open-cell rigid foam that simulates the ultrasonic properties of cancellous bone

Materials that simulate the ultrasonic properties of tissues are used widely for clinical and research purposes. However, relatively few materials are known to simulate the ultrasonic properties of cancellous bone. The goal of the present study was to investigate the suitability of using a polymer, open-cell rigid foam (OCRF) produced by Sawbones®. Measurements were performed on OCRF specimens with four different densities. Ultrasonic speed of sound and normalized broadband ultrasonic attenuation were measured with a 0.5 MHz transducer. Three backscatter parameters were measured with a 5 MHz transducer: apparent integrated backscatter, frequency slope of apparent backscatter, and normalized mean of the backscatter difference. X-ray micro-computed tomography was used to measure the microstructural characteristics of the OCRF specimens. The trabecular thickness and relative bone volume of the OCRF specimens were similar to those of human cancellous bone, but the trabecular separation was greater. In most cases, the ultrasonic properties of the OCRF specimens were similar to values reported in the literature for cancellous bone, including dependence on density. In addition, the OCRF specimens exhibited an ultrasonic anisotropy similar to that reported for cancellous bone.

Optical imaging of propagating ultrasonic wave fronts resulting from ultrasonic pulses incident on heel bones using refracto-vibrometry

Ultrasonic measurements of the heel bone (calcaneus) are used commonly for osteoporosis screening. Pulses emitted by an ultrasound transducer are incident on the calcaneus, and the transmitted wave fronts are detected with a separate transducer. In the current in-vitro study, full field videos of propagating ultrasonic wave fronts incident on a calcaneus sample, along with transmitted and backscattered waves were obtained using refracto-vibrometry. Pulses were emitted by a 500 kHz Panametrics V303 transducer. To optically detect ultrasonic wave fronts, the measurement beam from a Polytec PSV-400 scanning laser Doppler vibrometer laser was directed through a water tank towards a stationary retroreflective surface. Acoustic wave fronts (density variations) which pass through the measurement laser cause variations in the integrated optical path length between the vibrometer and retroreflector. The time-varying signals detected by the vibrometer at numerous scan points were used to determine the time evolutio...

Optical imaging of propagating Mach cones in water using refracto-vibrometry

Refracto-vibrometry was used to optically image propagating Mach cones in water. These Mach cones were produced by ultrasonic longitudinal and shear waves traveling through submerged 12.7 mm diameter metal cylinders. Full-field videos of the propagating wave fronts were obtained using refracto-vibrometry. A laser Doppler vibrometer, directed at a retroreflective surface, sampled time-varying water density at numerous scan points. Wave speeds were determined from the Mach cone apex angles; the measured longitudinal and shear wave speeds in steel (6060 ± 170 m/s and 3310 ± 110 m/s, respectively) and beryllium (12 400 ± 700 m/s and 8100 ± 500 m/s) agreed with published values.

Optically Detecting Wavefronts and Wave Speeds in Water Using Refracto-Vibrometry

Refracto-vibrometry is a technique that uses a laser Doppler vibrometer to measure acoustic pressure fields. The vibrometer laser is directed through a medium towards a stationary retroreflective surface. Acoustic waves (density variations) for which the wavefronts pass through the laser, as the beam travels from the vibrometer to the retroreflector and back, cause variations in the integrated optical path length. This results in a time-varying modulation of the laser signal returning to the vibrometer, enabling optical detection of the acoustic wavefronts. In the current experiment, a Polytec PSV-400 scanning laser Doppler vibrometer, sampled at 100 MHz, monitored the waves emitted by a 1 MHz Panametrics V303 ultrasound transducer immersed in a water tank. The time-varying signal detected by the vibrometer at numerous scan points was used to generate videos of the time evolution of acoustic wavefronts; these videos will be presented. Refracto-vibrometry was also used for optical measurements of the time of flight of ultrasonic waves through different materials, including samples of lead and fabricated bone. This enabled determination of wave propagation speeds. The wave speeds obtained with optical detection using refracto-vibrometry were in agreement with measurements using a conventional ultrasonic transducer to detect the wavefronts.

Multi-parameter analysis of bladder mechanical properties using ultrasound bladder vibrometry

Bladder wall mechanical properties are important indicators of bladder compliance. This study compares the effectiveness of the Kelvin-Voigt, Maxwell, and fractional Kelvin-Voigt rheological models in capturing the mechanical properties of normal (compliant) and aberrant (non-compliant) ex-vivo pig bladder walls. Bladders were filled to different volumes, varying their thickness and internal pressure, and excited by the acoustic radiation force. Pulse-echo ultrasound imaged anti-symmetrical Lamb waves traveling along the bladder wall. Two-dimensional Fourier analysis generated velocity-frequency dispersion curves for the Lamb wave propagation. Fitting these experimental curves against theoretical curves from the models yielded values for bladder elasticity and viscosity. Pressure, measured simultaneously, was used as a point of comparison with elasticity. Our findings indicate an increasing trend in both elasticity for the rheological models and recorded pressure with increasing volume. This rate was obse...