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- Attenuation (6)
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- Ultrasonics (3)
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Articles 1 - 7 of 7
Full-Text Articles in Engineering
In Vivo Ultrasonic Attenuation Slope Estimates For Detecting Cervical Ripening In Rats: Preliminary Results, Timothy A. Bigelow, Barbara L. Mcfarlin, William D. O'Brien Jr., Michael L. Oelze
In Vivo Ultrasonic Attenuation Slope Estimates For Detecting Cervical Ripening In Rats: Preliminary Results, Timothy A. Bigelow, Barbara L. Mcfarlin, William D. O'Brien Jr., Michael L. Oelze
Timothy A. Bigelow
To effectively postpone preterm birth, cervical ripening needs to be detected and delayed. As the cervix ripens, the spacing between the collagen fibers increases and fills with water, hyaluronan, decorin, and enzymes suggesting that the ultrasonic attenuation of the cervix should decrease. The decrease in ultrasonic attenuation may be detectable, leading to an effective means of detecting cervical ripening. Herein, the traditional attenuation slope-estimation algorithm based on measuring the downshift in center frequency of the ultrasonic backscattered signal with propagation depth was modified and applied to the cervix of rats. The modified algorithm was verified using computer simulations and an …
Impact Of Local Attenuation Approximations When Estimating Correlation Length From Backscattered Ultrasound Echoes, Timothy A. Bigelow, William D. O'Brien
Impact Of Local Attenuation Approximations When Estimating Correlation Length From Backscattered Ultrasound Echoes, Timothy A. Bigelow, William D. O'Brien
Timothy A. Bigelow
Estimating the characteristic correlation length of tissue microstructure from the backscattered power spectrum could improve the diagnostic capability of medical ultrasound. Previously, size estimates were obtained after compensating for source focusing, the frequency-dependent attenuation along the propagation path (total attenuation), and the frequency-dependent attenuation in the scattering region (local attenuation). In this study, the impact of approximations of the local attenuation on the scatterer size estimate was determined using computer simulations and theoretical analysis. The simulations used Gaussian impedance distributions with an effective radius of 25 μm randomly positioned in a homogeneous half-space sonified by a spherically focused source (f/1 …
Signal Processing Strategies That Improve Performance And Understanding Of The Quantitative Ultrasound Spectral Fit Algorithm, Timothy A. Bigelow, William D. O'Brien
Signal Processing Strategies That Improve Performance And Understanding Of The Quantitative Ultrasound Spectral Fit Algorithm, Timothy A. Bigelow, William D. O'Brien
Timothy A. Bigelow
Quantifying the size of the tissue microstructure using the backscattered power spectrum has had limited success due to frequency-dependent attenuation along the propagation path, thus masking the frequency dependence of the scatterer size. Previously, the SPECTRAL FIT algorithm was developed to solve for total attenuation and scatterer size simultaneously [Bigelow et al., J. Acoust. Soc. Am. 117, 1431-1439 (2005)]. Herein, the outcomes from signal processing strategies on the SPECTRAL FIT algorithm are investigated. The signal processing methods can be grouped into two categories, viz., methods that improve the performance of the algorithm and methods that provide insight. The methods that …
A Model For Estimating Ultrasound Attenuation Along The Propagation Path To The Fetus From Backscattered Waveforms, Timothy A. Bigelow, William D. O'Brien
A Model For Estimating Ultrasound Attenuation Along The Propagation Path To The Fetus From Backscattered Waveforms, Timothy A. Bigelow, William D. O'Brien
Timothy A. Bigelow
Accurate estimates of the ultrasound pressure and/or intensity incident on the developing fetus on a patient-specific basis could improve the diagnostic potential of medical ultrasound by allowing the clinician to increase the transmit power while still avoiding the potential for harmful bioeffects. Neglecting nonlinear effects, the pressure/intensity can be estimated if an accurate estimate of the attenuation along the propagation path (i.e., total attenuation) can be obtained. Herein, a method for determining the total attenuation from the backscattered power spectrum from the developing fetus is proposed. The boundaries between amnion and either the fetus' skull or soft tissue are each …
Estimation Of Total Attenuation And Scatterer Size From Backscattered Ultrasound Waveforms, Timothy A. Bigelow, Michael L. Oelze, William D. O'Brien
Estimation Of Total Attenuation And Scatterer Size From Backscattered Ultrasound Waveforms, Timothy A. Bigelow, Michael L. Oelze, William D. O'Brien
Timothy A. Bigelow
Quantitative ultrasound techniques using backscattered echoes have had limited success in vivo due to the frequency-dependent attenuation along the entire propagation path masking the frequency dependence of the backscatter. Herein, total attenuation and scatterer size are estimated simultaneously by an analysis of the in vivo backscattered power spectrum using two approaches. The simulations used to evaluate the two approaches used frequencies between 4 and 11 MHz with an effective scatterer radius of 25 μm. The first approach was based on approximations of the in vivo backscattered power spectrum (i.e., assumed Gaussian function), wherein attenuation and size were estimated by assuming …
Scatterer Size Estimation In Pulse-Echo Ultrasound Using Focused Sources: Calibration Measurements And Phantom Experiments, Timothy A. Bigelow, William D. O'Brien
Scatterer Size Estimation In Pulse-Echo Ultrasound Using Focused Sources: Calibration Measurements And Phantom Experiments, Timothy A. Bigelow, William D. O'Brien
Timothy A. Bigelow
In a companion paper [T. A. Bigelow and W. D. O'Brien Jr., J. Acoust. Soc. Am. 116, 578 (2004)], theory, supported by simulations, showed that accurate scatterer size estimates could be obtained using highly focused sources provided that the derived generalized attenuation-compensation function was used and the velocity potential field near the focus could be approximated as a three-dimensional Gaussian. Herein, the theory is further evaluated via experimental studies. A calibration technique is developed to find the necessary equivalent Gaussian dimensions for a focused source using reflections obtained from a rigid plane scanned through the focus. Then, the theoretical analysis …
Scatterer Size Estimation In Pulse-Echo Ultrasound Using Focused Sources: Theoretical Approximations And Simulation Analysis, Timothy A. Bigelow, William D. O'Brien
Scatterer Size Estimation In Pulse-Echo Ultrasound Using Focused Sources: Theoretical Approximations And Simulation Analysis, Timothy A. Bigelow, William D. O'Brien
Timothy A. Bigelow
The speckle in ultrasound images has long been thought to contain information related to the tissue microstructure. Many different investigators have analyzed the frequency characteristics of the backscattered signals to estimate the scatterer acoustic concentration and size. Previous work has been mostly restricted to unfocused or weakly focused ultrasound sources, thus limiting its implementation with diagnostically relevant fields. Herein, we derive equations capable of estimating the size of a-scatterer for any reasonably focused source provided that the velocity potential field in the focal region can be approximated as a three-dimensional Gaussian beam, scatterers are a sufficient distance from the source, …