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BRL Abstracts Database |
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Your search for ultrasound produced 3296 results. Page 146 out of 330
| Title |
Improving conformal tumour heating by adaptively removing control points from waveform diversity beamforming calculations: A simulation study. |
| Author |
Jennings MR,Mcgough RJ. |
| Journal |
Int J Hyperthermia |
| Volume |
|
| Year |
2010 |
| Abstract |
Waveform diversity is a phased array beamforming strategy that determines an optimal sequence of excitation signals to maximise power at specified tumour control points while simultaneously minimising power delivered to sensitive normal tissues. Waveform diversity is combined with mode scanning, a deterministic excitation signal synthesis algorithm, and an adaptive control point removal algorithm in an effort to achieve higher, more uniform tumour temperatures. Simulations were evaluated for a 1444 element spherical section ultrasound phased array that delivers therapeutic heat to a 3 cm spherical tumour model located 12 cm from the array. By selectively deleting tumour control points, the tumour volume heated above 42°C increased from 2.28 cm3 to 11.22 cm3. At the expense of a slight increase in the normal tissue volume heated above the target temperature of 42°C, the size of the tumour volume heated above 42°C after tumour points were deleted was almost five times larger than the size of the original heated tumour volume. Several other configurations were also simulated, and the largest heated tumour volumes, subject to a 43°C peak temperature constraint, were achieved when the tumour control points were located along the back edge of the tumour and laterally around the tumour periphery. The simulated power depositions obtained from the results of the adaptive control point removal algorithm, when optimised for waveform diversity combined with mode scanning, consistently increased the penetration depth and the size of the heated tumour volume while increasing the heated normal tissue volume by a small amount. |
| Title |
Improving lateral resolution in ultrasonic imaging by utilizing nulls in the beam pattern. |
| Author |
Reeg J, Oelze ML |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2015 |
| Abstract |
Reduction of lateral sidelobes results in improved ultrasonic imaging. In general, apodization is used to lower sidelobes in exchange for increasing the width of the mainlobe and thus decreasing lateral resolution. Null Subtraction Imaging (NSI) is a technique that uses different on-receive apodizations on copies of the same image to to reduce sidelobe levels while also improving lateral resolution. In the NSI technique, several apodization functions are applied on receive. The first apodization weight is applied having a zero mean value when summed across the aperture. This places a null at the broadside of the receive pattern. The second apodization is the same as the first apodization except that a constant offset in weight is applied (non-zero mean). The third apodization is the transpose of the second. The images created with the different weighting schemes are then added to form a new image with improved sidelobe performance and dramatically better lateral resolution compared to conventional apodization. To evaluate the performance of this technique, experiments were performed with an ATS539 phantom containing wire targets to assess lateral resolution and cylinder targets to assess contrast. A 9L4 array was used in the measurements connected to an Ultrasonix RP system with a SonixDAQ. Plane waves were emitted from the array and ultrasound echoes were received by each array element. Image reconstruction involved using Delay and Sum beamforming with apodization. Images were constructed using NSI and compared with rectangular weighted apertures. In experiments, the lateral resolution was observed to improve by a factor of five or better when compared to rectangular apodization. Image quality was assessed by estimation of lateral resolution (-3-dB receive beamwidth), the mainlobe to sidelobe ratio (MSR) in dB and estimation of the contrast-to-noise ratio (CNR). At f/# = 1 focusing with NSI, the -6-dB beamwidth on receive as measured from a small wire target in th- ATS phantom was 0.414λ. Sidelobes were observed to decrease at each f/# by an average of 17 dB with NSI compared to rectangular apodization. However, contrast of hyperechoic targets were lost when utilizing the NSI scheme. |
| Title |
Improving performance of pulse compression in a doppler ultrasound system using amplitude modulated chirps and wiener filtering. |
| Author |
Cowe J, Gittins J, Evans DH. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2008 |
| Abstract |
The use of coded excitation and pulse compression in transcranial Doppler (TCD) ultrasound systems is in the very early stages; the optimal processing scheme has yet to be determined. This study uses linear frequency-modulated (FM) chirps with 0.8-MHz bandwidth and compares the use of pulses with and without amplitude modulation and also matched filtering vs. Wiener filtering. The results demonstrate that using amplitude-modulated pulses vastly improves the axial resolution and provides a more predictable mainlobe-to-sidelobe distance in the radiofrequency (RF) signal. It is also shown that a Wiener filter can provide better performance than a matched filter, in terms of axial resolution and sidelobe level in the RF signal and signal-to-noise ratio in conventional sonograms. Although this study uses a TCD system, the techniques described are equally as applicable in other Doppler ultrasound devices. |
| Title |
Improving the quality of attenuation imaging using full angular spatial compounding |
| Author |
Zenteno O, Luchies A, Oelze M, Lavarello R |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2014 |
| Abstract |
The quantitative imaging of attenuation coefficients slope (ACS) has the potential to improve medical diagnostics. However, attempts to characterize ACS using pulse-echo data have been limited by the large statistical variations in the
estimates. Previous studies demonstrated that it is possible to extend the trade-off between variance and spatial resolution of quantitative ultrasound, spectral-based parameters by the use of full angular (i.e., 360◦) spatial compounding (FASC). In the present work, the use of FASC has been extended to the estimation of ACS and its performance has been experimentally evaluated using two physical phantoms. The ACSs of the background and inclusion regions were estimated using insertion loss measurements to be 0.41 and 0.75 dB/cm/MHz for Phantom #1, and 0.54 and 1.04 dB/cm/MHz for Phantom #2, respectively. Pulseecho
data were collected using a 7.5 MHz, f/4 transducer at 30 angles of view uniformly distributed between 0 and 360º. Single view ACS maps were generated using a spectral log difference method with 0.6 by 0.6 mm data blocks. The FASC images were constructed by assigning to a pixel the median of its corresponding
estimates from all 30 angles of view. The reduction in the variance of the FASC estimates compared to the variance of estimates from a single view (i.e., variance averaged from the 30 single views) in the inclusion and background regions were 89.18% and 88.71% for Phantom #1 and 92.33% and 86.98% for Phantom #2. Moreover, in all the cases the estimation bias in the inclusion and
background regions using FASC was lower than 9.0%. These results suggest that the variance of attenuation coefficient slope estimation can be significantly reduced without sacrificing spatial resolution by the use of full angular spatial compounding. |
| Title |
Improving the quality of QUS imaging using full angular spatial compounding. |
| Author |
Lavarello RJ, Sanchez JR, Oelze ML. |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2008 |
| Abstract |
Quantitative ultrasound (QUS) imaging techniques make use of information from backscattered echoes discarded in conventional B-mode imaging. Using scattering models and spectral fit methods, properties of tissue microstructure can be estimated. The variance of QUS estimates is usually reduced by processing data obtained from a region of interest (ROI) whose dimensions are larger than the resolution cell of B-mode imaging, which limits the spatial resolution of the technique. In this work, the use of full angular (i.e., 360 degrees) spatial compounding is proposed to extend the trade-off between estimate variance and spatial resolution of QUS. Simulations were performed using f/4, 10-MHz transducer with 50% -6-dB bandwidth and a synthetic phantom consisting of two eccentric circular cylindrical regions. The inner and outer cylinders had radii of 7 mm and 12.5 mm, respectively, and nine scatterers per resolution cell. The average scatterer diameters (ASDs) for the outer and inner cylinders were 50 μm and 25 μm, respectively. ASD estimates were obtained using radio frequency data at up to 128 angles of view. When using ROIs of size 16λ by 16λ, the use of multiple view data reduced the ASD standard deviations in the outer and inner cylinders from 7.4 μm and 14.4 μm to 1.5 μm and 2.5μm, respectively. When using ROIs of size 8λ by 8λ, the use of multiple view data reduced the ASD standard deviations in the outer and inner cylinders from 13.7 μm and 19.6 μm to 2.5 μm and 3.7 μm, respectively. Experimental validation was obtained using a 10 MHz, f/4 transducer to analyze a 2 cm diameter homogeneous agar phantom with embedded glass spheres of diameter between 45 μm and 53 μm. When using ROIs of size 10λ by 10λ and 32 angles of view, the ASD standard deviation was reduced from 24.6 μm to 4.8 μm. This value was below 10.4 μm, the ASD standard deviation obtained using single view data and ROIs of size 20λ by 20λ. Therefore, the use of full angular compounding was found to significantly improve the trade-off between spatial resolutions in QUS imaging and precision of QUS estimates. These results suggest that QUS imaging and precision of QUS estimates. These results suggest that QUS imaging can achieve optimal performance on a platform capable of producing views of an object from 360 degrees, e.g., a tomographic breat cancer. |
| Title |
Improving the quality of QUS imaging using full angular spatial compounding. |
| Author |
Lavarello RJ, Sanchez JR, Oelze ML. |
| Journal |
IEEE Int Ultrasonics Symp Proc |
| Volume |
|
| Year |
2008 |
| Abstract |
Quantitative ultrasound (QUS) imaging techniques make use of information from backscattered echoes discarded in conventional B-mode imaging. Using scattering models and spectral fit methods, properties of tissue microstructure can be estimated. The variance of QUS estimates is usually reduced by processing data obtained from a region of interest (ROI) whose dimensions are larger than the resolution cell of B-mode imaging, which limits the spatial resolution of the technique. In this work, the use of full angular (i.e., 360 degrees) spatial compounding is proposed to extend the trade-off between estimate variance and spatial resolution of QUS. Simulations were performed using f/4, 10-MHz transducer with 50% -6-dB bandwidth and a synthetic phantom consisting of two eccentric circular cylindrical regions. The inner and outer cylinders had radii of 7 mm and 12.5 mm, respectively, and nine scatterers per reso;ution cell. The average scatterer diameters (ASDs) for the outer and inner cylinders were 50 micrometer and 25 micrometer, respectively. ASD estimates were obtained using radio frequency data at up to 128 angles of view. When using ROIs of size 16 |
| Title |
Improving the statistics of quantitative ultrasound techniques with deformation compounding: an experimental study. |
| Author |
Herd MT, Hall TJ, Jiang J, Zagzebski JA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2011 |
| Abstract |
Many quantitative ultrasound (QUS) techniques are based on estimates of the radio-frequency (RF) echo signal power spectrum. Historically, reliable spectral estimates required spatial averaging over large regions-of-interest (ROIs). Spatial compounding techniques have been used to obtain robust spectral estimates for data acquired over small regions of interest. A new technique referred to as "deformation compounding" is another method for providing robust spectral estimates over smaller regions of interest. Motion tracking software is used to follow an ROI while the tissue is deformed (typically by pressing with the transducer). The deformation spatially reorganizes the scatterers so that the resulting echo signal is decorrelated. The RF echo signal power spectrum for the ROI is then averaged over several frames of RF echo data as the tissue is deformed, thus, undergoing deformation compounding. More specifically, averaging spectral estimates among the uncorrelated RF data acquired following small deformations allows reduction in the variance of the power spectral density estimates and, thereby, improves accuracy of spectrum-based tissue property estimation. The viability of deformation compounding has been studied using phantoms with known attenuation and backscatter coefficients. Data from these phantoms demonstrates that a deformation of about 2% frame-to-frame average strain is sufficient to obtain statistically-independent echo signals (with correlations of less than 0.2). Averaging five such frames, where local scatterer reorganization has taken place due to mechanical deformations, reduces the average percent standard deviation among power spectra by 26% and averaging 10 frames reduces the average percent standard deviation by 49%. Deformation compounding is used in this study to improve measurements of backscatter coefficients. These tests show deformation compounding is a promising method to improve the accuracy of spectrum-based quantitative ultrasound for tissue characterization. |
| Title |
Improving ultrasound mammography instrumentation: investigation of defocusing and use of compressed breast phantoms. |
| Author |
Fry-Kelly E. |
| Journal |
Radiology |
| Volume |
|
| Year |
1985 |
| Abstract |
No abstract available. |
| Title |
In Memoriam: Frederic Louis LIzzi, Eng.Sc.D.,1942-2005. |
| Author |
Feleppa EJ, Ketterling JA. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
2005 |
| Abstract |
No abstract available. |
| Title |
In SITU exposimetry: The ovarian ultrasound examination. |
| Author |
Siddiqi TA, O'Brien WD Jr, Meyer RA, Sullivan JM, Miodovnik M. |
| Journal |
Ultrasound Med Biol |
| Volume |
|
| Year |
1991 |
| Abstract |
We have constructed a specialized in vivo exposimetry system and developed and tested customized software using specially fabricated hydrophones. We placed the hydrophones in the lateral vaginal fornix as close to the ovary as possible (usually 1-2 cm from the ovary) and.determined selected first-order and second-order ultrasonic field quantities during a routine ultrasound examination of the ovary. Our sonographic measurements yielded mean ultrasound beam path distances of 7.6 cm. (n = 18) in the presence of a distended bladder and 7.0 cm. (n = 25) in the presence of an empty bladder with an average group insertion loss of 6.2 dB and 7.3 dB, respectively. Using a Fixed Attenuation Model, the tissue attenuation coefficient value was 2.98 dB/MHz; whereas for the Overlying Tissue Model the value was 0.72 dB/cm-MHz. These data are both specific and unique in that they have been systematically obtained in situ. |
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